Every networking student should have a solid understanding of TCP/IP subnetting (Loshin, 1997). Subnetting’s importance in modern networking is reflected by its many and varied uses. It can enhance network performance by splitting up collision and broadcast domains in a routed network (Odom, 2000). Large networks can be organized into separate subnets representing departmental, geographical, functional, or other divisions (Feit, 1997). Since hosts on different subnets can only access each other through routers, which can be configured to apply security restrictions, subnetting can also serve as a tool for implementing security policies (Bulette, 1998). Dividing a large network into subnets and delegating administrative responsibility for each subnet can make administration of a large network easier. Routers can require that a WAN link connecting two networks must itself form a separate subnet (Bulette, 1998). Troubleshooting, diagnosing, and fixing problems in a TCP/IP internetwork typically require thorough familiarity with subnetting. Network design requires both the ability to understand and carry out subnetting.