| 8.1 |  | Introduction to Firewalls |
| 8.1.1 |  | Firewalls and firewall technologies |

| What is a firewall? By conventional definition, a firewall is a partition made of fireproof material designed to prevent the spread of fire from one part of a building to another. Firewalls are also used to isolate hazardous areas, such as engine rooms, from safer ones, such as living quarters. In both cases, the goal is to keep the hazardous areas from gaining access to the safe areas.

When applying the term to a computer network, a firewall provides a single point of defense between networks and protects one network from the other. It is a system or group of systems that enforces an access control policy between two or more networks . Usually, a firewall protects the private network of a company from the public or shared networks to which it is connected .

A firewall is a network gateway that enforces the the rules of network security. It evaluates each network packet against the policies of network security, which is a collection of security rules, conventions, and procedures governing communications in to and out of a network. Firewalls can monitor all the network traffic and alert the IT staff to any attempts to circumvent security or to any patterns of inappropriate use.

Why is a firewall needed?
The firewall exists to enforce the enterprise security. It enables a company to do business online, while providing the necessary security between the internal network of the enterprise and an external network. This external network can be an extranet linking the enterprise to its corporate partners or an Internet link through which the enterprise gains access to customers or remote users. This means that a perimeter firewall makes an ideal location for outward-facing resources such as Web and FTP servers. A firewall can be configured to allow Internet access to these systems while blocking or filtering admission to other protected resources.

Usually, IP traffic forwarding is disabled on the firewall to ensure that all traffic between the internal network and external networks passes through the firewall. This allows the firewall to inspect all network packets that traverse the network boundary. In addition to access control, the firewall also provides a natural focal point for the administration of other network security measures.