I have a F16 x86-64 installation with the latest updates, with two windows guests. A Win7 x64 and a WinXP SP3 guest. Both guests are setup for default NAT networking as configured by Fedora.
These issues did not change with the batch of KVM/QEMU updates that came through in the last days.
On the Win7 x64 guest, networking just works. I have tried both the default rtl8139 device, and the virtio drivers.
But on the WinXP guest I have tried almost every virtual network device, I just cannot get a usable network connection.
With the default rtl8139, pcnet or virtio device, windows shows link, but generally does not manage to get a network address. Generally, because there is the occasional exception where it does manage to get a network address, but typically that is where things stop working. If I'm lucky I might get a few pings through before things seem to stop working completely.
With the ne2k_pci driver, I manage to get a network address most of the time, but the connection is pretty much unusable. For instance pinging a server, that from the host has a 0% packet loss will instead have 50-70% loss. And typically loss comes in batches, so it is able to get a few pings through and then it stops working again for a while. I have had on a few occasions that the network would work for a minute or two before it dropped out, and I cannot even ping the default gateway any more.
I have not tried the e1000 yet, as that driver apparently did not ship with WinXP and I would need to go find the driver, but considering the issues with all the other devices seem related I don't think it will make a difference anyway.
I would love to hear some suggestions, or if anyone has been able to get WinXP SP3 working properly in KVM on Fedora 16.