12.04 LTS KVM guest losing network connectivity

[webo]

I'm running an Ubuntu 12.04 LTS VM host and using KVM for guest machines.

I'm having an issue with a KVM of mine that runs Zimbra and loses network connectivity (it's bridged) from the outside after a few hours. When I go back to the VM host and into the console for the guest, it works fine (almost like moving the mouse to get rid of a screensaver) but when I leave it untouched for a while, I suddenly lose the ability to connect to it.

I've tried both the virtio and e1000 drivers but I'm still running into this issue. Any suggestions?

[TheFu]

What are your host and guest network, bridge, driver settings?
I haven't seen any network issues on my 10.04 or 12.04 KVM servers. I always manually create a bridge ... never use the automatic version that libvirt created. When I started, the libvirt bridge was a usermode-TUN device ... I believe. i.e. slow.