PTR delegation

Michael Milligan milli at
Thu Jun 4 01:41:42 UTC 2009

Scott Haneda wrote:
> On Jun 3, 2009, at 11:53 AM, Scott Haneda wrote:
>> 1) Is it possible to determine what ip range/space has been given to
>> user of that IP space?  For example, in a colocation environment, I am
>> given say, a /24, and I want to look that up and see if it really is a
>> /24.  I have found the -x option which is making life a lot easier to
>> find PTR records.

Only your local router knows for sure.  DNS reverse-mapping delegation
and routes in the routing tables often have little or no relation to
each other.  They are used for entirely different purposes, of course.

>> 2) Given an IP that does not have a PTR, how do I determine if it has
>> been "sub delegated" (?) to the user of that IP?   I need to learn
>> whether or not I need to contact the IP provider, and ask for a PTR
>> record, or if I need to add one in myself.

Follow the delegations.  Or find where a missing delegation should be...

> I was thinking and testing, and I believe I can answer part of my own
> question, but please correct and advise where I am wrong.
> Given an ip of
> $dig -x
> 3589    IN    PTR
> So I clearly have a PTR, but I want to see who has been delegated
> control of the PTR.
> Dropping the trailing 2
> $dig NS
>    3538    IN    NS
>    3538    IN    NS
>    3538    IN    NS
> This to me looks like in this case is going to control the PTR
> zones?

Zone (not plural), yes.

> I can go to and do a lookup there, and find that I have been
> dished out a /26, how do I use dig to get that same answer?

You really can't.  See above.  All you can do is follow the delegation
path and see where it ends.  In the case of a *routed* subnet smaller
than a /24 prefix, then you may or may not be able to get it delegated
to you in DNS ala RFC 2317 depending on the competence or desire/will of
your co-lo provider to do it.


Michael Milligan                                   -> milli at

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