I have 3 new HP DL360G9 servers all running Server 2012 R2 standard with the Hyper-V role installed. All the servers have the built in Intel 331FLR 4 port gigabit nic. I have the ports teamed into 2 pairs to create a 2 Gig connection to 2 different networks. There is a Hyper-V virtual switch connected to each team which provides connectivity for all my VMs and the host machine to both networks. I do not have any VLANs setup and it is a very basic setup. They have been running fine for 8 months and now all the sudden I am having network outages and finding the dreaded mac address conflict message in my Windows logs. I checked the mac addresses in powershell and found that the mac address assigned to one of the virtual switches is the same as one of the pNICs (which is normal) and the same as one of the teams (which is not normal and causing the error). All 3 machines are like this. Deleting the vswitch and re-creating it does not resolve the issue. It will not allow me to change the mac address via the administrator powershell session. I followed the documentation when setting up all 3 machines. I find it strange that it is just now having an issue.
What am I missing here and what do you do to resolve this?
Best Answer
You may have assigned the same IP Address to a Microsoft Host and then created a Virtual Switch (Hyper-V Manager). Microsoft uses it's owned MAC address range plus the last Octet of the IP address. So if you assigned the same IP node address to some other Virtual Switch previously, you will need to delete the Virtual Switch with the conflicting MAC address pool range and create a new one. The new Virtual Switch should have a different MAC address pool range and clear up the conflict.