|  | 10.1 | IP Addressing and Subnetting
| 10.1.2 | The role of host network on a routed network
In this section, you will learn basic concepts you need to understand before configuring an IP address. By examining various network requirements, you can select the correct class of address and define how to establish IP subnets. Each device or interface must have a host number that does not have all 0s in the host field. A host address of all 1s is reserved for an IP broadcast into that network. A host value of 0 means "this network" or "the wire itself" (e.g. 172.16.0.0). A value of 0 is also used, though rarely, for IP broadcasts in some early TCP/IP implementations. The routing table contains entries for network or wire addresses; it usually contains no information about hosts. An IP address and a subnet mask on an interface achieve three purposes: They enable the system to process the receipt and transmission of packets. They specify the device's local address. They specify a range of addresses that share the cable with the device.