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

[Curtis Villamizar <curtis () ans net>]

In message <199512140726.BAA08568 () 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.

Curtis