Different kinds and needs:
A firewall system can be Hardware, Software, or both. These devices will filter information that comes through the Internet to your computer.

Many companies and individual people will have a need for some form of protection from hackers who gain access to their networks (whether it is a personal computer or a business network) through the Internet. That's where the firewall protection will be necessary.

If a company has employees who need to work from their homes (Telecommuters) and also access the Internet, firewalls will ensure that only authorized users can access the network over the Internet.

Let’s just say that you are an individual user of the Internet. If you’re logged onto the Internet all the time, you should have some sort of a firewall in place, because if you don’t you are vulnerable to hackers. Staying logged on all the time gives an unauthorized person time to work on entering your computer without you knowing.

You might be an employee who works for a large corporation; the company you work for should have a firewall in place. If the company doesn’t have a firewall, they are prone to viruses and hackers, and that can be fatal when you own a business.

A firewall works by inspecting the requests and data that passes between the private network and the Internet.

Thankfully Firewalls are customizable:
There are four common Methodologies:

• Proxy server
• Packet filter
• Application gateway
• Circuit gateway

You can add or remove some filters based on certain conditions:

IP addresses

This is a unique four-part numeric address assigned to each computer on the Internet.

Domain names

This is also called (DNS) a naming system used for computers on the Internet. Example: Middlebury Community Schools Network - Domain name is MCSNET.

Protocols-IP, TCP, HTTP

This is a set of rules and procedures that determine how a computer System receives and transmits data.

Here are four examples of firewalls, ranging from very expensive to Free:

1. A Hardware Device:
   Cost: $2,316.00
   
   That is rack- mountable and is 2 inches high: SONICWALL PRO 300 INTERNET SECURITY APPLIANCE
   
   
   
   This device is made for medium sized businesses and branch offices.
   
   "A standards-based appliance, the PRO 300 requires no operating system maintenance often found in software-based security products. The PRO 300 fits perfectly into a large corporate network infrastructure and can be managed by a wide array of local or remote options including CLI, Web-interface, and SNMP. For centralized management and policy setting, the award-winning SonicWALL Global Management System is designed to reduce administration overhead as security requirements scale."
   
   Source: www.sonicwall.com
   
   
2. A software device:
   Price: $39.95
   
   This one is considered an award-winning personal firewall. It is trusted by millions and now includes online privacy protection.
        New, More Intuitive Interface Provides Greater Ease of Use with a completely updated look and feel
        New Privacy Protection
        New Ad Blocking Features
        Enhanced Alert Advisor
        Enhanced Support for Local Area Networks, Including Wireless Networks
        For Windows 98 SE, Me, NT, 2000 and XP
   
   Source: www.zonealarm.com
   
   
3. Electronic Watch Dog
   Cost: $87.95
   "Police say a barking dog is an excellent way to deter burglars and this one never needs food, water or to be taken for a walk. The Electronic Watch Dog is the ideal watchdog because he does what even the best living, breathing watchdog can't do (without some of the annoying problems that go with owning a dog). With his electronic radar eyes, the Electronic Watch Dog can "see" through thick doors, walls and glass. And once his cord is plugged in, he'll stay on duty around the clock, indefinitely. The Electronic Watch Dog can protect homes, apartments, mobile homes, RV's, jewelry stores, hotels, factories, warehouses, public and private buildings of virtually every kind."
   
   
   • Reliable 24-hour protection
   • No Installation required
   • Protection with none of the problems of owning a real dog.
   • Very realistic--barking gets louder and more frequent as intruder gets closer.
   • Switches from the watchdog to the tranquil sounds of nature with the simple switch of a button.
   • Variable distance sensitivity (up to 30') as well as volume control.
   • Senses movement through walls, doors, and glass to alert you of a visitor's arrival.
   • Maintenance free.
   
   Source: www.electronicwatchdog.com
   
   
4. Free Software
   Lucky for us, there are programs to keep hackers at bay. Even better, there are free firewall programs available on the Internet to download. You must take note: these free firewalls are available for personal use. They can also be licensed for commercial use.
   
   
   ZoneAlarm
   from ZoneLabs
   OS: 95/98/ME/NT/2000
   
   Features
   
   • Login Authentication
   • Trusted Applications
   • MD5 Signature Support
   • Customizable Security Levels
   Source: www.zonelabs.com