basic-mpls-configuration-guide-mpls-router-id.pdf

8/16/2019 BASIC-MPLS-Configuration-Guide-MPLS-Router-ID.pdf

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BASIC MPLS - Router-ID

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 asfollows:

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 isselected 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 ofthe 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 thenext 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.


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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 theinterface. This forced change in the LDP router ID tears down any existingLDP 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, releaseslabel bindings learned via the LDP sessions, and interrupts MPLS

forwarding activity associated with the bindings.

MPLS Router-IDNetStepByStep-R2(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 ofthis 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 thisinterface.

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).



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A request can specify that the entire database be displayed, or that the display belimited 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 entireLIB.

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


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

Video Cheat Sheet

R2

conf t

mpls ldp router-id loopback 0 force

basic-mpls-configuration-guide-mpls-router-id.pdf

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