Layer 2 Tunneling Protocol Version 3

The Layer 2 Tunneling Protocol Version 3 feature expands Cisco’s support of Layer 2 VPNs. Layer 2 Tunneling Protocol Version 3 (L2TPv3) is an IETF l2tpext working group draft that provides several enhancements to L2TP to tunnel any Layer 2 payload over L2TP. Specifically, L2TPv3 defines the L2TP protocol for tunneling Layer 2 payloads over an IP core network by using Layer 2 VPNs.

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 Layer 2 Tunneling Protocol Version 3

  • Before you configure an xconnect attachment circuit for a provider edge (PE) device (see the Configuring the Xconnect Attachment Circuit task), the Cisco Express Forwarding (formerly known as CEF) feature must be enabled. To enable Cisco Express Forwarding on an interface, use the ip cef or ip cef distributed command.

  • You must configure a loopback interface on the router for originating and terminating the L2TPv3 traffic. The loopback interface must have an IP address that is reachable from the remote PE device at the other end of an L2TPv3 control channel.

Restrictions for Layer 2 Tunneling Protocol Version 3

General L2TPv3 Restrictions

  • Cisco Express Forwarding must be enabled for the L2TPv3 feature to function. The xconnect configuration mode is blocked until Cisco Express Forwarding is enabled. On distributed platforms, such as the Cisco 7500 series, if Cisco Express Forwarding is disabled while a session is established, the session is torn down. The session remains down until Cisco Express Forwarding is reenabled. To enable Cisco Express Forwarding, use the ip cef or ip cef distributed command.

  • The number of sessions on PPP, High-Level Data Link Control (HDLC), Ethernet, or 802.1q VLAN ports is limited by the number of interface descriptor blocks (IDBs) that the router can support. For PPP, HDLC, Ethernet, and 802.1q VLAN circuit types, an IDB is required for each circuit.

  • When L2TPv3 is used to tunnel Frame Relay D channel data-link connection identifiers (DLCIs), an IDB is not required for each circuit. As a result, the memory requirements are much lower. The scalability targets for the Engineering Field Test (EFT) program are 4000 L2TP session.

  • To convert an interface with Any Transport over MPLS (AToM) xconnect to L2TPv3 xconnect, remove the AToM configuration from the interface and then configure L2TPv3. Some features may not work if L2TPv3 is configured before removing the AToM configuration.

  • Frame Relay support includes only 10-bit DLCI addressing. The L2TPv3 feature does not support Frame Relay extended addressing.

  • The interface keepalive feature is automatically disabled on the interface to which xconnect is applied, except for Frame Relay encapsulation, which is required for Local Management Interface (LMI).

  • Static L2TPv3 sessions do not support Frame Relay LMI interworking.

  • Static L2TPv3 sessions do not interoperate with Universal Tunnel Interface (UTI) using keepalives.

  • Layer 2 fragmentation of IP packets and Intermediate System-to-Intermediate System (IS-IS) fragmentation through a static L2TPv3 session are not supported.

  • Layer 3 fragmentation is not recommended because of performance degradation.

  • The L2TPv3 Layer 2 (IP packet) fragmentation feature (see the Configuring the L2TPv3 Pseudowire task) is not supported when the customer edge (CE) router is running special Layer 2 options such as Layer 2 sequencing, compression, or encryption. Examples of these options are Frame Relay compression and fragmentation or PPP compression. In these scenarios, the IP payload is not in a format that is compatible with IP fragmentation.

  • The Stateful Switchover (SSO), Route Processor Redundancy (RPR) and RPR+ components of the HA functions are supported only at the coexistence level. If you attempt a switchover using SSO, RPR, or RPR+, the tunnels will fail and then eventually recover after an undetermined time duration. This includes both IPv4 and IPv6 traffic.

  • Interworking is not allowed when sequencing is enabled.

  • Untagged packets (native VLAN) forwarding for xconnect that is configured on the dot1q subinterface is not supported.

  • L2TPv3 xconnect is not supported on an EtherSwitch module. This limitation is also applicable to switch virtual interfaces (SVI) that are physically terminated on an EtherSwitch module interface.

  • Only Ethernet, HDLC, Frame Relay and VLAN (802.1Q, QinQ, and QinAny) attachment circuits are supported; EVC is not supported.

  • The IP local interface must be a loopback interface and the loopback interface cannot be in a VRF. Configuring any other interface with the "ip local interface" command results in a nonoperational setting.

VLAN-Specific Restrictions

  • A PE device is responsible only for static VLAN membership entries that are configured manually on the device. Dynamic VLAN membership entries, entry aging, and membership discovery are not supported.

  • Implicit tagging for VLAN memberships operating on other layers, such as membership by MAC address, protocol type at Layer 2, or membership by IP subnet at Layer 3, is not supported.

  • Point-to-multipoint and multipoint-to-point configurations are not supported. There is a 1:1 relationship between an attachment circuit and an L2TPv3 session.

IPv6 Protocol Demultiplexing for L2TPv3 Restrictions

  • IPv6 protocol demultiplexing is supported only for Ethernet traffic.

  • IPv6 protocol demultiplexing is supported over noninterworking sessions.

L2TPv3 Control Message Hashing Restrictions

  • L2TPv3 control channel authentication configured using the digest command requires bidirectional configuration on the peer devices. A shared secret must be configured on the communicating nodes.

  • For a compatibility matrix of all the L2TPv3 authentication methods, see the Valid Configuration Scenarios table in the IPv6 Protocol Demultiplexing section.

L2TPv3 Digest Secret Graceful Switchover Restrictions

  • This feature works only with authentication passwords configured using the L2TPv3 Control Message Hashing feature. L2TPv3 control channel authentication passwords configured with the older, Challenge Handshake Authentication Protocol (CHAP)-like authentication system cannot be updated without tearing down L2TPv3 tunnels and sessions.

  • In Cisco IOS Release 12.0(30)S, a maximum of two passwords can be configured simultaneously using the digest secret command.

For more information about the L2TPv3 Control Message Hashing feature, see the L2TPv3 Control Message Hashing section.

Quality of Service Restrictions in L2TPv3 Tunneling

Quality of service (QoS) policies configured with the modular QoS CLI (MQC) are supported in L2TPv3 tunnel sessions with the following restrictions:

Frame Relay Interface (Non-ISE/E5)

On the Cisco 7500 series with distributed CEF (dCEF), in a QoS policy applied to a Frame Relay interface configured for L2TPv3, only the MQC commands match fr-dlci in class-map configuration mode and bandwidth in policy-map configuration mode are supported. (See the task: "Configuring QoS for L2TPv3 on the Cisco 7500 Series Example".)

On the Cisco 12000 series, a QoS policy is supported in TSC-based L2TPv3 tunnel sessions on the Frame Relay interfaces of a 2-port channelized OC-3/STM-1 (DS1/E1) or 6-port channelized T3 (T1) line card with the following restrictions:

The police command is supported as follows:

  • Only the transmit option for the action keyword is supported with the conform-action command.

  • Only the set-frde-transmit option for the action keyword is supported with the exceed-action command.

  • Only the drop option for the action keyword is supported with the violate-action command.

  • Backward explicit congestion notification (BECN) and forward explicit congestion notification (FECN) configuration are not supported.

  • The type of service (ToS) byte must be configured in IP headers of tunneled Frame Relay packets when you configure the L2TPv3 pseudowire (see the Configuring the L2TPv3 Pseudowire task).

All standard restrictions for configuring QoS on Cisco 12000 series line cards apply to configuring QoS for L2TPv3 on Cisco 12000 series 2-port Channelized OC-3/STM-1 (DS1/E1) or 6-port Channelized T3 line cards.

On the ingress side of a Cisco 12000 series Frame Relay interface configured for TSC-based L2TPv3 tunneling: weighted random early detection (WRED) and modified deficit round robin (MDRR) configurations are not supported.

On the egress side of a Cisco 12000 series Frame Relay interface configured for TSC-based L2TPv3 tunneling:

  • MDRR is the only queueing strategy supported.

  • WRED is the only packet drop strategy supported.

  • MDRR is supported only in the following modes:

    With both a low latency (priority) queue and class-default queue configured. (The low latency queue is supported only in combination with the class-default queue, and cannot be configured with normal distributed round robin (DRR) queues.) Without a low latency queue configured. (In this case, only six queues are supported, including the class-default queue.)

  • Egress queueing is determined according to the IP precedence values configured for classes of L2TPv3 Frame Relay traffic using the match ip precedence command, instead of on a per-DLCI basis.

For an example, see How to Configure Layer 2 Tunneling Protocol Version 3.

Edge Engine (ISE/E5) Interface

On the Cisco 12000 series, a QoS policy is supported in native L2TPv3 tunnel sessions on ISE/E5 interfaces (see Table 2 and Table 3 for a list of supported line cards) with the restriction that on a Frame Relay or ATM ISE/E5 interface, traffic policing supports only the following conform, exceed, and violate values for the action argument of the police command:

  • conform-action actions set-prec-tunnel set-dscp-tunnel transmit

  • exceed-action actions drop set-clp (ATM only) set-dscp-tunnel set-dscp-tunnel and set-clp (ATM only) set-dscp-tunnel and set-frde (Frame Relay only) set-frde (Frame Relay only)set-prec-tunnel set-prec-tunnel and set-clp (ATM only) set-prec-tunnel and set-frde (Frame Relay only) transmit

  • violate-action actions drop

Frame Relay ISE/E5 interface

  • FECN and BECN configuration are not supported.

  • Marking the Frame Relay discard eligible (DE) bit using a MQC set command is not supported. To set (mark) the DE bit, use the police exceed-action actions command in policy-map configuration mode.

  • Configuring Tofab MDRR or WRED using legacy QoS (not MQC) commands is supported and is based on the tunnel precedence value.

  • Egress queueing on a Packet-over-SONET ISE/E5 interface is class-based when configured using MQC.

  • Egress queueing on a per-DLCI basis is not supported.

ATM ISE/E5 interface

  • Traffic shaping is supported on ATM egress interfaces for the following service categories:

  • Lowest priority: UBR (unspecified bit rate) Second priority: VBR-nrt (variable bit rate nonreal-time) Highest priority: VBR-rt (VBR real time) Highest priority: CBR (constant bit rate)

  • Note that VBR-rt and CBR share the same high-priority shaping. ATM traffic shaping restricts traffic to the maximum rate configured on an ATM VC or PVP with due priority among the respective service categories.

  • You can configure queue limits for an ATM VC or PVP. The queue limits are dual thresholds in which two different thresholds can be configured for CLP=1 cells and CLP0+1 cells. The CLP1 threshold must be lower than the queue limit threshold so that CLP=1 cells are dropped earlier than CLP=0 cells when packets start to fill the queue.

  • Although the dual-rate, 3-Color Marker policer is not supported on ATM ISE/E5 interfaces (as on Frame Relay ISE/E5 interfaces), the ATM Forum Traffic Management Version 4.1-compliant Generic Cell Rate Algorithm (GCRA) policer is supported. The GCRA policer uses rate, peak rate, delay tolerance, and ATM maximum burst size, and supports the following actions:

    set-dscp-tunnel and set-clp-transmit .

Protocol Demultiplexing Interface

Protocol demultiplexing requires a combination of an IP address and the xconnect command configured on the interface. The interface is then treated as a regular L3. To apply QoS on the Layer 2 IPv6 traffic, you must classify the IPv6 traffic into a separate class before applying any feature(s) to it.

