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  • From: Steven Champeon <schampeo AT hesketh.com>
  • To: InterNetWorkers <internetworkers AT lists.ibiblio.org>
  • Subject: Re: [internetworkers] anti-spam
  • Date: Fri, 13 Jun 2003 14:27:44 -0400

on Fri, Jun 13, 2003 at 02:14:28PM -0400, David Minton wrote:
> On 6/13/03 2:05 PM, "Steven Champeon" <schampeo AT hesketh.com> wrote:
> > So contact your ISP and have them assign you rDNS for your IP that
> > doesn't resolve to
> >
> > durham-ar1-4-64-253-233.durham.dsl-verizon.net
>
> If I am using a DUN RBL (list of Dial-Up Networking address), does it matter
> what his reverse lookup is?

Well, that depends on how you're using it ;) The way my rulesets work, they
take the IP of the connecting server and reverse resolve it into a hostname,
and then check that hostname against a set of patterns.

Most DNSBLs work on the basis of whether the reversed IP (4.3.2.1) is
listed and has a specific value in the DNS zone for the BL. At least,
that is how they work under recent versions of sendmail with the dnsbl
feature. The IP comes from &${client_addr}, which is the IP of the
connecting host. I'm pretty sure it isn't derived from rDNS of the HELO
hostname, though I know some checks for forward-and-reverse are done,
so it could be, I suppose.

> I figure he will be in the block listed as DUN by Verizon, and get
> blocked. Either the user or ISP would need to report that specific IP
> to all of the DUN RBL's and have it removed. Not sure if that would
> happen, based on all of the time necessary.

That's why I'm using rDNS. I'm also using the PDL, but I find it pretty
weak WRT actually finding dynamic ranges. I'm blocking eight times as
much spam using my rules as I ever was using PDL.

--
hesketh.com/inc. v: (919) 834-2552 f: (919) 834-2554 w: http://hesketh.com
Book publishing is second only to furniture delivery in slowness. -b. schneier




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