Included with Red Hat Enterprise Linux are advanced tools for network packet filtering — the process of controlling network packets as they enter, move through, and exit the network stack within the kernel. Kernel versions prior to 2.4 relied on ipchains for packet filtering and used lists of rules applied to packets at each step of the filtering process. The introduction of the 2.4 kernel brought with it iptables (also called netfilter), which is similar to ipchains but greatly expands the scope and control available for filtering network packets.

This chapter focuses on packet filtering basics, defines the differences between ipchains and iptables, explains various options available with iptables commands, and explains how filtering rules can be preserved between system reboots.

For instructions on constructing iptables rules or setting up a firewall based on these rules, refer to Section 18.7, “Additional Resources”.