The following match criterion is used to classify Layer 2 IPv6 traffic on a protocol demultiplexing interface: 

class-map match-ipv6
     match protocol ipv6

In the absence of a class to handle Layer 2 IPv6 traffic, the service policy is not accepted on a protocol demultiplexing interface.

Information About Layer 2 Tunneling Protocol Version 3

L2TPv3 provides a method for delivering L2TP services over an IPv4 (non-UDP) backbone network. It encompasses the signaling protocol as well as the packet encapsulation specification.

L2TPv3 Header Description

The migration from UTI to L2TPv3 also requires the standardization of the UTI header. As a result, the L2TPv3 header has the new format shown in the figure below.

Figure 1. L2TPv3 Header Format

Each L2TPv3 packet contains an L2TPv3 header that includes a unique session ID representing one session and a variable cookie length. The L2TPv3 session ID and the Tunnel Cookie field length are assigned through the CLI. See the How to Configure Layer 2 Tunneling Protocol Version 3 section for more information on the CLI commands for L2TPv3.

Session ID

The L2TPv3 session ID identifies the session context on the decapsulating system. For dynamic sessions, the value of the session ID is selected to optimize the context identification efficiency of the decapsulating system. A decapsulation implementation may, therefore, elect to support a smaller session ID bit field. In this L2TPv3 implementation, an upper value for the L2TPv3 session ID was set at 023. The L2TPv3 session ID value 0 is reserved for use by the protocol. For static sessions, the session ID is manually configured.


Note

The local session ID must be unique on the decapsulating system and is restricted to the least significant ten bits.

Session Cookie

The L2TPv3 header contains a control channel cookie field. The control channel cookie field has a variable length of 0, 4, or 8 bytes according to the cookie length supported by a given platform for packet decapsulation. The control channel cookie length can be configured manually for static sessions or determined dynamically for dynamic sessions.

The variable cookie length does not present a problem when the same platform is at both ends of an L2TPv3 control channel. However, when different platforms interoperate across an L2TPv3 control channel, both platforms need to encapsulate packets with a 4-byte cookie length.

Pseudowire Control Encapsulation

The L2TPv3 pseudowire control encapsulation consists of 32 bits (4 bytes) and contains information used to sequence L2TP packets (see the Sequencing section). For the purposes of sequencing, only the first bit and bits 8 to 31 are relevant. Bit 1 indicates whether the Sequence Number field, bits 8 to 31, contains a valid sequence number and is to be updated.

L2TPv3 Operation

L2TPv3 includes the following features:

  • Xconnect for Layer 2 tunneling through a pseudowire over an IP network

  • Layer 2 VPNs for PE-to-PE device service using xconnect that supports Ethernet and VLAN, including both static and dynamic (using the new L2TPv3 signaling) forwarded sessions

The initial Cisco IOS software supported only the following features:

  • Layer 2 tunneling (as used in an L2TP access concentrator or LAC) to an attachment circuit, not Layer 3 tunneling

  • L2TPv3 data encapsulation directly over IP (IP protocol number 115), not using the UDP

  • Point-to-point sessions, not point-to-multipoint or multipoint-to-point sessions

  • Sessions between the same Layer 2 protocols, such as Ethernet-to-Ethernet and VLAN-to-VLAN, but not VLAN-to-Ethernet

The attachment circuit is the physical interface or subinterface attached to the pseudowire.

The figure below shows how the L2TPv3 feature is used for setting up VPNs using Layer 2 tunneling over an IP network. All traffic between two customer network sites is encapsulated in IP packets carrying L2TP data messages and sent across an IP network. The backbone devices of the IP network treat the traffic as any other IP traffic and need not know anything about the customer networks.

Figure 2. L2TPv3 Operation

In the figure above, the PE devices R1 and R2 provide L2TPv3 services. The R1 and R2 devices communicate with each other using a pseudowire over the IP backbone network through a path comprising interfaces int1 and int2, the IP network, and interfaces int3 and int4.

In this example, the customer edge (CE) devices R3 and R4 communicate through a pair of xconnect Ethernet or VLAN interfaces using an L2TPv3 session. The L2TPv3 session tu1 is a pseudowire configured between interface int1 on R1 and interface int4 on R2. Any packet arriving on interface int1 on R1 is encapsulated and sent through the pseudowire control channel (tu1) to R2. R2 decapsulates the packet and sends it on interface int4 to R4. When R4 needs to send a packet to R3, the packet follows the same path in reverse.

Note the following features regarding the L2TPv3 operation:

  • All packets received on interface int1 are forwarded to R4. R3 and R4 cannot detect the intervening network.

  • For Ethernet interfaces, any packet received from LAN1 by R1 on Ethernet interface e1 is encapsulated directly in IP and sent through the pseudowire session tu2 to R2 interface e2, where it is sent on LAN2.

  • A VLAN on an Ethernet interface can be mapped to an L2TPv3 session.

L2TPv3 Features

L2TPv3 provides xconnect support for Ethernet and VLAN using Static and Dynamic sessions.

Static L2TPv3 Sessions

Typically, the L2TP control plane is responsible for negotiating session parameters, such as the session ID or the cookie, to set up the session. However, some IP networks require sessions to be configured so that no signaling is required for session establishment. You can set up static L2TPv3 sessions for a PE device by configuring fixed values for the fields in the L2TP data header. A static L2TPv3 session allows the PE device to tunnel Layer 2 traffic as soon as the attachment circuit to which the session is bound comes up.

Static configuration allows sessions to be established without dynamically negotiating control connection parameters. This means that although sessions are displayed in the show l2tun session command output, no control channel information is displayed in the show l2tun tunnel command output.


Note

In an L2TPv3 static session, you can still run the L2TP control channel to perform peer authentication and dead-peer detection. If the L2TP control channel cannot be established or is torn down because of a hello failure, the static session is also torn down.

If you use a static L2TPv3 session, you cannot perform circuit interworking, such as LMI, because there is no facility to exchange control messages. To perform circuit interworking, you must use a dynamic session.

Dynamic L2TPv3 Sessions

A dynamic L2TP session is established through the exchange of control messages containing attribute-value (AV) pairs. Each AV pair contains information about the nature of the Layer 2 link being forwarded, including the payload type and virtual circuit (VC) ID.

Multiple L2TP sessions, one for each forwarded Layer 2 circuit, can exist between a pair of PE devices and can be maintained by a single control channel. Session IDs and cookies are dynamically generated and exchanged as part of a dynamic session setup. Information such as sequencing configuration is also exchanged. Circuit state changes (UP/DOWN) are conveyed using the set link info (SLI) message.

Control Channel Parameters

The L2TP class configuration procedure creates a template of L2TP control channel parameters that can be inherited by different pseudowire classes. L2TP control channel parameters are used in control channel authentication, keepalive messages, and control channel negotiation. In an L2TPv3 session, the same L2TP class must be specified in the pseudowire configured on the PE device at each end of the control channel. Configuring L2TP control channel parameters is optional. However, the L2TP class must be configured before it is associated with a pseudowire class (see the Configuring the L2TPv3 Pseudowire task).

L2TPv3 Control Channel Authentication Parameters

Two methods of control channel message authentication are available: the L2TPv3 Control Message Hashing feature and CHAP-style L2TP control channel. The L2TPv3 Control Message Hashing feature introduces a more robust authentication method than the older, CHAP-style L2TP control channel method of authentication. You may choose to enable both the methods of authentication to ensure interoperability with peers that support only one of these methods of authentication, but this configuration will yield control of the authentication method used on the peer PE device. Enabling both the methods of authentication should be considered as an interim solution to solve backward compatibility issues during software upgrades.

The principal difference between the two methods of authentication lies in the L2TPv3 Control Message Hashing feature using the entire message in the hash instead of computing the hash over selected contents of a received control message. In addition, instead of including the hash digest in only the start control channel replay (SCCRP) and start control channel connected (SCCCN) messages, it includes it in all messages.

Support for L2TP control channel authentication is maintained for backward compatibility. Either or both authentication methods can be enabled to allow interoperability with peers supporting only one of the authentication methods.

The table below shows a compatibility matrix for the different L2TPv3 authentication methods. PE1 is running the new authentication method. The possible authentication configurations for PE1 are shown in the first column. The other columns represent PE2 running software with different available authentication options. The tables cells in these columns indicate compatible configuration options for PE2. If any PE1/PE2 authentication configuration poses ambiguity about the authentication method used, the winning authentication method is indicated in bold. If both the old and new authentication methods are enabled on PE1 and PE2, both types of authentication occur.

Table 1. Compatibility Matrix for L2TPv3 Authentication Methods

PE1 Authentication Configuration

PE2 Supporting Old Authentication1

PE2 Supporting New Authentication2

PE2 Supporting Old and New Authentication3

None

None

None

New integrity check

None

New integrity check

Old authentication

Old authentication

—

Old authentication

Old authentication and new authentication

Old authentication and new integrity check

New authentication

—

New authentication

New authentication

Old authentication and new authentication

New integrity check

None

None

New integrity check

None

New integrity check

Old and new authentication

Old authentication

New authentication

Old authentication

New authentication

Old and new authentication

Old authentication and new integrity check

Old authentication and new integrity check

Old authentication

—

Old authentication

Old authentication and new authentication

Old authentication and new integrity check

1 Any PE software that supports only the old CHAP-like authentication system.
2 Any PE software that supports only the new message digest authentication and integrity checking authentication system, but does not understand the old CHAP-like authentication system. This type of software may be implemented by other vendors based on the latest L2TPv3 draft.
3 Any PE software that supports both the old CHAP-like authentication and the new message digest authentication and integrity checking authentication system.

Ethernet over L2TPv3

The Ethernet over L2TPv3 feature provides support for Ethernet-based Layer 2 payload tunneling over IP core networks using L2TPv3.

The Ethernet over L2TPv3 feature supports the following like-to-like switching modes:

  • Ethernet port mode

  • Ethernet VLAN mode

  • Ethernet VLAN mode with VLAN rewrite

  • Ethernet QinQ and QinAny mode


Note

The QinQ over L2TPv3 support feature includes QinAny over L2TPv3, which has a fixed outer VLAN tag and a variable inner VLAN tag.

The Ethernet over L2TPv3 feature supports the following types of internetworking:

  • Ethernet port to VLAN (routed)

  • Ethernet port to VLAN (bridged)

  • QinQ to Ethernet VLAN or Port Interworking (routed)

  • QinQ to Ethernet VLAN or Port Interworking (bridged)


Note

QinAny Interworking is not a valid configuration because the inner VLAN tag is undetermined.

GEC over L2TPv3

Gigabit EtherChannel (GEC) over Layer 2 Tunneling Protocol Version 3 (L2TPv3) provides support for GEC-based Layer 2 payload tunneling over IP core networks using L2TPv3. GEC also known as port channel is integrated with Ethernet and dot1q attachment circuits (ACs).

A port channel bundles physical links into a channel group to create a single logical link that provides the aggregate bandwidth of up to eight physical links. If a member port within a port channel fails, the traffic previously carried over the failed link switches to the remaining member ports within the port channel.

Interworking switching is supported in the following scenarios:

  • The customer-edge-provider-edge (CE-PE) connecting interface on the local PE is a port-channel interface without dot1q encapsulation. The CE-PE connecting interface on the remote PE is a port-channel interface with dot1q encapsulation.
  • The CE-PE connecting interface on the local PE is a port-channel interface with or without dot1q encapsulation. The CE-PE connecting interface on the remote PE is an Ethernet interface with or without dot1q encapsulation.

The figure below illustrates a port channel over IP core networks using L2TPv3. CE1 and CE2 are connected to L2TP Control Connection Endpoints (LCCE) and through port channels. The LCCE is connected to the IP core network using L2TPv3.

