Originally posted here by ark_templar
N00B Q
so hope u guys dont flame me for it but what are the different types of firewalls as in differrent ways they work in for eg:
the one in my univ works on the basis of certain letters or words in the URL which it blocks internal access to are there different ways of doing the same thing

thanx in advance for any info provided
If it's filtering based on content, then it's more than likely an application layer proxy, not technically a firewall. The terminology has become more than a little skewed as perimeter devices become more and more integrated, but traditional firewalls did not have the ability to make these kinds of decisions. Traditionally, firewalls work only on network layer information, such as IP addresses and ports. Today, though, people commonly refer to any device that filters at the perimeter as a firewall. There are basically as many types of these as there are layers in the OSI model. The only differentiation is the amount of the packet that is processed.

For example, it doesn't take long for a traditional firewall to process a packet up to the network layer and make a decision based on an IP address. It takes much more time for a packet to be processed to the application layer, it's actual content, and have a decision made on the actual payload. The benefits are usually worth it, though. A network layer firewall can say "Don't allow this traffic in on port 81, because I'm only accepting web traffic on port 80." An application layer firewall can say "Don't allow this traffic in on port 80 because I only allow web traffic in, and the payload of this packet does not contain HTTP traffic."

Hope this helps.