Re: [OT] Reverse DNS

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• In reply to: Mark Haney: "[OT] Reverse DNS"
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Date: Fri, 25 Jun 2004 16:28:11 -0400
To: For users of Fedora Core releases <fedora-list@redhat.com>

On Fri, Jun 25, 2004 at 04:05:56PM -0400, Mark Haney wrote:
> I'm having a discussion with my boss over reverse DNS and I want to know
> if my logic is correct. Who exactly resolves the reverse DNS queries? I
> say it's the name server that serves up the regular DNS, but my boss
> insists it is our ISP which isn't our primary DNS provider. Is there any
> DNS FAQ's that explain this. I thought I knew how this worked, but now
> I'm confused.

        Your boss is probably closer to right. Unless your ISP has
delegated the reverse zone to you, then they probably control the
reverse look-ups. It COULD be the same name server if you had both
your forward domain and your reverse pointer zone in the in-addr.arpa.
zone served by the same name server, but nothing requires it. But
it doesn't HAVE to be your ISP either. They can delegate it to you,
generally if you have a big enough block (/24 or better). Blocks
of /25 or smaller get stickier to delegate and the ISP probably would
prefer to manage it themselves.

        To reverse lookup an IPv4 address, you reverse the octets and
append the .in-addr.arpa. domain to it and do a type PTR lookup (which
"host" does implicitly when you give it an IPv4 address).

[mhw@alcove mhw]$ host alcove.wittsend.com
alcove.wittsend.com has address 130.205.12.10

[mhw@alcove mhw]$ host 130.205.12.10
10.12.205.130.in-addr.arpa domain name pointer alcove.wittsend.com.

        Sooo... Who has the name servers for those zones (drop the last
component and look up the NS records):

[mhw@alcove mhw]$ host -t NS wittsend.com.
wittsend.com name server banshee.wittsend.com.
wittsend.com name server ehecatl.iss.net.
wittsend.com name server ns.commandcorp.com.

[mhw@alcove mhw]$ host -t NS 12.205.130.in-addr.arpa
12.205.130.in-addr.arpa name server banshee.wittsend.com.
12.205.130.in-addr.arpa name server ns.commandcorp.com.

        Not quite the same. Close, in my case, since I do control both
the domain and the netblock so I control both the forward and reverse
lookup zones.

        IPv6 reverse lookups get even groddier... Reverse the nibbles...
All 32 of them...

> --
> Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

> Mark Haney
> Network, Database and Systems Administration
> DoctorDirectory.com Inc.

        Mike

-- 
 Michael H. Warfield    |  (770) 985-6132   |  mhw@WittsEnd.com
  /\/\|=mhw=|\/\/       |  (678) 463-0932   |  http://www.wittsend.com/mhw/
  NIC whois:  MHW9      |  An optimist believes we live in the best of all
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