Siemens SIMATIC ET 200AL System Manual page 997

Parameter assignment/addressing
3.2 Device name and IP address
Generating IP addresses
The IP addresses of the IO devices are generated by STEP 7 and first assigned to the IO
devices when the CPU starts up. In addition, for some IO devices (e.g., SCALANCE X,
S7-300 CPs), it is possible not to obtain the IP address during startup of the IO controller, but
rather to set it beforehand on the device (see Permitting changes to the device name and IP
address directly on the device (Page 60)).
The IP addresses of the IO devices always have the same subnet mask as the IO controller
and are assigned from the IP address of the IO controller in ascending order. The IP address
can be changed manually, if necessary.
For devices with several PROFINET interfaces (e.g., CPU 1516-3 PN/DP), the IP addresses
must be located in different subnets.
Default router
The default router is used when data has to be forwarded via TCP/IP or UDP to a partner
located outside the local network.
In STEP 7, the default router is named Router. You can activate the use of a router in the
Inspector window of a CPU with the "Use router" check box in the "IP protocol" section.
STEP 7 assigns the local IP address to the default router by default.
The router address that is set on the PROFINET interface of the IO controller is
automatically transferred for the configured IO devices.
Subnet mask
The bits set in the subnet mask decide the part of the IP address that contains the address
of the network.
In general, the following applies:
● The network address is obtained from the AND operation of the IP address and subnet
mask.
● The device address is obtained from the AND NOT operation of the IP address and
subnet mask.
Example of the subnet mask
Subnet mask: 255.255.0.0 (decimal) = 11111111.11111111.00000000.00000000 (binary)
IP address: 192.168.0.2 (decimal) = 11000000.10101000.00000000.00000010 (binary)
Meaning: The first 2 bytes of the IP address determine the network - i.e., 192.168. The last
two bytes address the device, i.e. 0.2.
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PROFINET with STEP 7 V15
Function Manual, 12/2017, A5E03444486-AH