# Configuring IS-IS for MPLS

IS-IS has several commands to provide support for MPLS. See JunosE BGP and MPLS Configuration Guide, for a detailed discussion of MPLS. If you configure your tunnel with the tunnel mpls autoroute announce isis command, MPLS attempts to register the tunnel endpoint with IS-IS. You must enable this registration with IS-IS by issuing the mpls traffic-eng command.

When you configure a node as the downstream endpoint of an LSP, you must provide a stable interface as the router ID for the endpoint. Typically you select a loopback interface because of its inherent stability. Use the mpls traffic-eng router-id command to specify the router ID.

By default, IS-IS always uses the MPLS tunnel to reach the MPLS endpoint. Best paths determined by IS-IS SPF calculations are not considered. You can enable the consideration of best paths by issuing the mpls spf-use-any-best-path command. As a result, IS-IS considers metrics for IGP paths and the tunnel metric, and might forward traffic along a best path, through the MPLS tunnel, or both.

Several show commands enable monitoring of MPLS information. See Monitoring IS-IS for more information.

MPLS traffic engineering requires that IS-IS generate the new-style TLVs that enable wider metrics. Use the metric-style wide command to generate the new-style TLVs. If you are using some IS-IS routers that still do not understand the new-style TLVs, use the metric-style transition command. See Extensions for Traffic Engineering and Configuring Global IS-IS Parameters for detailed information about using the metric-style commands.

mpls spf-use-any-best-path

- Use to enable SPF calculations to consider the IGP (IS-IS) best paths as well as the MPLS tunnel for forwarding traffic to the MPLS endpoint.
- By default, the MPLS tunnel is always selected for traffic to the tunnel endpoint; IGP paths are not considered. For traffic beyond the endpoint, the tunnel is considered equally with any other path.
- Example
  host1(config-router)#mpls spf-use-any-best-path
- Use the no version to disable the use of IGP best paths.
- See mpls spf-use-any-best-path

mpls traffic-eng

- Use to enable flooding of MPLS traffic engineering link information into the specified IS-IS level. Flooding is disabled by default.
- Example
  host1(config-router)#mpls traffic-eng level-1
- Use the no version to disable flooding.
- See mpls traffic-eng

mpls traffic-eng router-id

- Use to specify a very stable interface to be used as a router ID for MPLS traffic engineering. Typically you specify a loopback interface to provide the greatest stability, because this is flooded to all nodes. The interface acts as the destination node for tunnels originating at other nodes.
- Example
  host1(config-router)#mpls traffic-eng router-id loopback 0
- Use the no version to remove the interface as a router ID.
- See mpls traffic-eng router-id