Siemens SIMATIC PROFINET Function Manual page 198

Functions
5.8 Device replacement without exchangeable medium
Typical source of danger
When replacing an IO device ("standard case"), it is almost guaranteed that the replaced
device will be connected according to the configured port interconnection.
The figure below shows a scenario whereby the connections of two identical PROFINET
cables are swapped at two switch ports. Because the IO controller assigns the device names
according to the preset topology, the incorrect connection of the devices has serious effects
on the naming.
Due to the control of different actuators, the plant could become hazardous in this case.
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Switch with connected PROFINET cables
Device A, device name "IOD-1": controls motor 1
Device B, device name "IOD-10": controls motor 10
Device A controls motor 10!
Device B controls motor 1!
PROFINET with STEP 7 V14
Function Manual, 09/2016, A5E03444486-AG