Subject: Re: Variable length internet addresses in TCP/IP: history

From: [email-masked] (Noel Chiappa)
Date: Wed, 15 Feb 2012 17:14:07 -0500 (EST)

> From: Steve Crocker <[email-masked]>

    > a variable length address looks more like source routing.
    > ...
    > the network portion, fashioned to seem like a source route.
    > ... the division of the network portion into routing steps will be
    > specified in advance or will be interpreted at each step.

This is sort of tangential, and I apologize for that, but...

I hear this assertion (that hierarchical addresses are effectively a
source route) a fair amount, and I'd like to push back on it, because I
think it's somewhat misleading, and confuses beginners more than it helps
them.

The thing is that at each level, a hierarchical address is _very limited_ in
what it can pick as the 'next hop' of the 'source route': it cannot go
sideways in the hierarchy (e.g. from A.p to A.q), and it cannot go up
(e.g. from A.p to B). It can only select one of the 'next layer down'
elements: i.e. from A.p, it can only select one of A.p.1 ... A.p.{n}.

It may seem in some ways a bit like a route, but it's really not (and,
like I said, I have seen beginners get terribly confused in trying to fit
it into that paradigm).

	Noel