[Pdns-users] TCP listener hangs with fd error on recursor

Josh Berry jberry at plus.net
Mon Dec 21 11:30:25 UTC 2009

On Mon, Dec 21, 2009 at 10:07:18AM +0000, Josh Berry wrote:

> Can you tell us if you are behind a firewall? Perhaps iptables on the host
> itself?

The server is not behind a firewall, it is behind a load balancer (Nortel Application Switch 2216 E) with a simple ACL (that just restricts access to our own IP ranges) in front of it.

> Are you running with --fork?


>> Dec 19 16:10:21 pcl-cachedns03 pdns_recursor[21800]: Error writing TCP answer to Connection reset by peer
>> Dec 19 16:10:21 pcl-cachedns03 pdns_recursor[21800]: STL error: Tried to remove unlisted fd 410 from multiplexer

> Well, this is very useful debugging information. I can't see how this would
> lead to TCP stopping working.

> When you observe that the TCP listener has died, do you get a connection
> refused when you try to connect to TCP/53? Or a timeout? Or do you get a
> connection but no answer?

The actual TCP socket stops responding. I am checking locally on the box using both 'dig +tcp...' and with a check that opens a TCP connection to port 53 and times it - both stopped responding. I'm afraid I can't provide any more detail than that until it happens again, at which point I could do some more diagnostics.

The log messages above always appear as the listener dies however.


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