From the course: Networking Foundations: IP Addressing

Classful addressing

From the course: Networking Foundations: IP Addressing

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Classful addressing

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- [Instructor] When the designers of the TCP/IP suite of protocols began to disseminate the IP addresses, they did so using what is called a classful methodology. Here's exactly how they did it. They created a class A address range. Notice the class A address range goes from 0.0.0.0 up to 127.255.255,255.255. They did this by taking those 32 bits and setting the very first bit, the leftmost bit what we call the high order bit, they set that to zero. So they preset that bit to zero and this accommodates 128 networks. Now a class A address scheme is as you can see, there's few of these relatively, so you've got relatively few networks at 128 but notice each of those networks can accommodate 16 million approximately hosts. My goodness, that's a lot of hosts in one of those class A networks. The class B range is 128.0.0.0 up to one 191.255.255.255. The high order bits, the first two bits were preset to 10. This made for the ability to create 16,384 networks. And each of those networks could roughly 65,000 hosts. You see what they were doing here. Class A IP address schemes were reserved for huge networks. class B, their thought process was medium-sized networks. And then the class C is 192.0.0.0 up to 223.255.255.255 and they did this by presetting those high order bits, to 110. You can create over 2 million of these networks and each can only contain 256 hosts. So isn't this interesting that you can now look at your IP address and you can place it into one of these classes. For instance, I just checked my IP address 192.168.1.11 and you see that I can clearly tell that this is one of those class C addresses. In fact, I'm kind of cheating, aren't I? If it begins with a 192 in the first octet, you know you're class C. Now I know what you're wondering. Are there any other address classes? Well, the answer is yes. There is a class D range and the class D range is really important. It runs from 224.0.0.0 to 239.255.255.255. Notice the high order bits are 1110 and the class D address space is reserved for multicast. Multicasting is awesome. It's a great alternative to broadcasting and with multicasting you are sending data to a group of receivers and as you might guess, those group of receivers are addressed in a particular multicast range. There's one more address class they defined and that's the class E range. Notice it's from 240 up to 255.255.255.254. And the high order bits are set 1111 The class E range is not important. Yep, we're going to pretty much ignore this range today. It was set aside for experimental purposes and there's probably no better proof that they didn't think that they would ever run out of addresses by saving so many of the address space they're in reserve for experimental purposes. Wow. It looks really wasteful now, doesn't it? Especially given that we are in an IP address shortage type dilemma. So these classes are very, very important to understand and it's really critical that we see this how they originally disseminated the address space.

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