Firewall is a barrier between Local Area Network (LAN) and the Internet. It allows keeping private resources confidential and minimizes the security risks. It controls network traffic, in both directions.
The following diagram depicts a sample firewall between LAN and the internet. The connection between the two is the point of vulnerability. Both hardware and the software can be used at this point to filter network traffic.
There are two types of Firewall system: One works by using filters at the network layer and the other works by using proxy servers at the user, application, or network layer.
Firewall management must be addressed by both system managers and the network managers.
The amount of filtering a firewall varies. For the same firewall, the amount of filtering may be different in different directions.