IP address classes

Each IP address breaks down into the following sections:

IP addresses are divided into five classes, as shown in Figure 7. The shaded areas represent the address class. The first three classes are most commonly used.

Figure 7: 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.