The vCenter Server for Windows must configure all port groups to VLAN 4095 unless Virtual Guest Tagging (VGT) is required.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-94749	VCWN-65-000019	SV-104579r1_rule		Medium

Description
When a port group is set to VLAN 4095, this activates VGT mode. In this mode, the vSwitch passes all network frames to the guest VM without modifying the VLAN tags, leaving it up to the guest to deal with them. VLAN 4095 should be used only if the guest has been specifically configured to manage VLAN tags itself. If VGT is enabled inappropriately, it might cause denial-of-service or allow a guest VM to interact with traffic on an unauthorized VLAN.

Description

When a port group is set to VLAN 4095, this activates VGT mode. In this mode, the vSwitch passes all network frames to the guest VM without modifying the VLAN tags, leaving it up to the guest to deal with them. VLAN 4095 should be used only if the guest has been specifically configured to manage VLAN tags itself. If VGT is enabled inappropriately, it might cause denial-of-service or allow a guest VM to interact with traffic on an unauthorized VLAN.

STIG	Date
VMware vSphere 6.5 vCenter Server for Windows Security Technical Implementation Guide	2020-03-27

Details

Check Text ( C-93939r1_chk )
From the vSphere Web Client go to Networking >> Select a distributed switch >> Select a distributed port group >> Configure >> Settings >> Policies. Review the port group VLAN tags and verify they are not set to 4095. or From a PowerCLI command prompt while connected to the vCenter server run the following command: Get-VDPortgroup \| select Name, VlanConfiguration If any port group is configured with VLAN 4095 and is not documented as a needed exception, this is a finding.

Check Text ( C-93939r1_chk )

From the vSphere Web Client go to Networking >> Select a distributed switch >> Select a distributed port group >> Configure >> Settings >> Policies.

Review the port group VLAN tags and verify they are not set to 4095.

or

From a PowerCLI command prompt while connected to the vCenter server run the following command:
Get-VDPortgroup | select Name, VlanConfiguration

If any port group is configured with VLAN 4095 and is not documented as a needed exception, this is a finding.

Fix Text (F-100867r1_fix)
From the vSphere Web Client go to Networking >> Select a distributed switch >> Select a distributed port group >> Configure >> Settings >> Policies. Click "Edit" and under the VLAN section change the VLAN ID to an appropriate VLAN ID other than "4095" and click "OK". or From a PowerCLI command prompt while connected to the vCenter server run the following command: Get-VDPortgroup "portgroup name" \| Set-VDVlanConfiguration -VlanId "New VLAN#"

Fix Text (F-100867r1_fix)

From the vSphere Web Client go to Networking >> Select a distributed switch >> Select a distributed port group >> Configure >> Settings >> Policies. Click "Edit" and under the VLAN section change the VLAN ID to an appropriate VLAN ID other than "4095" and click "OK".

or

From a PowerCLI command prompt while connected to the vCenter server run the following command:
Get-VDPortgroup "portgroup name" | Set-VDVlanConfiguration -VlanId "New VLAN#"