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Re: Only some IPs accessable?

Cross-posted to 2 groups.

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Henrik Carlqvist <Henrik.Carlqvist@deadspam.com> wrote:
>"NoHtmlMailsPlease" <UsePlainText@dog.edu> wrote:
>> and then I'd like to understand how/why/where linux puts the DNS-IPs
>> given by the ISP, and how they are then used.
>
>The answer is really simple. The DNS servers used are those listed in
>/etc/resolv.conf
>
>How they are used might be a little bit more complicated. Having more than
>one DNS server listed in /etc/resolv.conf might be good for redundancy,
>but it might also slow things down. For some reason it seems as if the
>system waits for all servers to answer even if the first server gives a
>correct answer.

That should not happen.  This quote is from the
RESOLV.CONF(5) man page:

  "On a normally configured system this file should not
  be necessary.  The only name server to be queried will
  be on the local machine; the domain name is determined
  from the hostname and the domain search path is
  constructed from the domain name.

  The different configuration options are:

  nameserver Name server IP address
     Internet address (in dot notation) of a name server
     that the resolver should query.  Up to MAXNS
     (currently 3, see <resolv.h>) name servers may be
     listed, one per keyword.  If there are multiple
     servers, the resolver library queries them in the
     order listed.  If no nameserver entries are
     present, the default is to use the name server on
     the local machine.  (The algorithm used is to try a
     name server, and if the query times out, try the
     next, until out of name servers, then repeat trying
     all the name servers until a maximum number of
     retries are made.)"

The gist is that there is no point in listing more than
3 name servers.  But in any event the first one is the
only one that will ever be queried if the first query is
successful, which also assumes that either there is no
local DNS server or that it has failed.

The reason for more than one server to be listed is so
that a single server need not have 100% availability for
DNS to be 100% available.

-- 
Floyd L. Davidson                <http://www.apaflo.com/>
Ukpeagvik (Barrow, Alaska)              floyd@apaflo.com

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Thread

Only some IPs accessable? "NoHtmlMailsPlease" <UsePlainText@dog.edu> - 2011-10-07 22:42 +0200
  Re: Only some IPs accessable? Frank Boehm <fraboehm@gmx.de> - 2011-10-08 07:39 +0000
  Re: Only some IPs accessable? Chris Davies <chris-usenet@roaima.co.uk> - 2011-10-08 14:24 +0100
    Re: Only some IPs accessable? Ivan Shmakov <ivan@gray.siamics.net> - 2011-10-08 23:18 +0700
      Re: Only some IPs accessable? Chris Davies <chris-usenet@roaima.co.uk> - 2011-10-08 21:29 +0100
    Re: Only some IPs accessable? "NoHtmlMailsPlease" <UsePlainText@dog.edu> - 2011-10-12 15:09 +0200
      Re: Only some IPs accessable? Ralph Spitzner <rasp@spitzner.org> - 2011-10-12 17:24 +0200
        Re: Only some IPs accessable? Chris Davies <chris-usenet@roaima.co.uk> - 2011-10-13 10:55 +0100
      Re: Only some IPs accessable? Henrik Carlqvist <Henrik.Carlqvist@deadspam.com> - 2011-10-12 22:22 +0200
      Re: Only some IPs accessable? Chris Davies <chris-usenet@roaima.co.uk> - 2011-10-13 11:01 +0100
        Re: Only some IPs accessable? "NoHtmlMailsPlease" <UsePlainText@dog.edu> - 2011-10-14 23:00 +0200
          Re: Only some IPs accessable? Henrik Carlqvist <Henrik.Carlqvist@deadspam.com> - 2011-10-15 11:46 +0200
            Re: Only some IPs accessable? floyd@apaflo.com (Floyd L. Davidson) - 2011-10-15 04:59 -0800
              Re: Only some IPs accessable? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-10-15 16:39 +0000
                Re: Only some IPs accessable? floyd@apaflo.com (Floyd L. Davidson) - 2011-10-15 08:50 -0800
                Re: Only some IPs accessable? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-10-15 16:58 +0000
                Re: Only some IPs accessable? Richard Kettlewell <rjk@greenend.org.uk> - 2011-10-15 19:07 +0100
              Re: Only some IPs accessable? Henrik Carlqvist <Henrik.Carlqvist@deadspam.com> - 2011-10-15 19:50 +0200
                Re: Only some IPs accessable? floyd@apaflo.com (Floyd L. Davidson) - 2011-10-15 12:30 -0800
                Re: Only some IPs accessable? Ralph Spitzner <rasp@spitzner.org> - 2011-10-19 18:14 +0200

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