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|{{Admon/note | | '''[http://en.wikipedia.org/wiki/Iptables Iptables] is the built-in firewall for LINUX'''. Iptables is a '''list of rules'''. Each rule is placed into a particular chain and when data is sent '''into''', '''out of''' or '''through''' a PC the data. If data matches a specified rule, it must “jump” to an existing '''condition'''. Simple conditions include '''ACCEPT''', '''DROP''' and '''LOG''' but there are also more complex conditions that can be applied and there is even the option to create your own conditions.
When using iptables, the '''Filter''' table is important because it contains the following essential '''chains''':<br><br>
'''INPUT:'''<br>Data is checked against the INPUT chain to see if it is '''allowed into''' the PC.<br><br>'''OUTPUT:'''<br>Data is checked against the OUTPUT chain to see if it is <u>allowed to go outside</u> of the PC.<br><br>'''FORWARD:'''<br>PC is acting as a router it does not actually send or receive data, it <u>FORWARDS</u> data from one machine to another.
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