What Is a Firewall?

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A network firewall protects a computer network from unauthorized access. Network firewalls may be hardware devices, software programs, or a combination of the two.

Network firewalls guard an internal computer network, for example, a home, school, business, or  intranet, against malicious access from the outside. They may also be configured to limit access to the outside from internal users.

Network Firewalls 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.

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.

Also Known As: proxy, gateway