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Path: utzoo!linus!decvax!ittatc!dcdwest!sdcsvax!ncr-sd!greg
From: greg@ncr-sd.UUCP (Greg Noel)
Newsgroups: net.mail
Subject: Re: More thoughts on mail relays
Message-ID: <322@ncr-sd.UUCP>
Date: Tue, 5-Nov-85 17:57:25 EST
Article-I.D.: ncr-sd.322
Posted: Tue Nov  5 17:57:25 1985
Date-Received: Fri, 8-Nov-85 08:15:27 EST
References: <1813@umcp-cs.UUCP> <1746@peora.UUCP> <909@plus5.UUCP> <1761@peora.UUCP>
Reply-To: greg@ncr-sd.UUCP (Greg Noel)
Organization: NCR Corporation, Torrey Pines
Lines: 68

I don't want to enter this philosophical debate; I think the two sides
are both right and wrong, and that the discussion will eventually reveal
that they are trying to do the same thing different ways, and that the
cross-fertilization of ideas will be mutually beneficial.  But I do want
to point out one misconception that shows that the issue is more subtle
than meets the eye.

In article <1761@peora.UUCP> jer@peora.UUCP (J. Eric Roskos) writes:
>  ..... what's the difference between (assuming
>a site that only has Unix mail and no router) writing
>
>	petsd!vax135!ucbvax!sam@slowvax.ARPA
>or
>	petsd!vax135!ucbvax!slowvax.ARPA!sam
>
>It just involves permuting the last two name tokens, and replacing the last
>@ with a !.

No, this doesn't work.  As a case in point, Peter Honeyman sent me a note
last week.  I presume that he just used the reverse path of a news item
rather than calculating the path, since the message went from his machine
(down) to princeton to seismo, then over the ARPAnet to noscvax, then via
UUCP to me.  If you look at the reverse path at each point, it is:
    hop 1 -- down!honey
    hop 2 -- princeton!down!honey
    hop 3 -- princeton!down!honey@seismo.something.GOV
    hop 4 -- noscvax!princeton!down!honey@seismo.something.GOV
Applying the simple algorithm above, this reverse route becomes
    noscvax!princeton!down!seismo.something.GOV!honey
instead of the correct
    noscvax!seismo.something.GOV!princeton!down!honey
which would reach him, assuming that noscvax would handle this form of
address (I don't know if it does).  This is yet another case of the 
confusion between an \address/ and a \route/ and each network's bias
toward one over the other.  In terms of the discussion before us, what
would happen to your first example if vax135 suddenly became an ARPAnet
gateway?  Then it would have both @ and ! routing available, and it would
be able to reach \both/ possible destinations; it would have a hard time
deciding what to do with the message.  The point is that \you/ would have
to change how the mail is sent, based upon a change in status that you
can't control and of which you may not even be aware.

>However, I wrote the router with the intent that someday it would become
>a gateway, since we have machines here that are not on the UUCP network.
>If we ever make that conversion, I will have to add the change to rmail
>which the person at NCR in Torrey Pines recommended awhile back, whereby
>the domain table also specifies the program to run to exit the UUCP network

Hmmmmm.....  Thank you, I think, although that is not quite what I was
recommending -- I wanted the "UUCP network" just to be a special case of
a generalized network routing, handled by the same logic as all other
networks and invoked in the same manner as all other networks.  The thing
I was trying to emphasize was that network routing is something that can
be done pretty much indepentantly of the details of how the route is
physically implemented; in other words, to borrow an expression out of
context, that the physical transport layer is a implementation decision
that can be factored out of the choice of which link is to be chosen to
use for the message.

Perhaps when our copy of smail arrives (that's a \hint/, Mark), I will
have a chance to actually explore some of those ideas -- it may turn out
that the seperation between decision and implementation isn't workable
for some reason we don't yet know.

I didn't get a chance to proof this for spelling; I hope it isn't \too/
awful.
-- 
-- Greg Noel, NCR Rancho Bernardo    Greg@ncr-sd.UUCP or Greg@nosc.ARPA