The three main types of firewall technology are:

(i)Packet Filtering Firewalls:

This type of firewall focuses on detecting 'packets' and blocks all but selected network traffic. It is typically limited in functionality to filtering; thus you may not receive information as to the origin of the communications, internal users, time and file sizes transmitted and other statistical information.

(ii)Proxy Servers:

Proxy Servers allow indirect access to and from the Internet by breaking the client/server model. Thus every client/server communication will require two connections, one from the client to the firewall (which acts as a 'proxy' for the desired server, and one from the firewall to the desired server). This system has the advantage of being able to provide detailed information, but scalability can be an issue.

(iii)Application Gateway:

An Application Gateway provides the highest level of security possible and provides full application layer awareness without interposing a proxy server. It works by extracting the state-related information required for security decisions from all application layers and maintains this information in dynamic state tables for evaluating subsequent connection attempts. This provides a solution that is highly secure, offering high performance and scalability.