Quite recently I upgraded my XCP-ng box and added an Intel X520-DA2 network interface card (NIC). The latter comes with dual SFP+ ports and is widely available on the used market for very little money.
So I installed the NIC, turned on the machine and saw: nothing.
One possible solution is to perform an emergency network reset. At least that was the approach that was mostly returned from Google. It works, but you ruin your complete network setup.
Luckily the correct way is much easier. If you have a look at the XCP-ng network documentation, there is even a dedicated section to adding a physical NIC. You simply have to run the command
xe pif-scan host-uuid=<HOST UUID> .
To get the host UUID, you can run
xe host-list. Or if you have only one machine in your home lab, just use the completion functionality by pressing
<TAB> 3 times like this: