18.3.2. Command Options
Command options instruct
iptables to perform a specific action. Only one command option is allowed per
iptables command. With the exception of the help command, all commands are written in upper-case characters.
iptables commands are as follows:
-A— Appends the
iptablesrule to the end of the specified chain. This is the command used to add a rule when rule order in the chain does not matter.
-C— Checks a particular rule before adding it to the user-specified chain. This command can help you construct complicated
iptablesrules by prompting you for additional parameters and options.
-D— Deletes a rule in a particular chain by number (such as
5for the fifth rule in a chain). You can also type the entire rule, and
iptablesdeletes the rule in the chain that matches it.
-E— Renames a user-defined chain. This does not affect the structure of the table.
-F— Flushes the selected chain, which effectively deletes every rule in the the chain. If no chain is specified, this command flushes every rule from every chain.
-h— Provides a list of command structures, as well as a quick summary of command parameters and options.
-I— Inserts a rule in a chain at a point specified by a user-defined integer value. If no number is specified,
iptablesplaces the command at the top of the chain.
WarningBe aware when using the
-Ioption that the order of the rules within a chain are important for determining which rules apply to which packets.
-L— Lists all of the rules in the chain specified after the command. To list all rules in all chains in the default
filtertable, do not specify a chain or table. Otherwise, the following syntax should be used to list the rules in a specific chain in a particular table:
iptables -L <chain-name> -t <table-name>Additional options for the
-Lcommand option, which provide rule numbers and allow more verbose rule descriptions, are described in Section 18.3.6, “Listing Options”.
-N— Creates a new chain with a user-specified name.
-P— Sets the default policy for the specified chain, so that when packets traverse an entire chain without matching a rule, they are sent on to the specified target, such as ACCEPT or DROP.
-R— Replaces a rule in the specified chain. The rule's number must be specified after the chain's name. The first rule in a chain corresponds to rule number one.
-X— Deletes a user-specified chain. Deleting a built-in chain for any table is not allowed.
-Z— Zeros the byte and packet counters in all chains for a table.