Can't get online with a X20CP0410 by ETH1, only by serial connection

The CPU can’t be reached over ethernet because CPU has no IP. It was configured fixed but for some reason it lost his IP. If I connect via serial connection I can compare the software and check the online info but software cannot be downloaded over serial. In the existing project the USB options “USB install” and “USB user-partition install” are switched off. (maybe that was a mistake).
Does anyone know how to proceed to download the project or set the IP?

Hello,

You can try Determining a PLC’s IP Address using Wireshark.

Or install a project on a target system with a USB flash drive - scenario 1, with restarting the target system in BOOT mode.