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Lecture TCP-IP protocol suite - Chapter 5: IP addresses: Classless addressing

When you finish this chapter, you should: Understand the concept of classless addressing, be able to find the first and last address given an IP address, be able to find the network address given a classless IP address, be able to create subnets from a block of classless IP addresses, understand address allocation and address aggregation. | Chapter 5 Subnetting/Supernetting and Classless Addressing CONTENTS SUBNETTING SUPERNETTING CLASSLESS ADDRSSING SUBNETTING 5.1 IP addresses are designed with two levels of hierarchy. Figure 5-1 A network with two levels of hierarchy (not subnetted) Figure 5-2 A network with three levels of hierarchy (subnetted) Figure 5-3 Addresses in a network with and without subnetting Figure 5-4 Hierarchy concept in a telephone number Figure 5-5 Default mask and subnet mask Finding the Subnet Address Given an IP address, we can find the subnet address the same way we found the network address in the previous chapter. We apply the mask to the address. We can do this in two ways: straight or short-cut. Straight Method In the straight method, we use binary notation for both the address and the mask and then apply the AND operation to find the subnet address. Example 1 What is the subnetwork address if the destination address is 200.45.34.56 and the subnet mask is 255.255.240.0? Solution 11001000 . | Chapter 5 Subnetting/Supernetting and Classless Addressing CONTENTS SUBNETTING SUPERNETTING CLASSLESS ADDRSSING SUBNETTING 5.1 IP addresses are designed with two levels of hierarchy. Figure 5-1 A network with two levels of hierarchy (not subnetted) Figure 5-2 A network with three levels of hierarchy (subnetted) Figure 5-3 Addresses in a network with and without subnetting Figure 5-4 Hierarchy concept in a telephone number Figure 5-5 Default mask and subnet mask Finding the Subnet Address Given an IP address, we can find the subnet address the same way we found the network address in the previous chapter. We apply the mask to the address. We can do this in two ways: straight or short-cut. Straight Method In the straight method, we use binary notation for both the address and the mask and then apply the AND operation to find the subnet address. Example 1 What is the subnetwork address if the destination address is 200.45.34.56 and the subnet mask is 255.255.240.0? Solution 11001000 00101101 00100010 00111000 11111111 11111111 11110000 00000000 11001000 00101101 00100000 00000000 The subnetwork address is 200.45.32.0. Short-Cut Method ** If the byte in the mask is 255, copy the byte in the address. ** If the byte in the mask is 0, replace the byte in the address with 0. ** If the byte in the mask is neither 255 nor 0, we write the mask and the address in binary and apply the AND operation. Example 2 What is the subnetwork address if the destination address is 19.30.80.5 and the mask is 255.255.192.0? Solution See Figure 5.6 Figure 5-6 Example 2 Figure 5-7 Comparison of a default mask and a subnet mask The number of subnets must be a power of 2. Example 3 A company is granted the site address 201.70.64.0 (class C). The company needs six subnets. Design the subnets. Solution The number of 1s in the default mask is 24 (class C). Solution (Continued) The company needs six subnets. This number 6 is not a power of 2. The next number that is a power of 2 is 8 (23). We .