NOTE: AMD PCnet-PCI NICs not supported
The “PCnet-PCI II” virtual adapter is not supported in the pcn driver.
“PCnet-PCI III” is known to have issues with DHCP and perhaps other traffic.
For best results, use one of the Intel PRO/1000 adapters (e1000g driver).
Note that if you want PXE boot support for Intel adapters you will also need the Oracle VM VirtualBox Extension Pack from https://www.virtualbox.org/wiki/Downloads