[AusNOG] ICMP weirdness inside Internode's network

Lincoln Dale ltd at cisco.com
Fri Oct 28 17:37:28 EST 2011

On 28/10/2011, at 1:52 PM, Julien Goodwin wrote:
> My first guess is just broken ICMP handling inside MPLS tunnels, but without
> knowledge of Internode's network internals I can't make an intelligent suggestion.

not likely anything broken, more likely you ran the traceroute at a time when a lot of other people also happened to be running a trace route or something else which elicited ICMP responses from the router(s) in question.

in short, ICMP responses are ALWAYS rate limited to some sane packet/sec level by routers (pick your router vendor, they all do this).

its sort of in the same bucket as "why its not meaningful to ping a router" to determine round-trip.
a. the router control plane responses to that, not whatever the data plane, b. it often does it when it feels like it, i.e. low priority task,



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