ghudson at MIT
Jan 15, 1999, 5:32 AM
Post #25 of 56
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Some notes on Dan's latest MXPS proposal, in the interest of maximal
awareness:
Russ Allbery suggested that it looked "very similar to an RFC format."
It bears no resemblance to any RFC I've seen. What Russ is thinking
of is son-of-RFC2052bis, which specifies a new RR type (SRV) which
looks like a generalized MX record. The standard name for a SRV
record (which is not not not an A record, no way, no how) according to
that draft is _foo._bar.domain. While I think the SRV record is the
best thing since sliced bread for new protocols, it doesn't have any
application for Dan in this area because he isn't interested in doing
an extra DNS lookup for all but epsilon of every current mail
delivery. (Incidentally, the way to use SRV as a protocol switch here
would be to do a single SRV query for _mail._tcp.domain and use the
port number in the returned records to decide which protocol to use.
But that's still an extra DNS lookup for every current mail receiver.)
Racer X asked about the underscores in Dan's proposal. Is the
domain-name part of an MX record a hostname? This is an interesting
question; it depends on who you ask. Paul Vixie (author of BIND) says
yes, while kre (co-chair of the dnsind working group) says no. The
host requirements RFC supports Paul, by my reading, but I'm just this
guy. At any rate, my past experience suggests that Dan couldn't give
a rat's ass whether the RFCs say it's okay, he only cares about what
works. Putting an underscore in the string "_magic" makes it unlikely
that anyone has existing MX records which will cause a false positive
for QMTP.
So what about BIND and putting underscores in A records? For modern
versions of BIND, you'll have to configure named to turn off checking
for underscores, or it will enforce that every A record in the master
file conforms to the hostname rules. I'm no BIND expert, but I
believe this requires BIND 8, and you can say in named.conf:
options { check-names master ignore; };
or zone "foo" { check-names ignore; ... };
If you have slave servers outside your administrative control, they
will give warnings and you might get flack about it. If this is a
problem or if you're using BIND 4.9.x, then the sky doesn't fall; you
just don't get to tell people to transfer mail to you using QMTP.
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