hardMultiple Choice
CCNP Practice Question: Runs the following command on Switch SW1: SW1#…
A network engineer runs the following command on Switch SW1:
SW1# show interfaces gi0/1 trunk
Port Mode Encapsulation Status Native vlan Gi0/1 on 802.1q trunking 1
Port Vlans allowed on trunk Gi0/1 10,20
Port Vlans allowed and active in management domain Gi0/1 10,20
Port Vlans in spanning tree forwarding state and not pruned Gi0/1 10,20
Based on this output, what can be concluded?
⚠ Common exam trap
Cisco often tests the distinction between the native VLAN and the allowed VLAN list; candidates mistakenly assume that the native VLAN is always permitted on the trunk, but the allowed list explicitly controls which VLANs can pass traffic, and the native VLAN must be included in that list to be forwarded.
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
✓
Only VLANs 10 and 20 are allowed on this trunk.
The output shows that the 'Vlans allowed on trunk' list contains only VLANs 10 and 20. This means the trunk has been explicitly configured to permit only those VLANs, and all other VLANs (including VLAN 1) are pruned or blocked from traversing the trunk. Therefore, only VLANs 10 and 20 are allowed, making option C correct.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
VLAN 1 is allowed on this trunk.
Why it's wrong here
The 'Vlans allowed on trunk' line explicitly lists only 10 and 20. VLAN 1 is absent from that list, and because the allowed list is restrictive, frames belonging to VLAN 1 are neither transmitted nor received on this trunk. Even though VLAN 1 often serves as the default native VLAN, it must also appear in the allowed list to be carried; here it does not.
- ✗
The trunk is using DTP dynamic desirable mode.
Why it's wrong here
The show interfaces trunk output reports 'Mode: on', which corresponds to the static 'switchport mode trunk' command. Dynamic desirable is a separate DTP setting that actively negotiates trunking by sending DTP frames, while 'on' permanently forces trunking without relying on DTP negotiation with the neighbor. Therefore the interface is not in dynamic desirable mode.
- ✓
Only VLANs 10 and 20 are allowed on this trunk.
Why this is correct
The output explicitly contains 'Vlans allowed on trunk: 10,20'. On Cisco Catalyst switches, this line is the definitive list of VLANs permitted to traverse the trunk link; all other VLANs, including VLAN 1, are pruned or dropped at ingress. Thus only VLANs 10 and 20 are eligible for trunking, making this statement correct.
- ✗
The native VLAN is 10.
Why it's wrong here
The 'Native VLAN' field in the trunk output shows 1, not 10. The native VLAN is the VLAN that traverses the trunk without an 802.1Q tag, and it defaults to VLAN 1 on Cisco switches. Since the allowed list includes only 10 and 20, VLAN 1 is not actually forwarded despite being configured as native, but the configured native VLAN value remains 1.
Visual reference
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 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 350-401 exam.