Firewall FAQ

By Staff writers, TechRepublic
30 July 2004 11:46 AM
Tags: security, firewall, faq, network

What are the different types of firewalls?

The different types of firewalls are:

  • Packet filter - A packet filter looks at each packet entering the network and, based on its policies, permits or denies these packets. A Cisco IOS Access Control List (ACL) is a basic firewall that works in this way.

  • Stateful packet filter - A stateful packet filter also has rules; however, it keeps track of the TCP connection state so it is able to monitor the -conversations" as they happen on the network. It knows the normal flow of the conversations and knows when the conversations are over. Thus, it more intelligently is able to permit and deny packets entering the network. Because of this, a stateful packet filter (stateful firewall) is much more secure than a regular packet filter.

  • Application gateway - An application gateway is a system that works for certain applications only. It knows the "language" that that application/protocol uses and it monitors all communications. An example would be an SMTP gateway.

  • Proxy server - A proxy server performs network transactions on your behalf. The most common use for this is a Web-proxy server. A Web proxy will take requests from users' Web browsers, get the Web pages from the Internet, and return them to the user's browser.
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