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MXRECEIV.FAQ
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1994-04-26
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Q: An explanation of MX-Receivers and Their Role in Handling Fido Mail
Originally posted by Burt Juda
Area: INTERNET
Date : Apr 25 '94, 06:06
From : bitbucket@ftp.fidonet.org 1:1/31.0
To : All
Subj : An Explanation of MX-receivers
────────────────────────────────────────────────────────────────────────────────
[Automated Posting]
An Explanation of MX-Receivers and Their Role in Handling Fido Mail
===================================================================
Machines which are physically connected to the Internet each have a
unique Internet Protocol address (often called an "IP address"),
4 decimal numbers between 0 and 254 separated by dots (ie: my workstation,
zeus.ieee.org is 140.98.2.1). These numbers are used in the headers of
the encapsulated packets (all data is broken up into chunks and eack has
a header showing origination and destination) transmitted over the Internet.
The "Domain Name Service" is a distributed system of having the data at
different locations and is effectively a "database" of mappings between
the "names" that machines are known as and their "IP addresses".
In order to communicate with a system one's machine must get the
IP-address of the machine it wants to talk to from the DNS first.
These are stored in the DNS in what are known as "A" records.
Machines which have IP-addresses exchange "mail" using a protocol
called SMTP (Simple Mail Transfer Protocol), communicating on port 25
of the set of IP sockets.
However, there are many machines which have "names" but are NOT connected
physically to the Internet, those doing UUCP and other reasons. In order
to get mail to such a system, the DNS contains an "MX" record.
The "MX" record, instead of giving a dotted-quad IP-address, holds the
"name" of the system which *does* have an IP-address and knows how to get
mail to the real destination system. An "MX" record *must* point to
the *real name* of the machine which is accepting mail for the destination
system. A machine may have several names, but the "MX" records *must*
point to it's TRUE name (that which is returned by the `hostname` command
on a UNIX system). The machine which is pointed to by the "MX" record
is known as the "MX-receiver" for the destination system.
The reason that the "MX" record *must* point to the TRUE name of the
MX-receiver is that *it* will in turn query the DNS and will compare
its `hostname` with any MX-records found. The MX-records also have a
number which is a "Precedence" number. They are tried in order, but
always skipping any MX-records which point to itself. If the MX-record
with the *lowest* precedence number points to itself, then it *must*
have the proper rules in its mailer configuration to deliver the mail
via means OTHER than SMTP, otherwise an error will result.
This means that an "MX-receiver" system *must* install the proper handling
in its configuration for the destination system *BEFORE* the "MX" record
is installed in the DNS. Otherwise, errors can result, mail loops
develop, and the mail cannot be delivered.
Here's a couple of examples of the DNS records from .fidonet.org ...
These are a *PARTIAL LISTING* as EXAMPLES only.
The information shown here is *NOT* current. For up-to-date DNS
information for the .fidonet.org domain, obtain the file FIDONET.DNS
either via Anonymous-FTP from ftp.fidonet.org in the /pub/fidonet/info
directory or via File-Request from 1:1/31.
; ====================== begin example DNS ======================
; Nameserver info for FIDONET.ORG domain
; the original of this file resides in:
; zeus.ieee.org:/usr/local/ns/fidonet.org
;
$ORIGIN fidonet.org.
@ IN SOA ZEUS.IEEE.ORG. HOSTMASTER.FIDONET.FIDONET.ORG. (
10303 ; serial (version of this file)
86400 ; refresh once a day
600 ; retry refresh every 10 minutes
36000000; expire after 1000 hours (over week)
86400 ; 259200 ; minimun TTL of 3 day
)
IN NS ZEUS.IEEE.ORG.
IN NS POLARIS.LLNL.GOV.
;
; Special Entries and Services
; ----------------------------
;
ns IN CNAME zeus.ieee.org.
fidonet IN CNAME zeus.ieee.org.
