I have Client Hyper-V on Win8, hosting a few VMs like ubuntu, a clean windows build-machine, etc. My VMs are connected to an external virtual-switch (shared with the management OS), and that works fine... for a while - they can see the world. However, after an indeterminate time, when I resume the guest VM it won't have internet access. It simply can't see out. Shutting down the guest completely and restarting it doesn't help.
Currently, the only way I can "cure" this is to suspend the guests, go into Virtual Switch Manager, remove my virtual-switches, re-add the same virtual-switches, and reactivate the guest OS. Then it immediately works. This even works if the guest was just paused (not fully shut down).
Is this a common fault? What can I do to prevent this?
Update: after experimentation, it seems I only need to delete / re-add the external virtual-switch. Until then, the guest OS thinks it is disconnected.