Out of curiosity I went out and bought a USB3 to Ethernet adapter (1Gbit, "j5Create") and hooked it up to one of the USB3 ports in the back. I then re-installed Proxmox just to be extra sure, and used the USB dongle in the installation step instead of the onboard NIC. Created a test container...
At this point I've re-installed proxmox with default config, just in case I meddled with something earlier. Still the same problem.
I also moved the IP range from 10.0xxx to 10.60xxx which is my network's DMZ. The plan was to move to this network eventually anyway, and it seems like I have...
I have a network 10.0.0.0/24 with a proxmox on 10.0.0.8
I created an Ubuntu server 20.04 VM 10.0.0.9 and an Ubuntu server 20.04 container 10.0.0.7
The proxmox machine is hooked up to a Unifi 16 XG L2 10Gbit switch using a single Gbit line for testing
That switch is hooked into a Unifi UDMP...