Figure 3. GEC over L2TPv3

Sequencing

Although the correct sequence of received Layer 2 frames is guaranteed by some Layer 2 technologies (by the nature of the link such as a serial line) or by the protocol itself, forwarded Layer 2 frames may be lost, duplicated, or reordered when they traverse a network as IP packets. If the Layer 2 protocol does not provide an explicit sequencing mechanism, you can configure L2TP to sequence its data packets according to the data channel sequencing mechanism described in the L2TPv3 IETF l2tpext working group draft.

A receiver of L2TP data packets mandates sequencing through the Sequencing Required AV pair when the session is being negotiated. A sender (or one that is manually configured to send sequenced packets) that receives this AV pair uses the Layer 2-specific pseudowire control encapsulation defined in L2TPv3.

You can configure L2TP to drop only out-of-order packets; you cannot configure L2TP to deliver the packets out-of-order. No reordering mechanism is available.

Interworking is not allowed when sequencing is enabled.

L2TPv3 Type of Service Marking

When Layer 2 traffic is tunneled across an IP network, information contained in the Type of Service (ToS) bits may be transferred to the L2TP-encapsulated IP packets in one of the following ways:

  • If the tunneled Layer 2 frames themselves encapsulate IP packets, it may be desirable to simply copy the ToS bytes of the inner IP packets to the outer IP packet headers. This action is known as "ToS byte reflection."

  • You can specify the ToS byte value used by all packets sent across the pseudowire. This is known as "Static ToS byte configuration".

For more details on how to configure ToS, see the Example Configuring a Negotiated L2TPv3 Session for Local HDLC Switching section.

Keepalive

The keepalive mechanism for L2TPv3 extends only to the endpoints of the tunneling protocol. L2TP has a reliable control message delivery mechanism that serves as the basis for the keepalive mechanism. The keepalive mechanism consists of an exchange of L2TP hello messages.

If a keepalive mechanism is required, the control plane is used, although it may not be used to bring up sessions. You can configure sessions manually.

In the case of static L2TPv3 sessions, a control channel between the two L2TP peers is negotiated through the exchange of start control channel request (SCCRQ), SCCRP, and SCCCN control messages. The control channel is responsible for maintaining only the keepalive mechanism through the exchange of hello messages.

The interval between hello messages is configurable per control channel. If one peer detects that the other peer has gone down through the keepalive mechanism, it sends a StopCCN control message and then notifies all the pseudowires to the peer about the event. This notification results in the teardown of both manually configured and dynamic sessions.

MTU Handling

It is important that you configure a Maximum Transmission Unit (MTU) appropriate for each L2TPv3 tunneled link. The configured MTU size ensures the following:

  • The lengths of the tunneled Layer 2 frames fall below the MTU of the destination attachment circuit.

  • The tunneled packets are not fragmented, which forces the receiving PE to reassemble them.

L2TPv3 handles the MTU as follows:

  • The default behavior is to fragment packets that are larger than the session MTU.

  • If you enable the ip dfbit set command in the pseudowire class, the default MTU behavior changes so that any packets that cannot fit within the tunnel MTU are dropped.

  • If you enable the ip pmtu command in the pseudowire class, the L2TPv3 control channel participates in the path MTU (PMTU) discovery.

If you enable this feature, the following processing is performed:

  • Internet Control Message Protocol (ICMP) unreachable messages sent back to the L2TPv3 device are deciphered and the tunnel MTU is updated accordingly. To receive ICMP unreachable messages for fragmentation errors, the Don’t Fragment (DF) bit in the tunnel header is either set according to the DF bit value received from the CE device or set statically if the ip dfbit set option is enabled. The tunnel MTU is periodically reset to the default value based on a periodic timer.

  • ICMP unreachable messages are sent back to the clients on the CE side. ICMP unreachable messages are sent to the CE whenever IP packets arrive on the CE-PE interface and have a packet size greater than the tunnel MTU. A Layer 2 header calculation is performed before the ICMP unreachable message is sent to the CE.

L2TPv3 Control Message Hashing

The L2TPv3 Control Message Hashing feature introduces a new and more secure authentication system that replaces the CHAP-like authentication system inherited from L2TPv2, which uses the Challenge and Challenge Response AV pairs in the SCCRQ, SCCRP, and SCCCN messages. The L2TPv3 Control Message Hashing feature incorporates an optional authentication or integrity check for all control messages.

The per-message authentication introduced by the L2TPv3 Control Message Hashing feature is designed to:

  • Perform a mutual authentication between L2TP nodes.

  • Check integrity of all control messages.

  • Guard against control message spoofing and replay attacks that would otherwise be trivial to mount against the network.

The new authentication method uses the following:

  • A computed, one-way hash over the header and body of the L2TP control message

  • A preconfigured, shared secret that must be defined on the communicating L2TP nodes

  • A local and remote random value exchanged using the Nonce AV pairs

Received control messages that lack any of the required security elements are dropped.

L2TPv3 control message integrity checking is a unidirectional mechanism that does not require the configuration of a shared secret. If integrity checking is enabled on the local PE device, control messages are sent with the message digest calculated without the shared secret or Nonce AV pairs and are verified by the remote PE device. If verification fails, the remote PE device drops the control message.

Enabling the L2TPv3 Control Message Hashing feature will impact performance during control channel and session establishment because additional digest calculation of the full message content is required for each sent and received control message. This is an expected trade-off for the additional security provided by this feature. In addition, network congestion may occur if the receive window size is too small. If the L2TPv3 Control Message Hashing feature is enabled, message digest validation must be enabled. Message digest validation deactivates the data path received sequence number update and restricts the minimum local receive window size to 35.

You may choose to configure control channel authentication or control message integrity checking. Control channel authentication requires participation by both peers and a shared secret must be configured on both devices. Control message integrity check is unidirectional and requires configuration on only one of the peers.

L2TPv3 Control Message Rate Limiting

The L2TPv3 Control Message Rate Limiting feature was introduced to counter the possibility of a denial-of-service (DoS) attack on a device running L2TPv3. The L2TPv3 Control Message Rate Limiting feature limits the rate at which SCCRQ control packets arriving at the PE that terminates the L2TPv3 tunnel can be processed. SCCRQ control packets initiate the process of bringing up the L2TPv3 tunnel and require a large amount of control plane resources of the PE device.

No configuration is required for the L2TPv3 Control Message Rate Limiting feature. This feature automatically runs in the background in supported releases.

L2TPv3 Digest Secret Graceful Switchover

Authentication of L2TPv3 control channel messages occurs using a password that is configured on all participating peer PE devices. Before the introduction of this feature, changing this password required removing of the old password from the configuration before adding the new password, causing an interruption in L2TPv3 services. The authentication password must be updated on all peer PE devices, which are often at different physical locations. It is difficult for all peer PE devices to be updated with the new password simultaneously to minimize interruptions in L2TPv3 services.

The L2TPv3 Digest Secret Graceful Switchover feature allows the password used to authenticate L2TPv3 control channel messages to be changed without tearing down the established L2TPv3 tunnels. This feature works only for authentication passwords configured with the L2TPv3 Control Message Hashing feature. Authentication passwords configured with the older, CHAP-like authentication system cannot be updated without tearing down L2TPv3 tunnels.

The L2TPv3 Digest Secret Graceful Switchover feature allows two control channel passwords to be configured simultaneously, so a new control channel password can be enabled without first removing the old password. Established tunnels are rapidly updated with the new password, but continue to use the old password until it is removed from the configuration. This allows authentication to continue normally with peer PE devices that have not yet been updated to use the new password. After all peer PE devices are configured with the new password, the old password can be removed from the configuration.

During the period when both a new and an old password are configured, authentication will occur only with the new password if the attempt to authenticate using the old password fails.

L2TPv3 Pseudowire

The pseudowire class configuration procedure creates a configuration template for the pseudowire. Use this template or class to configure session-level parameters for L2TPv3 sessions that are used to transport attachment circuit traffic over the pseudowire.

The pseudowire configuration specifies the characteristics of the L2TPv3 signaling mechanism, including the data encapsulation type, the control protocol, sequencing, Layer 3 fragmentation, payload-specific options, and IP properties. The setting that determines whether signaling is used to set up the pseudowire is also included.

If you specify the encapsulation l2tpv3 command, you cannot remove it by using the no encapsulation l2tpv3 command. You also cannot change the command setting by using the encapsulation mpls command. These methods result in the following error message: 

Encapsulation changes are not allowed on an existing pw-class.

To remove the command, you must delete the pseudowire by using the no pseudowire-class command. To change the type of encapsulation, remove the pseudowire by using the no pseudowire-class command, reestablish the pseudowire, and specify the new encapsulation type.

Manual Clearing of L2TPv3 Tunnels

This feature lets you clear L2TPv3 tunnels manually. Before the introduction of this feature, there was no provision to clear a specific L2TPv3 tunnel manually. This functionality provides users more control over an L2TPv3 network.

L2TPv3 Tunnel Management

New and enhanced commands have been introduced to facilitate the management and diagnosis of problems with xconnect configurations. No specific configuration tasks are associated with these commands.

  • debug vpdn --The output of this command includes authentication failure messages.

  • show l2tun session --The hostname keyword allows the peer hostname to be displayed in the output.

  • show l2tun tunnel --The authentication keyword allows the display of global information about L2TP control channel authentication AV pairs.

  • show xconnect --The output of this command displays information about xconnect attachment circuits and pseudowires. This command also provides a sortable, single point of reference for information about all xconnect configurations.

  • xconnect logging pseudowire status --This command enables syslog reporting of pseudowire status events.

For information about these Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or to the Cisco IOS Master Commands List, All Releases.

L2TPv3 Protocol Demultiplexing

The L2TPv3 Protocol Demultiplexing feature introduces the ability to provide native IPv6 support by utilizing a specialized IPv6 network to offload IPv6 traffic from the IPv4 network. The IPv6 traffic is tunneled to the IPv6 network transparently by using L2TPv3 pseudowires without affecting the configuration of the CE devices. IPv4 traffic is routed as usual within the IPv4 network, maintaining the existing performance and reliability of the IPv4 network.

The IPv4 PE devices must be configured to demultiplex the incoming IPv6 traffic from IPv4 traffic. The PE devices facing the IPv6 network do not require the IPv6 configuration. The configuration of the IPv6 network is beyond the scope of this document. For more information on configuring an IPv6 network, see the IPv6 Configuration Guide.

L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations

The L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations feature lets you configure an Ethertype other than 0x8100 on Gigabit Ethernet interfaces with the QinQ or Dot1Q encapsulation. You can set the custom Ethertype to 0x9100, 0x9200, or 0x88A8. This allows interoperability in a multivendor Gigabit Ethernet environment.

HDLC over L2TPv3

HDLC for Layer 2 Data Encapsulation provides encapsulation of port-to-port Layer 2 traffic. All HDLC traffic including IPv4, IPv6, and non-IP packet, such as IS-IS, is tunneled over L2TPv3. HDLC does not support interworking mode.


Note

L2TPv3 supports the IPv4 tunnel only for HDLC. The IPv4 tunnel supports IPv4 and IPv6 packets.

L2TPv3 Benefits

Simplifies Deployment of VPNs

L2TPv3 is an industry-standard Layer 2 tunneling protocol that ensures interoperability among vendors, thus increasing customer flexibility and service availability.

Omits the Need for MPLS

Service providers need not deploy Multiprotocol Label Switching (MPLS) in the core IP backbone to set up VPNs using L2TPv3 over the IP backbone, resulting in operational savings and increased revenue.

