Path: utzoo!mnetor!uunet!husc6!bloom-beacon!gatech!dcatla!dnwcv
From: dnwcv@dcatla.UUCP (William C. VerSteeg)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: More than one IP (sub)network on one ethernet cable
Message-ID: <2528@dcatla.UUCP>
Date: 18 Dec 87 19:55:12 GMT
References: <301351.871217.JBVB@AI.AI.MIT.EDU>
Reply-To: dnwcv@dcatla.UUCP (William C. VerSteeg)
Organization: DCA Inc., Alpharetta, GA
Lines: 36


The topic of discussion is how to tell a device that an IP network other
than his own is on his local cable. This _is_ an atypical configuration, 
but one that can arise in the following situation. 

A user has two ethernet cables joined by a link level (hardware address)
bridge. From each of these cables he has lots of IP traffic to the world
at large. He would want an IP router for each cable. The network numbers
should be different to limit traffic on the link level bridge. If the IP
network numbers were the same, the world would be forced to guess which
IP router to use, thus increasing load on the link level bridge.

Assuming distinct IP network numbers, an IP speaking
device on the first cable would then think that it had 
to go out the IP router to the world. Each packet would then 
rattle around the world, then go back in the second cable's 
router to gain access to a machine on the other cable. A more efficient,
direct method would be to use the link level bridge.

This could be done in two ways that I know of. 

1- Each device (router or non-router) could be told of
   networks that co-reside with his own on
   a particular interface. Are there any implementations that do this?
   Does anybody have source code to a package that does this?

2- The router on each cable could know about multiple networks on a single
   interface. The router could then send ICMP redirects. These redirects
   should straighten the route. Proteon claims
   to support this. Sun, among others does not.
   Are there any other implementations that do this? Does anybody have source 
   code to a package that does this?

	Thanks

	Bill VerSteeg