IPTables Firewall Tables

IPTables Firewall Tables
There are currently three independent tables (which tables are present at any time depends on the kernel configuration options and which modules are present).


This is the default table (if no -t option is  passed).   It contains  the built-in chains INPUT (for packets destined to local sockets), FORWARD (for packets  being routed  through the box), and OUTPUT (for locally-generated packets).

This  table  is  consulted  when a packet that creates a new connection is encountered.  It consists of three  built-ins: PREROUTING  (for  altering packets as soon as they come in), OUTPUT (for altering locally-generated packets before  routing),  and  POSTROUTING  (for  altering  packets as they are about to go out).

This table is used for specialized packet alteration.  Until kernel  2.4.17  it  had two built-in chains: PREROUTING (for altering incoming packets before routing)  and OUTPUT  (for altering  locally-generated  packets before routing).  Since kernel 2.4.18, three other built-in  chains  are  also  supported INPUT (for packets coming into the box itself), FORWARD (for altering packets being routed  through  the  box), and  POSTROUTING  (for altering packets as they are about to go out).

This table is used mainly for  configuring  exemptions  from connection  tracking in combination with the NOTRACK target. It registers at the netfilter hooks with higher priority and is  thus called before ip_conntrack, or any other IP tables. It provides the following built-in chains:  PREROUTING  (for packets  arriving  via  any  network  interface) OUTPUT (for packets generated by local processes)

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