Re: [nsp] ICMP Unreachable and CEF

From: Hank Nussbacher (
Date: Thu Jan 24 2002 - 04:25:00 EST

At 11:21 AM 24-01-02 +0200, Elijah Kagan wrote:
>I always thought that when a router forwards packets to Null0 it also
>generates ICMP Unreachable message to indicate this event. It seems that
>this is not the case on routers running CEF. I checked this on several
>platforms: 7500, 7200 and 3600. Whenever CEF is turned off I see those
>unreachables pouring in, with CEF on - nothing.
>Is this the expected behavior? Can anyone expand on this issue?

Hmmm. Try to make sure ICMP unreachables are "forced":

interface null0
ip unreachables

If still not, that is indeed weird and perhaps a bug.


>-- elijah
>P.S. I am running 12.0(x)S on 7200 and 7500.

This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:13:29 EDT