Many iptables commands have the following structure:

         iptables [-t <table-name>] <command><chain-name><parameter-1> \ <option-1><parameter-n><option-n>
      

The <table-name> option allows the user to select a table other than the default filter table to use with the command. The <command> option dictates a specific action to perform, such as appending or deleting the rule specified by the <chain-name> option. Following the <chain-name> are pairs of parameters and options that define what happens when a packet matches the rule.

When looking at the structure of an iptables command, it is important to remember that, unlike most other commands, the length and complexity of an iptables command can change based 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 iptables commands, it is helpful to recognize 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 iptables -h to view a comprehensive list of iptables command structures.