System Administration Guide: IP Services

Class B Network Numbers

A class B network number uses 16 bits for the network number and 16 bits for host numbers. The first byte of a class B network number is in the range 128–191. In the number, the first two bytes, 172.16, are registered with the IANA, and compose the network address. The last two bytes, 50.56, contain the host address, and are assigned at the discretion of the owner of the network number. The following figure graphically illustrates a class B address.

Figure 10–4 Byte Assignment in a Class B Address

Diagram shows bits 0-15 is network part and remaining
16 bits are host part of a 32 bit IPv4 Class B address.

Class B is typically assigned to organizations with many hosts on their networks.