Firewall

A firewall is a network security system, either hardware or software based,that controls incoming and outgoing network traffic based on a set of rules.

Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. 

  

    

Types of Firewall

Firewalls can be either hardware or software but the ideal firewall configuration will consist of both.

1.    Software firewall

Software firewalls are installed on your computer (like any software) and you can customize it; allowing you some control over its function and protection features.

2.    Hardware firewall

Hardware firewalls are usually routers with a built in Ethernet card and hub. 

 

     
Common Firewall Techniques

There are several types of firewall techniques that will prevent potentially harmful information from getting through.

Packet Filter

Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. 

Application Gateway

Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.

Circuit-level Gateway

Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.

Proxy Server

Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network address.