Configure CSPF Interface Constraint

Under the default condition, hops configured as interface addresses in an LSP path are resolved to the router ID.

An LSP can be configured that does not traverse a specified interface. The cspf-interface-constraint command forces the CSPF calculation to include any specified interface when creating an LSP.

To configure the device to always include a specified interface when forming an LSP, complete the following steps.

Configure the device.
```
device# configure
```
Enable the MPLS router.
```
device(config)# router mpls
```
Enable MPLS policy parameter configuration.
```
device(config-router-mpls)# policy
```

Configure interface IP address for CSPF computation.

device(config-router-mpls-policy)# cspf-interface-constraint

Example

The following example shows configuration of the device to always include a specified interface when forming an LSP.

device# configure
device(config)# router mpls
device(config-router-mpls)# policy
device(config-router-mpls-policy)# cspf-interface-constraint

The CSPF interface constraint feature may be dynamically turned on or off. Turning the feature off or on has no effect on LSPs that have already been established (primary and secondary). For LSPs that are currently retried, changing the constraint setting changes the behavior on the next retry such as when an LSP whose path is configured to use that interface fails to come up due to an interface down condition.

Note

The CSPF interface Constraint feature has significance for the ingress node only, where the CSPF calculation takes place for an LSP or a detour segment.