Private VLANs are used to solve VLAN ID limitations by adding a further segmentation of the logical broadcast domain into multiple smaller broadcast subdomains. Private VLANs are Promiscuous, Secondary VLANs can be either Isolated or Community - https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.networking.doc/GUID-C42AFA4A-1BDA-4ECC-B2D1-6E538771B2C3.html