Subject: RE: [RETRANSMIT] Re: Radical Surgery proposal: stop doingreverse for IPv6.

From: "Loomis, Rip" <[email-masked]>
Date: Mon, 24 Mar 2003 12:28:19 -0500

Jim Reid wrote :
> Reverse DNS does [have] uses, even for IPv6. They are not necessarily
> related to authentication. When reverse lookups of the hosts sending
> me email don't work, this is almost always an indication of spam. It
> would be nice to use this heuristic as the first line of defence
> against spam in an IPv6 world.

Exactly.  Reverse DNS does provide a useful non-security function that
cannot easily be provided in any other way, when I can force my
MTA to bounce e-mails with an envelope sender of "bgpugsley@$FREEMAIL.com"
but a source IP address that reverses to
"lsanca1-ar16-4-46-004-002.lsanca1.$BIGILEC.net".  This is not a
security-relevant feature, but it is a quite useful one.  I'd prefer
to be able to receive e-mails from valid $FREEMAIL users *and* to
be able to receive e-mails from folks with DSL connections through
$BIGILEC, while blocking folks who are forging headers/senders.  Reverse
DNS does allow me a good capability to do that, as a countermeasure for
folks who are spamming from home or (ab)using misconfigured home/SOHO
systems with good bandwidth.

Dean, since this functionality works today (and works rather well for
me as one part of a multi-layer filtering system), I would suggest that
if you believe it is dangerous then you work to improve the functionality
or the documentation--rather than removing the functionality.

Or do you not consider the above to be a reasonable use of reverse
DNS lookup?

  --Rip

There are some things that man was not meant to know...for everything
else, there's DNS.  (okay, I'm joking.)
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