[13980] in North American Network Operators' Group
Re: Geographic v. topological address allocation
daemon@ATHENA.MIT.EDU (Sean M. Doran)
Sun Nov 23 12:01:47 1997
To: Vadim Antonov <avg@pluris.com>
Cc: "Kent W. England" <kwe@geo.net>, nanog@merit.edu
From: "Sean M. Doran" <smd@clock.org>
Date: 23 Nov 1997 11:48:11 -0500
In-Reply-To: Vadim Antonov's message of "Fri, 21 Nov 1997 15:15:43 -0800"
Vadim Antonov <avg@pluris.com> writes:
> Sean Doran wrote:
>
> > As tli pointed out the top of the hierarchy is not
> > arbitrary, it must be default free.
>
> Sorry for the nitpicking, but this definition has at least two
> flaws:
>
> a) there's a bi-partite backbone configuration, where each half
> has default pointing to the other half. Both do not have to
> carry full routes. (Of course, this scheme has problems with
> packets destined to the blue, or can be extended to more than
> two partitions).
In effect, this entails the synthesis by equivalent areas
of a superior level into which each party can default.
I touched on this briefly in my previous message.
With variable length addressing this kind of joint
level-n-plus-one synthesis is easy; the new area simply
encompasses sufficient bits to distinguish each
level-n/level-n-plus-one IS participating in it.
> b) multihomed non-transit networks may want to be default-free
> and carry full routing to improve load sharing of outgoing
> traffic. Since they are non-transit, they cannot be considered
> "top of hierarchy".
Yes, I believe I also mentioned Yakov's "pull" (did you see his
slides at the IETF (and NANOG?) with which he presented
his push/pull definitions?) can be used to optimize
routing when strict hierarchical routing is inefficient.
> Bingo.
We are in sync, Vadim. Surprise surprise.
Sean.
P.S.:
> Note that IXPs are not "top" of the hierarchy, but just
> aggregators for essentially point-to-point links between
> tier-1 backbones.
This is a good way of putting it. I will steal it and use
it myself from time to time.
