[Pdns-users] stuck tcp sessions on recursor

Charles Sprickman spork at bway.net
Thu Feb 24 18:20:13 UTC 2011


I'm seeing an issue with tcp queries on powerdns recursor 3.2.  We run 
two instances of pdns recursor on an internal network and it's mainly hit 
by lots of qmail delivery servers.  They are doing a ton of lookups, I 
think we peak around 4000 queries/second.  With more people using 
dnssec, many providers returning insanely huge lists of mxers, and qmail's 
propensity for "any" queries, we're finding that our tcp queries are going 
way up.

What we are seeing is that when "max-tcp-clients" is exceeded, it appears 
that pdns is not properly closing sockets.  We then get a pile-up of 
qmail-remotes that are "stuck" and deliveries stop until pdns is 
restarted.  netstat shows the connections in state "CLOSED".

We're running FreeBSD 8.1 on all the hosts involved.  This mailing list 
post is interesting, and explains why these "CLOSED" sockets are in that 


Any pointers on how to troubleshoot this further?



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