Route table growth and hardware limits...talk to the filter

Forrest forrest at almighty.c64.org
Sun Sep 9 00:42:34 UTC 2007


On Sat, 8 Sep 2007, Russ White wrote:

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> 
> > Maybe this is a dumb question, but why isn't there a BGP option to just
> > filter more specific routes that have the same AS path as the larger
> > aggregate?  This would allow the networks that announce more specifics for
> > traffic engineering to still accomplish that, while throwing away the
> > garbage from someone else that decides to announce their /19 as 33 routes
> > for no apparent reason.  Sure, this would fail if a network decided to 
> > only announce /24's for example without a larger aggregate, but how many 
> > networks are really doing that?
> 
> http://www3.ietf.org/proceedings/03nov/I-D/draft-grow-bounded-longest-match-00.txt
> 
> As a matter of fact.
> 
> :-)
> 
> Russ

That draft seems pretty sensible and in my opinion does more good than the 
other options like filtering all routes that are longer than the RIR 
minimum or hoping that the offenders magically wake up one day and decide 
to clean up their announcements.  

I think my suggestion is less complicated than what is contained in the 
draft however.  I'm simply saying that we need an option, we'll call it 
squash-worthless-more-specifics, that you can apply on any specific BGP 
neighbor.  Supposing you receive the following routes......
 
192.168.0.0/16   AS11111 AS22222 AS33333
192.168.1.0/24   AS11111 AS22222 AS33333
192.168.2.0/24   AS11111 AS55555 AS44444 AS33333
192.168.3.0/24   AS11111 AS22222 AS33333

It would keep the 192.168.0.0/16 and 192.168.2.0/24 because they have 
different AS Paths and throw away 192.168.1.0/24 and 192.168.3.0/24.

Judging from the CIDR-REPORT this would eliminate alot of garbage without 
affecting connectivity to people that are multi-homing with smaller PA 
blocks, or announcing more specifics to different providers for traffic 
engineering.

Forrest
 




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