Contents

Implementing Tunnels

This module describes the various types of tunneling techniques available using Cisco IOS software. Configuration details and examples are provided for the tunnel types that use physical or virtual interfaces. Many tunneling techniques are implemented using technology-specific commands, and links are provided to the appropriate technology modules.

Tunneling provides a way to encapsulate arbitrary packets inside a transport protocol. Tunnels are implemented as a virtual interface to provide a simple interface for configuration. The tunnel interface is not tied to specific "passenger" or "transport" protocols, but rather is an architecture to provide the services necessary to implement any standard point-to-point encapsulation scheme.


Note

Cisco ASR 1000 Series Aggregation Services Routers support VPN routing and forwarding (VRF)-aware generic routing encapsulation (GRE) tunnel keepalive features.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Prerequisites for Implementing Tunnels

This module assumes that you are running Cisco IOS Release 12.2 software or a later release.

Restrictions for Implementing Tunnels

  • In early versions of Cisco IOS software, only processor switching was supported. Fast switching of GRE tunnels was introduced in Cisco IOS Release 11.1. Cisco Express Forwarding (CEF) switching is also now commonly used by the IPv6 and other tunneling protocols.

  • It is important to allow the tunnel protocol through a firewall and to allow it to pass access control list (ACL) checking.

  • Multiple point-to-point tunnels can saturate the physical link with routing information if the bandwidth is not configured correctly on the tunnel interface.

  • A tunnel looks like a single hop, and routing protocols may prefer a tunnel over a multihop physical path. This can be deceptive because the tunnel, although it may look like a single hop, may traverse a slower path than a multihop link. A tunnel is as robust and fast, or as unreliable and slow, as the links that it actually traverses. Routing protocols that make their decisions on the sole basis of hop count will often prefer a tunnel over a set of physical links. A tunnel might appear to be a one-hop, point-to-point link and have the lowest-cost path, but may actually cost more in terms of latency than an alternative physical topology. For example, in the topology shown in the figure below, packets from Host 1 will appear to travel across networks w, t, and z to get to Host 2 instead of taking the path w, x, y, and z because the tunnel hop count appears shorter. In fact, the packets going through the tunnel will still be traveling across Router A, B, and C, but they must also travel to Router D before coming back to Router C.

Figure 1. Tunnel Precautions: Hop Counts

  • If routing is not carefully configured, the tunnel may have a recursive routing problem. When the best path to the "tunnel destination" is via the tunnel itself, recursive routing causes the tunnel interface to flap. To avoid recursive routing problems, keep the control-plane routing separate from the tunnel routing using the following methods:
    • Use a different autonomous system number or tag.
    • Use a different routing protocol.
    • Use static routes to override the first hop (but watch for routing loops).

When you have recursive routing to the tunnel destination, the following error is displayed: 

%TUN-RECURDOWN Interface Tunnel 0
temporarily disabled due to recursive routing

Note

You cannot configure an IP tunnel or a GRE tunnel on Cisco 7600 series routers which has an MPLS Traffic Engineering (TE) tunnel as the egress path, because the configuration results in forwarding loops.

Information About Implementing Tunnels

Tunneling Versus Encapsulation

To understand how tunnels work, it is important to distinguish between the concepts of encapsulation and tunneling. Encapsulation is the process of adding headers to data at each layer of a particular protocol stack. The Open Systems Interconnection (OSI) reference model describes the functions of a network as seven layers stacked on top of each other. When data has to be sent from one host (a PC for example) on a network to another host, the process of encapsulation is used to add a header in front of the data at each layer of the protocol stack in descending order. The header must contain a data field that indicates the type of data encapsulated at the layer immediately above the current layer. As the packet ascends the protocol stack on the receiving side of the network, each encapsulation header is removed in the reverse order.

Tunneling encapsulates data packets from one protocol inside a different protocol and transports the data packets unchanged across a foreign network. Unlike encapsulation, tunneling allows a lower-layer protocol, or same-layer protocol, to be carried through the tunnel. A tunnel interface is a virtual (or logical) interface. For more details on other types of virtual interfaces, see the "Configuring Virtual Interfaces" module. Although many different types of tunnels have been created to solve different network problems, tunneling consists of three main components:

  • Passenger protocol--The protocol that you are encapsulating. Examples of passenger protocols are AppleTalk, connectionless network service (CLNS), IP, and IPX.

  • Carrier protocol--The protocol that does the encapsulating. Examples of carrier protocols are GRE, IP-in-IP, Layer 2 Tunneling Protocol (L2TP), multiprotocol label switching (MPLS), STUN, and DLSw+.

  • Transport protocol--The protocol used to carry the encapsulated protocol. The main transport protocol is IP.

To understand the process of tunneling, consider connecting two AppleTalk networks with a non-AppleTalk backbone, such as IP. The relatively high bandwidth consumed by the broadcasting of Routing Table Maintenance Protocol (RTMP) data packets can severely hamper the backbone’s network performance. This problem can be solved by tunneling AppleTalk through a foreign protocol, such as IP. Tunneling encapsulates an AppleTalk packet inside the foreign protocol packet (AppleTalk inside GRE inside IP), which is then sent across the backbone to a destination router. The destination router then removes the encapsulation from the AppleTalk packet and routes the packet.

Definition of Tunneling Types by OSI Layer

Tunnels are used by many different technologies to solve different network challenges, and the resulting variety of tunnel types makes it difficult to determine which tunneling technique to use. The different carrier protocols can be grouped according to the OSI layer model. The table below shows the different carrier protocols grouped by OSI layer. Below the table, each carrier protocol is defined, and if the tunnel configuration is not covered within this module, a link to the appropriate module is included.

Table 1 Carrier Protocol by OSI Layer

Layer

Carrier Protocol

2

  • PPPoA--Point-to-Point Protocol (PPP) over ATM

  • PPPoE--PPP over Ethernet

  • UDLR--Unidirectional link routing

3

  • BSTUN--Block Serial Tunneling

  • CLNS--Connectionless Network Service (CLNS)

  • GRE--Generic routing encapsulation

  • IP-in-IP--Internet Protocol encapsulated within IP

  • IPsec--IP Security

  • IPv6--IP version 6

  • L2F--Layer 2 Forwarding

  • L2TP--Layer 2 Tunneling Protocol

  • MPLS--Multiprotocol Label Switching

  • PPTP--Point-to-Point Tunneling Protocol

  • STUN--Serial Tunneling

4

  • DLSw+--Data-link switching plus

  • RBSCP--Rate-Based Satellite Control Protocol

  • SSL--Secure Socket Layer

BSTUN

A Block Serial Tunnel (BSTUN) enables support for devices using the Bisync data-link protocol. This protocol enables enterprises to transport Bisync traffic over the same network that supports their Systems Network Architecture (SNA) and multiprotocol traffic, eliminating the need for separate Bisync facilities.

For more details about configuring BSTUN, see the "Configuring Serial Tunnel and Block Serial Tunnel" module in the Cisco IOS Bridging and IBM Networking Configuration Guide.

CLNS

The ISO Connectionless Network Service (CLNS) protocol is a standard for the network layer of the OSI model. IP traffic can be transported over CLNS; for instance, on the data communications channel (DCC) of a SONET ring. An IP over CLNS tunnel (CTunnel) is a virtual interface that enhances interactions with CLNS networks, allowing IP packets to be tunneled through the Connectionless Network Protocol (CLNP) to preserve TCP/IP services. CLNS can also be used as a transport protocol with GRE as a carrier protocol (GRE/CLNS), carrying both IPv4 and IPv6 packets.

DLSw+

Data-link switching plus (DLSw+) is Cisco’s implementation of the DLSw standard for Systems Network Architecture (SNA) and NetBIOS devices, and it supports several additional features and enhancements. DLSw+ is a means of transporting SNA and NetBIOS traffic over a campus or WAN. The end systems can attach to the network over Token Ring, Ethernet, Synchronous Data Link Control (SDLC), Qualified Logical Link Control (QLLC), or Fiber Distributed Data Interface (FDDI). DLSw+ switches between diverse media and locally terminates the data links, keeping acknowledgments, keepalives, and polling off the WAN.

For more details about configuring DLSw+, see the "Configuring Data-Link Switching Plus" module in the Cisco IOS Bridging and IBM Networking Configuration Guide .

GRE

Generic routing encapsulation (GRE) is defined in RFC 2784. GRE is a carrier protocol that can be used with a variety of underlying transport protocols, and GRE can carry a variety of passenger protocols. RFC 2784 also covers the use of GRE with IPv4 as the transport protocol and the passenger protocol. Cisco IOS software supports GRE as the carrier protocol with many combinations of passenger and transport protocols.

For more details about GRE, see the Generic Routing Encapsulation.

IP-in-IP

IP-in-IP is a Layer 3 tunneling protocol--defined in RFC 2003--that alters the normal routing of an IP packet by encapsulating it within another IP header. The encapsulating header specifies the address of a router that would not ordinarily be selected as a next-hop router on the basis of the real destination address of the packet. The intermediate node decapsulates the packet, which is then routed to the destination as usual.

IPsec

In simple terms, IP Security (IPsec) provides secure tunnels between two peers, such as two routers. You define which packets are considered sensitive and should be sent through these secure tunnels, and you define the parameters that should be used to protect these packets by specifying characteristics of these tunnels. IPsec peers set up a secure tunnel and encrypt the packets that traverse the tunnel to the remote peer.

IPsec also works with the GRE and IP-in-IP, L2F, L2TP, and DLSw+ tunneling protocols; however, multipoint tunnels are not supported. Other Layer 3 tunneling protocols may not be supported for use with IPsec.

For more details about configuring IPSec, see the "Configuring Security for VPNs with IPSec" module in the Cisco IOS Security Configuration Guide.

IPv6

IP version 6 (IPv6) is a new version of the Internet Protocol based on and designed as the successor to IP version 4. IPv6 adds a much larger address space--128 bits--and improvements such as a simplified main header and extension headers. IPv6 is described initially in RFC 2460, Internet Protocol, Version 6 (IPv6) . The use of IPv6 as a carrier protocol is described in RFC 2473, Generic Packet Tunneling in IPv6 Specification .

L2F

Layer 2 Forwarding (L2F) tunneling is used in virtual private dialup networks (VPDNs). A VPDN allows separate and autonomous protocol domains to share common access infrastructure including modems, access servers, and ISDN routers by the tunneling of link-level (Layer 2) frames. Typical L2F tunneling use includes Internet service providers (ISPs) or other access service creating virtual tunnels to link to remote customer sites or remote users with corporate intranet or extranet networks.

L2TP

Layer 2 Tunneling Protocol (L2TP) is an open standard created by the Internet Engineering Task Force (IETF) that uses the best features of L2F and Point-to-Point Tunneling Protocol (PPTP). L2TP is designed to secure the transmission of IP packets across uncontrolled and untrusted network domains, and it is an important component of Virtual Private Networks (VPNs). VPNs extend remote access to users over a shared infrastructure while maintaining the same security and management policies as a private network.

For more details about configuring L2TP, see the Cisco IOS Dial Technologies Configuration Guide.

MPLS

Multiprotocol Label Switching (MPLS) is a high-performance packet forwarding technology that integrates the performance and traffic management capabilities of data-link-layer (Layer 2) switching with the scalability, flexibility, and performance of network-layer (Layer 3) routing. The MPLS architecture has been designed to allow data to be transferred over any combination of Layer 2 technologies, to support all Layer 3 protocols, and to scale. Using CEF, MPLS can efficiently enable the delivery of IP services over an ATM switched network. MPLS is an integration of Layer 2 and Layer 3 technologies. By making traditional Layer 2 features available to Layer 3, MPLS enables traffic engineering.

For more details about how MPLS traffic engineering uses tunnels, see the Cisco IOS Multiprotocol Label Switching Configuration Guide.

PPPoA

PPP over ATM (PPPoA) is mainly implemented as part of Asymmetric Digital Subscriber Line (ADSL). It relies on RFC 1483, operating in either Logical Link Control-Subnetwork Access Protocol (LLC-SNAP) or VC-Mux mode. A customer premises equipment (CPE) device encapsulates the PPP session based on this RFC for transport across the ADSL loop and the digital subscriber line access multiplexer (DSLAM).

PPPoE

RFC 2516 defines PPP over Ethernet (PPPoE) as providing the ability to connect a network of hosts over a simple bridging access device to a remote access concentrator or aggregation concentrator. As customers deploy ADSL, they must support PPP-style authentication and authorization over a large installed base of legacy bridging customer premises equipment (CPE). Using a form of tunneling encapsulation, PPPoE allows each host to use its own PPP stack, thus presenting the user with a familiar user interface. Access control, billing, and type of service (ToS) can be done on a per-user, rather than a per-site, basis.

For more details about configuring PPPoE, see the Cisco IOS Broadband Access Aggregation and DSL Configuration Guide.

PPTP

Point-to-Point Tunneling Protocol (PPTP) is a network protocol that enables the secure transfer of data from a remote client enterprise server by creating a VPN across TCP/IP data networks. PPTP supports on-demand, multiprotocol virtual private networking over public networks such as the Internet.

RBSCP

Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPsec), over satellite links without breaking the end-to-end model.

SSL Tunnels

Secure Socket Layer (SSL) is designed to make use of TCP sessions to provide a reliable end-to-end secure service. The main role of SSL is to provide security for web traffic. Security includes confidentiality, message integrity, and authentication. SSL achieves these elements of security through the use of cryptography, digital signatures, and certificates. SSL protects confidential information through the use of cryptography. Sensitive data is encrypted across public networks to achieve a level of confidentiality.

SSL is implemented using the Cisco Application and Content Networking System (ACNS). For more details about configuring SSL, see the latest Cisco ACNS Software Deployment and Configuration Guide .

STUN

Cisco’s Serial Tunneling (STUN) implementation allows Synchronous Data Link Control (SDLC) protocol devices and High-Level Data Link Control (HDLC) devices to connect to one another through a multiprotocol internetwork rather than through a direct serial link. STUN encapsulates SDLC frames in either the TCP/IP or the HDLC protocol. STUN provides a straight passthrough of all SDLC traffic (including control frames, such as Receiver Ready) end-to-end between Systems Network Architecture (SNA) devices.

For more details about configuring STUN, see the "Configuring Serial Tunnel and Block Serial Tunnel" module in the Cisco IOS Bridging and IBM Networking Configuration Guide .

UDLR Tunnels

Unidirectional link routing (UDLR) provides mechanisms for a router to emulate a bidirectional link to enable the routing of unicast and multicast packets over a physical unidirectional interface, such as a broadcast satellite link. However, there must be a back channel or other path between the routers that share a physical unidirectional link (UDL). A UDLR tunnel is a mechanism for unicast and multicast traffic; Internet Group Management Protocol (IGMP) UDLR is a related technology for multicast traffic.

For more details, see Cisco IOS IP Multicast Configuration Guide.

Benefits of Tunneling

The following are several situations in which tunneling (encapsulating traffic in another protocol) is useful:

  • To enable multiprotocol local networks over a single-protocol backbone.

  • To provide workarounds for networks that use protocols that have limited hop counts; for example, RIP version 1, AppleTalk (see the figure below).

  • To connect discontiguous subnetworks.

  • To allow virtual private networks across WANs.

Figure 2. Providing Workarounds for Networks with Limited Hop Counts

Tunnel ToS

Tunnel ToS allows you to tunnel your network traffic and group all your packets in the same specific ToS byte value. The ToS byte values and Time-to-Live (TTL) hop-count value can be set in the encapsulating IP header of tunnel packets for an IP tunnel interface on a router. The Tunnel ToS feature is supported for CEF, fast switching, and process switching.

The ToS and TTL byte values are defined in RFC 791. RFC 2474 and RFC 2780 obsolete the use of the ToS byte as defined in RFC 791. RFC 791 specifies that bits 6 and 7 of the ToS byte (the first two least significant bits) are reserved for future use and should be set to 0. The Tunnel ToS feature does not conform to this standard and allows you to set the whole ToS byte value, including bits 6 and 7, and to decide to which RFC standard the ToS byte of your packets should confirm.

Mobile IP Tunneling

New devices and business practices, such as PDAs and the next-generation of data-ready cellular phones and services, are driving interest in the ability of a user to roam while maintaining network connectivity. The requirement for data connectivity solutions for this group of users is very different than it is for the fixed dialup user or the stationary wired LAN user. Solutions need to accommodate the challenge of movement during a data session or conversation.

Mobile IP is a tunneling-based solution that takes advantage of the Cisco-created generic routing encapsulation (GRE) tunneling technology and simpler IP-in-IP tunneling protocol.

Mobile IP is comprises the following three components, as shown in the figure below:

  • Mobile node (MN)

  • Home agent (HA)

  • Foreign agent (FA)

Figure 3. Mobile IP Components and Use of Tunneling

An MN is a node, for example, a PDA, a laptop computer, or a data-ready cellular phone, that can change its point of attachment from one network or subnet to another. This node can maintain ongoing communications while using only its home IP address. In the figure above, the current location of the MN--a laptop computer--is shown in bold.

An HA is a router on the home network of the MN that maintains an association between the home IP address of the MN and its care-of address , which is the current location of the MN on a foreign or visited network. The HA redirects packets by tunneling them to the MN while it is away from home.

An FA is a router on a foreign network that assists the MN in informing its HA of its current care-of address. The FA detunnels packets that were tunneled by the HA and delivers them to the MN. The FA also acts as the default router for packets generated by the MN while it is connected to the foreign network.

The traffic destined for the MN is forwarded in a triangular manner. When a device on the Internet, called a correspondent node (CN), sends a packet to the MN, the packet is routed to the home network of the MN, the HA redirects the packet by tunneling to the care-of address (current location) of the MN on the foreign network, as shown in the figure above. The FA receives the packet from the HA and forwards it locally to the MN. However, packets sent by the MN are routed directly to the CN.

For more details about configuring Mobile IP, see the Cisco IOS IP Mobility Configuration Guide.

Generic Routing Encapsulation

Generic routing encapsulation (GRE) is defined in RFC 2784. GRE is a carrier protocol that can be used with a variety of underlying transport protocols and that can carry a variety of passenger protocols. RFC 2784 also covers the use of GRE with IPv4 as the transport protocol and the passenger protocol. Cisco IOS software supports GRE as the carrier protocol with many combinations of passenger and transport protocols such as:

The following descriptions of GRE tunnels are included:

GRE Tunnel IP Source and Destination VRF Membership

GRE Tunnel IP Source and Destination VRF Membership allows you to configure the source and destination of a tunnel to belong to any VRF tables. A VRF table stores routing data for each VPN. The VRF table defines the VPN membership of a customer site attached to the network access server (NAS). Each VRF table comprises an IP routing table, a derived CEF table, and guidelines and routing protocol parameters that control the information that is included in the routing table.

Previously, Generic Routing Encapsulation (GRE) IP tunnels required the IP tunnel destination to be in the global routing table. The implementation of this feature allows you to configure a tunnel source and destination to belong to any VRF. As with existing GRE tunnels, the tunnel becomes disabled if no route to the tunnel destination is defined.

EoMPLS over GRE

Ethernet over multiprotocol label switching (EoMPLS) is a tunneling mechanism that allows you to tunnel Layer 2 traffic through a Layer 3 MPLS network. EoMPLS is also known as Layer 2 tunneling.

EoMPLS effectively facilitates the Layer 2 extension over long distances. EoMPLS over GRE helps to create the GRE tunnel as hardware-based switched, and with high performance that encapsulates EoMPLS frames within the GRE tunnel. The GRE connection is established between the two core routers, and then the MPLS LSP is tunneled over.

GRE encapsulation is used to define a packet that has some additional header information added to it prior to being forwarded. De-encapsulation is the process of removing the additional header information when the packet reaches the destination tunnel endpoint.

When a packet is forwarded through a GRE tunnel, two new headers are appended at the front of the packet and hence the context of the new payload changes. After encapsulation, what was originally the data payload and separate IP header is now known as the GRE payload. A GRE header is added to the packet to provide information on the protocol type and also a recalculated checksum. Also, a new IP header is added to the front of the GRE header. This IP header contains the destination IP address of the tunnel.

The GRE header is appended to the packet (IP, L2VPN, L3VPN, etc.) before entering the tunnel. All routers along the path that receive the encapsulated packet will use the new IP header to determine where to send the packet in an effort for it to reach the tunnel endpoint.

In the IP forwarding case on reaching the tunnel destination endpoint, the new IP header and GRE header are removed from the packet and the original IP header is then used to forward the packet to it’s final destination.

In the EoMPLS over GRE cases, the new IP header and GRE header will be removed from the packet at the tunnel destination and the MPLS (VC or VPN) label will be used to forward the packets to the appropriate L2 attachment circuit or L3 VRF.

The following scenarios describe the L2VPN and L3VPN over GRE deployment on provider edge (PE) or provider (P) routers:

PE to PE GRE Tunnels

In the PE to PE GRE tunnels scenario, a customer does not generally transition any part of the core to MPLS but prefers to offer EoMPLS and basic MPLS VPN services. Hence, GRE tunneling of the MPLS labeled traffic is done between PEs. This is the most common scenario seen in various customers networks.

P to P GRE Tunnels

The P to P GRE tunnels scenario is one where MPLS has been enabled between PE and P routers, but the network core may have non-MPLS-aware routers or IP encryption boxes. In this scenario, GRE tunneling of the MPLS labeled packets is done between P routers.

PE to P GRE Tunnels

The PE to P GRE tunnels scenario demonstrates a network where the P to P nodes are MPLS-aware, while GRE tunneling is done between a PE to P non MPLS network segment.

The following features are required for the deployment of scenarios described above:

GRE Specific:

  • Tunnel endpoints can be loopbacks or physical interfaces.

  • Configurable tunnel keepalive timer parameters per end point, and syslog message must be generated when the keepalive timer expires.

  • BFD support for tunnel failures and for IGPs using tunnels.

  • IGP loadsharing across GRE tunnels.

  • IGP redundancy across GRE tunnels.

  • Fragmentation across GRE tunnels.

  • Ability to pass jumbo frames.

  • Support for all IGP control plane traffic.

  • Support for IP TOS preservation across tunnel.

  • Tunnel should be independent of endpoint physical interface types such as POS, Gig, TenGig, and ATM.

  • Support for up to 100 GRE tunnels.

EoMPLS Specific:

  • Port mode EoMPLS.

  • VLAN mode EoMPLS.

  • Pseudowire redundancy.

  • AToM sequencing.

  • Tunnel selection--ability to map a specific pseudowire or pw-class to a GRE tunnel.

  • IGP loadsharing and redundancy. See below for more information.

  • Support for up to 200 EoMPLS VCs.

MPLS-VPN Specific:

  • Support for PE Role with IPv4 VRFs

  • Support for all PE-CE protocols

  • Load sharing through multiple tunnels and equal-cost IGP paths with a single tunnel

  • Support for redundancy via unequal-cost IGP paths with a single tunnel

  • Support for the IP Precedence value being copied onto the EXP bits field of the MPLS label, and then onto the Precedence bits on the outer IPv4 ToS field of the GRE packet.

For a sample configuration sequence of EoMPLS over GRE, see Example Configuring EoMPLS over GRE. For more details about EoMPLS over GRE, see Deploying and Configuring MPLS Virtual Private Networks In IP Tunnel Environments .

Multipoint GRE Tunneling

Enhanced multipoint GRE (mGRE) tunneling technology provides a Layer 3 (L3) transport mechanism for use in IP networks. This same dynamic Layer 3 tunneling transport can be used within IP networks to transport VPN traffic across service provider and enterprise networks, as well as to provide interoperability for packet transport between IP and MPLS VPNs. This feature provides support for RFC 2547, which defines the outsourcing of IP-backbone services for enterprise networks.

Multipoint tunnels use the Next Hop Resolution Protocol (NHRP) in the same way that a Frame Relay multipoint interface uses information obtained by the reverse ARP mechanism to learn the Layer 3 addresses of the remote data-link connection identifiers (DLCIs).

In Cisco IOS Release 12.2(8)T and later releases, CEF-switching over mGRE tunnels was introduced. Previously, only process switching was available for mGRE tunnels. CEF-switching over mGRE tunnels enables CEF switching of IP traffic to and from multipoint GRE tunnels. Tunnel traffic can be forwarded to a prefix through a tunnel destination when both the prefix and the tunnel destination are specified by the application.

GRE CLNS Tunnel Support for IPv4 and IPv6 Packets

GRE tunneling of IPv4 and IPv6 packets through CLNS networks enables Cisco CLNS tunnels (CTunnels) to interoperate with networking equipment from other vendors. This feature provides compliance with RFC 3147.

The optional GRE services defined in header fields, such as checksums, keys, and sequencing, are not supported. Any packet that is received and requests such services will be dropped.

GRE IPv4 Tunnel Support for IPv6 Traffic

IPv6 traffic can be carried over IPv4 generic routing encapsulation (GRE) tunnels using the standard GRE tunneling technique that is designed to provide the services necessary to implement any standard point-to-point encapsulation scheme. As in IPv6 manually configured tunnels, GRE tunnels are links between two points, with a separate tunnel for each link. The tunnels are not tied to a specific passenger or transport protocol, but in this case, IPv6 is the passenger protocol, GRE is the carrier protocol, and IPv4 is the transport protocol.

The primary use of GRE tunnels is for stable connections that require regular secure communication between two edge routers or between an edge router and an end system. The edge routers and the end systems must be dual-stack implementations.

GRE has a protocol field that identifies the passenger protocol. GRE tunnels allow IS-IS or IPv6 to be specified as a passenger protocol, allowing both IS-IS and IPv6 traffic to run over the same tunnel. If GRE did not have a protocol field, it would be impossible to distinguish whether the tunnel was carrying IS-IS or IPv6 packets. The GRE protocol field is why it is desirable that you tunnel IS-IS and IPv6 inside GRE.

Overlay Tunnels for IPv6

Overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure (a core network or the Internet). (See the figure below.) By using overlay tunnels, you can communicate with isolated IPv6 networks without upgrading the IPv4 infrastructure between them. Overlay tunnels can be configured between border routers or between a border router and a host; however, both tunnel endpoints must support both the IPv4 and IPv6 protocol stacks. Cisco IOS IPv6 currently supports the following types of overlay tunneling mechanisms:

  • Manual

  • Generic routing encapsulation (GRE)

  • IPv4-compatible

  • 6to4

  • Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)

Figure 4. Overlay Tunnels


Note

Overlay tunnels reduce the maximum transmission unit (MTU) of an interface by 20 octets (assuming that the basic IPv4 packet header does not contain optional fields). A network that uses overlay tunnels is difficult to troubleshoot. Therefore, overlay tunnels that connect isolated IPv6 networks should not be considered as a final IPv6 network architecture. The use of overlay tunnels should be considered as a transition technique toward a network that supports both the IPv4 and IPv6 protocol stacks or just the IPv6 protocol stack.

Use the table below to help you determine which type of tunnel you want to configure to carry IPv6 packets over an IPv4 network.

Table 2 Suggested Usage of Tunnel Types to Carry IPv6 Packets over an IPv4 Network

Tunneling Type

Suggested Usage

Usage Notes

Manual

Simple point-to-point tunnels that can be used within a site or between sites.

Can carry IPv6 packets only.

GRE/IPv4

Simple point-to-point tunnels that can be used within a site or between sites.

Can carry IPv6, CLNS, and many other types of packets.

Compatible

Point-to-multipoint tunnels.

Uses the ::/96 prefix. Currently, we do not recommend using this tunnel type.

6to4

Point-to-multipoint tunnels that can be used to connect isolated IPv6 sites.

Sites use addresses from the 2002::/16 prefix.

ISATAP

Point-to-multipoint tunnels that can be used to connect systems within a site.

Sites can use any IPv6 unicast addresses.

Individual tunnel types are discussed in more detail in the following concepts, and we recommend that you review and understand the information on the specific tunnel type that you want to implement. When you are familiar with the type of tunnel you need, the table below provides a quick summary of the tunnel configuration parameters that you may find useful.

Table 3 Overlay Tunnel Configuration Parameters by Tunneling Type

Overlay Tunneling Type

Overlay Tunnel Configuration Parameter

Tunnel Mode

Tunnel Source

Tunnel Destination

Interface Prefix/Address

Manual

ipv6ip

An IPv4 address or a reference to an interface on which IPv4 is configured.

An IPv4 address.

An IPv6 address.

GRE/IPv4

gre ip

An IPv4 address.

An IPv6 address.

Compatible

ipv6ip auto-tunnel

Not required. These are all point-to-multipoint tunneling types. The IPv4 destination address is calculated, on a per-packet basis, from the IPv6 destination.

Not required. The interface address is generated as ::tunnel-source/96.

6to4

ipv6ip 6to4

An IPv6 address. The prefix must embed the tunnel source IPv4 address.

ISATAP

ipv6ip isatap

An IPv6 prefix in modified eui-64 format. The IPv6 address is generated from the prefix and the tunnel source IPv4 address.

IPv6 Manually Configured Tunnels

A manually configured tunnel is equivalent to a permanent link between two IPv6 domains over an IPv4 backbone. The primary use is for stable connections that require regular secure communication between two edge routers or between an end system and an edge router, or for connection to remote IPv6 networks.

An IPv6 address is manually configured on a tunnel interface, and manually configured IPv4 addresses are assigned to the tunnel source and the tunnel destination. The host or router at each end of a configured tunnel must support both the IPv4 and IPv6 protocol stacks. Manually configured tunnels can be configured between border routers or between a border router and a host. CEF switching can be used for IPv6 manually configured tunnels, or CEF switching can be disabled if process switching is needed.

Automatic 6to4 Tunnels

An automatic 6to4 tunnel allows isolated IPv6 domains to be connected over an IPv4 network to remote IPv6 networks. The key difference between automatic 6to4 tunnels and manually configured tunnels is that the tunnel is not point-to-point; it is point-to-multipoint. In automatic 6to4 tunnels, routers are not configured in pairs because they treat the IPv4 infrastructure as a virtual nonbroadcast multiaccess (NBMA) link. The IPv4 address embedded in the IPv6 address is used to find the other end of the automatic tunnel.