Supports Layer 2 Tunneling over IP for Any Payload

L2TPv3 provides enhancements to L2TP to support Layer 2 tunneling of any payload over an IP core network. L2TPv3 defines the base L2TP protocol as being separate from the Layer 2 payload that is tunneled.

Other Benefits

  • Provides cookies for authentication

  • Provides session state updates and multiple sessions

  • Supports interworking (Ethernet-VLAN, Ethernet-QinQ, and VLAN-QinQ)

Supported L2TPv3 Payloads


Note

Each L2TPv3 tunneled packet includes the entire Layer 2 frame of the payloads described in this section. If sequencing is required (see the Sequencing section), a Layer 2-specific sublayer (see the Pseudowire Control Encapsulation section) is included in the L2TPv3 header to provide the Sequence Number field.

Ethernet

An Ethernet frame arriving at a PE device is simply encapsulated in its entirety with an L2TP data header. At the other end, a received L2TP data packet is stripped of its L2TP data header. The payload, an Ethernet frame, is then forwarded to the appropriate attachment circuit.

Because the L2TPv3 tunneling protocol serves essentially as a bridge, it need not examine any part of an Ethernet frame. Any Ethernet frame received on an interface is tunneled, and any L2TP-tunneled Ethernet frame is forwarded out of the interface.


Note

Because of the way in which L2TPv3 handles Ethernet frames, an Ethernet interface must be configured to promiscuous mode to capture all traffic received on the Ethernet segment attached to the device. All frames are tunneled through the L2TP pseudowire.

VLAN

L2TPv3 supports VLAN memberships in the following ways:

  • Port-based, in which undated Ethernet frames are received

  • VLAN-based, in which tagged Ethernet frames are received

In L2TPv3, Ethernet xconnect supports port-based VLAN membership and the reception of tagged Ethernet frames. A tagged Ethernet frame contains a tag header (defined in 802.1Q), which is 4 bytes long and consists of a 2-byte tag protocol identifier (TPID) field and a 2-byte tag control information (TCI) field. The TPID indicates that a TCI follows. The TCI is further broken down into the following three fields:

  • User priority field

  • Canonical format indicator (CFI)

  • A 12-bit VLAN ID (VID)

For L2TPv3, an Ethernet subinterface configured to support VLAN switching may be bound to an xconnect service so that all Ethernet traffic, tagged with a VID specified on the subinterface, is tunneled to another PE. The VLAN Ethernet frames are forwarded in their entirety. The receiving PE may rewrite the VID of the tunneled traffic to another value before forwarding the traffic onto an attachment circuit.

To successfully rewrite VLANs, it may be necessary to disable the Spanning Tree Protocol (STP). This can be done on a per-VLAN basis by using the no spanning-tree vlan command.


Note

Because of the way in which L2TPv3 handles VLAN packets, the Ethernet interface must be configured in promiscuous mode to capture all traffic received on the Ethernet segment attached to the device. All frames are tunneled through the L2TP pseudowire.

IPv6 Protocol Demultiplexing

Upgrading a service provider network to support IPv6 is a long and expensive process. As an interim solution, the Protocol Demultiplexing for L2TPv3 feature introduces the ability to provide native IPv6 support by setting up a specialized IPv6 network and offloading IPv6 traffic from the IPv4 network. IPv6 traffic is tunneled transparently to the IPv6 network using L2TPv3 pseudowires without affecting the configuration of the CE devices. IPv4 traffic is routed as usual within the IPv4 network, maintaining the existing performance and reliability of the IPv4 network.

The figure below shows a network deployment that offloads IPv6 traffic from the IPv4 network to a specialized IPv6 network. The PE devices demultiplex the IPv6 traffic from the IPv4 traffic. IPv6 traffic is routed to the IPv6 network over an L2TPv3 pseudowire, while IPv4 traffic is routed normally. The IPv4 PE devices must be configured to demultiplex the incoming IPv6 traffic from the IPv4 traffic. The PE devices facing the IPv6 network do not require the IPv6 configuration.

Figure 4. Protocol Demultiplexing of IPv6 Traffic from IPv4 Traffic

If no IP address is configured, the protocol demultiplexing configuration is rejected. If an IP address is configured, the xconnect command configuration is rejected unless protocol demultiplexing is enabled in xconnect configuration mode before exiting that mode. If an IP address is configured with an xconnect command configuration and protocol demultiplexing is enabled, the IP address cannot be removed. To change or remove the configured IP address, the xconnect command configuration must first be disabled.

The table below shows the valid combinations of configurations.

Table 2. Valid Configuration Scenarios

Scenario

IP Address

xconnect Configuration

Protocol Demultiplexing Configuration

Routing

Yes

No

--

L2VPN

No

Yes

No

IPv6 Protocol Demultiplexing

Yes

Yes

Yes

Performance Impact of L2TPv3 on Cisco ASR 1000 Series Routers

L2TPv3 supports the following maximum number of attachment circuits and tunnels:

  • First-generation Cisco ASR 1000 Series Route Processor (RP1) with Embedded Services Processor 10 (ESP10)

    • Attachment circuits for Ethernet: 8000 per system in a typical user environment. This includes 4000 per port and 8000 per SPA.

    • L2TPv3 tunnels: 1000 (in a typical user environment) and 2000 (maximum).

  • Second-generation Cisco ASR 1000 Series Route Processor (RP2) with Embedded Services Processor 20 (ESP20)

    • Attachment circuits for Ethernet: 16,000 per system in a typical user environment. This includes 4000 per port and 8000 per SPA.

    • L2TPv3 tunnels: 2000 (in a typical user environment) and 4000 (maximum).

L2TPv3 adds tunnel encapsulation to TCP packets, which can cause fragmentation of big packets (packet size larger than the session MTU). Consider a scenario where a big TCP packet is followed by a small TCP packet (packet size smaller than the session MTU). After L2TPv3 encapsulation, the encapsulated big TCP packet will be fragmented, but the encapsulated small TCP packet will not be fragmented. On the Cisco ASR 1000 Series Routers, the fragmentation and reassembly of the big TCP packet requires an additional processor cycle. Because Cisco ASR 1000 Series Routers follow multithread processing, the small packet will need shorter processing time and may be forwarded ahead of the fragmented big packet. This process may result in packet sequence changes on the receiver's end.

As a workaround, you can enable the ip pmtu command to prevent the fragmentation of tunneled packets (see the "MTU Handling" section).

How to Configure Layer 2 Tunneling Protocol Version 3

Configuring L2TP Control Channel Parameters

After you enter L2TP class configuration mode, you can configure L2TP control channel parameters in any order. If you have multiple authentication requirements, you can configure multiple sets of L2TP class control channel parameters with different L2TP class names. However, only one set of parameters can be applied to a connection between any pair of IP addresses.

Configuring L2TP Control Channel Timing Parameters

The following L2TP control channel timing parameters can be configured in L2TP class configuration mode:

  • Packet size of the receive window used for the control channel

  • Retransmission parameters used for control messages

  • Timeout parameters used for the control channel

This task configures a set of timing control channel parameters in an L2TP class. All of the timing control channel parameter configurations are optional and may be configured in any order. If these parameters are not configured, default values are applied.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. l2tp-class [l2tp-class-name ]
  4. retransmit {initial retries initial-retries | retries retries | timeout {max | min } timeout }
  5. timeout setup seconds
  6. exit

DETAILED STEPS

  Command or Action Purpose
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

l2tp-class [l2tp-class-name ]

Example:
Device(config)# l2tp-class class1

Specifies the L2TP class name and enters L2TP class configuration mode.

  • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.

Step 4

retransmit {initial retries initial-retries | retries retries | timeout {max | min } timeout }

Example:
Device(config-l2tp-class)# retransmit retries 10

(Optional) Configures parameters that affect the retransmission of control packets.

  • initial retries —Specifies how many SCCRQs are resent before giving up on the session. Valid values for the initial-retries argument range from 1 to 1000. The default value is 2.

  • retries —Specifies how many retransmission cycles occur before determining that the peer PE device is not responding. Valid values for the retries argument range from 1 to 1000. The default value is 15.

  • timeout {max | min }—Specifies maximum and minimum retransmission intervals (in seconds) for resending control packets. Valid values for the timeout argument range from 1 to 8. The default maximum interval is 8. The default minimum interval is 1.

Step 5

timeout setup seconds

Example:
Device(config-l2tp-class)# timeout setup 400

(Optional) Configures the amount of time, in seconds, allowed to set up a control channel.

  • Valid values for the seconds argument range from 60 to 6000. The default value is 300.

Step 6

exit

Example:
Device(config-l2tp-class)# exit

Exits L2TP class configuration mode.

Configuring L2TPv3 Control Channel Authentication Parameters

Configuring Authentication for the L2TP Control Channel

The L2TP control channel method of authentication is the older, CHAP-like authentication system inherited from L2TPv2.

The following L2TP control channel authentication parameters can be configured in L2TP class configuration mode:

  • Authentication for the L2TP control channel

  • Password used for L2TP control channel authentication

  • Local hostname used for authenticating the control channel

This task configures a set of authentication control channel parameters in an L2TP class. All of the authentication control channel parameter configurations are optional and may be configured in any order. If these parameters are not configured, default values are applied.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. l2tp-class [l2tp-class-name ]
  4. authentication
  5. password [0 | 7 ] password
  6. hostname name
  7. exit

DETAILED STEPS

  Command or Action Purpose
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

l2tp-class [l2tp-class-name ]

Example:
Device(config)# l2tp-class class1

Specifies the L2TP class name and enters L2TP class configuration mode.

  • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.

Step 4

authentication

Example:
Device(config-l2tp-class)# authentication

(Optional) Enables authentication for the control channel between PE devices.

Step 5

password [0 | 7 ] password

Example:
Device(config-l2tp-class)# password cisco

(Optional) Configures the password used for control channel authentication.

  • [0 | 7 ]—(Optional) Specifies the input format of the shared secret. The default value is 0 .
    • 0 —Specifies that a plain-text secret is entered.
    • 7 —Specifies that an encrypted secret is entered.

  • password —Defines the shared password between peer devices.

Step 6

hostname name

Example:
Device(config-l2tp-class)# hostname yb2

(Optional) Specifies a hostname used to identify the device during L2TP control channel authentication.

  • If you do not use this command, the default hostname of the device is used.

Step 7

exit

Example:
Device(config-l2tp-class)# exit

Exits L2TP class configuration mode.

Configuring L2TPv3 Control Message Hashing

This task configures L2TPv3 Control Message Hashing feature for an L2TP class.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. l2tp-class [l2tp-class-name ]
  4. digest [secret [0 | 7 ] password ] [hash {md5 | sha }]
  5. digest check
  6. hidden
  7. exit

DETAILED STEPS

  Command or Action Purpose
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

l2tp-class [l2tp-class-name ]

Example:
Device(config)# l2tp-class class1

Specifies the L2TP class name and enters L2TP class configuration mode.

  • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.

Step 4

digest [secret [0 | 7 ] password ] [hash {md5 | sha }]

Example:
Device(config-l2tp-class)# digest secret cisco hash sha

(Optional) Enables L2TPv3 control channel authentication or integrity checking.

  • secret —(Optional) Enables L2TPv3 control channel authentication.

Note 

If the digest command is issued without the secret keyword option, L2TPv3 integrity checking is enabled.

  • [0 | 7 ]—Specifies the input format of the shared secret. The default value is 0 .
    • 0 —Specifies that a plain-text secret is entered.
    • 7 —Specifies that an encrypted secret is entered.

