Siemens SIMATIC NET SCALANCE SC-600 Configuration Manual page 34

Technical basics
3.1 IP address
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.
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.
Masking additional subnets
Using the subnet mask, you can further structure a subnet assigned to one of the
address classes A, B or C and form "private" subnets by setting further lower-level digits
of the subnet mask to "1". For each bit set to "1", the number of "private" networks
doubles and the number of nodes contained in them is halved. Externally, the network
still looks like a single network.
Example:
You change the default subnet mask for a subnet of address class B (e.g. IP address
129.80.xxx.xxx) as follows:
Masks
Default subnet mask
Subnet mask
Result:
All devices with addresses from 129.80.1.xxx to 129.80.127.xxx are on one IP subnet, all
devices with addresses from 129.80.128.xxx to 129.80.255.xxx are on another IP subnet.
34
Decimal
255.255.0.0
255.255.128.0
SCALANCE SC-600 Web Based Management (WBM)
Configuration Manual, 10/2021, C79000-G8976-C475-03
Binary
11111111.11111111.00000000.
00000000
11111111.11111111.10000000.
00000000