Network class

The first byte of the IP address determines the network class and as such represents the division into network address and node address:

Range of values
(byte 1 of the IP address)

Network class

Example: Complete network address

Meaning

0 – 127

A

10.1.22.3

10 = Network address

1.22.3 = Node address

128 – 191

B

172.16.52.4

172.16 = Network address

52.4 = Node address

192 – 223

C

192.168.10.4

192.168.10 = Network address

4 = Node address

Node addresses that consist only of zeros or ones are not permitted. The smallest address (all bits are zero) describes the network itself and the largest address (all bits are 1) is reserved for the broadcast.

This rough division is not sufficient for a number of networks. The networks also use an explicit, adjustable subnet mask.