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eliminating information that should not be there. This provides security for

the computers connected to your router, because computers from the

outside cannot access or send information directly to any computer on

your network. The router determines which computer the information

should be forwarded to and sends it. If the information is not intended for

any computer on your network, the data is discarded. This keeps any

unwanted or harmful information from accessing or damaging your

network.

Introduction to Firewalls

A firewall is a device that sits between your computer and the Internet that

prevents unauthorized access to or from your network. A firewall can be a

computer using firewall software or a special piece of hardware built

specifically to act as a firewall. In most circumstances, a firewall is used to

prevent unauthorized Internet users from accessing private networks or

corporate LAN’s and Intranets.

A firewall watches all of the information moving to and from your network

and analyzes each piece of data. Each piece of data is checked against a

set of criteria that the administrator configures. If any data does not meet

the criteria, that data is blocked and discarded. If the data meets the

criteria, the data is passed through. This method is called packet filtering.

A firewall can also run specific security functions based on the type of

application or type of port that is being used. For example, a firewall can

be configured to work with an FTP or Telnet server. Or a firewall can be

configured to work with specific UDP or TCP ports to allow certain

applications or games to work properly over the Internet.

Introduction to Local Area Networking

Local Area Networking (LAN) is the term used when connecting several

computers together over a small area such as a building or group of

buildings. LAN’s can be connected over large areas. A collection of LAN’s

connected over a large area is called a Wide Area Network (WAN).

A LAN consists of multiple computers connected to each other. There are

many types of media that can connect computers together. The most

common media is CAT5 cable (UTP or STP twisted pair wire.) On the

other hand, wireless networks do not use wires; instead they communicate

over radio waves. Each computer must have a Network Interface Card

(NIC), which communicates the data between computers. A NIC is usually

a 10Mbps network card, or 10/100Mbps network card, or a wireless

network card.

Most networks use hardware devices such as hubs or switches that each

cable can be connected to in order to continue the connection between

computers. A hub simply takes any data arriving through each port and

forwards the data to all other ports. A switch is more sophisticated, in that

a switch can determine the destination port for a specific piece of data. A

switch minimizes network traffic overhead and speeds up the communication over