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.
The iptables commands are as follows:
  • -A — Appends the iptables rule 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 iptables rules by prompting you for additional parameters and options.
  • -D — Deletes a rule in a particular chain by number (such as 5 for the fifth rule in a chain). You can also type the entire rule, and iptables deletes 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, iptables places the command at the top of the chain.

    Warning

    Be aware when using the -A or -I option 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 filter table, 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 -L command 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.