I just talked to someone on the iPXE IRC channel and got some helpful information. The RTL8153 should be supported as both the USB NIC and iPXE support ECM! Please try enable more debugging to see what’s going on ‘DEBUG=usb,xhci,usbnet,usbhub’…
And there is another (old) thread here: [url]http://fogproject.org/forum/threads/realtek-8153-usb-network-adapter.10302/[/url]
I suppose you’ve set ‘Legacy only’ in BIOS…