Path: utzoo!attcan!uunet!cs.utexas.edu!mailrus!jarvis.csri.toronto.edu!neat.cs.toronto.edu!rayan
From: rayan@cs.toronto.edu (Rayan Zachariassen)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Mail Source Routing (was Re: New Host-Requirement RFCs)
Message-ID: <89Oct29.140055est.2431@neat.cs.toronto.edu>
Date: 29 Oct 89 19:01:24 GMT
References: <2560@munnari.oz.au> <8910282254.AA10351@volition.pa.dec.com>
Lines: 32

Dave writes:

>Note that IP-level routing can, albeit slowly, discover alternate routes.

Note also that IP-level routing is qualitatively different from Mail routing,
in that the latter is single-hop Point-to-Point (on the Internet at least)
which doesn't leave a lot of room for the refinement of the routing decision
that takes place with IP-level routing.

Another key point wrt the Australian problem (which, as Amanda points out
is the same on all IP-islands about to get full connectivity -- we went
through it here) is that there is no nice way to prevent the world at
large from zipping right through the IP gateway and talk directly to
internal hosts if they know about them (e.g. due to coherent
nameservers).  If one has full control of all the mailers on the island
then arranging to send outbound mail through a gateway is not a
(technical) problem.  If one doesn't, the only solution that doesn't require
cooperation is to partition both worlds' mail access (e.g. hack routers at
the link to redirect smtp packets).  Neither of these choices are desirable.

While I'm at it, there's a third undesirable choice: have a high-priority
MX pointing at the gateway, and arrange that the mail server on it rejects
connections from hosts within the island, but accepts them from hosts on
the outside.  There are various ways of accomplishing this, but it means
a LOT of "are you there?" traffic to that gateway and the obvious MX
maintenance problem.  Due to the G-B links in the Australia scenario, this
is obviously not acceptable, but it would work if G-B was well-connected and
packets were cheap.

rayan

(this is still more tcp-ip'ish than maildropper'ish... umm, namedropper'ish :-)