7
Startup
TCP/IP addressing and subnetworks
Manual – PROFINET IO Interfaces, Field Distributors
77
7.2.4
Network classes
The first byte of the IP address determines the network class and as such represents
the division into network addresses and node addresses.
Range of val-
ues
Byte 1
Network
class
Complete
network address
(example)
Explanation
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
This rough division is not sufficient for a number of networks. They also use an expli-
cit, adjustable subnet mask.
7.2.5
Subnetwork mask
A subnet mask is used to divide the network classes into even finer sections. Like the
IP address, the subnet mask is represented by 4 decimal numbers separated by
decimal points.
Example: 255.255.255.128
Each decimal number stands for one byte (= 8 bits) of the subnet mask and can also
be represented using binary code (→ following table).
Byte 1
Byte 2
Byte 3
Byte 4
11111111
.
11111111
.
11111111
.
10000000
If you compare the IP addresses with the subnet masks, you see that in the binary
representation of the subnet mask all ones determine the network address and all the
zeros determine the node address (see following table).
Byte 1
Byte 2
Byte 3
Byte 4
IP address
decimal
192
. 168.
. 10
. 129
binary
11000000 . 10101000 . 00001010
. 10000001
Subnet mask
decimal
255
. 255
. 255
. 128
binary
11111111 . 11111111 . 11111111
. 10000000
The class C network with the address 192.168.10. is further subdivided by the subnet
mask 255.255.255.128. 2 networks are created with the address 192.168.10.0 and
192.168.10.128.
The following node addresses are permitted in the two networks:
•
192.168.10.1 – 192.168.10.126
•
192.168.10.129 – 192.168.10.254
The network nodes use logic AND operation for the IP address and the subnet mask
to determine whether there is a communication partner in the same network or in a dif-
ferent network. If the communication partner is in a different network, the standard
gateway is addressed for passing on the data.
22870857/EN – 12/2016
