Xref: utzoo comp.protocols.tcp-ip:12144 comp.protocols.tcp-ip.domains:218
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!rpi!bu.edu!bu-it!kwe
From: kwe@bu-it.bu.edu (Kent England)
Newsgroups: comp.protocols.tcp-ip,comp.protocols.tcp-ip.domains
Subject: Re: parallel networks problem
Message-ID: <60719@bu.edu.bu.edu>
Date: 16 Jul 90 16:59:59 GMT
References: <7050@star.cs.vu.nl>
Sender: news@bu.edu.bu.edu
Reply-To: kwe@bu-it.bu.edu (Kent England)
Followup-To: comp.protocols.tcp-ip
Organization: Boston University
Lines: 59

In article <7050@star.cs.vu.nl>, sater@cs.vu.nl (Staveren van Hans) writes:
> Recently I posted a question to these groups to which, to my surprise,
> I received no reactions at all. This seems strange since it addresses a
> problem that many of us are going to face. Now there is of course the
> possibility that this is so obvious that you were all embarrassed by
> the question, but I doubt it.
> 
> Suppose part of a network looks like this
> 
>   ---------------------------------------------------------  network A
> 		|			|		|
> 	-----------------	-----------------   ----------
> 	|      A.1      |	|      A.2	|   |  A.3   |
> 	|    Host foo	|	|    Host bar	|   |Host zot|
> 	|      B.6	|	|      B.7      |   |        |
> 	-----------------	-----------------   ----------
> 		|			|
>   --------------------------------------------------------- network B
> 
> so two parallel networks with some multihomed and some singlehomed hosts.
> Further suppose that network B is preferable to network A, because of
> load, politics or because it is 10x as fast (hint: FDDI vs Ethernet).
> How would one set up addressing and routing for such a configuration?
> 

	What is the Internet Protocol supposed to do?  In the TCP/IP
frame of reference, IP was designed to route internet datagrams from
source address to destination address.  IP understands interfaces.

	But applications understand hosts/servers/service-entities.
How does one tie an "entity" to a "set of addresses" as one moves
down the protocol stack?  How does one deal with so-called multi-homed
hosts?  The answer is, IP does not deal with the issue.  Should it?
Good philosophical question... and can of worms.

	Let us assume that IP should not deal with entities, only
interfaces (addresses).  Can the applications (or some other level
in the stack) deal with the translation of entity name to "ordered
set of addresses"?  I think they can.

	I would suggest that the place to attack this problem is in
the resolver.  I recall discussions in times past about whether the
name servers should be able to do this based on source address, but
it seemed to me at that time that that was impossible for the name
servers to do, since the source entity could be multi-homed.

	The resolver will need to be able to get some kind of
routing or preference metric from the network layer.  Many options.

	I would also suggest that there are many places in the
protocol stack where a domain name would work better than an ip-
address.  Of course, machines may have many names, but at least
we have the concept of canonical name.  We also have the concept
of multicast (implying groups of servers that are in some sense
equivalent).  So we are torn in search of the correct paradigm
and are tied to others' past decisions in the history of TCP/IP.
More grist for the philosophers...

	--Kent