Access vs Trunk Port Frame Tagging Rules
Short answer
A An access port sends frames untagged because it belongs to one VLAN, while a trunk port can send tagged frames plus untagged native-VLAN frames, so only option A is correct.
Question
Key Takeaways
It tests egress tagging rules for access and trunk ports, with the absolute word “only” as the trap because trunk ports also send untagged native-VLAN frames.
This question tests how access and trunk ports handle VLAN tagging on egress. The correct choice is A: access ports send untagged frames for their single VLAN, while trunk ports can also send untagged native-VLAN traffic.
Common mistake: A common mistake is choosing B, assuming every frame on a trunk must carry an 802.1Q tag; in reality the native VLAN is transmitted untagged, so “only tagged” is false.
Expert Analysis
What the port types actually do
The question contrasts egress tagging behaviour on access and trunk ports. An access port is bound to a single VLAN; ingress untagged frames are classified into that VLAN internally, and egress frames are sent untagged to the attached host. Option A therefore matches standard access-link behaviour. The supplied discussion makes the same point: access ports belong to a single VLAN and send and receive untagged frames, with VLAN tagging handled inside the switch.
Why B and D are the same trap
Trunk ports carry multiple VLANs. They normally send tagged frames so the peer can identify the VLAN, but they also send frames for the native VLAN untagged. That exception defeats both B (“only tagged”) and D (“only untagged”). C simply reverses A; access ports do not emit tagged frames toward a normal host. The key word is “only” — it turns a broadly true statement into a false absolute when an exception exists.
Adjacent decision: what changes the answer
If the scenario changed from an access port to a hybrid port, or asked about ingress rather than egress, you would need to inspect the port’s VLAN tagging configuration rather than rely on access/trunk defaults. If the link were a trunk and the question asked about the native VLAN specifically, the correct description would be untagged for that VLAN; for other allowed VLANs, tagged. If a host were misconfigured to expect tags on an access port, the design would be wrong, not the rule.
Operational consequence
Getting this backwards causes real outages: an access host cannot parse 802.1Q tags, so tagged egress breaks connectivity; assuming a trunk sends only tagged frames can hide native-VLAN leakage or mismatches. When troubleshooting, check both port mode and native VLAN, because a trunk’s untagged traffic is the usual surprise.
Verdict
A is the only correct option. Treat “access = untagged egress for its single VLAN” and “trunk = tagged for allowed VLANs, untagged for the native VLAN” as the decision rule.
Exam Strategy
When a question uses the word “only,” test it against the native VLAN exception. For trunk links, ask whether the frame belongs to the native VLAN or another VLAN; for access links, ask whether the switch adds a tag internally before forwarding. Draw the ingress and egress behaviour for one frame, then eliminate any option that ignores the native VLAN or assumes frame contents change based on port type. This method transfers to hybrid ports and inter-switch links.
Frequently Asked Questions
Does a trunk port send untagged frames?
Why can an access port send untagged frames when the switch assigns it a VLAN?
Would changing the native VLAN make option D correct?
Community Votes
100% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 4 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 4
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Fmoura17 👍 1 Answered AA. Access ports can only send untagged frames. A ✅ – Access ports belong to a single VLAN and send/receive untagged frames. The switch handles VLAN tagging internally. B ❌ – Trunk ports send both tagged and untagged frames. The native VLAN is sent untagged on a trunk port. C ❌ – Access ports send untagged, not tagged frames. D ❌ – Trunk ports send tagged frames (not untagged), except for the native VLAN.
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branly 👍 1 Answered AA. Access ports can only send untagged frames. This is because, according to the search results, an access interface can connect only to an access link, and Ethernet frames transmitted on the access link are untagged. An access interface adds a VLAN tag to packets and sets the VID field in the VLAN tag to the default VLAN ID. The access link transmits only the packets with the default VLAN ID.
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akamg 👍 1I think A is correct
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Chleong 👍 1 Answered AAAAAAA
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