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# What is a Firewall

A firewall is a fence between your computer or your internal network and the outside world or the Internet. A particular firewall implementation might use one or more of the methods listed here to provide that barrier.

* Packet filtering
* Stateful packet filtering
* User authentication
* Client application authentication

At a minimum, a firewall will filter incoming packets based on parameters such as packet size, source IP address, protocol, and destination port.