What Is a Network Firewall?

Network firewalls protect an entire network from incoming intrusions

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A network firewall protects a computer network from unauthorized access. It might be a hardware device, software program, or a combination of the two.

Network firewalls guard an internal computer network against malicious access from the outside, such as malware-infested websites or vulnerable open network ports. You can find them anywhere a network is used, like at home, school, business, or even an intranet.

A network firewall may also be configured to limit access to the outside from internal users, as in the case of parental controls or workplace locks, both of which commonly prevent access to gambling and adult websites, among many other content types.

How a Firewall Works

When a firewall is used at its full potential, it constantly monitors all incoming and outgoing traffic. What makes a firewall different from just a traffic analyzer is that it can also be set up to block certain things.

A firewall might disable particular applications from accessing the network, block URLs from loading, and prevent traffic through certain network ports.

Some firewalls can even be used in mode where they block everything until you explicitly allow each single access. This is one way to block everything on a network so that you can manually set up safeguards against network-related threats.

Network Firewall Software and Broadband Routers

Many home network router products include built-in firewall support.

The administrative interface of these routers includes configuration options for the firewall. Router firewalls can be turned off (disabled), or they can be set to filter certain types of network traffic through so-called firewall rules.

Tip: See How to Enable Your Wireless Router's Built-in Firewall to learn more, including how to check that the router even supports a firewall.

Lots of software firewall programs exist that you install directly onto the hard drive of the computer that needs it. These firewalls, however, only protect the computer that's running it; network firewalls protect the entire network. Much like a network firewall, computer-based firewalls can be disabled, too.

In addition to dedicated firewall programs are antivirus programs that often include a built-in firewall with the installation.

Network Firewalls and Proxy Servers

Another common form of network firewall is a proxy server. Proxy servers act as an intermediary between internal computers and external networks by receiving and selectively blocking data packets at the network boundary.

These network firewalls also provide an extra measure of safety by hiding internal LAN addresses from the outside internet. In a proxy server firewall environment, network requests from multiple clients appear to the outsider as all coming from the same proxy server address.