What Does Firewall Mean?

A firewall is software or hardware that can be configured to block data from certain locations, applications, or ports while still allowing relevant and necessary data to pass through.


Firewalls are used to block unauthorized access to or from networks that have different levels of trust. They work by enforcing security policies and are used to prevent malicious actors from gaining access to private networks connected to the Internet. A firewall may be implemented through hardware, software or a combination of both.

Firewalls at the perimeter of a network can be augmented by Zero Trust policies to ensure network access is granted appropriately and securely at every access layer of the OSI Model.

Techopedia Explains Firewall

Firewalls are sometimes perceived as being old-fashioned because they are designed to protect a network from its perimeter, but in reality, they play an important role in Zero Trust Architectures (ZTAs).

How Do Firewalls Work?

Firewalls generally use two or more of the following methods to protect a network’s perimeter:

  • Packet Filtering: Firewalls filter packets that attempt to enter or leave a network and either accept or reject them depending on the predefined set of filter rules.
  • Application Gateway: The application gateway technique employs security methods applied to certain applications such as Telnet and File Transfer Protocol servers.
  • Circuit-Level Gateway: A circuit-level gateway applies these methods when a connection such as Transmission Control Protocol is established and packets start to move.
  • Proxy Servers: Proxy servers can mask real network addresses and intercept every message that enters or leaves a network.
  • Stateful Inspection or Dynamic Packet Filtering: This method compares not just the header information, but also a packet’s most important inbound and outbound data parts. These are then compared to a trusted information database for characteristic matches. This determines whether the information is authorized to cross the firewall into the network.

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Margaret Rouse

Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…