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, 129.144, are assigned by the InterNIC, and compose the network address. The last two bytes, 50.56, compose 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 5–5 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.