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From Andrzej Adam Filip <>
Subject DUL/DUL+ redesign to improve DNS cache hit ratio [Was: TTL and DNSBLs]
Date Tue, 05 Jul 2011 21:26:16 GMT
"David F. Skoll" <> wrote:
> On Mon, 04 Jul 2011 13:52:00 +0200
> Axb <> wrote:
>> BLs generally adjust their negative TTL to get a practical balance 
>> between query load and positive hits.
>> Gaming these settings can become a costly process.
> My experiments on real mail servers show that DNS caching is quite
> ineffective for DNSBLs (at least for typical ones like Spamhaus that
> use a short TTL on the order of 15-30 minutes.)
> Results of my experiments are in these slides (PDF):
> Executive summary: On a very quiet mail server, assuming a 15-minute
> TTL, there was only a 50% cache hit rate on DNSBL lookups.  On a
> fairly busy mail server, the cache hit rate fell to 22%.
> The problem, of course, is that most mail servers are hit by
> connections from all over the place... spammers have a lot of IP
> addresses to choose from, so you don't get much repetition within the
> TTL of a typical DNSBL.  If you really need high-performance DNSBL
> lookups, you need to arrange for a zone transfer and run a local
> authoritative name server for the DNSBL.

Would you recommend redesigning (mainly) DUL/DUL+ DNSBL lists to improve
DNS cache hit ratio?

[pl>en: Andrew] Andrzej Adam Filip :
The Second Law of Thermodynamics:
If you think things are in a mess now, just wait!
  -- Jim Warner

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