Computer networks use the Domain Name System (DNS) to determine the IP address associated with a domain name. This process is also known as forward DNS resolution. Reverse DNS (rDNS) is the inverse process of this: the resolution of an IP address to its designated domain name. This document explains how reverse DNS works and how to configure it for your zone.

IPv4
One or more /24 type zones need to be created if your address space has a prefix length between /17 and /24. If your prefix length is between /16 and /9 you will have to request one or more delegations for /16 type zones.

For example, if you have been allocated 10.155.16.0/22, you need to create four reverse zones:

16.155.10.in-addr.arpa.
17.155.10.in-addr.arpa.
18.155.10.in-addr.arpa.
19.155.10.in-addr.arpa.

IPv6
If you have been allocated an IPv6 block that is not on a nibble boundary, you will need to go down to the next nibble and create multiple zones to cover the entire block.

For example, an allocation such as 2001:db8::/29 will result in eight reverse zones of /32 each:

8.b.d.0.1.0.0.2.ip6.arpa.
9.b.d.0.1.0.0.2.ip6.arpa.
a.b.d.0.1.0.0.2.ip6.arpa.
b.b.d.0.1.0.0.2.ip6.arpa.
c.b.d.0.1.0.0.2.ip6.arpa.
d.b.d.0.1.0.0.2.ip6.arpa.
e.b.d.0.1.0.0.2.ip6.arpa.
f.b.d.0.1.0.0.2.ip6.arpa.