I want to know about tagged and untagged vlan mechanism then I try to configure like this enter image description here

When I connected PC3 to trunk port on Packet Tracer, It doesn't work and a switch dropped PC3's frame if I configured like below:

enter image description here

else if I've configured like this (also add native VLAN on trunk allowed command )

enter image description here

It work, the switch didn't drop a frame. Could anyone explain me what was happen in this situation?

  • Please, never use an image for test in your question. Simply copy the text and paste it into your question and use the Preformatted-text option ({}).
    – Ron Maupin
    Jun 16, 2020 at 13:46

1 Answer 1


The PC knows nothing about VLAN, so when it sends a frame, it is an untagged one.

Since the port has "native VLAN 1" when an untagged frame enter the port, it is associated with VLAN 1. If VLAN 1 is not in the list in the allowed VLAN, it is dropped.

So when you add VLAN 1 in the allowed VLAN, you allow the frame to goes in.

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