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Firewall is an essential network security tool that monitors and regulates data traffic. It prevents malicious activity such as cyberattacks, identity theft and financial fraud by screening out threats originating from remote servers and networks.

Firewalls can be either software or hardware devices. Software firewalls are computer programs you can install on user devices while a hardware firewall establishes a barrier between networks. Both firewalls can be configured via the command line or a Web interface, depending on the product and deployment model.

The first generation of firewalls were designed as hardware appliances. These firewalls scanned individual data packets, allowing or blocking them based on a set of rules defining a specific service access policy. Later firewall generations developed to surpass the limits of these first generation products by implementing a variety of filtering methods.

Network layer or packet filters inspect each packet at a relatively low level of the TCP/IP protocol stack, deciding whether to allow or block it based on its IP address and port. Despite their lower level of inspection, they provide a higher degree of security than firewalls that do not perform network layer inspection.

Proxy firewalls, also known as application-level or layer 7 firewalls, read and filter incoming and outgoing application protocols like FTP and HTTP. They save information about open connections, which allows them to evaluate incoming and outgoing data with more context than firewalls that use only network and transport layer filters (e.g., packets with ICMP or UDP).