Why did you not just login to the device, and switched off "Broadcast to multicast", or changed the destination address?

Edit: Some brands of Network-KVM use this, so that you can control the target device from another device, like e.g. an App on a tablet. That way you don't have to stand next to the target device in the noisy and cold machine room

The KVM didn't have any documentation on anything related to its network interface. I ran a port scan on it but didn't know if there was a way to log into it.