This rush to connect to the rest of the world leaves private computers and networks vulnerable for hackers to gain unauthorized access to the computer s or network s private resources. A connection directly to the Internet is a connection directly to every other network attached to it. One of the methods of keeping intruders away is have a Firewall installed as software or hardware between the computer and the outside connectivity point. Firewalls are used to create security checkpoints on the boundaries of private computers or networks just like controlled borders around nations are done. The firewall routing function provides an inspection capability for all communication passing between the private computer or network to the Internet.
Filters normally drop inbound connection attempts and allow outbound connection attempts.
Filters restrict inbound access to certain IP ranges. The NAT host takes requests from all internal network hosts, thus hiding their identity from the public network. NAT provides multiplexing of a single IP address across an entire network, i.e., one public IP address is converted into many inside the internal network. Proxies allow the complete disconnection of the flow of network-level protocols through a firewall and restrict traffic only the higher level protocols. Proxies stand in for outbound connection attempts to servers and then make the request to the actual target server on behalf of the client.