IPTables is divided the package traffic using three kinds of tables. Every table has few chains. The three important table is a Filter table, NAT table and Mangle table, and let us continue with more detail only at Inside the Computers.
Filter table is the table contains chain and rules which has function to do in or out package filtering. NAT table has function as a table at modified or doing in or out package translate peripherals. The modified is to change the addressing and communication ports inside the package, becoming a form known by the peripherals inside or outside. Examples is NAT/PAP dan IP masquerading.
The third table is mangle table which has function to do modified packaging data, but the function is more to the marking to the package. This modification happen at the field level from IP protocol such as type of service, etc.
Inside the filter table there is three chain which will service package filtering data, which is INPUT, OUTPUT and FORWARDING. Why we write it with capital letter, because that’s the way we write in the process of making of filter.
Chain INPUT is useful to do the filtering to data package. OUTPUT is chain which connect to all the out package. Chain FORWARD is the most effective, it will make our computers become a router. All this chain is doing all filtering data package which in to the machine but not for those machine itself, but it will through to the other peripherals. From those three chain we can make a filtering system as we need.
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