Siemens SIMATIC NET CP 343-1 ERPC Manual page 22

Installation and commissioning
3.4 Module replacement
Storage of the STEP 7 configuration data on the CPU can be selected in the properties
dialog of the CP in the "Options" tab in "Module replacement without PG". We recommend
that you store the configuration data on the CPU if the configuration memory of the CPU
allows.
To use ERPC communication, you must first load the ERPC firmware on the CP before
commissioning a new CP.
Replacing the CP with an S7 Ethernet CP without ERPC functionality is not possible.
Module replacement: Special feature when using the ERPC functions
If you use the ERPC functions on the CP, you will first need to load the ERPC firmware on
the new CP before you replace the module. See also section Downloading the ERPC
firmware (Page 69).
NOTICE
Module replacement if a fault occurs
If the ERP subscriber cannot be reached, note the following:
 The buffered frames are not stored on the C-PLUG.
 Buffered but not yet transferred data is lost when you replace the module.
Module replacement: Special feature of IP address assignment from a DHCP server
During configuration in the properties dialog, you can specify the IP configuration for the CP.
One option here is that the CP obtains the IP address from a DHCP server.
NOTICE
When replacing a module, please remember that the factory set MAC address of the new
module differs from that of the previous module. When the factoryset MAC address of the
new module is sent to the DHCP server, this will return either a different or possibly even
no IP address.
Ideally, you should therefore configure IP as follows:
Always configure a client ID if you want to obtain the same IP address from the DHCP
server after replacing the module.
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CP 343-1 ERPC
Manual, 03/2010, C79000-G8976-C239-02