An automatic 6to4 tunnel may be configured on a border router in an isolated IPv6 network, which creates a tunnel on a per-packet basis to a border router in another IPv6 network over an IPv4 infrastructure. The tunnel destination is determined by the IPv4 address of the border router extracted from the IPv6 address that starts with the prefix 2002::/16, where the format is 2002:border-router-IPv4-address ::/48. Following the embedded IPv4 address are 16 bits that can be used to number networks within the site. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks. 6to4 tunnels are configured between border routers or between a border router and a host.

The simplest deployment scenario for 6to4 tunnels is to interconnect multiple IPv6 sites, each of which has at least one connection to a shared IPv4 network. This IPv4 network could be the global Internet or a corporate backbone. The key requirement is that each site have a globally unique IPv4 address; the Cisco IOS software uses this address to construct a globally unique 6to4/48 IPv6 prefix. As with other tunnel mechanisms, appropriate entries in a Domain Name System (DNS) that map between hostnames and IP addresses for both IPv4 and IPv6 allow the applications to choose the required address.

Automatic IPv4-Compatible IPv6 Tunnels

Automatic IPv4-compatible tunnels use IPv4-compatible IPv6 addresses. IPv4-compatible IPv6 addresses are IPv6 unicast addresses that have zeros in the high-order 96 bits of the address and an IPv4 address in the low-order 32 bits. They can be written as 0:0:0:0:0:0:A.B.C.D or ::A.B.C.D, where "A.B.C.D" represents the embedded IPv4 address.

The tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of IPv4-compatible IPv6 addresses. The host or router at each end of an IPv4-compatible tunnel must support both the IPv4 and IPv6 protocol stacks. IPv4-compatible tunnels can be configured between border routers or between a border router and a host. Using IPv4-compatible tunnels is an easy method to create tunnels for IPv6 over IPv4, but the technique does not scale for large networks.


Note

IPv4-compatible tunnels were initially supported for IPv6, but are currently being deprecated. Cisco now recommends that you use a different IPv6 tunneling technique named ISATAP tunnels.

ISATAP Tunnels

The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) is an automatic overlay tunneling mechanism that uses the underlying IPv4 network as a nonbroadcast multiaccess (NBMA) link layer for IPv6. ISATAP is designed for transporting IPv6 packets within a site where a native IPv6 infrastructure is not yet available; for example, when sparse IPv6 hosts are deployed for testing. ISATAP tunnels allow individual IPv4/IPv6 dual-stack hosts within a site to communicate with other such hosts on the same virtual link, basically creating an IPv6 network using the IPv4 infrastructure.

The ISATAP router provides standard router advertisement network configuration support for the ISATAP site. This feature allows clients to automatically configure themselves as they would do if they were connected to an Ethernet. It can also be configured to provide connectivity out of the site. ISATAP uses a well-defined IPv6 address format composed of any unicast IPv6 prefix (/64), which can be link-local or global (including 6to4 prefixes), enabling IPv6 routing locally or on the Internet. The IPv4 address is encoded in the last 32 bits of the IPv6 address, enabling automatic IPv6-in-IPv4 tunneling.

While the ISATAP tunneling mechanism is similar to other automatic tunneling mechanisms, such as IPv6 6to4 tunneling, ISATAP is designed for transporting IPv6 packets within a site, not between sites.

ISATAP uses unicast addresses that include a 64-bit IPv6 prefix and a 64-bit interface identifier. The interface identifier is created in modified EUI-64 format in which the first 32 bits contain the value 000:5EFE to indicate that the address is an IPv6 ISATAP address. The table below shows the layout of an ISATAP address.

Table 4 ISATAP address example

64 Bits

32 Bits

32 Bits

Link local or global IPv6 unicast prefix

0000:5EFE

IPv4 address of the ISATAP link

As shown in the table above, an ISATAP address consists of an IPv6 prefix and the ISATAP interface identifier. This interface identifier includes the IPv4 address of the underlying IPv4 link. The following example shows what an actual ISATAP address would look like if the prefix is 2001:0DB8:1234:5678::/64 and the embedded IPv4 address is 10.173.129.8. In the ISATAP address, the IPv4 address is expressed in hexadecimal as 0AAD:8108.

Example

2001:0DB8:1234:5678:0000:5EFE:0AAD:8108

Rate-Based Satellite Control Protocol Tunnels

Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPsec), over satellite links without breaking the end-to-end model.

Satellite links have several characteristics that affect the performance of IP protocols over the link. The figure below shows that satellite links can have a one-way delay of 275 milliseconds. A round-trip time (RTT) of 550 milliseconds is a very long delay for TCP. Another issue is the high error rates (packet loss rates) that are typical of satellite links as compared to wired links in LANs. Even the weather affects satellite links, causing a decrease in available bandwidth and an increase in RTT and packet loss.

Figure 5. Typical Satellite Link

Long RTT keeps TCP in a slow start mode, which increases the time before the satellite link bandwidth is fully used. TCP and Stream Control Transmission Protocol (SCTP) interpret packet loss events as congestion in the network and start to perform congestion recovery procedures, which reduce the traffic being sent over the link.

Although available satellite link bandwidths are increasing, the long RTT and high error rates experienced by IP protocols over satellite links are producing a high bandwidth-delay product (BDP).

To address the problem of TCP being kept in a slow start mode when a satellite link is used, a disruptive performance enhancing proxy (PEP) solution is often introduced into the network. In the figure below, you can see that the transport connection is broken up into three sections with hosts on the remote side connecting to the Internet through their default router. The router sends all Internet-bound traffic to the TCP PEP, which terminates the TCP connection to the Internet. The PEP generates a local TCP ACK (TCP spoofing) for all data. Traffic is buffered and retransmitted through a single PEP protocol connection over the satellite link. The second PEP receives the data from the satellite link and retransmits the data over separate TCP connections to the Internet. TCP transmission is disrupted, so dropped packets are not interpreted as TCP congestion and can be retransmitted from buffered data. Minimal TCP ACKs and reduced TCP slow starts allow more bandwidth to be used.

Figure 6. Disruptive TCP PEP Solution

One of the disadvantages to using disruptive TCP PEP is the breaking of the end-to-end model. Some applications cannot work when the flow of traffic is broken, and the PEP has no provision for handling encrypted traffic (IPsec). New transport protocols such as SCTP require special handling or additional code to function with disruptive TCP PEP. An additional managed network component is also required at every satellite router.

RBSCP has been designed to preserve the end-to-end model and provide performance improvements over the satellite link without using a PEP solution. IPsec encryption of clear-text traffic (for example a VPN service configuration) across the satellite link is supported. RBSCP allows two routers to control and monitor the sending rates of the satellite link, thereby increasing the bandwidth utilization. Lost packets are retransmitted over the satellite link by RBSCP, preventing the end host TCP senders from going into slow start mode.

RBSCP is implemented using a tunnel interface as shown in the figure below. The tunnel can be configured over any network interface supported by Cisco IOS software that can be used by a satellite modem or internal satellite modem network module. IP traffic is sent across the satellite link with appropriate modifications and enhancements that are determined by the router configuration. Standard routing or policy-based routing can be used to determine the traffic to be sent through the RBSCP tunnel.

Figure 7. Nondisruptive RBSCP Solution

RBSCP tunnels can be configured for any of the following features:

  • Time Delay --One of the RBSCP routers can be configured to hold frames due for transmission through the RBSCP tunnel. The delay time increases the RTT at the end host and allows RBSCP time to retransmit lost TCP frames or other protocol frames. If the retransmission is successful, it prevents lost frame events from reaching the end host where congestion procedures would be enabled. In some cases, the retransmission can be completed by RBSCP without inserting the delay. This option should be used only when the RTT of the satellite link is greater than 700 milliseconds.

  • ACK Splitting --Performance improvements can be made for clear-text TCP traffic using acknowledgement (ACK) splitting in which a number of additional TCP ACKs are generated for each TCP ACK received. TCP will open a congestion window by one maximum transmission unit (MTU) for each TCP ACK received. Opening the congestion window results in increased bandwidth becoming available. Configure this feature only when the satellite link is not using all the available bandwidth. Encrypted traffic cannot use ACK splitting.

  • Window Stuffing --Clear-text TCP and SCTP traffic can benefit from the RBSCP window stuffing feature. RBSCP can buffer traffic so that the advertised window can be incremented up to the available satellite link bandwidth or the available memory in the router. The end host that sends the packets is fooled into thinking that a larger window exists at the receiving end host and sends more traffic. Use this feature with caution because the end host may send too much traffic for the satellite link to handle and the resulting loss and retransmission of packets may cause link congestion.

  • SCTP Drop Reporting --SCTP uses an appropriate byte counting method instead of ACK counting to determine the size of the transmission window, so ACK splitting does not work with SCTP. The RBSCP tunnel can generate an SCTP packet-dropped report for packets dropped across the satellite but not as a result of congestion loss. This SCTP drop reporting is on by default and provides a chance to retransmit the packet without affecting the congestion window size. Actual congestion losses are still reported, and normal recovery mechanisms are activated.

Path MTU Discovery

Path MTU Discovery (PMTUD) can be enabled on a GRE or IP-in-IP tunnel interface. When PMTUD (RFC 1191) is enabled on a tunnel interface, the router performs PMTUD processing for the GRE (or IP-in-IP) tunnel IP packets. The router always performs PMTUD processing on the original data IP packets that enter the tunnel. When PMTUD is enabled, packet fragmentation is not permitted for packets that traverse the tunnel because the Don’t Fragment (DF) bit is set on all the packets. If a packet that enters the tunnel encounters a link with a smaller MTU, the packet is dropped and an ICMP message is sent back to the sender of the packet. This message indicates that fragmentation was required (but not permitted) and provides the MTU of the link that caused the packet to be dropped.

For more detailed information about PMTUD, see the IP Fragmentation and PMTUD document.


Note

PMTUD on a tunnel interface requires that the tunnel endpoint be able to receive ICMP messages generated by routers in the path of the tunnel. Check that ICMP messages can be received before using PMTUD over firewall connections.

Use the tunnel path-mtu-discovery command to enable PMTUD for the tunnel packets, and use the show interfaces tunnel command to verify the tunnel PMTUD parameters. PMTUD currently works only on GRE and IP-in-IP tunnel interfaces.

QoS Options for Tunnels

A tunnel interface supports many of the same quality of service (QoS) features as a physical interface. QoS provides a way to ensure that mission-critical traffic has an acceptable level of performance. QoS options for tunnels include support for applying generic traffic shaping (GTS) directly on the tunnel interface and support for class-based shaping using the modular QoS CLI (MQC). Tunnel interfaces also support class-based policing, but they do not support committed access rate (CAR).


Note

Service policies are not supported on tunnel interfaces on the Cisco 7500 series routers.

GRE tunnels allow the router to copy the IP precedence bit values of the ToS byte to the tunnel or the GRE IP header that encapsulates the inner packet. Intermediate routers between the tunnel endpoints can use the IP precedence values to classify the packets for QoS features such as policy routing, weighted fair queueing (WFQ), and weighted random early detection (WRED).

When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets that travel across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. Tunnel packets can, however, be classified before tunneling and encryption can occur by using the QoS preclassify feature on the tunnel interface or on the crypto map.


Note

Class-based WFQ (CBWFQ) inside class-based shaping is not supported on a multipoint interface.

For examples of how to implement some QoS features on a tunnel interface, see the Example Configuring QoS Options on Tunnel Interfaces.

How to Implement Tunnels

Determining the Tunnel Type

Before configuring a tunnel, you must determine what type of tunnel you need to create.

SUMMARY STEPS

    1.    Determine the passenger protocol.

    2.    Determine the tunnel CLI type.

    3.    Determine the tunnel mode command keyword, if appropriate.


DETAILED STEPS
    Step 1   Determine the passenger protocol.

    The passenger protocol is the protocol that you are encapsulating.

    Step 2   Determine the tunnel CLI type.

    The table below shows how to determine the tunnel CLI command required for the transport protocol that you are using in the tunnel.

    Table 5 Determining the Tunnel CLI by the Transport Protocol

    Transport Protocol

    Tunnel CLI Command

    CLNS

    ctunnel ( with optional mode gre keywords)

    Other

    tunnel mode ( with appropriate keyword)

    Step 3   Determine the tunnel mode command keyword, if appropriate.

    The table below shows how to determine the appropriate keyword to use with the tunnel mode command. In the tasks that follow in this module, only the relevant keywords for the tunnel mode command are displayed.

    Table 6 Determining the tunnel mode Command Keyword

    Keyword

    Purpose

    dvmrp

    Use the dvmrp keyword to specify that the Distance Vector Multicast Routing Protocol encapsulation will be used.

    gre ip

    Use the gre ip keywords to specify that GRE encapsulation over IP will be used.

    gre ipv6

    Use the gre ipv6 keywords to specify that GRE encapsulation over IPv6 will be used.

    gre multipoint

    Use the gre multipoint keywords to specify that multipoint GRE (mGRE) encapsulation will be used.

    ipip [decapsulate-any]

    Use the ipip keyword to specify that IP-in-IP encapsulation will be used. The optional decapsulate-any keyword terminates any number of IP-in-IP tunnels at one tunnel interface. Note that this tunnel will not carry any outbound traffic; however, any number of remote tunnel endpoints can use a tunnel configured this way as their destination.

    ipv6

    Use the ipv6 keyword to specify that generic packet tunneling in IPv6 will be used.

    ipv6ip

    Use the ipv6ip keyword to specify that IPv6 will be used as the passenger protocol and IPv4 as both the carrier (encapsulation) and transport protocol. When additional keywords are not used, manual IPv6 tunnels are configured. Additional keywords can be used to specify IPv4-compatible, 6to4, or ISATAP tunnels.

    mpls

    Use the mpls keyword to specify that MPLS will be used for configuring Traffic Engineering (TE) tunnels.

    rbscp

    Use the rbscp keyword to specify that RBSCP tunnels will be used.

    What to Do Next

    To configure an RBSCP tunnel to carry IP data packets over a satellite or other long-distance delay link with high error rates, proceed to the Configuring the RBSCP Tunnel.

    Configuring a GRE Tunnel

    Perform this task to configure a GRE tunnel. A tunnel interface is used to pass protocol traffic across a network that does not normally support the protocol. To build a tunnel, a tunnel interface must be defined on each of two routers and the tunnel interfaces must reference each other. At each router, the tunnel interface must be configured with a L3 address. The tunnel endpoints, tunnel source, and tunnel destination must be defined, and the type of tunnel must be selected. Optional steps can be performed to customize the tunnel.

    Remember to configure the router at each end of the tunnel. If only one side of a tunnel is configured, the tunnel interface may still come up and stay up (unless keepalive is configured), but packets going into the tunnel will be dropped.

    In Cisco IOS Release 12.2(8)T and later releases, CEF-switching over multipoint GRE tunnels was introduced. Previously, only process switching was available for multipoint GRE tunnels.

    GRE Tunnel Keepalive

    Keepalive packets can be configured to be sent over IP-encapsulated GRE tunnels. You can specify the rate at which keepalives will be sent and the number of times that a device will continue to send keepalive packets without a response before the interface becomes inactive. GRE keepalive packets may be sent from both sides of a tunnel or from just one side.

    Before You Begin

    Ensure that the physical interface to be used as the tunnel source in this task is up and configured with the appropriate IP address. For hardware technical descriptions and information about installing interfaces, see the hardware installation and configuration publication for your product.


    Note

    GRE tunnel keepalive is not supported in cases where virtual route forwarding (VRF) is applied to a GRE tunnel.

    >
    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface type number

      4.    bandwidth kbps

      5.    keepalive [period [retries]]

      6.    tunnel source {ip-address | interface-type interface-number}

      7.    tunnel destination {hostname | ip-address}

      8.    tunnel key key-number

      9.    tunnel mode {gre ip| gre multipoint}

      10.    ip mtu bytes

      11.    ip tcp mss mss-value

      12.    tunnel path-mtu-discovery [age-timer {aging-mins| infinite}]

      13.    end


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Router> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.

       
      Step 2 configure terminal


      Example:
      Router# configure terminal
       

      Enters global configuration mode.

       
      Step 3 interface type number


      Example:
      Router(config)# interface tunnel 0
       

      Specifies the interface type and number and enters interface configuration mode.

      • To configure a tunnel, use tunnel for the type argument.

      • On some router platforms such as the Cisco 7500 series, the number argument may consist of a slot, port adapter, and port number. For more details, see the interface command in the Cisco IOS Interface and Hardware Component Command Reference.

       
      Step 4 bandwidth kbps


      Example:
      Router(config-if)# bandwidth 1000
       

      Sets the current bandwidth value for an interface and communicates it to higher-level protocols. Specifies the tunnel bandwidth to be used to transmit packets.

      • Use the kbpsargument to set the bandwidth, in kilobits per second (kbps).

      Note   

      This is a routing parameter only; it does not affect the physical interface. The default bandwidth setting on a tunnel interface is 9.6 kbps. You should set the bandwidth on a tunnel to an appropriate value.

       
      Step 5 keepalive [period [retries]]


      Example:
      Router(config-if)# keepalive 3 7
       

      (Optional) Specifies the number of times that the device will continue to send keepalive packets without response before bringing the tunnel interface protocol down.

      • GRE keepalive packets may be configured either on only one side of the tunnel or on both.

      • If GRE keepalive is configured on both sides of the tunnel, the period and retries arguments can be different at each side of the link.

      Note   

      This command is supported only on GRE point-to-point tunnels.

       
      Step 6 tunnel source {ip-address | interface-type interface-number}


      Example:
      Router(config-if)# tunnel source Ethernet 1
       

      Configures the tunnel source.

      • Use the ip-addressargument to specify the source IP address.

      • Use the interface-typeand interface-numberarguments to specify the interface to use.

      Note   

      The tunnel source and destination IP addresses must be defined on two separate devices.

       
      Step 7 tunnel destination {hostname | ip-address}


      Example:
      Router(config-if)# tunnel destination 172.17.2.1
       

      Configures the tunnel destination.

      • Use the hostnameargument to specify the name of the host destination.

      • Use the ip-addressargument to specify the IP address of the host destination.

      Note   

      The tunnel source and destination IP addresses must be defined on two separate devices.

       
      Step 8 tunnel key key-number


      Example:
      Router(config-if)# tunnel key 1000
       

      (Optional) Enables an ID key for a tunnel interface.

      • Use the key-numberargument to identify a tunnel key that is carried in each packet.

      • Tunnel ID keys can be used as a form of weak security to prevent improper configuration or injection of packets from a foreign source.

      Note   

      This command is supported only on GRE tunnel interfaces. We do not recommend relying on this key for security purposes.

       
      Step 9 tunnel mode {gre ip| gre multipoint}


      Example:
      Router(config-if)# tunnel mode gre ip
       

      Specifies the encapsulation protocol to be used in the tunnel.

      • Use the gre ip keywords to specify that GRE over IP encapsulation will be used.

      • Use the gre multipoint keywords to specify that multipoint GRE (mGRE) will be used.

       
      Step 10 ip mtu bytes


      Example:
      Router(config-if)# ip mtu 1400
       

      (Optional) Set the maximum transmission unit (MTU) size of IP packets sent on an interface.

      • If an IP packet exceeds the MTU set for the interface, the Cisco IOS software will fragment it unless the DF bit is set.

      • All devices on a physical medium must have the same protocol MTU in order to operate.

      Note   

      If the tunnel path-mtu-discovery command is enabled in Step 12, do not configure this command.

       
      Step 11 ip tcp mss mss-value


      Example:
      Router(config-if)# ip tcp mss 250
       

      (Optional) Specifies the maximum segment size (MSS) for TCP connections that originate or terminate on a router.

      • Use the mss-value argument to specify the maximum segment size for TCP connections, in bytes.

       
      Step 12 tunnel path-mtu-discovery [age-timer {aging-mins| infinite}]


      Example:
      Router(config-if)# tunnel path-mtu-discovery
       

      (Optional) Enables Path MTU Discovery (PMTUD) on a GRE or IP-in-IP tunnel interface.

      • When PMTUD is enabled on a tunnel interface, PMTUD will operate for GRE IP tunnel packets to minimize fragmentation in the path between the tunnel endpoints.

       
      Step 13 end


      Example:
      Router(config-if)# end
       

      Exits interface configuration mode and returns to privileged EXEC mode.

       

      What to Do Next

      Proceed to the Verifying Tunnel Configuration and Operation.

      Configuring GRE IPv6 Tunnels

      Perform this task to configure a GRE tunnel on an IPv6 network. GRE tunnels can be configured to run over an IPv6 network layer and transport IPv6 and IPv4 packets through IPv6 tunnels.

      Before You Begin

      When GRE IPv6 tunnels are configured, IPv6 addresses are assigned to the tunnel source and the tunnel destination. The tunnel interface can have either IPv4 or IPv6 addresses (this is not shown in the task below). The host or device at each end of the configured tunnel must support both IPv4 and IPv6 protocol stacks.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    interface tunnel tunnel-number

        4.    tunnel source {ipv6-address | interface-type interface-number}

        5.    tunnel destination ipv6-address

        6.    tunnel mode gre ipv6

        7.    end


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Device> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.

         
        Step 2 configure terminal


        Example:
        Device# configure terminal
         

        Enters global configuration mode.

         
        Step 3 interface tunnel tunnel-number


        Example:
        Device(config)# interface tunnel 0
         

        Specifies a tunnel interface and number and enters interface configuration mode.

         
        Step 4 tunnel source {ipv6-address | interface-type interface-number}


        Example:
        Device(config-if)# tunnel source ethernet 0
         

        Specifies the source IPv6 address or the source interface type and number for the tunnel interface.

        • If an interface type and number are specified, the interface must be configured with an IPv6 address.

        Note   

        Only the syntax used in this context is displayed. For more details, see the IPv6 Command Reference.

         
        Step 5 tunnel destination ipv6-address


        Example:
        Device(config-if)# tunnel destination 2001:0DB8:0C18:2::300
         

        Specifies the destination IPv6 address for the tunnel interface.

        Note   

        Only the syntax used in this context is displayed. For more details, see the IPv6 Command Reference.

         
        Step 6 tunnel mode gre ipv6


        Example:
        Device(config-if)# tunnel mode gre ipv6
         

        Specifies a GRE IPv6 tunnel.

        Note   

        The tunnel mode gre ipv6 command specifies GRE as the encapsulation protocol for the tunnel interface. Only the syntax used in this context is displayed. For more details, see the IPv6 Command Reference.

         
        Step 7 end


        Example:
        Device(config-if)# end
         

        Exits interface configuration mode and returns to privileged EXEC mode.

         

        What to Do Next

        Proceed to the “Verifying Tunnel Configuration and Operation” section.

        Configuring GRE Tunnel IP Source and Destination VRF Membership

        This task explains how to configure the source and destination of a tunnel to belong to any virtual private network (VPN) routing/forwarding (VRFs) tables


        Note

        Cisco 10000 Series Routers

        • The VRF associated with the tunnel vrf command is the same as the VRF associated with the physical interface over which the tunnel sends packets (outer IP packet routing).

        • The VRF associated with the tunnel by using the ip vrf forwarding command is the VRF that the packets are to be forwarded in as the packets exit the tunnel (inner IP packet routing).

        • The Cisco 10000 series router does not support the fragmentation of multicast packets passing through a multicast tunnel.

        >
        SUMMARY STEPS

          1.    enable

          2.    configure {terminal | memory | network}

          3.    interface tunnel slot

          4.    ip vrf forwarding vrf-name

          5.    ip address ip-address subnet-mask

          6.    tunnel source {ip-address | type number}

          7.    tunnel destination {hostname | ip-address}

          8.    tunnel vrf vrf-name


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 enable


          Example:
          Router> enable
           

          Enables higher privilege levels, such as privileged EXEC mode.

          • Enter your password if prompted.

           
          Step 2 configure {terminal | memory | network}


          Example:
          Router# configure terminal
           

          Enters global configuration mode.

           
          Step 3 interface tunnel slot


          Example:
          Router(config)# interface tunnel 0
           

          Enters interface configuration mode for the specified interface.

           
          Step 4 ip vrf forwarding vrf-name


          Example:
          Router(config-if)# ip vrf forwarding green
           

          Defines the VRF.

           
          Step 5 ip address ip-address subnet-mask


          Example:
          Router(config-if)# ip address 10.7.7.7 255.255.255.255
           

          Specifies the ip address and subnet mask.

           
          Step 6 tunnel source {ip-address | type number}


          Example:
          Router(config-if)# tunnel source loop 0
           

          Specifies the tunnel source.

           
          Step 7 tunnel destination {hostname | ip-address}


          Example:
          Router(config-if)# tunnel destination 10.5.5.5
           

          Defines the tunnel destination.

           
          Step 8 tunnel vrf vrf-name


          Example:
          Router(config-if)# tunnel vrf finance1
           

          Defines the VRF.

           

          What to Do Next

          Proceed to the Verifying Tunnel Configuration and Operation.

          Configuring a CTunnel

          Perform this task to configure an IP over CLNS tunnel (CTunnel). To configure a CTunnel between a single pair of routers, a tunnel interface must be configured with an IP address, and a tunnel destination must be defined. The destination network service access point (NSAP) address for Router A would be the NSAP address of Router B, and the destination NSAP address for Router B would be the NSAP address of Router A. Ideally, the IP addresses used for the virtual interfaces at either end of the tunnel should be in the same IP subnet. Remember to configure the router at each end of the tunnel.

          CTunnel

          A CTunnel lets you transport IP traffic over Connectionless Network Service (CLNS), for example, on the data communications channel (DCC) of a SONET ring. CTunnels allow IP packets to be tunneled through the Connectionless Network Protocol (CLNP) to preserve TCP/IP services.

          Configuring a CTunnel allows you to telnet to a remote router that has only CLNS connectivity. Other management facilities can also be used, such as Simple Network Management Protocol (SNMP) and TFTP, which otherwise would not be available over a CLNS network.

          SUMMARY STEPS

            1.    enable

            2.    configure terminal

            3.    interface ctunnel interface-number

            4.    ip address ip-address mask

            5.    ctunnel destination remote-nsap-address

            6.    end

            7.    show interfaces ctunnel interface-number


          DETAILED STEPS
             Command or ActionPurpose
            Step 1 enable


            Example:
            Router> enable
             

            Enables privileged EXEC mode.

            • Enter your password if prompted.

             
            Step 2 configure terminal


            Example:
            Router# configure terminal
             

            Enters global configuration mode.

             
            Step 3 interface ctunnel interface-number


            Example:
            Router(config)# interface ctunnel 102
             

            Creates a virtual interface to transport IP over a CLNS tunnel and enters interface configuration mode.

            Note   

            The interface number must be unique for each CTunnel interface.

             
            Step 4 ip address ip-address mask


            Example:
            Router(config-if)# ip address 10.0.0.1 255.255.255.0
             

            Enables IP on the interface.

            • Use the ip-addressand mask arguments to specify the IP address and mask for the interface.

             
            Step 5 ctunnel destination remote-nsap-address


            Example:
            Router(config-if)# ctunnel destination 49.0001.2222.2222.2222.00
             

            Specifies the destination NSAP address of the CTunnel, where the packets exit the tunnel.

            • Use the remote-nsap-addressargument to specify the NSAP address at the CTunnel endpoint.

             
            Step 6 end


            Example:
            Router(config-if)# end
             

            Exits interface configuration mode and returns to privileged EXEC mode.

             
            Step 7 show interfaces ctunnel interface-number


            Example:
            Router# show interfaces ctunnel 102
             

            (Optional) Displays information about an IP over CLNS tunnel.

            • Use the interface-number argument to specify a CTunnel interface.

            • Use this command to verify the CTunnel configuration.

             

            Troubleshooting Tips

            Use the ping command to diagnose basic network connectivity issues.

            What to Do Next

            Proceed to the Verifying Tunnel Configuration and Operation.

            Configuring GRE CLNS CTunnels to Carry IPv4 and IPv6 Packets

            Perform this task to configure a CTunnel in GRE mode to transport IPv4 and IPv6 packets in a CLNS network.

            To configure a CTunnel between a single pair of routers, a tunnel interface must be configured with an IP address, and a tunnel destination must be defined. The destination network service access point (NSAP) address for Router A would be the NSAP address of Router B, and the destination NSAP address for Router B would be the NSAP address of Router A. Ideally, the IP addresses used for the virtual interfaces at either end of the tunnel should be in the same IP subnet. Remember to configure the router at each end of the tunnel.

            Tunnels for IPv4 and IPv6 Packets over CLNS Networks

            Configuring the ctunnel mode gre command on a CTunnel interface enables IPv4 and IPv6 packets to be tunneled over CLNS in accordance with RFC 3147. Compliance with this RFC should allow interoperation between Cisco equipment and that of other vendors in which the same standard is implemented.

            RFC 3147 specifies the use of GRE for tunneling packets. The implementation of this feature does not include support for GRE services defined in header fields, such as those used to specify checksums, keys, or sequencing. Any packets received that specify the use of these features will be dropped.

            The default CTunnel mode continues to use the standard Cisco encapsulation, which will tunnel only IPv4 packets. If you want to tunnel IPv6 packets, you must use the GRE encapsulation mode. Both ends of the tunnel must be configured with the same mode for either method to work.

            Before You Begin

            • An IPv4 or IPv6 address must be configured on a CTunnel interface, and manually configured CLNS addresses must be assigned to the CTunnel destination.

            • The host or router at each end of a configured CTunnel must support both the IPv4 and IPv6 protocol stacks.

            • The CTunnel source and destination must both be configured to run in the same mode.


            Note

            GRE services, such as those used to specify checksums, keys, or sequencing, are not supported. Packets that request use of those features will be dropped.