  • password —Defines the shared secret between peer devices. The value entered for the password argument must be in the format that matches the input format specified by the [0 | 7 ] keyword option.

  • hash {md5 | sha }—(Optional) Specifies the hash function to be used in per-message digest calculations.
    • md5 —Specifies HMAC-MD5 hashing.
    • sha —Specifies HMAC-SHA-1 hashing.

The default hash function is md5 .

Step 5

digest check

Example:
Device(config-l2tp-class)# digest check

(Optional) Enables the validation of the message digest in received control messages.

  • Validation of the message digest is enabled by default.

Note 

Validation of the message digest cannot be disabled if authentication has been enabled using the digest secret command. If authentication has not been configured with the digest secret command, the digest check can be disabled to increase performance.

Step 6

hidden

Example:
Device(config-l2tp-class)# hidden

(Optional) Enables AV pair hiding when sending control messages to an L2TPv3 peer.

  • AV pair hiding is disabled by default.

  • Only the hiding of the cookie AV pair is supported.

  • If a cookie is configured in L2TP class configuration mode (see the section "Manually Configuring L2TPv3 Session Parameters"), enabling AV pair hiding causes that cookie to be sent to the peer as a hidden AV pair using the password configured with the digest secret command.

Note 

AV pair hiding is enabled only if authentication has been enabled using the digest secret command, and no other authentication method is configured.

Step 7

exit

Example:
Device(config-l2tp-class)# exit

Exits L2TP class configuration mode.

Configuring L2TPv3 Digest Secret Graceful Switchover

Perform this task to make the transition from an old L2TPv3 control channel authentication password to a new L2TPv3 control channel authentication password without disrupting established L2TPv3 tunnels.

Before you begin

Before performing this task, you must enable control channel authentication as documented in the Configuring L2TPv3 Control Message Hashing task.


Note

This task is not compatible with authentication passwords configured with the older, CHAP-like control channel authentication system.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. l2tp-class l2tp-class-name
  4. digest [secret [0 | 7 ] password ] [hash {md5 | sha }]
  5. end
  6. show l2tun tunnel all
  7. configure terminal
  8. l2tp-class [l2tp-class-name ]
  9. no digest [secret [0 | 7 ] password [hash {md5 | sha }]
  10. end
  11. show l2tun tunnel all

DETAILED STEPS

  Command or Action Purpose
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

l2tp-class l2tp-class-name

Example:
Device(config)# l2tp-class class1

Specifies the L2TP class name and enters L2TP class configuration mode.

Step 4

digest [secret [0 | 7 ] password ] [hash {md5 | sha }]

Example:
Device(config-l2tp-class)# digest secret cisco2 hash sha

Configures a new password to be used in L2TPv3 control channel authentication.

  • A maximum of two passwords may be configured at any time.

Note 

Authentication will now occur using both the old and new passwords.

Step 5

end

Example:
Device(config-l2tp-class)# end

Ends your configuration session by exiting to privileged EXEC mode.

Step 6

show l2tun tunnel all

Example:
Device# show l2tun tunnel all

(Optional) Displays the current state of Layer 2 tunnels and information about configured tunnels, including local and remote L2TP hostnames, aggregate packet counts, and control channel information.

  • Tunnels should be updated with the new control channel authentication password within a matter of seconds. If a tunnel does not update to show that two secrets are configured after several minutes have passed, the tunnel can be cleared manually and a defect report should be filed with the Cisco Technical Assistance Center (TAC). To clear an L2TPv3 tunnel manually, perform the task described in the section “Manually Clearing L2TPv3 Tunnels. ”

Note 

Issue this command to determine whether any tunnel is using the new password for control channel authentication. The output displayed for each tunnel in the specified L2TP class should show that two secrets are configured.

Step 7

configure terminal

Example:
Device# configure terminal

Enters global configuration mode.

Step 8

l2tp-class [l2tp-class-name ]

Example:
Device(config)# l2tp-class class1

Specifies the L2TP class name and enters L2TP class configuration mode.

  • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.

Step 9

no digest [secret [0 | 7 ] password [hash {md5 | sha }]

Example:
Device(config-l2tp-class)# no digest secret cisco hash sha

Removes the old password used in L2TPv3 control channel authentication.

Note 

Do not remove the old password until all peer PE devices have been updated with the new password.

Step 10

end

Example:
Device(config-l2tp-class)# end

Ends your configuration session by exiting to privileged EXEC mode.

Step 11

show l2tun tunnel all

Example:
Device# show l2tun tunnel all

(Optional) Displays the current state of Layer 2 tunnels and information about configured tunnels, including local and remote L2TP hostnames, aggregate packet counts, and control channel information.

  • Tunnels should no longer be using the old control channel authentication password. If a tunnel does not update to show that only one secret is configured after several minutes have passed, that tunnel can be cleared manually and a defect report should be filed with TAC. To clear an L2TPv3 tunnel manually, perform the task described in the section “Manually Clearing L2TPv3 Tunnels.”

Note 

Issue this command to ensure that all tunnels are using only the new password for control channel authentication. The output displayed for each tunnel in the specified L2TP class should show that one secret is configured.

Configuring L2TP Control Channel Maintenance Parameters

The L2TP hello packet keepalive interval control channel maintenance parameter can be configured in L2TP class configuration mode.

This task configures the interval used for hello messages in an L2TP class. This control channel parameter configuration is optional. If this parameter is not configured, the default value is applied.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. l2tp-class [l2tp-class-name ]
  4. hello interval
  5. exit

DETAILED STEPS

  Command or Action Purpose
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

l2tp-class [l2tp-class-name ]

Example:
Device(config)# l2tp-class class1

Specifies the L2TP class name and enters L2TP class configuration mode.

  • The l2tp-class-name argument is optional. However, to configure multiple L2TP classes, you must specify a unique l2tp-class-name for each one.

Step 4

hello interval

Example:
Device(config-l2tp-class)# hello 100

(Optional) Specifies the exchange interval (in seconds) used between L2TP hello packets.

  • Valid values for the interval argument range from 0 to 1000. The default value is 60.

Step 5

exit

Example:
Device(config-l2tp-class)# exit

Exits L2TP class configuration mode.

Configuring the L2TPv3 Pseudowire

Perform this task to configure the L2TPv3 pseudowire.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. pseudowire-class [pw-class-name ]
  4. encapsulation l2tpv3
  5. protocol {l2tpv3 | none } [l2tp-class-name ]
  6. ip local interface interface-name
  7. ip pmtu
  8. ip tos {value value | reflect }
  9. ip dfbit set
  10. ip ttl value
  11. ip protocol {l2tp | protocol-number }
  12. sequencing {transmit | receive | both }
  13. exit

DETAILED STEPS

  Command or Action Purpose
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

pseudowire-class [pw-class-name ]

Example:

Device(config)# pseudowire-class etherpw

Enters pseudowire class configuration mode and optionally specifies the name of the L2TP pseudowire class.

Step 4

encapsulation l2tpv3

Example:

Device(config-pw)# encapsulation l2tpv3

Specifies that L2TPv3 is used as the data encapsulation method to tunnel IP traffic.

Step 5

protocol {l2tpv3 | none } [l2tp-class-name ]

Example:

Device(config-pw)# protocol l2tpv3 class1

(Optional) Specifies the L2TPv3 signaling protocol to be used to manage the pseudowires created with the control channel parameters in the specified L2TP class (see the section "Configuring L2TP Control Channel Parameters").

  • If the l2tp-class-name argument is not specified, the default values for L2TP control channel parameters are used. The default protocol option is l2tpv3 .

  • If you do not want to use signaling in the L2TPv3 sessions created with this pseudowire class, enter protocol none .

Step 6

ip local interface interface-name

Example:

Device(config-pw)# ip local interface e0/0

Specifies the PE device interface whose IP address is to be used as the source IP address for sending tunneled packets.

  • The same or a different local interface name can be used for each of the pseudowire classes configured between a pair of PE devices.

Note 

This command must be configured for pseudowire-class configurations using L2TPv3 as the data encapsulation method.

Step 7

ip pmtu

Example:

Device(config-pw)# ip pmtu

(Optional) Enables the discovery of the PMTU for tunneled traffic and helps fragmentation.

  • This command enables the processing of ICMP unreachable messages that indicate fragmentation errors in the backbone network that carries L2TPv3 session traffic. Also, this command enables MTU checking for IP packets sent into the session and that have the DF bit set. Any IP packet larger than the MTU is dropped and an ICMP unreachable message is sent. MTU discovery is disabled by default.

Note 

The ip pmtu command is not supported if you disabled signaling with the protocol none command in Step 5.

  • This command must be enabled in the pseudowire class configuration to enable fragmentation of IP packets before the data enters the pseudowire.

Note 

To enable fragmentation of IP packets before the data enters the pseudowire, Cisco recommends that you also enter the ip dfbit set command in pseudowire class configuration mode. This allows the PMTU to be obtained more rapidly.

Note 

When the ip pmtu command is enabled, the DF bit is copied from the inner IP header to the outer IP header. If no IP header is found inside the Layer 2 frame, the DF bit in the outer IP is set to 0.

Step 8

ip tos {value value | reflect }

Example:

Device(config-pw)# ip tos reflect

(Optional) Configures the value of the ToS byte in IP headers of tunneled packets, or reflects the ToS byte value from the inner IP header.

  • Valid values for the value argument range from 0 to 255. The default ToS byte value is 0.

Step 9

ip dfbit set

Example:

Device(config-pw)# ip dfbit set
(Optional) Configures the value of the DF bit in the outer headers of tunneled packets.

  • Use this command if (for performance reasons) you do not want reassembly of tunneled packets on the peer PE device.

  • This command is disabled by default.

Step 10

ip ttl value

Example:

Device(config-pw)# ip ttl 100

(Optional) Configures the value of the time to live (TTL) byte in the IP headers of tunneled packets.

  • Valid values for the value argument range from 1 to 255. The default TTL byte value is 255.

Step 11

ip protocol {l2tp | protocol-number }

Example:

Device(config-pw)# ip protocol l2tp

(Optional) Configures the IP protocol to be used for tunneling packets.

Step 12

sequencing {transmit | receive | both }

Example:

Device(config-pw)# sequencing both

(Optional) Specifies the direction in which sequencing of data packets in a pseudowire is enabled:

  • transmit —Updates the Sequence Number field in the headers of data packets sent over the pseudowire according to the data encapsulation method that is used.

  • receive —Keeps the Sequence Number field in the headers of data packets received over the pseudowire. Out-of-order packets are dropped.

  • both —Enables both the transmit and receive options.

Step 13

exit

Example:

Device(config-pw)# exit

Exits pseudowire class configuration mode.

Configuring the Xconnect Attachment Circuit

The virtual circuit identifier that you configure creates the binding between a pseudowire configured on a PE device and an attachment circuit in a CE device. The virtual circuit identifier configured on the PE device at one end of the L2TPv3 control channel must also be configured on the peer PE device at the other end.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type slot / port
  4. xconnect peer-ip-address vcid pseudowire-parameters [sequencing {transmit | receive | both }]
  5. exit

DETAILED STEPS

  Command or Action Purpose
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 type slot / port

Example:

Device(config)# interface ethernet 0/0

Specifies the interface by type (for example, Ethernet), slot, and port number, and enters interface configuration mode.

Step 4

xconnect peer-ip-address vcid pseudowire-parameters [sequencing {transmit | receive | both }]

Example:

Device(config-if)# xconnect 10.0.3.201 123 pw-class vlan-xconnect

Specifies the IP address of the peer PE device and the 32-bit virtual circuit identifier shared between the PE at each end of the control channel.

