Hi,
The LINX route servers currently support this. For what it's worth we took a
straw poll at the last LINX meeting of the ~100 attendees only 1 network was
doing any filtering on the route server. Everyone else was being
'promiscuous'. It may be different at AMSIX however although LINX staff
assumed it was a must have feature the general feeling was it wasn't
imperative, particularly if it sacrificed stability.
As ever YMMV
Pete
On Wed, Mar 18, 2009 at 10:32 AM, Claudio Jeker <cje...@diehard.n-r-g.com>wrote:
> On Wed, Mar 18, 2009 at 11:00:32AM +0100, Arnoud Vermeer wrote:
> > I have a problem with filtering on the current route server
> > implementation. I currently have the following setup:
> >
> > >* 10.0.1.0/24 10.0.1.0/24
> >
> > +-----------+ +-----------+
> > | AS1 | | AS2 |
> > | 10.0.0.50 | | 10.0.0.51 |
> > +-----------+ +-----------+
> > | |
> > | |
> > +---+-----------+---+
> > | RS |
> > | 10.0.0.49 |
> > +-----+-----+
> > |
> > | deny to { 10.0.0.52 } AS 1
> > |
> > +-----+-----+
> > | AS3 |
> > | 10.0.0.52 |
> > +-----------+
> >
> > (or http://www.freshway.biz/files/20090318-problem-filter.txt for the
> > correct ASCII)
> >
> > Both AS1 and AS2 announce the same prefix, but the route server selects
> > the AS1 path because of the lower nexthop value. Now I add a filter to
> > AS3. I deny to send any prefixes to AS3 that match AS1. Now AS3 doesn't
> > receive the 10.0.1.0/24 prefix at all. It should however receive it from
> > AS2.
> >
> > Quagga overcomes this problem by making a per-filtered-peer RIB and then
> > do best path selection
> > (
> http://www.quagga.net/docs/docs-multi/Description-of-the-Route-Server-model.html
> ).
> > I think this is just an ugly and complicated work-around as it doesn't
> > solve the core of the problem.
> >
> > In my eyes the best solution will be to disable the best-path-selection
> > on the route server altogether, and send all routes (except the
> > filtered) to the peer.
> >
> > Arguments to do this:
> > - As shown above, the best path selection breaks on the route server
> > when applying filters.
> > - A route server should not make any best-path selection, because the
> > peers criteria could be completely different than the route server.
> > - The function of the route server is to 'collect' all the routes and
> > send them to all of the peers, not to 'collect a subset' of the routes
> > and send that to its peers.
> >
> > I would love to hear your thoughts on this subject. Would it be hard to
> > implement this feature?
> >
>
> BGP only supports one path per prefix and peer. If you send multiple ones
> as you propose the later ones will overwrite the first one no matter what.
> To support your idea we would need a per-filtered-peer local-RIB because
> the route-server needs to do the best path selection for the peer.
>
> --
> :wq Claudio
