What are IP Address Classes and Ranges?
We now understand that when we take a look at an IP address. We really don’t know which of those thirty-two (32) bits represent the network and which have those thirty-two bit represent the host. Unless we’ve got a critical piece of information do you remember what that critical piece of information was? It’s the subnet mask, the subnet mask draws that dividing line saying that these are the network bits and these are the host bits. How do we know what that subnet mask is? We’re going to see that we can set that dividing line ourselves but there are defaults Those defaults are different for some of our different IP address classes. So let’s talk about these five different IP version 4 (IPv4) classes.
IP Address Classes:
‘A’,’B’,’C, ‘D’ and ‘E’ and understand that classes ‘A’, ‘B’ and ‘C’ they are the only IP address classes of IPv4 addresses. That is going to assign to a host address class ‘D’ and we use class ‘D’ address in multicast. But we send to a destination multicast address no computer no host is over going to assigned this range. It’s a destination only address and as a result, we see it doesn’t even have a default subnet mask. What we’ve always heard that we use class ‘E’ addresses for experimental purposes. I’ve never seen such an experiment. I’ve never seen class E used anywhere and you probably will neither see especially with the advent of IP version six (IPv6). But that’s what we’re probably read in the literature that is used for experimental purposes and we can see in the diagram that we’ve got classful mask written as a dotted decimal and written in prefix notation.
We’ve got a classful mask for IP address classes ‘A’,’B’ and ‘C’ this classful mask is the default subnet mask. For addresses in that clients for example, if we had an IP address of 10.1.2.3 and I told you that we were using the classful mask that would tell you that the first 8 bits represented the network and the remaining twenty-four (24) bits represented the host. Again we’re going to be able to adjust that default but it’s important to memorize. We should memorize the default of the classful subnet masks. For these three different IP address classes addresses and you can determine the class of address simply by looking at the first octet. If the value that the first octet isn’t a range of 1 through 126 (1-126) its class A, if it in the range of 128 through 191 (128-191) its class B, if it’s on the range of 192 through 223 (192-223) its class C.
Understand IP classes Subnet Mask:
Here is a very common point of confusion. Many people think that if we change the default subnet mask which we can do. We could say that subnet mask of 10.1.2.3 address must be twenty-four bits instead of having eight. Many people look at that and say oh well now it’s a class C address. That’s not true big point here is that class of IP address is entirely dependent on that for the first octet. It doesn’t a matter what the subnet mask is. It doesn’t matter what we have an octet 2,3 and 4. It’s entirely determined by the first octet regardless of subnet mask length that’s a big point that many people get tripped up on.
Loopback IP address:
As we’re looking at these ranges of addresses you might notice that there’s a conspicuous absence 127. Why is 127 not include is either class A or Class B? Well, the answer is simple, that we use 127 for a loopback IP address. It’s your local address if you want to make sure that TCP/IP stack is working on your computer. You could ping 127.0.0.1 and if that ping is successful then you know that you’re machine or your host has successfully loaded the TCP/IP stack. Another question that might come from this discussion is where does a company get their range of IP addresses to assign to their devices? Well, publicly routable IP addresses and shortly will be distinguishing between the public and private IP address.
Internet’s core infrastructure Organizations:
Publicly routable IP addresses are managed by “ICANN” that is Internet Corporation for Assigned Names and Numbers. It’s a nonprofit organization. They don’t directly assign the block of numbers to your company or to your service providers. But instead, it gives a block of numbers to an international registry. For example, In North America, we have “ARIN” that’s is American Registry for Internet Numbers. Outside of North America, we have “IANA” that is the Internet Assigned Number Authority which was operated by ICANN. By the way in some of the literature, you might see reference to InterNIC that’s the Internet Network Information Center. That was the predecessor to ICANN but it’s switched over to ICANN in September 1998.
Default Subnet Mask:
The big take away from this article is that we have five classes of IP addresses. When it comes to IP version 4 (IPv4) only three of those class are going to assign it to host. Those are IP address classes ‘A’, ‘B’ and C. We can determine each of this classes having default classful subnet mask. And we have got 255.0.0.0 for class A, 255.255.0.0 for class B and 255.255.255.0 for class C. We can entirely determine the class of IPv4 address just by looking at the first octet. If we see the IP address of 10.1.2.3 doesn’t matter what the subnet mask is because we have 10 in the first octet. We can see in the diagram that falls in the range of 1-126 that’s all the information we need to know and that’s the class A address.
Key Points for IP Address Classes:
- Class A, B, and C addresses are assigned to hosts.
- A Class “D” used for multicast.
- IPv4 Class “E” used for experimental purposes.
- Classful Mask also knew as the “Default Mask” or a “Natural Mask”.
- 10.1.2.3 has a classful mask of 255.0.0.0 because the value in the first octet (10) is in the class A range of 1-126.
- The class of IP address is entirely determined by the value in the first octet.
- 127.0.0.1 is a “local loopback” IP address of a host.
- ICANN is Internet Corporation for Assigned Names and Numbers, it’s a nonprofit organization.
- In North America, we have ARIN American Registry for Internet Numbers.
- IANA (Internet Assigned Number Authority).
- “InterNIC” Is internet Network Information Center that’s the predecessor of ICANN.
- IPv4 has five classes of IP Addresses.
- The first Octet determines the address class.