Читать книгу Networking All-in-One For Dummies - Lowe Doug, Doug Lowe - Страница 159

IP stands for Internet Protocol, and its primary purpose is to enable communications between networks. As a result, a 32-bit IP address actually consists of two parts:

 The network ID (or network address): Identifies the network on which a host computer can be found

 The host ID (or host address): Identifies a specific device on the network indicated by the network ID

Most of the complexity of working with IP addresses has to do with figuring out which part of the complete 32-bit IP address is the network ID and which part is the host ID, as described in the following sections.

As I describe the details of how host IDs are assigned, you may notice that two host addresses seem to be unaccounted for. For example, the Class C addressing scheme, which uses eight bits for the host ID, allows only 254 hosts — not the 256 hosts you’d expect. The host ID can’t be 0 (the host ID is all zeros) because that address is always reserved to represent the network itself. And the host ID can't be 255 (the host ID is all ones) because that host ID is reserved for use as a broadcast request that’s intended for all hosts on the network.