  • The peer device ID (IP address) and virtual circuit ID must be a unique combination on the device.

  • At least one of the following pseudowire class parameters must be configured for the pseudowire-parameters argument:
    • encapsulation {l2tpv3 [manual ] | mpls }—Specifies the tunneling method used to encapsulate data in the pseudowire:
      • l2tpv3 —L2TPv3 is the tunneling method to be used.
      • manual —(Optional) No signaling is to be used in the L2TPv3 control channel. This command places the device in xconnect configuration mode for the manual configuration of L2TPv3 parameters for the attachment circuit.
      • mpls —MPLS is the tunneling method to be used.

  • pw-class {pw-class-name }—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken.

  • The optional encapsulation parameter specifies the method of pseudowire tunneling used: L2TPv3 or MPLS. Enter manual if you do not want signaling to be used in the L2TPv3 control channel. The encapsulation l2tpv3 manual keyword combination enters xconnect configuration submode. See the section "Manually Configuring L2TPv3 Session Parameters" for the other L2TPv3 commands that you must enter to complete the configuration of the L2TPv3 control channel. If you do not enter an encapsulation value, the encapsulation method entered with the password command in the Configuring the Xconnect Attachment Circuit task is used.

  • The optional pw-class parameter binds the xconnect statement to a specific pseudowire class. The pseudowire class then serves as the template configuration for all attachment circuits bound to it. Specify the pseudowire-class option if you need to configure more advanced options.

Note 

You must configure either the encapsulation or the pw-class option or both.

Note 

If you select L2TPv3 as your data encapsulation method, you must specify the pw-class keyword.

  • The optional sequencing parameter specifies whether sequencing is required for packets that are received, sent, or both received and sent.

Step 5

exit

Example:

Device(config-if)# exit

Exits interface configuration mode.

Manually Configuring L2TPv3 Session Parameters

When you bind an attachment circuit to an L2TPv3 pseudowire for the xconnect service by using the xconnect l2tpv3 manual command (see the section "Configuring the Xconnect Attachment Circuit") because you do not want signaling, you must configure L2TP-specific parameters to complete the L2TPv3 control channel configuration.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type slot / port
  4. xconnect peer-ip-address vc-id encapsulation l2tpv3 manual pw-class pw-class-name
  5. l2tp id local-session-id remote-session-id
  6. l2tp cookie local size low-value [high-value ]
  7. l2tp cookie remote size low-value [high-value ]
  8. l2tp hello l2tp-class-name
  9. exit
  10. exit

DETAILED STEPS

  Command or Action Purpose
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 type slot / port

Example:

Device(config)# interface ethernet 0/0

Specifies the interface by type (for example, Ethernet), slot, and port number, and enters interface configuration mode.

Step 4

xconnect peer-ip-address vc-id encapsulation l2tpv3 manual pw-class pw-class-name

Example:

Device(config-if)# xconnect 10.0.3.201 123 encapsulation l2tpv3 manual pw-class vlan-xconnect

Specifies the IP address of the peer PE device and the 32-bit virtual circuit identifier shared between the PE at each end of the control channel, and enters xconnect configuration mode.

  • The peer device ID (IP address) and virtual circuit ID must be a unique combination on the device.

  • The encapsulation l2tpv3 manual parameter specifies that L2TPv3 is to be used as the pseudowire tunneling method.

  • The mandatory pw-class pw-class-name keyword and argument combination specifies the pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken.

Step 5

l2tp id local-session-id remote-session-id

Example:

Device(config-if-xconn)# l2tp id 222 111

Configures the identifiers for the local L2TPv3 session and for the remote L2TPv3 session on the peer PE device.

  • This command is required to complete the attachment circuit configuration and a static L2TPv3 session configuration.

Step 6

l2tp cookie local size low-value [high-value ]

Example:

Device(config-if-xconn)# l2tp cookie local 4 54321

(Optional) Specifies the value that the peer PE must include in the cookie field of incoming (received) L2TP packets.

  • The size of the cookie field can be 4 or 8 bytes. If you do not enter this command, no cookie value is included in the header of L2TP packets.

  • If you configure the cookie length in incoming packets as 8 bytes, you must specify a 4-byte high value and a 4-byte low value.

Step 7

l2tp cookie remote size low-value [high-value ]

Example:

Device(config-if-xconn)# l2tp cookie remote 4 12345

(Optional) Specifies the value that the device includes in the cookie field of outgoing (sent) L2TP packets.

  • The size of the cookie field can be 4 or 8 bytes. If you do not enter this command, no cookie value is included in the header of L2TP packets.

  • If you configure the cookie length in outgoing packets as 8 bytes, you must specify a 4-byte high value and a 4-byte low value.

Step 8

l2tp hello l2tp-class-name

Example:

Device(config-if-xconn)# l2tp hello l2tp-defaults

(Optional) Specifies the L2TP class name to be used (see the section "Configuring L2TP Control Channel Parameters") for control channel configuration parameters, including the interval to use between hello keepalive messages.

Note 

This command assumes that there is no control plane to negotiate control channel parameters and that a control channel is to be used to provide keepalive support through an exchange of L2TP hello messages. By default, no hello messages are sent.

Step 9

exit

Example:

Device(config-if-xconn)# exit

Exits xconnect configuration mode.

Step 10

exit

Example:

Device(config-if)# exit

Exits interface configuration mode.

Configuring Protocol Demultiplexing for L2TPv3

Configuring Protocol Demultiplexing for Ethernet Interfaces

Perform this task to configure the Protocol Demultiplexing feature on an Ethernet interface.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type slot / port
  4. ip address ip-address mask [secondary ]
  5. xconnect peer-ip-address vcid pw-class pw-class-name
  6. match protocol ipv6
  7. exit
  8. exit

DETAILED STEPS

  Command or Action Purpose
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 type slot / port

Example:
Device(config)# interface ethernet 0/1

Specifies the interface by type, slot, and port number, and enters interface configuration mode.

Step 4

ip address ip-address mask [secondary ]

Example:
Device(config-if)# ip address 172.16.128.4

Sets a primary or secondary IP address for an interface.

Step 5

xconnect peer-ip-address vcid pw-class pw-class-name

Example:
Device(config-if)# xconnect 10.0.3.201 888 pw-class demux

Specifies the IP address of the peer PE device and the 32-bit VCI shared between the PE at each end of the control channel, and enters xconnect configuration mode.

  • The peer device ID (IP address) and virtual circuit ID must be a unique combination on the device.

  • pw-class pw-class-name —The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken. The pw-class parameter binds the xconnect statement to a specific pseudowire class. The pseudowire class then serves as the template configuration for all attachment circuits bound to it.

Note 

The L2TPv3 session can also be provisioned manually. See the section "Manually Configuring L2TPv3 Session Parameters" for information about manually configuring the L2TPv3 session parameters.

Step 6

match protocol ipv6

Example:
Device(config-if-xconn)# match protocol ipv6

Enables protocol demultiplexing of IPv6 traffic.

Step 7

exit

Example:
Device(config-if-xconn)# exit

Exits xconnect configuration mode.

Step 8

exit

Example:
Device(config-if)# exit

Exits interface configuration mode.

Configuring an L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations

The L2TPv3 Custom Ethertype for dot1q and QinQ Encapsulations feature lets you configure an Ethertype other than 0x8100 on Gigabit Ethernet interfaces with QinQ or dot1Q encapsulations. You can set the custom Ethertype to 0x9100, 0x9200, or 0x88A8. To define the Ethertype field type, you use the dot1q tunneling ethertype command.

Perform this task to set a custom Ethertype.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. dot1q tunneling ethertype {0x88A8 | 0x9100 | 0x9200 }
  5. exit

DETAILED STEPS

  Command or Action Purpose
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 type number

Example:

Device(config)# interface gigabitethernet 1/0/0

Specifies an interface and enters interface configuration mode.

Step 4

dot1q tunneling ethertype {0x88A8 | 0x9100 | 0x9200 }

Example:

Device(config-if)# dot1q tunneling ethertype 0x9100

Defines the Ethertype field type used by peer devices when implementing Q-in-Q VLAN tagging.

Step 5

exit

Example:

Device(config-if)# exit

Exits interface configuration mode.

Configuring GEC over L2TPv3

Perform this task to configure Gigabit EtherChannel (GEC) over Layer 2 Tunneling Protocol Version 3 (L2TPv3).

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface Loopback0
  4. ip address ip-address
  5. exit
  6. pseudowire-class [pw-class-name]
  7. encapsulation l2tpv3
  8. ip local interface interface-name
  9. exit
  10. interface port-channel channel-number
  11. xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name
  12. exit
  13. interface gigabitethernet interface-type-number
  14. channel-group channel-group-number
  15. end

DETAILED STEPS

  Command or Action Purpose
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 Loopback0

Example:

Device(config)# interface Loopback0

Creates a loopback interface and enters interface configuration mode.

Step 4

ip address ip-address

Example:

Device(config-if)# ip address 10.1.0.1 255.255.255.255

Assigns an IP address to the interface.

Step 5

exit

Example:

Device(config-if)# exit

Exits interface configuration mode.

Step 6

pseudowire-class [pw-class-name]

Example:

Device(config)# pseudowire-class l2tpv3

Enters pseudowire class configuration mode and optionally specifies the name of the Layer 2 Tunneling Protocol (L2TP) pseudowire class.

Step 7

encapsulation l2tpv3

Example:

Device(config-pw)# encapsulation l2tpv3

Specifies that L2TPv3 is used as the data encapsulation method to tunnel IP traffic.

Step 8

ip local interface interface-name

Example:

Device(config-pw)# ip local interface loopback0

Specifies the provider edge (PE) interface whose IP address is to be used as the source IP address for sending tunneled packets.

  • Use the same local interface name for all pseudowire classes that are configured between a pair of PE devices.
Note 
This command must be configured for pseudowire-class configurations using L2TPv3 as the data encapsulation method.
Step 9

exit

Example:

Device(config-pw)# exit

Exits pseudowire class configuration mode and enters global configuration mode.

Step 10

interface port-channel channel-number

Example:

Device# interface port-channel 1

Defines a port channel and enters interface configuration mode.

Step 11

xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name

Example:

Device(config-subif)# xconnect 10.0.3.201 1234 encapsulation l2tpv3 pw-class l2tpv3

Specifies the IP address of the peer PE device and the 32-bit virtual circuit identifier (VCI) shared between the PE at each end of the control channel.

  • The combination of the peer device ID and the VCI must be unique.

  • pw-class pw-class-name—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken. The pw-class parameter binds xconnect to a specific pseudowire class. The pseudowire class then serves as a template for all attachment circuits bound to it.

Step 12

exit

Example:

Device(config-subif)# exit

Exits subinterface configuration mode and enters global configuration mode.

Step 13

interface gigabitethernet interface-type-number

Example:

Device(config)# interface gigabitEthernet 0/0/0

Enters interface configuration mode.

Step 14

channel-group channel-group-number

Example:

Device(config-if)# channel-group 1

Add the interface to an EtherChannel group.

Step 15

end

Example:

Device(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Configuring GEC with Dot1Q

Perform this task to configure Gigabit EtherChannel (GEC) with VLAN over Layer 2 Tunneling Protocol Version 3 (L2TPv3).

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface port-channel interface-number
  4. encapsulation dot1q vlan-id
  5. xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name
  6. end

DETAILED STEPS

  Command or Action Purpose
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 port-channel interface-number

Example:

Device(config)# interface port-channel 1.1

Defines a port channel and enters subinterface configuration mode.

