Dell 4820T or S3100 hybrid ports
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By default dell switch ports can carry one VLAN untagged or multiple VLANs tagged. To have a native VLAN on trunk port (One untagged VLAN while others are tagged on same port), the port settings have to be changed to portmode hybrid using:
  config t
    interface <> 
      no switchport
      portmode hybrid
      switchport
After that in respective VLANs add ports as tagged or untagged based on requirement.
Refer:
Home > Switch configuration notes > Dell 4820T or S3100 hybrid ports

