FirewallA firewallis a means of protecting a network from unwanted users. Firewalls differ in function and are designed to meet the various needs and resources of networked organizations.
A firewall provides a local networked environment (LAN) with protection from external networks. The type of firewall chosen by an organization varies according to which of the following statements reflect the network manager's philosophy:
The first statement would apply to a corporation that is willing to accept some risk in order to ensure maximum use of outside networks, such as the Internet. The second statement applies to corporations that want to disallow most types of external communication. These corporations would probably spend the greatest amount of money on their security system.
Firewalls can protect a network from a number of security risks. They are configured to keep those with unauthenticated logins from entering the local network to steal information or spread viruses. In addition, a firewall can serve as a security check-point for all network communication, as it enables a network administrator to monitor the type of communication occurring in the network.
Unfortunately, a firewall can not protect a network from all types of insurgencies. It only works when attacks come from within the network. Many organizations will also face security leaks via telephones, fax machines, and modems. Thus, firewalls can be only one part of an effective security system.
There are two basic types of firewalls: application-level and network-level. Historically, there were many differences between application and network level firewalls, but today they are beginning to look more like each other. The application-level firewalls run using proxy servers. A proxy server is an intermediary (gateway) computer between the local area network and external networks. The proxy permits no direct traffic between networks. It is application- specific. This means that each protocol must be programmed to be accepted by the proxy. When a local network user wishes to access something from the Internet, the request must go through the proxy server. The proxy server is able to audit the traffic going through it.
The network-level firewall is based on the source of the communication. Since it pays attention to network information, and not the application information, it is not able to recognize where packets of information have come from. However, the newest firewalls of this type have improved methods of collecting information about the information passing through them. Unlike the application-level network that typically runs via a proxy server, network-level firewalls route traffic directly through them. This requires that they have a valid IP (Internet Protocol) address block. Network-level firewalls are normally faster and more transparent than application-level firewalls.