"Using HP ProLiant Network Teaming Software with Microsoft® Windows® Server 2008 Hyper-V or with Microsoft® Windows® Server 2008 Hyper-V R2" HOWTO, 4th edition

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6. Assign the new virtual network to a new virtual machine: Check the Enable virtual LAN
Identification box and enter the desired VLAN identifier (ID).
NOTE
We recommend that you do not use a VLAN ID of “1” when
you configure virtual machines.
End of procedure.