Firewall is an application installed on a computer or computer network and work to prevent them from piercing access interference from entitled outside parties. The firewall also works to protect the data that exists in a computer or computer network, protect from data theft or spying. All access activities that enter or exit in a network must be through this firewall. Firewalls also be used for detecting and monitoring all in out network data. Firewall tasks are monitoring and maintaining network elements such as source (the source of the data packet originated), destination, the protocol that is used and the content of the package the data itself.

So, the firewall can be used by Internet users to protect the network from interference outside parties with a way to block the transmission of data from a particular address, prevent the exchange of data between certain units of the computer, reject the package with certain contents of data, and prevent the using of certain protocols in data exchange. While some techniques on the firewall such as:

Proxy Server which captures the contents of the data packets that enter and exit hide the address information networks. Application Gateway, apply the security mechanism for special applications such as FTP and Telnet. Circuit Level Gateway; make the security mechanism of TCP or UDP connections. Packet Filter, which monitors in out packet data network and filtrate based on the rules that have been previously configured.