Subnetted IP Area & DNS

[Kevin Darcy]

Andreas Müller wrote:

> Hello,
>
> i've an subnetted ip area (193.96.203.16/28) and i would like to install an
> primary dns server on my side.
>
> The DNS Server runs fine, but only the reverse lookup fails.
> I would like to manage the reverse entry's by myself... I think there are
> two ways to resolv the problem:
>  - Use the Resolver from the ISP for Reverse Lookup (bad solutions)
> - Use my own DNS Server...
>
> Does anybody has an idea how to manage these problem.

The reverse DNS namespace is delegated _normally_ only on octet boundaries.
Therefore, in order to be able to manage the reverse DNS for a /28, you need
to resort to "abnormal" forms of delegation. The two prevalent kinds are a)
delegating each reverse record as a separate zone (given that this is a /28,
with presumably only 14 usable addresses, this may be a viable option in your
case, but understandably folks with /27's or larger address ranges balk at the
number of zone definitions this option requires), or b) following RFC 2317,
the holder of the /24 parent domain can alias (CNAME) each record to PTRs in a
zone you control. Note that you don't have to follow the RFC 2317 examples
slavishly -- with your parent's concurrence, the PTRs can be contained in
*any* zone you control, even a "forward" zone like example.com. Ultimately,
how you "delegate" this /28 range is something you need to come to agreement
on with your provider. So the first step would be to discuss the matter with
them.


- Kevin