We all know that the safest method of keeping unauthorized persons out of our computer is to never connect it to the outside world. Since we all know that we will not be completely separate from that outside world, we need to have something between our computer and that world. Firewalls are defined as systems, software or hardware based, that handle the approval or rejection of each connection attempt between our computer and the external world of computers. Firewalls are located at the gateways of your computer or network. They act as border guards for the compute or network.
Firewalls provide a centralized location for external security services.
By their nature, firewalls create bottlenecks between the internal and external computers as all traffic between them must pass through a single point of control. We need firewall technology because of the nature of the Internet protocols. Security service provided by nearly all firewalls function using three fundamental methods of operation. There are also two other security services concerning encryption that are part of these systems providing five total services. The encryption services are Encrypted Authentication and Encrypted Tunnels.