MPLS Configuration Tasks

This topic describes the mandatory MPLS configuration tasks and those that are optional.

MPLS Configuration Tasks

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Mandatory:

• Enable CEF switching.

• Configure TDP or LDP on every label-enabled interface.

Optional:

• Configure the MPLS ID.

• Configure MTU size for labeled packets.

• Configure IP TTL propagation.

• Configure conditional label advertising.

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MPLS V2.0-3-4

To enable MPLS, you must first enable CEF switching. Depending on the Cisco IOS software version, you may need to establish the range for the label pool.

You must enable Tag Distribution Protocol (TDP) or Label Distribution Protocol (LDP) on the interface by using either tag switching or label switching.

Optionally, the maximum size of labeled packets may be changed.

By default, the TTL field is copied from the IP header and placed in the MPLS label when a packet enters an MPLS network. To prevent core routers from responding with (Internet Control Message Protocol [ICMP]) TTL exceeded messages, disable TTL propagation. If TTL propagation is disabled, the value in the TTL field of the label is 255.

Note Ensure that all routers have TTL propagation either enabled or disabled. If TTL is enabled in some routers and disabled in others, the result may be that a packet leaving the MPLS domain will have a larger TTL value than when it entered.

By default, a router will generate and propagate labels for all networks that it has in the routing table. If label switching is required for only a limited number of networks (for example, only for router loopback addresses), configure the conditional label advertising.

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