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From: dls@mentor.cc.purdue.edu (David L Stevens)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Hosts whose IP numbers end in 0...
Message-ID: <13647@mentor.cc.purdue.edu>
Date: 5 Sep 90 17:21:02 GMT
References: <9008311641.AA02779@braden.isi.edu> <12619306165.20.PADLIPSKY@A.ISI.EDU>
Organization: PUCC UNIX Group
Lines: 29

I think Michael Padlipsky's analysis hit the hammer on the nose, is right
on the nail, or whatever mixed metaphor you like... :-)

	My arguments assume "gateway not attached or administered by the
same people who do the network on whose address the filtered address lives."
In other words, as I said, take the DLS challenge: if you can't answer the
question "Is 128.210.50.127 a host or a broadcast address?" you have no
business filtering it out on the grounds that it's a broadcast.
	The most unfortunate part is that I think many naive gateway
administrators will presume more than they should and will answer the question
"sure, I can tell" when they really can't.
	So my opinion, beyond any RFC arguments, and which I don't expect
or even want to become "law," is that filtering, except in very carefully
considered cases, just shouldn't be done at all. You see, if it's done wrong,
it affects people well outside those that can have it changed and, worse, the
primary benefits only affect those behind the net, anyway. If some non-128.210
gateway is filtering broadcasts, what I say is "don't be nice to me-- if I
don't want to see them, *I'll* filter them." The broadcast happens, after all,
on my nets.
	Now, certainly, if there are generated replies from all of my hosts
to the source of this broadcast, the remote guy and all the intervening
gateways have a problem too. But should we accept loss of legitimate
connectivity as a sacrifice for doing the wrong thing it what should be
relatively infrequent, anomalous cases? Most protocols know already whether
receiving on a broadcast address is legitimate or not, anyway, so I think
the gain, as far filtering broadcasts in particular, is absolutely minimal
for anyone outside the network of the filtered address.
-- 
					+-DLS  (dls@mentor.cc.purdue.edu)