[Bug 94940] Re: mdns listed in nsswitch.conf causes excessive time for dns lookups

[Joel Maslak]

Can confirm this affects me on Oneiric Beta 2.  Host has working IPv4
and IPv6 network.  All networks have working reverse DNS, but not all
hosts have actual DNS entries (this is true of both IPv4 and IPv6).

Fix for me is to remove mdns4 from the nsswitch.conf.

"sudo /sbin/arp" takes a long time to look up hostnames.  This makes
facter take a long time to run (+1 minute longer than necessary).  This
in turn makes puppet take a substantially longer time to run (100+
seconds vs. 28 seconds).

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https://bugs.launchpad.net/bugs/94940

Title:
  mdns listed in nsswitch.conf causes excessive time  for dns lookups

Status in “avahi” package in Ubuntu:
  Confirmed
Status in “nss-mdns” package in Ubuntu:
  Confirmed
Status in “nss-mdns” package in Debian:
  New

Bug description:
  Binary package hint: avahi-daemon

  I encountered this problem on a machine that is integrated into our
  work network. I performed a dist-upgrade to Feisty on my desktop and
  all went well. I've noticed recently that any dns based work seemed to
  take a significantly longer time then normal.

  My system is getting dns information on our company internal systems
  from two dns servers. Previously, if I tried to establish an ssh
  connection with another system I could generally expect the connection
  in under 3 secs.

  After the dist-upgrade the time went from under 3 seconds to
  approximately 25 seconds. After searching around the system I found an
  entry in /etc/nsswitch.conf that cause me a little concern. The line
  in question is:

     hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4

  I looked around a bit and it seems that the references to mdns are
  really talking about communication with the Avahi mDNS/DNS-SD daemon.
  Since this looks to be a part of a zeroconf configuration I wasn't
  expecting too much in my current environment, as we really only have
  three Mac's.

  What concerned me is the idea that if we hit files with no answer
  there is a delay while we hit the other options until we hit dns,
  which is where the information I seek existed.

  For an experiment I tried two separate tests. The first changed the
  line to looks like:

      hosts:          files dns mdns4_minimal [NOTFOUND=return] mdns

  The change should have improved the time, but I was still looking at
  approximately 23 seconds to return a command prompt on the destination
  machine.

  Finally, I change the entry to simply:

      hosts:          files dns

  After this change I was again receiving the destination command prompt
  in under 3 seconds. I don't know if simply changing the file will
  correct the problem long-term or not. Seems to help me, but might be
  the way to go for most Ubuntu users.

  ProblemType: Bug
  Architecture: i386
  Date: Thu Mar 22 18:10:54 2007
  DistroRelease: Ubuntu 7.04
  Uname: Linux samdesk 2.6.20-12-generic #2 SMP Wed Mar 21 20:55:46 UTC 2007 i686 GNU/Linux

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