Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!mcgill-vision!snorkelwacker!bloom-beacon!ora!minya!jc
From: jc@minya.UUCP (John Chambers)
Newsgroups: comp.protocols.tcp-ip
Subject: Limited routing between IP networks.
Message-ID: <416@minya.UUCP>
Date: 3 Jul 90 03:28:19 GMT
Lines: 44

Well, here I am again with Yet Another Dumb Question...

The puzzle this week, which TFM doesn't seem to help much, comes from
a client who has various sets of machines, normally each set being one
IP network or subnet, or maybe two.  At times they want to interconnect 
the sets via a SLIP link, and when this is done, we should set up routing 
so that any machine in set A can talk to any machine in set B.  Later, 
and in generally overlapping, set B will be connected to set C, and any
machine in set B should talk to any machine in set C.

The tricky part that I can't answer is that they DON'T want the relation
to be transitive.  In the above case, machines in set A should not be
able to communicate with those in set C.  If they can, we don't get
the contract.  The most important configuration will be essentially
a star, with one central set having lots of links out to other sets,
but in fact, an arbitrary graph is a better picture to plan on.

Part of the problem, of course, is that it pretty much needs to be
automated.  If the solution requires any understanding of IP routing
on the part of the users, it won't work.  Solutions that require a
network hacker going in as super-user on each machine and adjusting
routing tables by hand are totally outside the ballpark.  We need
to provide a command of the form "Link host1 host2", which will
establish the link and set up the routing.  Later on another command
may be used to shut down the link (or more likely they will just
turn the modem off and walk away ;-).  

So can IP handle this?  More specifically, can any of the common routing
tools (arp, routed, gated, whateverd) be used so as to get the desired
limited routing.  If so, how might one do it?

I've been suggesting that they should pay me to rewrite routed and/or
gated to do the job the way they want.  This would probably be fun and
profitable and all that, but I suspect that it might be a waste, since
I do sorta have this suspicion that existing tools might already be up 
to the job, if I could decrypt the manuals.  (Let's see, they appear to 
be using mostly English words, and a syntax that is somewhat like that 
of English; the cleartext is likely in an Indo-European language... ;-)

-- 
Uucp: ...!{harvard.edu,ima.com,eddie.mit.edu,ora.com}!minya!jc (John Chambers)
Home: 1-617-484-6393
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