Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!mentor.cc.purdue.edu!dls
From: dls@mentor.cc.purdue.edu (David L Stevens)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  Using the 4.2 broadcast addr with 4.3 systems
Message-ID: <3842@mentor.cc.purdue.edu>
Date: 2 Sep 89 19:57:40 GMT
References: <8909021836.AA24117@ucbvax.Berkeley.EDU>
Reply-To: dls@mentor.cc.purdue.edu (David L Stevens)
Organization: PUCC UNIX Group
Lines: 34


	Re: "what about a multicast group." You can't. That's my whole point.
Multicast, broadcast and host addresses all have an IP network part and if
it's a collection of hosts (multicast or broadcast), they have to have the
same IP network part (otherwise you can't route there!). Thus, you can't
address a set of machines on the same physical network with different IP
network parts.
	If you still can't see that, try it. Set up 3 networks, A, B and C.
The gateway on A and C have the A and C IP net numbers and are the only ones
on B; B has no IP net number. How do you address a broadcast packet for "B"
(ie, to go to both A and C gateways) in your scheme?
	And I'll turn it around, since you don't seem to agree that routing
is more of a problem with single IP addresses. What do you gain from having
IP addresses identify "machines."? Right now, I can debug routing problems
by depending on the fact that I can address individual interfaces. If you
take that away from me, shouldn't there be a reason? Further, user-level
programs like gated, can choose route advertising using correct masks [what is
the netmask on one of these proposed multi-IP-address networks?] and special
processing per interface based on high-level things, like IP network numbers,
and not low level things, like interface device numbers.
	You can (and should) already have a single hostname for the multiple
IP addresses on a multihomed host, so you can always use names or, for that
matter, pick any one of the IP addresses. What do you gain by making me lose
flexibility?
	From where I sit, it looks like a gratuitous change that would break
lots of things that you haven't thought about. Things that I haven't thought
about yet, either. And what you gain you could get (if you really wanted it)
by using the IP address you have to get a DNS canonical name and then using
the canonical name to get an IP address (not necessarily the same one you
started with). Every interface address, with this, would get you to a single of
the interface addresses and you wouldn't break all of the goodies I've grown
fond of. We'd both be happy. Right?
-- 
					+-DLS  (dls@mentor.cc.purdue.edu)