Technical basics
3
3.1 Structure of an IPv4 address
The IPv4 address consists of 4 decimal numbers separated by a dot. Each decimal number can
have a value from 0 to 255.
Example: 192.168.16.2
The IPv4 address is composed of:
● Address of the (sub)network
● The address of the node (generally also called end node, host or network node)
Subnet mask
The subnet mask consists of four decimal numbers with the range from 0 to 255, each number
separated by a period; example: 255.255.0.0
The binary representation of the 4 subnet mask decimal numbers must contain a series of
consecutive 1s from the left and a series of consecutive 0s from the right.
The "1" values determine the network address within the IPv4 address. The "0" values
determine the device address within the IPv4 address.
Example:
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
Subnet mask: 255.255.0.0 = 11111111.11111111.00000000.00000000
In the example for the IP address mentioned above, the subnet mask shown here has the
following meaning:
The first 2 bytes of the IP address determine the subnet - i.e. 192.168. The last two bytes
address the device, i.e. 16.2.
The following applies in general:
● The network address results from the AND combination of IPv4 address and subnet mask.
● The device address results from the AND-NOT combination of IPv4 address and subnet
mask.
SCALANCE S615 Web Based Management
Configuration Manual, 11/2019, C79000-G8976-C388-08 31
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