I'll do my best to explain this as its confusing. I have Qemu/Virtual Machine Manager on my host PC. I created an Ubuntu VM and assigned two PCI slots (which are physical network cards) to it within Virtual Machine Manager; specifically PCI 0000:09:00.0 and PCI 0000:07:00.0. On the VM host these adapters come up with this mapping:
PCI 0000:09:00.0, Plugging cable in brings up enp6s0, and the NIC located physically at the bottom of my PC lights up
PCI 0000:07:00.0, Plugging cable in brings up enp7s0, and the NIC located physically at the top of my PC lights up
I now remove PCI 0000:07:00.0 from this Ubuntu VM on the host within Virtual Machine Manager and attach this to a different VM, lets refer to this as VM2. When this device starts up this is what happens regarding the mapping:
PCI 0000:07:00.0, plugging cable into the top NIC does NOT bring up the port. HOWEVER, if I plug this into the bottom NIC on my PC, the link light comes up, and my network interface comes up on the VM!
Interestingly, when the original VM starts, it now uses the top NIC in my PC. So it's like the physical mapping changes it.
Now, this is not so much a problem for me (well any more, since I discovered this incredibly annoying and difficult-to-figure-out problem), but I would absolutely like to understand is why/how this happens. Can someone explain why it does that, and ideally how to stop it doing that? (I'm most interested in why this happens).
