Beginning in Windows 10 1709, Hyper-V networking included a “Default Switch” to help simplify Internet connectivity to guest VMs. The idea is that this switch would automatically share whatever Internet connection is used by the Host, then NAT the addresses to the guests. This sharing is accomplished using the Internet Connection Sharing (ICS) service on the Host.
While in theory this makes the networking of guests easier, one particular challenge with this solution still exists today with Windows 10 1803….occasionally this guest loses it’s ability to work through the Host’s connection. And thereby the guest has no Internet access. So, if you’re faced with this issue, try restarting the ICS service on the host to restore connectivity.
For Internet connection issues with the default switch on a Windows 7 guest VM, I found the best solution to be changing the “Automatic metric” settings on the NICs in the VM. This workaround/solution was posted in a TechNet forum thread, but the details are copied below for ease of reading.
“Go to <Network and Sharing><Change Adapter Settings> and right click your wired and wireless adapters one at a time to change the properties. Select IPv4, click <Properties> then click <Advanced>. For each one, clear the “Automatic metric” check box and assign the metric value manually. I set the wireless to 1 and the wired to 2, which gave me the behavior I wanted.”