IP sets are a framework inside the Linux 2.4.x and 2.6.x kernel, which can be administered by the ipset 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 collection by iptables at one swoop;
• dynamically update iptables rules against IP addresses or ports without performance penalty;
• express complex IP address and ports based rulesets with one single iptables rule and benefit from the speed of IP sets

IP sets was written by Jozsef Kadlecsik and it is based on ippool by Joakim Axelsson, Patrick Schaaf and Martin Josefsson.
Many thanks to them for their wonderful work!