According to this site, ESXi supports 3 patterns vlan. 1st is Virtual Switch tagging, 2nd is External Switch tagging, 3rd is Virtual Guest tagging.
Virtual Switch tagging
In this environment, ESXi physical NIC sends out packets with vlan tagging. Then, GuestVMs receive a packet without vlan tagging from ESXi physical NIC. So,
- GuestVMs don't require vlan tagging configuration on Guest OS layer
- External Switch opposite of ESXi should be configure vlan tag
External Switch tagging
With this configuration, all physical interfaces are untagged on ESXi. ESXi physical NIC and GuestVMs receive a untagged packet only from external switch. External Switch should be configured to send untag packets to ESXi.
Configuring vSwitch vlan ID as 4095 enables that GuestVMs can receive all tagged vlan packets. 4095 seems to mean as vlan tagging pass through. I have never tried this but I want to try in the future.