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Re: linux clients didn't use 2nd or 3rd server

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josh wrote:
>
> Hi folks,
>   I would like to ask a linux clients (RHEL/CentOS 5.5) dns setting
> question:
> my problem is that, I setup the desktops' /etc/resolve.conf like
>
> search mydomain.edu.tw
> nameserver (ip of dns1)
> nameserver (ip of dns2)
> nameserver (ip of dns3)
> when dns1 is not functioning for whatever reason (server crash,
> network down, hw,,), all my linux desktop/servers that rely on it
> seemed frozen (because of dns lookup problem), but there were 2nd and
> 3rd dns entries for them, why did this symptom still there? shouldn'd
> they switch to/start to lookup names by using 2nd dns since this is
> what they are for? any timeout or further settings I am missing?

The UNIX stub resolver uses the first listed server until it times out,
then tries the second listed server until it times out, then the third
listed server until times out.  That's 30 seconds per server listed so
90 seconds to fail.  That's for each and every name lookup.

There are a few ways to help this.

Look at nscd which caches the names that have been used recently.  That
gives some simple help when one is available but not the first one in
the list.

Or run a cache only nameserver and point /etc/resolv.conf to 
yourself .  It follows the chain of delegation, keeps statistics on
which servers are currently responding, caches results.

One major thing you have learned - DNS is like AC power and routing
tables.  It is not an optional service.

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Thread

Re: linux clients didn't use 2nd or 3rd server Doug Freyburger <dfreybur@yahoo.com> - 2011-03-29 14:54 +0000
  Re: linux clients didn't use 2nd or 3rd server The Natural Philosopher <tnp@invalid.invalid> - 2011-03-29 17:52 +0100
    Re: linux clients didn't use 2nd or 3rd server Bjørn Steensrud <bjornst+usenet@skogkatt.homelinux.org> - 2011-04-01 16:38 +0200
      Re: linux clients didn't use 2nd or 3rd server Doug Freyburger <dfreybur@yahoo.com> - 2011-04-01 16:47 +0000
        Re: linux clients didn't use 2nd or 3rd server The Natural Philosopher <tnp@invalid.invalid> - 2011-04-01 19:05 +0100

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