From: leichter@lrw.com (Jerry Leichter)
Newsgroups: comp.dcom.telecom
Subject: That Email Address
Date: 21 Aug 92 14:54:42 GMT
Organization: TELECOM Digest
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 12, Issue 651, Message 7 of 7

There've been several totally confused postings on the issue of Mr.
King's Email address.  Some facts; these all refer to DECnet Phase IV,
which is in use today and has been for something like ten years.

1.  DECnet address syntax uses "node::" as a prefix.  This syntax is
used in many places, not just mail - access to the network is built
into the file system, so you can refer to a remote file as
NODE::THAT.FILE.

2.  In general, just as in TCP/IP, you can refer to any node from
anywhere.  That is, you just use "node::" from any node on the
network.  The mechanism used is like the old HOSTS.  table; it is
possible to set up a machine that doesn't know everyone's name.  This
was common in the old days when machines were small.  To get around
this, you can, in most cases (it depends on the network service
involved) use "poor man's routing", a holdover from DECnet Phase II:
You use a syntax like "node1::node2::something".  What this really
does is just send "node2::something" off to node1; you hope it knows
who node2 is.  (There is another reason to do this which I'll come
back to later.)

3.  DEC's Enet actually supports two different mail systems over the
same physical network.

a.  MAIL-11, also known as VAXMAIL, comes standard with VMS.
Addresses are just user login names.  To get to PERSON on node THERE,
you send mail to THERE::PERSON.  MAIL-11 supports poor man's routing;
the return address will show the entire route (which may or may not be
needed to get back).  You have to know the node someone has an account
on, and their login name (which might not be their English name), to
send them mail.

b.  ALL-IN-1 MAIL (which also goes under other names these days) can
be set up in many ways.  On DEC's Enet, it is set up so that addresses
have the form "English.Name@Location", where Location is a three-
letter site code, the same one used for sending intra-company mail.

Engineers use VAX MAIL; managers use ALL-IN-1 MAIL.  (These are broad
generalizations.)

VAX MAIL and ALL-IN-1 MAIL are about as closely related as UUCP-based
mail and SMTP-based mail.  Exactly as for UUCP vs. SMTP, there are
various gateways provided that connect the two systems.  Exactly as
for stuff that crosses the UUCP/SMTP boundary, the return addresses
can get very convoluted, and they can sometimes be unusable.

There are also gateways that connect VAX MAIL to Internet mail.
Needless to say, messages that have crossed through BOTH an ALL-IN-1
MAIL to VAX MAIL gateway, AND a VAX MAIL to Internet mail gateway, are
even more likely to have strange-looking addresses.

4.  Just to add to the confusion, DECnet Phase IV has run over its
design limit of about 65,000 distinct nodes.  (Keep in mind that
32-bit IP addresses are becoming a limiting factor, too, and that
DECnet Phase IV pre-dates TCP/IP.)  This gets worked around by a hack:
Some node numbers, by convention, are reserved for "hidden areas", and
never propagated network-wide.  (This is done by abusing some of the
software.)  Since a hidden node H can't be seen directly, it always
has to be reached by poor man's routing through some gateway node G,
as G::H::.  Many individual workstations are set up this way.  As far
as I know, you never have to pass through two gateways - there are no
"doubly hidden" nodes.  Since G is usually a "well known" node at the
site where H lives, the difference between G::H:: and the Internet
@H.G is more apparent than real.


Jerry