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Firewalls protect private networks, endpoint devices within those networks, and the data traveling between them. They work by examining each packet of information that comes into a network, and then based on pre-programmed rules either allows the information to enter or blocks it from entering. Firewalls are designed to prevent hackers, viruses, Trojan horses, worms, spyware and other malware from attacking your business.

The data that is sent between computers on a network are identified by unique identifiers that designate where the information originated from, where it’s going to and which network host it needs to communicate with. These identifiers are called ports, and they range in number from 0 to 65,535. Each port indicates the type of data that is being sent. For example, a web server typically uses port 80. A firewall examines each packet of data to see if the information is headed to an internal host that should be allowed to receive it. If the firewall doesn’t have a rule to allow that information, it will drop the packet and it won’t be received.

In the late 1980s, various staff at AT&T Bell Labs worked on a concept that would become a fundamental foundation for future firewall systems. Reid, Vixie and Mogul each played roles in developing the early idea of a circuit-level gateway firewall that didn’t need to reauthorize every single data packet but rather vetted ongoing connections and permitted them. This was the precursor to the stateful inspection firewalls that are still used today.