Firewall A firewall protects a computer network from unauthorized access. Firewalls may be hardware devices, software programs, or a combination of the two. A firewall typically guards an internal network against malicious access from the outside; however, firewalls may also be configured to limit access to the outside from internal users.
Perhaps the most familiar form of Internet firewall is a proxy server. Proxy servers act as an intermediary between internal and external computers by receiving and selectively blocking data packets at the network boundary. These firewalls also provide an extra measure of safety by hiding internal LAN addresses from the outside. In a proxy server firewall environment, network requests from multiple clients appear to the outsider as all coming from the same proxy server address.