 be expanded, as there is space after each used subnet equal to the size of the subnet in use. This method also allows for the largest possible subnet to be available at any given time. I like this method because it's simple and it reasonably balances the need for subnet expandability while keeping the largest free space available for as long as possible. Reverse Binary Reverse binary is Cisco's recommended method for IP subnet allocation. In this method, subnets are allocated by counting in binary, but with the most and least sig- nificant bits reversed. Figure 36-8 shows how reverse binary works. By reversing the significant bit order, we create a mirror image of the numbers in binary (shown on the right). These numbers happen to correspond to the subnets that should be used, in order, regardless of size. The pattern may be continued for as long as is useful. By allocating subnets in this order, we end up spacing the subnets SO that no two subnets are adjacent unless the subnets are of varying sizes (a distinct possibility using VLSM). This method also offers the reasonable tradeoff of allowing the largest possible re- maining addressable space while offering the expandability desired. The real difference between this method and the divide-by-half method is the size of the largest remaining block in the source IP network. Chapter 36: IP Design 192.168.1.0/28 192.168.1.0/27 192.168.1.16/28 192.168.1.0/26 192.168.1.0/26 192.168.1.32/28 192.168.1.32/28 192.168.1.48/28 192.168.1.48/28 192.168.1.0/25 192.168.1.0/25 192.168.1.0/25 192.168.1.0/25 192.168.1.64/28 192.168.1.64/28 192.168.1.64/28 192.168.1.64/28 192.168.1.80/28 192.168.1.80/28 192.168.1.80/28 192.168.1.80/28 192.168.1.96/28 192.168.1.96/28 192.168.1.96/28 192.168.1.96/27 192.168.1.112/28 192.168.1.112/28 192.168.1.112/28 192.168.1.128/28 192.168.1.128/28 192.168.1.128/28 192.168.1.128/28 192.168.1.128/28 192.168.1.128/28 192.168.1.128/28 192.168.1.128/28 192.168.1.144/28 192.168.1.144/28 192.168.1.144/28 192.168.1.144/28 192.168.1.144/28 192.168.1.144/28