IPv4 Address Classes Explained: Class A, B, C, D, E Identification Guide

Hello everyone. Welcome back. In today's lecture we will see the part one of class full addressing. We will start the

session with the outcomes. Upon the completion of the session the learner will be able to outcome number one. We

will understand various classes of IPv4 address. Outcome number two. We will identify the class of IP address with

the help of an activity. Let's dive into the topic directly. Basically we have five classes of IPv4 addresses. Class A,

class B, class C, class D, and class E. We know very well that IPv4 addresses can be represented in two ways. It can

be represented either in binary notation or in dotted decimal notation. We know IPv4 addresses are 32 bits long. These

32 bits are organized into four octets or four bytes and each byte will be eight bits long. So we have four bytes

in an IPv4 address. These four bytes can also be called as four octets because every octet is going to contain eight

bits. So 8 + 8 + 8 + 8 is equal to 32 bits and that's why IPv4 addresses are of 32 bits long. And class A means out

of these 32 bits and the first byte that is the first octet's first bit, the most significant bit. If it is zero, then it

is class A. If the first two bits in the first byte are 10, that is the starting of the IPv4 address in binary, if they

are 10, then it do belong to class B. If the first three bits are 110, then it do belong to class C. If it is 1110, that

is if the IPv4 address starts with 1110, then it is class D. The first four bits of the first byte or the first octet of

an IPv4 address are four ones, then it is class E. So, if it is represented in binary, we need to see what are the bit

values. Whether the IP address is belonging to class A, B, C, D, or E. In case if it is given in a dotted decimal

notation, say if the first byte or the first octet is between 0 and 127, it is belonging to class A. In case if it is

between 1 28 and 191, it belongs to class B. If it is 192 to 223, it is class C. If it is between 224 and

239, it is class D. And if the first byte or the first octet is between 240 and 255,

then it is class E. How these values can be generated? In an IPv4 address in a dotted decimal notation, every octet

will be between 0 and 255. Let's see the various classes of IPv4 address in a detailed manner. Say, we

know we have five classes of IPv4 addresses and we have seen in the previous slide that what is the range of

each class. We are going to see things elaborately now. We have seen in the previous slide that the class A is first

octet's first bit is fixed. That is, it is 0. So, when we say this 0 is fixed and in the first octet, we have four

octets in an IPv4 address and we are concerned only about the first octet. In the first octet, the first bit is

reserved. That is, it is 0. And we have remaining seven bits. The starting of this class will be all zeros in the

seven bits because the first bit is 0 and the ending of the IP address in class A will be all seven ones. That is,

this 0 is fixed and we have seven zeros in the remaining seven bits and we have seven ones in the remaining seven bits.

And this is the starting of the class A IP address, and this is the end of the class A IP address. If this is the

starting of the IP address, what will be the value? If all eight bits are zero, it is zero, and this bit is zero, that

is the position 128 is zero, and we have ones in all other places. So, when we sum these positions, we will be getting

127, and that is why this is zero, that is the starting in the decimal it is zero, and the ending is 127.

So, we'll be getting 127 here. And let's move on to class B. In class B, the first two bits is 10, which is fixed.

So, when we have the first two bits that is fixed as 10, and we'll be having the remaining six bits as zero here, and

that is the starting of the IPv4 address in class B, and the remaining six bits will be one in class B. Please ponder

one thing very clearly, that we are concerned only on the first octet in order to find the class of the IP

address. So, what will be the decimal value? When we see the decimal value, this is 128, and there are no ones in

the remaining bit. So, the starting will be 128, and the ending will be 191. So, when we add the positions, we'll be

getting 191. To know the positions of these numbers, I request you to watch my previous lecture, where I have

illustrated how to convert the decimal into binary, and binary into decimal. Then coming to class C, we know in class

C the first three bits are fixed, which is 110. When we have 110 is fixed in the places, we will be having obviously five

bits left. And these five bits, and the starting will be all zeros, and the ending will be all ones. And when we

convert the binary into decimal, we will be getting 192 as the starting, and 220, that is this binary equivalent will be

223 in decimal. And this is the class C address. And coming to class D, we know the IP address will start with 1110. So,

1110 is fixed. When 1110 is fixed, we are left with only four bits. The starting of this will be 1110 and 0000,

and the ending will be 11101111. When we convert this into decimal, we'll be getting 224 as the starting of the IP

address of class D and 239 as the ending of the IP address in class D. Let's now move on to class E. In class E, we know

the starting of the IP address will be all four ones. When all four ones are fixed, we have only four bits remaining.

And these four bits, the starting will be all zeros, and the ending will be all ones. And when it is all zero in the

last four places of the first octet, then the decimal equivalent will be 240, and the final value will be 255.

So, the starting of class E is 240, and the ending of class E is 255. And just recall, what is the starting value in an

octet? It's zero, right? In decimal, it is zero. And what is the final value in an octet? It is obviously 255. Between

zero and 255 in the first octet, we have five classes. These class A, B, C are for general purpose, and class D is for

multicasting purpose, and class E is reserved for experimental and research purpose. I'm not going into the details

of these things in this lecture. Anyway, we are going to deal about this elaborately in the next lecture. This

lecture is intended to know how many classes and how each class is identified. Let's now move on to the

activity. The activity is, find the class of the following dotted decimal IPv4 addresses. So, we are given with

some IPv4 addresses, and we are required to identify or find the class of the IPv4 address. IPv4 addresses can be

given either in the dotted decimal format or in the binary format. In this activity, the IPV4 address is given in

the dotted decimal format. So, these are the IP addresses given. How to identify the class of the IP address? We are

required to focus on the first octet. If the first octet is between 0 and 127, it is class A. If it is between 128 and

191, it is class B. If the first octet is between 192 and 223, it is class C. Between 224 and 239, it is class D. And

between 240 and 255, it is class E. The first octet in this IP address is 192. So, this is between 192 and 223. So,

obviously, it is class C. Let's move on to the next value. This is starting with 10. If the first octet is between 0 and

127, it is class A. And coming to the third one, and this octet is between 128 and 191. So,

obviously, it is class B. And the class for the last IP address is class D. This is a multicast address. Why? If it is

between 224 and 239, obviously, it is class D, which is mainly reserved for multicast purpose. If you want to solve

these questions, so you should be very proficient with this table. Just refer the first octet values and identify the

class. The question may be given either in the dotted decimal notation or in the binary notation.

Now, let's see the homework question. The question is find the class of the following IPV4

addresses. And we are given with four IPV4 addresses, but this time the IPV4 addresses are given in the binary

notation. Four questions are given. Just observe the bits in the first octet and find the class of these IPV4 addresses.

Pause this video for a while. Take the help of this slide and try solving this problem.

And post your answers in the comment section. I hope now you understood the various

classes of IPv4 address and we will be able to identify the class of IP address if it is given either in the binary form

or in the dotted decimal form. I hope you guys enjoyed the lecture and thank you for watching.