As an example, suppose an organization is given the block 17.12.14.0/26, which contains 64 addresses (2(32-26) = 64). The organization has three offices and needs to divide the addresses into three subblocks of 32, 16, and 16 addresses. We can find the new masks by using the following arguments: Suppose the mask for the first subnet is n1, then 232- n1 must be 32, which means that n1 =27. Suppose the mask for the second subnet is n2, then 232- n2 must be 16, which means that n2 = 28. Suppose the mask for the subnet is n3, then 232- n3 must be 16, which means that n3 =28. This means that we have the masks 27, 28, 28 with the organization mask being 26. Figure 19.7 shows one configuration for the above scenario. More Levels of Hierarchy The structure of classless addressing does not restrict the number of hierarchical levels. An organization can divide the granted block of addresses into subblocks. Each subblock can in turn be divided into smaller subblocks, and so on. One example of this is seen in the ISPs. A national ISP can divide a granted large block into smaller blocks and assign each of them to a regional ISP. A regional ISP can divide the block received from the national ISP into smaller blocks and assign each one to a local ISP. A local ISP can divide the block received from the regional ISP into smaller blocks and assign each one to a different organization. Finally, an organization can divide the received block and make several subnets out of it. IPv4 Header Datagram Packets in the IPv4 layer are called datagrams. Figure 20.5 shows the IPv4 datagram format.
As an example, suppose an organization is given the block 17.12.14.0/26, which contains 64 addresses (2(32-26) = 64). The organization has three offices and needs to divide the addresses into three subblocks of 32, 16, and 16 addresses. We can find the new masks by using the following arguments: Suppose the mask for the first subnet is n1, then 232- n1 must be 32, which means that n1 =27. Suppose the mask for the second subnet is n2, then 232- n2 must be 16, which means that n2 = 28. Suppose the mask for the subnet is n3, then 232- n3 must be 16, which means that n3 =28. This means that we have the masks 27, 28, 28 with the organization mask being 26. Figure 19.7 shows one configuration for the above scenario. More Levels of Hierarchy The structure of classless addressing does not restrict the number of hierarchical levels. An organization can divide the granted block of addresses into subblocks. Each subblock can in turn be divided into smaller subblocks, and so on. One example of this is seen in the ISPs. A national ISP can divide a granted large block into smaller blocks and assign each of them to a regional ISP. A regional ISP can divide the block received from the national ISP into smaller blocks and assign each one to a local ISP. A local ISP can divide the block received from the regional ISP into smaller blocks and assign each one to a different organization. Finally, an organization can divide the received block and make several subnets out of it. IPv4 Header Datagram Packets in the IPv4 layer are called datagrams. Figure 20.5 shows the IPv4 datagram format.
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