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From: hedrick@ATHOS.RUTGERS.EDU (Charles Hedrick)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Ethernet Bridge
Message-ID: <8711011649.AA01017@athos.rutgers.edu>
Date: Sun, 1-Nov-87 11:49:43 EST
Article-I.D.: athos.8711011649.AA01017
Posted: Sun Nov  1 11:49:43 1987
Date-Received: Thu, 5-Nov-87 20:42:20 EST
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Now that source routing is becoming accepted, IP gateways are no
longer guaranteed to provide security.  A host can pretend to be
a host on a different subnet, but use source-routing in such a 
way that the other guy is told to route the packet back thru the
bad guy's real address.  The bad guy of course does not forward
the packet.

IP gateways are normally used because they provide isolation.  This
issue has been discussed so many times that I am reluctant to do it
once more.  In general, a LANbridge is more reasonable the fewer
Ethernets you have (making provisions for future growth), the fewer
different kinds of systems you have, and the better central control
you have over the systems on your network.  We have had disasters that
made every VMS system on a network connected by level 2 routing
unusable.  The problem should not get thru an IP gateway.  We have had
several disasters that were confined to a single Ethernet only because
of the use of IP gateways.  However if you have good network
monitoring and system management, a stable network/software
environment, or a small network, a level 2 system can be made to work.