Xref: utzoo comp.protocols.tcp-ip:12033 comp.protocols.tcp-ip.domains:182
Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!mips!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.protocols.tcp-ip,comp.protocols.tcp-ip.domains
Subject: Re: parallel networks problem
Message-ID: <63373@sgi.sgi.com>
Date: 4 Jul 90 18:04:53 GMT
References: <7050@star.cs.vu.nl>
Sender: vjs@rhyolite.wpd.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 49

In article <7050@star.cs.vu.nl>, sater@cs.vu.nl (Staveren van Hans) writes:
> Recently I posted a question ...
> Further suppose that network B is preferable to network A, because of
> load, politics or because it is 10x as fast (hint: FDDI vs Ethernet).
> How would one set up addressing and routing for such a configuration?
> ...
> 	Hans van Staveren
> 	Vrije Universiteit
> 	Amsterdam, Holland


This problem exists within FDDI itself.  FDDI is a dual ring of two 100Mbit
counter rotating rings.  100Mbit/sec is only 10 times faster than 10MHz
ethernet, and so is not considered "fast" by some of us.  Notice that
workstations today are 100 times faster than in the early 1980's when 10MHz
ethernet became popular (i.e. 0.25-1.0 VUPS then and 5 to 200 VUPS now)
(1 VUPS=1 "MIPS"=1 VAX 11/780).

The birthday paradox ensures that either an FDDI ring will almost never be
"wrapped" or it will be partitioned too much of the time.  This means that
dual attached, dual-MAC stations could at least in principle push more
bytes than single-MAC stations.

Unfortunately, the only currently publically demonstrated and known scheme
for using both rings involves using two IP networks, one for each ring.
This works, but is at best a clunky kludge.  In the absense of some smarter
routing, applications must somehow split their traffic between two IP
hostnumbers.  There are applications for which this is not a hardship, but
it is in general far from satisfying.

Proposals for combining both rings into a single IP network have been made,
but to the best of my knowledge, there is no such single-IP network proposal
that has had all of the holes, gotchas, and boundary cases covered.  The
single-network proposals involve varying but substantial amounts of
complexity in the link layers, including extensions to ARP.

As far as I know, the current draft standards (ie. IETF) suggest using a
dual-IP-network until a single-IP-network scheme is completed and accepted.

It would be really swell if someone could solve the FDDI-ethernet load
balancing problem that at least two people have mentioned in recent months
in this forum.  It would make the trivial to implement dual-IP-network
solution for FDDI tolerable, eliminating the need for the complicated
ARP and other link layer extensions needed for the single-IP-network ideas.


Vernon Schryver
Silicon Graphics
vjs@sgi.com