bugtraq - Re: Has anyone implemented "double forward DNS"?

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Message-ID: <20080902235922.GA9141@mail.planetcobalt.net>
Date: Wed, 3 Sep 2008 01:59:22 +0200
From: Ansgar Wiechers <bugtraq@...netcobalt.net>
To: bugtraq@...urityfocus.com
Subject: Re: Has anyone implemented "double forward DNS"?

On 2008-08-30 Duncan Simpson wrote:
> Double reverse DNS, which checks the name found using reverse DNS
> matches the IP adrdess enquired about is now common. I was wondering
> wether about has applied the same technique to forward DNS queries
> too.
> 
> The idea here is that a client that finds www.example.com is
> 192.168.3.42 does not trist this infiormation. Instead it looks up
> 42.3.168.192.in-addr.arpa and checks for a PTR record saying
> www.example.com. If one is not found then the result is disinformation
> and should not be used.

Wrong.

cobalt@...ome:~ $ host www.planetcobalt.net
www.planetcobalt.net    CNAME   chrome.planetcobalt.net
chrome.planetcobalt.net CNAME   planetcobalt.net
planetcobalt.net        A       217.10.9.49
cobalt@...ome:~ $ host 49.9.10.217.in-addr.arpa
49.9.10.217.in-addr.arpa        PTR     mail.planetcobalt.net
cobalt@...ome:~ $ host mail.planetcobalt.net
mail.planetcobalt.net   A       217.10.9.49
cobalt@...ome:~ $ _

You can have multiple names resolving to the same IP address, but just
one PTR record mapping that address back to a name.

Regards
Ansgar Wiechers
-- 
"All vulnerabilities deserve a public fear period prior to patches
becoming available."
--Jason Coombs on Bugtraq