[Dnsmasq-discuss] Cache Time Threshold

Paul Chambers bod at bod.org
Sat Apr 12 17:23:59 BST 2008

I agree with Simon. If your cache entries are disappearing after a few 
minutes, something's up.

Are you aware that dnsmasq will dump information about its cache 
contents and related stats into the log if you send SIGUSR1 to it? 
(provided you have log_queries turned on). That should help diagnose 
what's going on.

If all else fails, perhaps pdnsd 
(http://www.phys.uu.nl/~rombouts/pdnsd/) is worth a look. It has some 
abilities that seem relevant, including a persistent cache and the 
ability to hang onto cache entries when the associated server can't be 
reached (see purge_cache). I've no practical experience with it, so 
consider this just a pointer, not an endorsement.


Simon Kelley wrote:
> Nathan Jay Skoglund wrote:
>> I wonder if anybody has a way to extend the time that dnscache will 
>> remember lookups.  I have noticed that after only a few minutes dns 
>> lookups require more time, which indicate that they are heading 
>> upstream beyond dnsmasq when used as a cache.
>> You can read a somewhat futile discussion of the event here: 
>> <http://community.smoothwall.org/forum/viewtopic.php?f=20&t=28173>
>> http://community.smoothwall.org/forum/viewtopic.php?f=20&t=28173
>> This would really tickle my fancy, and probably really get adoration 
>> from satellite guys.
>> nathan
> My take on this is that the DNS admin set the Time-to-live, and it 
> shouldn't be over-ridden. If the DNS admin wanted a longer time, they 
> would have set it. Even if you get away with extending the TTL for 
> most domains, eventually you'll find one which breaks.
> I think this position is well articulated by this post which I found, 
> (and lifted, without permission) on a Gentoo list:
> >As an admin that occasionally has cause to shift traffic between coasts
> >for maintenance I hate *hate* anything that ignores my TTLs and
> >consider such software broken and bane upon our fair Internet.
> Cheers,
> Simon.
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