Configuring MPLS TE Forwarding Adjacency

---

This chapter describes how to configure Multiprotocol Label Switching (MPLS) traffic engineering (TE) forwarding adjacency on Cisco NX-OS devices.

This chapter includes the following sections:

• Finding Feature Information, page 17-242
• Information About MPLS TE Forwarding Adjacency, page 17-242
• Licensing Requirements for MPLS TE Forwarding Adjacency, page 17-243
• Prerequisites for MPLS TE Forwarding Adjacency, page 17-243
• Guidelines and Limitations for MPLS TE Forwarding Adjacency, page 17-244
• Default Settings for MPLS TE Forwarding Adjacency, page 17-244
• Configuring MPLS TE Forwarding Adjacency, page 17-244
• Verifying the MPLS TE Forwarding Adjacency Configuration, page 17-245
• Configuration Example for MPLS TE Forwarding Adjacency, page 17-246
• Additional References for MPLS TE Forwarding Adjacency, page 17-247
• Feature History for MPLS TE Forwarding Adjacency, page 17-247

Finding Feature Information

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 below.

Information About MPLS TE Forwarding Adjacency

MPLS TE forwarding adjacency allows you to handle a TE label-switched path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network that is based on the Shortest Path First (SPF) algorithm. Both Intermediate System-to-Intermediate System (IS-IS) and Open Shortest Path First (OSPF) are supported as the IGP.

A forwarding adjacency can be created between switches regardless of their location in the network. The switches can be located multiple hops from each other, as shown in Figure 17-1.

Figure 17-1 Forwarding Adjacency Topology

As a result, a TE tunnel is advertised as a link in an IGP network with the tunnel’s cost associated with it.

Switches outside of the TE domain see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.

TE tunnel interfaces are advertised in the IGP network just like any other links. Switches can then use these advertisements in their IGPs to compute the SPF even if they are not the headend of any TE tunnels.

Licensing Requirements for MPLS TE Forwarding Adjacency

Prerequisites for MPLS TE Forwarding Adjacency

Forwarding adjacency has the following prerequisites:

• You must enable the MPLS TE feature. See the “Configuring MPLS TE”.

Guidelines and Limitations for MPLS TE Forwarding Adjacency

Forwarding adjacency has the following configuration guidelines and limitations:

• Forwarding adjacency increases the size of the IGP database by advertising a TE tunnel as a link.
• When you enable forwarding adjacency on a TE tunnel, the link is advertised in the IGP network as a type, length, value (TLV) 22 object without any TE sub-TLV.
• You must configure MPLS TE forwarding adjacency tunnels bidirectionally.
• You cannot configure MPLS TE over the logical generic routing encapsulation (GRE) tunnel interface.

Note If both forwarding adjacency and autoroute announce are configured on a link, forwarding adjacency takes precedence. The autoroute configuration takes effect automatically if the forwarding adjacency configuration is removed, but not if the forwarding adjacency path fails.

Default Settings for MPLS TE Forwarding Adjacency

Table 17-1 lists the default settings for forwarding adjacency.

Configuring MPLS TE Forwarding Adjacency

You can configure a tunnel interface for an MPLS TE forwarding adjacency.

Note You must configure a forwarding adjacency on two LSP tunnels bidirectionally from A to B and B to A. Otherwise, the forwarding adjacency is advertised but not used in the IGP network.

Verifying the MPLS TE Forwarding Adjacency Configuration

To display the MPLS TE forwarding adjacency configuration, perform one of the following tasks:

For detailed information about the fields in the output from these commands, see the Cisco NX-OS MPLS Command Reference.

Configuration Example for MPLS TE Forwarding Adjacency

The following example shows how to configure a TE tunnel interface with forwarding adjacency and an IS-IS metric:

Note If both the forwarding adjacency command and the autoroute announce command appear in your configuration, the forwarding adjacency command takes precedence.

In Figure 17-2, if you have no forwarding adjacencies configured for the TE tunnels between B and F, and C and F, all the traffic that A must forward to F goes through B because B is the shortest path from A to F. (The cost from A to F is 15 through B and 20 through C.)

Figure 17-2 Using Forwarding Adjacencies

If you have forwarding adjacencies configured on the TE tunnels between B and F and C and F and also on the TE tunnels between F and B, and F and C, then when A computes the SPF algorithm, A sees two equal cost paths of 11 to F. As a result, traffic across the A–B and A–C links is shared.

Additional References for MPLS TE Forwarding Adjacency

For additional information related to the Forwarding Adjacency feature, see the following sections:

• Related Documents, page 17-247
• MIBs, page 17-247

Feature History for MPLS TE Forwarding Adjacency

Table 17-2 lists the release history for this feature.