[Dnsmasq-discuss] Enabling Reverse Lookup In A Live Environment

richardvoigt at gmail.com richardvoigt at gmail.com
Sun Nov 16 00:18:36 GMT 2008

On Sat, Nov 15, 2008 at 3:59 PM, Paul Chambers <bod at bod.org> wrote:
> Hmm... that's not how I understood it to work (not that I'm a DNS expert...)
> I thought reverse lookups worked their way down through the IP netblock
> assignments, and it would be up to the entity that ;owns' your IP address
> (i.e. your ISP) to resolve reverse lookups, or have some mechanism to
> delegate to you (latter is rare, AFAIK). Usually an ISP resolves it to some
> generated name like 12-34-56-78.static.ispname.com.

Well yes.  But it's "controls" rather than owns, in that when there's
a subassignment of a large block, that subassignment gets registered
with ARIN and the end network designates a DNS server for reverse

The biggest issue is that CIDR blocks aren't supported in reverse
lookups particularly well, DNS is broken out by the octets of the
address, so if your block is smaller than a /24 you'll need to
cooperate on reverse lookups with the other networks in the /24.

How big is the block in question?  If it's a /24 or larger, does ARIN
show that block subassigned to your organization?  If yes, then make
your DNS host the name server for the reverse block and set things up
there.  If no, have your ISP register the subassignment.  If you have
a small block, use dig or nslookup to find out what is the DNS server
for reverse lookups in that block, and contact that group to add PTR
records for your addresses.

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