Description of problem:

I am using Virtual Manager and have created a virtual machine running Ubuntu 10.04. However, the guest loses the network quite often. I think that it is related to downloading big files, or maybe high network traffic. I was able to reproduce it almost all the times by running 'apt-get upgrade' in the Ubuntu guest, which causes a big network traffic (with 200 updates to be applied :).

 After the network is lost, the only way I could find to recover is to reboot the guest, which is far from desirable in a production environment.

 The interesting thing is that the Ubuntu 10.04 guest run without problems with Fedora 14 host, but after I upgraded the host to Fedora 15, it started giving problems. However, the use under Fedora 14 was scarce, and therefore I cannot tell whether it is a regression or simply I didn't spot the problem before.

 Just for the record, I have seen similar problems but with a Ubuntu 10.04 host and a Debian Squeeze guest.
 
 Maybe it is related to Bug #734731, but in principle they seem different bugs.

 I attach the qemu.conf used in libvirt and the Ubuntu-10.04.xml which defines the virtual machine

Version-Release number of selected component (if applicable):
qemu-kvm-0.14.0-8.fc15.x86_64
qemu-system-x86-0.14.0-8.fc15.x86_64
qemu-img-0.14.0-8.fc15.x86_64
qemu-common-0.14.0-8.fc15.x86_64

How reproducible:
Most of the cases

Steps to Reproduce:
1.Install a Ubuntu 10.04 guest with Virtual Manager 
2.Run apt-upgrade in the guest

This is not however the way I did it, since I installed the guest under Fedora 14 and later on I upgraded the host to Fedora 15.