Traceroute

[alexanderc]

In the output of a traceroute is the IP address listed for that hop the address of the interface that the packet was received on or the address of the source interface that the router used for the return packet back to the traceroute source ?

Thanks

[pkhatri]

Hi,

It's the latter - the address of the source interface that the router used for the return packet back to the traceroute source.

Hope that helps - pls do remember to rate posts that help.

Paresh

[pkhatri]

You will find that the two addresses you mentioned will be different in scenarios where asymmetric routing is taking place so that the path from the original sender to the receiver is different to that from the receiver to the original sender.

Hope that helps - pls do remember to rate posts that help.

Paresh

[alexanderc]

Thats what i thought.

Thanks

[mheusinger]

Hello,

just as a side note: in an MPLS VPN environment a P router will use the address of the interface a labeled packet was received as source address. The reason is, that the ICMP packet might be label switched down the original LSP and thus the outgoing interface is NOT pointing towards the original source.

The details about this behaviour are spread across RFC3032, RFC3443, and an expired (?!) draft "ICMP Extensions for MPLS".

Hope this helps! Please rate all posts.

Regards, Martin