A firewall is a device (usually a router or a computer) installed between the internal network of an organization and the rest of the Internet. A firewall is designed to control the access to a system.



A firewall is classified as:

  • Packet filter firewall
  • Proxy-based firewall

Packet-filter Firewall

A packet filter firewall filters at the network or transport layer.

Proxy Firewall

A proxy firewall filters at the application layer. For example: an organization wants to implement the following policies regarding its Web pages: Only those Internet users who have previously established business relations with the company can have access; access to other users must be blocked. In this case proxy firewall is used.

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