I wanted to keep pop-3 mail checks from bringing up the link so I did what I
felt was obvious; I modified standard.filter to include the following right
after the "ignore tcp ip.tot_len=40,tcp.live" rule:

ignore tcp tcp.dest=tcp.pop-3
ignore tcp tcp.source=tcp.pop-3

(these are rules 6 and 7)

/etc/services defines:
pop-3           110/tcp                         # POP version 3
pop-3           110/udp

With debug set to 31, I get the following in syslog as fetcmail polls the
server:
May 21 00:50:47 layla diald[23015]: filter ignored rule 7 proto 6 len 135
seq 6220f279 ack 419c56cd flags  PUSH ACK packet 194.144.156.3,110 =>
194.144.158.243,26190

However, strangely enough, I still get this in dctrl's connection queue
display:

tcp    194.144.156.3/110    194.144.158.243,26190

It starts with a timeout of 15 seconds. The only thing in my filter rules
with a 15 second timeout is rule 1: accept tcp 15 tcp.syn.

And indeed, I sometimes see an "filter accepter rule 1" just before the
ignore message for rule 7. And that match refers to the same port number as
the rule 7 match. There isn't one rule 1 match for each rule 7 match,
however, and that makes the whole thing even stranger.

Now, when I started writing this letter I hadn't realized the significance
of those rule 1 matches and now that I have, I've just tried moving rule 7
to the top. The result is that port 110 connections no longer show up in
dctrl.

So, the message that started out as a plea for help has become a public
service announcement and a curiosity driven request for enlightenment. Why
did diald behave this way?

Haukur Hreinsson



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