CCNA Switching and Network Access Practice Question
Exhibit
SW1# show interfaces GigabitEthernet0/1 trunk Port Mode Encapsulation Status Native vlan Gi0/1 on 802.1q trunking 1 Port Vlans allowed on trunk Gi0/1 1-49,60-4094 Port Vlans allowed and active in management domain Gi0/1 1-49,60-4094 Port Vlans in spanning tree forwarding state and not pruned Gi0/1 1-49,60-4094
Refer to the exhibit. A network administrator is troubleshooting connectivity issues for hosts on VLAN 50 on SW1. The hosts on VLAN 50 cannot reach any devices outside SW1, even though the trunk link between SW1 and SW2 is up. The administrator issues the 'show interfaces GigabitEthernet0/1 trunk' command on SW1. Based on the output, what is the most likely cause of the issue?
⚠ Common exam trap
Cisco often tests the distinction between native VLAN misconfiguration and allowed VLAN list misconfiguration, where candidates mistakenly attribute all trunk issues to native VLAN mismatches rather than checking the allowed VLAN list.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VLAN 50 is not in the allowed VLAN list on the trunk.
The 'show interfaces GigabitEthernet0/1 trunk' output would list the allowed VLANs on the trunk. If VLAN 50 is not included in the allowed VLAN list, traffic from VLAN 50 will be dropped at the trunk, preventing hosts on SW1 from reaching devices outside SW1. This is the most likely cause because the trunk is up but VLAN 50 traffic is not forwarded.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The native VLAN on the trunk is misconfigured, causing VLAN 50 traffic to be dropped.
Why it's wrong here
A native VLAN mismatch affects only untagged frames; VLAN 50 is tagged traffic, so a native VLAN issue would not cause its isolation. The output shows native VLAN 1, which is default and not misconfigured.
- ✗
The trunk is operating in access mode instead of trunk mode, preventing VLAN 50 traffic.
Why it's wrong here
The output directly contradicts this claim: the Mode column reports 'on' and the Status column reports 'trunking.' In Cisco IOS, 'Mode' reflects the administrative trunking configuration (i.e., 'switchport mode trunk'), while 'Status' verifies the interface is currently operating as a trunk. If the port were in access mode, it would not display an allowed VLAN list or forwarding-state entries for multiple VLANs; an access port carries a single untagged VLAN. Therefore, VLAN 50's isolation is not due to the interface being in access mode.
- ✓
VLAN 50 is not in the allowed VLAN list on the trunk.
Why this is correct
The exhibit's 'Vlans allowed on trunk' line explicitly lists '1-49,60-4094', which omits VLAN 50. This configured allowed list filters which VLANs can traverse the trunk; any VLAN not listed is blocked, even if it is defined on the switch. The absence of VLAN 50 from the allowed list means its frames are dropped at the trunk interface, isolating hosts in VLAN 50 from other switches. This is the exact administrative misconfiguration causing the problem.
- ✗
Spanning tree protocol has blocked the trunk port for VLAN 50, isolating the hosts.
Why it's wrong here
The 'Vlans in spanning tree forwarding state' column shows the exact same list '1-49,60-4094', meaning VLAN 50 is not even participating in spanning tree on this trunk because it is not allowed, not that it is blocked.
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.
✓VLAN 50 is not in the allowed VLAN list on the trunk.Correct answer▾
Why this is correct
The exhibit's 'Vlans allowed on trunk' line explicitly lists '1-49,60-4094', which omits VLAN 50. This configured allowed list filters which VLANs can traverse the trunk; any VLAN not listed is blocked, even if it is defined on the switch. The absence of VLAN 50 from the allowed list means its frames are dropped at the trunk interface, isolating hosts in VLAN 50 from other switches. This is the exact administrative misconfiguration causing the problem.
✗The native VLAN on the trunk is misconfigured, causing VLAN 50 traffic to be dropped.Wrong answer — click to see why▾
Why this is wrong here
The assumption that a native VLAN mismatch can drop tagged VLAN traffic is a common misunderstanding.
✗The trunk is operating in access mode instead of trunk mode, preventing VLAN 50 traffic.Wrong answer — click to see why▾
Why this is wrong here
Misreading the output may lead to believing the trunk is not in trunking mode.
✗Spanning tree protocol has blocked the trunk port for VLAN 50, isolating the hosts.Wrong answer — click to see why▾
Why this is wrong here
Confusing spanning tree blocking with allowed VLAN filtering; the output shows no block state, only absence of the VLAN.
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?”
Visual reference
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
Key term
Allowed VLANs
Allowed VLANs are the specific VLANs whose traffic is permitted to pass over a specific trunk link between switches, acting as an access control filter for VLAN traffic on a port.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.