            >
            SUMMARY STEPS

              1.    enable

              2.    configure terminal

              3.    interface ctunnel interface-number

              4.    Do one of the following:

              • ip address ip-address mask
              • ipv6 address ipv6-prefix / prefix-length [eui-64]

              5.    ctunnel destination remote-nsap-address

              6.    ctunnel mode gre

              7.    end

              8.    show interfaces ctunnel interface-number


            DETAILED STEPS
               Command or ActionPurpose
              Step 1 enable


              Example:
              Router> enable
               

              Enables privileged EXEC mode.

              • Enter your password if prompted.

               
              Step 2 configure terminal


              Example:
              Router# configure terminal
               

              Enters global configuration mode.

               
              Step 3 interface ctunnel interface-number


              Example:
              Router(config)# interface ctunnel 102
               

              Creates a virtual interface to transport IP over a CLNS tunnel and enters interface configuration mode.

              Note   

              The interface number must be unique for each CTunnel interface.

               
              Step 4Do one of the following:
              • ip address ip-address mask
              • ipv6 address ipv6-prefix / prefix-length [eui-64]


              Example:
              Router(config-if)# ipv6 address 2001:0DB8:1234:5678::3/126
               

              Specifies the IPv4 or IPv6 network assigned to the interface and enables IPv4 or IPv6 packet processing on the interface.

              Note   

              For more information about IPv6 network, see the "Configuring Basic Connectivity for IPv6" module in the Cisco IOS IPv6 Configuration Guide.

               
              Step 5 ctunnel destination remote-nsap-address


              Example:
              Router(config-if)# ctunnel destination 192.168.30.1
               

              Specifies the destination NSAP address of the CTunnel, where the packets are extracted.

              • Use the remote-nsap-addressargument to specify the NSAP address at the CTunnel endpoint.

               
              Step 6 ctunnel mode gre


              Example:
              Router(config-if)# ctunnel mode gre
               

              Specifies a CTunnel running in GRE mode for both IPv4 and IPv6 traffic.

              Note   

              The ctunnel mode gre command specifies GRE as the encapsulation protocol for the tunnel.

               
              Step 7 end


              Example:
              Router(config-if)# end
               

              Exits interface configuration mode and returns to privileged EXEC mode.

               
              Step 8 show interfaces ctunnel interface-number


              Example:
              Router# show interfaces ctunnel 102
               

              (Optional) Displays information about an IP over CLNS tunnel.

              • Use the interface-number argument to specify a CTunnel interface.

              • Use this command to verify the CTunnel configuration.

               

              What to Do Next

              Proceed to the Verifying Tunnel Configuration and Operation.

              Configuring Manual IPv6 Tunnels

              This task explains how to configure a manual IPv6 overlay tunnel.

              Before You Begin

              With manually configured IPv6 tunnels, an IPv6 address is configured on a tunnel interface and manually configured IPv4 addresses are assigned to the tunnel source and the tunnel destination. The host or router at each end of a configured tunnel must support both the IPv4 and IPv6 protocol stacks.

              SUMMARY STEPS

                1.    enable

                2.    configure terminal

                3.    interface tunnel tunnel-number

                4.    ipv6 address ipv6-prefix / prefix-length [eui-64]

                5.    tunnel source {ip-address| interface-type interface-number}

                6.    tunnel destination ip-address

                7.    tunnel mode ipv6ip

                8.    end


              DETAILED STEPS
                 Command or ActionPurpose
                Step 1 enable


                Example:
                Router> enable
                 

                Enables privileged EXEC mode.

                • Enter your password if prompted.

                 
                Step 2 configure terminal


                Example:
                Router# configure terminal
                 

                Enters global configuration mode.

                 
                Step 3 interface tunnel tunnel-number


                Example:
                Router(config)# interface tunnel 0
                 

                Specifies a tunnel interface and number and enters interface configuration mode.

                 
                Step 4 ipv6 address ipv6-prefix / prefix-length [eui-64]


                Example:
                Router(config-if)# ipv6 address 2001:0DB8:1234:5678::3/126
                 

                Specifies the IPv6 network assigned to the interface and enables IPv6 processing on the interface.

                Note   

                For more information on configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

                 
                Step 5 tunnel source {ip-address| interface-type interface-number}


                Example:
                Router(config-if)# tunnel source ethernet 0
                 

                Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

                • If an interface is specified, the interface must be configured with an IPv4 address.

                 
                Step 6 tunnel destination ip-address


                Example:
                Router(config-if)# tunnel destination 192.168.30.1
                 

                Specifies the destination IPv4 address for the tunnel interface.

                 
                Step 7 tunnel mode ipv6ip


                Example:
                Router(config-if)# tunnel mode ipv6ip
                 

                Specifies a manual IPv6 tunnel.

                Note   

                The tunnel mode ipv6ip command specifies IPv6 as the passenger protocol and IPv4 as both the carrier (encapsulation) and transport protocol for the manual IPv6 tunnel.

                 
                Step 8 end


                Example:
                Router(config-if)# end
                 

                Exits interface configuration mode and returns to privileged EXEC mode.

                 

                What to Do Next

                Proceed to the Verifying Tunnel Configuration and Operation.

                Configuring 6to4 Tunnels

                This task explains how to configure a 6to4 overlay tunnel.

                Before You Begin

                With 6to4 tunnels, the tunnel destination is determined by the border-router IPv4 address, which is concatenated to the prefix 2002::/16 in the format 2002:border-router-IPv4-address::/48. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks.


                Note

                The configuration of only one IPv4-compatible tunnel and one 6to4 IPv6 tunnel is supported on a router. If you choose to configure both of these tunnel types on the same router, we strongly recommend that they not share the same tunnel source.

                The reason that a 6to4 tunnel and an IPv4-compatible tunnel cannot share the same interface is that both of them are NBMA "point-to-multipoint" access links and only the tunnel source can be used to reorder the packets from a multiplexed packet stream into a single packet stream for an incoming interface. So when a packet with an IPv4 protocol type of 41 arrives on an interface, that packet is mapped to an IPv6 tunnel interface on the basis of the IPv4 address. However, if both the 6to4 tunnel and the IPv4-compatible tunnel share the same source interface, the router cannot determine the IPv6 tunnel interface to which it should assign the incoming packet.

                IPv6 manually configured tunnels can share the same source interface because a manual tunnel is a "point-to-point" link, and both the IPv4 source and IPv4 destination of the tunnel are defined.

                >
                SUMMARY STEPS

                  1.    enable

                  2.    configure terminal

                  3.    interface tunnel tunnel-number

                  4.    ipv6 address ipv6-prefix / prefix-length [eui-64]

                  5.    tunnel source {ip-address| interface-type interface-number}

                  6.    tunnel mode ipv6ip 6to4

                  7.    exit

                  8.    ipv6 route ipv6-prefix / prefix-length tunnel tunnel-number


                DETAILED STEPS
                   Command or ActionPurpose
                  Step 1 enable


                  Example:
                  Router> enable
                   

                  Enables privileged EXEC mode.

                  • Enter your password if prompted.

                   
                  Step 2 configure terminal


                  Example:
                  Router# configure terminal
                   

                  Enters global configuration mode.

                   
                  Step 3 interface tunnel tunnel-number


                  Example:
                  Router(config)# interface tunnel 0
                   

                  Specifies a tunnel interface and number and enters interface configuration mode.

                   
                  Step 4 ipv6 address ipv6-prefix / prefix-length [eui-64]


                  Example:
                  Router(config-if)# ipv6 address 2002:c0a8:6301:1::1/64
                   

                  Specifies the IPv6 address assigned to the interface and enables IPv6 processing on the interface.

                  • The 32 bits following the initial 2002::/16 prefix correspond to an IPv4 address assigned to the tunnel source.

                  Note   

                  For more information about configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

                   
                  Step 5 tunnel source {ip-address| interface-type interface-number}


                  Example:
                  Router(config-if)# tunnel source ethernet 0
                   

                  Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

                  Note   

                  The interface type and number specified in the tunnel source command must be configured with an IPv4 address.

                   
                  Step 6 tunnel mode ipv6ip 6to4


                  Example:
                  Router(config-if)# tunnel mode ipv6ip 6to4
                   

                  Specifies an IPv6 overlay tunnel using a 6to4 address.

                   
                  Step 7 exit


                  Example:
                  Router(config-if)# exit
                   

                  Exits interface configuration mode and returns to global configuration mode.

                   
                  Step 8 ipv6 route ipv6-prefix / prefix-length tunnel tunnel-number


                  Example:
                  Router(config)# ipv6 route 2002::/16 tunnel 0
                   

                  Configures a static route for the IPv6 6to4 prefix 2002::/16 to the specified tunnel interface.

                  Note   

                  When configuring a 6to4 overlay tunnel, you must configure a static route for the IPv6 6to4 prefix 2002::/16 to the 6to4 tunnel interface.

                  • The tunnel number specified in the ipv6 route command must be the same tunnel number specified in the interface tunnelcommand.

                   

                  What to Do Next

                  Proceed to the Verifying Tunnel Configuration and Operation.

                  Configuring IPv4-Compatible IPv6 Tunnels

                  This task explains how to configure an IPv4-compatible IPv6 overlay tunnel.

                  Before You Begin

                  With an IPv4-compatible tunnel, the tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of IPv4-compatible IPv6 addresses. The host or router at each end of an IPv4-compatible tunnel must support both the IPv4 and IPv6 protocol stacks.


                  Note

                  IPv4-compatible tunnels were initially supported for IPv6, but Cisco now recommends that you use a different IPv6 overlay tunneling technique.

                  >
                  SUMMARY STEPS

                    1.    enable

                    2.    configure terminal

                    3.    interface tunnel tunnel-number

                    4.    tunnel source {ip-address| interface-type interface-number}

                    5.    tunnel mode ipv6ip auto-tunnel


                  DETAILED STEPS
                     Command or ActionPurpose
                    Step 1 enable


                    Example:
                    Router> enable
                     

                    Enables privileged EXEC mode.

                    • Enter your password if prompted.

                     
                    Step 2 configure terminal


                    Example:
                    Router# configure terminal
                     

                    Enters global configuration mode.

                     
                    Step 3 interface tunnel tunnel-number


                    Example:
                    Router(config)# interface tunnel 0
                     

                    Specifies a tunnel interface and number and enters interface configuration mode.

                     
                    Step 4 tunnel source {ip-address| interface-type interface-number}


                    Example:
                    Router(config-if)# tunnel source ethernet 0
                     

                    Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

                    Note   

                    The interface type and number specified in the tunnel source command must be configured with an IPv4 address.

                     
                    Step 5 tunnel mode ipv6ip auto-tunnel


                    Example:
                    Router(config-if)# tunnel mode ipv6ip auto-tunnel
                     

                    Specifies an IPv4-compatible tunnel using an IPv4-compatible IPv6 address.

                     

                    What to Do Next

                    Proceed to the Verifying Tunnel Configuration and Operation.

                    Configuring ISATAP Tunnels

                    This task describes how to configure an ISATAP overlay tunnel.

                    Before You Begin

                    The tunnel source command used in the configuration of an ISATAP tunnel must point to an interface that is configured with an IPv4 address. The ISATAP IPv6 address and prefix (or prefixes) advertised are configured for a native IPv6 interface. The IPv6 tunnel interface must be configured with a modified EUI-64 address because the last 32 bits in the interface identifier are constructed using the IPv4 tunnel source address.

                    SUMMARY STEPS

                      1.    enable

                      2.    configure terminal

                      3.    interface tunnel tunnel-number

                      4.    ipv6 address ipv6-prefix prefix-length [eui-64]

                      5.    no ipv6 nd suppress-ra

                      6.    tunnel source {ip-address | interface-type interface-number}

                      7.    tunnel mode ipv6ip isatap

                      8.    end


                    DETAILED STEPS
                       Command or ActionPurpose
                      Step 1 enable


                      Example:
                      Device> enable
                       

                      Enables privileged EXEC mode.

                      • Enter your password if prompted.

                       
                      Step 2 configure terminal


                      Example:
                      Device# configure terminal
                       

                      Enters global configuration mode.

                       
                      Step 3 interface tunnel tunnel-number


                      Example:
                      Device(config)# interface tunnel 1
                       

                      Specifies a tunnel interface and number and enters interface configuration mode.

                       
                      Step 4 ipv6 address ipv6-prefix prefix-length [eui-64]


                      Example:
                      Device(config-if)# ipv6 address 2001:0DB8:6301::/64 eui-64
                       

                      Specifies the IPv6 address assigned to the interface and enables IPv6 processing on the interface.

                      Note   

                      For more information on configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

                       
                      Step 5 no ipv6 nd suppress-ra


                      Example:
                      Device(config-if)# no ipv6 nd suppress-ra
                       

                      Enables sending of IPv6 device advertisements to allow client autoconfiguration.

                      • Sending of IPv6 device advertisements is disabled by default on tunnel interfaces.

                       
                      Step 6 tunnel source {ip-address | interface-type interface-number}


                      Example:
                      Device(config-if)# tunnel source GigabitEthernet 1/0/1
                       

                      Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

                      Note   

                      The interface type and number specified in the tunnel source command must be configured with an IPv4 address.

                       
                      Step 7 tunnel mode ipv6ip isatap


                      Example:
                      Device(config-if)# tunnel mode ipv6ip isatap
                       

                      Specifies an IPv6 overlay tunnel using an ISATAP address.

                       
                      Step 8 end


                      Example:
                      Device(config-if)# end
                       

                      Exits interface configuration mode and returns to privileged EXEC mode.

                       

                      What to Do Next

                      Proceed to the Verifying Tunnel Configuration and Operation.

                      Configuring the RBSCP Tunnel

                      Perform this task to configure the RBSCP tunnel. Remember to configure the router at each end of the tunnel.

                      Before You Begin

                      Ensure that the physical interface to be used as the tunnel source in this task is already configured.


                      Note
                      • RBSCP was designed for wireless or long-distance delay links with high error rates such as satellite links. If you do not have long-distance delay links with high error rates, do not implement this feature.
                      • If IP access control lists (ACLs) are configured on an interface that is used by an RBSCP tunnel, the RBSCP IP protocol (199) must be allowed to enter and exit that interface or the tunnel will not function.
                      • RBSCP has some performance limitations because traffic through the tunnel is process-switched.
                      >
                      SUMMARY STEPS

                        1.    enable

                        2.    configure terminal

                        3.    interface type number

                        4.    ip unnumbered interface-type interface-number

                        5.    tunnel source {ip-address | interface-type interface-number}

                        6.    tunnel destination {hostname | ip-address}

                        7.    tunnel bandwidth {receive | transmit} bandwidth

                        8.    tunnel mode rbscp

                        9.    tunnel rbscp ack-split split-size

                        10.    tunnel rbscp delay

                        11.    tunnel rbscp report

                        12.    tunnel rbscp window-stuff step-size

                        13.    end


                      DETAILED STEPS
                         Command or ActionPurpose
                        Step 1 enable


                        Example:
                        Router> enable
                         

                        Enables privileged EXEC mode.

                        • Enter your password if prompted.

                         
                        Step 2 configure terminal


                        Example:
                        Router# configure terminal
                         

                        Enters global configuration mode.

                         
                        Step 3 interface type number


                        Example:
                        Router(config)# interface tunnel 0
                         

                        Specifies the interface type and number and enters interface configuration mode.

                         
                        Step 4 ip unnumbered interface-type interface-number


                        Example:
                        Router(config-if)# ip unnumbered Ethernet 1
                         

                        Enables IP processing on an interface without assigning an explicit IP address.

                        • Whenever the unnumbered interface generates a packet (for example, for a routing update), it uses the address of the specified interface as the source address of the IP packet.

                         
                        Step 5 tunnel source {ip-address | interface-type interface-number}


                        Example:
                        Router(config-if)# tunnel source Ethernet 1
                         

                        Configures the tunnel source.

                        • Use the ip-addressargument to specify the IP address of the service provider.

                        • Use the interface-typeand interface-numberarguments to specify the interface to use. For RBSCP Cisco recommends specifying an interface as the tunnel source.

                         
                        Step 6 tunnel destination {hostname | ip-address}


                        Example:
                        Router(config-if)# tunnel destination 172.17.2.1
                         

                        Configures the tunnel destination.

                        • Use the hostnameargument to specify the name of the host destination.

                        • Use the ip-addressargument to specify the IP address of the host destination.

                         
                        Step 7 tunnel bandwidth {receive | transmit} bandwidth


                        Example:
                        Router(config-if)# tunnel bandwidth transmit 1000
                         

                        Specifies the tunnel bandwidth to be used to transmit packets.

                        • Use the bandwidthargument to specify the bandwidth.

                        Note   

                        The receive keyword is no longer used.

                         
                        Step 8 tunnel mode rbscp


                        Example:
                        Router(config-if)# tunnel mode rbscp
                         

                        Specifies the protocol to be used in the tunnel.

                        • Use the rbscp keyword to specify that RBSCP will be used as the tunnel protocol.

                         
                        Step 9 tunnel rbscp ack-split split-size


                        Example:
                        Router(config-if)# tunnel rbscp ack-split 6
                         

                        (Optional) Enables TCP acknowledgement (ACK) splitting with RBSCP tunnels.

                        • Use the split-size argument to specify the number of ACKs to send for every ACK received.

                        • The default number of ACKs is 4.

                         
                        Step 10 tunnel rbscp delay


                        Example:
                        Router(config-if)# tunnel rbscp delay
                         

                        (Optional) Enables RBSCP tunnel delay.

                        • Use this command only when the RTT measured between the two routers nearest to the satellite links is greater than 700 milliseconds.

                         
                        Step 11 tunnel rbscp report


                        Example:
                        Router(config-if)# tunnel rbscp report
                         

                        (Optional) Reports dropped RBSCP packets to SCTP.

                        • Reporting dropped packets to SCTP provides better bandwidth use because RBSCP tells the SCTP implementation at the end hosts to retransmit the dropped packets and this prevents the end hosts from assuming that the network is congested.

                         
                        Step 12 tunnel rbscp window-stuff step-size


                        Example:
                        Router(config-if)# tunnel rbscp window-stuff 1
                         

                        (Optional) Enables TCP window stuffing by increasing the value of the TCP window scale for RBSCP tunnels.

                        • Use the step-size argument to specify the step increment number.

                         
                        Step 13 end


                        Example:
                        Router(config-if)# end
                         

                        Exits interface configuration mode and returns to privileged EXEC mode.

                         

                        What to Do Next

                        This task must be repeated on the router on the other side of the satellite link. Substitute the sample IP addresses, hostnames, and other parameters for the appropriate values on the second router.

                        After the task is completed on the router on the other side of the satellite link, proceed to the Verifying RBSCP Tunnel Configuration and Operation.

                        Verifying Tunnel Configuration and Operation

                        This optional task explains how to verify tunnel configuration and operation. The commands contained in the task steps can be used in any sequence and may need to be repeated. The following commands can be used for GRE tunnels, IPv6 manually configured tunnels, and IPv6 over IPv4 GRE tunnels. This process includes the following general steps (details follow):

                        • On Router A, ping the IP address of the CTunnel interface of Router B.

                        • On Router B, ping the IP address of the CTunnel interface of Router A.

                        SUMMARY STEPS

                          1.    enable

                          2.    show interfaces tunnel number [accounting]

                          3.    ping [protocol] destination

                          4.    show ip route [address[mask]]

                          5.    ping [protocol] destination


                        DETAILED STEPS
                          Step 1   enable

                          Enables privileged EXEC mode. Enter your password if prompted.



                          Example:
                          Router> enable
                          Step 2   show interfaces tunnel number [accounting]

                          Assuming a generic example suitable for both IPv6 manually configured tunnels and IPv6 over IPv4 GRE tunnels, two routers are configured to be endpoints of a tunnel. Router A has Ethernet interface 0/0 configured as the source for tunnel interface 0 with an IPv4 address of 10.0.0.1 and an IPv6 prefix of 2001:0DB8:1111:2222::1/64. Router B has Ethernet interface 0/0 configured as the source for tunnel interface 1 with an IPv4 address of 10.0.0.2 and an IPv6 prefix of 2001:0DB8:1111:2222::2/64.

                          To verify that the tunnel source and destination addresses are configured, use the show interfaces tunnel command on Router A.



                          Example:
                          RouterA# show interfaces tunnel 0
Tunnel0 is up, line protocol is up 
  Hardware is Tunnel
  MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation TUNNEL, loopback not set
  Keepalive not set
  Tunnel source 10.0.0.1 (Ethernet0/0), destination 10.0.0.2, fastswitch TTL 255
  Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled
  Tunnel TTL 255
  Checksumming of packets disabled,  fast tunneling enabled
  Last input 00:00:14, output 00:00:04, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/0 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     4 packets input, 352 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     8 packets output, 704 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
                          Step 3   ping [protocol] destination

                          To check that the local endpoint is configured and working, use the ping command on Router A.



                          Example:
                          RouterA# ping
 2001:0DB8:1111:2222::2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:0DB8:1111:2222::2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/20/20 ms
                          Step 4   show ip route [address[mask]]

                          To check that a route exists to the remote endpoint address, use the show ip route command.



                          Example:
                          RouterA# show ip route 10.0.0.2
Routing entry for 10.0.0.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via Ethernet0/0
      Route metric is 0, traffic share count is 1
                          Step 5   ping [protocol] destination

                          To check that the remote endpoint address is reachable, use the ping command on Router A.

                          Note   

                          The remote endpoint address may not be reachable using the ping command because of filtering, but the tunnel traffic may still reach its destination.



                          Example:
                          RouterA# ping 10.0.0.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/21/28 ms

                          To check that the remote IPv6 tunnel endpoint is reachable, use the ping command again on Router A. The same note on filtering also applies to this example.



                          Example:
                          RouterA# ping 1::2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1::2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/20/20 ms

                          These steps may be repeated at the other endpoint of the tunnel.

                          Verifying RBSCP Tunnel Configuration and Operation

                          Perform one or both of the following optional tasks to verify the configuration and operation of the RBSCP tunnel configured in the Configuring the RBSCP Tunnel.

                          Verifying That the RBSCP Tunnel Is Active

                          Perform this task to verify that the RBSCP tunnel is active.

                          SUMMARY STEPS

                            1.    enable

                            2.    show rbscp [all| state| statistics] [tunnel tunnel-number]


                          DETAILED STEPS
                            Step 1   enable

                            Enables privileged EXEC mode. Enter your password if prompted.



                            Example:
                            Router> enable
                            Step 2   show rbscp [all| state| statistics] [tunnel tunnel-number]

                            Use this command with the state and tunnelkeywords to display information about the current state of the tunnel. In the following sample output the tunnel is shown in an open state.



                            Example:
                            Router# show rbscp state tunnel 1
Tunnel1 is up, line protocol is up
RBSCP operational state:  OPEN
RBSCP operating mode: (264h) ack-split window-stuffing inorder SCTP-report
 window step: 1
 drop scale: 0
 ACK split size: 4
 input drop scale: 2
 initial TSN: 1h
 fuzz factor: 0
 max burst: tunnel 0, network 0
 next TSN: 1h
 next sequence: 16Bh
 current outstanding: 0
 max out per RTT: 2062500
 packets since SACK: 0
 cumulative ack: 0h
 TSN at SACK: 0h
 last cumulative ack: 0h
 last delivered TSN: 0h
 next FWDTSN corr: 0h
 RTO: 704 ms
 RTT: 550 ms     srtt_sa: 4391   srtt_sv: 3
 sentQ: num packets: 0, num bytes: 0
 tmitQ: num packets: 0, num bytes: 0

                            Use this command with the statistics and tunnelkeywords to display statistical information about the tunnel. All counters display totals accumulated since the last clear rbscp command was issued.



                            Example:
                            Router# show rbscp statistics tunnel 0
Tunnel0 is up, line protocol is up
RBSCP protocol statistics:
 Init FWD-TSNs sent 0, received 0
 TUNNEL-UPs sent 0, received 0
 CLOSEDs sent 0, received 0
 TSNs sent 0, resent 0, lost by sender 0
 TSNs received 0 (duplicates 0)
 FWD-TSNs sent 144 (heartbeats 0)
 FWD-TSNs received 0 (ignored 0)
 FWD-TSNs caused 0 packet drops, 0 whole window drops
 SACKs sent 0, received 0 (ignored 0)
 Recovered with RTX 0
 Received with delay 0
 Most released at once 0
 Failed sends into the: tunnel 1, network 0
 Dropped due to: excess delay 0, tmit queue full 0
 Max on any queue: num packets: 0, num bytes: 0
 Max outstanding: 0

                            Verifying the RBSCP Traffic

                            Perform this task to verify that the traffic is being transmitted through the RBSCP tunnel and across the satellite link.

                            SUMMARY STEPS

                              1.    enable

                              2.    show interfaces tunnel number [accounting]


                            DETAILED STEPS
                              Step 1   enable

                              Enables privileged EXEC mode. Enter your password if prompted.



                              Example:
                              Router> enable
                              Step 2   show interfaces tunnel number [accounting]

                              Use this command to show that traffic is being transmitted through the RBSCP tunnel.



                              Example:
                              Router# show interfaces tunnel 0
Tunnel0 is up, line protocol is down 
 Hardware is Tunnel
 Internet address is 172.17.1.4/24
 MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, 
    reliability 255/255, txload 1/255, rxload 1/255
 Encapsulation TUNNEL, loopback not set
 Keepalive not set
 Tunnel source 172.17.1.2, destination 172.20.1.3
 Tunnel protocol/transport RBSCP/IP, key disabled, sequencing disabled
 Tunnel TTL 255
 Checksumming of packets disabled
 Tunnel transmit bandwidth 1000 (kbps)
 Tunnel receive bandwidth 8000 (kbps)
RBSCP operational state:  invalid (0h)
RBSCP operating mode: (2EEh) delay dual-delay drop-long-delay ack-split window-t
 window step: 3
 drop scale : 0
 ACK split size: 6
 input drop scale: 5
 initial TSN: 1h
 fuzz factor: 0
 next TSN: 1h
 next sequence: 1h
 current outstanding: 0
 max out per RTT: 550000
 packets since SACK: 0
 cumulative ack: 0h
 TSN at SACK: 1h
 last cumulative ack: 0h
 last delivered TSN: 0h
 next FWDTSN corr: 0h
 RTO: 704 ms
 RTT: 550 ms     srtt_sa: 0      srtt_sv: 4
 sentQ: num packets: 0, num bytes: 0
 tmitQ: num packets: 0, num bytes: 0
Last input never, output never, output hang never
 Last clearing of "show interface" counters never
 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
 Queueing strategy: fifo
 Output queue: 0/0 (size/max)
 5 minute input rate 0 bits/sec, 0 packets/sec
 5 minute output rate 0 bits/sec, 0 packets/sec
    0 packets input, 0 bytes, 0 no buffer
    Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
    0 packets output, 0 bytes, 0 underruns
    0 output errors, 0 collisions, 0 interface resets
    0 output buffer failures, 0 output buffers swapped out

                              Configuration Examples for Implementing Tunnels

                              Example Configuring GRE IPv4 Tunnels

                              The following example shows a simple configuration of GRE tunneling. Note that Ethernet interface 0/1 is the tunnel source for Router A and the tunnel destination for Router B. Fast Ethernet interface 0/1 is the tunnel source for Router B and the tunnel destination for Router A.

                              Router A

                              interface Tunnel0
 ip address 10.1.1.2 255.255.255.0
 tunnel source Ethernet0/1
 tunnel destination 192.168.3.2
 tunnel mode gre ip
!
interface Ethernet0/1
 ip address 192.168.4.2 255.255.255.0

                              Router B

                              interface Tunnel0
 ip address 10.1.1.1 255.255.255.0
 tunnel source FastEthernet0/1
 tunnel destination 192.168.4.2
 tunnel mode gre ip
!
interface FastEthernet0/1
 ip address 192.168.3.2 255.255.255.0

                              The following example configures a GRE tunnel running both IS-IS and IPv6 traffic between Router A and Router B.

                              Router A

                              ipv6 unicast-routing
clns routing
!
interface Tunnel0
 no ip address
 ipv6 address 2001:0DB8:1111:2222::1/64
 ipv6 router isis 
 tunnel source Ethernet0/0
 tunnel destination 10.0.0.2
 tunnel mode gre ip
!
interface Ethernet0/0
 ip address 10.0.0.1 255.255.255.0
!
router isis 
 network 49.0000.0000.000a.00

                              Router B 

                              ipv6 unicast-routing
clns routing
!
interface Tunnel0
 no ip address
 ipv6 address 2001:0DB8:1111:2222::2/64
 ipv6 router isis 
 tunnel source Ethernet0/0
 tunnel destination 10.0.0.1
 tunnel mode gre ip
!
interface Ethernet0/0
 ip address 10.0.0.2 255.255.255.0
!
router isis 
 network 49.0000.0000.000b.00
 address-family ipv6
 redistribute static
 exit-address-family

                              Example: Configuring GRE IPv6 Tunnels

                              The following example shows how to configure a GRE tunnel over an IPv6 transport. In this example, Ethernet0/0 has an IPv6 address, and this is the source address used by the tunnel interface. The destination IPv6 address of the tunnel is specified directly. In this example, the tunnel carries both IPv4 and IS-IS traffic. 

                              interface Tunnel0
 ip address 10.1.1.1 255.255.255.0
 ip router isis 
 tunnel source Ethernet0/0
 tunnel destination 2001:DB8:1111:2222::1
 tunnel mode gre ipv6
!
interface Ethernet0/0
 no ip address
 ipv6 address 2001:DB8:1111:1111::1/64
!
router isis 
 net 49.0001.0000.0000.000a.00

                              Example Configuring GRE Tunnel IP Source and Destination VRF Membership

                              In this example, packets received on interface e0 using VRF green, will be forwarded out of the tunnel through interface e1 using VRF blue. The figure below shows a simple tunnel scenario:

                              Figure 8. GRE Tunnel Diagram

                              The following example shows the configuration for the tunnel in the figure above. 

