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This chapter describes how to configure IP tunnels.
Your software release might not support all the features documented in this module. For the latest caveats and feature information, see the Bug Search Tool at https://tools.cisco.com/bugsearch/ and the release notes for your 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 "New and Changed Information"chapter or the Feature History table in this chapter.
This table includes only the updates for those releases that have resulted in additions or changes to the feature.
|
Feature Name |
Release |
Feature Information |
|---|---|---|
|
GRE tunnels |
7.3(0)DX(1) |
Support for M3 Series modules was added. |
|
GRE tunnels |
6.2(10) |
Support for F3 Series modules was added. |
|
Support for tunnel and its transport in different VRFs |
6.1(1) |
This feature was introduced. |
|
IP tunnels in VDC and VRF other than default |
4.2(1) |
This feature was introduced. |
|
IP tunnels |
4.0(1) |
This feature was introduced. |
IP tunnels can encapsulate a same-layer or higher layer protocol and transport the result over IP through a tunnel created between two devices.
IP tunnels consists of the following three main components:
Passenger protocol—The protocol that needs to be encapsulated. IPv4 is an example of a passenger protocol.
Carrier protocol—The protocol that is used to encapsulate the passenger protocol. Cisco NX-OS supports GRE as a carrier protocol.
Transport protocol—The protocol that is used to carry the encapsulated protocol. IPv4 is an example of a transport protocol.
An IP tunnel takes a passenger protocol, such as IPv4, and encapsulates that protocol within a carrier protocol, such as GRE. The device then transmits this carrier protocol over a transport protocol, such as IPv4.
You configure a tunnel interface with matching characteristics on each end of the tunnel.
You must enable the tunnel feature before you can see configure it. From Cisco NX-OS Release 4.2, the system automatically takes a checkpoint prior to disabling the feature, and you can roll back to this checkpoint. See the Cisco Nexus 7000 Series NX-OS System Management Configuration GuideCisco Nexus 7000 Series NX-OS System Management Configuration Guide for information about rollbacks and checkpoints.
 Note |
From Cisco NX-OS Release 5.1(1), the software supports multicasting over GRE tunnels. |
You can use generic routing encapsulation (GRE) as the carrier protocol for a variety of passenger protocols.
The figure below shows the IP tunnel components for a GRE tunnel. The original passenger protocol packet becomes the GRE payload and the device adds a GRE header to the packet. The device then adds the transport protocol header to the packet and transmits it.
Path maximum transmission unit (MTU) discovery (PMTUD) prevents fragmentation in the path between two endpoints by dynamically determining the lowest MTU along the path from the packet's source to its destination. PMTUD reduces the send MTU value for the connection if the interface receives information that the packet would require fragmentation.
When you enable PMTUD, the interface sets the Don't Fragment (DF) bit on all packets that traverse the tunnel. If a packet that enters the tunnel encounters a link with a smaller MTU than the MTU value for the packet, the remote link drops the packet and sends an ICMP message back to the sender of the packet. This message indicates that fragmentation was required (but not permitted) and provides the MTU of the link that dropped the packet.
Note |
PMTUD on a tunnel interface requires that the tunnel endpoint can receive ICMP messages generated by devices in the path of the tunnel. Check that ICMP messages can be received before using PMTUD over firewall connections. Cisco NX-OS software disables ICMP unreachable messages by default. ICMP unreachable messages can be enabled in the Cisco NX-OS software using the ip unreachables interface command. |
From Cisco NX-OS Release 4.2, you can configure tunnels in a nondefault VDC and a nondefault VRF. A tunnel configured in one VDC is isolated from a tunnel with the same number configured in another VDC. For example, Tunnel 0 in VDC 1 is independent of tunnel 0 in VDC 2.
Before Cisco NX-OS Release 6.1(1), a tunnel interface and tunnel transport should be in the same VRF. See the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide for information about VDCs and see the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration GuideCisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide for information about VRFs.
IP tunnels support stateful restarts. A stateful restart occurs on a supervisor switchover. After the switchover, Cisco NX-OS applies the runtime configuration after the switchover.
IP tunnels have the following prerequisites:
You must be familiar with TCP/IP fundamentals to configure IP tunnels.
You are logged on to the switch.
You must enable the tunneling feature in a device before you can configure and enable any IP tunnels.
IP tunnels have the following configuration guidelines and limitations:
Cisco NX-OS supports the GRE header defined in IETF RFC 2784. Cisco NX-OS does not support tunnel keys and other options from IETF RFC 1701.
Tunnels are supported only on the M Series cards on Cisco Nexus 7000 Series platforms.
Cisco NX-OS does not support the Web Cache Control Protocol (WCCP) on tunnel interfaces.
Tunnel features are supported only on M series and F3 series modules on Cisco Nexus 7000 Series and Cisco Nexus 7700 Series platforms.
Cisco NX-OS does not support GRE tunnel keepalives.
When the tunnelled (encapsulated) traffic is forwarded to the same interface from where the traffic was originally received (unencapsulated), make ensure that the IP redirects are disabled using the no ip redirects command.
