On Tue, Jan 23, 2024 at 4:00 PM Chris Adams <cma@cmadams.net> wrote:
Once upon a time, William Herrin <bill@herrin.us> said:
Nevertheless, in the protocol's design, the one expressed in the RFC's, AS path length = distance.
The RFC doesn't make any equivalence between AS path length and distance. You are the one trying to make that equivalence,
Respectfully Chris, you are mistaken. https://datatracker.ietf.org/doc/html/rfc4271#section-9.1.2.2 "a) Remove from consideration all routes that are not tied for having the smallest number of AS numbers present in their AS_PATH attributes." So literally, the first thing BGP does when picking the best next hop is to discard all but the routes with the shortest AS path. It also says that BGP implementations are -allowed- to use other selection criteria. And there are many situations where doing so is well advised and improves the result. But AS path length is unambiguously the default, off which a user has to move it. Regards, Bill Herrin -- William Herrin bill@herrin.us https://bill.herrin.us/