BGP filtering for own AS number

[Ivo Smits]

Op 6-1-2011 20:27, Martin Barry schreef:
> $quoted_author = "Ivo Smits" ;
>> On the dn42 network (http://www.dn42.net) we have been seeing quite
>> a few BGP ghost routes lately. After some research, it turns out
>> that bird may not correctly handle received AS-paths containing the
>> own AS number. Bird ignores incoming BGP routes containing the local
>> AS number - completely. This may result in an older, now invalid,
>> route not getting removed.
> This sounds like it's working correctly.
>
> Bird is effectively ignoring the route with it's own AS in the path.
>
> The older route will therefore not be displaced.
That does not make much sense to me. The sender can have only one 
useable route to that destination, so once it sends an update for that 
destination, one can safely assume that the old route is no longer used. 
Not doing so will most likely result in routing tables losing 
synchronization, resulting in loops and ghost routes.
> It would require a specific BGP withdrawal for the old route to go away in
> this context.
I've done another test and it turns out that bird does not send the 
withdrawal in this context.

Thanks for the quick reply.

Cheers,

Ivo