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

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Date:         Tue, 23 Nov 2004 14:06:40 +0100
To: aix-l@Princeton.EDU

Hi Holger,

that is o.k. You change the values and it works (now 15 seconds). But what
is the reason that the client don't go after 5 seconds over the second
entrie in the /etc/resolv.conf.
I think the client try to connect the first nameserver, after 5 seconds to
the second nameserver. If the second nameserver is o.k. the nslookup comes
back. After 5 seconds, not 15 seconds!

I don't understand this!

Best regards,
Frank

                      Holger.VanKoll@SW
                      ISSCOM.COM An: aix-l@Princeton.EDU
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                      23.11.2004 13:49
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for me it works, see below
what values did you set those variables to?

(0)root@sbe16098 173# time nslookup gd2y5d
*** Can't find server name for address 93.47.226.200:No response from
server
Server: dnsc.swissptt.ch
Address: 10.32.17.13

Name: gd2y5d.swissptt.ch
Address: 10.49.184.130

real 1m15.02s
user 0m0.00s
sys 0m0.00s
(0)root@sbe16098 174# export RES_RETRY=2
(0)root@sbe16098 175# export RES_TIMEOUT=5
(0)root@sbe16098 176# time nslookup gd2y5d
*** Can't find server name for address 93.47.226.200:No response from
server
Server: dnsc.swissptt.ch
Address: 10.32.17.13

Name: gd2y5d.swissptt.ch
Address: 10.49.184.130

real 0m15.01s
user 0m0.00s
sys 0m0.00s
(0)root@sbe16098 177# unset RES_RETRY RES_TIMEOUT
(0)root@sbe16098 178# time nslookup gd2y5d
*** Can't find server name for address 93.47.226.200:No response from
server
Server: dnsc.swissptt.ch
Address: 10.32.17.13

Name: gd2y5d.swissptt.ch
Address: 10.49.184.130

real 1m15.01s
user 0m0.00s
sys 0m0.00s

-----Original Message-----
From: IBM AIX Discussion List [mailto:aix-l@Princeton.EDU] On Behalf Of
fmu@OERAG.DE
Sent: Tuesday, November 23, 2004 1:35 PM
To: aix-l@Princeton.EDU
Subject: Antwort: Re: timeout by DNS? [Virus checked]

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
                      ZB.AT> Kopie:
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timeout by DNS? [Virus checked]
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                      23.11.2004 13:17
                      Bitte antworten
                      an IBM AIX
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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

|---------+--------------------------------->
| | |
| | hdkutz@HDKUTZ.DE |
| | |
| | Gesendet von: |
| | aix-l@Princeton.EDU |
| | 23.11.2004 12:48 |
| | Bitte antworten an |
| | aix-l |
| | |
|---------+--------------------------------->

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>-----------------------------------------------------------------------
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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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