; an example where an "A" record exists but Mail is handled
; by a different machine
ftp IN A 140.98.1.1
IN MX 10 zeus.ieee.org.
IN MX 20 rab.ieee.org.
;
; The gateway sites themselves
; ----------------------------
;
; if m2xenix is down, rain will queue mail for storage
busker IN MX 10 m2xenix.psg.com. ; 1:105/14
IN MX 20 rain.psg.com.
cmhgate IN MX 10 cis.OHIO-STATE.EDU. ; 1:226/20
compsol IN MX 10 sserve.cc.adfa.oz.au. ; 3:622/407
ehsnet IN MX 10 uxc.cso.uiuc.edu. ; 1:233/13
f-454 IN MX 10 uucp-gw.cc.uh.edu. ; 1:106/1024
; mail for 'fidonews' is queued thru 1:1/31 for delivery to 1:1/23
; special handling is need in the mailer config on zeus
fidonews IN MX 10 zeus.ieee.org. ; re-directed to 1:1/23
; these sites are handled specially by zeus which remaps the
; mail to a bang!path format and sends it back out via SMTP
; these will be phased out over time
fquest IN MX 10 zeus.ieee.org. ; 1:19/23
gisatl IN MX 10 zeus.ieee.org. ; 1:133/411
gstore IN MX 10 zeus.ieee.org. ; 1:103/234
; my home needs an Address record for SLIP to function when I use it
; mail is specially handled by re-naming to mcastl.ieee.org and
; sending thru my gateway at 1:107/10
mcastl IN A 140.98.200.3
IN MX 10 ZEUS.IEEE.ORG. ; 1:107/309
IN MX 20 RAB.IEEE.ORG.
IN MX 30 TAB.IEEE.ORG.
mcws IN MX 10 elroy.jpl.nasa.gov. ; 1:102/851
mechanic IN MX 10 myrddin.sybus.com. ; 1:3603/330
ofa123 IN MX 10 ics.uci.edu. ; 1:103/208
rochgte IN MX 10 valhalla.ee.rochester.edu. ;1:3613/333
; David Dodell's Waffle system is actually in between
; enuucp and solitud
solitud IN MX 10 enuucp.eas.asu.edu. ;1:300/23
; Nameserver "authority" is delegated to ns.web.apc.org for the
; sub-domain of "webfido"
webfido IN NS ns.web.apc.org. ; 1:250/406
IN NS ns.uunet.ca.
IN NS ns.UU.NET.
zorro9 IN MX 10 talcott.harvard.edu. ;1:16/390
;
;
; Each Net within FidoNet has a wildcard MX-record.
; The IP site which the mail is directed to is expected to have
; installed the sendmail or smail rules necessary to queue
; ALL mail for *.nNET.z#.fidonet.org for pickup by the
; appropriate gateway site.
;
; A wildcard MX-record is maintained for each Zone, so that
; there is always a "default" gateway for any new Nets which
; are placed in the Nodelist by the *C's.
; At present, the Zone-1 "default" MX points to zeus.ieee.org,
; which queues mail for gating by 1:1/31.
;
; Where possible, the gateway sitename is shown as a Comment
; behind a semi-colon after the MX-record.
;
;
$ORIGIN z1.fidonet.org.
;
; Zone 1 by Net (examples)
; =============
;
*.n260 IN MX 10 valhalla.ee.rochester.edu. ; rochgte
*.n261 IN MX 10 relay1.UU.NET. ; blkcat
IN MX 10 relay2.UU.NET. ; blkcat
;
*.n104 IN MX 10 ncar.ucar.edu.
*.n300 IN MX 10 noao.edu.
*.n310 IN MX 10 ncar.ucar.edu.
*.n312 IN MX 10 enuucp.eas.asu.edu.
;
*.n16 IN MX 10 talcott.harvard.edu. ; zorro9
*.n101 IN MX 10 talcott.harvard.edu. ; zorro9
*.n141 IN MX 10 bunker.shel.isc-br.com.
