Information, Computer and Network Security Terms Glossary and
A network firewall is a network based firewall devices that protect a computer network from unauthorized access. Network firewalls may be hardware devices, software programs, or a combination of the two. A network firewall typically guards an internal computer network against malicious access from the outside; however, network firewalls may also be configured to limit access to the outside from internal users.
Perhaps the most common form of network firewall is a proxy server. Proxy servers act as an intermediary between intranet and Internet computers by receiving and selectively blocking data packets at the network boundary. Network firewalls may also provide an extra functions 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.