Classless IN-ADDR.ARPA delegation

Classless IN-ADDR.ARPA delegation is a way to delegate reverse DNS authority for desired records without delegating the entire (sub)network. This means that ISPs can delegate control of reverse DNS for your IP addresses without also giving you control of other customers IPs in the same (sub)network.

Remember a few key points.


Unfortunately this scheme does not lend its self to delegating part of a class, hence it's name classLESS delegation. This why you would traditionally have to have your ISP manage reverse DNS for your / Thankfully there are some options that can be used.

  1. RFC 2317 - Classless IN-ADDR.ARPA delegation
  2. PTR delegation using Apex Override
  3. Cross IN-ADDR.ARPA delegation

There are some things to consider when choosing how to perform Classless IN-ADDR.ARPA delegation.

I have used each method (RFC 2317, then PTR delegation and now Cross Delegation) with remarkable success. The only problem that I ran in to with RFC 2317, was when a bot for a notorious spam black list chocked on RFC 2317. At which point in time I switched to PTR delegation. Recently I switched to Cross IN-ADDR.ARPA delegation b/c of the large number of tiny zones that PTR delegation requires.