IP addresses.

Introduction

So you have been hearing a lot about IP addresses lately. The tech support guy wants to know your IP so he can fix your computer, the feds tracked your uncle downloading kiddie porn by tracing his IP, Big Daddy and Hit Girl tracked down Kick-Ass by his IP address, what does all this mean? Well lets get started. IP stands Internet Protocol. There exists mountains of papers that will try and teach you about IP addresses but I've cut it down considerably to just the important stuff. I mean really who cares about IANA, binary, or CIDR notation?

Reading an IP address.

IP addresses are broken up into octets. for example, take the address 192.168.0.1 - the first octet comprises of 192 but the third and fourth octets are comprised of a single number. See the table below for further explanation. IP addresses can be static (meaning they never change), or dynamic. (meaning they can and will change often.)

To see your IP address in Windows XP, go to Start, Run, and type in "cmd". This will pull up a command line. Then simply type in the command "ipconfig" (with out the quotes.) and you should see a screen similar to this. This will tell me about all my NICs in my computer and their private IP addresses, subnets, (dont worry about subnets for now, we will dive into that later. Just know that in order for two or more computers to talk to each other, they have to be in the same class of IP ranges and have the same subnet.) and default gateway or router. DNS suffix usually means domain. Don't worry about these terms yet either. In this figure, you can see there are two NICS but one is not connected to anything.

To see your public IP address, you usually (not always, there exists programs to do it from the command line) have to go to a website like IP Chicken. Go on and give it a try. See Public vs Private below.

Classes of IP addresses.

There are 5 classes of IP addresses and they are as follows:

Most of the time, your private IP address will fall in class C.

Public vs Private

That's right, you usually have two types of addresses assigned to you, and can have many more combinations of public and private addresses.

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Side note:

"But sir, how can you have TWO IP addresses when i know for a fact an IP address is like a telephone number and unique to a computer!" Well, in reality IP addresses assigned to the network cards (NICs) instead of just the computer as a whole. So if a server needed an other IP address for something like a mail server, you would insert a new NIC or even fire up a virtual machine and assign a new address to your virtual NIC. The other computers in your network can share the same public IP addresses because of the router you have installed between your computer and the DSL or cable box.
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The public IP address is the address assigned by your internet service provider (ISP) and then "shared" to other computers in your network provided you have the right set up.

Closing

When you fire up your computer and get online, your ISP assigns your unique public address to your router and keeps a log of it, (hence the cops catching your uncle) the router than assigns you a private address and keeps a log as well. This is all done in the background without the end user noticing it. And there you have it. Short and sweet.