                              ip vrf blue
 rd 1:1
ip vrf green
 rd 1:2
interface loopback0
 ip vrf forwarding blue
 ip address 10.7.7.7 255.255.255.255
interface tunnel0
 ip vrf forwarding green
 ip address 10.3.3.3 255.255.255.0
 tunnel source loopback 0
 tunnel destination 10.5.5.5
 tunnel vrf blue
interface ethernet0
 ip vrf forwarding green
 ip address 10.1.1.1 255.255.255.0
interface ethernet1
 ip vrf forwarding blue
 ip address 10.2.2.2 255.255.255.0
 ip route vrf blue 10.5.5.5 255.255.255.0 ethernet 1

                              Example Routing Two AppleTalk Networks Across an IP-Only Backbone

                              The figure below is an example of connecting multiprotocol subnetworks across a single-protocol backbone. The configurations of Router A and Router B follow the figure.

                              Figure 9. Connecting AppleTalk Networks Across an IP-Only Backbone

                              Router A

                              interface ethernet 0
 description physics department AppleTalk LAN
 appletalk cable-range 4001-4001 32
 !
interface fddi 0
 description connection to campus backbone
 ip address 10.0.8.108 255.255.255.0
interface tunnel 0
 tunnel source fddi 0
 tunnel destination 10.0.21.20
 appletalk cable-range 5313-5313 1

                              Router B

                              interface ethernet 0
 description chemistry department AppleTalk LAN
 appletalk cable-range 9458-9458 3
 !
interface fddi 0
 description connection to campus backbone
 ip address 10.0.21.20 255.255.255.0
interface tunnel 0
 tunnel source fddi 0
 tunnel destination 10.0.8.108
 appletalk cable-range 5313-5313 2

                              Example Routing a Private IP Network and a Novell Network Across a Public Service Provider

                              The figure below is an example of routing a private IP network and a Novell network across a public service provider. The configurations of Router A and Router B follow the figure.

                              Router A

                              interface ethernet 0
 description Boston office
 ip address 10.1.1.1 255.255.255.0
 novell network 1e
!
interface serial 0
 description connection to public service provider
 ip address 172.17.2.1 255.255.255.0
!
interface tunnel 0
 tunnel source serial 0
 tunnel destination 172.28.5.2
 ip address 10.1.2.1 255.255.255.0
 novell network 1f

                              Router B

                              interface ethernet 0
 description Menlo Park office
 ip address 10.1.3.1 255.255.255.0
 novell network 31
 !
interface serial 4
 description connection to public service provider
 ip address 172.28.5.2 255.255.255.0
 !
interface tunnel 0
 tunnel source serial 4
 tunnel destination 172.17.2.1
 ip address 10.1.2.2 255.255.255.0
 novell network 1f

                              Example Configuring a CTunnel

                              The figure below illustrates the creation of a CTunnel between Router A and Router B, as accomplished in the configuration examples that follow.

                              Figure 10. Creation of a CTunnel

                              Router A

                              ip routing
clns routing
interface ctunnel 102
 ip address 10.0.0.1 255.255.255.0
 ctunnel destination 49.0001.2222.2222.2222.00
interface Ethernet0/1
 clns router isis 
router isis 
 network 49.0001.1111.1111.1111.00
router rip 
 network 10.0.0.0

                              Router B

                              ip routing
clns routing
interface ctunnel 201
 ip address 10.0.0.2 255.255.255.0
 ctunnel destination 49.0001.1111.1111.1111.00
interface Ethernet0/1
 clns router isis 
router isis
 network 49.0001.2222.2222.2222.00
router rip
 network 10.0.0.0

                              Example Configuring GRE CLNS CTunnels to Carry IPv4 and IPv6 Packets

                              The following example configures a GRE CTunnel running both IS-IS and IPv6 traffic between Router A and Router B in a CLNS network. The ctunnel mode gre command provides a method of tunneling that is compliant with RFC 3147 and should allow tunneling between Cisco equipment and third-party networking devices.

                              Router A

                              ipv6 unicast-routing 
clns routing 
interface ctunnel 102 
 ipv6 address 2001:0DB8:1111:2222::1/64
 ctunnel destination 49.0001.2222.2222.2222.00 
 ctunnel mode gre
interface Ethernet0/1 
 clns router isis 
router isis 
 network 49.0001.1111.1111.1111.00

                              Router B

                              ipv6 unicast-routing 
clns routing 
interface ctunnel 201 
 ipv6 address 2001:0DB8:1111:2222::2/64 
 ctunnel destination 49.0001.1111.1111.1111.00 
 ctunnel mode gre
interface Ethernet0/1 
 clns router isis 
router isis 
 network 49.0001.2222.2222.2222.00

                              To turn off GRE mode and restore the CTunnel to the default Cisco encapsulation routing only between endpoints on Cisco equipment, use either the no ctunnel mode command or the ctunnel mode cisco command. The following example shows the same configuration modified to transport only IPv4 traffic.

                              Router A

                              ip routing 
clns routing 
interface ctunnel 102 
 ip address 10.2.2.5 255.255.255.0 
 ctunnel destination 49.0001.2222.2222.2222.00 
 ctunnel mode cisco
interface Ethernet0/1 
 clns router isis 
router isis 
 network 49.0001.1111.1111.1111.00

                              Router B

                              ip routing 
clns routing 
interface ctunnel 201 
 ip address 10.0.0.5 255.255.255.0 
 ctunnel destination 49.0001.1111.1111.1111.00 
 ctunnel mode cisco
interface Ethernet0/1 
 clns router isis 
router isis 
 network 49.0001.2222.2222.2222.00

                              Example Configuring Manual IPv6 Tunnels

                              The following example configures a manual IPv6 tunnel between Router A and Router B. In the example, tunnel interface 0 for both Router A and Router B is manually configured with a global IPv6 address. The tunnel source and destination addresses are also manually configured.

                              Router A 

                              interface ethernet 0
 ip address 192.168.99.1 255.255.255.0
interface tunnel 0
 ipv6 address 2001:0db8:c18:1::3/126
 tunnel source ethernet 0
 tunnel destination 192.168.30.1
 tunnel mode ipv6ip

                              Router B 

                              interface ethernet 0
 ip address 192.168.30.1 255.255.255.0
interface tunnel 0
 ipv6 address 2001:0db8:c18:1::2/126
 tunnel source ethernet 0
 tunnel destination 192.168.99.1
 tunnel mode ipv6ip

                              Example Configuring 6to4 Tunnels

                              The following example configures a 6to4 tunnel on a border router in an isolated IPv6 network. The IPv4 address is 192.168.99.1, which translates to the IPv6 prefix of 2002:c0a8:6301::/48. The IPv6 prefix is subnetted into 2002:c0a8:6301::/64 for the tunnel interface: 2002:c0a8:6301:1::/64 for the first IPv6 network and 2002:c0a8:6301:2::/64 for the second IPv6 network. The static route ensures that any other traffic for the IPv6 prefix 2002::/16 is directed to tunnel interface 0 for automatic tunneling.

                              interface Ethernet0
 description IPv4 uplink
 ip address 192.168.99.1 255.255.255.0
!
interface Ethernet1
 description IPv6 local network 1
 ipv6 address 2002:c0a8:6301:1::1/64 
!
interface Ethernet2
 description IPv6 local network 2
 ipv6 address 2002:c0a8:6301:2::1/64 
!
interface Tunnel0
 description IPv6 uplink
 no ip address
 ipv6 address 2002:c0a8:6301::1/64 
 tunnel source Ethernet0
 tunnel mode ipv6ip 6to4
!
ipv6 route 2002::/16 Tunnel0

                              Example Configuring IPv4-Compatible IPv6 Tunnels

                              The following example configures an IPv4-compatible IPv6 tunnel that allows BGP to run between a number of routers without having to configure a mesh of manual tunnels. Each router has a single IPv4-compatible tunnel, and multiple BGP sessions can run over each tunnel, one to each neighbor. Ethernet interface 0 is used as the tunnel source. The tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of an IPv4-compatible IPv6 address. Specifically, the IPv6 prefix 0:0:0:0:0:0 is concatenated to an IPv4 address (in the format 0:0:0:0:0:0:A.B.C.D or ::A.B.C.D) to create the IPv4-compatible IPv6 address. Ethernet interface 0 is configured with a global IPv6 address and an IPv4 address (the interface supports both the IPv6 and IPv4 protocol stacks).

                              Multiprotocol BGP is used in the example to exchange IPv6 reachability information with the peer 10.67.0.2. The IPv4 address of Ethernet interface 0 is used in the low-order 32 bits of an IPv4-compatible IPv6 address and is also used as the next-hop attribute. Using an IPv4-compatible IPv6 address for the BGP neighbor allows the IPv6 BGP session to be automatically transported over an IPv4-compatible tunnel.

                              interface tunnel 0
 tunnel source Ethernet 0
 tunnel mode ipv6ip auto-tunnel
interface ethernet 0
 ip address 10.27.0.1 255.255.255.0
 ipv6 address 3000:2222::1/64
router bgp 65000
 no synchronization
 no bgp default ipv4-unicast
 neighbor ::10.67.0.2 remote-as 65002
address-family ipv6
 neighbor ::10.67.0.2 activate
 neighbor ::10.67.0.2 next-hop-self
 network 2001:2222:d00d:b10b::/64

                              Example Configuring ISATAP Tunnels

                              The following example shows the tunnel source defined on Ethernet 0 and the tunnel mode command used to configure the ISATAP tunnel. Router advertisements are enabled to allow client autoconfiguration.

                              interface Tunnel1
 tunnel source ethernet 0
 tunnel mode ipv6ip isatap
 ipv6 address 2001:0DB8::/64 eui-64
 no ipv6 nd suppress-ra

                              Example Configuring the RBSCP Tunnel

                              In the following example, Router 1 and Router 2 are configured to send traffic through an RBSCP tunnel over a satellite link.

                              Router 1

                              interface Tunnel 0
 ip unnumbered ethernet1
 tunnel source ethernet1
 tunnel destination 172.17.2.1
 tunnel bandwidth transmit 1000
 tunnel mode rbscp
 tunnel rbscp ack-split 6
 tunnel rbscp report
!
interface ethernet1
 description Satellite Link
 ip address 172.20.1.2 255.255.255.0

                              Router 2

                              interface Tunnel 0
 ip unnumbered ethernet1
 tunnel source ethernet1
 tunnel destination 172.20.1.2
 tunnel bandwidth transmit 1000
 tunnel mode rbscp
 tunnel rbscp ack-split 6
 tunnel rbscp report
!
interface ethernet1
 description Satellite Link
 ip address 172.17.2.1 255.255.255.0

                              Example Configuring Routing for the RBSCP Tunnel

                              To control the type of traffic that uses the RBSCP tunnel, you must configure the appropriate routing. If you want to direct all traffic through the tunnel, you can configure a static route.


                              Note

                              To prevent routing flaps, remember to configure the tunnel interface as passive if dynamic routing protocols are used.

                              The following example shows how to use policy-based routing to route some specific protocol types through the tunnel. In this example, an extended access list allows TCP, Stream Control Transmission Protocol (SCTP), Encapsulating Security Payload (ESP) protocol, and Authentication Header (AH) traffic to travel through the tunnel. All IP traffic is denied.

                              Router 1 (Local Side)

                              interface Tunnel1
 ip unnumbered FastEthernet1/1
 tunnel source FastEthernet1/1
 tunnel destination 10.12.0.20
 tunnel mode rbscp
 tunnel ttl 5
 tunnel bandwidth transmit 30000
 tunnel rbscp window-stuff 1
 tunnel rbscp ack-split 4
!
interface FastEthernet0/0
 ip address 10.13.0.1 255.255.255.0
 ip policy route-map rbscp-pbr
 duplex auto
 speed auto
!
interface FastEthernet1/1
 description Satellite Link
 ip address 10.12.0.1 255.255.255.0
 duplex auto
 speed auto
!
ip route 10.15.0.0 255.255.255.0 FastEthernet1/1
!
ip access-list extended rbscp-acl
 permit tcp any 10.15.0.0 0.0.0.255
 permit 132 any 10.15.0.0 0.0.0.255
 permit esp any 10.15.0.0 0.0.0.255
 permit ahp any 10.15.0.0 0.0.0.255
 deny ip any any
!
route-map rbscp-pbr permit 10
 match ip address rbscp-acl
 set interface Tunnel1

                              Router 2 (Remote Side)

                              ip dhcp pool CLIENT
 import all
 network 10.15.0.0 255.255.255.0
 default-router 10.15.0.1
 domain-name engineer.chicago.il.us
 dns-server 10.10.0.252
!
interface Tunnel1
 ip unnumbered FastEthernet0/1
 tunnel source FastEthernet0/1
 tunnel destination 10.12.0.1
 tunnel mode rbscp
 tunnel ttl 5
 tunnel bandwidth transmit 30000
 tunnel rbscp window-stuff 1
 tunnel rbscp ack-split 4
!
interface FastEthernet0/0
 description Local LAN
 ip address 10.15.0.1 255.255.255.0
 ip policy route-map rbscp-pbr
 duplex auto
 speed auto
!
interface FastEthernet0/1
 description Satellite Link
 ip address 10.12.0.20 255.255.255.0
 duplex auto
 speed auto
!
ip route 0.0.0.0 0.0.0.0 FastEthernet0/1
!
ip access-list extended rbscp-acl
 permit tcp any any
 permit 132 any any
 permit esp any any
 permit ahp any any
 deny ip any any
!
route-map rbscp-pbr permit 10
 match ip address rbscp-acl
 set interface Tunnel1

                              Example Configuring QoS Options on Tunnel Interfaces

                              The following sample configuration applies generic traffic shaping (GTS) directly on the tunnel interface. In this example the configuration shapes the tunnel interface to an overall output rate of 500 kbps. For more details on GTS, see the " Regulating Packet Flow Using Traffic Shaping " chapter of the Cisco IOS Quality of Service Solutions Configuration Guide. 

                              interface Tunnel0 
 ip address 10.1.2.1 255.255.255.0 
 traffic-shape rate 500000 125000 125000 1000 
 tunnel source 10.1.1.1 
 tunnel destination 10.2.2.2

                              The following sample configuration shows how to apply the same shaping policy to the tunnel interface with the Modular QoS CLI (MQC) commands. For more details on MQC, see the "Modular Quality of Service Command-Line Interface" chapter of the Cisco IOS Quality of Service Solutions Configuration Guide . 

                              policy-map tunnel 
 class class-default 
 shape average 500000 125000 125000
! 
interface Tunnel0 
 ip address 10.1.2.1 255.255.255.0 
 service-policy output tunnel 
 tunnel source 10.1.35.1 
 tunnel destination 10.1.35.2

                              Policing Example

                              When an interface becomes congested and packets start to queue, you can apply a queueing method to packets that are waiting to be transmitted. Cisco IOS logical interfaces--tunnel interfaces in this example--do not inherently support a state of congestion and do not support the direct application of a service policy that applies a queueing method. Instead, you need to apply a hierarchical policy. Create a "child" or lower-level policy that configures a queueing mechanism, such as low latency queueing with the priority command and class-based weighted fair queueing (CBWFQ) with the bandwidth command. 

                              policy-map child 
 class voice 
 priority 512

                              Create a "parent" or top-level policy that applies class-based shaping. Apply the child policy as a command under the parent policy because admission control for the child class is done according to the shaping rate for the parent class. 

                              policy-map tunnel 
 class class-default 
 shape average 2000000 
 service-policy child

                              Apply the parent policy to the tunnel interface. 

                              interface tunnel0 
 service-policy tunnel

                              In the following example, a tunnel interface is configured with a service policy that applies queueing without shaping. A log message is displayed noting that this configuration is not supported. 

                              interface tunnel1
 service-policy output child
 Class Based Weighted Fair Queueing not supported on this interface

                              For more details on QoS traffic policing, see the Cisco IOS Quality of Service Solutions Configuration Guide .

                              Example Configuring EoMPLS over GRE

                              The following sample provides the EoMPLS over GRE configuration sequence:

                              PE1 Configuration

                              vrf definition VPN1
 rd 100:1
 address-family ipv4
 route-target both 100:1
 exit-address-family
 !
mpls label protocol ldp
mpls ldp neighbor 10.10.10.11 targeted 
mpls ldp router-id Loopback0 force
!
interface Tunnel0
 ip address 100.1.1.11 255.255.255.0
 mpls label protocol ldp
 mpls ip
 keepalive 10 3
 tunnel source TenGigabitEthernet2/1/0
 tunnel destination 50.1.3.2
!
interface Loopback0
 ip address 10.10.10.10 255.255.255.255
 !
interface TenGigabitEthernet2/1/0 
 mtu 9216
 ip address 10.1.1.1 255.255.255.0
!
interface TenGigabitEthernet9/1
 no ip address
!
interface TenGigabitEthernet9/1.11
 vrf forwarding VPN1
 encapsulation dot1Q 300
 ip address 192.168.1.1 255.255.255.0
!
interface TenGigabitEthernet9/2
 mtu 9216
 no ip address
xconnect 10.10.10.11 200 encapsulation mpls
!
router bgp 65000
 bgp log-neighbor-changes
 neighbor 10.10.10.11 remote-as 65000
 neighbor 10.10.10.11 update-source Loopback0
neighbor 192.168.1.2 remote-as 100
 !
address-family vpnv4
  neighbor 10.10.10.11 activate
  neighbor 10.10.10.11 send-community extended
 !
 address-family ipv4 vrf VPN1
  no synchronization
  neighbor 192.168.1.2 remote-as 100
  neighbor 192.168.1.2 activate
  neighbor 192.168.1.2 send-community extended
!
ip route 10.10.10.11 255.255.255.255 Tunnel0
ip route 10.1.3.0 255.255.255.0 10.1.1.2
PE2 Configuration
vrf definition VPN1
 rd 100:1
 address-family ipv4
 route-target both 100:1
exit-address-family
 !
mpls ldp neighbor 10.10.10.10 targeted
mpls label protocol ldp
mpls ldp router-id Loopback0 force
!
interface Tunnel0
 ip address 100.1.1.10 255.255.255.0
 mpls label protocol ldp
 mpls ip
 keepalive 10 3
 tunnel source TenGigabitEthernet3/3/0
 tunnel destination 10.1.1.1
!
interface Loopback0
 ip address 10.10.10.11 255.255.255.255
!
interface TenGigabitEthernet2/1
 mtu 9216
 no ip address
 xconnect 10.10.10.10 200 encapsulation mpls  
!
interface TenGigabitEthernet2/3
 mtu 9216
 no ip address
!
interface TenGigabitEthernet2/3.11
 vrf forwarding VPN1
 encapsulation dot1Q 300
 ip address 192.168.2.1 255.255.255.0
!
interface TenGigabitEthernet3/3/0
 mtu 9216
 ip address 10.1.3.2 255.255.255.0
!
router bgp 65000
 bgp log-neighbor-changes
 neighbor 10.10.10.10 remote-as 65000
 neighbor 10.10.10.10 update-source Loopback0
 neighbor 192.168.2.2 remote-as 200
 !
 address-family vpnv4
  neighbor 10.10.10.10 activate
  neighbor 10.10.10.10 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf VPN1
  no synchronization
  neighbor 192.168.2.2 remote-as 200
  neighbor 192.168.2.2 activate
  neighbor 192.168.2.2 send-community extended
 exit-address-family
¡
ip route 10.10.10.10 255.255.255.255 Tunnel0
ip route 10.1.1.0 255.255.255.0 10.1.3.1

                              Where to Go Next

                              If you have implemented IPv6 tunnels, you may want to proceed to one of the following modules:

                              • If you have configured an automatic 6to4 tunnel, you can design your IPv6 network around the /48 6to4 prefix that you have created from your IPv4 address.

                              • If you want to implement routing protocols, see the " Implementing RIP for IPv6 ," " Implementing IS-IS for IPv6 ," " Implementing OSPF for IPv6 ," or " Implementing Multiprotocol BGP for IPv6 " modules.

                              • If you want to implement security features for your IPv6 network, see the " Implementing Security for IPv6 " module.

                              Additional References

                              Related Documents

                              Related Topic

                              Document Title

                              Cisco IOS commands

                              Cisco IOS Master Commands List, All Releases

                              Tunnel commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                              Cisco IOS Interface and Hardware Component Command Reference

                              CLNS commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                              Cisco IOS ISO CLNS Command Reference

                              IP commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                              • Cisco IOS IP Addressing Services Command Reference

                              • Cisco IOS IP Application Services Command Reference

                              • Cisco IOS IP Routing Protocols Command Reference

                              IPv6 commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                              Cisco IOS IPv6 Command Reference

                              IPv6 Features

                              Cisco IOS IPv6 Configuration Guide

                              Regulating Packet Flow on a Per-Interface Basis - Using Generic Traffic Shaping

                              Cisco IOS Quality of Service Solutions Configuration Guide

                              Modular QoS CLI configuration

                              Cisco IOS Quality of Service Solutions Configuration Guide

                              Virtual interface configuration

                              Cisco IOS Interface and Hardware Component Configuration Guide

                              Configuration example for GRE over IP Security (IPSec) where the GRE/IPSec tunnel is going through a firewall doing Network Address Translation (NAT)

                              Configuring IPSec/​GRE with NAT

                              Configuring Multiprotocol Label Switching

                              Cisco IOS Multiprotocol Label Switching Configuration Guide

                              Standards

                              Standard

                              Title

                              No new or modified standards are supported, and support for existing standards has not been modified.

                              --

                              MIBs

                              MIB

                              MIBs Link

                              No new or modified MIBs are supported, and support for existing MIBs has not been modified.

                              To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

                              http:/​/​www.cisco.com/​go/​mibs

                              RFCs

                              RFC

                              Title

                              RFC 791

                              Internet Protocol

                              RFC 1191

                              Path MTU Discovery

                              RFC 1323

                              TCP Extensions for High Performance

                              RFC 1483

                              Multiprotocol Encapsulation over ATM Adaptation Layer 5

                              RFC 2003

                              IP Encapsulation Within IP

                              RFC 2018

                              TCP Selective Acknowledgment Options

                              RFC 2460

                              Internet Protocol, Version 6 (IPv6)

                              RFC 2473

                              Generic Packet Tunneling in IPv6 Specification

                              RFC 2474

                              Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers

                              RFC 2516

                              A Method for Transmitting PPP over Ethernet (PPPoE)

                              RFC 2547

                              BGP/MPLS VPNs

                              RFC 2780

                              IANA Allocation Guidelines for Values in the Internet Protocol and Related Headers

                              RFC 2784

                              Generic Routing Encapsulation (GRE)

                              RFC 2890

                              Key and Sequence Number Extensions to GRE

                              RFC 2893

                              Transition Mechanisms for IPv6 Hosts and Routers

                              RFC 3056

                              Connection of IPv6 Domains via IPv4 Clouds

                              RFC 3147

                              Generic Routing Encapsulation over CLNS Networks

                              Technical Assistance

                              Description

                              Link

                              The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

                              http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

                              Feature Information for Implementing Tunnels

                              The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

                              Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to . An account on Cisco.com is not required.
                              Table 7 Feature Information for Implementing Tunnels

                              Feature Name

                              Releases

                              Feature Configuration Information

                              CEF-Switched Multipoint GRE Tunnels

                              12.2(8)T

                              15.0(1)M

                              The CEF-Switched Multipoint GRE Tunnels feature enables CEF switching of IP traffic to and from multipoint GRE tunnels. Tunnel traffic can be forwarded to a prefix through a tunnel destination when both the prefix and the tunnel destination are specified by the application.

                              This feature introduces CEF switching over multipoint GRE tunnels. Previously, only process switching was available for multipoint GRE tunnels.

                              No commands were introduced or modified by this feature.

                              CLNS Support for GRE Tunneling of IPv4 and IPv6 Packets in CLNS Networks

                              12.3(7)T

                              12.2(25)S

                              12.2(33)SRA

                              Support of the GRE tunnel mode allows Cisco CTunnels to transport IPv4 and IPv6 packets over CLNS-only networks in a manner that allows interoperation between Cisco networking equipment and that of other vendors. This feature provides compliance with RFC 3147.

                              The following command was introduced by this feature: ctunnel mode.

                              GRE Tunnel IP Source and Destination VRF Membership

                              12.0(23)S

                              12.2(20)S

                              12.2(27)SBC

                              12.3(2)T

                              12.2(33)SRA

                              12.2(33)SRB

                              12.2(31)SB5

                              12.4(15)T

                              Allows you to configure the source and destination of a tunnel to belong to any VPN VRF table.

                              In 12.0(23)S, this feature was introduced.

                              In 12.2(20)S this feature became available on Cisco 7304 router using the NSE-100 in the PXF processing path.

                              In 12.2(31)SB5, support was added for the Cisco 10000 series router for the PRE2 and PRE3.

                              The following command was introduced to support this feature: tunnel vrf.

                              GRE Tunnel Keepalive

                              12.2(8)T

                              12.0(23)S

                              15.0(1)M

                              Cisco IOS XE 3.1.0SG

                              15.3(1)S

                              15.1(2)SY

                              The GRE Tunnel Keepalive feature provides the capability of configuring keepalive packets to be sent over IP-encapsulated generic routing encapsulation (GRE) tunnels. You can specify the rate at which keepalives will be sent and the number of times that a device will continue to send keepalive packets without a response before the interface becomes inactive. GRE keepalive packets may be sent from both sides of a tunnel or from just one side.

                              The following command was introduced by this feature: keepalive (tunnel interfaces).

                              IP Tunnel-- SSO

                              15.1(1)SY

                              High availability support was added to IP Tunnels.

                              No new commands were introduced or modified by this feature.

                              Rate-Based Satellite Control Protocol

                              12.3(7)T

                              Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPSec), over satellite links without breaking the end-to-end model.

                              The following commands were introduced or modified by this feature: clear rbscp, debug tunnel rbscp, show rbscp, tunnel bandwidth, tunnel mode, tunnel rbscp ack-split, tunnel rbscp delay, tunnel rbscp input-drop, tunnel rbscp long-drop, tunnel rbscp report, tunnel rbscp window-stuff.

                              Tunnel ToS

                              12.0(17)S

                              12.0(17)ST

                              12.2(8)T

                              12.2(14)S

                              15.0(1)M

                              The Tunnel ToS feature allows you to configure the ToS and Time-to-Live (TTL) byte values in the encapsulating IP header of tunnel packets for an IP tunnel interface on a router. The Tunnel ToS feature is supported on Cisco Express Forwarding (CEF), fast switching, and process switching forwarding modes.

                              The following commands were introduced or modified by this feature: show interfaces tunnel, tunnel tos, tunnel ttl.

                              Implementing Tunnels

                              Contents

                              Implementing Tunnels

                              This module describes the various types of tunneling techniques available using Cisco IOS software. Configuration details and examples are provided for the tunnel types that use physical or virtual interfaces. Many tunneling techniques are implemented using technology-specific commands, and links are provided to the appropriate technology modules.

                              Tunneling provides a way to encapsulate arbitrary packets inside a transport protocol. Tunnels are implemented as a virtual interface to provide a simple interface for configuration. The tunnel interface is not tied to specific "passenger" or "transport" protocols, but rather is an architecture to provide the services necessary to implement any standard point-to-point encapsulation scheme.


                              Note

                              Cisco ASR 1000 Series Aggregation Services Routers support VPN routing and forwarding (VRF)-aware generic routing encapsulation (GRE) tunnel keepalive features.

                              Finding Feature Information

                              Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

                              Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

                              Prerequisites for Implementing Tunnels

                              This module assumes that you are running Cisco IOS Release 12.2 software or a later release.

                              Restrictions for Implementing Tunnels

                              • In early versions of Cisco IOS software, only processor switching was supported. Fast switching of GRE tunnels was introduced in Cisco IOS Release 11.1. Cisco Express Forwarding (CEF) switching is also now commonly used by the IPv6 and other tunneling protocols.

                              • It is important to allow the tunnel protocol through a firewall and to allow it to pass access control list (ACL) checking.

                              • Multiple point-to-point tunnels can saturate the physical link with routing information if the bandwidth is not configured correctly on the tunnel interface.

                              • A tunnel looks like a single hop, and routing protocols may prefer a tunnel over a multihop physical path. This can be deceptive because the tunnel, although it may look like a single hop, may traverse a slower path than a multihop link. A tunnel is as robust and fast, or as unreliable and slow, as the links that it actually traverses. Routing protocols that make their decisions on the sole basis of hop count will often prefer a tunnel over a set of physical links. A tunnel might appear to be a one-hop, point-to-point link and have the lowest-cost path, but may actually cost more in terms of latency than an alternative physical topology. For example, in the topology shown in the figure below, packets from Host 1 will appear to travel across networks w, t, and z to get to Host 2 instead of taking the path w, x, y, and z because the tunnel hop count appears shorter. In fact, the packets going through the tunnel will still be traveling across Router A, B, and C, but they must also travel to Router D before coming back to Router C.

                              Figure 1. Tunnel Precautions: Hop Counts

                              • If routing is not carefully configured, the tunnel may have a recursive routing problem. When the best path to the "tunnel destination" is via the tunnel itself, recursive routing causes the tunnel interface to flap. To avoid recursive routing problems, keep the control-plane routing separate from the tunnel routing using the following methods:
                                • Use a different autonomous system number or tag.
                                • Use a different routing protocol.
                                • Use static routes to override the first hop (but watch for routing loops).

                              When you have recursive routing to the tunnel destination, the following error is displayed: 

                              %TUN-RECURDOWN Interface Tunnel 0
temporarily disabled due to recursive routing

                              Note

                              You cannot configure an IP tunnel or a GRE tunnel on Cisco 7600 series routers which has an MPLS Traffic Engineering (TE) tunnel as the egress path, because the configuration results in forwarding loops.

