Linux Firewalls, Third Edition

Optimized iptables Firewall from Chapter 5

For most systems on DSL, cable modem, and lower-speed leased line connections, the chances are good that the Linux network code can handle packets faster than the network connection can. Particularly because firewall rules are order-dependent and difficult to construct, organizing the rules for readability is probably a bigger win than organizing for speed.

In addition to general rule ordering, iptables supports user-defined rule lists, or chains, that you can use to optimize your firewall rules. Passing a packet from one chain to another based on values in the packet header provides a means to selectively test the packet against a subset of the INPUT, OUTPUT, or FORWARD rules rather than testing the ...