Fixed in a tick, solving Mulicast issues in Hyper-V VMs

Fixed in a Tick

I’m teaching a Hyper-V course this week in our Leeds office, and whilst here we had an issue with a Hyper-V virtual machine.

The machine was being used as a ghost server, with one machine connected and streaming down an image (Unicast) all was good, good speed, and the image dropped fine. However with multiple machine connected (Multicast) the speed dropped off and was unusable.

What we did was to go into Hyper-V manager, right click on the VM and edit it’s settings.

Then we highlighted the network adapter and enabled the following

Enable spoofing of MAC addresses we then retried the operation of multiple connections to the ghost server, and hey presto all was good, good speed and the images dropped fine.

Without enabling Enable spoofing of MAC addresses the following conditions apply, and that’s why Multicast didn’t work within the VM.

The virtual switch port that connects the virtual network adapter sends and receives packets that contain any valid MAC address.

The virtual network adapter MAC address cannot be moved or associated with another virtual switch port.

The virtual switch port does not forward unicast flooded packets (packets that are forwarded to all switch ports if the destination MAC address is not found in the switch forwarding table) to the virtual network adapter.

You cannot override the virtual network adapter MAC address configuration using the NetworkAddress key in the virtual machine registry.