206 Fieldbus Communication
WAGO-I/O-SYSTEM 750
750-880, 750-880/025-000 ETHERNET Programmable Fieldbus Controller
Manual
Version 1.0.1
dependent upon the number of subnets to be addressed and the number of
subscribers per subnet.
Table 77: Class B Address with Field for Subnet IDs
1
8
16
24
32
1 0
...
Network ID
Subnet ID
Host ID
Subnet Mask
A subnet mask was introduced to encode the subnets in the Internet. This involves
a bit mask, which is used to mask out or select specific bits of the IP address. The
mask defines the subscriber ID bits used for subnet coding, which denote the ID
of the subscriber. The entire IP address range theoretically lies between 0.0.0.0
and 255.255.255.255. Each 0 and 255 from the IP address range are reserved for
the subnet mask.
The standard masks depending upon the respective network class are as follows:
•
Class A Subnet mask:
Table 78: Subnet mask for Class A network
255 .0 .0 .0
•
Class B Subnet mask:
Table 79: Subnet mask for Class B network
255 .255 .0 .0
•
Class C Subnet mask:
Table 80: Subnet mask for Class C network
255 .255 .255 .0
Depending on the subnet division the subnet masks may, however, contain other
values beyond 0 and 255, such as 255.255.255.128 or 255.255.255.248.
Your network administrator allocates the subnet mask number to you.
Together with the IP address, this number determines which network your PC and
your node belongs to.
The recipient node, which is located on a subnet initially, calculates the correct
network number from its own IP address and the subnet mask.
Only then does it check the node number and delivers the entire packet frame, if it
corresponds.
Table 81: Example for an IP address from a Class B network
IP address
172.16.233.200
10101100 00010000 11101001 11001000
Subnet mask
255.255.255.128
11111111 11111111 11111111 10000000
Net ID
172.16.0.0
10101100 00010000 00000000 00000000
Subnet ID
0.0.233.128
00000000 00000000 11101001 10000000
Host ID
0.0.0.72
00000000 00000000 00000000 01001000
