20+ practice questions focused on VLANs and Trunking — one of the most tested topics on the ENCOR 350-401 exam. Each question includes a detailed explanation so you learn why the right answer is correct.
Start VLANs and Trunking PracticeA network engineer is troubleshooting a connectivity issue between two switches, SW1 and SW2, connected via a trunk link. SW1 is a Cisco Catalyst 3850 running IOS-XE, and SW2 is a Cisco Catalyst 2960 running IOS. The trunk is configured as a dynamic desirable mode on SW1 and dynamic auto on SW2. The engineer notices that the trunk is not forming. What is the most likely cause?
Explanation: Option A is correct because when DTP modes are dynamic desirable (SW1) and dynamic auto (SW2), the trunk should form successfully if both switches support DTP and the encapsulation matches. However, if the native VLAN is mismatched, the trunk will not form because Cisco switches use DTP frames to negotiate trunking, and a native VLAN mismatch causes DTP to fail, preventing the trunk from coming up. This is a common issue that overrides the DTP negotiation.
An engineer is configuring a new access switch for a branch office. The switch must support multiple VLANs for different departments: VLAN 10 (Engineering), VLAN 20 (Sales), and VLAN 30 (Management). The uplink to the distribution switch is a trunk. The engineer wants to ensure that only the required VLANs are allowed on the trunk and that the native VLAN is changed from the default to VLAN 99 for security reasons. Which configuration commands should the engineer apply on the access switch's uplink interface?
Explanation: Option A is correct because it explicitly sets the interface to trunk mode, changes the native VLAN from the default VLAN 1 to VLAN 99 for security, and uses the 'allowed vlan' command to permit only VLANs 10, 20, and 30 on the trunk. This ensures that only the required department VLANs are carried, reducing unnecessary broadcast traffic and preventing VLAN hopping attacks by changing the native VLAN.
A network engineer is deploying a new server farm with multiple servers connected to a Cisco Nexus 9000 switch. Each server is dual-homed to two separate access switches for redundancy. The servers are configured with NIC teaming in active-standby mode. The engineer wants to ensure that if the active link fails, traffic continues without interruption. The access switches are connected to each other via a trunk. Which technology should the engineer implement on the access switches to prevent loops and allow both uplinks to be active?
Explanation: A is correct because a vPC (Virtual Port Channel) allows two access switches to appear as a single logical device to the server, enabling both uplinks to be active simultaneously while preventing loops. This is essential for active-standby NIC teaming, as vPC ensures that if one link fails, the other continues forwarding traffic without requiring STP to block a port, thus providing seamless failover and loop-free operation.
An engineer is troubleshooting a problem where a host in VLAN 20 cannot communicate with a host in VLAN 30, even though both are connected to the same access switch. The access switch is configured with VLANs 20 and 30, and the uplink to the distribution switch is a trunk that allows both VLANs. The distribution switch has SVIs for both VLANs and IP routing is enabled. The engineer verifies that the trunk is up and both VLANs are allowed. What is the most likely cause of the communication failure?
Explanation: Hosts in different VLANs must communicate through a Layer 3 device. The correct default gateway for each host should be the IP address of the SVI on the distribution switch for its respective VLAN. If the hosts are configured with an incorrect or no default gateway, traffic cannot be routed between VLAN 20 and VLAN 30, even though the trunk and SVIs are properly configured.
A network engineer is configuring a new Cisco Catalyst 9300 switch to connect to an existing network. The uplink to the core switch is configured as a trunk. The engineer wants to ensure that all VLANs except VLAN 1 are allowed on the trunk, and that the native VLAN is set to VLAN 999. Which configuration should the engineer apply on the uplink interface?
Explanation: Option A is correct because the 'switchport trunk allowed vlan except 1' command explicitly permits all VLANs except VLAN 1 on the trunk, while the 'switchport trunk native vlan 999' command sets the native VLAN to 999, ensuring that untagged frames on the trunk belong to VLAN 999 instead of the default VLAN 1. This meets the requirement to exclude VLAN 1 from the allowed list and change the native VLAN.
+15 more VLANs and Trunking questions available
Practice all VLANs and Trunking questions1. Baseline your knowledge
Start with 10 questions to gauge your current understanding of VLANs and Trunking. This tells you whether you need a concept refresher or just practice.
2. Review every explanation
For each question — right or wrong — read the full explanation. Understanding why an answer is correct is more valuable than knowing the answer itself.
3. Focus on exam traps
VLANs and Trunking questions on the 350-401 frequently use trap wording. Look for subtle differences in answers that test your precision, not just general knowledge.
4. Reach 80% consistently
Do repeated sessions until you score 80%+ three times in a row. Then move to mixed-mode practice to test cross-topic recall under realistic conditions.
The exact number varies per candidate. VLANs and Trunking is tested as part of the ENCOR 350-401 blueprint. Practicing with targeted VLANs and Trunking questions ensures you can handle any format or difficulty that appears.
Yes. Courseiva provides free 350-401 practice questions across all exam topics and domains. The platform includes topic-based practice, mock exams, missed-question review, bookmarked questions, and readiness tracking — no account required.
Difficulty is subjective, but VLANs and Trunking is a high-priority exam concept tested in multiple ways — direct recall, scenario analysis, and command-output interpretation. Consistent practice is the best way to build confidence.
Launch a full VLANs and Trunking practice session with instant scoring and detailed explanations.
Start VLANs and Trunking Practice →