Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site unicus.UUCP
Path: utzoo!mnetor!yetti!unicus!emc
From: emc@unicus.UUCP (Eric M. Carroll)
Newsgroups: comp.mail.headers
Subject: Re: Another reason to hate smail
Message-ID: <470@unicus.UUCP>
Date: Fri, 16-Jan-87 22:12:12 EST
Article-I.D.: unicus.470
Posted: Fri Jan 16 22:12:12 1987
Date-Received: Sat, 17-Jan-87 08:35:46 EST
References: <14239@amdcad.UUCP> <5484@ukma.ms.uky.csnet> <467@unicus.UUCP> <14337@amdcad.UUCP>
Reply-To: emc@unicus.UUCP (Eric M. Carroll)
Organization: Unicus Software Inc., Toronto, Ont.
Lines: 50
Keywords: domains gateways Zones
Summary: addresses may not be directly routable; all you know are peer domain gateways

phil@amdcad.UUCP (Phil Ngai) writes, quoting me:
>>Really
>>what I need is a table that associates a domain to my prefered transport
>>mechanism (ie resolve the physical network to be used), then does the routing 
>>lookup inside the associated connection graph for that physical network.
> 
> No, you're making the same mistake that I complained about originally.
> You need to associate a transport mechanism with an *address*, not a
> domain. My site (amdcad) is in the .COM domain but that does not mean
> we are on the ARPA Internet, much to the surprise of many people's
> mailers.

    But that is my point. .com implies nothing about how to get there.
You cannot associate a transport mechanism to the address 
"Eric.M.Carroll@bar.foo.unicus.com" because you know nothing of the 
structure of the Unicus Zone. You will, however, recognize the domain
.unicus.com, because we are both registered in the Uucp Zone. Thus you 
have an implicit transport mechanism (uucp, which is assumed by smail) 
and a route (from the pathalias database). 

    Your problem is one of a multi-connection site not knowing that it 
shared a zone with you. Say I am on an x.25 network, ethernet and uucp. 
When I recognize a domain, say ".c.d" in the address "user@a.b.c.d" I 
now need two more things: what to use to get there, and how to send it. 
I know about an internal Unicus Zone (possibly all on the ethernet, but 
not necessarily) and all its subdomains (I am the authority for it),
gateways connected to the x.25 network and gateways available via uucp 
(registered in the uucp Zone). So recognizing the gateway then allows me
to find a transport mechanism (ie. the common physical connection, 
possibly multi-hop), and a route over it. If there is no common connection, 
it is unreachable, and perhaps I shouldn't know about it; either way I 
kick it up to the ".d" authority in one of the Zones I am registered in,
or ask a specially designated peer (a domain server) who to send it to
instead of really delivering it. What you saw was a "punt" decision 
reached without resolving the domain with respect to all the domains 
that the gateway in fact knew about. And that is because things like 
smail and sendmail have built-in assumptions about what transport 
mechanism to use, and getting around that requires unpleasant special-casing.
The concept of one domain to one network is still with us from the 
origins of domaining in the Arpa community - it really was a homogenous
enviroment there, and the assumption was valid. It is not valid any longer.

Sorry for the length, but I wanted to make this clear. If I have
misunderstood something, I need to find out about it!

	Eric Carroll
	Unicus Corporation, 
	Toronto Ont.
	{utzoo!utcs!yetti, seismo!mnetor}!unicus!emc
	maybe soon: emc@unicus.com (Any ARPA sites with x.25 out there?)