A firewall is a set of related programs, located at a network gateway server, that protects the resources of a private network from users of other networks. (The term also implies the security policy that is used with the programs.) An enterprise with an intranet that allows its workers access to the wider Internet installs a firewall to prevent outsiders from accessing its own private data resources and for controlling what outside resources its own users have access to.
Basically, a firewall, working closely with a router program, filters all network packets to determine whether to forward them to their intended destination. A firewall also includes or works with a proxy server that makes network requests on behalf of workstation users. A firewall is often installed in a specially designated computer separate from the rest of the network so that no incoming request can get directly at private network resources.
There are a number of firewall screening methods. A simple one is to screen requests to make sure they come from acceptable (previously identified) domain names and IP addresses. For mobile users, firewalls allow remote access in to the private network by the use of secure logon procedures and authentication certificates.
Hubs, Switches and Routers
Hubs, Switches and Routers are all devices that direct data between computers and other devices on your network. They come both in the standard CAT5 or CAT6 connection and wireless, which is able to relay data to your more mobile devices.
Network cards fit in computers, laptops and printers to connect them to the rest of the network. Most network cards use a direct connection using a CAT5 cable, similar to a telephone cable. For laptops and mobile devices such as Pocket PC's and Palm Pilots, or in areas that installing network cables might be costly or dangerous, it may be beneficial to use wireless network cards.