 Hello everyone, I am Kanchan Khedikar working as an assistant professor in computer science and engineering department at Valchan Institute of Technology, Soulapur. In my last video we have seen IPv4 classful addressing. In this video I will explain two level and three level classful addressing. The learning outcomes are at the end of this session student will be able to describe the two level and three level addressing of classful addresses. They will determine the number of block addresses, range of addresses and subnetwork mask for subnetwork. Student will also be able to differentiate between subnetting and supernetting. Now, let's start with the two level addressing. The range of addresses allocated to an organization in classful addressing was a block of addresses in class A, B or C. Now this diagram shows two level addressing in classful addresses. Here 32 bit addresses is divided into two parts net ID and host ID. Here net ID is represented by n bits and host ID represented by 32 minus n bit. So class A has n equal to 8. Class B has n equal to 16 and class C has n equal to 24 bit net ID. Now the information extraction in classful addressing. So information means the number of addresses present into a block then what is the first address and the last address of the block. So for this or to calculate the number of addresses of a block the first step is the number of addresses in the block n can be find using this formula n equal to 2 raised to power 32 minus n. To find the first address we need to keep the n leftmost bit as it is and 32 minus n rightmost bit to 0. Similarly to find out the last address we need to keep n leftmost bit as it is and 32 minus n rightmost bit to once. Let me explain the same concept with the help of this diagram. So here to find out the first address we have to keep n IDs as it is and the host IDs to 0s. Similarly to find out the last address we need to keep n ID as it is and the rightmost bit to 1. Now let me explain the same concept with the help of one example. An address in a block is 100.22.20.21 then find the number of addresses in the block also find the first and last address of a block. So here is the solution address 100.22.20.21 is in between the range of 0 and 127 hence it belongs to class A. So the value of n for class A is 8. So the number of addresses in this block can be find out with the help of formula n equal to 2 raise to power 32 minus n. So here the value of small n is 8 therefore 2 raise to power 24 is more than 16 lakhs. So for a given particular address the number of addresses are more than 16 lakhs. And the first address as I said earlier we need to keep the network ID as it is and we have to set the rightmost bit to 0s. So therefore the first address is 100.0.0 and the last address is 100.255.255.255. Now let's see the another concept network mask. Network mask is also known as default mask. Default mask in class full addressing is a 32 bit number. n leftmost bit set to 1s and the 32 minus n rightmost bit set to 0s. Now here are three default masks in class full addressing. So for class A the mask is or the default mask is 255.0.0.0. For class B the default mask is 255.255.0.0 and for class C the default mask is 255.255.255.0. Now let's see the another concept of class full addressing three level addressing. Three level addressing gives two concept supernetting and subnetting. Subnetting an idea of splitting the block to smaller blocks is known as subnetting. The network is divided into several smaller subnetworks. Each subnetwork having its own subnetwork address. Subnet mask is used when the network is not subnetted but subnetwork mask is required when the network is subnetted. So here is a diagram which shows network mask as well as subnetwork mask. In network mask net ID and host ID is present which is represented by n bit and 32 minus n bit. In subnetworking there is a splitting of blocks. So here the host IDs are decreases. So subnet ID is represented by n i bits whereas host ID is represented by 32 minus n i bits. Now three level addressing here from this diagram we can conclude that the subnetting increases the length of net ID and decreases the length of host ID. To calculate the subnet ID for each subnetwork we have this formula n sub equal to n plus log of s to the base 2 where n sub is length of each subnet ID, n is length of net ID and s is number of subnet which must be a power of 2. Think about these two questions and write down the answer. The first question is find the subnet mask or the default mask for the following addresses. There are total four addresses A, B, C, D and the second question is determine the subnetwork mask for a given address and that address is 200 dot 200 dot 14 dot 25. Now pause the video and write down the answer. Now here the solution is for the first address 192 dot 168 dot 15 dot 16 the default mask is 255 dot 255 dot 255 dot 0. Why? Because this class or this address is belongs to class C and class C has 255 dot 255 dot 255 dot 0 default mask. Like this for the further three addresses have this default mask. So for second address that is 60 dot 120 dot 27 dot 18 the default subnet mask is 255 dot 0 dot 0 because it belongs to class A, third address belongs to class C and the fourth address belongs to class B. So that is why its default mask is 255 dot 255 dot 0 dot 0. Now let us see the solution for another question that is determine the subnetwork mask for a given address and the address is 200 dot 200 dot 14 dot 25. Given addresses belongs to class C therefore the default mask is 255 dot 255 dot 255 dot 0. According to the formula n sub equal to n plus log s to the base 2 n equal to 24 and s equal to 8 which is the power of 2 that is 2 raise to power 3. So if we put the value of n and s in our given formula we will get the n sub equal to 27 because the log of the value of the log 2 raise to power 3 base 2 is 3. So here n sub equal to 27 this diagram shows how the subnetwork works. So here 3 number of ones are extended. So instead of 24 there are 27 ones in subnetworking. So the subnetwork mask is 255 dot 255 dot 255 dot 224. Now let us see the concept of super netting. Now the idea is to combining the several class C blocks to create the larger range of addresses. Subnetwork networks are combined to create the subnetwork. Subnetwork mask is required when the network is supernated and exactly reverse of the subnet. So here the supernet mask for class C has less ones and subnet mask. Now this diagram shows the comparison of subnet mask, default mask and supernet mask. So here the subnet mask in this diagram the subnet mask where the net IDs are increased in default mask it is specified and in supernet mask the net IDs are decreased. Now supernating decreases the length of net ID and increases the length of host ID. To find the length of supernet ID we have this formula n super equal to n minus log C to the base 2 where n super defines the length of the supernet ID, n is length of net ID and C defines the number of class C blocks that are combined. So let us see the disadvantages of classful addressing. As we know in classful addressing class A and class B addresses are wasted. So here the subnetting first disadvantage is subnetting and supernetting in classful addressing did not solve the address depletion problem whereas it made the distribution of addresses and the routing process more difficult. So in this video we have learnt about the IPv4 2 level and 3 level addressing and also the concept of supernetting and subnetting. These are the references. Thank you.