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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 LANs 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, the 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 to-
gether over a small area such as a building or group of buildings. LANs can be connected
over large areas. A collection of LANs 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 a 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 Inter-
face Card (NIC), which communicates the data between computers. A NIC is usually a
10Mbps network card, a 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 it can determine the destination port for a specific piece of
data. A switch minimizes network traffic overhead and speeds up the communication
over a network.
Networks take some time to plan and implement correctly. There are many ways to
configure your network. You may want to take some time to determine the best network
set-up for your needs.
