Siemens SIMATIC NET SCALANCE S615 Configuration Manual page 20

Technical basics
2.1 IPv4 address, subnet mask and address of the gateway
Relationship between the IPv4 address and subnet mask
The first decimal number of the IPv4 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 IPv4 address
0 to 127
128 to 191
192 to 223
Classless Inter-Domain Routing (CIDR)
CIDR is a method that groups several IPv4 addresses into an address range by representing
an IPv4 address combined with its subnet mask. To do this, a suffix is appended to the IPv4
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:
IPv4 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
Relationship between IPv4 address and gateway address
The only positions of the IPv4 address and gateway address that may differ are those in
which "0" appears in the subnet mask.
Example:
You have entered the following: 255.255.255.0 for the subnet mask; 141.30.0.5 for the IPv4
address and 141.30.128.0 for the gateway address. Only the fourth decimal number of the
IPv4 address and gateway address may be different. In the example, however, the 3rd
position is different.
You must, therefore, change one of the following in the example:
The subnet mask to: 255.255.0.0 or
the IPv4 address to: 141.30.128.1 or
the gateway address to: 141.30.0.1
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Subnet mask
255.x.x.x
255.255.x.x
255.255.255.x
SCALANCE S615 Web Based Management
Configuration Manual, 05/2015, C79000-G8976-C388-02