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From: hedrick@ATHOS.RUTGERS.EDU (Charles Hedrick)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Multiple subnets on one physical network
Message-ID: <8711122040.AA11870@athos.rutgers.edu>
Date: Thu, 12-Nov-87 15:40:37 EST
Article-I.D.: athos.8711122040.AA11870
Posted: Thu Nov 12 15:40:37 1987
Date-Received: Thu, 19-Nov-87 20:31:33 EST
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The truth is that every different implementation has its own quirks,
and you're going to have to find a combination of features that works
with the particular set of implementations that you have.  The
cleanest thing is probably to have each interface on the gateway have
a single address.  The Unix versions that I know of only require that
the gateway be on a directly connected network.  You can tell them
that all the subnets are directly connected, by using "route add" with
a zero metric.  So there is no problem.  It is true that many systems
(not just Unix) will try to forward packets for addresses that they
don't recognize.  4.3 can have this turned off.  In a situation where
there are multiple subnets on one cable, I would use a broadcast
address of 255.255.255.255, rather than mentioning the specific net
number.  4.3 lets you set the broadcast address to be used on an
interface.  So do some other systems.  Whether all of yours do is
anybody's guess.  I'm afraid you're going to have to look in detail at
each system you have and find a combination of things that works.