This topic is very important to build a virtual data center or when you want to have a nested ESXi in your environment and you dont know how to configure the main distributed switch and the nested distributed switch.
Let me explain about the all types of VLAN. In general in vDS we have 4 types of VLAN configuration:
- VLAN Trunking
- Private VLAN
In this type the Portgroup can receive only untagged Traffic. in this case we should connect the uplink to a switchport with ACCESS configuration.
Moreover, if in your nested environment you have a port group with none configuration (default), you have to have a VLAN ID or None configuration in your uplink vDS switch.
In this case vDS will tag every packet with a specific VLAN ID and the uplink should connect to switchport with TRUNK configuration. If we connect this port to an uplink with access port configuration, the destination switch will drop the packet, because it has a VLAN ID already.
Note: Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across the network.
We can use this type for Virtual Guest Tagging (VGT).In this case switch allows the traffic to reach the virtual machine which is conected to this port group.
If you need to have a nested datacenter within your virtual data center and you have many vlan configurations, you can configure one portgroup as VLAN trunking and specify this for nested virtual datacenter, then you can build a nested vDS within your nested ESXi hosts and configure it to have their own VLAN.Actually VLAN trunking in this case can act as a trunk port for nested ESXi servers.Moreover, you should define the nested portgroup as VLAN type and define a specific VLAN for this, and finally allow Promiscuous on your main portgroup.
This is a Cisco technology and you can find the detail about that in follwoing link: