Performance. You can't have someone destroying the whole internet by advertising 99999999 link states, and you can't limit the number of links someone can have to prevent that, either. BGP is considered a path-vector protocol, as it uses a path to avoid loops. On 23 August 2025 16:49:27 CEST, Saku Ytti via NANOG <nanog@lists.nanog.org> 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.
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