One of my colleagues today asked me if it was possible to use VLAN ID 4095 for the “management” network of ESXi. This VLAN ID is however reserved for a very specific purpose.
This particular VLAN ID is only to be used for “Virtual Guest Tagging” (VGT). It basically means that the VLAN ID is stripped off at the Guest OS layer and not at the portgroup layer. In other words the VLAN trunk(multiple VLANs on a single wire) is extended to the virtual machine and the virtual machine will need to deal with it.
When will you use this? To be honest there aren’t many use cases any more. In the past it was used to increase the number of VLANs for a VM. The limit of 4 NICs for VI3 meant a maximum of 4 portgroups / VLANs per VM. However with vSphere the maximum amount of NICs went up to 10 and as such the amount of VLANs for a single VM also went up to 10.
Before people start to get excited about Virtual Guest Tagging, I personally prefer to stay away it. It heavily complicates the configuration of the VM and the vSwitch/dvSwitch and adds additional unneeded “stress” on your VMs vCPU.