troubleshooting bind

Marseglia, Michael Michael.marseglia at
Mon Apr 9 16:55:47 UTC 2012


  I'm troubleshooting a DNS issue we recently experienced where records were unresolveable, response NXDOMAIN, from the caching DNS server.  I flushed the cache using rndc flush and I received the host's ip.

  There were no errors in the system log so I'm enabling debug logging should it occur again.  I'm still not sure what caused the NXDOMAIN response it so I'm reviewing my BIND config and taking a look at the default values.

  When configuring BIND for an internal corporate network with a thousand clients should any of the default values be tweaked?  I've searched for tuning guidance but I haven't found any yet.

  I've taken interest in the tcp-clients, max-ncache-ttl, max-cache-ttl, cleaning-interval and max-cache-size values.  These are all currently set to default.

  I'm guessing in a more volatile network with DHCP and frequent provisioning/deprovisioning of hosts I would want to lower the max-ncache-ttl and max-cache-ttl values.  Is this correct?

  Regarding the tcp-clients option, where can I find the current connection count and how do I know if I'm coming close to this number?  In what type of environment would it be expected to hit the default threshold of 100?

  Lastly, if max-cache-size is set to unlimited what happens if BIND consumes all the available memory?  Will the linux kernel terminate the process?  How can I find the value of the current cache size?

Mike Marseglia
Network Engineer, CharterCARE
p: 401-456-2331
c: 401-248-4867
e: michael.marseglia at<mailto:michael.marseglia at>
t: @mmars

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