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Re: Simple? Question...

  • From: John Hawkinson
  • Date: Mon Feb 07 13:06:28 2000

> Can someone please tell me what I need to do in order to have secondary
> interfaces on a Cisco report themselfs as the alias IP rather than the
> primary interface IP address in a traceroute?

This is a confusing way to state the question...it implies some
standard for what it means to "report oneself as an alias IP," and I
think you will find that there is no standard interpretation of that
language.

> Example:
> 
> FastEthernet 1/0/1 has a primary address of 10.1.1.1
> It has a secondary address of 172.16.1.1
> 
> In a traceroute, where it would be expected that the box report itself as
> 172.16.1.1, it is reporting itself as 10.1.1.1
> 
> Is there a way to remedy this situation and have it report itself as the
> IP address that is actually being used for that flow?

No. Upon receipt of the packet, a router (R1) does not have any data
about what IP address the prior hop (R0) may have used to decide to
forward the packet to R1. It merely knows that it came in on that
interface, and might now a MAC address if it was a multiple-access
interface.

So R1 can only send ICMP time exceededs (traceroute responses) from
one address per interface, and it chooses (rightly so) the canonical,
primary address of the interface.

If you wanted to acheive this functionality, you could do it with tunnels,
wherein the rotuer would receive the traffic on a tunnel interface with
your 172.16.1.1 address.

--jhawk

p.s.: Is it asking too much to request people identify themselves by name?





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