What is a Firewall?



A Firewall is a computer system or network designed to block unauthorized access by permitting the authorized communications. Firewall is a device or a system configured to deny, encrypt, decrypt all computer traffic among varying security domains based on a set of rules. Firewalls can be implemented either on the hardware or software or on combination of both. Firewalls usually stop the non-permitted internet users from getting the access to the private networks, mainly intranets. All the traffic passes through the firewall and it examines each message and blocks the ones that do not meet the specified security norms.

Firewalls make use of several techniques to block unauthorized accesses like Packet filters, Application gateways, Circuit level gateways and Proxy servers. Packet filters keep a look at each packet of data entering and leaving the network and thus accepts and rejects as per the user defined rules. Its quite effective and transparent but difficult to configure.


Other technique is the Application gateways. It is quite effective as it applies security norms to the applications like FTP and Telnet but subsequently leads to performance degradations. The Circuit level gateway also applies security norms like application gateways whenever a UDP or TCP link is established. Data packets thus move between the hosts without further inspection. In this way proxy server intercepts the messages entering and leaving the network and thus successfully hides the real network addresses.

A Firewall regulates the flow of traffic between computer networks of varying trust levels, basically among the non trustable zone Internet and the trusted zone, an internal network. But there lies a zone between the trusted and mistrusted zones referred to as the perimeter network or Demilitarized zone.

For effective results and protection, firewall needs to be properly configured. A firewall pretends to work within explicitly allowed rule sets. Thus, effective firewall configuration requires the detailed understanding of the network applications along with the checkpoints essential for the organizations every day operations.

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