The Learning Center

Why Is Your IP Address Broken into Four Sections?

Most likely, you've already checked your IP address at WhatIsMyIPAddress.com a few times. Usually you're just checking to see if it's changed or not.

Your IP address at home will be different from the IP address at your work office. And that IP address will be different from the one you would have if you used the free wireless hotspot at a coffee shop or hotel.

But they all have one thing in common: They will be in four sections, separated by three periods or dots. That is the common structure for all IPv4 addresses (v4 stands for "version 4").

Have you ever wondered what those four sections represent? Here's a quick overview: There will be some technical terms, but they're nothing to be worried about. You will still be able to understand the basics of what's going on with your IP address.

We don't think like computers do.

At the heart of everything to do with computers is this fact: Computers have a language and method all their own. Everything you see on your screen has a format that your computer understands and translates into words numbers and pictures.

Computers turn everything into numbers that are a combination of zeroes and ones. If a computer sees the decimal number (a number you recognize) 2,530, it turns that number into a longer string made up of only zeros and ones—0000100111100010. That's called a binary number. Aren't you glad your computer doesn't talk to you in binary code? Computers calculate everything using the binary system.

  • The decimal number 256 in binary form is 00000001. Take special notice that "00000001" is comprised of eight numbers, called "bits" in the binary system.

Every little bit helps.

Every IP address is made up of 32 bits. Here's an illustration of what that means:

Let's take the IP address 76.240.249.145. My computer—and all of the networking hardware and software—sees it as a 32-bit address in binary form that is subdivided into four 8-bit parts, called "octets."

76 in binary form is 01001100 (the first 8-bit segment, or octet)
240 " " 11110000 (octet)
249 " " 11111001 (octet)
145 " " 10010001 (octet)

Or you can simply see it in four parts: part1.part2.part3.part4.

What are the four parts about?

  • Every IP address—such as 76.240.249.145—is also divided into two sections that define 1) your network and 2) your computer, or host.
  • Those two sections comprise the basic structure of IP addresses: the network ID and the host ID. All computers on the same network share the same network ID. Each computer (sometimes called a "network interface") has its own unique host ID.
  • The four IP address parts do NOT have to be divided equally—it's not always the case that two parts make up the network ID and two address parts make up the host ID. The network ID may be one, two or three of the parts, leaving the last part for the host ID.

How the parts come together to define the IP address's network ID and host ID also determines what Class of network that IP address is associated with.

  • If an IP address's network ID is defined by the first part of the IP address, the computer is connected to a Class A network. Class A networks are very large and could have approximately 17 million hosts/computers connected to it!
  • If the network ID is comprised of the first two parts of the address, the computer is connected to a Class B network. Class B networks are smaller than Class A ones and can have about 65,000 hosts.
  • If the network ID is comprised of parts 1, 2 and 3 of the IP address, the computer is connected to Class C network. A Class C network can accommodate only about 254 computers...but there can be more than two million Class C networks.

Class act.

From now on, whenever you see your IP address, you'll know that each section is actually an octet that's part of a 32-bit number. Just don't bother sharing that knowledge with anyone—it won't interest anybody who isn't in the IT department.

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