Connecting a Raspberry Pi 4B computer to the ConnectBox (WLAN router) from Unitymedia//UPC may not work properly.
If you connect the Raspberry Pi directly via LAN cable to the ConnectBox, packet losses might occur. Probably an issue with the odd ConnectBox hardware.
The solution is relatively simple. If you hang a switch between the ConnectBox and the Raspberry Pi, the connection works without problems.
More information on the issue:
- Packet loss on eth0 [Raspberry Pi 4 Model B]
https://www.raspberrypi.org/forums/viewtopic.php?t=253337 - Raspberry Pi 4 high packet loss over ethernet #3292
https://github.com/raspberrypi/linux/issues/3292