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From: hedrick@ARAMIS.RUTGERS.EDU (Charles Hedrick)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: help
Message-ID: <8711220500.AA10549@aramis.rutgers.edu>
Date: Sun, 22-Nov-87 00:00:28 EST
Article-I.D.: aramis.8711220500.AA10549
Posted: Sun Nov 22 00:00:28 1987
Date-Received: Tue, 24-Nov-87 04:42:01 EST
References: <8711210325.AA28823@topaz.rutgers.edu>
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Organization: The ARPA Internet
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The author describes a configuration having a mix of vendors, administrators,
and network technologies, and asks how to make a level-2 bridge work within
it.  My recommendation would be:
 1) not to do it.  I think it is a big mistake to let level 2 technology
	cross administrative boundaries.  Personally I prefer level 3
	technology everywhere, but there are good arguments on both sides.
	But I see nothing in favor of leve 2 technology connecting networks
	where different people are going to be responsible for diagnosing
	problems.  Since this issue has come up so many times, I now have
	a canned response which I will  mail to the original poster
	under separate cover (to avoid boring the rest of you).  We believe
	that the next generation of gateways (based on 68020 processors
	instead of 68000), which should be available in December or January
	from at least cisco and Proteon, will have throughput close to that
	of a bridge.  The primary performance limitation will then be
	on long back-to-back strings of packets.  That will be resolved
	by new Ethernet controllers, which should also be available shortly.
	Even in the current generation, throughput with gateways is enough
	for most networks.  From your description, I believe you would
	see no performance problems from using routers instead of
	bridges.
 2) if you must do it, I would set the subnet mask to 255.255.255.0
	on those machines were you can have multiple subnets on one
	interface.  All BSD-based systems allow this, and I think 
	many others as well.  On a BSD system, you say
		route add x.y.z.0 youraddress 0
	for each subnet that you want to add as being local.  For systems
	where this is not possible, I would set the subnet mask to
	255.255.0.0.  If you have any such systems, then any actual level
	3 gateways that may be present in your configuration (Apollo?)
	will have to be able to do proxy ARP.