Re: BGP prefix filter list

[Mel Beckman <mel () beckman org>]

Bill,

Come on now. The definition of an autonomous system is well established in RFC1930, which is still Best Current 
Practice:

https://tools.ietf.org/html/rfc1930#section-3

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.

This is not an “approximate explanation“. It’s a standard, as strong as any standard that exists for the Internet.

How is your statement "Prefixes from the same AS are not required to have direct connectivity to each other and many do 
not” supported by the published standard? :-)

 -mel

On May 30, 2019, at 10:42 AM, William Herrin <bill () herrin us<mailto:bill () herrin us>> wrote:

> On Thu, May 30, 2019 at 10:11 AM Mel Beckman <mel () beckman org<mailto:mel () beckman org>> wrote:
> > Are your sure about your Error #2, where you say "Prefixes from the same AS are not required to have direct 
> > connectivity to each other and many do not."?
> >
> > From BGP definitions:
> >
> > The AS represents a connected group of one or more blocks of IP addresses, called IP prefixes, that have been 
> > assigned to that organization and provides a single routing policy to systems outside the AS.

From -what- BGP definitions? This one? https://www.scribd.com/document/202454953/Computer-Networking-Definitions

Lots of things get claimed in books and CS courses that are neither reflected in the standards nor match universal 
practice. Heck, most networking courses still teach class A, B and C... definitions which were explicitly invalidated a 
quarter of a century ago.

Even where authors are knowledgeable, they're constrained to present approximate explanations lest the common use get 
lost in the minutiae. When you want to act on the knowledge in an unusual way, you do not have that luxury. The experts 
in the IRTF Routing Research Group spent something like 6 years trying to find a way to filter the BGP RIB in the 
middle without damaging the Internet. They came up with zip. A big zero. They all but proved that it's impossible to 
build a routing protocol that aggregates anything anywhere but at the edges while still obeying the most basic policy 
constraints like not stealing transit. Forget getting BGP to do it, they couldn't come up with an entirely new protocol 
that did better.

Regards,
Bill Herrin

--
William Herrin
bill () herrin us<mailto:bill () herrin us>
https://bill.herrin.us/