Unwanted ISDN connections caused by BIND

Jim Reid jim at mpn.cp.philips.com
Mon Aug 9 17:55:49 UTC 1999


>>>>> "Bernd" == Bernd =?iso-8859-1?Q?P=F6rner?= <Bernd> writes:

    Bernd> We have a linux box acting as DNS, mail and proxy server. We are
    Bernd> connected to our provider via an ISDN line. Our BIND version is
    Bernd> 8.1.2-22.

    Bernd> Every time the machine boots it makes an unwanted ISDN connection to the
    Bernd> provider, exactly in the moment when BIND starts. Also later, in
    Bernd> irregular intervals, the machine makes unwanted ISDN connection. I ran
    Bernd> "isdnctrl verbose 3" to find out which process makes these connections.
    Bernd> They are made via UDP protocol over port 53 (which is BIND's port).

This is to be expected. Your name server has to talk to other name
servers, especially if it has to resolve external names. What you
could do is configure your PPP/ISDN code to only let DNS traffic out
if the serial line is already up. [OTOH, that might stop external
lookups from working, zone transfers might fail, valid zones could
expire, etc, etc.] Another approach would be to keep the line up for
one PPT-charging-unit after the DNS lookup in the hope that someone
generates some off-site traffic - web access or whatever - soon after
they'd looked up the external name.

You might also want to take a look at the dialup option in
BIND8.2.1. It won't stop your name server sending queries to external 
name servers. [Probably nothing can.] However it might help minimise
the amount of ISDN traffic that the name server generates.

    Bernd> Another curious thing:
    Bernd> If BIND is started during boot-up, sendmail is unable to start during
    Bernd> boot-up. After boot process is over I can start sendmail
    Bernd> ("/sbin/init.d/sendmail start") without problems.
    Bernd> If BIND isn't started during boot-up, sendmail can be started without
    Bernd> problems during boot-up.

Presumably your sendmail is giving up on the DNS if your local name
server isn't running or else resolving on some other name server if
the local one isn't up and running. If that local server is started,
it might be waiting for the ISDN line to come up before it's able to
handle any queries. So sendmail waits on the name server which waits
on your ISDN modem which waits on the PTT and your ISP. Sounds
reasonable, no?


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