CCNA Switching and Network Access Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  All VLANs except the native VLAN stop forwarding immediately.

  Why it's wrong here

  A native VLAN mismatch only affects frames that traverse the trunk without a VLAN tag; all other VLANs continue to be forwarded normally because their frames carry the 802.1Q tag. The trunk does not stop forwarding any VLAN, and tagged traffic for VLANs 2-4094 remains unaffected. The issue is localized to the untagged traffic and control-plane protocols like CDP, STP, or DTP that rely on the native VLAN.

  When this WOULD be correct

  In a different scenario, if the question stated that a switch was configured to drop all VLAN traffic except the native VLAN due to a specific security policy, then this option could be correct. This would imply a configuration that restricts forwarding based on VLAN settings.

• ✓

  Untagged frames can be interpreted as belonging to different VLANs on each switch.

  Why this is correct

  With a native VLAN mismatch, each switch places untagged 802.1Q frames into its locally configured native VLAN. For example, if Switch A's native VLAN is 10 and Switch B's is 20, a single untagged frame will be associated with VLAN 10 on one side and VLAN 20 on the other, effectively crossing broadcast domains and potentially exposing traffic to the wrong VLAN. This misclassification can lead to security breaches, routing loops, or connectivity anomalies because VLAN membership is not preserved end-to-end.

• ✗

  The trunk automatically converts to an access port.

  Why it's wrong here

  The operational mode of a trunk port is determined by manual configuration (switchport mode trunk) or DTP negotiation, and a native VLAN mismatch does not alter this administrative state. The port remains in trunking mode and continues to carry tagged frames for multiple VLANs; only the handling of untagged frames is affected. There is no mechanism in the switch that automatically converts a trunk to an access port based on a native VLAN mismatch.

  When this WOULD be correct

  In a different scenario where the question states that a trunk port is configured incorrectly and the switch is set to automatically convert misconfigured ports, option C could be correct. For example, if the exam asks what happens when a trunk port is misconfigured and the switch has a feature enabled that forces a trunk to revert to access mode, then this option would apply.

• ✗

  STP is disabled on the trunk until the mismatch is corrected.

  Why it's wrong here

  STP continues to operate on all VLANs, including the native VLAN, because each VLAN maintains its own spanning-tree instance. While a native VLAN mismatch can cause BPDUs (which are sent untagged) to be received on the wrong VLAN, potentially leading to STP inconsistencies or loops, STP itself is never disabled. The protocol still runs and may transition ports to blocking states, but the trunk does not lose STP functionality due to the mismatch.

  When this WOULD be correct

  In a different scenario where the question specifies that a trunk link has been configured to disable STP for performance reasons, a native VLAN mismatch could lead to STP being disabled, making this option correct. The question would need to clarify that STP behavior is altered due to specific configurations.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”