                              Information About Implementing Tunnels

                              Tunneling Versus Encapsulation

                              To understand how tunnels work, it is important to distinguish between the concepts of encapsulation and tunneling. Encapsulation is the process of adding headers to data at each layer of a particular protocol stack. The Open Systems Interconnection (OSI) reference model describes the functions of a network as seven layers stacked on top of each other. When data has to be sent from one host (a PC for example) on a network to another host, the process of encapsulation is used to add a header in front of the data at each layer of the protocol stack in descending order. The header must contain a data field that indicates the type of data encapsulated at the layer immediately above the current layer. As the packet ascends the protocol stack on the receiving side of the network, each encapsulation header is removed in the reverse order.

                              Tunneling encapsulates data packets from one protocol inside a different protocol and transports the data packets unchanged across a foreign network. Unlike encapsulation, tunneling allows a lower-layer protocol, or same-layer protocol, to be carried through the tunnel. A tunnel interface is a virtual (or logical) interface. For more details on other types of virtual interfaces, see the "Configuring Virtual Interfaces" module. Although many different types of tunnels have been created to solve different network problems, tunneling consists of three main components:

                              • Passenger protocol--The protocol that you are encapsulating. Examples of passenger protocols are AppleTalk, connectionless network service (CLNS), IP, and IPX.

                              • Carrier protocol--The protocol that does the encapsulating. Examples of carrier protocols are GRE, IP-in-IP, Layer 2 Tunneling Protocol (L2TP), multiprotocol label switching (MPLS), STUN, and DLSw+.

                              • Transport protocol--The protocol used to carry the encapsulated protocol. The main transport protocol is IP.

                              To understand the process of tunneling, consider connecting two AppleTalk networks with a non-AppleTalk backbone, such as IP. The relatively high bandwidth consumed by the broadcasting of Routing Table Maintenance Protocol (RTMP) data packets can severely hamper the backbone’s network performance. This problem can be solved by tunneling AppleTalk through a foreign protocol, such as IP. Tunneling encapsulates an AppleTalk packet inside the foreign protocol packet (AppleTalk inside GRE inside IP), which is then sent across the backbone to a destination router. The destination router then removes the encapsulation from the AppleTalk packet and routes the packet.

                              Definition of Tunneling Types by OSI Layer

                              Tunnels are used by many different technologies to solve different network challenges, and the resulting variety of tunnel types makes it difficult to determine which tunneling technique to use. The different carrier protocols can be grouped according to the OSI layer model. The table below shows the different carrier protocols grouped by OSI layer. Below the table, each carrier protocol is defined, and if the tunnel configuration is not covered within this module, a link to the appropriate module is included.

                              Table 1 Carrier Protocol by OSI Layer

                              Layer

                              Carrier Protocol

                              2

                              • PPPoA--Point-to-Point Protocol (PPP) over ATM

                              • PPPoE--PPP over Ethernet

                              • UDLR--Unidirectional link routing

                              3

                              • BSTUN--Block Serial Tunneling

                              • CLNS--Connectionless Network Service (CLNS)

                              • GRE--Generic routing encapsulation

                              • IP-in-IP--Internet Protocol encapsulated within IP

                              • IPsec--IP Security

                              • IPv6--IP version 6

                              • L2F--Layer 2 Forwarding

                              • L2TP--Layer 2 Tunneling Protocol

                              • MPLS--Multiprotocol Label Switching

                              • PPTP--Point-to-Point Tunneling Protocol

                              • STUN--Serial Tunneling

                              4

                              • DLSw+--Data-link switching plus

                              • RBSCP--Rate-Based Satellite Control Protocol

                              • SSL--Secure Socket Layer

                              BSTUN

                              A Block Serial Tunnel (BSTUN) enables support for devices using the Bisync data-link protocol. This protocol enables enterprises to transport Bisync traffic over the same network that supports their Systems Network Architecture (SNA) and multiprotocol traffic, eliminating the need for separate Bisync facilities.

                              For more details about configuring BSTUN, see the "Configuring Serial Tunnel and Block Serial Tunnel" module in the Cisco IOS Bridging and IBM Networking Configuration Guide.

                              CLNS

                              The ISO Connectionless Network Service (CLNS) protocol is a standard for the network layer of the OSI model. IP traffic can be transported over CLNS; for instance, on the data communications channel (DCC) of a SONET ring. An IP over CLNS tunnel (CTunnel) is a virtual interface that enhances interactions with CLNS networks, allowing IP packets to be tunneled through the Connectionless Network Protocol (CLNP) to preserve TCP/IP services. CLNS can also be used as a transport protocol with GRE as a carrier protocol (GRE/CLNS), carrying both IPv4 and IPv6 packets.

                              DLSw+

                              Data-link switching plus (DLSw+) is Cisco’s implementation of the DLSw standard for Systems Network Architecture (SNA) and NetBIOS devices, and it supports several additional features and enhancements. DLSw+ is a means of transporting SNA and NetBIOS traffic over a campus or WAN. The end systems can attach to the network over Token Ring, Ethernet, Synchronous Data Link Control (SDLC), Qualified Logical Link Control (QLLC), or Fiber Distributed Data Interface (FDDI). DLSw+ switches between diverse media and locally terminates the data links, keeping acknowledgments, keepalives, and polling off the WAN.

                              For more details about configuring DLSw+, see the "Configuring Data-Link Switching Plus" module in the Cisco IOS Bridging and IBM Networking Configuration Guide .

                              GRE

                              Generic routing encapsulation (GRE) is defined in RFC 2784. GRE is a carrier protocol that can be used with a variety of underlying transport protocols, and GRE can carry a variety of passenger protocols. RFC 2784 also covers the use of GRE with IPv4 as the transport protocol and the passenger protocol. Cisco IOS software supports GRE as the carrier protocol with many combinations of passenger and transport protocols.

                              For more details about GRE, see the Generic Routing Encapsulation.

                              IP-in-IP

                              IP-in-IP is a Layer 3 tunneling protocol--defined in RFC 2003--that alters the normal routing of an IP packet by encapsulating it within another IP header. The encapsulating header specifies the address of a router that would not ordinarily be selected as a next-hop router on the basis of the real destination address of the packet. The intermediate node decapsulates the packet, which is then routed to the destination as usual.

                              IPsec

                              In simple terms, IP Security (IPsec) provides secure tunnels between two peers, such as two routers. You define which packets are considered sensitive and should be sent through these secure tunnels, and you define the parameters that should be used to protect these packets by specifying characteristics of these tunnels. IPsec peers set up a secure tunnel and encrypt the packets that traverse the tunnel to the remote peer.

                              IPsec also works with the GRE and IP-in-IP, L2F, L2TP, and DLSw+ tunneling protocols; however, multipoint tunnels are not supported. Other Layer 3 tunneling protocols may not be supported for use with IPsec.

                              For more details about configuring IPSec, see the "Configuring Security for VPNs with IPSec" module in the Cisco IOS Security Configuration Guide.

                              IPv6

                              IP version 6 (IPv6) is a new version of the Internet Protocol based on and designed as the successor to IP version 4. IPv6 adds a much larger address space--128 bits--and improvements such as a simplified main header and extension headers. IPv6 is described initially in RFC 2460, Internet Protocol, Version 6 (IPv6) . The use of IPv6 as a carrier protocol is described in RFC 2473, Generic Packet Tunneling in IPv6 Specification .

                              L2F

                              Layer 2 Forwarding (L2F) tunneling is used in virtual private dialup networks (VPDNs). A VPDN allows separate and autonomous protocol domains to share common access infrastructure including modems, access servers, and ISDN routers by the tunneling of link-level (Layer 2) frames. Typical L2F tunneling use includes Internet service providers (ISPs) or other access service creating virtual tunnels to link to remote customer sites or remote users with corporate intranet or extranet networks.

                              L2TP

                              Layer 2 Tunneling Protocol (L2TP) is an open standard created by the Internet Engineering Task Force (IETF) that uses the best features of L2F and Point-to-Point Tunneling Protocol (PPTP). L2TP is designed to secure the transmission of IP packets across uncontrolled and untrusted network domains, and it is an important component of Virtual Private Networks (VPNs). VPNs extend remote access to users over a shared infrastructure while maintaining the same security and management policies as a private network.

                              For more details about configuring L2TP, see the Cisco IOS Dial Technologies Configuration Guide.

                              MPLS

                              Multiprotocol Label Switching (MPLS) is a high-performance packet forwarding technology that integrates the performance and traffic management capabilities of data-link-layer (Layer 2) switching with the scalability, flexibility, and performance of network-layer (Layer 3) routing. The MPLS architecture has been designed to allow data to be transferred over any combination of Layer 2 technologies, to support all Layer 3 protocols, and to scale. Using CEF, MPLS can efficiently enable the delivery of IP services over an ATM switched network. MPLS is an integration of Layer 2 and Layer 3 technologies. By making traditional Layer 2 features available to Layer 3, MPLS enables traffic engineering.

                              For more details about how MPLS traffic engineering uses tunnels, see the Cisco IOS Multiprotocol Label Switching Configuration Guide.

                              PPPoA

                              PPP over ATM (PPPoA) is mainly implemented as part of Asymmetric Digital Subscriber Line (ADSL). It relies on RFC 1483, operating in either Logical Link Control-Subnetwork Access Protocol (LLC-SNAP) or VC-Mux mode. A customer premises equipment (CPE) device encapsulates the PPP session based on this RFC for transport across the ADSL loop and the digital subscriber line access multiplexer (DSLAM).

                              PPPoE

                              RFC 2516 defines PPP over Ethernet (PPPoE) as providing the ability to connect a network of hosts over a simple bridging access device to a remote access concentrator or aggregation concentrator. As customers deploy ADSL, they must support PPP-style authentication and authorization over a large installed base of legacy bridging customer premises equipment (CPE). Using a form of tunneling encapsulation, PPPoE allows each host to use its own PPP stack, thus presenting the user with a familiar user interface. Access control, billing, and type of service (ToS) can be done on a per-user, rather than a per-site, basis.

                              For more details about configuring PPPoE, see the Cisco IOS Broadband Access Aggregation and DSL Configuration Guide.

                              PPTP

                              Point-to-Point Tunneling Protocol (PPTP) is a network protocol that enables the secure transfer of data from a remote client enterprise server by creating a VPN across TCP/IP data networks. PPTP supports on-demand, multiprotocol virtual private networking over public networks such as the Internet.

                              RBSCP

                              Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPsec), over satellite links without breaking the end-to-end model.

                              SSL Tunnels

                              Secure Socket Layer (SSL) is designed to make use of TCP sessions to provide a reliable end-to-end secure service. The main role of SSL is to provide security for web traffic. Security includes confidentiality, message integrity, and authentication. SSL achieves these elements of security through the use of cryptography, digital signatures, and certificates. SSL protects confidential information through the use of cryptography. Sensitive data is encrypted across public networks to achieve a level of confidentiality.

                              SSL is implemented using the Cisco Application and Content Networking System (ACNS). For more details about configuring SSL, see the latest Cisco ACNS Software Deployment and Configuration Guide .

                              STUN

                              Cisco’s Serial Tunneling (STUN) implementation allows Synchronous Data Link Control (SDLC) protocol devices and High-Level Data Link Control (HDLC) devices to connect to one another through a multiprotocol internetwork rather than through a direct serial link. STUN encapsulates SDLC frames in either the TCP/IP or the HDLC protocol. STUN provides a straight passthrough of all SDLC traffic (including control frames, such as Receiver Ready) end-to-end between Systems Network Architecture (SNA) devices.

                              For more details about configuring STUN, see the "Configuring Serial Tunnel and Block Serial Tunnel" module in the Cisco IOS Bridging and IBM Networking Configuration Guide .

                              UDLR Tunnels

                              Unidirectional link routing (UDLR) provides mechanisms for a router to emulate a bidirectional link to enable the routing of unicast and multicast packets over a physical unidirectional interface, such as a broadcast satellite link. However, there must be a back channel or other path between the routers that share a physical unidirectional link (UDL). A UDLR tunnel is a mechanism for unicast and multicast traffic; Internet Group Management Protocol (IGMP) UDLR is a related technology for multicast traffic.

                              For more details, see Cisco IOS IP Multicast Configuration Guide.

                              Benefits of Tunneling

                              The following are several situations in which tunneling (encapsulating traffic in another protocol) is useful:

                              • To enable multiprotocol local networks over a single-protocol backbone.

                              • To provide workarounds for networks that use protocols that have limited hop counts; for example, RIP version 1, AppleTalk (see the figure below).

                              • To connect discontiguous subnetworks.

                              • To allow virtual private networks across WANs.

                              Figure 2. Providing Workarounds for Networks with Limited Hop Counts

                              Tunnel ToS

                              Tunnel ToS allows you to tunnel your network traffic and group all your packets in the same specific ToS byte value. The ToS byte values and Time-to-Live (TTL) hop-count value can be set in the encapsulating IP header of tunnel packets for an IP tunnel interface on a router. The Tunnel ToS feature is supported for CEF, fast switching, and process switching.

                              The ToS and TTL byte values are defined in RFC 791. RFC 2474 and RFC 2780 obsolete the use of the ToS byte as defined in RFC 791. RFC 791 specifies that bits 6 and 7 of the ToS byte (the first two least significant bits) are reserved for future use and should be set to 0. The Tunnel ToS feature does not conform to this standard and allows you to set the whole ToS byte value, including bits 6 and 7, and to decide to which RFC standard the ToS byte of your packets should confirm.

                              Mobile IP Tunneling

                              New devices and business practices, such as PDAs and the next-generation of data-ready cellular phones and services, are driving interest in the ability of a user to roam while maintaining network connectivity. The requirement for data connectivity solutions for this group of users is very different than it is for the fixed dialup user or the stationary wired LAN user. Solutions need to accommodate the challenge of movement during a data session or conversation.

                              Mobile IP is a tunneling-based solution that takes advantage of the Cisco-created generic routing encapsulation (GRE) tunneling technology and simpler IP-in-IP tunneling protocol.

                              Mobile IP is comprises the following three components, as shown in the figure below:

                              • Mobile node (MN)

                              • Home agent (HA)

                              • Foreign agent (FA)

                              Figure 3. Mobile IP Components and Use of Tunneling

                              An MN is a node, for example, a PDA, a laptop computer, or a data-ready cellular phone, that can change its point of attachment from one network or subnet to another. This node can maintain ongoing communications while using only its home IP address. In the figure above, the current location of the MN--a laptop computer--is shown in bold.

                              An HA is a router on the home network of the MN that maintains an association between the home IP address of the MN and its care-of address , which is the current location of the MN on a foreign or visited network. The HA redirects packets by tunneling them to the MN while it is away from home.

                              An FA is a router on a foreign network that assists the MN in informing its HA of its current care-of address. The FA detunnels packets that were tunneled by the HA and delivers them to the MN. The FA also acts as the default router for packets generated by the MN while it is connected to the foreign network.

                              The traffic destined for the MN is forwarded in a triangular manner. When a device on the Internet, called a correspondent node (CN), sends a packet to the MN, the packet is routed to the home network of the MN, the HA redirects the packet by tunneling to the care-of address (current location) of the MN on the foreign network, as shown in the figure above. The FA receives the packet from the HA and forwards it locally to the MN. However, packets sent by the MN are routed directly to the CN.

                              For more details about configuring Mobile IP, see the Cisco IOS IP Mobility Configuration Guide.

                              Generic Routing Encapsulation

                              Generic routing encapsulation (GRE) is defined in RFC 2784. GRE is a carrier protocol that can be used with a variety of underlying transport protocols and that can carry a variety of passenger protocols. RFC 2784 also covers the use of GRE with IPv4 as the transport protocol and the passenger protocol. Cisco IOS software supports GRE as the carrier protocol with many combinations of passenger and transport protocols such as:

                              The following descriptions of GRE tunnels are included:

                              GRE Tunnel IP Source and Destination VRF Membership

                              GRE Tunnel IP Source and Destination VRF Membership allows you to configure the source and destination of a tunnel to belong to any VRF tables. A VRF table stores routing data for each VPN. The VRF table defines the VPN membership of a customer site attached to the network access server (NAS). Each VRF table comprises an IP routing table, a derived CEF table, and guidelines and routing protocol parameters that control the information that is included in the routing table.

                              Previously, Generic Routing Encapsulation (GRE) IP tunnels required the IP tunnel destination to be in the global routing table. The implementation of this feature allows you to configure a tunnel source and destination to belong to any VRF. As with existing GRE tunnels, the tunnel becomes disabled if no route to the tunnel destination is defined.

                              EoMPLS over GRE

                              Ethernet over multiprotocol label switching (EoMPLS) is a tunneling mechanism that allows you to tunnel Layer 2 traffic through a Layer 3 MPLS network. EoMPLS is also known as Layer 2 tunneling.

                              EoMPLS effectively facilitates the Layer 2 extension over long distances. EoMPLS over GRE helps to create the GRE tunnel as hardware-based switched, and with high performance that encapsulates EoMPLS frames within the GRE tunnel. The GRE connection is established between the two core routers, and then the MPLS LSP is tunneled over.

                              GRE encapsulation is used to define a packet that has some additional header information added to it prior to being forwarded. De-encapsulation is the process of removing the additional header information when the packet reaches the destination tunnel endpoint.

                              When a packet is forwarded through a GRE tunnel, two new headers are appended at the front of the packet and hence the context of the new payload changes. After encapsulation, what was originally the data payload and separate IP header is now known as the GRE payload. A GRE header is added to the packet to provide information on the protocol type and also a recalculated checksum. Also, a new IP header is added to the front of the GRE header. This IP header contains the destination IP address of the tunnel.

                              The GRE header is appended to the packet (IP, L2VPN, L3VPN, etc.) before entering the tunnel. All routers along the path that receive the encapsulated packet will use the new IP header to determine where to send the packet in an effort for it to reach the tunnel endpoint.

                              In the IP forwarding case on reaching the tunnel destination endpoint, the new IP header and GRE header are removed from the packet and the original IP header is then used to forward the packet to it’s final destination.

                              In the EoMPLS over GRE cases, the new IP header and GRE header will be removed from the packet at the tunnel destination and the MPLS (VC or VPN) label will be used to forward the packets to the appropriate L2 attachment circuit or L3 VRF.

                              The following scenarios describe the L2VPN and L3VPN over GRE deployment on provider edge (PE) or provider (P) routers:

                              PE to PE GRE Tunnels

                              In the PE to PE GRE tunnels scenario, a customer does not generally transition any part of the core to MPLS but prefers to offer EoMPLS and basic MPLS VPN services. Hence, GRE tunneling of the MPLS labeled traffic is done between PEs. This is the most common scenario seen in various customers networks.

                              P to P GRE Tunnels

                              The P to P GRE tunnels scenario is one where MPLS has been enabled between PE and P routers, but the network core may have non-MPLS-aware routers or IP encryption boxes. In this scenario, GRE tunneling of the MPLS labeled packets is done between P routers.

                              PE to P GRE Tunnels

                              The PE to P GRE tunnels scenario demonstrates a network where the P to P nodes are MPLS-aware, while GRE tunneling is done between a PE to P non MPLS network segment.

                              The following features are required for the deployment of scenarios described above:

                              GRE Specific:

                              • Tunnel endpoints can be loopbacks or physical interfaces.

                              • Configurable tunnel keepalive timer parameters per end point, and syslog message must be generated when the keepalive timer expires.

                              • BFD support for tunnel failures and for IGPs using tunnels.

                              • IGP loadsharing across GRE tunnels.

                              • IGP redundancy across GRE tunnels.

                              • Fragmentation across GRE tunnels.

                              • Ability to pass jumbo frames.

                              • Support for all IGP control plane traffic.

                              • Support for IP TOS preservation across tunnel.

                              • Tunnel should be independent of endpoint physical interface types such as POS, Gig, TenGig, and ATM.

                              • Support for up to 100 GRE tunnels.

                              EoMPLS Specific:

                              • Port mode EoMPLS.

                              • VLAN mode EoMPLS.

                              • Pseudowire redundancy.

                              • AToM sequencing.

                              • Tunnel selection--ability to map a specific pseudowire or pw-class to a GRE tunnel.

                              • IGP loadsharing and redundancy. See below for more information.

                              • Support for up to 200 EoMPLS VCs.

                              MPLS-VPN Specific:

                              • Support for PE Role with IPv4 VRFs

                              • Support for all PE-CE protocols

                              • Load sharing through multiple tunnels and equal-cost IGP paths with a single tunnel

                              • Support for redundancy via unequal-cost IGP paths with a single tunnel

                              • Support for the IP Precedence value being copied onto the EXP bits field of the MPLS label, and then onto the Precedence bits on the outer IPv4 ToS field of the GRE packet.

                              For a sample configuration sequence of EoMPLS over GRE, see Example Configuring EoMPLS over GRE. For more details about EoMPLS over GRE, see Deploying and Configuring MPLS Virtual Private Networks In IP Tunnel Environments .

                              Multipoint GRE Tunneling

                              Enhanced multipoint GRE (mGRE) tunneling technology provides a Layer 3 (L3) transport mechanism for use in IP networks. This same dynamic Layer 3 tunneling transport can be used within IP networks to transport VPN traffic across service provider and enterprise networks, as well as to provide interoperability for packet transport between IP and MPLS VPNs. This feature provides support for RFC 2547, which defines the outsourcing of IP-backbone services for enterprise networks.

                              Multipoint tunnels use the Next Hop Resolution Protocol (NHRP) in the same way that a Frame Relay multipoint interface uses information obtained by the reverse ARP mechanism to learn the Layer 3 addresses of the remote data-link connection identifiers (DLCIs).

                              In Cisco IOS Release 12.2(8)T and later releases, CEF-switching over mGRE tunnels was introduced. Previously, only process switching was available for mGRE tunnels. CEF-switching over mGRE tunnels enables CEF switching of IP traffic to and from multipoint GRE tunnels. Tunnel traffic can be forwarded to a prefix through a tunnel destination when both the prefix and the tunnel destination are specified by the application.

                              GRE CLNS Tunnel Support for IPv4 and IPv6 Packets

                              GRE tunneling of IPv4 and IPv6 packets through CLNS networks enables Cisco CLNS tunnels (CTunnels) to interoperate with networking equipment from other vendors. This feature provides compliance with RFC 3147.

                              The optional GRE services defined in header fields, such as checksums, keys, and sequencing, are not supported. Any packet that is received and requests such services will be dropped.

                              GRE IPv4 Tunnel Support for IPv6 Traffic

                              IPv6 traffic can be carried over IPv4 generic routing encapsulation (GRE) tunnels using the standard GRE tunneling technique that is designed to provide the services necessary to implement any standard point-to-point encapsulation scheme. As in IPv6 manually configured tunnels, GRE tunnels are links between two points, with a separate tunnel for each link. The tunnels are not tied to a specific passenger or transport protocol, but in this case, IPv6 is the passenger protocol, GRE is the carrier protocol, and IPv4 is the transport protocol.

                              The primary use of GRE tunnels is for stable connections that require regular secure communication between two edge routers or between an edge router and an end system. The edge routers and the end systems must be dual-stack implementations.

                              GRE has a protocol field that identifies the passenger protocol. GRE tunnels allow IS-IS or IPv6 to be specified as a passenger protocol, allowing both IS-IS and IPv6 traffic to run over the same tunnel. If GRE did not have a protocol field, it would be impossible to distinguish whether the tunnel was carrying IS-IS or IPv6 packets. The GRE protocol field is why it is desirable that you tunnel IS-IS and IPv6 inside GRE.

                              Overlay Tunnels for IPv6

                              Overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure (a core network or the Internet). (See the figure below.) By using overlay tunnels, you can communicate with isolated IPv6 networks without upgrading the IPv4 infrastructure between them. Overlay tunnels can be configured between border routers or between a border router and a host; however, both tunnel endpoints must support both the IPv4 and IPv6 protocol stacks. Cisco IOS IPv6 currently supports the following types of overlay tunneling mechanisms:

                              • Manual

                              • Generic routing encapsulation (GRE)

                              • IPv4-compatible

                              • 6to4

                              • Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)

                              Figure 4. Overlay Tunnels


                              Note

                              Overlay tunnels reduce the maximum transmission unit (MTU) of an interface by 20 octets (assuming that the basic IPv4 packet header does not contain optional fields). A network that uses overlay tunnels is difficult to troubleshoot. Therefore, overlay tunnels that connect isolated IPv6 networks should not be considered as a final IPv6 network architecture. The use of overlay tunnels should be considered as a transition technique toward a network that supports both the IPv4 and IPv6 protocol stacks or just the IPv6 protocol stack.

                              Use the table below to help you determine which type of tunnel you want to configure to carry IPv6 packets over an IPv4 network.

                              Table 2 Suggested Usage of Tunnel Types to Carry IPv6 Packets over an IPv4 Network

                              Tunneling Type

                              Suggested Usage

                              Usage Notes

                              Manual

                              Simple point-to-point tunnels that can be used within a site or between sites.

                              Can carry IPv6 packets only.

                              GRE/IPv4

                              Simple point-to-point tunnels that can be used within a site or between sites.

                              Can carry IPv6, CLNS, and many other types of packets.

                              Compatible

                              Point-to-multipoint tunnels.

                              Uses the ::/96 prefix. Currently, we do not recommend using this tunnel type.

                              6to4

                              Point-to-multipoint tunnels that can be used to connect isolated IPv6 sites.

                              Sites use addresses from the 2002::/16 prefix.

                              ISATAP

                              Point-to-multipoint tunnels that can be used to connect systems within a site.

                              Sites can use any IPv6 unicast addresses.

                              Individual tunnel types are discussed in more detail in the following concepts, and we recommend that you review and understand the information on the specific tunnel type that you want to implement. When you are familiar with the type of tunnel you need, the table below provides a quick summary of the tunnel configuration parameters that you may find useful.

                              Table 3 Overlay Tunnel Configuration Parameters by Tunneling Type

                              Overlay Tunneling Type

                              Overlay Tunnel Configuration Parameter

                              Tunnel Mode

                              Tunnel Source

                              Tunnel Destination

                              Interface Prefix/Address

                              Manual

                              ipv6ip

                              An IPv4 address or a reference to an interface on which IPv4 is configured.

                              An IPv4 address.

                              An IPv6 address.

                              GRE/IPv4

                              gre ip

                              An IPv4 address.

                              An IPv6 address.

                              Compatible

                              ipv6ip auto-tunnel

                              Not required. These are all point-to-multipoint tunneling types. The IPv4 destination address is calculated, on a per-packet basis, from the IPv6 destination.

                              Not required. The interface address is generated as ::tunnel-source/96.

                              6to4

                              ipv6ip 6to4

                              An IPv6 address. The prefix must embed the tunnel source IPv4 address.

                              ISATAP

                              ipv6ip isatap

                              An IPv6 prefix in modified eui-64 format. The IPv6 address is generated from the prefix and the tunnel source IPv4 address.

                              IPv6 Manually Configured Tunnels

                              A manually configured tunnel is equivalent to a permanent link between two IPv6 domains over an IPv4 backbone. The primary use is for stable connections that require regular secure communication between two edge routers or between an end system and an edge router, or for connection to remote IPv6 networks.

                              An IPv6 address is manually configured on a tunnel interface, and manually configured IPv4 addresses are assigned to the tunnel source and the tunnel destination. The host or router at each end of a configured tunnel must support both the IPv4 and IPv6 protocol stacks. Manually configured tunnels can be configured between border routers or between a border router and a host. CEF switching can be used for IPv6 manually configured tunnels, or CEF switching can be disabled if process switching is needed.

                              Automatic 6to4 Tunnels

                              An automatic 6to4 tunnel allows isolated IPv6 domains to be connected over an IPv4 network to remote IPv6 networks. The key difference between automatic 6to4 tunnels and manually configured tunnels is that the tunnel is not point-to-point; it is point-to-multipoint. In automatic 6to4 tunnels, routers are not configured in pairs because they treat the IPv4 infrastructure as a virtual nonbroadcast multiaccess (NBMA) link. The IPv4 address embedded in the IPv6 address is used to find the other end of the automatic tunnel.

                              An automatic 6to4 tunnel may be configured on a border router in an isolated IPv6 network, which creates a tunnel on a per-packet basis to a border router in another IPv6 network over an IPv4 infrastructure. The tunnel destination is determined by the IPv4 address of the border router extracted from the IPv6 address that starts with the prefix 2002::/16, where the format is 2002:border-router-IPv4-address ::/48. Following the embedded IPv4 address are 16 bits that can be used to number networks within the site. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks. 6to4 tunnels are configured between border routers or between a border router and a host.

                              The simplest deployment scenario for 6to4 tunnels is to interconnect multiple IPv6 sites, each of which has at least one connection to a shared IPv4 network. This IPv4 network could be the global Internet or a corporate backbone. The key requirement is that each site have a globally unique IPv4 address; the Cisco IOS software uses this address to construct a globally unique 6to4/48 IPv6 prefix. As with other tunnel mechanisms, appropriate entries in a Domain Name System (DNS) that map between hostnames and IP addresses for both IPv4 and IPv6 allow the applications to choose the required address.

                              Automatic IPv4-Compatible IPv6 Tunnels

                              Automatic IPv4-compatible tunnels use IPv4-compatible IPv6 addresses. IPv4-compatible IPv6 addresses are IPv6 unicast addresses that have zeros in the high-order 96 bits of the address and an IPv4 address in the low-order 32 bits. They can be written as 0:0:0:0:0:0:A.B.C.D or ::A.B.C.D, where "A.B.C.D" represents the embedded IPv4 address.

                              The tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of IPv4-compatible IPv6 addresses. The host or router at each end of an IPv4-compatible tunnel must support both the IPv4 and IPv6 protocol stacks. IPv4-compatible tunnels can be configured between border routers or between a border router and a host. Using IPv4-compatible tunnels is an easy method to create tunnels for IPv6 over IPv4, but the technique does not scale for large networks.


                              Note

                              IPv4-compatible tunnels were initially supported for IPv6, but are currently being deprecated. Cisco now recommends that you use a different IPv6 tunneling technique named ISATAP tunnels.

