Re: Aggregating channels...

[Henning Brauer <lists-openbsdtech@bsws.de>]

On Mon, Dec 17, 2001 at 12:49:12PM +0100, Arvid Grøtting wrote:
> Joe Abley <jabley@automagic.org> writes: 
> > In order to balance (share) world->ME traffic through the connections
> > to both A and B it is necessary for A to leak the covered prefix
> > coresponding to ME's A-derived PA netblock as well as A's supernet,
> > so the world sees two paths for the same-length prefix. This is the
> > additional clue requirement that Henning mentioned.
> As many transit providers filter BGP routes quite aggressively, a PA
> solution has the added advantage that if your specific route gets
> filtered for having too long a netmask, the A-allocated supernet route
> will still be out there.

ACK.

> Announce e.g. a /25, and it won't reach us as such, because both our
> providers filter away anything more specific than a /24.  More
> draconian policies have beed rumored to exist, and will probably
> proliferate as the BGP routing tables grow.  (Filtering on the
> minimum, or even the default, allocation size of each RIR-allocated /8
> could become common soon enough.)

Well, a /25 will be quite often filtered - it's just to small. However, 50%
of the routing table consists of routes smaller /20, and at least 30% are
/24 routes, so any provider filtering these is just plain stupid.

-- 
* Henning Brauer, hostmaster@bsws.de, http://www.bsws.de    *
* BS Web Services, Roedingsmarkt 14, 20459 Hamburg, Germany *
Unix is very simple, but it takes a genius to understand the simplicity.
(Dennis Ritchie)