@Sebastian-Roth Does the FOS kernel contain the realtek driver that is part of the official linux kernel or does it contain the latest driver from realtek. I’ve seen several recommendations to use the realtek drivers over the linux kernel drivers.
aruhuno, just so I understand this. You booted into debug mode and the FOS kernel did not pick up an ip address and the link light stayed off. You executed the udhcpc command (only) and the interface came up and it picked up an IP address. If this was an spanning tree issue, I think we would see the issue sooner in the booting process, since each time (during pxe booting) the transition between kernels happens the network adapter should be reset and the link dropped.
If you watch the link light during the entire target device booting, the link light should momentarily shut off during PXE rom -> iPXE kernel startup and then when the FOS kernel starts.