Excerpts from yangyang. wang on Mon, Sep 08, 2008 09:20:38PM +0800:
Hi, everyone:
For routing scalability issues, I have a question: why not deploy AS number based routing scheme? BGP is path vector protocol and the shortest paths are calculated based on traversed AS numbers. The prefixes in the same AS almost have the same AS_PATH associated, and aggregating prefixes according to AS will shrink BGP routing table significantly. I don't know what comments the ISPs make on this kind of routing scheme.
-yang
It might be the right level of granularity for policy but is too coarse for routing. You want to be able to route on prefixes (even if not everyone does it) for flexibility/TE. Also, ASNs are not aggregatable so we can't use them to represent a large number of independently routed networks.