•  A computer firewall is a software program that prevents unauthorized access to or from a private network.
  • Firewalls are tools that can be used to improve the security of computers connected to a network, such as LAN or the Internet. They are an integral part of a security for your network. 
  • You can implement a firewall in either hardware or software form, or a combination of both.


  • A firewall absolutely isolates your computer from the Internet using a "wall of code" that inspects each individual "packet" of data as it arrives at either side of the firewall — inbound to or outbound from your computer — to determine whether it should be allowed to pass or be blocked. 
  • When we need to prevent unauthorized access of third party in a private network, firewalls are used. 
  • firewall monitors & controls the traffic flow between the Internet and private network on the basis of a set of user-defined rules.
  • firewalls is easy to install, setup and operate.
  • Most people think that a firewall is a of device that is installed on the network, and it controls the traffic that passes through the network.
  • In simple definition, firewalls are nothing but a system that secure your computer.
  • In the age of high-speed Internet Access, you electronically connect your computer to a broad network , unless you have installed a personal firewall, you have limited control and from which you have limited protection.
  • In a way, connecting to the internet via high-speed connection is like leaving the front door of your house open and unlocked.
  • No matter which firewall you choose, ensure a proper configuration as any mistake can cause more damage to you than no firewall at all.

A Personal firewall is important when:

  • You surf the internet at home using an 'always on' broadband connection.
  • You connect to the internet via a public WiFi network in a park, cafe or airport.
  • You run a home network which needs to be kept isolated from the internet.
  • You wish to be kept informed when any program on your computer attempts to connect to the internet.

There are three basic types of firewalls :

1) Packet Filter Firewall : 
  • Packet Filter Firewall controls the network access by analyzing the outgoing and incoming packets. 
  • It lets a packet pass or block its way by comparing it with pre-established criteria like allowed IP addresses, packet type, port number, etc. 
  • Packet filtering technique is suitable for small networks but gets complex when implemented to larger networks. 
  • It is to be noted that these types of firewalls cannot prevent all types of attacks. 
2) Stateful Inspection : 
  • Stateful Packet Inspection (SPI), which is also sometimes called dynamic packet filtering, is a powerful firewall architecture which examines traffic streams from end to end. 
  • These smart and fast firewalls use an intelligent way to ward off the unauthorized traffic by analyzing the packet headers . 
  • These firewalls works at the network layer in the OSI model and are more secured than the basic packet filtering firewalls. 
3) Circuit level gateways 
  • Circuit level gateways are the second generation of firewall architectures. 
  • Circuit level gateways work at the session layer of the OSI model. 
  • It is basically a packet filter with additional features. 
  • The circuit level gateway examines and validates TCP and UDP sessions before if open up a connection or circuit through the firewall.
  • So it will provide more security than the static packet and dynamic packet filter. The decisions to accept or deny packet is based on examining the 
                                           =>Source address 
                                           =>Destination address 
                                           =>Application or protocol 
                                           =>Source port number