The vCenter Server must configure all port groups to a value other than that of the native virtual local area network (VLAN).

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-258939	SRG-APP-000516	VCSA-80-000272	SV-258939r961863_rule	2024-12-16	2

Description
ESXi does not use the concept of native VLAN. Frames with VLAN specified in the port group will have a tag, but frames with VLAN not specified in the port group are not tagged and therefore will end up belonging to native VLAN of the physical switch. For example, frames on VLAN 1 from a Cisco physical switch will be untagged, because this is considered as the native VLAN. However, frames from ESXi specified as VLAN 1 will be tagged with a "1"; therefore, traffic from ESXi that is destined for the native VLAN will not be correctly routed (because it is tagged with a "1" instead of being untagged), and traffic from the physical switch coming from the native VLAN will not be visible (because it is not tagged). If the ESXi virtual switch port group uses the native VLAN ID, traffic from those virtual machines will not be visible to the native VLAN on the switch, because the switch is expecting untagged traffic.

Description

ESXi does not use the concept of native VLAN. Frames with VLAN specified in the port group will have a tag, but frames with VLAN not specified in the port group are not tagged and therefore will end up belonging to native VLAN of the physical switch. For example, frames on VLAN 1 from a Cisco physical switch will be untagged, because this is considered as the native VLAN. However, frames from ESXi specified as VLAN 1 will be tagged with a "1"; therefore, traffic from ESXi that is destined for the native VLAN will not be correctly routed (because it is tagged with a "1" instead of being untagged), and traffic from the physical switch coming from the native VLAN will not be visible (because it is not tagged). If the ESXi virtual switch port group uses the native VLAN ID, traffic from those virtual machines will not be visible to the native VLAN on the switch, because the switch is expecting untagged traffic.

ℹ️ Check
If distributed switches are not used, this is not applicable. From the vSphere 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 the native VLAN ID of the attached physical switch. 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 the native VLAN of the ESXi hosts attached physical switch, this is a finding.

ℹ️ Check

If distributed switches are not used, this is not applicable. From the vSphere 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 the native VLAN ID of the attached physical switch. 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 the native VLAN of the ESXi hosts attached physical switch, this is a finding.

✔️ Fix
From the vSphere Client, go to "Networking". Select a distributed switch >> Select a distributed port group >> Configure >> Settings >> Policies. Click "Edit". Click the "VLAN" tab. Change the VLAN ID to a nonnative VLAN. 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

From the vSphere Client, go to "Networking". Select a distributed switch >> Select a distributed port group >> Configure >> Settings >> Policies. Click "Edit". Click the "VLAN" tab. Change the VLAN ID to a nonnative VLAN. 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#"