iptables Features
iptables uses the concept of separate rule tables for different kinds of packet processing functionality. These rule tables are implemented as functionally separate table modules. The three primary modules are the rule filter table, the NAT nat table, and the specialized packet-handling mangle table. Each of these three table modules has its own associated module extensions that are dynamically loaded when first referenced, unless you've built them directly into the kernel.
The filter table is the default table. The other tables are specified by a command-line option. The basic filter table features include these:
Chain-related operations on the three built-in chains (INPUT, OUTPUT, and FORWARD) and on user-defined chains
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