Tomado de http://www.tecmint.com/linux-iptables-firewall-rules-examples-commands/ Managing network traffic is one of the toughest jobs a system administrators has to deal with. He must configure the firewall in such a way that it will meet the system and users requirements for both incoming and outgoing connections, without leaving the system vulnerable to attacks.  25 IPtables Firewall Rules for Linux This is where iptables come in handy. Iptables is a Linux command line firewall that allows system administrators to manage incoming and outgoing traffic via a set of configurable table rules. Iptables uses a set of tables which have chains that contain set of built-in or user defined rules. Thanks to them a system administrator can properly filter the network traffic of his system. Per iptables manual, there are currently 3 types of tables: FILTER – this is the default table, which contains the built in chains for:INPUT – packages destined for local socketsFORWARD – packets ro