Recursor 3.6.0 released

Jun 20, 2014

This is a performance, feature and bugfix update to 3.5/3.5.3. It contains important fixes for slightly broken domain names, which your users expect to work anyhow. It also brings robust resilience against certain classes of attacks.

Changes between RC1 and release:


New features:

  • commit aadceba: Implement minimum-ttl-override config setting, plus runtime configurability via ‘rec_control set-minimum-ttl’.
  • Lots of work on the JSON API, which is exposed via Aki Tuomi’s ‘yahttp’. Massive thanks to Christian Hofstaedtler for delivering this exciting new functionality. Documentation & demo forthcoming, but code to use it is available on GitHub.
  • Lua modules can now use ‘pdnslog(INFO..’), as described in ticket 1074, implemented in commit 674a305
  • Adopt any-to-tcp feature to the recursor. Based on a patch by Winfried Angele. Closes ticket 836commit 56b4d21 and commit e661a20.
  • commit 2c78bd5: implement built-in statistics dumper using the ‘carbon’ protocol, which is also understood by metronome (our mini-graphite). Use ‘carbon-server’, ‘carbon-ourname’ and ‘carbon-interval’ settings.
  • New setting ‘udp-truncation-threshold’ to configure from how many bytes we should truncate. commit a09a8ce.
  • Proper support for CHaos class for CHAOS TXT queries. commit c86e1f2, addition for lua in commit f94c53d, some warnings in commit 438db54 however.
  • Added support for Lua scripts to drop queries w/o further processing. commit 0478c54.
  • Kevin Holly added qtype statistics to recursor and rec_control (get-qtypelist) (commit 79332bf)
  • Add support for include-files in configuration, also reload ACLs and zones defined in them (commit 829849dcommit 242b90ecommit 302df81).
  • Paulo Anes contributed server-down-max-fails which helps combat Recursive DNS based amplification attacks. Described in this post. Also comes with new metric ‘failed-host-entries’ in commit 406f46f.
  • commit 21e7976: Implement “followCNAMERecords” feature in the Lua hooks.


  • commit 06ea901: make pdns-distributes-queries use a hash so related queries get sent to the same thread. Original idea by Winfried Angele. Astoundingly effective, approximately halves CPU usage!
  • commit b13e737: –help now writes to stdout instead of stderr. Thanks Winfried Angele.
  • To aid in limiting DoS attacks, when truncating a response, we actually truncate all the way so only the question remains. Suggested inticket 1092, code in commit add935a.
  • No longer experimental, the switch ‘pdns-distributes-queries’ can improve multi-threaded performance on Linux (various cleanup commits).
  • Update to embedded PolarSSL, plus remove previous AES implementation and shift to PolarSSL (commit e22d9b4commit 990ad9a)
  • commit 92c0733 moves various Lua magic constants into an enum namespace.
  • set group and supplementary groups before chroot (commit 6ee50ceticket 1198).
  • commit 4e9a20e: raise our socket buffer setting so it no longer generates a warning about lowering it.
  • commit 4e9a20e: warn about Linux suboptimal IPv6 settings if we detect them.
  • SIGUSR2 turns on a ‘trace’ of all DNS traffic, a second SIGUSR2 now turns it off again. commit 4f217ce.
  • Various fixes for Lua 5.2.
  • commit 81859ba: No longer attempt to answer questions coming in from port 0, reply would not reach them anyhow. Thanks to Niels Bakker and ‘sid3windr’ for insight & debugging. Closes ticket 844.
  • commit b1a2d6c: now, I’m not one to get OCD over things, but that log message about stats based on 1801 seconds got to me. 1800 now.


  • 0c9de4fc: stay away from getaddrinfo unless we really can’t help it for ascii ipv6 conversions to binary
  • commit 08f3f63: fix average latency calculation, closing ticket 424.
  • commit 75ba907: Some of our counters were still 32 bits, now 64.
  • commit 2f22827: Fix statistics and stability when running with pdns-distributes-queries.
  • commit 6196f90: avoid merging old and new additional data, fixes an issue caused by weird (but probably legal) Akamai behaviour
  • commit 3a8a4d6: make sure we don’t exceed the number of available filedescriptors for mthreads. Raises performance in case of DoS. See this post for further details.
  • commit 7313fe6: implement indexed packet cache wiping for recursor, orders of magnitude faster. Important when reloading all zones, which causes massive cache cleaning.
  • rec_control get-all would include ‘cache-bytes’ and ‘packetcache-bytes’, which were expensive operations, too expensive for frequent polling. Removed in commit 8e42d27.
  • All old workarounds for supporting Windows of the XP era have been removed.
  • Fix issues on S390X based systems which have unsigned characters (commit 916a0fd)

About the author

Peter van Dijk

Peter van Dijk

Senior Developer at PowerDNS


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