Firewalls and Intrusion Detection

Introduction to Firewalls

A firewall is a computer or group of computers that stand between  trusted networks (such as LAN) and untrusted networks (such as the Internet), inspecting all traffic passing between them.

A firewall can be a router, a personal computer, or a collection of hosts, that is set up specifically to shield a private network from security attack that comes from an external entity 

The basic function of a firewall is to screen network traffic for the purpose of Preventing unauthorized access between computer networks.

To be effective in their operation, firewalls must have the following attributes:

All communications must pass through the firewall

The firewall permits only traffic that is authorized

The firewalls can withstand attacks upon itself