Path: utzoo!attcan!uunet!oddjob!matt
From: matt@oddjob.UChicago.EDU (Ka Kahula)
Newsgroups: news.sysadmin,chi.mail
Subject: Re: How does "routing" responsibility work? (.US Domain)
Message-ID: <14946@oddjob.UChicago.EDU>
Date: 25 Jul 88 16:10:29 GMT
References: <8576@ihlpa.ATT.COM> <397@comdesign.UUCP> <309@clout.Jhereg.MN.ORG>
Organization: Koyaanisqatsi
Lines: 41

I see some misinformation floating around news.sysadmin which I want
to correct.

If a host with a name like w.x.y.z exists, there need not be any
hosts with the names x.y.z, y.z, or z.  There will generally be a
name server FOR the domain z, and possibly some subdomains of z, but
those name servers need not be within the domain z.

Examples:  tycho.yerkes.uchicago.edu exists and is the primary name
server for domain yerkes.uchicago.edu.  However, there is NO HOST
with the name yerkes.uchicago.edu, nor uchicago.edu, nor edu.  Name
servers for these DOMAINS do exist, but the names of the servers are
not identical to the names of the domains.

Host clout.chi.il.us exists, but there are neither hosts called
chi.il.us and il.us nor name servers for such domains.  Name servers
for us exist, but they are not themselves in domain us.  Those
servers COULD choose to give away authority for some subdomain(s) of
us, but they do not, in fact, do so.

When a random internet host a.b.c.edu (which uses the domain lookup
system) wants to send mail to clout.chi.il.us, it does not pass the
message up and down some ladder of hosts, but rather it tries to find
the correct "mail exchanger" (MX).  If a.b.c.edu does not already
have any information cached about the us domain, it will ask a "root"
server "Who are the MXs for clout.chi.il.us".  It will not get a
direct answer but will be told "The NSs (name servers) for us are
venera.isi.edu and vaxa.isi.edu".  a.b.c.edu will then repeat its
query to one of those servers, getting the reply, "There is one MX
for clout.chi.il.us with preference level of 10 and name
oddjob.uchicago.edu".  a.b.c.edu will then attempt to connect to
oddjob with SMTP and pass the mail message.  In general, it will not
try any other method to deliver the mail.

Mail routing AMONG uucp-only hosts in the us domain is a different
question, and one which must be settled by the uucp managers
themselves.  It will probably be decided in different ways in
different places, but it will not be simply "up the ladder/down the
ladder" because sites like "il.us" do not exist.
________________________________________________________
Matt Crawford	     		matt@oddjob.uchicago.edu