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C00002 00002	This is a copy of the file HLP:DOMAINS.HLP at SUMEX, written by Mark
C00003 00003	<Overview>
C00005 00004	<Domain System Transition>
C00008 00005	<ARPANET vs Internet>
C00010 00006	<Who maintains the host table and what is in it?>
C00012 00007	<Why do I get mail from systems I can't reply to?>
C00014 00008	<How does a host get in the host table?>
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This is a copy of the file HLP:DOMAINS.HLP at SUMEX, written by Mark
Crispin and copied on 28 April 1986.  No changes have yet been made to
describe the situation here at SAIL.
<Overview>
		    A FIRST COURSE ON DOMAINS
			  Mark Crispin

     This document describes some of what is happening in the
world of host namings, to let our user community know what is
happening and why the REPLY command no longer works in certain
cases.  It started out as a message to a user at SUMEX, and has,
I hope, been made into a generally useful tutorial.

     I was a member of the committee that invented domains.  I
remembered, in those foolish days, how simple it all sounded.
Now I know the true meaning behind "Frankenstein".

     The SUMEX 2060's name in the new scheme of things is:

==>		SUMEX-AIM.Stanford.EDU		<==

This is the host name that should be used on business cards, etc.
in place of the former SUMEX-AIM.ARPA.

    Please note (this is important): "SUMEX.Stanford.EDU" is NOT
a valid name in the domain system, although certain entities may
accept it.  Do *NOT* use this name or give it out as your net
address.
<Domain System Transition>

     The domain system transition is a project to migrate from a
scheme of host name/address registration in which the complete
database is kept in a global host table to a new "domain" system
in which the database is distributed across a large set of name
servers, who are identified by their "domain" of operation.  This
domain is tree-structured; at the top are domains such as COM for
commercial, GOV for government, EDU for educational, etc.  Some
domains, such as UK, refer to separate countries (the USA is big
enough to have several top-level domains instead of a USA
domain...we paid for Internet and run it, so we get to make the
rules!).  Below are organizational names, such as Stanford.

     SUMEX's name is SUMEX-AIM.Stanford.EDU, which means "go to
the EDU name server, find Stanford, now go there (Stanford) and
find SUMEX-AIM, now go there (SUMEX-AIM)".  Regretfully this
means that the old commonly used nicknames "SUMEX" and "AIM" no
longer work.

     Domains were supposed to be an easy transition.  In reality,
the schedule has slipped worse than new buildings at Stanford.
This is now a major project, and the most important component is
to try to insulate the user community from the trauma which is
making all the system people pull their hair.
<ARPANET vs Internet>

     The ARPANET hasn't really existed since January 1983,
although the name is still used to refer to network 10 on the
Internet.  Internet is essentially a "network of networks", some
of which use ARPANET technology, some using Ethernet technology,
some using radio, some using tin-cans and string...  However, it
is all transparent to the users; the interface is the same from
one to the other.  A year or so ago, what was the ARPANET was
partitioned into two networks (the other being MILNET); few users
noticed any difference at all.

     Today, ARPANET is often used as a generic term for
"Internet" and sometimes the terms are interchangable.  However,
Internet is the correct word.  What is ARPANET today is merely a
small part (albeit part of the core) of the Internet.
<Who maintains the host table and what is in it?>

     The host table is developed and maintained by the Internet
Network Information Center (NIC) at SRI International.  SUMEX
maintains a local copy of the NIC table, unmodified from SRI.
When they update their table we get the updates and install it as
is on our system.  While we "store" a copy here, we really only
do so for the convenience of the TOPS-20 operating system -- when
we convert to domains even this vestige of the small ARPANET of
the past will vanish.

     The host table contains the following information about a
node: its primary name, its nicknames, its Internet address(es),
its operating system, its CPU type, and the protocols which it
supports.  All the information except for the primary name and at
least one address are optional.

     SUMEX's local copy is stored on SYSTEM:HOSTS.TXT.
<Why do I get mail from systems I can't reply to?>

     The message in question should have been qualified by the
mail software at the sender prior to being sent out on the
Internet.  While domain names are now valid only those names
which are also registered in the host table should be used.
Consequently the problem is a bug in the mail software at the
host which sent the message to SUMEX.

     This is not at all uncommon, and the situation will become
(much) worse before it becomes better as the Internet enters a
serious stage of flux.  This problem could have been alleviated
by additional advance planning, but so many individuals
(thousands) had to be coordinated on all of this that it is a
miracle that we are as far as we are now.
<How does a host get in the host table?>

     Hosts are registered in the host table by having some
responsible delegate contact the NIC with the appropriate
information.  When the NIC host table is updated, the NIC
announces the updates, and an automatic procedure at SUMEX
retrieves the updated host table from the NIC and installs it
here.  Obviously, this procedure is prone to failure and the
non-registration of many hosts which can mail to Internet hosts
such as SUMEX but which (for whatever reason) aren't registered.
This is a major problem and is THE problem that domains try to
solve.