CCNA Switching and Network Access Practice Question
A trunk link between two switches is up, but voice phones connected through one access switch no longer receive the correct voice VLAN treatment. Data users still pass traffic. Which area should be checked first?
⚠ Common exam trap
Be cautious not to assume that a general network issue is the cause when only specific traffic types are affected. Focus on the specific VLAN configuration first.
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
✓
Whether the voice VLAN is being carried and handled correctly across the switching path.
The first area to check is the end-to-end handling of the voice VLAN across the switching path. In practical terms, the data VLAN can still work while the voice VLAN experiences a forwarding, configuration, or policy problem. Because the phones depend on the correct voice VLAN behavior, that VLAN path should be examined first rather than assuming the whole trunk is broken. This is a selective-services troubleshooting question. One class of traffic can fail even when ordinary user data still works.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Whether the voice VLAN is being carried and handled correctly across the switching path.
Why this is correct
The correct focus is verifying that the voice VLAN is configured and permitted consistently across the entire switching path: the access ports connected to phones must carry the auxiliary voice VLAN, and the trunk between the switches must include that VLAN in its allowed list without stripping or re-tagging it incorrectly. Because the trunk is up but phones fail selectively, the fault almost certainly lies in voice VLAN propagation or 802.1Q tagging, not in physical connectivity or routing. Checking the voice VLAN's allowed status and native VLAN behavior on the trunk will reveal the misconfiguration.
- ✗
Whether OSPFv3 neighbors are fully adjacent on the phone switch ports.
Why it's wrong here
OSPFv3 is a Layer 3 IPv4/IPv6 routing protocol that forms adjacencies only on routed interfaces, not on Layer 2 access ports used for phones or on classic switch trunks. The symptom is a selective voice VLAN forwarding failure, which is independent of any OSPFv3 adjacency state, since routing table convergence does not affect 802.1Q tagging on a trunk. Thus, verifying OSPFv3 neighbors would be pointless when the root cause is a state mismatch in the switching database.
When this WOULD be correct
In a question focused on OSPFv3 configurations, where the scenario involves troubleshooting routing issues on a network with voice and data traffic, checking OSPFv3 neighbor adjacency would be relevant to ensure proper routing of packets, including those for voice traffic.
- ✗
Whether the wireless controller has the correct guest SSID.
Why it's wrong here
The failure occurs on a wired trunk between two switches, where IP phones are connected via Ethernet. A wireless controller's guest SSID affects only WLAN client traffic, not wired voice VLANs or 802.1Q trunk tagging. Since the symptom is isolated to phones on the wired switching path, inspecting wireless configuration cannot reveal why the voice VLAN is not being forwarded.
When this WOULD be correct
In a question focused on troubleshooting wireless network issues, where the problem involves guest access and voice traffic being improperly handled due to incorrect SSID settings on a wireless controller, this option would be correct.
- ✗
Whether BGP uses a lower metric than the static route.
Why it's wrong here
BGP is an Exterior Gateway Protocol that selects paths using attributes like AS-path and local preference, not a lower metric in the same sense as IGP cost, and it operates at Layer 3. The trunk's voice VLAN issue is entirely a Layer 2 concern involving 802.1Q encapsulation and allowed VLAN lists. Even if a static route's administrative distance or metric were misconfigured, it would not prevent IP phone traffic from being switched across the trunk.
When this WOULD be correct
In a question about routing protocols where BGP is used to manage traffic between multiple networks, and the exam asks about ensuring optimal path selection for voice traffic, this option would be correct if the context involves verifying that BGP metrics influence the routing decisions for voice packets.
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.
✓Whether the voice VLAN is being carried and handled correctly across the switching path.Correct answer▾
Why this is correct
The correct focus is verifying that the voice VLAN is configured and permitted consistently across the entire switching path: the access ports connected to phones must carry the auxiliary voice VLAN, and the trunk between the switches must include that VLAN in its allowed list without stripping or re-tagging it incorrectly. Because the trunk is up but phones fail selectively, the fault almost certainly lies in voice VLAN propagation or 802.1Q tagging, not in physical connectivity or routing. Checking the voice VLAN's allowed status and native VLAN behavior on the trunk will reveal the misconfiguration.
✗Whether OSPFv3 neighbors are fully adjacent on the phone switch ports.Wrong answer — click to see why▾
Why this is wrong here
OSPFv3 is an IPv6 routing protocol and has no role in Layer 2 voice VLAN handling on access ports. The issue is about VLAN assignment and trunking, not routing protocol adjacency.
★ When this WOULD be the correct answer
In a question focused on OSPFv3 configurations, where the scenario involves troubleshooting routing issues on a network with voice and data traffic, checking OSPFv3 neighbor adjacency would be relevant to ensure proper routing of packets, including those for voice traffic.
Why candidates choose this
Students might confuse OSPFv3 with OSPFv2 or think that any routing protocol issue could affect connectivity, but the problem is specifically about voice VLAN treatment, which is a Layer 2 function.
✗Whether the wireless controller has the correct guest SSID.Wrong answer — click to see why▾
Why this is wrong here
The scenario involves wired switches and IP phones, not wireless LAN. Guest SSID configuration on a wireless controller is unrelated to voice VLAN treatment on a wired trunk link.
★ When this WOULD be the correct answer
In a question focused on troubleshooting wireless network issues, where the problem involves guest access and voice traffic being improperly handled due to incorrect SSID settings on a wireless controller, this option would be correct.
Why candidates choose this
Test-takers might associate 'voice' with wireless voice (VoWiFi) or think that a wireless controller could influence wired VLAN assignment, but the question clearly describes a wired access switch and trunk.
✗Whether BGP uses a lower metric than the static route.Wrong answer — click to see why▾
Why this is wrong here
BGP is an exterior routing protocol used for interdomain routing, not for Layer 2 VLAN handling. The symptom is about voice VLAN treatment on a trunk, which is unrelated to BGP metrics or static routes.
★ When this WOULD be the correct answer
In a question about routing protocols where BGP is used to manage traffic between multiple networks, and the exam asks about ensuring optimal path selection for voice traffic, this option would be correct if the context involves verifying that BGP metrics influence the routing decisions for voice packets.
Why candidates choose this
Students might think that any routing protocol could affect traffic flow, but the issue is at Layer 2, and BGP metrics do not influence VLAN assignment or trunk behavior.
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
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
Voice VLAN
A Voice VLAN is a separate virtual local area network configured on a network switch to carry voice traffic, such as from IP phones, ensuring quality of service and security by isolating it from data traffic.
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 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.