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From "David F. Skoll" <...@roaringpenguin.com>
Subject Re: TTL and DNSBLs (was Re: SpamTips.org: Why run your own DNS server?)
Date Thu, 07 Jul 2011 14:16:59 GMT
On Thu, 7 Jul 2011 16:10:36 +0200
Matus UHLAR - fantomas <uhlar@fantomas.sk> wrote:

> Do you have memory for your nameserver limited or not?

No.  I simulated a name server with an infinite cache size.

> Does it only expire RR's when they time out?

Yes.

> what logs did you procvess?

The mail log from sendmail.

> Do you log responses with informations if they came out of cache?

I ran a simulation.  I had a Perl script that simulated a name server
with infinite cache, and I based the lookup timeouts on the time
stamps in the logs.  Basically, I kept a big hash of when each IP
address would be looked up and the timestamp of last lookup.  If the
IP address was encountered again within the TTL, then it was counted
as a cache hit.  If it was encountered after the TTL would have expired,
it was counted as a cache miss and the timestamp was updated (to simulate
a cache refresh.)

> well, connections to our mailservers _do_ repeat, expecially for 
> servers like google, facebook or similar services.

Yes, *good* ones repeat.  But *bad* ones don't, and unfortunately the bad
ones outnumber the good ones by a wide margin.

Regards,

David.

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