Switch Port Handling of Untagged Frames and PVID

H12-811 By islever Editorial Last updated

VLAN Principles and Configuration

Short answer

B False, because the PVID is a port attribute, not a frame tag, and handling of untagged frames varies by port type.

Question

When a switch port receives a frame that does not carry a VLAN tag, it must add a PVID to the frame.
  1. True
  2. False Correct Answer

Key Takeaways

The main trap is confusing the static PVID configuration on a port with the dynamic addition of a VLAN tag to a frame; also, not all ports automatically tag incoming untagged frames.

This question tests understanding of VLAN tagging mechanics and PVID assignment on Huawei switches, clarifying why the statement is false.

Common mistake: Candidates often choose True, assuming all ports automatically tag untagged frames with the PVID value, ignoring the distinction between PVID and VLAN tags and the configurability of Hybrid ports.

Expert Analysis

The statement is False because it conflates the Port Default VLAN ID (PVID) with a VLAN tag. The PVID is an attribute of the switch port itself, not a piece of data carried in the frame. When an untagged frame enters a port, the switch assigns the frame to the VLAN identified by that port's PVID, but it does not 'add a PVID' to the frame. Instead, it may add a VLAN tag containing the VLAN ID corresponding to the PVID, depending on the port type.

Furthermore, the behavior is not universal across all port types. On an Access port, incoming untagged frames are accepted and associated with the PVID, and outgoing frames are typically stripped of tags. On a Hybrid port, the administrator can explicitly configure whether untagged frames are accepted or dropped, and whether tagged frames are sent out as tagged or untagged. Therefore, the absolute claim that a port 'must' add a tag is incorrect due to both terminological inaccuracy and configurable variability.

Official Reference

https://support.huawei.com/enterprise/en/doc/EDOC1000089036/60b1f2f0/basic-concepts-of-vlan

This link opens the official vendor documentation in a new tab.

Exam Strategy

Always distinguish between port attributes (like PVID) and frame contents (VLAN tags). Remember that while Access ports have fixed behaviors, Hybrid ports offer flexible configuration for both ingress and egress tagging, making absolute statements about port behavior suspicious.

Frequently Asked Questions

What is the PVID?

The PVID (Port Default VLAN ID) is the default VLAN identifier assigned to a switch port. It is used to classify incoming untagged frames into a specific VLAN.

Do all ports add VLAN tags to untagged frames?

No. Access ports associate untagged frames with the PVID but do not add tags to them upon egress. Hybrid ports can be configured to accept untagged frames without adding tags or to drop them entirely.

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Discussion 18 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 18

  1. Allenrok 👍 3
    Indeed, when the port of a switch receives a frame that does not have a VLAN tag then a tag is added which is the same as the PVID, but the question says "add a PVID to the frame" and therein lies the error because what is added is a VLAN tag with a value equal to the PVID but not that a PVID is added. PVID stands for Port Default VLAN ID and it is the VLAN ID of an interface, that is, PVID is associated to ports not to frames. Adding a VLAN ID to the frame is not the same as adding a PVID to the frame, PVID is for ports only. For this reason the answer is false
  2. FerioSiqueira 👍 2 Answered B
    When an interface receives an untagged frame, the interface adds a tag with the PVID to the frame and sends the frame to the switch for processing. When an interface receives a tagged frame, the switch does not add a tag with the PVID to the frame. https://support.huawei.com/enterprise/en/doc/EDOC1000089036/60b1f2f0/basic-concepts-of-vlan
  3. Mamusfregene 👍 2 Answered A
    When an **Access port has a PVID (default VLAN) configured.
  4. Fmoura17 👍 1 Answered B
    B. False Not every port automatically tags untagged frames with a PVID. The behavior depends on the port type and configuration: Some ports may be configured to drop untagged frames entirely. On Hybrid ports, handling of untagged frames is flexible and configurable. So while many ports do tag untagged frames with the PVID, it is not an absolute rule that they must — making the statement False.
  5. cascartillo 👍 1
    When an interface receives an untagged frame, the interface adds a tag with the PVID to the frame and sends the frame to the switch for processing. When an interface receives a tagged frame, the switch does not add a tag with the PVID to the frame.
Show 13 more comments
  1. cascartillo 👍 1
    No in fact it is a very feasible and logical answer. I did the exam a few weeks ago and and i failed for 500 points because the exam logic has that kind of tricky questions.
  2. NickENG 👍 1 Answered A
    When a frame is received without a tag in an access port, the switch accept it and adds the PVID.
  3. TITI 👍 1
    Answer A The question "When a switch port receives a frame that does not carry a VLAN tag"
  4. Allenrok 👍 1
    After receiving an untagged frame and adds a VLAN tag carrying the PVID of the interface.
  5. Mrlaloxi 👍 1
    you're being too meticulous, these question don't have traps
  6. buggybombastis10 👍 1
    If packet doesn't have vlan tag it will added the pvid
  7. Mrlaloxi 👍 1
    So the answer would be A. True? why you choose B
  8. ahmedhellopacket 👍 1
    hello mostafiz did you take the exam ?
  9. Silveira 👍 1 Answered A
    Resposta correta (A): True
  10. Mrlaloxi 👍 1
    where it says acces port?
  11. eeadbff 👍 1 Answered A
    PVID for untagged frames
  12. Mostafiz137 👍 1
    This will be false.
  13. hafizhou 👍 1
    BBBBBBBBBB

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