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What is a Firewall?
By definition, a firewall is a gateway that limits access between networks in accordance with local security policy.
Lets say you didn't have a firewall. You purchased a new computer, hooked it up and even activated your anti-virus because everyone knows how bad computer viruses are. Heck, you even grabbed the top-rated Spyware remover just to be extra safe. Now you think you are ready to safely surf the web and perhaps do some online banking. If this was all you did to secure your computer you would be wide open to a variety of probes, attacks and maybe even break-ins.
In simple English a firewall is a "wall" between you and all the bad stuff floating around on the internet. Like a physical firewall whose job is to keep a fire from spreading a computer firewall is designed to keep your computer safe.
Cable Internet or DSL users are especially vulnerable since they are so easy to probe but being on dial-up doesn't make you safe.
I know what you're thinking and I will try to break the above statement down for you in English so you can understand just what a firewall is and how it works. Once you do you'll see why a firewall is one the most important tools in your home or office security arsenal.
Lets say you didn't have a firewall. You purchased a new computer, hooked it up and even activated your anti-virus because everyone knows how bad computer viruses are. Heck, you even grabbed the top-rated Spyware remover just to be extra safe. Now you think you are ready to safely surf the web and perhaps do some online banking. If this was all you did to secure your computer you would be wide open to a variety of probes, attacks and maybe even break-ins.
In simple English a firewall is a "wall" between you and all the bad stuff floating around on the internet. Like a physical firewall whose job is to keep a fire from spreading a computer firewall is designed to keep your computer safe.
Firewalls use one or more of three methods to control traffic flowing in and out of the network:
- Packet filtering - Packets (small pieces of data) are analyzed against a set of filters. Packets that make it through the filters are sent to the requesting system and all others are discarded.
- Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa.
- Stateful inspection - A method that compares certain parts of a packet against a database of trusted information. Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded.
How does a Firewall filter Internet traffic?
Filters are just the rules or conditions set by you for what traffic goes in and out of your network. You can use them in any combination and add or delete them as you see fit. Some of the most popular filters are:
- IP addresses - Every machine on the Internet is assigned a unique address called an IP address. IP addresses are 32-bit numbers, normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this: 216.27.61.137. For example, if a certain IP address is reading too many files from a server, the firewall can block all traffic to or from that IP address.
- Domain names - It can be hard to remember the numbers that make up an IP address and IP addresses change, so all servers on the Internet have easily recognizable names, called domain names. For example, it is easier for most of us to remember www.fraudguides.com than it is to remember 216.27.61.137. Someone might want to block all access to certain domain names, or allow access only to specific domain names. This is a lot easier than keeping a list of offending IP addresses, especially since they can change.
- Protocols - The protocol is the pre-defined way that someone who wants to use a service talks with that service. The "someone" could be a person, but more often it is a computer program like a web browser. Protocols are often text, and simply describe how the client and server will have their conversation. The http in the Web's protocol. Some common protocols that you can set firewall filters for include:
- IP (Internet Protocol) - the main delivery system for information over the Internet
- TCP (Transmission Control Protocol) - used to break apart and rebuild information that travels over the Internet
- HTTP (Hyper Text Transfer Protocol) - used for Web pages
- FTP (File Transfer Protocol) - used to download and upload files
- UDP (User Datagram Protocol) - used for information that requires no response, such as streaming audio and video
- ICMP (Internet Control Message Protocol) - used by a router to exchange the information with other routers
- SMTP (Simple Mail Transport Protocol) - used to send text-based information (e-mail)
- SNMP (Simple Network Management Protocol) - used to collect system information from a remote computer
- Telnet - used to perform commands on a remote computer
These protocols can be allowed or denied in all kinds of ways. On a large network you could allow a certain protocol between you and another computer but ban it for everyone else.
- Ports - Any server machine makes its services available to the Internet using numbered ports, one for each service that is available on the server (see How Web Servers Work for details). For example, if a server machine is running a Web (HTTP) server and an FTP server, the Web server would typically be available on port 80, and the FTP server would be available on port 21. A company might block port 21 access on all machines but one inside the company.
- Specific words and phrases - This can be anything. The firewall will sniff (search through) each packet of information for an exact match of the text listed in the filter. For example, you could instruct the firewall to block any packet with the word "X-rated" in it. The key here is that it has to be an exact match. The "X-rated" filter would not catch "X rated" (no hyphen). But you can include as many words, phrases and variations of them as you need.
Windows XP and some other operating systems come with a firewall pre-installed but you can also download the firewall of your choice if you don't have one on your computer.
Hardware firewalls are usually included in your cable or DSL router. Hardware routers are considered to be the most secure and using one with a software firewall give any network a high degree of security. These firewalls are not expensive and can be found in a broadband router/hub/modem bundle for as low as $100.
Either a software or hardware firewall will secure any small business or home network but it is important that this is not left out
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