WLAN Roaming Frame Types and Channel Constraints

H12-821 By islever Editorial Last updated

Roaming technology

Short answer

CD These options are false because roaming uses a Reassociation Request (not Association) and APs do not need to be on the same channel.

Question

Which of the following statements about WLAN roaming are false? (Choose all that apply.)
  1. APs with which a STA is associated before and after roaming can work on different channels.
  2. During roaming, the STA sends a Reassociation Request frame containing home AP information to the foreign AP.
  3. During roaming, the STA sends an Association Request frame containing home AP information to the foreign AP. Correct Answer
  4. APs with which a STA is associated before and after roaming must work on the same channel. Correct Answer

Key Takeaways

The main trap is confusing Association vs. Reassociation frames; remember that moving between APs in the same ESS requires Reassociation, which carries the previous AP's BSSID.

Identify false statements about WLAN roaming. The correct answers are C and D, as roaming utilizes Reassociation Requests and supports different channels for source and target APs.

Common mistake: Selecting B as false because students might think the home AP info isn't needed, or selecting A/D incorrectly by assuming strict channel alignment is required for any type of roaming.

Expert Analysis

Layer 2 Roaming Mechanics and Channel Flexibility

The question asks to identify false statements regarding WLAN roaming. To solve this, we must distinguish between the frame types used in association versus reassociation and understand the constraints on channel usage during a roam.

Statement A is True: Access Points (APs) serving a client before and after roaming can indeed operate on different channels. In modern Wi-Fi networks, especially those using Layer 3 roaming or even Layer 2 roaming with overlapping cells, clients frequently move between APs on different frequencies. This flexibility is a key feature of seamless roaming.

Statement D is False: Contradicting Statement A, claiming that APs must work on the same channel is incorrect. As established, roaming across different channels is standard and supported by IEEE 802.11 standards. Therefore, D is a false statement.

Statement C is False: When a station (STA) moves from one AP to another within the same Basic Service Set (BSS) or between BSSs but remaining in the same Extended Service Set (ESS), it performs a reassociation, not an initial association. The frame used for this handover is the Reassociation Request, not the Association Request. The Association Request is only used when initially joining a network. Thus, C is a false statement.

Statement B is True: During the reassociation process, the STA sends a Reassociation Request frame to the new (foreign) AP. Crucially, this frame includes the BSSID (MAC address) of the previous (home) AP. This allows the new AP to communicate with the old AP to transfer context information (like security keys) efficiently, ensuring the session continues without full renegotiation.

Since the question asks for the false statements, both C and D are incorrect assertions about how roaming works.

Exam Strategy

When analyzing roaming questions, always check if the scenario implies movement between APs. If so, look for 'Reassociation' rather than 'Association'. Also, verify if the question imposes artificial constraints like 'same channel'; unless specified as a specific legacy limitation, modern roaming supports channel changes.

Frequently Asked Questions

What is the difference between Association and Reassociation?

Association is the initial connection to an AP. Reassociation occurs when a client moves from one AP to another within the same ESS, allowing for context transfer.

Can a client roam between APs on different channels?

Yes, clients can roam between APs operating on different channels. This is common in layered or mesh deployments and does not break the connection.

More H12-821 FAQ →

Community Votes

C
50%
D
50%

50% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 1 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 1

  1. Adi_1 👍 1
    A — TRUE APs before and after roaming can work on different channels. This is normal and expected — roaming across different channels is standard behavior (especially Layer 3 roaming). B — TRUE During roaming, the STA sends a Reassociation Request frame (not a plain Association Request) to the foreign AP, and this frame does contain the BSSID of the previous (home) AP. This is how the foreign AP knows a roam is occurring. C — FALSE The STA sends a Reassociation Request, not an Association Request. An Association Request is used for the initial connection, not for roaming. This statement is incorrect. D — FALSE APs before and after roaming do not need to work on the same channel. Roaming across different channels is completely supported. Requiring the same channel would be an unnecessary and incorrect constraint.

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