BECKHOFF Fieldbus Components: Ethernet

Network Classes

Three different network classes are distinguished. They specify how many address bits are reserved for the Network -ID and how many for the computer number (or node number). The difference is located in the first 3 bits of the IP address.

Number of bits
for the Network ID
Possible number
of networks
Number of bits for
the node address
Possible number of
nodes per network
A 7 126 24 16 777 214
B 14 16 382  16 65 536
C 21 2 097 150  8 254


Ethernet - Network Classes 1:Warning An IP address must be unique within the entire connected network!


Ethernet - Network Classes 2:


Ethernet - Network Classes 3:Note In a communication with another Ethernet devices, the IP address set must have the same network class. Example: Your PC has address, which means that the Bus Coupler must have address (each xxx stands for a number between 0...255. The 0 is normally used for routers/switches, and should therefore be reserved).

In order to see the PC's own address, the command ipconfig can be entered into a DOS window under Windows NT/2000/XP.