[comp.mail.sendmail] sigh

vixie@decwrl.dec.com (Paul A Vixie) (07/06/89)

See what happens when you stop reading netnews for a few months?

>> As it's been told to me (and from what I've read), it's always safe to take
>> the rightmost fully-qualified domain name and dump everything to the left
>> of it (in the bang-path sense).

Steve, what you've been told is wrong.

Here's an example.  Moral follows.

Decwrl is the MX for KG6KF.AMPR.ORG.  Decwrl does not have a UUCP connection
to KG6KF; it forwards through VIXIE.SF.CA.US.  It is fairly common for folks
who want to send to an Amateur Packet Radio station from the Internet to use:

	callsign%callsign.ampr.org@KF6KF.AMPR.ORG

Since KG6KF's MX points at Decwrl, decwrl will end up emitting a uux
transaction something along the lines of

	vixie!noe!kg6kf.ampr.org!callsign%callsign

Now, it's a very good thing that "vixie" doesn't rip out everything to the
left of the first FQDM in the UUCP path, or it would discover that the
"best way" to deliver to kg6kf.ampr.org is BACK THROUGH DECWRL.

This is but one example.  I have a feeling that I'll end up dragging in more.

The Moral: don't short-circuit.  If you don't like the path someone uses,
complain or change the maps or write better public domain mailer software.
If someone issues a UUCP path, you do the least damage to your karma if
you DO WHAT IT SAYS.  If they want you to pick a route, they'll arrange
for the "next hop" to be something that isn't a direct neighbor of yours,
in which case you can bloody well do what you please with it.

Listen up, Curtis -- this means you, too.  And Matt, and Mel, and Brian,
and most especially Eliot.

I'd better say it again, several times, since people always mix this up:

	if you don't like the paths people use, change the source mailers
	if you don't like the paths people use, change the source mailers
	if you don't like the paths people use, change the source mailers

This can be done with better maps, better software, or education.  Quoting
myself:

>> There is no problem solved by re-routing that cannot be solved otherwise;
>> there are problems CAUSED by re-routing that cannot be solved at all.

Any takers?  Anybody need another round of this argument?  I have the last
things I said on this subject during each argument I've had on it -- these
were the showstoppers -- the things nobody could answer -- the things that
ended the arguments with everybody going home and grumbling about how I was
wrong but that they couldn't prove it and wasn't the world and awful place...
--
Paul Vixie
Work:    vixie@decwrl.dec.com    decwrl!vixie    +1 415 853 6600
Play:    paul@vixie.sf.ca.us     vixie!paul      +1 415 864 7013

rsalz@bbn.com (Rich Salz) (07/06/89)

The rule for MX stuff is that once it leaves the Internet, you're on
your own.  You stuff it back into the Internet, you've got problems.

One common problem is possible mail loops.  Rewording Paul's article
(which is just explaining the same thing that happens with UCAR/Fido,
which started this whole chain):

]Decwrl is the MX for KG6KF.AMPR.ORG; it forwards the mail to Vixie for
]delivery.  "It creates a path like
]	vixie!noe!kg6kf.ampr.org!callsign%callsign"
]If there weren't a direct decwrl->vixie connection, there would be
]problems.
(BTW, does it really use a % hack?  Ick...)

Damn straight.  By advertising an MX record you're taking it out
of the Internet, but now you're worried about what will happen if you
interject it back into the Internet system.

>The Moral: don't short-circuit.

Wrong.  The Moral:  don't put full domain names into email paths if
they're going through the Internet and you don't want them short-circuited.
Hack the path to be something like
	noe!packet_radio!kg6kf_ampr_org!callsign!callsign

>I'd better say it again, several times, since people always mix this up:
>	if you don't like the paths people use, change the source mailers

If you shoot mail into the Internet with a fully-qualified domain name
in the address -- yes, Paul, even if it's in the Path line -- than you
should expect people to follow it.

UUCP host names don't come with an enforceable central naming authority,
but domain names do.  If you don't want to use them, CHANGE YOUR GATEWAY
CODE!
	/r$
-- 
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