PTR delegation

Paul Ebersman list-bind-users at
Wed Jun 3 19:14:30 UTC 2009

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

Sadly, it depends. Lots of folks don't keep up PTR records for customers
or subdelegate PTR for assigned addr space, nor is there any guaranteed
way to tie PTR records to ip addr assignments.

Various whois tools ( is a nice one)
will give you some of the ARIN registry info for address space and
routing registry info (see also, for
routing registries). But it assumes that the provider keeps this all up
to date.

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

You can find out who owns the appropriate zone for a PTR record by using
dig. Just be aware that nothing other than good practice dictates that
the owner of an address range does or even can keep up the PTR records
corresponding to them.

At the least, with dig and whois, you should be able to find some
contact to get things rolling.

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