 of any servers. You'll only need to change the sub- net masks and default gateways. Before After Server farm 10.100.100.0/26 10.100.100.64/26 Server farm 10.100.100.0/24 10.100.100.128/26 10.100.100.192/26 Figure 34-5. Subnetting an existing range Allocating IP Network Space This kind of thing happens more often than you might think. Perhaps a decision will be made that all of the Oracle servers should be on their own physical network, for security reasons. No problem! Because you were smart enough to allocate their IP space along subnet boundaries, the entire range can easily be pulled out and moved to another interface. All the IP addresses will stay the same; only the subnet masks will change. The catch (isn't there always a catch?) is that you must be vigilant! If even one IP address is allocated in violation of these rules, you will have to renumber something to move a section of the existing network. Allocating IP Subnets When allocating IP subnets within a network, care should be taken to allocate them in a logical fashion. When allocating subnets, you should strive for two goals: Allow for the largest possible remaining addressable space (i.e., the largest subnets possible in the remaining space). Allow as many subnets as possible to be expanded into the surrounding available space. As you will see, achieving both of these goals is a balancing act. I've encountered three methods for allocating IP subnets. I'll call these methods sequential, divide by half, and reverse binary. Sequential Most people's first inclination seems to be to allocate IP addresses and IP subnets in numerical order. That is, they allocate the first numerical subnet, then the next, and SO on. If such a person were subnetting the 192.168.100.0/24 network into /30 subnets, they would likely get allocated in this order: 0, 4, 8, 12, etc. Sequential allo- cation of subnets in a network is what most admins seem naturally prone to do. It works, it's easy to understand, and it's pretty easy to tell where the next available network will be.