                              ISATAP Tunnels

                              The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) is an automatic overlay tunneling mechanism that uses the underlying IPv4 network as a nonbroadcast multiaccess (NBMA) link layer for IPv6. ISATAP is designed for transporting IPv6 packets within a site where a native IPv6 infrastructure is not yet available; for example, when sparse IPv6 hosts are deployed for testing. ISATAP tunnels allow individual IPv4/IPv6 dual-stack hosts within a site to communicate with other such hosts on the same virtual link, basically creating an IPv6 network using the IPv4 infrastructure.

                              The ISATAP router provides standard router advertisement network configuration support for the ISATAP site. This feature allows clients to automatically configure themselves as they would do if they were connected to an Ethernet. It can also be configured to provide connectivity out of the site. ISATAP uses a well-defined IPv6 address format composed of any unicast IPv6 prefix (/64), which can be link-local or global (including 6to4 prefixes), enabling IPv6 routing locally or on the Internet. The IPv4 address is encoded in the last 32 bits of the IPv6 address, enabling automatic IPv6-in-IPv4 tunneling.

                              While the ISATAP tunneling mechanism is similar to other automatic tunneling mechanisms, such as IPv6 6to4 tunneling, ISATAP is designed for transporting IPv6 packets within a site, not between sites.

                              ISATAP uses unicast addresses that include a 64-bit IPv6 prefix and a 64-bit interface identifier. The interface identifier is created in modified EUI-64 format in which the first 32 bits contain the value 000:5EFE to indicate that the address is an IPv6 ISATAP address. The table below shows the layout of an ISATAP address.

                              Table 4 ISATAP address example

                              64 Bits

                              32 Bits

                              32 Bits

                              Link local or global IPv6 unicast prefix

                              0000:5EFE

                              IPv4 address of the ISATAP link

                              As shown in the table above, an ISATAP address consists of an IPv6 prefix and the ISATAP interface identifier. This interface identifier includes the IPv4 address of the underlying IPv4 link. The following example shows what an actual ISATAP address would look like if the prefix is 2001:0DB8:1234:5678::/64 and the embedded IPv4 address is 10.173.129.8. In the ISATAP address, the IPv4 address is expressed in hexadecimal as 0AAD:8108.

                              Example

                              2001:0DB8:1234:5678:0000:5EFE:0AAD:8108

                              Rate-Based Satellite Control Protocol Tunnels

                              Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPsec), over satellite links without breaking the end-to-end model.

                              Satellite links have several characteristics that affect the performance of IP protocols over the link. The figure below shows that satellite links can have a one-way delay of 275 milliseconds. A round-trip time (RTT) of 550 milliseconds is a very long delay for TCP. Another issue is the high error rates (packet loss rates) that are typical of satellite links as compared to wired links in LANs. Even the weather affects satellite links, causing a decrease in available bandwidth and an increase in RTT and packet loss.

                              Figure 5. Typical Satellite Link

                              Long RTT keeps TCP in a slow start mode, which increases the time before the satellite link bandwidth is fully used. TCP and Stream Control Transmission Protocol (SCTP) interpret packet loss events as congestion in the network and start to perform congestion recovery procedures, which reduce the traffic being sent over the link.

                              Although available satellite link bandwidths are increasing, the long RTT and high error rates experienced by IP protocols over satellite links are producing a high bandwidth-delay product (BDP).

                              To address the problem of TCP being kept in a slow start mode when a satellite link is used, a disruptive performance enhancing proxy (PEP) solution is often introduced into the network. In the figure below, you can see that the transport connection is broken up into three sections with hosts on the remote side connecting to the Internet through their default router. The router sends all Internet-bound traffic to the TCP PEP, which terminates the TCP connection to the Internet. The PEP generates a local TCP ACK (TCP spoofing) for all data. Traffic is buffered and retransmitted through a single PEP protocol connection over the satellite link. The second PEP receives the data from the satellite link and retransmits the data over separate TCP connections to the Internet. TCP transmission is disrupted, so dropped packets are not interpreted as TCP congestion and can be retransmitted from buffered data. Minimal TCP ACKs and reduced TCP slow starts allow more bandwidth to be used.

                              Figure 6. Disruptive TCP PEP Solution

                              One of the disadvantages to using disruptive TCP PEP is the breaking of the end-to-end model. Some applications cannot work when the flow of traffic is broken, and the PEP has no provision for handling encrypted traffic (IPsec). New transport protocols such as SCTP require special handling or additional code to function with disruptive TCP PEP. An additional managed network component is also required at every satellite router.

                              RBSCP has been designed to preserve the end-to-end model and provide performance improvements over the satellite link without using a PEP solution. IPsec encryption of clear-text traffic (for example a VPN service configuration) across the satellite link is supported. RBSCP allows two routers to control and monitor the sending rates of the satellite link, thereby increasing the bandwidth utilization. Lost packets are retransmitted over the satellite link by RBSCP, preventing the end host TCP senders from going into slow start mode.

                              RBSCP is implemented using a tunnel interface as shown in the figure below. The tunnel can be configured over any network interface supported by Cisco IOS software that can be used by a satellite modem or internal satellite modem network module. IP traffic is sent across the satellite link with appropriate modifications and enhancements that are determined by the router configuration. Standard routing or policy-based routing can be used to determine the traffic to be sent through the RBSCP tunnel.

                              Figure 7. Nondisruptive RBSCP Solution

                              RBSCP tunnels can be configured for any of the following features:

                              • Time Delay --One of the RBSCP routers can be configured to hold frames due for transmission through the RBSCP tunnel. The delay time increases the RTT at the end host and allows RBSCP time to retransmit lost TCP frames or other protocol frames. If the retransmission is successful, it prevents lost frame events from reaching the end host where congestion procedures would be enabled. In some cases, the retransmission can be completed by RBSCP without inserting the delay. This option should be used only when the RTT of the satellite link is greater than 700 milliseconds.

                              • ACK Splitting --Performance improvements can be made for clear-text TCP traffic using acknowledgement (ACK) splitting in which a number of additional TCP ACKs are generated for each TCP ACK received. TCP will open a congestion window by one maximum transmission unit (MTU) for each TCP ACK received. Opening the congestion window results in increased bandwidth becoming available. Configure this feature only when the satellite link is not using all the available bandwidth. Encrypted traffic cannot use ACK splitting.

                              • Window Stuffing --Clear-text TCP and SCTP traffic can benefit from the RBSCP window stuffing feature. RBSCP can buffer traffic so that the advertised window can be incremented up to the available satellite link bandwidth or the available memory in the router. The end host that sends the packets is fooled into thinking that a larger window exists at the receiving end host and sends more traffic. Use this feature with caution because the end host may send too much traffic for the satellite link to handle and the resulting loss and retransmission of packets may cause link congestion.

                              • SCTP Drop Reporting --SCTP uses an appropriate byte counting method instead of ACK counting to determine the size of the transmission window, so ACK splitting does not work with SCTP. The RBSCP tunnel can generate an SCTP packet-dropped report for packets dropped across the satellite but not as a result of congestion loss. This SCTP drop reporting is on by default and provides a chance to retransmit the packet without affecting the congestion window size. Actual congestion losses are still reported, and normal recovery mechanisms are activated.

                              Path MTU Discovery

                              Path MTU Discovery (PMTUD) can be enabled on a GRE or IP-in-IP tunnel interface. When PMTUD (RFC 1191) is enabled on a tunnel interface, the router performs PMTUD processing for the GRE (or IP-in-IP) tunnel IP packets. The router always performs PMTUD processing on the original data IP packets that enter the tunnel. When PMTUD is enabled, packet fragmentation is not permitted for packets that traverse the tunnel because the Don’t Fragment (DF) bit is set on all the packets. If a packet that enters the tunnel encounters a link with a smaller MTU, the packet is dropped and an ICMP message is sent back to the sender of the packet. This message indicates that fragmentation was required (but not permitted) and provides the MTU of the link that caused the packet to be dropped.

                              For more detailed information about PMTUD, see the IP Fragmentation and PMTUD document.


                              Note

                              PMTUD on a tunnel interface requires that the tunnel endpoint be able to receive ICMP messages generated by routers in the path of the tunnel. Check that ICMP messages can be received before using PMTUD over firewall connections.

                              Use the tunnel path-mtu-discovery command to enable PMTUD for the tunnel packets, and use the show interfaces tunnel command to verify the tunnel PMTUD parameters. PMTUD currently works only on GRE and IP-in-IP tunnel interfaces.

                              QoS Options for Tunnels

                              A tunnel interface supports many of the same quality of service (QoS) features as a physical interface. QoS provides a way to ensure that mission-critical traffic has an acceptable level of performance. QoS options for tunnels include support for applying generic traffic shaping (GTS) directly on the tunnel interface and support for class-based shaping using the modular QoS CLI (MQC). Tunnel interfaces also support class-based policing, but they do not support committed access rate (CAR).


                              Note

                              Service policies are not supported on tunnel interfaces on the Cisco 7500 series routers.

                              GRE tunnels allow the router to copy the IP precedence bit values of the ToS byte to the tunnel or the GRE IP header that encapsulates the inner packet. Intermediate routers between the tunnel endpoints can use the IP precedence values to classify the packets for QoS features such as policy routing, weighted fair queueing (WFQ), and weighted random early detection (WRED).

                              When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets that travel across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. Tunnel packets can, however, be classified before tunneling and encryption can occur by using the QoS preclassify feature on the tunnel interface or on the crypto map.


                              Note

                              Class-based WFQ (CBWFQ) inside class-based shaping is not supported on a multipoint interface.

                              For examples of how to implement some QoS features on a tunnel interface, see the Example Configuring QoS Options on Tunnel Interfaces.

                              How to Implement Tunnels

                              Determining the Tunnel Type

                              Before configuring a tunnel, you must determine what type of tunnel you need to create.

                              SUMMARY STEPS

                                1.    Determine the passenger protocol.

                                2.    Determine the tunnel CLI type.

                                3.    Determine the tunnel mode command keyword, if appropriate.


                              DETAILED STEPS
                                Step 1   Determine the passenger protocol.

                                The passenger protocol is the protocol that you are encapsulating.

                                Step 2   Determine the tunnel CLI type.

                                The table below shows how to determine the tunnel CLI command required for the transport protocol that you are using in the tunnel.

                                Table 5 Determining the Tunnel CLI by the Transport Protocol

                                Transport Protocol

                                Tunnel CLI Command

                                CLNS

                                ctunnel ( with optional mode gre keywords)

                                Other

                                tunnel mode ( with appropriate keyword)

                                Step 3   Determine the tunnel mode command keyword, if appropriate.

                                The table below shows how to determine the appropriate keyword to use with the tunnel mode command. In the tasks that follow in this module, only the relevant keywords for the tunnel mode command are displayed.

                                Table 6 Determining the tunnel mode Command Keyword

                                Keyword

                                Purpose

                                dvmrp

                                Use the dvmrp keyword to specify that the Distance Vector Multicast Routing Protocol encapsulation will be used.

                                gre ip

                                Use the gre ip keywords to specify that GRE encapsulation over IP will be used.

                                gre ipv6

                                Use the gre ipv6 keywords to specify that GRE encapsulation over IPv6 will be used.

                                gre multipoint

                                Use the gre multipoint keywords to specify that multipoint GRE (mGRE) encapsulation will be used.

                                ipip [decapsulate-any]

                                Use the ipip keyword to specify that IP-in-IP encapsulation will be used. The optional decapsulate-any keyword terminates any number of IP-in-IP tunnels at one tunnel interface. Note that this tunnel will not carry any outbound traffic; however, any number of remote tunnel endpoints can use a tunnel configured this way as their destination.

                                ipv6

                                Use the ipv6 keyword to specify that generic packet tunneling in IPv6 will be used.

                                ipv6ip

                                Use the ipv6ip keyword to specify that IPv6 will be used as the passenger protocol and IPv4 as both the carrier (encapsulation) and transport protocol. When additional keywords are not used, manual IPv6 tunnels are configured. Additional keywords can be used to specify IPv4-compatible, 6to4, or ISATAP tunnels.

                                mpls

                                Use the mpls keyword to specify that MPLS will be used for configuring Traffic Engineering (TE) tunnels.

                                rbscp

                                Use the rbscp keyword to specify that RBSCP tunnels will be used.

                                What to Do Next

                                To configure an RBSCP tunnel to carry IP data packets over a satellite or other long-distance delay link with high error rates, proceed to the Configuring the RBSCP Tunnel.

                                Configuring a GRE Tunnel

                                Perform this task to configure a GRE tunnel. A tunnel interface is used to pass protocol traffic across a network that does not normally support the protocol. To build a tunnel, a tunnel interface must be defined on each of two routers and the tunnel interfaces must reference each other. At each router, the tunnel interface must be configured with a L3 address. The tunnel endpoints, tunnel source, and tunnel destination must be defined, and the type of tunnel must be selected. Optional steps can be performed to customize the tunnel.

                                Remember to configure the router at each end of the tunnel. If only one side of a tunnel is configured, the tunnel interface may still come up and stay up (unless keepalive is configured), but packets going into the tunnel will be dropped.

                                In Cisco IOS Release 12.2(8)T and later releases, CEF-switching over multipoint GRE tunnels was introduced. Previously, only process switching was available for multipoint GRE tunnels.

                                GRE Tunnel Keepalive

                                Keepalive packets can be configured to be sent over IP-encapsulated GRE tunnels. You can specify the rate at which keepalives will be sent and the number of times that a device will continue to send keepalive packets without a response before the interface becomes inactive. GRE keepalive packets may be sent from both sides of a tunnel or from just one side.

                                Before You Begin

                                Ensure that the physical interface to be used as the tunnel source in this task is up and configured with the appropriate IP address. For hardware technical descriptions and information about installing interfaces, see the hardware installation and configuration publication for your product.


                                Note

                                GRE tunnel keepalive is not supported in cases where virtual route forwarding (VRF) is applied to a GRE tunnel.

                                >
                                SUMMARY STEPS

                                  1.    enable

                                  2.    configure terminal

                                  3.    interface type number

                                  4.    bandwidth kbps

                                  5.    keepalive [period [retries]]

                                  6.    tunnel source {ip-address | interface-type interface-number}

                                  7.    tunnel destination {hostname | ip-address}

                                  8.    tunnel key key-number

                                  9.    tunnel mode {gre ip| gre multipoint}

                                  10.    ip mtu bytes

                                  11.    ip tcp mss mss-value

                                  12.    tunnel path-mtu-discovery [age-timer {aging-mins| infinite}]

                                  13.    end


                                DETAILED STEPS
                                   Command or ActionPurpose
                                  Step 1 enable


                                  Example:
                                  Router> enable
                                   

                                  Enables privileged EXEC mode.

                                  • Enter your password if prompted.

                                   
                                  Step 2 configure terminal


                                  Example:
                                  Router# configure terminal
                                   

                                  Enters global configuration mode.

                                   
                                  Step 3 interface type number


                                  Example:
                                  Router(config)# interface tunnel 0
                                   

                                  Specifies the interface type and number and enters interface configuration mode.

                                  • To configure a tunnel, use tunnel for the type argument.

                                  • On some router platforms such as the Cisco 7500 series, the number argument may consist of a slot, port adapter, and port number. For more details, see the interface command in the Cisco IOS Interface and Hardware Component Command Reference.

                                   
                                  Step 4 bandwidth kbps


                                  Example:
                                  Router(config-if)# bandwidth 1000
                                   

                                  Sets the current bandwidth value for an interface and communicates it to higher-level protocols. Specifies the tunnel bandwidth to be used to transmit packets.

                                  • Use the kbpsargument to set the bandwidth, in kilobits per second (kbps).

                                  Note   

                                  This is a routing parameter only; it does not affect the physical interface. The default bandwidth setting on a tunnel interface is 9.6 kbps. You should set the bandwidth on a tunnel to an appropriate value.

                                   
                                  Step 5 keepalive [period [retries]]


                                  Example:
                                  Router(config-if)# keepalive 3 7
                                   

                                  (Optional) Specifies the number of times that the device will continue to send keepalive packets without response before bringing the tunnel interface protocol down.

                                  • GRE keepalive packets may be configured either on only one side of the tunnel or on both.

                                  • If GRE keepalive is configured on both sides of the tunnel, the period and retries arguments can be different at each side of the link.

                                  Note   

                                  This command is supported only on GRE point-to-point tunnels.

                                   
                                  Step 6 tunnel source {ip-address | interface-type interface-number}


                                  Example:
                                  Router(config-if)# tunnel source Ethernet 1
                                   

                                  Configures the tunnel source.

                                  • Use the ip-addressargument to specify the source IP address.

                                  • Use the interface-typeand interface-numberarguments to specify the interface to use.

                                  Note   

                                  The tunnel source and destination IP addresses must be defined on two separate devices.

                                   
                                  Step 7 tunnel destination {hostname | ip-address}


                                  Example:
                                  Router(config-if)# tunnel destination 172.17.2.1
                                   

                                  Configures the tunnel destination.

                                  • Use the hostnameargument to specify the name of the host destination.

                                  • Use the ip-addressargument to specify the IP address of the host destination.

                                  Note   

                                  The tunnel source and destination IP addresses must be defined on two separate devices.

                                   
                                  Step 8 tunnel key key-number


                                  Example:
                                  Router(config-if)# tunnel key 1000
                                   

                                  (Optional) Enables an ID key for a tunnel interface.

                                  • Use the key-numberargument to identify a tunnel key that is carried in each packet.

                                  • Tunnel ID keys can be used as a form of weak security to prevent improper configuration or injection of packets from a foreign source.

                                  Note   

                                  This command is supported only on GRE tunnel interfaces. We do not recommend relying on this key for security purposes.

                                   
                                  Step 9 tunnel mode {gre ip| gre multipoint}


                                  Example:
                                  Router(config-if)# tunnel mode gre ip
                                   

                                  Specifies the encapsulation protocol to be used in the tunnel.

                                  • Use the gre ip keywords to specify that GRE over IP encapsulation will be used.

                                  • Use the gre multipoint keywords to specify that multipoint GRE (mGRE) will be used.

                                   
                                  Step 10 ip mtu bytes


                                  Example:
                                  Router(config-if)# ip mtu 1400
                                   

                                  (Optional) Set the maximum transmission unit (MTU) size of IP packets sent on an interface.

                                  • If an IP packet exceeds the MTU set for the interface, the Cisco IOS software will fragment it unless the DF bit is set.

                                  • All devices on a physical medium must have the same protocol MTU in order to operate.

                                  Note   

                                  If the tunnel path-mtu-discovery command is enabled in Step 12, do not configure this command.

                                   
                                  Step 11 ip tcp mss mss-value


                                  Example:
                                  Router(config-if)# ip tcp mss 250
                                   

                                  (Optional) Specifies the maximum segment size (MSS) for TCP connections that originate or terminate on a router.

                                  • Use the mss-value argument to specify the maximum segment size for TCP connections, in bytes.

                                   
                                  Step 12 tunnel path-mtu-discovery [age-timer {aging-mins| infinite}]


                                  Example:
                                  Router(config-if)# tunnel path-mtu-discovery
                                   

                                  (Optional) Enables Path MTU Discovery (PMTUD) on a GRE or IP-in-IP tunnel interface.

                                  • When PMTUD is enabled on a tunnel interface, PMTUD will operate for GRE IP tunnel packets to minimize fragmentation in the path between the tunnel endpoints.

                                   
                                  Step 13 end


                                  Example:
                                  Router(config-if)# end
                                   

                                  Exits interface configuration mode and returns to privileged EXEC mode.

                                   

                                  What to Do Next

                                  Configuring GRE IPv6 Tunnels

                                  Perform this task to configure a GRE tunnel on an IPv6 network. GRE tunnels can be configured to run over an IPv6 network layer and transport IPv6 and IPv4 packets through IPv6 tunnels.

                                  Before You Begin

                                  When GRE IPv6 tunnels are configured, IPv6 addresses are assigned to the tunnel source and the tunnel destination. The tunnel interface can have either IPv4 or IPv6 addresses (this is not shown in the task below). The host or device at each end of the configured tunnel must support both IPv4 and IPv6 protocol stacks.

                                  SUMMARY STEPS

                                    1.    enable

                                    2.    configure terminal

                                    3.    interface tunnel tunnel-number

                                    4.    tunnel source {ipv6-address | interface-type interface-number}

                                    5.    tunnel destination ipv6-address

                                    6.    tunnel mode gre ipv6

                                    7.    end


                                  DETAILED STEPS
                                     Command or ActionPurpose
                                    Step 1 enable


                                    Example:
                                    Device> enable
                                     

                                    Enables privileged EXEC mode.

                                    • Enter your password if prompted.

                                     
                                    Step 2 configure terminal


                                    Example:
                                    Device# configure terminal
                                     

                                    Enters global configuration mode.

                                     
                                    Step 3 interface tunnel tunnel-number


                                    Example:
                                    Device(config)# interface tunnel 0
                                     

                                    Specifies a tunnel interface and number and enters interface configuration mode.

                                     
                                    Step 4 tunnel source {ipv6-address | interface-type interface-number}


                                    Example:
                                    Device(config-if)# tunnel source ethernet 0
                                     

                                    Specifies the source IPv6 address or the source interface type and number for the tunnel interface.

                                    • If an interface type and number are specified, the interface must be configured with an IPv6 address.

                                    Note   

                                    Only the syntax used in this context is displayed. For more details, see the IPv6 Command Reference.

                                     
                                    Step 5 tunnel destination ipv6-address


                                    Example:
                                    Device(config-if)# tunnel destination 2001:0DB8:0C18:2::300
                                     

                                    Specifies the destination IPv6 address for the tunnel interface.

                                    Note   

                                    Only the syntax used in this context is displayed. For more details, see the IPv6 Command Reference.

                                     
                                    Step 6 tunnel mode gre ipv6


                                    Example:
                                    Device(config-if)# tunnel mode gre ipv6
                                     

                                    Specifies a GRE IPv6 tunnel.

                                    Note   

                                    The tunnel mode gre ipv6 command specifies GRE as the encapsulation protocol for the tunnel interface. Only the syntax used in this context is displayed. For more details, see the IPv6 Command Reference.

                                     
                                    Step 7 end


                                    Example:
                                    Device(config-if)# end
                                     

                                    Exits interface configuration mode and returns to privileged EXEC mode.

                                     

                                    What to Do Next

                                    Proceed to the “Verifying Tunnel Configuration and Operation” section.

                                    Configuring GRE Tunnel IP Source and Destination VRF Membership

                                    This task explains how to configure the source and destination of a tunnel to belong to any virtual private network (VPN) routing/forwarding (VRFs) tables


                                    Note

                                    Cisco 10000 Series Routers

                                    • The VRF associated with the tunnel vrf command is the same as the VRF associated with the physical interface over which the tunnel sends packets (outer IP packet routing).

                                    • The VRF associated with the tunnel by using the ip vrf forwarding command is the VRF that the packets are to be forwarded in as the packets exit the tunnel (inner IP packet routing).

                                    • The Cisco 10000 series router does not support the fragmentation of multicast packets passing through a multicast tunnel.

                                    >
                                    SUMMARY STEPS

                                      1.    enable

                                      2.    configure {terminal | memory | network}

                                      3.    interface tunnel slot

                                      4.    ip vrf forwarding vrf-name

                                      5.    ip address ip-address subnet-mask

                                      6.    tunnel source {ip-address | type number}

                                      7.    tunnel destination {hostname | ip-address}

                                      8.    tunnel vrf vrf-name


                                    DETAILED STEPS
                                       Command or ActionPurpose
                                      Step 1 enable


                                      Example:
                                      Router> enable
                                       

                                      Enables higher privilege levels, such as privileged EXEC mode.

                                      • Enter your password if prompted.

                                       
                                      Step 2 configure {terminal | memory | network}


                                      Example:
                                      Router# configure terminal
                                       

                                      Enters global configuration mode.

                                       
                                      Step 3 interface tunnel slot


                                      Example:
                                      Router(config)# interface tunnel 0
                                       

                                      Enters interface configuration mode for the specified interface.

                                       
                                      Step 4 ip vrf forwarding vrf-name


                                      Example:
                                      Router(config-if)# ip vrf forwarding green
                                       

                                      Defines the VRF.

                                       
                                      Step 5 ip address ip-address subnet-mask


                                      Example:
                                      Router(config-if)# ip address 10.7.7.7 255.255.255.255
                                       

                                      Specifies the ip address and subnet mask.

                                       
                                      Step 6 tunnel source {ip-address | type number}


                                      Example:
                                      Router(config-if)# tunnel source loop 0
                                       

                                      Specifies the tunnel source.

                                       
                                      Step 7 tunnel destination {hostname | ip-address}


                                      Example:
                                      Router(config-if)# tunnel destination 10.5.5.5
                                       

                                      Defines the tunnel destination.

                                       
                                      Step 8 tunnel vrf vrf-name


                                      Example:
                                      Router(config-if)# tunnel vrf finance1
                                       

                                      Defines the VRF.

                                       

                                      What to Do Next

                                      Configuring a CTunnel

                                      Perform this task to configure an IP over CLNS tunnel (CTunnel). To configure a CTunnel between a single pair of routers, a tunnel interface must be configured with an IP address, and a tunnel destination must be defined. The destination network service access point (NSAP) address for Router A would be the NSAP address of Router B, and the destination NSAP address for Router B would be the NSAP address of Router A. Ideally, the IP addresses used for the virtual interfaces at either end of the tunnel should be in the same IP subnet. Remember to configure the router at each end of the tunnel.

                                      CTunnel

                                      A CTunnel lets you transport IP traffic over Connectionless Network Service (CLNS), for example, on the data communications channel (DCC) of a SONET ring. CTunnels allow IP packets to be tunneled through the Connectionless Network Protocol (CLNP) to preserve TCP/IP services.

                                      Configuring a CTunnel allows you to telnet to a remote router that has only CLNS connectivity. Other management facilities can also be used, such as Simple Network Management Protocol (SNMP) and TFTP, which otherwise would not be available over a CLNS network.

                                      SUMMARY STEPS

                                        1.    enable

                                        2.    configure terminal

                                        3.    interface ctunnel interface-number

                                        4.    ip address ip-address mask

                                        5.    ctunnel destination remote-nsap-address

                                        6.    end

                                        7.    show interfaces ctunnel interface-number


                                      DETAILED STEPS
                                         Command or ActionPurpose
                                        Step 1 enable


                                        Example:
                                        Router> enable
                                         

                                        Enables privileged EXEC mode.

                                        • Enter your password if prompted.

                                         
                                        Step 2 configure terminal


                                        Example:
                                        Router# configure terminal
                                         

                                        Enters global configuration mode.

                                         
                                        Step 3 interface ctunnel interface-number


                                        Example:
                                        Router(config)# interface ctunnel 102
                                         

                                        Creates a virtual interface to transport IP over a CLNS tunnel and enters interface configuration mode.

                                        Note   

                                        The interface number must be unique for each CTunnel interface.

                                         
                                        Step 4 ip address ip-address mask


                                        Example:
                                        Router(config-if)# ip address 10.0.0.1 255.255.255.0
                                         

                                        Enables IP on the interface.

                                        • Use the ip-addressand mask arguments to specify the IP address and mask for the interface.

                                         
                                        Step 5 ctunnel destination remote-nsap-address


                                        Example:
                                        Router(config-if)# ctunnel destination 49.0001.2222.2222.2222.00
                                         

                                        Specifies the destination NSAP address of the CTunnel, where the packets exit the tunnel.

                                        • Use the remote-nsap-addressargument to specify the NSAP address at the CTunnel endpoint.

                                         
                                        Step 6 end


                                        Example:
                                        Router(config-if)# end
                                         

                                        Exits interface configuration mode and returns to privileged EXEC mode.

                                         
                                        Step 7 show interfaces ctunnel interface-number


                                        Example:
                                        Router# show interfaces ctunnel 102
                                         

                                        (Optional) Displays information about an IP over CLNS tunnel.

                                        • Use the interface-number argument to specify a CTunnel interface.

                                        • Use this command to verify the CTunnel configuration.

                                         

                                        Troubleshooting Tips

                                        Use the ping command to diagnose basic network connectivity issues.

                                        What to Do Next

                                        Configuring GRE CLNS CTunnels to Carry IPv4 and IPv6 Packets

                                        Perform this task to configure a CTunnel in GRE mode to transport IPv4 and IPv6 packets in a CLNS network.

                                        To configure a CTunnel between a single pair of routers, a tunnel interface must be configured with an IP address, and a tunnel destination must be defined. The destination network service access point (NSAP) address for Router A would be the NSAP address of Router B, and the destination NSAP address for Router B would be the NSAP address of Router A. Ideally, the IP addresses used for the virtual interfaces at either end of the tunnel should be in the same IP subnet. Remember to configure the router at each end of the tunnel.

                                        Tunnels for IPv4 and IPv6 Packets over CLNS Networks

                                        Configuring the ctunnel mode gre command on a CTunnel interface enables IPv4 and IPv6 packets to be tunneled over CLNS in accordance with RFC 3147. Compliance with this RFC should allow interoperation between Cisco equipment and that of other vendors in which the same standard is implemented.

                                        RFC 3147 specifies the use of GRE for tunneling packets. The implementation of this feature does not include support for GRE services defined in header fields, such as those used to specify checksums, keys, or sequencing. Any packets received that specify the use of these features will be dropped.

                                        The default CTunnel mode continues to use the standard Cisco encapsulation, which will tunnel only IPv4 packets. If you want to tunnel IPv6 packets, you must use the GRE encapsulation mode. Both ends of the tunnel must be configured with the same mode for either method to work.

                                        Before You Begin

                                        • An IPv4 or IPv6 address must be configured on a CTunnel interface, and manually configured CLNS addresses must be assigned to the CTunnel destination.

                                        • The host or router at each end of a configured CTunnel must support both the IPv4 and IPv6 protocol stacks.

                                        • The CTunnel source and destination must both be configured to run in the same mode.


