Hyper-V Program Manager
The other day I was trying to boot a virtual machine over the network using my Windows Deployment Services (WDS) Server. This normally works fine – but for some reason I was getting nothing but errors. Sometimes I would get a DHCP failure, other times I received varied PXE error messages:
After some investigation I stumbled on to the problem. There was a MAC address conflict. While Hyper-V will not let MAC address conflicts happen on a single server – but you can still have conflicts happen between multiple Hyper-V servers. John Howard has talked about this extensively here: http://blogs.technet.com/b/jhoward/archive/2008/07/15/hyper-v-mac-address-allocation-and-apparent-network-issues-mac-collisions-can-cause.aspx
Once I realized what was happening – I quickly changed the virtual machine to use a static MAC address and set the MAC address to a unique value:
Then network installation worked fine.
this problem occurs much more then you'd think. I think the algorithm should be modified, only using the last to octets is not enough as far as I can tell. We've have a lot of vlans and two hyper-v servers can easily have the last two octets the same.
I do agree that the algorithm is far from perfect. We almost need something like a DHCP server for MAC addresses. Mind you, if you are using SCVMM for provisioning they ensure that conflicts do not happen.