CCNA Switching and Network Access Practice Question
A network administrator is configuring a new Cisco Catalyst switch and needs to ensure that the native VLAN for 802.1Q trunk port GigabitEthernet1/0/1 is VLAN 99, which is not the default. The administrator enters the command 'switchport trunk native vlan 99' on the interface. However, after applying the configuration, the administrator notices that untagged traffic from the native VLAN is not being forwarded correctly. What is the most likely cause of this issue?
⚠ Common exam trap
The trap here is assuming that configuring the native VLAN on one side is sufficient, overlooking the requirement for matching native VLANs on both ends of a trunk.
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
✓
The native VLAN must be configured on both ends of the trunk link, and the other end is still using the default native VLAN.
The native VLAN on an 802.1Q trunk must be consistent on both ends. If one side uses VLAN 99 and the other uses VLAN 1, untagged frames are classified differently, leading to connectivity problems for devices in the native VLAN. Ensuring both switches use the same native VLAN resolves the issue.
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 99 must be created in the VLAN database before it can be used as the native VLAN.
Why it's wrong here
While VLAN 99 should exist for proper operation, the switch does not require the VLAN to be pre-created to accept the native VLAN configuration. The switch will allow the command, but without the VLAN defined, traffic may not forward correctly. However, the primary issue here is the mismatch on the other end of the trunk.
- ✗
The native VLAN configuration requires the 'switchport mode trunk' command to be applied first.
Why it's wrong here
The interface must be in trunk mode for the native VLAN to take effect, but the scenario implies the port is already a trunk. If it were not, the command would be accepted but not operational. The more critical problem is the native VLAN mismatch between switches, which is a common cause of untagged traffic issues.
- ✓
The native VLAN must be configured on both ends of the trunk link, and the other end is still using the default native VLAN.
Why this is correct
For 802.1Q trunks, the native VLAN must match on both ends; otherwise, untagged traffic is interpreted differently, causing forwarding failures or VLAN mismatches. The other end likely still uses VLAN 1, so untagged frames are placed into VLAN 1 instead of VLAN 99, breaking connectivity for that VLAN.
- ✗
The command 'switchport trunk native vlan 99' is only valid on access ports, not on trunk ports.
Why it's wrong here
The command is specifically for trunk ports to set the native VLAN for untagged traffic. Access ports use 'switchport access vlan' to assign a VLAN. Using the trunk native VLAN command on an access port would be ineffective, but the administrator applied it to a trunk port, so the command itself is appropriate.
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Related to this question
Learn chapter
Troubleshoot: Missing or Wrong Default Gateway
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.