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Firewalls are digital security devices that protect networks from unwanted traffic and limit access to only trusted communications. They can be software installed on a computer or hardware that attaches to a network device such as a router or switch.

A firewall is a network security system that checks incoming and outgoing traffic against a set of pre-programmed rules to keep it safe. It can also be used to restrict which users on the network can access specific areas.

There are different types of firewalls, including packet filtering, stateful inspection, proxy firewall (aka application-level gateway), and next generation firewalls. Each has its own strengths and weaknesses.

Packet Filtering

The oldest and most common form of a firewall, a network layer or packet filter examines packets at a lower level in the TCP/IP protocol stack. If the packet does not match a pre-established rule set, it is discarded or blocked.

Stateful filters look at the source and destination address, protocol, and port number of each incoming packet. It may also check if the packet is related to one previously passed, which can mitigate an attack known as port scanning.


A proxy firewall or application-level gateway resembles a mirror of your computer and detects malicious actors trying to connect to it. Then, it blocks the connection or redirects the information to another server.