When you install Hyper-V R2 (download) role now it reserves a single wired NIC in the machine for management of the parent partition. If you have only a single NIC in your server, you will not be able you select a NIC to create an external network when you are installing the role.  Hyper-V R2 also has a new default when creating an External Virtual Network. By default the new external virtual network is not exposed to the parent partition for it to share. In order to enable the parent partition to share the NIC, there is a new checkbox that you must enable under the physical NIC dropdown box.[…]

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