Step 4

encapsulation dot1q vlan-id

Example:

Device(config-subif)# encapsulation dot1q 100

Specifies that dot1q is used as the data encapsulation method to tunnel IP traffic.

Step 5

xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name

Example:

Device(config-subif)# xconnect 10.0.3.201 1234 encapsulation l2tpv3 pw-class l2tpv3

Specifies the IP address of the peer provider edge (PE) device and the 32-bit virtual circuit identifier (VCI) that is shared between the PE device at each end of the control channel.

  • The combination of the peer device ID and the VCI must be unique.

  • pw-class pw-class-name—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken. The pw-class parameter binds xconnect to a specific pseudowire class. The pseudowire class then serves as a template for all attachment circuits bound to it.

Step 6

end

Example:

Device# end

Exits subinterface configuration mode and returns to privileged EXEC mode .

Configuring GEC with QinQ

Perform this task to configure Gigabit EtherChannel (GEC) with queue-in-queue (QinQ) over Layer 2 Tunneling Protocol Version 3 (L2TPv3).

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface port-channel interface-number
  4. encapsulation dot1q vlan-id second-dot1q second-vlan-id
  5. xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name
  6. end

DETAILED STEPS

  Command or Action Purpose
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 port-channel interface-number

Example:

Device(config)# interface port-channel 1.1

Defines the subinterface as a port channel and enters subinterface configuration mode.

Step 4

encapsulation dot1q vlan-id second-dot1q second-vlan-id

Example:

Device(config-subif)# encapsulation dot1q 100 second-dot1q 200

Specifies that QinQ is used as the data encapsulation method to tunnel IP traffic.

Step 5

xconnect peer-ip-address encapsulation l2tpv3 pw-class pw-class-name

Example:

Device(config-subif)# xconnect 10.0.3.202 1234 encapsulation l2tpv3 pw-class l2tpv3

Specifies the IP address of the peer provider edge (PE) device and the 32-bit virtual circuit identifier (VCI) that is shared between the PE device at each end of the control channel.

  • The combination of the peer device ID and the VCI must be unique.

  • pw-class pw-class-name—The pseudowire class configuration from which the data encapsulation type (L2TPv3) is taken. The pw-class parameter binds xconnect to a specific pseudowire class. The pseudowire class then serves as a template for all attachment circuits bound to it.

Step 6

end

Example:

Device# end

Exits subinterface configuration mode and returns to privileged EXEC mode.

Manually Clearing L2TPv3 Tunnels

Perform this task to manually clear a specific L2TPv3 tunnel and all the sessions in that tunnel.

SUMMARY STEPS

  1. enable
  2. clear l2tun {l2tp-class l2tp-class-name | tunnel id tunnel-id | local ip ip-address | remote ip ip-address | all }

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

clear l2tun {l2tp-class l2tp-class-name | tunnel id tunnel-id | local ip ip-address | remote ip ip-address | all }

Example:

Device# clear l2tun tunnel id 56789

Clears the specified L2TPv3 tunnel. (This command is not available if there are no L2TPv3 tunnel sessions configured.)

  • l2tp-class l2tp-class-name —All L2TPv3 tunnels with the specified L2TP class name are torn down.

  • tunnel id tunnel-id —The L2TPv3 tunnel with the specified tunnel ID are torn down.

  • local ip ip-address —All L2TPv3 tunnels with the specified local IP address are torn down.

  • remote ip ip-address —All L2TPv3 tunnels with the specified remote IP address are torn down.

  • all —All L2TPv3 tunnels are torn down.

Configuration Examples for Layer 2 Tunneling Protocol Version 3


Note

The IP addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.

Example: Configuring a Static L2TPv3 Session for an Xconnect Ethernet Interface

L2TPv3 is the only encapsulation method that supports a manually provisioned session setup. This example shows how to configure a static session configuration in which all control channel parameters are set up in advance. There is no control plane used and no negotiation phase to set up the control channel. The PE device starts sending tunneled traffic as soon as the Ethernet interface (int e0/0) comes up. The virtual circuit identifier, 123, is not used. The PE sends L2TP data packets with session ID 111 and cookie 12345. In turn, the PE expects to receive L2TP data packets with session ID 222 and cookie 54321. 

l2tp-class l2tp-defaults
 retransmit initial retries 30
 cookie-size 8
pseudowire-class ether-pw
 encapsulation l2tpv3
 protocol none
 ip local interface Loopback0
interface Ethernet 0/0
 xconnect 10.0.3.201 123 encapsulation l2tpv3 manual pw-class ether-pw
 l2tp id 222 111
 l2tp cookie local 4 54321
 l2tp cookie remote 4 12345
 l2tp hello l2tp-defaults

Example: Configuring a Negotiated L2TPv3 Session for an Xconnect VLAN Subinterface

The following is a sample configuration of a dynamic L2TPv3 session for a VLAN xconnect interface. In this example, only VLAN traffic with a VLAN ID of 5 is tunneled. In the other direction, the L2TPv3 session identified by a virtual circuit identifier of 123 receives forwarded frames whose VLAN ID fields are rewritten to contain the value 5. L2TPv3 is used as both the control plane protocol and the data encapsulation. 

l2tp-class class1
 authentication
 password secret
pseudowire-class vlan-xconnect
 encapsulation l2tpv3
 protocol l2tpv3 class1
 ip local interface Loopback0
interface Ethernet0/0.1
 encapsulation dot1q 5
 xconnect 10.0.3.201 123 pw-class vlan-xconnect

Example: Configuring a Negotiated L2TPv3 Session for Local HDLC Switching

The following is a sample configuration of a dynamic L2TPv3 session for local HDLC switching. In this example, note that it is necessary to configure two different IP addresses at the endpoints of the L2TPv3 pseudowire because the virtual circuit identifier must be unique for a given IP address. 


interface loopback 1
 ip address 10.0.0.1 255.255.255.255
interface loopback 2
 ip address 10.0.0.2 255.255.255.255
pseudowire-class loopback1
 encapsulation l2tpv3
 ip local interface loopback1
pseudowire-class loopback2
 encapsulation l2tpv3
 ip local interface loopback2
interface s0/0
 encapsulation hdlc
 xconnect 10.0.0.1 100 pw-class loopback2
interface s0/1
 encapsulation hdlc
 xconnect 10.0.0.2 100 pw-class loopback1

Example: Verifying an L2TPv3 Session

To display information about current L2TPv3 sessions on a device, use the show l2tun session brief command. 

Device# show l2tun session brief
L2TP Session Information Total tunnels 1 sessions 1
LocID      TunID      Peer-address    State     Username, Intf/                 
                                      sess/cir  Vcid, Circuit                   
2391726297 2382731778 6.6.6.6         est,UP    100, Gi0/2/0

To display detailed information about current L2TPv3 sessions on a device, use the show l2tun session all command. 

Device# show l2tun session all
L2TP Session Information Total tunnels 1 sessions 1
Session id 2391726297 is up, logical session id 36272, tunnel id 2382731778
  Remote session id is 193836624, remote tunnel id 2280318174
  Locally initiated session
  Unique ID is 12
Session Layer 2 circuit, type is Ethernet, name is GigabitEthernet0/2/0
  Session vcid is 100
  Circuit state is UP
    Local circuit state is UP
    Remote circuit state is UP
Call serial number is 98300002
Remote tunnel name is l2tp-asr-2
  Internet address is 6.6.6.6
Local tunnel name is l2tp-asr-1
  Internet address is 3.3.3.3
IP protocol 115
  Session is L2TP signaled
  Session state is established, time since change 00:05:25
    94 Packets sent, 58 received
    9690 Bytes sent, 5642 received
  Last clearing of counters never
  Counters, ignoring last clear:
    94 Packets sent, 58 received
    9690 Bytes sent, 5642 received
    Receive packets dropped:
      out-of-order:             0
      other:                    0
      total:                    0
Send packets dropped:
      exceeded session MTU:     0
      other:                    0
      total:                    0
  DF bit off, ToS reflect disabled, ToS value 0, TTL value 255
  Sending UDP checksums are disabled
  Received UDP checksums are verified
  No session cookie information available
  FS cached header information:
    encap size = 24 bytes
    45000014 00000000 ff73a965 03030303
    06060606 0b8db650 
  Sequencing is off
  Conditional debugging is disabled
  SSM switch id is 4101, SSM segment id is 12294

Example: Verifying an L2TP Control Channel

The L2TP control channel is used to negotiate capabilities, monitor the health of the peer PE device, and set up various components of an L2TPv3 session.

To display information about L2TP control channels to other L2TP-enabled devices for all L2TP sessions on the device, use the show l2tun tunnel command. 
Device# show l2tun tunnel
L2TP Tunnel Information Total tunnels 1 sessions 1
LocTunID   RemTunID   Remote Name   State  Remote Address  Sessn L2TP Class/
                                                           Count VPDN Group 
2382731778 2280318174 l2tp-asr-2    est    6.6.6.6         1     l2tp_default_cl
To display detailed information about L2TP control channels to other L2TP-enabled devices for all L2TP sessions on the device, use the show l2tun tunnel all command. 
Device# show l2tun tunnel all 
L2TP Tunnel Information Total tunnels 1 sessions 1
Tunnel id 2382731778 is up, remote id is 2280318174, 1 active sessions
  Locally initiated tunnel
  Tunnel state is established, time since change 00:02:59
  Tunnel transport is IP  (115)
  Remote tunnel name is l2tp-asr-2
    Internet Address 6.6.6.6, port 0
  Local tunnel name is l2tp-asr-1
    Internet Address 3.3.3.3, port 0
  L2TP class for tunnel is l2tp_default_class
  Counters, taking last clear into account:
    54 packets sent, 35 received
    5676 bytes sent, 3442 received
  Last clearing of counters never
  Counters, ignoring last clear:
    54 packets sent, 35 received
    5676 bytes sent, 3442 received
Control Ns 5, Nr 4
  Local RWS 1024 (default), Remote RWS 1024
  Control channel Congestion Control is disabled
  Tunnel PMTU checking disabled
  Retransmission time 1, max 1 seconds
  Unsent queuesize 0, max 0
  Resend queuesize 0, max 2
  Total resends 0, ZLB ACKs sent 2
  Total out-of-order dropped pkts 0 
  Total out-of-order reorder pkts 0 
  Total peer authentication failures 0
  Current no session pak queue check 0 of 5
  Retransmit time distribution: 0 0 0 0 0 0 0 0 0 
  Control message authentication is disabled

Example: Configuring L2TPv3 Control Channel Authentication

The following example shows how to configure CHAP-style authentication of the L2TPv3 control channel: 
l2tp-class class0
 authentication
 password cisco
The following example shows how to configure control channel authentication using the L2TPv3 Control Message Hashing feature: 
l2tp-class class1
 digest secret cisco hash sha
 hidden
The following example shows how to configure control channel integrity checking and how to disable validation of the message digest using the L2TPv3 Control Message Hashing feature: 
l2tp-class class2
 digest hash sha
 no digest check
The following example shows how to disable the validation of the message digest using the L2TPv3 Control Message Hashing feature: 
l2tp-class class3
 no digest check

Example: Configuring L2TPv3 Digest Secret Graceful Switchover

The following example shows how to use the L2TPv3 Digest Secret Graceful Switchover feature to change the L2TP control channel authentication password for the L2TP class named class1. This example assumes that you already have an old password configured for the L2TP class named class1. 

