DNS order in /etc/resolv.conf . How does that work

[Barry Margolin]

In article <4.3.1.0.20000428124303.00bb2ab0 at hpwp3.technodat.co.at>,
Christian Krackowizer  <ckrackowiz at std.schuler-ag.com> wrote:
>At 19:37 27.04.2000, you wrote:
>
>> >If the Server  A or the named on Server A dies will the queries be left
>> >hanging or immediately the Server B should pick up and answer the queries. I
>> >thought that in the event this happened Server B will pick up
>> >instantaneously. But apparently that did not happen . Is there a setting
>> >somewhere which one has to set so that it picks up the second listed server
>> >immediately if Server A does not respond. Could somebody throw some light on
>> >this so that I  can understand the proper use of the  DNS order.
>>
>>The only way that you know that A is down is due to a timeout waiting for a
>>response.  The resolver will send a query to A, wait a few seconds, and
>>then query B, wait a few seconds, and then query C.  If this times out it
>>will repeat the process with a longer timeout for each server.
>>
>>Also, it doesn't remember from one lookup to the next that A was down, so
>>there will be a delay before asking B for *every* name you look up.  So
>>make sure that A is a reliable machine.
>
>Hmm, I don't think that this was is what the poster was asking. I read it 
>more like the old problem 'failover of clients': When an already running 
>program, which always start with NS A, 'loses' NS A, it normally does not 
>automatically select NS B but waits for a timeout (if programmed!) or hangs 
>infinitely!

No, I don't think so.  You seem to be talking about failover among multiple
A records for things like web servers.  But the original message was
specifically about nameservers listed in /etc/resolv.conf (it was in the
part of the message that I didn't bother quoting in my reply).  Failover
for them takes place automatically within the resolver libraries.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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