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From "David F. Skoll" <>
Subject Re: TTL and DNSBLs (was Re: Why run your own DNS server?)
Date Tue, 05 Jul 2011 20:37:14 GMT
On Tue, 5 Jul 2011 12:20:18 +0200
Michelle Konzack <> wrote:

> > 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?

My simulation assumed the same TTL for all addresses.  But that's not
relevant to cache effectiveness since most IPs are not listed in a
DNSBL (and you end up using the negative-cache-TTL.)

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

If most targets are not listed, per-IP TTLs don't matter.



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