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you might have many users that require their own subnetwork. Additionally, you can have subnetworks for special hosts such as servers. Each of these factors needs to be considered in the network count. You also have to consider any special security or administrative own-ership needs that require additional networks.

One useful tool in this address-planning process is a network diagram. A diagram allows you to see the networks and make a more accurate count. As an example, the corporate internetwork in Figure 6-21 needs to accommodate 800 hosts in its four locations and the WAN connections. To accommodate 800 hosts in the four company locations, you use binary arithmetic to allocate a /22 block, which leaves 10 bits for host addresses

(2¹⁰ – 2 = 1022).

Allocating Addresses

With a count of the networks and the number of hosts for each network completed, you need to start allocating addresses from your overall block of addresses. This process begins by allocating network addresses for the locations that require the most hosts and work downward to the point-to-point links. This process ensures that large enough blocks of addresses are made available to accommodate the hosts and networks for these locations.

When making the divisions and assignment of available subnets, make sure that there are adequately sized address blocks available for the larger demands. Also, plan carefully to ensure that the address blocks assigned to the subnet do not overlap. A helpful tool in this planning process is a spreadsheet. You can place the addresses in columns to visualize the allocation of the addresses. This helps prevent the duplication of address assignments. Figure 6-22 shows the use of a spreadsheet to plan address allocation.

With the major blocks of the example network allocated, you subnet any of the locations that require further dividing. In this example, you divide the corporate HQ into two net-works. The subnets for this location are shown in Figure 6-23. This further division of the addresses is often called subnetting the subnets. As with any subnetting, you need to care-fully plan the address allocation so that you have available blocks of addresses.