Qemu

Qemu without the guest:
1.has a mechanism by which it will advertise the availability of 8139,NE2000 network controllers
to the guest. So when the guest boots up it will automatically pick up 8139 and NE2000 drivers
from the kernel
2.So only these two drivers can be used to create a virtual ethernet driver on top of the host network system using qemu
3.It utilises bridging utilities brutility to create a virtual network comprising of guest networks
and host network
4.there is also a mode in qemu where an application tcpip stack is used to simulate the network

5.Again similar to the n/w interface UART is also advertised by the qemu

kqemu + processor hardware support can give near equal performance for a guest os