[Today's post comes to us courtesy of Martina Grom, Technet Team Blog Austria]
When you install the Hyper-V Role on your SBS 2008 Primary Server the DHCP Service will no longer be able to assign IP addresses to your client machines. The reason for this is that we do not support the Hyper-V role on the SBS 2008 Primary Server . The SBS wizard expects only one network adapter and binds DHCP to that network interface. Similar problems with DHCP can be experienced if you are using 2 NICs, this is also an unsupported topology, for more information on support network topologies for SBS 2008 see http://blogs.technet.com/sbs/archive/2008/09/16/sbs-2008-supported-networking-topology.aspx .
For more information, please read these KB Articles: KB968250 and KB958829 .
We do support Hyper-V in SBS 2008 environments in three scenarios, which are described here: http://blogs.technet.com/sbs/archive/2008/09/15/sbs-2008-and-virtualization.aspx .
For further reading concerning Hyper-V and SBS 2008, please refer to: http://technet.microsoft.com/en-us/library/dd239207(WS.10).aspx .
