The network address is the first part of the IP address for every host in the network you manage. The network address identifies part of a total IP address as the network, and leaves the rest of the IP address to identify a particular host on that network.
The Network Information Centers or NICs (including the original InterNIC) that assign network addresses for the Internet take into account the fact that different organizations manage different numbers of hosts. An NIC therefore assigns you a network ID belonging to one of the following three classes, based on how many hosts you have, or expect to have, on your network: class A, class B, or class C. Each class uses progressively more of the IP address to identify the network, and therefore leave you with fewer numbers to uniquely identify your hosts.
The following table shows the network classes available from an NIC. The portion of each IP address that is reserved for host and subnet addresses is shown by x's. This table will enable you to tell the network class of a given IP address:
| Class | IP address range | Description |
|---|---|---|
| A | 0.x.x.x - 127.x.x.x | Three bytes can be used for host and subnet addresses; addresses beginning with 0 or 127 are reserved for special use, such as 127.0.0.1 for the loopback address |
| B | 128.0.x.x - 191.255.x.x | Two bytes can be used for host and subnet addresses |
| C | 192.0.0.x - 223.255.255.x | One byte can be used for host and subnet addresses |
| D | 224.0.0.0 - 239.255.255.255 | Multicast addresses |
| E | 240.0.0.0 - 247.255.255.255 | Reserved and experimental addresses |