North American Network Operators Group

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Re: dnsbl's? - an informal survey

  • From: Crist J. Clark
  • Date: Fri May 30 14:02:01 2003

Oh, the irony of this thread being initiated by someone with an address. ;)

I don't have an answer for the originator, but this reminded me of
something about DNSBLs that I've been meaning to ask. Does anyone know
of a black hole list of dynamic cable and DSL clients? What I really
want is one that mimics AOLs block list of dynamic IPs.

I HUGE portion of the spam we were (and still are) receiving came out
of,,,, etc. DSL and cable
customers, and almost no legitimate mail. Manangement resisted
blocking those IPs until AOL lead the way. "If they can't send to AOL
either, they can't complain that we're being unreasonable. They'll
have to break down and fix their mail servers."

However, trying to figure out which blocks of IPs these ISPs use for
dynamic connections (which we want to block) versus static allocations
(which we may not wish to) is non-trival. The few "dynamic" DNSBLs
I've found haven't provided enough documentation about what they
actually are trying to include. Plus, when I tested them, they didn't
seem to block some of the most obvious culprits.

(Before anyone starts arguing the merits of blocking dynamic
addresses, you might as well try to tell me why you need to run an
open relay and I shouldn't block it. I have a dynamic address at
home, and I am blocked by my own filters at work. I figured out long
ago that my home MTA needs to route outgoing email via my ISP's
outgoing SMTP servers, and it has never caused me any problems.)
Crist J. Clark                     |     [email protected]
                                   |     [email protected]    |     [email protected]