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From Michelle Konzack <linux4miche...@tamay-dogan.net>
Subject Re: TTL and DNSBLs (was Re: SpamTips.org: Why run your own DNS server?)
Date Tue, 05 Jul 2011 10:20:18 GMT
Hello David F. Skoll,

Am 2011-07-04 09:24:19, hacktest Du folgendes herunter:
> 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.)

Is the TTL set global or are the TTLs set by IP?

> 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%.

I have a local bind9 which implement my private list and it set the  TTL
per target which is quiet effectiv

> 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.

1+

This can be costly, since the zone transfers are only for  bigger  usage
and not more free...

> Regards,
> David.

Thanks, Greetings and nice Day/Evening
    Michelle Konzack

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