Options Used Within Iptables Commands; Structure Of Options; Command Options - Red Hat ENTERPRISE LINUX 4.5.0 Reference Manual

Chapter 18. iptables
rewritten network filter. For more specific information, refer to the Linux Packet Filtering
HOWTO referenced in
3. Options Used within
Rules for filtering packets are put in place using the
of the packet are most often used as criteria:
• Packet Type — Specifies the type of packets the command filters.
• Packet Source/Destination — Specifies which packets the command filters based on the
source or destination of the packet.
• Target — Specifies what action is taken on packets matching the above criteria.
For more information on specific options which address these aspects of a packet, refer to
Section 3.4, "
iptables
The options used with given
and conditions of the overall rule, for the rule to be valid. The remainder of this section explains
commonly-used options for the
3.1. Structure of
Many commands have the following structure:
iptables
iptables [-t <table-name>] <command><chain-name><parameter-1> \
<option-1><parameter-n><option-n>
The option allows the user to select a table other than the default
<table-name>
use with the command. The
appending or deleting the rule specified by the
are pairs of parameters and options that define what happens when a packet
<chain-name>
matches the rule.
When looking at the structure of an
most other commands, the length and complexity of an
on its purpose. A command to remove a rule from a chain can be very short, while a command
designed to filter packets from a particular subnet using a variety of specific parameters and
options can be rather lengthy. When creating
that some parameters and options may create the need for other parameters and options to
further specify the previous option's request. To construct a valid rule, this must continue until
every parameter and option that requires another set of options is satisfied.
Type to view a comprehensive list of
iptables -h

3.2. Command Options

330
Section 7, "Additional
iptables
Match Options" and Section 3.5, "Target
rules must be grouped logically, based on the purpose
iptables
command.
iptables
Options
iptables
option dictates a specific action to perform, such as
<command>
iptables
Resources".
Commands
command. The following aspects
iptables
Options".
option. Following the
<chain-name>
command, it is important to remember that, unlike
command can change based
iptables
commands, it is helpful to recognize
iptables
command structures.
iptables
table to
filter