What is a Firewall?
Firewall acts as the first line of defense for your network by monitoring and filtering incoming threats based on pre-programmed rules that also dictate which users can access specific areas of your network. Ideally, your firewall will check every incoming threat to determine whether it is malicious or not.
Firewalls can be hardware- or software-based systems that monitor incoming and outgoing network traffic, acting as vigilant gatekeepers that divide legitimate from malicious traffic. These systems use a variety of filtering methods to assess the surface of data packets—small segments of files dismantled by transfer protocols for distribution to destination devices—and compare them against a set of rules designed to recognize threats.
Packet filtering is the earliest and most basic form of firewall that checks the contents of a data packet against a set of security rules. The rules are determined based on the source and destination IP address of a data packet, its contents, and port numbers—a unique designation between 0 and 65,535 that helps identify the purpose of each data packet (e.g., web servers typically use port 80).
Developed in the late 1980s by Mogul, Reid, and Vixie at Digital Equipment Corp, this packet filter technology introduced the concept of vetting external connections before they can reach computers on an internal network. Some consider it to be the first true firewall system, but others note that this early packet filter technology was really a component piece of technology that supported the later development of real firewall systems.