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Path: utzoo!watmath!clyde!burl!hou3c!POSTEL@USC-ISIF.ARPA
From: POSTEL@USC-ISIF.ARPA
Newsgroups: net.mail.headers
Subject: re: domains
Message-ID: <552@hou3c.UUCP>
Date: Mon, 7-May-84 22:47:40 EDT
Article-I.D.: hou3c.552
Posted: Mon May  7 22:47:40 1984
Date-Received: Sat, 12-May-84 08:29:01 EDT
Sender: ka@hou3c.UUCP (Kenneth Almquist)
Lines: 77
To: morris@HARVARD
Cc: header-people@MIT-MC


Robert:

Enclosed is a note i recently sent to the Namedroppers list that addresses
the point you raise.  (To join Namedroppers send a request to 
"Namedroppers-Request@SRI-NIC.ARPA".)  In general, what ever information
you want hosts in the ARPA-Internet to be able to resolve has to be available
in lookup name servers accessible via ARPA-Internet protocols.  If it is
sufficient that the only thing that can be done is find the Internet Address
of the relay host into your domain then the database is simply the entry
mapping "*.DOMAIN" into "Relay-Host-Address".  If you want ARPA-Internet
hosts to be able to determine before sending mail that the destination host
actually exists, then a full database to the host level is needed. If you
want ARPA-Internet hosts to be able to check if the recipient mailbox is
valid and to determine if there is a forwarding address etc, then a database to that level of detail must be available.

--jon.

Date:  3 May 1984 20:07:38 PDT
From: POSTEL@USC-ISIF
Subject: Inter-Enviromnent Name Service

Hi:

There are two parts to the domain name system.  The first is the 
introduction of domain style names.  The second is the introduction of 
domain name lookup service.

In both cases, the design is intended to be widely applicable in a 
variety of communication environments, not just the ARPA-Internet.

We have a reasonable expectation that the domain style names will be 
used in a variety of environments.  We have (so far) little reason to 
expect that the domain name lookup service will be implemented in any 
environment other than the ARPA-Internet.

However, for a host in the ARPA-Internet to make use of a domain style 
name (from any environment) that host must be able to lookup that name 
using the domain name service via ARPA-Internet protocols.

This means that every domain style name from any environment that is to 
be meaningfull to ARPA-Internet hosts must be listed in some domain name
lookup server in the ARPA-Internet.

Suppose there were some domain (let us call it XYZ) in some environment 
(let us call it PQR) not even sharing any common element with the 
ARPA-Internet or any of the domains overlapping the ARPA-Internet, yet 
communication between hosts in XYZ and hosts in the ARPA-Internet is 
possible via some third parties.  For this communication to be possible,
some domain name lookup servers in the ARPA-Internet would have to be 
able to answer queries about host names in the XYZ domain.

At first blush, this would seem to require that a complete detailed and 
up-to-date copy of the database of hosts from the XYZ domain would have 
to be maintained in a domain name lookup server in the ARPA-Internet, at
locations possibly far removed from any part of the XYZ domain.

But, what is the necessary information in this database?  If, as is 
likely, all the communication between ARPA-Internet hosts and hosts in 
the XYZ domain is routed via a particular relay host, then all the 
entries in the database will point to that relay host.

If it is desired to verify that a particular host name in the XYZ domain
is valid, then the full database is required.  If it is sufficient to 
find the address of the relay to the XYZ domain, then the database can 
be a single entry for the name "*.XYZ" with the address of the relay 
host.  That is, any query with a domain style name ending in ".XYZ" will
match the entry, and will receive a reply indicating the relay host.

Please notice that the situation is symmetric.  If the XYZ domain hosts 
used a procedure similar to that of the ARPA-Internet hosts in resolving
host names then the domains overlapping the ARPA-Internet would have to 
provide databases describing their domains in a form suitable to the 
name servers of the PQR environment. 

--jon.
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