IPv6 as a carrier or a passenger/transport protocol is not supported in GRE Tunnels.
|
Parameter |
Default |
|---|---|
|
Path MTU discovery age timer |
10 minutes |
|
Path MTU discovery minimum MTU |
64 |
|
Tunnel feature |
Disabled |
Configuring IP Tunnels
You must enable the tunneling feature before you can configure any IP tunnels.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch# configure terminal |
Enters global configuration mode. |
|
Step 2 |
switch(config)# feature tunnel |
Allows the creation of a new tunnel interface. To disable the tunnel interface feature, use the no form of this command. |
|
Step 3 |
(Optional) switch(config)# show feature |
(Optional)
Displays information about the features enabled on the device. |
|
Step 4 |
(Optional) switch(config)# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
From Cisco NX-OS Release 6.1 and later releases, you can configure the tunnel source and the tunnel destination in different VRFs. Ensure that you have enabled the tunneling feature.
You can create a tunnel interface and then configure this logical interface for your IP tunnel.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch# configure terminal |
Enters global configuration mode. |
|
Step 2 |
switch(config)#interface tunnel number |
Creates a new tunnel interface. |
|
Step 3 |
switch(config-if)# tunnel source {ip-address | interface-name} |
Configures the source address for this IP tunnel. |
|
Step 4 |
switch(config-if)# tunnel destination {ip-address | host-name} |
Configures the destination address for this IP tunnel. |
|
Step 5 |
switch(config-if)# tunnel use-vrf vrf-name |
Uses the configured VRF to look up the tunnel IP destination address. |
|
Step 6 |
(Optional) switch(config-if)# show interfaces tunnel number |
(Optional)
Displays the tunnel interface statistics. |
|
Step 7 |
(Optional) switch(config-if)# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
Use the no interface tunnel command to remove the tunnel interface and all associated configuration.
|
Command |
Purpose |
|---|---|
|
no interface tunnel number |
Deletes the tunnel interface and the associated configuration. |
You can configure the following optional parameters to tune the tunnel in interface configuration mode:
|
Command |
Purpose |
|---|---|
|
description string |
Configures a description for the tunnel. |
|
mtu value |
Sets the MTU of IP packets sent on an interface. |
|
tunnel ttl value |
Sets the tunnel time-to-live value. The range is from 1 to 255. |
switch# configure terminal
switch(config)# interface tunnel 1
switch(config-if)# tunnel source ethernet 1/2
switch(config-if)# tunnel destination 192.0.2.1
switch(config-if)# copy running-config startup-configYou can set a tunnel interface to GRE tunnel mode.
Ensure that you have enabled the tunneling feature.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch# configure terminal |
Enters global configuration mode. |
|
Step 2 |
switch(config)# interface tunnel number |
Creates a new tunnel interface. |
|
Step 3 |
switch(config-if)# tunnel mode gre ip |
Sets this tunnel mode to GRE. |
|
Step 4 |
(Optional) switch(config-if)# show interfaces tunnel number |
(Optional)
Displays the tunnel interface statistics. |
|
Step 5 |
(Optional) switch(config-if)# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
Use the tunnel path-mtu discovery command to enable path MTU discovery on a tunnel.
|
Command |
Purpose |
|---|---|
|
tunnel path-mtu-discovery [age-timer min] [min-mtu bytes] |
|
You can add a tunnel interface to a VRF.
Ensure that you have enabled the tunneling feature.
Before you configure this feature for the entire system, ensure that you are in the correct VDC. To change the VDC, use the switchto vdc command.
Assign the IP address for a tunnel interface after you have configured the interface for a VRF.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
switch# configure terminal |
Enters global configuration mode. |
|
Step 2 |
switch(config)# interface tunnel number |
Enters interface configuration mode. |
|
Step 3 |
switch(config-if)# vrf member vrf-name |
Adds this interface to a VRF. |
|
Step 4 |
switch(config-vrf)# ip address ip-prefix/length |
Configures an IP address for this interface. You must do this step after you assign this interface to a VRF. |
|
Step 5 |
(Optional) switch(config-vrf)# show vrf [vrf-name] interface interface-type number |
(Optional)
Displays VRF information. |
|
Step 6 |
(Optional) switch(config-vrf)# copy running-config startup-config |
(Optional)
Copies the running configuration to the startup configuration. |
switch# configure terminal
switch(config)# interface tunnel 0
switch(config-if)# vrf member RemoteOfficeVRF
switch(config-if)# ip address 209.0.2.1/16
switch(config-if)# copy running-config startup-configThese examples show a simple GRE tunnel. Ethernet 1/2 is the tunnel source for router A and the tunnel destination for router B. Ethernet interface 2/1 is the tunnel source for router B and the tunnel destination for router A.
feature tunnel
interface tunnel 0
ip address 209.165.20.2/8
tunnel source ethernet 1/2
tunnel destination 192.0.2.2
tunnel mode gre ip
tunnel path-mtu-discovery 25 1500
interface ethernet1/2
ip address 192.0.2.55/8
feature tunnel
interface tunnel 0
ip address 209.165.20.1/8
tunnel source ethernet2/1
tunnel destination 192.0.2.55
tunnel mode gre ip
interface ethernet 2/1
ip address 192.0.2.2/8Use one of the following commands to verify IP tunnel configuration information:
|
Command |
Purpose |
|---|---|
|
show interface tunnel number |
Displays the configuration for the tunnel interface (MTU, protocol, transport, and VRF). Displays input and output packets, bytes, and packet rates. |
|
show interface brief | include Tunnel |
Displays the operational status, IP address, encapsulation type, and MTU of the tunnel interface. |
|
show interface tunnel number description |
Displays the configured description of the tunnel interface. |
|
show interface tunnel number status |
Displays the operational status of the tunnel interface. |
|
show interface tunnel number status err-disabled |
Displays the error disabled status of the tunnel interface. |
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