'''[http://en.wikipedia.org/wiki/Iptables Iptables] is the built-in firewall for LINUX''' consisting of a '''list of rules''' (or '''"tables of policies"'''). If data matches a specified <u>policy</u>, it must “jump” to an existing '''condition'''. Simple conditions include '''ACCEPT''', '''REJECT''', '''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.