Only getting 100 Mbit in Hyper V Guest from 1 Gigabit network connection

Verify that you're not using any of the "Legacy NICs" in your Virtual Machines? These are limited to 100mbps. This may be causing the Virtual Network (bound to the physical NIC) to negotiate the lower speed.

Other things to do: - Update NIC drivers - Force 1gbps operation in Device Manager - Replace the patch lead connecting the problem NIC - check cable. Two threads above had a similar problem solved by replacing a cable.