Siemens SIMATIC NET System Manual page 29

Correct values:
255.255.0.0 D = 1111 1111.1111 1111.0000 0000.0000 0000 B
255.255.128.0 D = 1111 1111.1111 1111.1000 0000.0000 0000 B
255.254.0.0 D = 1111 1111.1111 1110.0000 0000.0000.0000 B
Incorrect value:
255.255.1.0 D = 1111 1111.1111 1111.0000 0001.0000 0000 B
Relationship between the IP address and subnet mask
The first decimal number of the IP address (from the left) determines the structure of the
subnet mask with regard to the number of "1" values (binary) as follows (where "x" is the
host address):
First decimal number of the IP address
0 to 127
128 to 191
192 to 223
Classless Inter-Domain Routing (CIDR)
CIDR is a method that groups several IP addresses into an address range by representing
an IP address combined with its subnetwork mask. To this purpose, a suffix is appended to
the IP address that specifies the number of bits of the network mask set to 1. Using the
CIDR notation, routing tables can be reduced in size and the available address ranges put to
better use.
Example:
IP address 192.168.0.0 with subnet mask 255.255.255.0
The network part of the address covers 3 x 8 bits in binary representation; in other words, 24
bits.
This results in the CIDR notation 192.168.0.0/24.
The host part covers 1 x 8 bits in binary notation. This results in an address range of 2 to the
power 8, in other words 256 possible addresses.
Value range for gateway address
The address consists of four decimal numbers taken from the range 0 to 255, each number
being separated by a period; example: 141.80.0.1
Range of values for IP address and gateway address
The only parts of the IP address and network transition address that may differ are those in
which "0" appears in the subnet mask.
Example:
Industrial Ethernet
System Manual, 09/2019, C79000-G8976-C242-10
Basics of communication with Industrial Ethernet
1.3 Technologies of Industrial Ethernet
Subnet mask
255.x.x.x
255.255.x.x
255.255.255.x
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