IP sets are a framework inside the Linux kernel since 2.4.x, 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.

ipset may be the proper tool for you, if you want to

o store multiple IP addresses or port numbers and match against the collection
by iptables at one swoop;

o dynamically update iptables rules against IP addresses or ports without
performance penalty;

o express complex IP address and ports based rulesets with one single iptables
rule and benefit from the speed of IP sets