First, make sure that your nameservers are authoritative for the domain. Typically the ISP handles RDNS.
Assuming that your nameservers are, you'd create a zone and records normally. Assume the network is 216.1.2.0:
zone "0.2.1.216.in-addr.arpa" {
type master;
file "/var/named/216.1.2.rev";
};
In file "/var/named/216.1.2.rev":
2.1.216.in-addr.arpa. IN SOA (usual stuff)
100.2.1.216.in-addr.arpa. IN PTR servername.domain.
and so forth.