Why Do I Need a Firewall - IP Addresses and Ports

With the rapid growth of the Internet and the growing availability of high speed Internet access, along with home networks, security has become a necessity in the computer world. It is however one of those necessities that many of us to overlook - or if we do not overlook, do not fully understand.

There are never any absolutes, but for the sake of this article we will assume that the various scenarios which I put forth are the case - as they often times are.

If you have a high speed connection in your house, or any Internet connection for that matter, you have what is technically called a network. Even if you only have one computer in the house. This is because whenever you are connected to the Internet your computers is connected to thousands, if not hundreds of thousands, of other unknown computers which creates a network.

Any time a computer connects to a network, or multiple networks connect to other networks there are a series of issues which immediately become concerns that must be addressed in order to maintain a secure computer environment.

As a result, regardless of whether they are willing, capable, or aware, every home user by default becomes a Network Systems Administrator. Professionally, a Network Systems Administrator spends a growing the majority of their time not in establishing how a network functions, rather they are preoccupied with security concerns. Among, but not limited to, these concerns are things like the following:

How you protect confidential information from those who do not need access to it?
How do you protect your network from outside attacks and accidents?
How do you protect your network from being used to perpetrate attacks?

The only fool-proof answer to any of these questions of course is to never connect your computer to a network. Given however that we want, even need nowadays, to connect to the Internet and the features and services which come along with it, this is not a viable solution. How then can we go about achieving such protection?

The short and simple answer is use a firewall for your computer. Anything beyond that answer immediately ceases to be short or simple. (Remembering that we are trying to keep things simple)

Let us take a quick look at how computers and networks work. Every computer really, and All computers in a network have an IP address - or Internet Protocol Address. We could get ourselves quickly distracted with public and private addresses, but for now we are only going to concern ourselves with the public IP; the number assigned to your computer which is visible to the outside world. An easy way to think of an IP address is that it is a great deal like the phone number or street address for your house.

Example:

A user is located at IP xxx.xxx.xxx.xxx and they open a web browser and call up this website. The server which displays the site; the host; is located at the IP zzz.zzz.zzz. zzz and needs to return the requested page to the correct machine. It looks at the address; phone number; from which the request came, and returns the results to it; in other words, the page you are currently looking at.

If this were not the case, the machine located at xxx.xxx.xxx.xxx would make a request from the server at zzz. zzz. zzz. zzz who might broadcast the results to yyy.yyy.yyy.yyy; clearly the wrong macine. This would not only get very confusing very fast, it would also render the Internet useless because requested information would be being sent to random locations - rather than the requesting source.

To avoid this confusion the solution was to assign a unique set of numbers to every machine connected to the Internet. This means that whether you are aware of it or not, you, like every good server, have an address on the Internet. That is the first piece of information I, or anyone else, needs to get into your machine.

So, now that we know you become a member of a network whenever you connect to the Internet and that we have the very basics of IP addresses out-of-the-way, let us tackle ports.

Using the analogy of the street address for the IP, let us think of each computer in your network as a house. Like all good houses, this one has doors. Where the door on your home designed to let people come and go, the doors on your computer allows information to come and go.

But where you only have two or three doors to your house, a computer has over 60,000; 65,535 to be exact. Obviously you need a way to lock these doors. The se doorways on your computer are technically known as ports.

So if I know what your IP address is; street address; I now have a whole lot of doors to try and sneak into your house through.

Are you curious how many of these doors are open right now on your computer? Visit https://www.grc.com/x/ne.dll?bh0bkyd2 and look just below the "Proceed" button in the center of your browser. You will find your IP address - Internet street address. Now click the "Proceed" button and click the link labeled, "Common Ports" and sit back and wait.

How long you have to wait will depend on how fast your Internet connection is. When the test is finished it will display a list of common computer ports and their state. Anything "Closed" is good, anything which comes back as "Stealth" is very good, and anything which comes back as "Open" really should be looked at.

How did you do? In the spirit of fairness, I have five ports open. The five which I have open are acceptable because they allow you to send e-mail to my server, and access my web sites. Of course if you are not offering these services to the outside world than having these ports open would be a security risk.

So what does it mean? What are these ports really and why should I care if they are open or not? I Cover this in an article titled Computer Ports and Traffic.