nanog mailing list archives
Re: why not AS number based prefixes aggregation
From: "William Herrin" <herrin-nanog () dirtside com>
Date: Mon, 8 Sep 2008 10:35:14 -0400
On Mon, Sep 8, 2008 at 9:20 AM, yangyang. wang <wyystar () gmail com> wrote:
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, Two reasons: 1. The AS# alone is insufficiently granular to support traffic engineering for inbound traffic. 2. It would overload a location function on the existing identity function. The AS# presently identifies the entity announcing the routes. Routes from the same AS# come from the same entity. If we routed by AS#, the AS# would also serve to specify the entity's location in the network graph. One of the implications of the research in the RRG is that this identity + location functional overloading is the root cause of our route table problems. Specifically, the IP address both provides a node identity for use by the layer-4 protocols and a layer-3 location within the network graph. Had the IP protocol separated the two functions, it would be almost as trivial to expand the routing system as it is to expand the DNS system because the location part effectively aggregates by topology while the identity part has a nasty habit of changing locations. Unfortunately that realization doesn't appear to have left any corrective actions which are both clean and compatible with the existing system. Regards, Bill Herrin -- William D. Herrin ................ herrin () dirtside com bill () herrin us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004
Current thread:
- why not AS number based prefixes aggregation yangyang. wang (Sep 08)
- Re: why not AS number based prefixes aggregation Nathan Ward (Sep 08)
- Re: why not AS number based prefixes aggregation Scott Brim (Sep 08)
- Re: why not AS number based prefixes aggregation Owen DeLong (Sep 08)
- Re: why not AS number based prefixes aggregation yangyang. wang (Sep 08)
- Re: why not AS number based prefixes aggregation Dave Israel (Sep 08)
- Re: why not AS number based prefixes aggregation Benson Schliesser (Sep 08)
- Re: why not AS number based prefixes aggregation William Herrin (Sep 08)
- Re: why not AS number based prefixes aggregation Christopher Morrow (Sep 08)
- Re: why not AS number based prefixes aggregation Jeroen Massar (Sep 08)
- Re: why not AS number based prefixes aggregation Ricardo Oliveira (Sep 08)
- RE: why not AS number based prefixes aggregation Paul Francis (Sep 08)
- Re: why not AS number based prefixes aggregation Jean-François Mezei (Sep 08)
- RE: why not AS number based prefixes aggregation Paul Francis (Sep 09)
- RE: why not AS number based prefixes aggregation Paul Francis (Sep 08)
- <Possible follow-ups>
- RE: why not AS number based prefixes aggregation Boyd, Benjamin R (Sep 08)