Niels Bakker wrote:
Every piece of BGP documentation I have ever seen says that this attribute documents the ASes that the route has actually passed through.
I think the above paragraph of RFC 1771 disagrees with you.
Please quote properly; the context was AS_path, not AS_set. David Schwartz was right on the mark here.
As far as the RFC is concerned, the AS-set is part of the AS-path. See Section 4.3, which says the AS-path is "a well-known mandatory attribute that is composed of a sequence of AS path segments. Each AS path segment is represented by a triple <path segment type, path segment length, path segment value>," where path segment type is 1 for AS_SEQUENCE and 2 for AS_SET. The RFC also says:
An AS_SET implies that the destinations listed in the NLRI can be reached through paths that traverse at least some of the constituent autonomous systems.
which is exactly what we are doing. Regards, Lorenzo