Sprint BGP filters in 207.x.x.x?

Curtis Villamizar curtis at ans.net
Sat Dec 16 02:53:05 UTC 1995

In message <199512140726.BAA08568 at freeside.fc.net>, Jeremy Porter writes:
> >>If we had a good method for people to indicate routes that they didn't want
>  to
> >>be aggregated, then more proxy aggregation could be done safely.
> >> 
> >
> >	If I may...  The idea of using a routing registry for
> >	this purpose has been suggested before. I still think
> >	it is a valid approach.  Could be very useful in assisting
> >	with better proxy aggregation for all.
> Let me just say I think the RR has some good uses, i.e.
> finding out what people intended the routing to look like, etc.
> I don't really understand how a RR can help with proxy aggregation
> seeing as the route objects really only provide origin AS
> and regular aggregation.  

The additional clues can be found in the aut-num for dual homed AS.
If a route is registered with more than one origin AS and you route
differently to these two AS, that's a clue to look carefully before
proxying too.

> It seems to me dual homed sites which are the concence of
> proxy aggregation, can be detected with a reasonably full set
> of routes, i.e. the second from AS from the origin in the ASPATH
> being different.  (Or some split in the path outside of an
> AS communinity or confederation).

The secondary route may not be advertised to you if the primary
suppresses the advertisement.  For example if previders are A and B
and they peer with each other, I may think I can aggregate some prefix
over provider A, but B may not be advertising a backup path since it
is preferring the same primary through A.


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