reverse dns records, standard delegation and classless delegation

Reverse DNS records permit the lookup of the host name corresponding to an ip address. Direct management of the mapping of host names to ip addresses requires that control of the reverse zone be delegated to the managing party.

The two forms of delegation are standard delegation on a standard subnet boundary and classless delegation by means of CNAME records. (see rfc 3172) edgedirector name servers can handle both types of delegation as long as the correct delegated zone name is specified.

In either type of delegation, the records are kept in a separate dns zone ending in in-addr.arpa.

In practice:

• A standard delegation on a subnet boundary uses the standard name. The delegating name server simply returns a referral to your dns server.

• A classless delegation will also end in in-addr.arpa but are preceded by the delegation naming convention used by the upstream party granting the delegation. The delegating name server contains cname records for each individual address and returns a referral to your dns server and the appropriate cname record contents. There are several recommended naming conventions. The correct one to use is determined by the delegating name server.

zone name examples

zone name for standard delegation of 192.168.100.0/24

    100.168.192.in-addr.arpa

zone name for classless delegation of 192.168.100.64/26

    subnet prefix using '/'        64/26.100.168.192.in-addr.arpa

    subnet prefix using '-'        64-26.100.168.192.in-addr.arpa

    ip range                      64-127.100.168.192.in-addr.arpa

    ip start                          64.100.168.192.in-addr.arpa