Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!NSIPO.NASA.GOV!medin
From: medin@NSIPO.NASA.GOV ("Milo S. Medin", NASA ARC NSI Project Office)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Can subnets be separated by another net?
Message-ID: <9007091856.AA01804@cincsac.arc.nasa.gov>
Date: 9 Jul 90 10:56:12 GMT
References: <9007090939.AA11396@decpa.pa.dec.com>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 23


Tony, you are of course right.  All the modern IGP designers learned from
the mistakes of the past and do/will support variable length masks.  I was
just differentiating OSPF's support for this sample topology in
comparison to "old style" IGP's like RIP, IGRP, etc, which do not carry
around mask information with the route information.  But to be fair to them,
the routers IP forwarders didn't support variable length masks either,
with the possible exception of fuzzballs, which were trailblazers for 
many of the concepts now common in the Internet.

					Thanks,
					   Milo


PS The "old style" protocols are still adequate for many people's 
topologies, and are still widely used.  It's just that these days,
people want a lot more from their IGP's, like variable length mask 
support, authentication, multicast updates, rapid convergence, 
route tagging, low overhead, etc...  OSPF was built with all these goals 
in mind, whereas the others didn't have nearly as full of a plate 
requirements wise when they were built...  Of course, that's why the
IETF formed a working group to build such a protocol.  And Dual IS-IS 
should also be able to do those things as well...