Linux Firewalls, Third Edition

iptables Syntax

As presented earlier, iptables uses the concept of separate rule tables for different packet processing functionality. Nondefault tables are specified by a command-line option. Three tables are available:

• filter— The filter table is the default table. It contains the actual firewall filtering rules. The built-in chains include these:

  • INPUT

  • OUTPUT

  • FORWARD

• nat— The nat table contains the rules for Source and Destination Address and Port Translation. These rules are functionally distinct from the firewall filter rules. The built-in chains include these:

  • PREROUTING (DNAT/REDIRECT)

  • OUTPUT (DNAT/REDIRECT)

  • POSTROUTING (SNAT/MASQUERADE)

• mangle— The mangle table contains rules for setting specialized packet-routing flags. These flags are then ...