                                        Note

                                        GRE services, such as those used to specify checksums, keys, or sequencing, are not supported. Packets that request use of those features will be dropped.

                                        >
                                        SUMMARY STEPS

                                          1.    enable

                                          2.    configure terminal

                                          3.    interface ctunnel interface-number

                                          4.    Do one of the following:

                                          • ip address ip-address mask
                                          • ipv6 address ipv6-prefix / prefix-length [eui-64]

                                          5.    ctunnel destination remote-nsap-address

                                          6.    ctunnel mode gre

                                          7.    end

                                          8.    show interfaces ctunnel interface-number


                                        DETAILED STEPS
                                           Command or ActionPurpose
                                          Step 1 enable


                                          Example:
                                          Router> enable
                                           

                                          Enables privileged EXEC mode.

                                          • Enter your password if prompted.

                                           
                                          Step 2 configure terminal


                                          Example:
                                          Router# configure terminal
                                           

                                          Enters global configuration mode.

                                           
                                          Step 3 interface ctunnel interface-number


                                          Example:
                                          Router(config)# interface ctunnel 102
                                           

                                          Creates a virtual interface to transport IP over a CLNS tunnel and enters interface configuration mode.

                                          Note   

                                          The interface number must be unique for each CTunnel interface.

                                           
                                          Step 4Do one of the following:
                                          • ip address ip-address mask
                                          • ipv6 address ipv6-prefix / prefix-length [eui-64]


                                          Example:
                                          Router(config-if)# ipv6 address 2001:0DB8:1234:5678::3/126
                                           

                                          Specifies the IPv4 or IPv6 network assigned to the interface and enables IPv4 or IPv6 packet processing on the interface.

                                          Note   

                                          For more information about IPv6 network, see the "Configuring Basic Connectivity for IPv6" module in the Cisco IOS IPv6 Configuration Guide.

                                           
                                          Step 5 ctunnel destination remote-nsap-address


                                          Example:
                                          Router(config-if)# ctunnel destination 192.168.30.1
                                           

                                          Specifies the destination NSAP address of the CTunnel, where the packets are extracted.

                                          • Use the remote-nsap-addressargument to specify the NSAP address at the CTunnel endpoint.

                                           
                                          Step 6 ctunnel mode gre


                                          Example:
                                          Router(config-if)# ctunnel mode gre
                                           

                                          Specifies a CTunnel running in GRE mode for both IPv4 and IPv6 traffic.

                                          Note   

                                          The ctunnel mode gre command specifies GRE as the encapsulation protocol for the tunnel.

                                           
                                          Step 7 end


                                          Example:
                                          Router(config-if)# end
                                           

                                          Exits interface configuration mode and returns to privileged EXEC mode.

                                           
                                          Step 8 show interfaces ctunnel interface-number


                                          Example:
                                          Router# show interfaces ctunnel 102
                                           

                                          (Optional) Displays information about an IP over CLNS tunnel.

                                          • Use the interface-number argument to specify a CTunnel interface.

                                          • Use this command to verify the CTunnel configuration.

                                           

                                          What to Do Next

                                          Configuring Manual IPv6 Tunnels

                                          This task explains how to configure a manual IPv6 overlay tunnel.

                                          Before You Begin

                                          With manually configured IPv6 tunnels, an IPv6 address is configured on a tunnel interface and manually configured IPv4 addresses are assigned to the tunnel source and the tunnel destination. The host or router at each end of a configured tunnel must support both the IPv4 and IPv6 protocol stacks.

                                          SUMMARY STEPS

                                            1.    enable

                                            2.    configure terminal

                                            3.    interface tunnel tunnel-number

                                            4.    ipv6 address ipv6-prefix / prefix-length [eui-64]

                                            5.    tunnel source {ip-address| interface-type interface-number}

                                            6.    tunnel destination ip-address

                                            7.    tunnel mode ipv6ip

                                            8.    end


                                          DETAILED STEPS
                                             Command or ActionPurpose
                                            Step 1 enable


                                            Example:
                                            Router> enable
                                             

                                            Enables privileged EXEC mode.

                                            • Enter your password if prompted.

                                             
                                            Step 2 configure terminal


                                            Example:
                                            Router# configure terminal
                                             

                                            Enters global configuration mode.

                                             
                                            Step 3 interface tunnel tunnel-number


                                            Example:
                                            Router(config)# interface tunnel 0
                                             

                                            Specifies a tunnel interface and number and enters interface configuration mode.

                                             
                                            Step 4 ipv6 address ipv6-prefix / prefix-length [eui-64]


                                            Example:
                                            Router(config-if)# ipv6 address 2001:0DB8:1234:5678::3/126
                                             

                                            Specifies the IPv6 network assigned to the interface and enables IPv6 processing on the interface.

                                            Note   

                                            For more information on configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

                                             
                                            Step 5 tunnel source {ip-address| interface-type interface-number}


                                            Example:
                                            Router(config-if)# tunnel source ethernet 0
                                             

                                            Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

                                            • If an interface is specified, the interface must be configured with an IPv4 address.

                                             
                                            Step 6 tunnel destination ip-address


                                            Example:
                                            Router(config-if)# tunnel destination 192.168.30.1
                                             

                                            Specifies the destination IPv4 address for the tunnel interface.

                                             
                                            Step 7 tunnel mode ipv6ip


                                            Example:
                                            Router(config-if)# tunnel mode ipv6ip
                                             

                                            Specifies a manual IPv6 tunnel.

                                            Note   

                                            The tunnel mode ipv6ip command specifies IPv6 as the passenger protocol and IPv4 as both the carrier (encapsulation) and transport protocol for the manual IPv6 tunnel.

                                             
                                            Step 8 end


                                            Example:
                                            Router(config-if)# end
                                             

                                            Exits interface configuration mode and returns to privileged EXEC mode.

                                             

                                            What to Do Next

                                            Configuring 6to4 Tunnels

                                            This task explains how to configure a 6to4 overlay tunnel.

                                            Before You Begin

                                            With 6to4 tunnels, the tunnel destination is determined by the border-router IPv4 address, which is concatenated to the prefix 2002::/16 in the format 2002:border-router-IPv4-address::/48. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks.


                                            Note

                                            The configuration of only one IPv4-compatible tunnel and one 6to4 IPv6 tunnel is supported on a router. If you choose to configure both of these tunnel types on the same router, we strongly recommend that they not share the same tunnel source.

                                            The reason that a 6to4 tunnel and an IPv4-compatible tunnel cannot share the same interface is that both of them are NBMA "point-to-multipoint" access links and only the tunnel source can be used to reorder the packets from a multiplexed packet stream into a single packet stream for an incoming interface. So when a packet with an IPv4 protocol type of 41 arrives on an interface, that packet is mapped to an IPv6 tunnel interface on the basis of the IPv4 address. However, if both the 6to4 tunnel and the IPv4-compatible tunnel share the same source interface, the router cannot determine the IPv6 tunnel interface to which it should assign the incoming packet.

                                            IPv6 manually configured tunnels can share the same source interface because a manual tunnel is a "point-to-point" link, and both the IPv4 source and IPv4 destination of the tunnel are defined.

                                            >
                                            SUMMARY STEPS

                                              1.    enable

                                              2.    configure terminal

                                              3.    interface tunnel tunnel-number

                                              4.    ipv6 address ipv6-prefix / prefix-length [eui-64]

                                              5.    tunnel source {ip-address| interface-type interface-number}

                                              6.    tunnel mode ipv6ip 6to4

                                              7.    exit

                                              8.    ipv6 route ipv6-prefix / prefix-length tunnel tunnel-number


                                            DETAILED STEPS
                                               Command or ActionPurpose
                                              Step 1 enable


                                              Example:
                                              Router> enable
                                               

                                              Enables privileged EXEC mode.

                                              • Enter your password if prompted.

                                               
                                              Step 2 configure terminal


                                              Example:
                                              Router# configure terminal
                                               

                                              Enters global configuration mode.

                                               
                                              Step 3 interface tunnel tunnel-number


                                              Example:
                                              Router(config)# interface tunnel 0
                                               

                                              Specifies a tunnel interface and number and enters interface configuration mode.

                                               
                                              Step 4 ipv6 address ipv6-prefix / prefix-length [eui-64]


                                              Example:
                                              Router(config-if)# ipv6 address 2002:c0a8:6301:1::1/64
                                               

                                              Specifies the IPv6 address assigned to the interface and enables IPv6 processing on the interface.

                                              • The 32 bits following the initial 2002::/16 prefix correspond to an IPv4 address assigned to the tunnel source.

                                              Note   

                                              For more information about configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

                                               
                                              Step 5 tunnel source {ip-address| interface-type interface-number}


                                              Example:
                                              Router(config-if)# tunnel source ethernet 0
                                               

                                              Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

                                              Note   

                                              The interface type and number specified in the tunnel source command must be configured with an IPv4 address.

                                               
                                              Step 6 tunnel mode ipv6ip 6to4


                                              Example:
                                              Router(config-if)# tunnel mode ipv6ip 6to4
                                               

                                              Specifies an IPv6 overlay tunnel using a 6to4 address.

                                               
                                              Step 7 exit


                                              Example:
                                              Router(config-if)# exit
                                               

                                              Exits interface configuration mode and returns to global configuration mode.

                                               
                                              Step 8 ipv6 route ipv6-prefix / prefix-length tunnel tunnel-number


                                              Example:
                                              Router(config)# ipv6 route 2002::/16 tunnel 0
                                               

                                              Configures a static route for the IPv6 6to4 prefix 2002::/16 to the specified tunnel interface.

                                              Note   

                                              When configuring a 6to4 overlay tunnel, you must configure a static route for the IPv6 6to4 prefix 2002::/16 to the 6to4 tunnel interface.

                                              • The tunnel number specified in the ipv6 route command must be the same tunnel number specified in the interface tunnelcommand.

                                               

                                              What to Do Next

                                              Configuring IPv4-Compatible IPv6 Tunnels

                                              This task explains how to configure an IPv4-compatible IPv6 overlay tunnel.

                                              Before You Begin

                                              With an IPv4-compatible tunnel, the tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of IPv4-compatible IPv6 addresses. The host or router at each end of an IPv4-compatible tunnel must support both the IPv4 and IPv6 protocol stacks.


                                              Note

                                              IPv4-compatible tunnels were initially supported for IPv6, but Cisco now recommends that you use a different IPv6 overlay tunneling technique.

                                              >
                                              SUMMARY STEPS

                                                1.    enable

                                                2.    configure terminal

                                                3.    interface tunnel tunnel-number

                                                4.    tunnel source {ip-address| interface-type interface-number}

                                                5.    tunnel mode ipv6ip auto-tunnel


                                              DETAILED STEPS
                                                 Command or ActionPurpose
                                                Step 1 enable


                                                Example:
                                                Router> enable
                                                 

                                                Enables privileged EXEC mode.

                                                • Enter your password if prompted.

                                                 
                                                Step 2 configure terminal


                                                Example:
                                                Router# configure terminal
                                                 

                                                Enters global configuration mode.

                                                 
                                                Step 3 interface tunnel tunnel-number


                                                Example:
                                                Router(config)# interface tunnel 0
                                                 

                                                Specifies a tunnel interface and number and enters interface configuration mode.

                                                 
                                                Step 4 tunnel source {ip-address| interface-type interface-number}


                                                Example:
                                                Router(config-if)# tunnel source ethernet 0
                                                 

                                                Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

                                                Note   

                                                The interface type and number specified in the tunnel source command must be configured with an IPv4 address.

                                                 
                                                Step 5 tunnel mode ipv6ip auto-tunnel


                                                Example:
                                                Router(config-if)# tunnel mode ipv6ip auto-tunnel
                                                 

                                                Specifies an IPv4-compatible tunnel using an IPv4-compatible IPv6 address.

                                                 

                                                What to Do Next

                                                Configuring ISATAP Tunnels

                                                This task describes how to configure an ISATAP overlay tunnel.

                                                Before You Begin

                                                The tunnel source command used in the configuration of an ISATAP tunnel must point to an interface that is configured with an IPv4 address. The ISATAP IPv6 address and prefix (or prefixes) advertised are configured for a native IPv6 interface. The IPv6 tunnel interface must be configured with a modified EUI-64 address because the last 32 bits in the interface identifier are constructed using the IPv4 tunnel source address.

                                                SUMMARY STEPS

                                                  1.    enable

                                                  2.    configure terminal

                                                  3.    interface tunnel tunnel-number

                                                  4.    ipv6 address ipv6-prefix prefix-length [eui-64]

                                                  5.    no ipv6 nd suppress-ra

                                                  6.    tunnel source {ip-address | interface-type interface-number}

                                                  7.    tunnel mode ipv6ip isatap

                                                  8.    end


                                                DETAILED STEPS
                                                   Command or ActionPurpose
                                                  Step 1 enable


                                                  Example:
                                                  Device> enable
                                                   

                                                  Enables privileged EXEC mode.

                                                  • Enter your password if prompted.

                                                   
                                                  Step 2 configure terminal


                                                  Example:
                                                  Device# configure terminal
                                                   

                                                  Enters global configuration mode.

                                                   
                                                  Step 3 interface tunnel tunnel-number


                                                  Example:
                                                  Device(config)# interface tunnel 1
                                                   

                                                  Specifies a tunnel interface and number and enters interface configuration mode.

                                                   
                                                  Step 4 ipv6 address ipv6-prefix prefix-length [eui-64]


                                                  Example:
                                                  Device(config-if)# ipv6 address 2001:0DB8:6301::/64 eui-64
                                                   

                                                  Specifies the IPv6 address assigned to the interface and enables IPv6 processing on the interface.

                                                  Note   

                                                  For more information on configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

                                                   
                                                  Step 5 no ipv6 nd suppress-ra


                                                  Example:
                                                  Device(config-if)# no ipv6 nd suppress-ra
                                                   

                                                  Enables sending of IPv6 device advertisements to allow client autoconfiguration.

                                                  • Sending of IPv6 device advertisements is disabled by default on tunnel interfaces.

                                                   
                                                  Step 6 tunnel source {ip-address | interface-type interface-number}


                                                  Example:
                                                  Device(config-if)# tunnel source GigabitEthernet 1/0/1
                                                   

                                                  Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

                                                  Note   

                                                  The interface type and number specified in the tunnel source command must be configured with an IPv4 address.

                                                   
                                                  Step 7 tunnel mode ipv6ip isatap


                                                  Example:
                                                  Device(config-if)# tunnel mode ipv6ip isatap
                                                   

                                                  Specifies an IPv6 overlay tunnel using an ISATAP address.

                                                   
                                                  Step 8 end


                                                  Example:
                                                  Device(config-if)# end
                                                   

                                                  Exits interface configuration mode and returns to privileged EXEC mode.

                                                   

                                                  What to Do Next

                                                  Configuring the RBSCP Tunnel

                                                  Perform this task to configure the RBSCP tunnel. Remember to configure the router at each end of the tunnel.

                                                  Before You Begin

                                                  Ensure that the physical interface to be used as the tunnel source in this task is already configured.


                                                  Note
                                                  • RBSCP was designed for wireless or long-distance delay links with high error rates such as satellite links. If you do not have long-distance delay links with high error rates, do not implement this feature.
                                                  • If IP access control lists (ACLs) are configured on an interface that is used by an RBSCP tunnel, the RBSCP IP protocol (199) must be allowed to enter and exit that interface or the tunnel will not function.
                                                  • RBSCP has some performance limitations because traffic through the tunnel is process-switched.
                                                  >
                                                  SUMMARY STEPS

                                                    1.    enable

                                                    2.    configure terminal

                                                    3.    interface type number

                                                    4.    ip unnumbered interface-type interface-number

                                                    5.    tunnel source {ip-address | interface-type interface-number}

                                                    6.    tunnel destination {hostname | ip-address}

                                                    7.    tunnel bandwidth {receive | transmit} bandwidth

                                                    8.    tunnel mode rbscp

                                                    9.    tunnel rbscp ack-split split-size

                                                    10.    tunnel rbscp delay

                                                    11.    tunnel rbscp report

                                                    12.    tunnel rbscp window-stuff step-size

                                                    13.    end


                                                  DETAILED STEPS
                                                     Command or ActionPurpose
                                                    Step 1 enable


                                                    Example:
                                                    Router> enable
                                                     

                                                    Enables privileged EXEC mode.

                                                    • Enter your password if prompted.

                                                     
                                                    Step 2 configure terminal


                                                    Example:
                                                    Router# configure terminal
                                                     

                                                    Enters global configuration mode.

                                                     
                                                    Step 3 interface type number


                                                    Example:
                                                    Router(config)# interface tunnel 0
                                                     

                                                    Specifies the interface type and number and enters interface configuration mode.

                                                     
                                                    Step 4 ip unnumbered interface-type interface-number


                                                    Example:
                                                    Router(config-if)# ip unnumbered Ethernet 1
                                                     

                                                    Enables IP processing on an interface without assigning an explicit IP address.

                                                    • Whenever the unnumbered interface generates a packet (for example, for a routing update), it uses the address of the specified interface as the source address of the IP packet.

                                                     
                                                    Step 5 tunnel source {ip-address | interface-type interface-number}


                                                    Example:
                                                    Router(config-if)# tunnel source Ethernet 1
                                                     

                                                    Configures the tunnel source.

                                                    • Use the ip-addressargument to specify the IP address of the service provider.

                                                    • Use the interface-typeand interface-numberarguments to specify the interface to use. For RBSCP Cisco recommends specifying an interface as the tunnel source.

                                                     
                                                    Step 6 tunnel destination {hostname | ip-address}


                                                    Example:
                                                    Router(config-if)# tunnel destination 172.17.2.1
                                                     

                                                    Configures the tunnel destination.

                                                    • Use the hostnameargument to specify the name of the host destination.

                                                    • Use the ip-addressargument to specify the IP address of the host destination.

                                                     
                                                    Step 7 tunnel bandwidth {receive | transmit} bandwidth


                                                    Example:
                                                    Router(config-if)# tunnel bandwidth transmit 1000
                                                     

                                                    Specifies the tunnel bandwidth to be used to transmit packets.

                                                    • Use the bandwidthargument to specify the bandwidth.

                                                    Note   

                                                    The receive keyword is no longer used.

                                                     
                                                    Step 8 tunnel mode rbscp


                                                    Example:
                                                    Router(config-if)# tunnel mode rbscp
                                                     

                                                    Specifies the protocol to be used in the tunnel.

                                                    • Use the rbscp keyword to specify that RBSCP will be used as the tunnel protocol.

                                                     
                                                    Step 9 tunnel rbscp ack-split split-size


                                                    Example:
                                                    Router(config-if)# tunnel rbscp ack-split 6
                                                     

                                                    (Optional) Enables TCP acknowledgement (ACK) splitting with RBSCP tunnels.

                                                    • Use the split-size argument to specify the number of ACKs to send for every ACK received.

                                                    • The default number of ACKs is 4.

                                                     
                                                    Step 10 tunnel rbscp delay


                                                    Example:
                                                    Router(config-if)# tunnel rbscp delay
                                                     

                                                    (Optional) Enables RBSCP tunnel delay.

                                                    • Use this command only when the RTT measured between the two routers nearest to the satellite links is greater than 700 milliseconds.

                                                     
                                                    Step 11 tunnel rbscp report


                                                    Example:
                                                    Router(config-if)# tunnel rbscp report
                                                     

                                                    (Optional) Reports dropped RBSCP packets to SCTP.

                                                    • Reporting dropped packets to SCTP provides better bandwidth use because RBSCP tells the SCTP implementation at the end hosts to retransmit the dropped packets and this prevents the end hosts from assuming that the network is congested.

                                                     
                                                    Step 12 tunnel rbscp window-stuff step-size


                                                    Example:
                                                    Router(config-if)# tunnel rbscp window-stuff 1
                                                     

                                                    (Optional) Enables TCP window stuffing by increasing the value of the TCP window scale for RBSCP tunnels.

                                                    • Use the step-size argument to specify the step increment number.

                                                     
                                                    Step 13 end


                                                    Example:
                                                    Router(config-if)# end
                                                     

                                                    Exits interface configuration mode and returns to privileged EXEC mode.

                                                     

                                                    What to Do Next

                                                    This task must be repeated on the router on the other side of the satellite link. Substitute the sample IP addresses, hostnames, and other parameters for the appropriate values on the second router.

                                                    After the task is completed on the router on the other side of the satellite link, proceed to the Verifying RBSCP Tunnel Configuration and Operation.

                                                    Verifying Tunnel Configuration and Operation

                                                    This optional task explains how to verify tunnel configuration and operation. The commands contained in the task steps can be used in any sequence and may need to be repeated. The following commands can be used for GRE tunnels, IPv6 manually configured tunnels, and IPv6 over IPv4 GRE tunnels. This process includes the following general steps (details follow):

                                                    • On Router A, ping the IP address of the CTunnel interface of Router B.

                                                    • On Router B, ping the IP address of the CTunnel interface of Router A.

                                                    SUMMARY STEPS

                                                      1.    enable

                                                      2.    show interfaces tunnel number [accounting]

                                                      3.    ping [protocol] destination

                                                      4.    show ip route [address[mask]]

                                                      5.    ping [protocol] destination


                                                    DETAILED STEPS
                                                      Step 1   enable

                                                      Enables privileged EXEC mode. Enter your password if prompted.



                                                      Example:
                                                      Router> enable
                                                      Step 2   show interfaces tunnel number [accounting]

                                                      Assuming a generic example suitable for both IPv6 manually configured tunnels and IPv6 over IPv4 GRE tunnels, two routers are configured to be endpoints of a tunnel. Router A has Ethernet interface 0/0 configured as the source for tunnel interface 0 with an IPv4 address of 10.0.0.1 and an IPv6 prefix of 2001:0DB8:1111:2222::1/64. Router B has Ethernet interface 0/0 configured as the source for tunnel interface 1 with an IPv4 address of 10.0.0.2 and an IPv6 prefix of 2001:0DB8:1111:2222::2/64.

                                                      To verify that the tunnel source and destination addresses are configured, use the show interfaces tunnel command on Router A.



                                                      Example:
                                                      RouterA# show interfaces tunnel 0
Tunnel0 is up, line protocol is up 
  Hardware is Tunnel
  MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation TUNNEL, loopback not set
  Keepalive not set
  Tunnel source 10.0.0.1 (Ethernet0/0), destination 10.0.0.2, fastswitch TTL 255
  Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled
  Tunnel TTL 255
  Checksumming of packets disabled,  fast tunneling enabled
  Last input 00:00:14, output 00:00:04, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/0 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     4 packets input, 352 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     8 packets output, 704 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
                                                      Step 3   ping [protocol] destination

                                                      To check that the local endpoint is configured and working, use the ping command on Router A.



                                                      Example:
                                                      RouterA# ping
 2001:0DB8:1111:2222::2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:0DB8:1111:2222::2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/20/20 ms
                                                      Step 4   show ip route [address[mask]]

                                                      To check that a route exists to the remote endpoint address, use the show ip route command.



                                                      Example:
                                                      RouterA# show ip route 10.0.0.2
Routing entry for 10.0.0.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via Ethernet0/0
      Route metric is 0, traffic share count is 1
                                                      Step 5   ping [protocol] destination

                                                      To check that the remote endpoint address is reachable, use the ping command on Router A.

                                                      Note   

                                                      The remote endpoint address may not be reachable using the ping command because of filtering, but the tunnel traffic may still reach its destination.



                                                      Example:
                                                      RouterA# ping 10.0.0.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/21/28 ms

                                                      To check that the remote IPv6 tunnel endpoint is reachable, use the ping command again on Router A. The same note on filtering also applies to this example.



                                                      Example:
                                                      RouterA# ping 1::2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1::2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/20/20 ms

                                                      These steps may be repeated at the other endpoint of the tunnel.

                                                      Verifying RBSCP Tunnel Configuration and Operation

                                                      Perform one or both of the following optional tasks to verify the configuration and operation of the RBSCP tunnel configured in the Configuring the RBSCP Tunnel.

                                                      Verifying That the RBSCP Tunnel Is Active

                                                      Perform this task to verify that the RBSCP tunnel is active.

                                                      SUMMARY STEPS

                                                        1.    enable

                                                        2.    show rbscp [all| state| statistics] [tunnel tunnel-number]


                                                      DETAILED STEPS
                                                        Step 1   enable

                                                        Enables privileged EXEC mode. Enter your password if prompted.



                                                        Example:
                                                        Router> enable
                                                        Step 2   show rbscp [all| state| statistics] [tunnel tunnel-number]

                                                        Use this command with the state and tunnelkeywords to display information about the current state of the tunnel. In the following sample output the tunnel is shown in an open state.



                                                        Example:
                                                        Router# show rbscp state tunnel 1
Tunnel1 is up, line protocol is up
RBSCP operational state:  OPEN
RBSCP operating mode: (264h) ack-split window-stuffing inorder SCTP-report
 window step: 1
 drop scale: 0
 ACK split size: 4
 input drop scale: 2
 initial TSN: 1h
 fuzz factor: 0
 max burst: tunnel 0, network 0
 next TSN: 1h
 next sequence: 16Bh
 current outstanding: 0
 max out per RTT: 2062500
 packets since SACK: 0
 cumulative ack: 0h
 TSN at SACK: 0h
 last cumulative ack: 0h
 last delivered TSN: 0h
 next FWDTSN corr: 0h
 RTO: 704 ms
 RTT: 550 ms     srtt_sa: 4391   srtt_sv: 3
 sentQ: num packets: 0, num bytes: 0
 tmitQ: num packets: 0, num bytes: 0

                                                        Use this command with the statistics and tunnelkeywords to display statistical information about the tunnel. All counters display totals accumulated since the last clear rbscp command was issued.



                                                        Example:
                                                        Router# show rbscp statistics tunnel 0
Tunnel0 is up, line protocol is up
RBSCP protocol statistics:
 Init FWD-TSNs sent 0, received 0
 TUNNEL-UPs sent 0, received 0
 CLOSEDs sent 0, received 0
 TSNs sent 0, resent 0, lost by sender 0
 TSNs received 0 (duplicates 0)
 FWD-TSNs sent 144 (heartbeats 0)
 FWD-TSNs received 0 (ignored 0)
 FWD-TSNs caused 0 packet drops, 0 whole window drops
 SACKs sent 0, received 0 (ignored 0)
 Recovered with RTX 0
 Received with delay 0
 Most released at once 0
 Failed sends into the: tunnel 1, network 0
 Dropped due to: excess delay 0, tmit queue full 0
 Max on any queue: num packets: 0, num bytes: 0
 Max outstanding: 0

                                                        Verifying the RBSCP Traffic

                                                        Perform this task to verify that the traffic is being transmitted through the RBSCP tunnel and across the satellite link.

                                                        SUMMARY STEPS

                                                          1.    enable

                                                          2.    show interfaces tunnel number [accounting]


                                                        DETAILED STEPS
                                                          Step 1   enable

                                                          Enables privileged EXEC mode. Enter your password if prompted.



                                                          Example:
                                                          Router> enable
                                                          Step 2   show interfaces tunnel number [accounting]

                                                          Use this command to show that traffic is being transmitted through the RBSCP tunnel.



                                                          Example:
                                                          Router# show interfaces tunnel 0
Tunnel0 is up, line protocol is down 
 Hardware is Tunnel
 Internet address is 172.17.1.4/24
 MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, 
    reliability 255/255, txload 1/255, rxload 1/255
 Encapsulation TUNNEL, loopback not set
 Keepalive not set
 Tunnel source 172.17.1.2, destination 172.20.1.3
 Tunnel protocol/transport RBSCP/IP, key disabled, sequencing disabled
 Tunnel TTL 255
 Checksumming of packets disabled
 Tunnel transmit bandwidth 1000 (kbps)
 Tunnel receive bandwidth 8000 (kbps)
RBSCP operational state:  invalid (0h)
RBSCP operating mode: (2EEh) delay dual-delay drop-long-delay ack-split window-t
 window step: 3
 drop scale : 0
 ACK split size: 6
 input drop scale: 5
 initial TSN: 1h
 fuzz factor: 0
 next TSN: 1h
 next sequence: 1h
 current outstanding: 0
 max out per RTT: 550000
 packets since SACK: 0
 cumulative ack: 0h
 TSN at SACK: 1h
 last cumulative ack: 0h
 last delivered TSN: 0h
 next FWDTSN corr: 0h
 RTO: 704 ms
 RTT: 550 ms     srtt_sa: 0      srtt_sv: 4
 sentQ: num packets: 0, num bytes: 0
 tmitQ: num packets: 0, num bytes: 0
Last input never, output never, output hang never
 Last clearing of "show interface" counters never
 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
 Queueing strategy: fifo
 Output queue: 0/0 (size/max)
 5 minute input rate 0 bits/sec, 0 packets/sec
 5 minute output rate 0 bits/sec, 0 packets/sec
    0 packets input, 0 bytes, 0 no buffer
    Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
    0 packets output, 0 bytes, 0 underruns
    0 output errors, 0 collisions, 0 interface resets
    0 output buffer failures, 0 output buffers swapped out

                                                          Configuration Examples for Implementing Tunnels

                                                          Example Configuring GRE IPv4 Tunnels

                                                          The following example shows a simple configuration of GRE tunneling. Note that Ethernet interface 0/1 is the tunnel source for Router A and the tunnel destination for Router B. Fast Ethernet interface 0/1 is the tunnel source for Router B and the tunnel destination for Router A.

                                                          Router A

                                                          interface Tunnel0
 ip address 10.1.1.2 255.255.255.0
 tunnel source Ethernet0/1
 tunnel destination 192.168.3.2
 tunnel mode gre ip
!
interface Ethernet0/1
 ip address 192.168.4.2 255.255.255.0

                                                          Router B

                                                          interface Tunnel0
 ip address 10.1.1.1 255.255.255.0
 tunnel source FastEthernet0/1
 tunnel destination 192.168.4.2
 tunnel mode gre ip
!
interface FastEthernet0/1
 ip address 192.168.3.2 255.255.255.0

                                                          The following example configures a GRE tunnel running both IS-IS and IPv6 traffic between Router A and Router B.

