[Xorp-users] How to AS prepend ?

[Bruce Simpson]

Sébastien Namèche wrote:
> ...
> Nop, it's a "u32" (at least for 1.6).

Sorry, I was looking at as-path-list. Next...

>> Is this not your desired result? Your local-as is clearly set to 64512.
>
> Yes, but this is not exactly what we want. We would like to prepend 
> our AS to one of the prefix distributed from OSPF to BGP.

What is your desired as-path on the redistributed route(s), in the 
output you'd expect to see in the BGP routing table ?

> ...
> Our goal is to announce the first prefix to this peer so that the 
> route through this router will be the best.

That looks fine, subject to AS local-pref. Does this part work for you 
as expected?

> At the same time, we also want to announce another prefix, but this 
> router will act as a "backup" route for "X.Y.W.0/23". This prefix will 
> be announced by another router with a shortest path. So we need to 
> prepend our AS to the path of the second prefix for this router.

So your intention is in fact to announce the same prefix X.Y.W.0/23, 
from the XORP BGP router, but with your AS path prepended to the 
existing AS path advertised by another BGP router which already 
announces prefix X.Y.W.0/23?

This isn't going to work if you're directly applying the policy to the 
route redistributed from OSPF, as described earlier; it sounds as though 
you need to inject this prefix announcement manually, and/or specify the 
AS of your peer with the shortest path explicitly.

thanks,
BMS