nslookup, dig, and host when name server is down

Gilles Espinasse g.esp at free.fr
Sun Apr 12 18:06:48 UTC 2009


----- Original Message ----- 
From: "Ming-Ching Tiew" <mctiew at yahoo.com>
To: <busybox at busybox.net>
Sent: Sunday, April 12, 2009 3:04 PM
Subject: Re: nslookup, dig, and host when name server is down


>
> FYI, I tested this above configuration, and it did not work as expected.
>
> This is my test configuration :-
>
> 1. Setup a name server on machine A.
>
> 2. Setup 'dnsmasq' on a uclibc-based machine B where it is
>    configured to lookup /etc/resolv.conf2, inside which
>    there is one name server, which is specified as
>    machine A's IP.
>
> 3. Have /etc/resolv.conf which has 127.0.0.1 as the
>    only name server.
>
> 4. Run a client on machine B, say 'nslookup' or 'dig' to lookup
>    some hosts which has been configured for name server in machine A.
>
>    This resolution works perfectly. All names configured in machine A
>    can be resolved in machine B.
>
> 5. Kill the name server on machine A.
>
> 6. Immediately 'nslookup' and 'dig' get blocked for a long
>    time, and eventually it displayed timeout error.
>
I suppose you did not define a local domain.
dnsmasq did not know it is not needed to forward  those related address
queries to the upstream servers. So everything is forwarded
Apply the advice on this message
http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2009q1/002807.html

    Gilles



> Version: uclibc 0.9.30-rc2
>          dnsmasq 2.47
>
> I am puzzled. There is absolutely no caching behaviour at all.
> Restoring the name server on machine B will also restore DNS
> service in machine B.
>
> Instead of killing name server on machine A, I also tested
> bring down the network on machine A ( which is the more likely
> occurance ), the same blocking and timeout behaviour happens again.
>
> Regards.
>
>
>
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