Hyper-V & VMM MAC address managment

scvmm_VMnetMACstatic

I’ve just tripped over a fact when working with Hyper-V clusters and Virtual Machine Manager which probably isn’t that widely known.

For simplicity sakes I usually assign a dynamic MAC addresses via the radio button option within the NIC properties of a VM in SCVMM, assuming it will be taken out of its global MAC address range.

But in reality it will be taken out of the MAC address range of the Hyper-V host configured in the Virtual Network Manager’s Global Network Settings… and since every Hyper-V host has a different range configured in order to avoid duplicate assignments, VMs always get new MAC addresses when live-migrating or failing-over to another host! The drawbacks of that happening is a whole other story…

So if you have SCVMM deployed I’d always recommend choosing a static MAC address for a VM. When using the button Generate it indeed is taken out of SCVMM’s global MAC address range.

scvmm_VMnetMACstatic

By the way, this design still seems be the same withing Server 2012 & SCVMM 2012!

One response to Hyper-V & VMM MAC address managment

I noticed that if you leave it as dynamic and perform a live migration… all of a sudden you can’t ping the ip of the machine anymore.. I think it doesn’t flush the old mac out of ARP so the switch thinks there is a collision.

– Brandon

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