Losses: Privacy. Telling your competitors what all your links and private peerings are may not be what you want. You might not advertise all your prefixes to some of your neighbors, but you still need the link for other prefixes. If you are only advertising the link, then any neighbor could send you traffic that you don't want to provide transit for. So you drop it. How does your neighbor know? You send him the routes for traffic you are willing to transit traffic for. Or you advertise relationships with the links. Then you get soBGP. Kind Regards, Jakob Heitz. Saku Ytti wrote:
The SPF discussion reminded me of a question I've been thinking about.
Why do we use distance vector EGP? Why do we advertise prefixes?
BGP made sense when we didn't have to worry about degenerates, when the Internet was largely academic. Prefix is configured once to the site where it exists, and no one else does anything, very optimal.
But is that sensible today? When we have to also configure the prefix out-of-band locally on every site, potentially 3 times, RPKI (RTR maybe), prefix-list (for BGP) and access-list (for antispoof). So if we discover ASN/Prefix association anyhow out-of-band, why do we need to see +million prefixes in-band?
What if EGP would flood link-states? What would we win? What would we lose?
Potential wins: - flooded link-states could be signed, so we could verify both AS1->AS2, AS2<-AS1 link-state exists with valid signatures. You couldn't hijack ASN, the entire path could be validated. - initial convergence would be 50-100 times faster - lot less signalling/flapping - loop free alternatives for rapid convergence
We could see some problems, for TE reasons I might advertise different prefixes from different sites with the same AS. I'm not sure if that is a legitimate concern, those are niche cases and for those cases we could just register more ASNs and move the ASNs instead of prefixes. But I'm sure there are more obvious weaknesses that don't immediately spring to mind.