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Networking your computers lets employees work together by sharing files, information and resources. But when your network is also connected to the Internet, it opens the door for outsiders to snoop on network activity or even use your resources without permission. That's where a firewall comes in. A firewall protects your local area network (LAN) - or even a single computer - against outside intrusion. Firewalls work as filters between the outside world and a private network, approving some types of traffic (such as when you want to access a Web page) and blocking others (when unauthorized users attempt to access your network). The term "firewall" is borrowed from architecture, but it doesn't actually refer to any one device. A firewall could be either a piece of hardware or software, and a network may use more that one type of firewall in order to provide extra security. There are two common types of firewall: *A packet-filtering firewall applies predefined rules to filter the chunks of data, or packets, that pass through it. The filter accepts or rejects packets based upon the originating computer's network address or other characteristics. The packet filter may be a computer, or it may be part of a separate piece of hardware, such as a router. *A proxy server, also known as a gateway, acts as a middleman that relays data between the network and the outside world. The proxy prevents outsiders from gathering information about computers inside the network. The proxy can also screen packets based on their application type (Web access or email, for example) or other identifying traits. A firewall may also screen internal traffic on a network, separating different departments or branches of a large company. In some cases, a company will configure a proxy server to block employee access to certain types of Internet content, such as streaming audio or video. |