IPV4 & IPV6

• An IP address in the IPV4 standard has four numbers separated by three decimals, as in: 70.74.251.42
• An IP address in the IPV6 standard has eight hexadecimal numbers (base-16) separated by colons, as in 2001:0cb8:85a3:0000:0000:8a2e:0370:7334. Because IPV6 is still a very new standard, we'll concentrate on the more common IPV4 for this article.
• Each number in an IPV4 number is called an "octet" because it's a base-10 equivalent of an 8-digit base-2 (binary) number used in routing network traffic. For example, the octet written as 42 stands for 00101010. Each digit in the binary number is the placeholder for a certain power of two from 20 to 27, reading from right to left. That means that in 00101010, you have one each of 21, 23 and 25. So, to get the base-10 equivalent, just add 21 + 23 + 25 = 2 + 8 + 32 = 42. For more about how IP addresses are constructed, see our article"What is an IP address?"
• There are only 256 possibilities for the value of each octect: the numbers 0 through 255.
• Certain addresses and ranges are designated by the IANA as reserved IP addresses, which means they have a specific job in IP. For example, the IP address 127.0.0.1 is reserved to identify the computer you're currently using. So, talking to 127.0.0.1 is just talking to yourself!

Where does your computer's IP address come from? If we're talking about your desktop or laptop computer, it probably comes from a Dynamic Host Configuration Protocol (DHCP) server on your network. The job of a DHCP server is to make sure your computer has the IP address and other network configuration it needs whenever you're online. Because this is "dynamic," the IP address for your computer will probably change from time to time, such as when you shut down your computer for a few days. As the user, you'll probably never notice all this taking place. See the sidebar on this page for hints on where to find the IP address assigned to your computer or mobile device.

Web servers and other computers that need a consistent point of contact use static IP addresses. This means that the same IP address is always assigned to that system's network interface when it's online. To make sure that interface always gets the same IP address, IP associates the address with the Media Access Control (MAC) address for that network interface. Every network interface, both wired and wireless, has a unique MAC address embedded in it by the manufacturer.

For more information on IP addresses, see the IANA, operated by the Internet Corporation for Assigned Names and Numbers (ICANN). Now, though, let's look at the other side of the DNS equation: domain names.