If DECnet Phase IV support is required under Hyper-V, MAC address spoofing must be enable.  However, Microsoft Hyper-V versions prior to Windows Server 2008 R2 Hyper-V and Hyper-V Server 2008 R2 do not support MAC address spoofing.  This prevents the MAC address change inherent in a DECnet Phase IV installation.  DECnet Phase IV support under Hyper-V requires a Hyper-V release that supports MAC address spoofing.