You must have a router ID for the neighbor router being linked in order to configure discovery for the local router.

A stable router ID is required at either end of the link to ensure the link will be successful. If you do not assign a router ID to the routers, the system will default to the global router ID. Default router IDs are subject to change causing an unstable link.

Configuration

If the mpls ldp router-id command is not executed, the LDP router ID is determined as follows:

1. The IP addresses of all operational interfaces are examined.

2. If these IP addresses include loopback interface addresses, the largest such loopback address is selected as the LDP router ID.

3. Otherwise, the largest IP address pertaining to an operational interface is selected as the LDP router ID.

The normal (default) method for determining the LDP router ID may result in a router ID that is not usable in certain situations. For example, an IP address selected as the LDP router ID might not be advertisable by the routing protocol to a neighboring router. The mpls ldp router-id command provides a means for specifying an interface whose IP address is to be used as the LDP router ID. The specified interface must be operational for its IP address to be used as the LDP router ID.

When executed without the force keyword, the mpls ldp router-id command modifies the method for determining the LDP router ID by causing selection of the IP address of the specified interface argument (provided that the interface is operational) the next time it is necessary to select an LDP router ID. The effect of the command is delayed until the next time it is necessary to select an LDP router ID, which is typically the next time the interface whose address is the current LDP router ID is shut down or the address itself is not configured.

When executed with the force keyword, the effect of the mpls ldp router-id command depends on the current state of the specified interface:

a. If the interface is up (operational) when the mpls ldp router-id force command is issued and if its IP address is not currently the LDP router ID, the LDP router ID is forcibly changed to the IP address of the interface. This forced change in the LDP router ID tears down any existing LDP sessions, releases label bindings learned via the LDP sessions, and interrupts MPLS forwarding activity associated with the bindings.

b. If the interface is down (not operational) when the mpls ldp router-id force command is issued, when the interface transitions to up, the LDP router ID is forcibly changed to the IP address of the interface. This forced change in the LDP router ID tears down any existing LDP sessions, releases label bindings learned via the LDP sessions, and interrupts MPLS forwarding activity associated with the bindings.

MPLS Router-ID

R1(config)# mpls ldp router-id loopback 0 force

* Use to specify a preferred interface for the Label Distribution Protocol (LDP) router ID.

* Use this command in global configuration mode.

* To disable the interface from being used as the LDP router ID, use the no form of this command.

Verification

# show mpls ldp neighbor

* Use to display the status of Label Distribution Protocol (LDP) sessions * Use this command in privileged EXEC mode. * Use the keyword address to identify the neighbor with this IP address. * Use the keyword interface to define the LDP

neighbors accessible over this interface.

* This command displays information about all LDP neighbors if no optional keywords or arguments are specified.

# show mpls ldp bindings

* Use to display the contents of the label information base (LIB). * Use this command in privileged EXEC mode. * A request can specify that the entire database be displayed, or that the display be limited to a subset of entries according to the Prefix, Input or output label values or ranges and Neighbor advertising the label. * If no optional keyword or argument is supplied, the command displays the entire LIB.

# show mpls interfaces

* Use to display information about interfaces on which MPLS is enabled.

Troubleshoot

# debug mpls

* To display debugging information about MPLS VPN MIB, use the debug mpls vpn command in EXEC mode. * To disable debugging, use the no form of this command.

# debug mpls ldp peer state-machine

* Use to display information about state transitions for label distribution protocol (LDP) sessions.

* Use this command in privileged EXEC mode.

* To disable this feature, use the no form of this command.

# debug mpls ldp messages sent

* To display specific information (such as message type, source, and destination) regarding label distribution protocol (LDP) messages sent to and received from LDP peers

* Use this command in privileged EXEC mode.

* To disable this feature, use the no form of this command.