We often come across the term firewall. Though I have a general idea about this term I want to have a detailed reading about this concept. If anyone know some useful links or references kindly post it in this discussion for us to read.

If you want to have a detailed understanding of how a firewall works the following link is very useful. The site has detailed and clear explanation about the working technology of firewall.
http://www.howstuffworks.com/firewall.html

Firewall is a system or technology which is designed either by using hardware or software or by using both and thereby prevents unauthorized access to or from a private network. The firewall has various types of techniques like Packet filter, Application gateway, Circuit-level gateway, Proxy server. It is common technology that is mainly used in Internet