Antwort: Re: timeout by DNS? [Virus checked]

fmu_at_OERAG.DE
Date: 11/23/04

  • Next message: Libor Laubacher: "Re: Eserver p5 installation" 
    Date:         Tue, 23 Nov 2004 13:34:47 +0100
To: aix-l@Princeton.EDU

    Hi Vesna,

    thanks for your answer.
    Your explanation is good and something about this I found in the Internet.
    Which I do not understand, if the first entry is wrong or the first
    nameserver was crashed, the second entry should function after 5 seconds.
    But why functioned that not and it does run all cycles through (75s).

    Best regards,
    Frank Mueller

                          Vesna Vranesic
                          <vesna.vranesic@R An: aix-l@Princeton.EDU
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    The quotation I have found few years ago about this issue:

    "On AIX, a DNS query will wait a total of 75 seconds before

    failing over to the second nameserver entry in the resolv.conf.
    The 75 sec timeout period comes from two values RES_RETRY and
    RES_TIMEOUT. The way it works is the dns client will try to contact the
    dns server, then if it doesn't get an answer back it will wait 5 seconds
    and try again, then it will wait 10 secs and try again, 20 sec and try
    again, 40 secs and try again.
    .
    5 + 10 + 20 + 40 = 75 seconds
    If you want to change these on the dns client do the following:
    .
    # export RES_RETRY=value
    # export RES_TIMEOUT=value
    .
    The timeout is defined by two values :
          RES_TIMEOUT (default 5 sec)
          RES_RETRY (defautl 4 times)
          Each retry the initial timeout value is multipied by 2
    .
          Example :
          5 + 10 + 20 + 40 = 75 <--- default timeout
    .
          The Cust can export other values to change this behaviour
    .
          Example :
          export RES_TIMEOUT=10
          export RES_RETRY=2
    .
          10 + 20 = 30 seconds timeout
    .
    In order for these to remain in effect after a reboot you need to vi

    /etc/environment and add these in the file."

    I am not sure if something has changed recently (read: for AIX5L).

    Ciao
    Vesna

    |---------+--------------------------------->
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    | | hdkutz@HDKUTZ.DE |
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    | | Gesendet von: |
    | | aix-l@Princeton.EDU |
    | | 23.11.2004 12:48 |
    | | Bitte antworten an |
    | | aix-l |
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    On Tue, Nov 23, 2004 at 12:25:38PM +0100, Holger.VanKoll@SWISSCOM.COM
    wrote:
    > >Now I change the first entrie to a wrong IP-adress for the first
    > nameserver, the nslookup needs a long time to go to the second
    > nameserver.
    > then, dont do that ;-)
    >
    > >Now my question is, what is the parameter to tune the timeout for DNS?
    >
    > well, the timeouts for nslookup , host, dig are different - so it looks
    > like its up to the application
    > nslookup has (afair) a -timeout= option
    >
    > I doubt there is a system-wide parameter that you can tune
    >
    > if dns-response time is critical, run a local caching-only nameserver
    Hmm. Why isn't "options rotate" like in Linux or Solaris implemented in
    AIX?
    Recently we had a problem with our Production Nameserver. All Solaris and
    Linux
    Boxes went fine, only AIX got into trouble resolving Names from the
    secondary
    Nameserver, waiting for timeout of the primary DNS.

    Cheers,
    ku 

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  • Next message: Libor Laubacher: "Re: Eserver p5 installation"

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