Firewall's

A Fire wall does as it says, stops fires and other intruders.

Type of Firewall

There are hardware and software firewall's.
Hardware firewall's can look like a router or modem and connect on one side to the open world via the modem and the other side is the access connection to your network or can easily be between two adjacent networks that only have limited connectivity between them. A good software firewall such as Zonealarm will perform adequately for most domestic and home office situations. A dedicated firewall maybe required for a business depending on the access requirements.

Ports

Imagine a wall made of bricks and each brick had an individual number from 1 to 65000.
Each brick is identical to a port in a firewall in that if something on one side needs to go through the wall it has to go through a port / brick.
Firewall bricks should have a special property in that they can allow things through in one direction and not the other. More information and a check program can be run from the GRC web site following the shields up links.

Configuration

Unless you are familiar with the ports and other network requirements then leave well alone otherwise you could open your system up to unwanted intruders inadvertently.

Where to fit a firewall