Path: utzoo!utgpu!water!watmath!clyde!bellcore!faline!thumper!ulysses!ucbvax!GOVERNMENT-CENTER.BBN.COM!rcallon
From: rcallon@GOVERNMENT-CENTER.BBN.COM (Ross Callon)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: connecting Internets?
Message-ID: <8805210151.AA09745@ucbvax.Berkeley.EDU>
Date: 20 May 88 20:13:30 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 53

Drew;

I think the answer is a qualified yes.  There are several "sub-issues"
however.  In a sense the issues involved in interconnecting multiple
existing "Internets" are the same as those in having the Internet grow to
encompass a large number of administrative domains, except for the added
problem of address overlap (which is probably NOT the worst problem).

In terms of address overlap, the solution depends upon whether you use the
DoD IP or the ISO IP.  With the DoD IP, I am not aware of any work on how
to map between two overlapping inconsistent address sets.  The obvious
choice would be to more or less hand-configure some sort of translation,
and have big tables in the gateways on the boundary.  Exactly how this is
done may depend on whether you run out of network numbers for any
particular class of network address.  For example, if a class A address on
one side maps to a class B address on the other, then the host part of the
address would also have to change.  All of this seems potentially ugly.
The ISO protocol, on the other hand, comes complete with globally unique
addresses.  For example, consider the proposed ways in which addressing
could be done with the ISO IP in the DoD Internet (see RFC986, IDEA003, and
a revision of both which is about to come out as a new RFC).  Here the
first three octets of the address specify "DoD Internet", and addresses are
globally unique even with respect to Internets in some other part of the
world.

Another potentially more serious question regards how to route in a future
world of multiple "Internets" (or a multi-domain Internet).  It can be
assumed that most of the administrative domains in the world will have
strict restrictions on what sort of traffic they are willing to carry for
what users.  For example, a particular domain may be willing to carry any
traffic which is strictly internal, traffic between this domain and
neighbors only for specific users and/or applications, and transit traffic
only for a small number of outside domains and specified applications.  The
domain may be very willing to carry electronic mail traffic for their main
competitor, because they want to make copies for themselves (the main
competitor may, for the same reason, be unwilling to use this service).

One can easily envision all sorts of other "policy constraints" affecting
routing.  Thus routing will need to look at all sorts of administrative and
policy considerations.  The IETF Open Routing working group is currently
thinking about how one may do this.  IDEA003 represents a first draft of
the requirements for inter-AS (or Inter-domain) routing, but is only in
draft form (there is a list of proposed updates to be made in the future).
We are currently working on several proposals for how to actually do
routing in this environment.  The Autonomous Networks Task Force is also
working on related issues.

There are other issues that are likely to come up when multiple "Internets"
are interconnected.  For example, there may be a need for congestion
control to be sensitive to administrative policies and contractural
arrangements.  

Ross