On Mon, Jul 29, 2013 at 09:33:55AM +0200, OCEANET - Cédric BASSAGET wrote:
> Hello,
>
> I'm trying to replace two cisco routers by two openBGPd routers.
> A have 3 neighbors, two with 4-bytes AS, and one which only supports
> 2-bytes AS for now.
> I have a 4-bytes AS too.
>
> So in my bgpd.conf, I have :
>
> ...
> AS <my 4bytes> <a 2bytes AS>
> network z.z.z.z/21
> ...
> neighbor <neighbor's ip address> #a neighbor which supports 4 bytes AS
> {
> remote-as <neighbor's AS>
> set prepend-self 1
> }
> ...
> neighbor <neighbor's ip address> #a neighbor which supports 2 bytes
> AS only
> {
> remote-as <neighbor's AS>
> set prepend-self 2
> }
> ...
>
> My problem is that my second neighbor return this message :
>
> neighbor : received notification: error in UPDATE message, AS-Path
> unacceptable
>
> I think bgpd is trying to prepend the neighbor which does not support
> 4bytes AS with... a 4 bytes AS, due to the "set prepend-self 2".
>
> Now, time for the questions :
> - Is it openBGPd's normal behavior ?
> - Is there a way to force prepending with the 2 bytes AS ? I saw
> "announce as-4byte (yes|no)" in manpage, is this option designed for that ?
>
OpenBGPD will prepend with AS_TRANS (23456) if the system has a 4-byte AS.
This comes from the fact that internally all AS_PATHes are 4-byte and we
"deflate" the AS_PATH for those session that can only handle the 2-byte
ones. Doing that causes all 4-byte AS nummbers to be replaced with
AS_TRANS.
What 2-byte AS are you using for the old connection? By default AS_TRANS
would be used and then enforce neighbor-as would not trigger.
--
:wq Claudio
