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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 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 a network.