BGP filtering for own AS number

[Ondrej Zajicek]

On Thu, Jan 06, 2011 at 09:23:06PM +0100, Ivo Smits wrote:
> 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.

You are right. Surprisingly, it seems that RFC 4271 does not explictly
specify how to handle such case. But generally, it is bad behavior
to just ignore an update that is invalid for any reason - receiver
should either interpret it as a withdraw or drop the session.
I will check that and fix it.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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