IP address classes
Each IP address breaks down into two parts:
Net ID—Identifies a network. The first several bits of a net ID, known as the class field or class bits, identify the class of the IP address.
Host ID—Identifies a host on a network.
IP addresses are divided into five classes, shown in Figure 12. The shaded areas represent the address class. The first three classes are widely used.
Figure 12: IP address classes
Table 1: IP address classes and ranges
Class | Address range | Remarks |
|---|---|---|
A | 0.0.0.0 to 127.255.255.255 | The IP address 0.0.0.0 is used by a host at startup for temporary communication. This address is never a valid destination address. Addresses starting with 127 are reserved for loopback test. Packets destined to these addresses are processed locally as input packets rather than sent to the link. |
B | 128.0.0.0 to 191.255.255.255 | N/A |
C | 192.0.0.0 to 223.255.255.255 | N/A |
D | 224.0.0.0 to 239.255.255.255 | Multicast addresses. |
E | 240.0.0.0 to 255.255.255.255 | Reserved for future use except for the broadcast address 255.255.255.255. |