PTR zone / VLSM issue

[Chris Thompson]

[Top-posting de-swizzled]

On Mar 15 2009, Ben Bridges wrote:

>From: bind-users-bounces at lists.isc.org on behalf of Alan Clegg
[...]
>>Charles Lee wrote:
>>
>>> I believe its format should be:  96-127.51.212.195.in-addr.arpa
>>>
>>> The problem I seem to be having is what order the 96-127 should be in,
>>> because in normal format the network is 195.212.51.96-127 (we basically
>>> run address .96 to address .127)
>>>
>>> Can anyone help out with the proper format of the zone and what a PTR
>>> record would look like?
>>
>>It matters not a bit nor a twiddle, as it is just a label that needs to
>>be "pointed to" by the actual in-addr label elsewhere.
>>
>>96.fred.51.212.195.in-addr.arpa.        IN PTR  mymachine.foo.com.
>>
>>would work fine as long as you had:
>>
>>fred.51.212.195.in-addr.arpa. IN NS    delegated.foo.com.
>>96.51.212.195.in-addr.arpa.   IN CNAME 96.fred.51.212.195.in-addr.arpa.
>>
>>on the nameserver that was actually delegated 51.212.195.in-addr.arpa.
>>
>>(feel free to use $GENERATE to create the above CNAMEs)
>
>I agree, it's arbitrary.  If you are wanting to format the name 
>of your zone similarly to the RFC, I believe the format would be
>96/27.51.212.195.in-addr.arpa (for the subnet 195.212.51.96/27).

Except, of course, that RFC 2317 also says

| The examples here use "/" because it was felt to be more visible and
| pedantic reviewers felt that the 'these are not hostnames' argument
| needed to be repeated.  We advise you not to be so pedantic, and to
| not precisely copy the above examples, e.g.  substitute a more
| conservative character, such as hyphen, for "/".

Half-recommending the use of / was an abomination IMO, not because
it is a non-hostname character in the RFC 1123 sense, but because 
it makes it very awkward to use zone names as file name components.

The real point for the OP is: whatever the naming convention used,
you have to agree it with the delegating authority (unless you are
in the happy position of *being* the delegating authority as well).
All too likely, they will not offer you any choice in the matter.

-- 
Chris Thompson
Email: cet1 at cam.ac.uk