[c-nsp] Traceroutes and AS Numbers

[Justin M. Streiner]

On Wed, 20 Dec 2006, Christian Koch wrote:

> When performing traceroutes,the AS number is displayed, where is it
> pulling that info from?

Are you talking about running a traceroute from a router, or from a 
machine that has an AS-aware traceroute client?

If it's the former, the AS number comes from the routing table on the 
router you're tracing from.  Keep in mind that the AS number you'd see on 
a hop across a boundary interface would be for the AS that originates the 
parent block that the /30 or /31 on that boundary interface comes from.

Sometimes that can cause some confusion.

If it's the latter, the traceroute client is probably querying a route 
registry like the RADB or something similar.  If the information there 
isn't as up to date as your BGP FIB, that would explain the discrepancy 
you're seeing.

jms

> I have an issue where we are splitting our US and UK networks due to an
> acquisition... When performing a traceroute from UK, the traceroute is
> is reflecting the new UK AS on our US routers..
>
> Any ideas what can be causing this?
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
>