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From: hedrick@TOPAZ.RUTGERS.EDU (Charles Hedrick)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  How do you break up a B class number?
Message-ID: <8708030231.AA12937@topaz.rutgers.edu>
Date: Sun, 2-Aug-87 22:31:14 EDT
Article-I.D.: topaz.8708030231.AA12937
Posted: Sun Aug  2 22:31:14 1987
Date-Received: Mon, 3-Aug-87 03:48:22 EDT
References: <8707310648.AA04517@RUTGERS.EDU>
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We currently use multiple subnet numbers for two cases: a system
of Ethernets connected by bridges, and a single Ethernet that has
3 different groups on it that expect to move to different Ethernets
shortly.  Our gateways are from Cisco.  Unix can be set up to
know that several different networks are on the same cable.  Add the
extra subnets by using
  route add ..subnet.. ..local host address.. 0
The Cisco gateways have a similar ability.  The only problem we
have is that I don't like putting route commands in all the startup
files for the individual machines.  At the moment we are using
  route add default ..local host address.. 0
and depending upon the Cisco gateways to do proxy ARP.  (For non-Unix
hosts, we just don't tell them about subnetting, which gives the same
effect.)  Thus we don't have to make any changes on our hosts.  But
this is not my favorite way of doing routing.  I'd rather be able to
have a default route to a gateway, and have a form of ICMP redirect
that says "do it yourself, dummy" for hosts that are on the same
Ethernet but have different network numbers.  But if you are willing
to access proxy ARP, there doesn't seem to be any problem with using
multiple subnet numbers on one network.