When trying to open a console session to a virtual machine within the VMware vSphere Client you may receive a black screen and the following error message: “ Unable to connect to the MKS: Host address lookup for server”, “ failed: No such host is known”.Īlthough there are a couple of things that can cause this error the most common reason is that the host is unable to resolve the name of the VMware ESX or ESXi host on which this VM is running. If the "MAC Address Changes" policy is set to accept (or true, via PowerCLI), this is a finding.įor each virtual switch and port group, click Edit settings (dots) and change "MAC Address Changes" to reject.Here’s an old favourite of mine. Get-VirtualPortGroup | Get-SecurityPolicy View the properties on each virtual switch and port group and verify "MAC Address Changes" is set to reject.įrom a PowerCLI command prompt while connected to the ESXi host, run the following commands: VMware vSphere 6.7 ESXi Security Technical Implementation Guideĭetails Check Text ( C-42547r674869_chk )įrom the vSphere Client, go to Configure > Networking > Virtual Switches. Switch-level settings can be overridden at the Portgroup level.
Reject MAC Changes can be set at the vSwitch and/or the Portgroup level. It will affect applications that require this functionality, how a layer 2 bridge will operate, and applications that require a specific MAC address for licensing. This will prevent VMs from changing their effective MAC address. This allows it to stage malicious attacks on the devices in a network by impersonating a network adaptor authorized by the receiving network.
If the virtual machine operating system changes the MAC address, it can send frames with an impersonated source MAC address at any time.
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