BGP prefix filter list

William Herrin bill at
Thu May 30 19:48:14 UTC 2019

> On Thu, May 30, 2019 at 10:58 AM Mel Beckman <mel at> wrote:
> > Come on now. The definition of an autonomous system is well established
in RFC1930, which is still Best Current Practice:
> >

Your quote wasn't from the RFC. Sorry, my google fu is only good enough to
find your actual quote, not the similar one you didn't reference.

> > An AS is a connected group of one or more IP prefixes run by one
> >       or more network operators which has a SINGLE and CLEARLY DEFINED
> >       routing policy.

Interesting but it bears little resemblance to modern practice. Consider an
anycast announcement, for example, where multiple distributed servers at
isolated pops terminate the packet. Consider Amazon where both region-local
unicast announcements and global anycast announcements all originate from
AS 16509. Indeed the whole concept of traffic engineering rests on the
premise that an AS' routing policy is NOT the same at every border.

Bill Herrin

William Herrin
bill at
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