                                                          Router A

                                                          ipv6 unicast-routing
clns routing
!
interface Tunnel0
 no ip address
 ipv6 address 2001:0DB8:1111:2222::1/64
 ipv6 router isis 
 tunnel source Ethernet0/0
 tunnel destination 10.0.0.2
 tunnel mode gre ip
!
interface Ethernet0/0
 ip address 10.0.0.1 255.255.255.0
!
router isis 
 network 49.0000.0000.000a.00

                                                          Router B 

                                                          ipv6 unicast-routing
clns routing
!
interface Tunnel0
 no ip address
 ipv6 address 2001:0DB8:1111:2222::2/64
 ipv6 router isis 
 tunnel source Ethernet0/0
 tunnel destination 10.0.0.1
 tunnel mode gre ip
!
interface Ethernet0/0
 ip address 10.0.0.2 255.255.255.0
!
router isis 
 network 49.0000.0000.000b.00
 address-family ipv6
 redistribute static
 exit-address-family

                                                          Example: Configuring GRE IPv6 Tunnels

                                                          The following example shows how to configure a GRE tunnel over an IPv6 transport. In this example, Ethernet0/0 has an IPv6 address, and this is the source address used by the tunnel interface. The destination IPv6 address of the tunnel is specified directly. In this example, the tunnel carries both IPv4 and IS-IS traffic. 

                                                          interface Tunnel0
 ip address 10.1.1.1 255.255.255.0
 ip router isis 
 tunnel source Ethernet0/0
 tunnel destination 2001:DB8:1111:2222::1
 tunnel mode gre ipv6
!
interface Ethernet0/0
 no ip address
 ipv6 address 2001:DB8:1111:1111::1/64
!
router isis 
 net 49.0001.0000.0000.000a.00

                                                          Example Configuring GRE Tunnel IP Source and Destination VRF Membership

                                                          In this example, packets received on interface e0 using VRF green, will be forwarded out of the tunnel through interface e1 using VRF blue. The figure below shows a simple tunnel scenario:

                                                          Figure 8. GRE Tunnel Diagram

                                                          The following example shows the configuration for the tunnel in the figure above. 

                                                          ip vrf blue
 rd 1:1
ip vrf green
 rd 1:2
interface loopback0
 ip vrf forwarding blue
 ip address 10.7.7.7 255.255.255.255
interface tunnel0
 ip vrf forwarding green
 ip address 10.3.3.3 255.255.255.0
 tunnel source loopback 0
 tunnel destination 10.5.5.5
 tunnel vrf blue
interface ethernet0
 ip vrf forwarding green
 ip address 10.1.1.1 255.255.255.0
interface ethernet1
 ip vrf forwarding blue
 ip address 10.2.2.2 255.255.255.0
 ip route vrf blue 10.5.5.5 255.255.255.0 ethernet 1

                                                          Example Routing Two AppleTalk Networks Across an IP-Only Backbone

                                                          The figure below is an example of connecting multiprotocol subnetworks across a single-protocol backbone. The configurations of Router A and Router B follow the figure.

                                                          Figure 9. Connecting AppleTalk Networks Across an IP-Only Backbone

                                                          Router A

                                                          interface ethernet 0
 description physics department AppleTalk LAN
 appletalk cable-range 4001-4001 32
 !
interface fddi 0
 description connection to campus backbone
 ip address 10.0.8.108 255.255.255.0
interface tunnel 0
 tunnel source fddi 0
 tunnel destination 10.0.21.20
 appletalk cable-range 5313-5313 1

                                                          Router B

                                                          interface ethernet 0
 description chemistry department AppleTalk LAN
 appletalk cable-range 9458-9458 3
 !
interface fddi 0
 description connection to campus backbone
 ip address 10.0.21.20 255.255.255.0
interface tunnel 0
 tunnel source fddi 0
 tunnel destination 10.0.8.108
 appletalk cable-range 5313-5313 2

                                                          Example Routing a Private IP Network and a Novell Network Across a Public Service Provider

                                                          The figure below is an example of routing a private IP network and a Novell network across a public service provider. The configurations of Router A and Router B follow the figure.

                                                          Router A

                                                          interface ethernet 0
 description Boston office
 ip address 10.1.1.1 255.255.255.0
 novell network 1e
!
interface serial 0
 description connection to public service provider
 ip address 172.17.2.1 255.255.255.0
!
interface tunnel 0
 tunnel source serial 0
 tunnel destination 172.28.5.2
 ip address 10.1.2.1 255.255.255.0
 novell network 1f

                                                          Router B

                                                          interface ethernet 0
 description Menlo Park office
 ip address 10.1.3.1 255.255.255.0
 novell network 31
 !
interface serial 4
 description connection to public service provider
 ip address 172.28.5.2 255.255.255.0
 !
interface tunnel 0
 tunnel source serial 4
 tunnel destination 172.17.2.1
 ip address 10.1.2.2 255.255.255.0
 novell network 1f

                                                          Example Configuring a CTunnel

                                                          The figure below illustrates the creation of a CTunnel between Router A and Router B, as accomplished in the configuration examples that follow.

                                                          Figure 10. Creation of a CTunnel

                                                          Router A

                                                          ip routing
clns routing
interface ctunnel 102
 ip address 10.0.0.1 255.255.255.0
 ctunnel destination 49.0001.2222.2222.2222.00
interface Ethernet0/1
 clns router isis 
router isis 
 network 49.0001.1111.1111.1111.00
router rip 
 network 10.0.0.0

                                                          Router B

                                                          ip routing
clns routing
interface ctunnel 201
 ip address 10.0.0.2 255.255.255.0
 ctunnel destination 49.0001.1111.1111.1111.00
interface Ethernet0/1
 clns router isis 
router isis
 network 49.0001.2222.2222.2222.00
router rip
 network 10.0.0.0

                                                          Example Configuring GRE CLNS CTunnels to Carry IPv4 and IPv6 Packets

                                                          The following example configures a GRE CTunnel running both IS-IS and IPv6 traffic between Router A and Router B in a CLNS network. The ctunnel mode gre command provides a method of tunneling that is compliant with RFC 3147 and should allow tunneling between Cisco equipment and third-party networking devices.

                                                          Router A

                                                          ipv6 unicast-routing 
clns routing 
interface ctunnel 102 
 ipv6 address 2001:0DB8:1111:2222::1/64
 ctunnel destination 49.0001.2222.2222.2222.00 
 ctunnel mode gre
interface Ethernet0/1 
 clns router isis 
router isis 
 network 49.0001.1111.1111.1111.00

                                                          Router B

                                                          ipv6 unicast-routing 
clns routing 
interface ctunnel 201 
 ipv6 address 2001:0DB8:1111:2222::2/64 
 ctunnel destination 49.0001.1111.1111.1111.00 
 ctunnel mode gre
interface Ethernet0/1 
 clns router isis 
router isis 
 network 49.0001.2222.2222.2222.00

                                                          To turn off GRE mode and restore the CTunnel to the default Cisco encapsulation routing only between endpoints on Cisco equipment, use either the no ctunnel mode command or the ctunnel mode cisco command. The following example shows the same configuration modified to transport only IPv4 traffic.

                                                          Router A

                                                          ip routing 
clns routing 
interface ctunnel 102 
 ip address 10.2.2.5 255.255.255.0 
 ctunnel destination 49.0001.2222.2222.2222.00 
 ctunnel mode cisco
interface Ethernet0/1 
 clns router isis 
router isis 
 network 49.0001.1111.1111.1111.00

                                                          Router B

                                                          ip routing 
clns routing 
interface ctunnel 201 
 ip address 10.0.0.5 255.255.255.0 
 ctunnel destination 49.0001.1111.1111.1111.00 
 ctunnel mode cisco
interface Ethernet0/1 
 clns router isis 
router isis 
 network 49.0001.2222.2222.2222.00

                                                          Example Configuring Manual IPv6 Tunnels

                                                          The following example configures a manual IPv6 tunnel between Router A and Router B. In the example, tunnel interface 0 for both Router A and Router B is manually configured with a global IPv6 address. The tunnel source and destination addresses are also manually configured.

                                                          Router A 

                                                          interface ethernet 0
 ip address 192.168.99.1 255.255.255.0
interface tunnel 0
 ipv6 address 2001:0db8:c18:1::3/126
 tunnel source ethernet 0
 tunnel destination 192.168.30.1
 tunnel mode ipv6ip

                                                          Router B 

                                                          interface ethernet 0
 ip address 192.168.30.1 255.255.255.0
interface tunnel 0
 ipv6 address 2001:0db8:c18:1::2/126
 tunnel source ethernet 0
 tunnel destination 192.168.99.1
 tunnel mode ipv6ip

                                                          Example Configuring 6to4 Tunnels

                                                          The following example configures a 6to4 tunnel on a border router in an isolated IPv6 network. The IPv4 address is 192.168.99.1, which translates to the IPv6 prefix of 2002:c0a8:6301::/48. The IPv6 prefix is subnetted into 2002:c0a8:6301::/64 for the tunnel interface: 2002:c0a8:6301:1::/64 for the first IPv6 network and 2002:c0a8:6301:2::/64 for the second IPv6 network. The static route ensures that any other traffic for the IPv6 prefix 2002::/16 is directed to tunnel interface 0 for automatic tunneling.

                                                          interface Ethernet0
 description IPv4 uplink
 ip address 192.168.99.1 255.255.255.0
!
interface Ethernet1
 description IPv6 local network 1
 ipv6 address 2002:c0a8:6301:1::1/64 
!
interface Ethernet2
 description IPv6 local network 2
 ipv6 address 2002:c0a8:6301:2::1/64 
!
interface Tunnel0
 description IPv6 uplink
 no ip address
 ipv6 address 2002:c0a8:6301::1/64 
 tunnel source Ethernet0
 tunnel mode ipv6ip 6to4
!
ipv6 route 2002::/16 Tunnel0

                                                          Example Configuring IPv4-Compatible IPv6 Tunnels

                                                          The following example configures an IPv4-compatible IPv6 tunnel that allows BGP to run between a number of routers without having to configure a mesh of manual tunnels. Each router has a single IPv4-compatible tunnel, and multiple BGP sessions can run over each tunnel, one to each neighbor. Ethernet interface 0 is used as the tunnel source. The tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of an IPv4-compatible IPv6 address. Specifically, the IPv6 prefix 0:0:0:0:0:0 is concatenated to an IPv4 address (in the format 0:0:0:0:0:0:A.B.C.D or ::A.B.C.D) to create the IPv4-compatible IPv6 address. Ethernet interface 0 is configured with a global IPv6 address and an IPv4 address (the interface supports both the IPv6 and IPv4 protocol stacks).

                                                          Multiprotocol BGP is used in the example to exchange IPv6 reachability information with the peer 10.67.0.2. The IPv4 address of Ethernet interface 0 is used in the low-order 32 bits of an IPv4-compatible IPv6 address and is also used as the next-hop attribute. Using an IPv4-compatible IPv6 address for the BGP neighbor allows the IPv6 BGP session to be automatically transported over an IPv4-compatible tunnel.

                                                          interface tunnel 0
 tunnel source Ethernet 0
 tunnel mode ipv6ip auto-tunnel
interface ethernet 0
 ip address 10.27.0.1 255.255.255.0
 ipv6 address 3000:2222::1/64
router bgp 65000
 no synchronization
 no bgp default ipv4-unicast
 neighbor ::10.67.0.2 remote-as 65002
address-family ipv6
 neighbor ::10.67.0.2 activate
 neighbor ::10.67.0.2 next-hop-self
 network 2001:2222:d00d:b10b::/64

                                                          Example Configuring ISATAP Tunnels

                                                          The following example shows the tunnel source defined on Ethernet 0 and the tunnel mode command used to configure the ISATAP tunnel. Router advertisements are enabled to allow client autoconfiguration.

                                                          interface Tunnel1
 tunnel source ethernet 0
 tunnel mode ipv6ip isatap
 ipv6 address 2001:0DB8::/64 eui-64
 no ipv6 nd suppress-ra

                                                          Example Configuring the RBSCP Tunnel

                                                          In the following example, Router 1 and Router 2 are configured to send traffic through an RBSCP tunnel over a satellite link.

                                                          Router 1

                                                          interface Tunnel 0
 ip unnumbered ethernet1
 tunnel source ethernet1
 tunnel destination 172.17.2.1
 tunnel bandwidth transmit 1000
 tunnel mode rbscp
 tunnel rbscp ack-split 6
 tunnel rbscp report
!
interface ethernet1
 description Satellite Link
 ip address 172.20.1.2 255.255.255.0

                                                          Router 2

                                                          interface Tunnel 0
 ip unnumbered ethernet1
 tunnel source ethernet1
 tunnel destination 172.20.1.2
 tunnel bandwidth transmit 1000
 tunnel mode rbscp
 tunnel rbscp ack-split 6
 tunnel rbscp report
!
interface ethernet1
 description Satellite Link
 ip address 172.17.2.1 255.255.255.0

                                                          Example Configuring Routing for the RBSCP Tunnel

                                                          To control the type of traffic that uses the RBSCP tunnel, you must configure the appropriate routing. If you want to direct all traffic through the tunnel, you can configure a static route.


                                                          Note

                                                          To prevent routing flaps, remember to configure the tunnel interface as passive if dynamic routing protocols are used.

                                                          The following example shows how to use policy-based routing to route some specific protocol types through the tunnel. In this example, an extended access list allows TCP, Stream Control Transmission Protocol (SCTP), Encapsulating Security Payload (ESP) protocol, and Authentication Header (AH) traffic to travel through the tunnel. All IP traffic is denied.

                                                          Router 1 (Local Side)

                                                          interface Tunnel1
 ip unnumbered FastEthernet1/1
 tunnel source FastEthernet1/1
 tunnel destination 10.12.0.20
 tunnel mode rbscp
 tunnel ttl 5
 tunnel bandwidth transmit 30000
 tunnel rbscp window-stuff 1
 tunnel rbscp ack-split 4
!
interface FastEthernet0/0
 ip address 10.13.0.1 255.255.255.0
 ip policy route-map rbscp-pbr
 duplex auto
 speed auto
!
interface FastEthernet1/1
 description Satellite Link
 ip address 10.12.0.1 255.255.255.0
 duplex auto
 speed auto
!
ip route 10.15.0.0 255.255.255.0 FastEthernet1/1
!
ip access-list extended rbscp-acl
 permit tcp any 10.15.0.0 0.0.0.255
 permit 132 any 10.15.0.0 0.0.0.255
 permit esp any 10.15.0.0 0.0.0.255
 permit ahp any 10.15.0.0 0.0.0.255
 deny ip any any
!
route-map rbscp-pbr permit 10
 match ip address rbscp-acl
 set interface Tunnel1

                                                          Router 2 (Remote Side)

                                                          ip dhcp pool CLIENT
 import all
 network 10.15.0.0 255.255.255.0
 default-router 10.15.0.1
 domain-name engineer.chicago.il.us
 dns-server 10.10.0.252
!
interface Tunnel1
 ip unnumbered FastEthernet0/1
 tunnel source FastEthernet0/1
 tunnel destination 10.12.0.1
 tunnel mode rbscp
 tunnel ttl 5
 tunnel bandwidth transmit 30000
 tunnel rbscp window-stuff 1
 tunnel rbscp ack-split 4
!
interface FastEthernet0/0
 description Local LAN
 ip address 10.15.0.1 255.255.255.0
 ip policy route-map rbscp-pbr
 duplex auto
 speed auto
!
interface FastEthernet0/1
 description Satellite Link
 ip address 10.12.0.20 255.255.255.0
 duplex auto
 speed auto
!
ip route 0.0.0.0 0.0.0.0 FastEthernet0/1
!
ip access-list extended rbscp-acl
 permit tcp any any
 permit 132 any any
 permit esp any any
 permit ahp any any
 deny ip any any
!
route-map rbscp-pbr permit 10
 match ip address rbscp-acl
 set interface Tunnel1

                                                          Example Configuring QoS Options on Tunnel Interfaces

                                                          The following sample configuration applies generic traffic shaping (GTS) directly on the tunnel interface. In this example the configuration shapes the tunnel interface to an overall output rate of 500 kbps. For more details on GTS, see the " Regulating Packet Flow Using Traffic Shaping " chapter of the Cisco IOS Quality of Service Solutions Configuration Guide. 

                                                          interface Tunnel0 
 ip address 10.1.2.1 255.255.255.0 
 traffic-shape rate 500000 125000 125000 1000 
 tunnel source 10.1.1.1 
 tunnel destination 10.2.2.2

                                                          The following sample configuration shows how to apply the same shaping policy to the tunnel interface with the Modular QoS CLI (MQC) commands. For more details on MQC, see the "Modular Quality of Service Command-Line Interface" chapter of the Cisco IOS Quality of Service Solutions Configuration Guide . 

                                                          policy-map tunnel 
 class class-default 
 shape average 500000 125000 125000
! 
interface Tunnel0 
 ip address 10.1.2.1 255.255.255.0 
 service-policy output tunnel 
 tunnel source 10.1.35.1 
 tunnel destination 10.1.35.2

                                                          Policing Example

                                                          When an interface becomes congested and packets start to queue, you can apply a queueing method to packets that are waiting to be transmitted. Cisco IOS logical interfaces--tunnel interfaces in this example--do not inherently support a state of congestion and do not support the direct application of a service policy that applies a queueing method. Instead, you need to apply a hierarchical policy. Create a "child" or lower-level policy that configures a queueing mechanism, such as low latency queueing with the priority command and class-based weighted fair queueing (CBWFQ) with the bandwidth command. 

                                                          policy-map child 
 class voice 
 priority 512

                                                          Create a "parent" or top-level policy that applies class-based shaping. Apply the child policy as a command under the parent policy because admission control for the child class is done according to the shaping rate for the parent class. 

                                                          policy-map tunnel 
 class class-default 
 shape average 2000000 
 service-policy child

                                                          Apply the parent policy to the tunnel interface. 

                                                          interface tunnel0 
 service-policy tunnel

                                                          In the following example, a tunnel interface is configured with a service policy that applies queueing without shaping. A log message is displayed noting that this configuration is not supported. 

                                                          interface tunnel1
 service-policy output child
 Class Based Weighted Fair Queueing not supported on this interface

                                                          For more details on QoS traffic policing, see the Cisco IOS Quality of Service Solutions Configuration Guide .

                                                          Example Configuring EoMPLS over GRE

                                                          The following sample provides the EoMPLS over GRE configuration sequence:

                                                          PE1 Configuration

                                                          vrf definition VPN1
 rd 100:1
 address-family ipv4
 route-target both 100:1
 exit-address-family
 !
mpls label protocol ldp
mpls ldp neighbor 10.10.10.11 targeted 
mpls ldp router-id Loopback0 force
!
interface Tunnel0
 ip address 100.1.1.11 255.255.255.0
 mpls label protocol ldp
 mpls ip
 keepalive 10 3
 tunnel source TenGigabitEthernet2/1/0
 tunnel destination 50.1.3.2
!
interface Loopback0
 ip address 10.10.10.10 255.255.255.255
 !
interface TenGigabitEthernet2/1/0 
 mtu 9216
 ip address 10.1.1.1 255.255.255.0
!
interface TenGigabitEthernet9/1
 no ip address
!
interface TenGigabitEthernet9/1.11
 vrf forwarding VPN1
 encapsulation dot1Q 300
 ip address 192.168.1.1 255.255.255.0
!
interface TenGigabitEthernet9/2
 mtu 9216
 no ip address
xconnect 10.10.10.11 200 encapsulation mpls
!
router bgp 65000
 bgp log-neighbor-changes
 neighbor 10.10.10.11 remote-as 65000
 neighbor 10.10.10.11 update-source Loopback0
neighbor 192.168.1.2 remote-as 100
 !
address-family vpnv4
  neighbor 10.10.10.11 activate
  neighbor 10.10.10.11 send-community extended
 !
 address-family ipv4 vrf VPN1
  no synchronization
  neighbor 192.168.1.2 remote-as 100
  neighbor 192.168.1.2 activate
  neighbor 192.168.1.2 send-community extended
!
ip route 10.10.10.11 255.255.255.255 Tunnel0
ip route 10.1.3.0 255.255.255.0 10.1.1.2
PE2 Configuration
vrf definition VPN1
 rd 100:1
 address-family ipv4
 route-target both 100:1
exit-address-family
 !
mpls ldp neighbor 10.10.10.10 targeted
mpls label protocol ldp
mpls ldp router-id Loopback0 force
!
interface Tunnel0
 ip address 100.1.1.10 255.255.255.0
 mpls label protocol ldp
 mpls ip
 keepalive 10 3
 tunnel source TenGigabitEthernet3/3/0
 tunnel destination 10.1.1.1
!
interface Loopback0
 ip address 10.10.10.11 255.255.255.255
!
interface TenGigabitEthernet2/1
 mtu 9216
 no ip address
 xconnect 10.10.10.10 200 encapsulation mpls  
!
interface TenGigabitEthernet2/3
 mtu 9216
 no ip address
!
interface TenGigabitEthernet2/3.11
 vrf forwarding VPN1
 encapsulation dot1Q 300
 ip address 192.168.2.1 255.255.255.0
!
interface TenGigabitEthernet3/3/0
 mtu 9216
 ip address 10.1.3.2 255.255.255.0
!
router bgp 65000
 bgp log-neighbor-changes
 neighbor 10.10.10.10 remote-as 65000
 neighbor 10.10.10.10 update-source Loopback0
 neighbor 192.168.2.2 remote-as 200
 !
 address-family vpnv4
  neighbor 10.10.10.10 activate
  neighbor 10.10.10.10 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf VPN1
  no synchronization
  neighbor 192.168.2.2 remote-as 200
  neighbor 192.168.2.2 activate
  neighbor 192.168.2.2 send-community extended
 exit-address-family
¡
ip route 10.10.10.10 255.255.255.255 Tunnel0
ip route 10.1.1.0 255.255.255.0 10.1.3.1

                                                          Where to Go Next

                                                          If you have implemented IPv6 tunnels, you may want to proceed to one of the following modules:

                                                          • If you have configured an automatic 6to4 tunnel, you can design your IPv6 network around the /48 6to4 prefix that you have created from your IPv4 address.

                                                          • If you want to implement routing protocols, see the " Implementing RIP for IPv6 ," " Implementing IS-IS for IPv6 ," " Implementing OSPF for IPv6 ," or " Implementing Multiprotocol BGP for IPv6 " modules.

                                                          • If you want to implement security features for your IPv6 network, see the " Implementing Security for IPv6 " module.

                                                          Additional References

                                                          Related Documents

                                                          Related Topic

                                                          Document Title

                                                          Cisco IOS commands

                                                          Cisco IOS Master Commands List, All Releases

                                                          Tunnel commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                                                          Cisco IOS Interface and Hardware Component Command Reference

                                                          CLNS commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                                                          Cisco IOS ISO CLNS Command Reference

                                                          IP commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                                                          • Cisco IOS IP Addressing Services Command Reference

                                                          • Cisco IOS IP Application Services Command Reference

                                                          • Cisco IOS IP Routing Protocols Command Reference

                                                          IPv6 commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                                                          Cisco IOS IPv6 Command Reference

                                                          IPv6 Features

                                                          Cisco IOS IPv6 Configuration Guide

                                                          Regulating Packet Flow on a Per-Interface Basis - Using Generic Traffic Shaping

                                                          Cisco IOS Quality of Service Solutions Configuration Guide

                                                          Modular QoS CLI configuration

                                                          Cisco IOS Quality of Service Solutions Configuration Guide

                                                          Virtual interface configuration

                                                          Cisco IOS Interface and Hardware Component Configuration Guide

                                                          Configuration example for GRE over IP Security (IPSec) where the GRE/IPSec tunnel is going through a firewall doing Network Address Translation (NAT)

                                                          Configuring IPSec/​GRE with NAT

                                                          Configuring Multiprotocol Label Switching

                                                          Cisco IOS Multiprotocol Label Switching Configuration Guide

                                                          Standards

                                                          Standard

                                                          Title

                                                          No new or modified standards are supported, and support for existing standards has not been modified.

                                                          --

                                                          MIBs

                                                          MIB

                                                          MIBs Link

                                                          No new or modified MIBs are supported, and support for existing MIBs has not been modified.

                                                          To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

                                                          http:/​/​www.cisco.com/​go/​mibs

                                                          RFCs

                                                          RFC

                                                          Title

                                                          RFC 791

                                                          Internet Protocol

                                                          RFC 1191

                                                          Path MTU Discovery

                                                          RFC 1323

                                                          TCP Extensions for High Performance

                                                          RFC 1483

                                                          Multiprotocol Encapsulation over ATM Adaptation Layer 5

                                                          RFC 2003

                                                          IP Encapsulation Within IP

                                                          RFC 2018

                                                          TCP Selective Acknowledgment Options

                                                          RFC 2460

                                                          Internet Protocol, Version 6 (IPv6)

                                                          RFC 2473

                                                          Generic Packet Tunneling in IPv6 Specification

                                                          RFC 2474

                                                          Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers

                                                          RFC 2516

                                                          A Method for Transmitting PPP over Ethernet (PPPoE)

                                                          RFC 2547

                                                          BGP/MPLS VPNs

                                                          RFC 2780

                                                          IANA Allocation Guidelines for Values in the Internet Protocol and Related Headers

                                                          RFC 2784

                                                          Generic Routing Encapsulation (GRE)

                                                          RFC 2890

                                                          Key and Sequence Number Extensions to GRE

                                                          RFC 2893

                                                          Transition Mechanisms for IPv6 Hosts and Routers

                                                          RFC 3056

                                                          Connection of IPv6 Domains via IPv4 Clouds

                                                          RFC 3147

                                                          Generic Routing Encapsulation over CLNS Networks

                                                          Technical Assistance

                                                          Description

                                                          Link

                                                          The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

                                                          http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

                                                          Feature Information for Implementing Tunnels

                                                          The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

                                                          Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to . An account on Cisco.com is not required.
                                                          Table 7 Feature Information for Implementing Tunnels

                                                          Feature Name

                                                          Releases

                                                          Feature Configuration Information

                                                          CEF-Switched Multipoint GRE Tunnels

                                                          12.2(8)T

                                                          15.0(1)M

                                                          The CEF-Switched Multipoint GRE Tunnels feature enables CEF switching of IP traffic to and from multipoint GRE tunnels. Tunnel traffic can be forwarded to a prefix through a tunnel destination when both the prefix and the tunnel destination are specified by the application.

                                                          This feature introduces CEF switching over multipoint GRE tunnels. Previously, only process switching was available for multipoint GRE tunnels.

                                                          No commands were introduced or modified by this feature.

                                                          CLNS Support for GRE Tunneling of IPv4 and IPv6 Packets in CLNS Networks

                                                          12.3(7)T

                                                          12.2(25)S

                                                          12.2(33)SRA

                                                          Support of the GRE tunnel mode allows Cisco CTunnels to transport IPv4 and IPv6 packets over CLNS-only networks in a manner that allows interoperation between Cisco networking equipment and that of other vendors. This feature provides compliance with RFC 3147.

                                                          The following command was introduced by this feature: ctunnel mode.

                                                          GRE Tunnel IP Source and Destination VRF Membership

                                                          12.0(23)S

                                                          12.2(20)S

                                                          12.2(27)SBC

                                                          12.3(2)T

                                                          12.2(33)SRA

                                                          12.2(33)SRB

                                                          12.2(31)SB5

                                                          12.4(15)T

                                                          Allows you to configure the source and destination of a tunnel to belong to any VPN VRF table.

                                                          In 12.0(23)S, this feature was introduced.

                                                          In 12.2(20)S this feature became available on Cisco 7304 router using the NSE-100 in the PXF processing path.

                                                          In 12.2(31)SB5, support was added for the Cisco 10000 series router for the PRE2 and PRE3.

                                                          The following command was introduced to support this feature: tunnel vrf.

                                                          GRE Tunnel Keepalive

                                                          12.2(8)T

                                                          12.0(23)S

                                                          15.0(1)M

                                                          Cisco IOS XE 3.1.0SG

                                                          15.3(1)S

                                                          15.1(2)SY

                                                          The GRE Tunnel Keepalive feature provides the capability of configuring keepalive packets to be sent over IP-encapsulated generic routing encapsulation (GRE) tunnels. You can specify the rate at which keepalives will be sent and the number of times that a device will continue to send keepalive packets without a response before the interface becomes inactive. GRE keepalive packets may be sent from both sides of a tunnel or from just one side.

                                                          The following command was introduced by this feature: keepalive (tunnel interfaces).

                                                          IP Tunnel-- SSO

                                                          15.1(1)SY

                                                          High availability support was added to IP Tunnels.

                                                          No new commands were introduced or modified by this feature.

                                                          Rate-Based Satellite Control Protocol

                                                          12.3(7)T

                                                          Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPSec), over satellite links without breaking the end-to-end model.

                                                          The following commands were introduced or modified by this feature: clear rbscp, debug tunnel rbscp, show rbscp, tunnel bandwidth, tunnel mode, tunnel rbscp ack-split, tunnel rbscp delay, tunnel rbscp input-drop, tunnel rbscp long-drop, tunnel rbscp report, tunnel rbscp window-stuff.

                                                          Tunnel ToS

                                                          12.0(17)S

                                                          12.0(17)ST

                                                          12.2(8)T

                                                          12.2(14)S

                                                          15.0(1)M

                                                          The Tunnel ToS feature allows you to configure the ToS and Time-to-Live (TTL) byte values in the encapsulating IP header of tunnel packets for an IP tunnel interface on a router. The Tunnel ToS feature is supported on Cisco Express Forwarding (CEF), fast switching, and process switching forwarding modes.

                                                          The following commands were introduced or modified by this feature: show interfaces tunnel, tunnel tos, tunnel ttl.