Device(config)# l2tp-class class1
Device(config-l2tp-class)# digest secret cisco2 hash sha
!
! Verify that all peer PE devices have been updated to use the new password before
! removing the old password.
!
Device(config-l2tp-class)# no digest secret cisco hash sha

Example: Verifying L2TPv3 Digest Secret Graceful Switchover

The following show l2tun tunnel all command output shows information about the L2TPv3 Digest Secret Graceful Switchover feature: 

Device# show l2tun tunnel all
! The output below displays control channel password information for a tunnel which has
! been updated with the new control channel authentication password.
!
Tunnel id 12345 is up, remote id is 54321, 1 active sessions
Control message authentication is on, 2 secrets configured
Last message authenticated with first digest secret
!
! The output below displays control channel password information for a tunnel which has
! only a single control channel authentication password configured.
!
Tunnel id 23456 is up, remote id is 65432, 1 active sessions
!
Control message authentication is on, 1 secrets configured
Last message authenticated with first digest secret
!
! The output below displays control channel password information for a tunnel which is
! communicating with a peer that has only the new control channel authentication password ! configured.
!
Tunnel id 56789 is up, remote id is 98765, 1 active sessions
!
Control message authentication is on, 2 secrets configured
Last message authenticated with second digest secret

Example: Configuring a Pseudowire Class for Fragmentation of IP Packets

The following is a sample configuration of a pseudowire class that will allow IP traffic generated from the CE device to be fragmented before entering the pseudowire: 

pseudowire class class1
 encapsulation l2tpv3
 ip local interface Loopback0
 ip pmtu
 ip dfbit set

Example: Configuring Protocol Demultiplexing for L2TPv3

The following example shows how to configure the L2TPv3 Protocol Demultiplexing feature on IPv4 PE devices. The PE devices facing the IPv6 network do not require the IPv6 configuration. 

interface ethernet 0/1
 ip address 172.16.128.4
 xconnect 10.0.3.201 888 pw-class demux
  match protocol ipv6

Example: Manually Clearing an L2TPv3 Tunnel

The following example demonstrates how to manually clear a specific L2TPv3 tunnel using the tunnel ID: 

clear l2tun tunnel 65432

Example: Configuring an L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations

The following example shows how to configure an Ethertype other than 0x8100 on Gigabit Ethernet interfaces with QinQ or dot1Q encapsulations. In this example, the Ethertype field is set to 0x9100 on Gigabit Ethernet interface 1/0/0. 

Device> enable
Device# configure terminal
Device(config)# interface gigabitethernet 1/0/0
Device(config-if)# dot1q tunneling ethertype 0x9100

Example: Configuring an L2TPv3 HDLC Like-to-Like Layer 2 Transport

Example: Configuring an L2TPv3 HDLC Like-to-Like Layer 2 Transport on Dynamic Mode

The following example shows how to configure xconnect on a serial interface with HDLC encapsulation on a dynamic mode. The dynamic mode uses L2TPv3 signaling in control channel to set up the L2TPv3 tunnel. 

pseudowire-class 774
 encapsulation l2tpv3
 protocol l2tpv3
 ip local interface GigabitEthernet0/0/1.774
!
interface Serial0/2/0:0
 no ip address
 xconnect 4.4.4.4 200 pw-class 774

Example: Configuring an L2TPv3 HDLC Like-to-Like Layer 2 Transport on Static Mode

The following example shows how to configure xconnect on a serial interface with HDLC encapsulation on a static mode. The static mode is used to disable signaling in the L2TPv3 control channel. Since signaling is disabled, you must specify the manual option in xconnect and configure L2TP-specific parameters to complete the L2TPv3 control channel configuration. 

pseudowire-class pe1-ether-pw
 encapsulation l2tpv3
 protocol none
 ip local interface Loopback1
!
interface Serial0/2/0:0
 no ip address
 xconnect 2.2.2.2 50 encapsulation l2tpv3 manual pw-class pe1-ether-pw
  l2tp id 111 111
  l2tp cookie local 4 54321
  l2tp cookie remote 4 12345

Example: Configuring GEC over L2TPv3

The following is a sample configuration of Gigabit EtherChannel (GEC) over Layer 2 Tunneling Protocol Version 3 (L2TPv3): 

Device> enable
Device# configure terminal
Device(config)# interface Loopback0
Device(config-if)# ip address 10.1.0.1 255.255.255.255
Device(config-if)# exit
Device(config)# pseudowire-class l2tpv3
Device(config-pw)# encapsulation l2tpv3
Device(config-pw)# ip local interface loopback0
Device(config-if)# exit
Device(config)# interface port-channel 1
Device(config-if)# xconnect 1.1.1.1 1234 encapsulation l2tpv3 pw-class l2tpv3 
Device(config-if)# exit
Device(config)# interface g0/0/0
Device(config-if)# channel-group 1
Device(config-if)# end

Example: Configuring GEC with Dot1q over L2TPv3

The following is a sample configuration of a Gigabit EtherChannel (GEC) with dot1q over Layer 2 Tunneling Protocol Version 3 (L2TPv3): 

Device> enable
Device# configure terminal
Device(config)# interface port-channel 1
Device(config-if)# interface port-channel 1.1
Device(config-subif)# encapsulation dot1q 100
Device(config-subif)# xconnect 10.0.0.2 1234 encapsulation l2tpv3 pw-class l2tpv3  
Device(config-subif)# end

Example: Configuring GEC with QinQ over L2TPv3

The following is a sample configuration of a Gigabit EtherChannel (GEC) with queue-in-queue (QinQ) over Layer 2 Tunneling Protocol Version 3 (L2TPv3): 

Device> enable
Device# configure terminal
Device(config)# interface port-channel 1
Device(config-if)# interface port-channel 1.1
Device(config-subif)# encapsulation dot1q 100 second-dot1q 200
Device(config-subif)# xconnect 10.0.0.3 1234 encapsulation l2tpv3 pw-class l2tpv3  
Device(config-subif)# end

Additional References

Related Documents

Related Topic

Document Title

Cisco IOS commands

Master Commands List, All Releases

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

Wide-Area Networking Command Reference

Layer 2 Tunnel Protocol Version 3

Layer 2 Tunneling Protocol Version 3

Any Transport over MPLS

Any Transport over MPLS

Cisco 12000 series routers hardware support

Cross-Platform Release Notes for Cisco IOS Release 12.0S

Cisco 7600 series routers hardware support

Cross-Platform Release Notes for Cisco IOS Release 12.2SR

Cisco 3270 series routers hardware support

Release Notes for Cisco IOS Software Release 12.2SE

Standards and RFCs

Standard/RFC

Title

draft-ietf-l2tpext-l2tp-base-03.txt

Layer Two Tunneling Protocol (Version 3) 'L2TPv3'

draft-martini-l2circuit-trans-mpls-09.txt

Transport of Layer 2 Frames Over MPLS

draft-ietf-pwe3-frame-relay-03.txt.

Encapsulation Methods for Transport of Frame Relay over MPLS Networks

draft-martini-l2circuit-encap-mpls-04.txt.

Encapsulation Methods for Transport of Layer 2 Frames Over IP and MPLS Networks

draft-ietf-pwe3-ethernet-encap-08.txt.

Encapsulation Methods for Transport of Ethernet over MPLS Networks

draft-ietf-pwe3-hdlc-ppp-encap-mpls-03.txt.

Encapsulation Methods for Transport of PPP/HDLC over MPLS Networks

draft-ietf-ppvpn-l2vpn-00.txt.

An Architecture for L2VPNs

MIBs

MIBs

MIBs Link

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

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

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 Layer 2 Tunneling Protocol Version 3

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 www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 3. Feature Information for Layer 2 Tunneling Protocol Version 3

Feature Name

Releases

Feature Information

Layer 2 Tunneling Protocol Version 3

XE 2.6

XE 2.6.2

XE 3.3S

XE 3.11S

The Layer 2 Tunneling Protocol Version 3 (L2TPv3) feature expands Cisco's support of Layer 2 VPNs.

In Cisco IOS XE Release 2.6, the following features were added:

  • Ethernet over L2TPv3

  • Layer 2 VPN (L2VPN): Syslog, SNMP Trap, and show Command Enhancements for AToM and L2TPv3

  • L2TPv3 Control Message Hashing

  • L2TPv3 Control Message Rate Limiting

  • L2TPv3 Digest Secret Graceful Switchover

  • L2TPv3 Protocol Demultiplexing

  • L2TPv3 Custom Ethertype for Dot1q and QinQ Encapsulations

In Cisco IOS XE Release 2.6.2, support was added for the ip pmtu command.

In Cisco IOS XE Release 3.3S, support for HDLC over L2TPv3 was added.

The following commands were introduced or modified: clear l2tun , debug vpdn , ip pmtu , l2tp cookie local , l2tp cookie remote l2tp hello , l2tp id , and xconnect .

Glossary

AV pairs —Attribute-value pairs.

CEF —Cisco Express Forwarding. The Layer 3 IP switching technology that optimizes network performance and scalability for networks with large and dynamic traffic patterns.

data-link control layer —Layer 2 in the SNA architectural model. Responsible for the transmission of data over a particular physical link. Corresponds approximately to the data link layer of the OSI model.

DCE —Data circuit-terminating equipment (ITU-T expansion). Devices and connections of a communications network that comprise the network end of the user-to-network interface.

DF bit —Don’t Fragment bit. The bit in the IP header that can be set to indicate that the packet should not be fragmented.

DTE —Data terminal equipment. The device at the user end of a user-network interface that serves as a data source, destination, or both.

HDLC —High-Level Data Link Control. A generic link-level communications protocol developed by the ISO. HDLC manages synchronous, code-transparent, serial information transfer over a link connection.

ICMP —Internet Control Message Protocol. A network protocol that handles network errors and error messages.

IDB — Interface descriptor block.

IS-IS —Intermediate System-to-Intermediate System. The OSI link-state hierarchical routing protocol based on DECnet Phase V routing, whereby ISs (devices) exchange routing information based on a single metric to determine network topology.

L2TP —An extension to PPP that merges features of two tunneling protocols: Layer 2 Forwarding (L2F) from Cisco Systems and Point-to-Point Tunneling Protocol (PPTP) from Microsoft. L2TP is an IETF standard endorsed by Cisco Systems and other networking industry leaders.

L2TPv3 —The draft version of L2TP that enhances functionality in RFC 2661 (L2TP).

LMI —Local Management Interface.

MPLS —Multiprotocol Label Switching. A switching method that forwards IP traffic using a label. This label instructs the devices in the network where to forward packets based on preestablished IP routing information.

MQC —Modular quality of service CLI.

MTU —Maximum Transmission Unit. The maximum packet size, in bytes, that a particular interface can handle.

PMTU —Path MTU.

PVC —Permanent virtual circuit. A virtual circuit that is permanently established. A Frame Relay logical link, whose endpoints and class of service are defined by network management. Analogous to an X.25 permanent virtual circuit, a PVC consists of the originating Frame Relay network element address, originating data-link control identifier, terminating Frame Relay network element address, and termination data-link control identifier. Originating refers to the access interface from which the PVC is initiated. Terminating refers to the access interface at which the PVC stops. Many data network customers require a PVC between two points. PVCs save the bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time. Data terminating equipment with a need for continuous communication uses PVCs.

PW —Pseudowire.

SNMP —Simple Network Management Protocol. The network management protocol used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices and manage configurations, statistics collection, performance, and security.

tunneling —Architecture that is designed to provide the services necessary to implement any standard point-to-point encapsulation scheme.

UNI —User-Network Interface.

VPDN —Virtual private dialup network. A network that allows separate and autonomous protocol domains to share common access infrastructure, including modems, access servers, and ISDN devices. A VPDN enables users to configure secure networks that take advantage of ISPs that tunnel remote access traffic through the ISP cloud.