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Configuring ICMP Message Tunneling

When you configure MPLS to tunnel through a routing domain, it is difficult to route a fragmented packet to its source address; for example, when the IP addresses carried in a packet are private (not globally unique) and MPLS is used to tunnel the packets through a public backbone.

When you configure ICMP message tunneling, an Internet Control Message Protocol (ICMP) message is sent to the source of a packet. The label stack is copied from the original packet to the ICMP message. The ICMP message is then label switched across the network. This causes the message to go to the original packet destination, rather than its source. Unless the message is label switched all the way to the destination host, it ends up unlabeled in a router that does know the source of the original packet, at which point the message is sent in the proper direction.

ICMP message tunneling can be useful for debugging and tracing purposes if the message is an ICMP time exceeded message.

To configure ICMP message tunneling, include the icmp-tunneling statement:




icmp-tunneling;

You can include this statement at the following hierarchy levels:

[edit protocols mpls]
[edit logical-systems logical-system-name protocols mpls]

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