IP sets are a framework inside the Linux 2.4.x and 2.6.x kernel which can be administered by the ipset(8) utility. Depending on the type, currently an IP set may store IP addresses, (TCP/UDP) port numbers or IP addresses with MAC addresses in a way which ensures lightning speed when matching an entry against a set.

If you want to

* store multiple IP addresses or port numbers and match against the entire collection using a single iptables rule. * dynamically update iptables rules against IP addresses or ports without performance penalty. * express complex IP address and ports based rulesets with a single iptables rule and benefit from the speed of IP sets.

then IP sets may be the proper tool for you.