*.n322 IN MX 10 talcott.harvard.edu. ; zorro9
*.n333 IN MX 10 talcott.harvard.edu. ; zorro9
*.n325 IN MX 10 sadye.emba.uvm.edu. ; wsyd
;
*.n18 IN MX 10 cybernet.cse.fau.edu. ; branch
*.n112 IN MX 10 cybernet.cse.fau.edu. ; branch
*.n116 IN MX 10 cybernet.cse.fau.edu. ; branch
*.n123 IN MX 10 cybernet.cse.fau.edu. ; branch
*.n3603 IN MX 10 myrddin.sybus.com. ; mechanic
*.n3604 IN MX 10 cybernet.cse.fau.edu. ; branch
*.n3605 IN MX 10 cybernet.cse.fau.edu. ; branch
;
; default Zone-1 forwarding
; -------------------------
;
; Wildcard record for *.z1.fidonet.org - handled via 1:1/31
; All Nets in Zone-1 which do not have its own MX-record
; will fall thru to here
;
* IN MX 10 zeus.ieee.org.
IN MX 20 rab.ieee.org.
;
; (For Zone-2, Randy gates traffic and sends across the pond to
; Henk Wevers for routing. There seem to be problems in FidoNet
; routing on the European side of the pond from there.)
;
$ORIGIN z2.fidonet.org.
* IN MX 10 m2xenix.psg.com.
IN MX 20 rain.psg.com.
;
$ORIGIN z3.fidonet.org.
*.n620 IN MX 10 sserve.cc.adfa.oz.au. ; compsol
*.n622 IN MX 10 sserve.cc.adfa.oz.au. ; compsol
* IN MX 10 jabaru.cec.edu.au.
;
;
; (Note: the Full DNS file is always available via File-Request from
; 1:1/31 or ; 1:107/309 as the filename FIDONET.ORG)
;
; ========================== end of example DNS ========================
This is extremely important for the .fidonet.org domain to function
properly, since the "Hostmaster" (me), maintaining the MX-records for
the domain is very dependent on all the MX-receivers having the proper
configurations. Many times, a site will hook up with someone who is
willing to pass mail/news to them via UUCP, but is NOT physically
connected to the Internet (does NOT have an IP-address and running
an SMTP mailer). Now what? This machine may also be a hop or two away
from the nearest "IP" node in the Path. Now we're dependent on *ALL* of
the systems in that path to have the proper configurations for handling
mail for the new site. Mostly, these systems depend on the "UUCP Maps"
for their path configurations. Now we have a Catch-22 situation.
I cannot submit the Map until the site is "tested" and the MX-record
installed in the DNS. Even once I do, it can take weeks or months
before the Map appears in the Newsgroup comp.mail.maps (fully Moderated
and usually comes thru monthly). In the meantime, the configurations
on all the systems in the dependent path are "broken" waiting on that
all-important Map for the new site. Mail goes into a real "loop".
To add insult to the whole process, the system names contained in a
UUCP Map (which most new sites will construct and send me) do NOT contain
the "Fully Qualified Domain Name" (the dotted name) of the systems
they connect to. Now it becomes a matter of guesswork to see if any of
the site(s) they connect to have an IP-address and can qualify as
an MX-receiver.
For the reasons outlined in the last two paragraphs, it is essential
for a new site to hook up with a system that has an IP-address and can
act as their MX-receiver. It's much easier if the proper Map procedures
were followed and their UUCP Map submission contained the proper
"#F mx.receiver.domain" line in their Maps, giving me the
Fully-Qualified-Domain-Name of their MX-receiver.
It's bad enough that I have to hand-edit each and every Map submitted,
because our wonderful FidoNet editors expand TABS to spaces and the
submission I send to the UUCP Map Coordinators *must* contain the proper
TAB separators, not spaces!
Burt Juda
Hostmaster, .fidonet.org
--- ECHOPOST 1.01
* Origin: When all else fails, read the instructions (1:1/31)