[routing-wg]a (perhaps) naive question...
Paul Francis francis at cs.cornell.edu
Tue Sep 30 22:18:41 CEST 2008
Well, if the AS-set doesn't fit, that's a problem. But it isn't necessarily the case that simply because an AS that gets, say, RIPE addresses is transcontental means that it can't be part of a "RIPE" aggregate. One would have to sit down and see how bad the paths are relative to the RIB savings. I don't suppose anyone has done such a study? PF > -----Original Message----- > From: Florian Weimer [mailto:fw at deneb.enyo.de] > Sent: Monday, September 29, 2008 7:31 PM > To: Paul Francis > Cc: Routing WG > Subject: Re: [routing-wg]a (perhaps) naive question... > > * Paul Francis: > > > I was wondering the other day why we don't do aggregating > in BGP along > > the lines of registry assignments. For instance, what > stops the set > > of ISPs within Europe from from taking the 15 or 20 > prefixes given to > > RIPE by IANA, and collectively aggregating those prefixes when > > advertising to non-RIPE ISPs? It seems to me that they could > > advertise all of their AS#'s as a huge AS-set for these prefixes. > > The latter probably doesn't work because the AS set size > would exceed the maximum size of a BGP UPDATE message. The > number of prefixes is also large than 20 due to the pre-RIR > swamp space. > > > Is there a technical issue that prevents this, or does the > > organizational effort needed simply outweigh the benefit that would > > accrue? > > It leads to worse routing decisions and does not reflect the > reality of autonomous systems spanning multiple continents. > (Anyone who is multi-homed to one of those trans-continentals > would probably need a globally visible prefix.) > > Actually, for ISPs in the RIPE region, it would make more > sense to aggregate the prefixes of ISPs *not* in the RIPE region. >