The answer is that VLAN 20 has not been created in the switch’s VLAN database. This is correct because the PC attached to the phone’s PC port successfully obtains an IP address on the access VLAN, proving the physical connection and switchport configuration are sound, but the phone itself remains stuck on “Configuring IP” since it cannot reach a DHCP server on its designated voice VLAN. On the CCNA 200-301 v2 exam, this scenario tests your understanding of how a voice VLAN operates independently from the access VLAN and that simply configuring the `switchport voice vlan 20` command is insufficient if the VLAN itself does not exist in the global VLAN database. A common trap is assuming the phone’s failure is due to a misconfigured switchport mode or PoE issue, but the PC’s connectivity rules those out. Remember the memory tip: “If the PC works but the phone won’t talk, check if the voice VLAN exists in the database, not just on the port.”
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Switch# show running-config interface GigabitEthernet0/5
Building configuration...
Current configuration : 185 bytes
!
interface GigabitEthernet0/5
switchport access vlan 10
switchport mode access
switchport voice vlan 20
no ip address
spanning-tree portfast
end
Switch# show vlan brief
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Gi0/1, Gi0/2, Gi0/3, Gi0/4
10 Data active Gi0/5, Gi0/6, Gi0/7
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup
A user connects a Cisco IP Phone with a PC attached to the phone's PC port to switch interface GigabitEthernet0/5. The PC obtains an IP address and can reach the network, but the phone displays "Configuring IP" and never registers. Based on the exhibit outputs, what is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
Switch# show running-config interface GigabitEthernet0/5
Building configuration...
Current configuration : 185 bytes
!
interface GigabitEthernet0/5
switchport access vlan 10
switchport mode access
switchport voice vlan 20
no ip address
spanning-tree portfast
end
Switch# show vlan brief
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Gi0/1, Gi0/2, Gi0/3, Gi0/4
10 Data active Gi0/5, Gi0/6, Gi0/7
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup
A
The switchport must be configured as a trunk to support voice VLANs.
Why wrong: On a Cisco switch, the voice VLAN feature works perfectly on access ports using the 'switchport voice vlan' command. It is not necessary to configure the port as a trunk.
B
VLAN 20 has not been created in the switch's VLAN database.
The 'show vlan brief' output lists only VLANs 1 and 10. VLAN 20 does not exist, so the switch discards any tagged frames arriving on the port with VLAN ID 20, causing the phone's DHCP/TFTP communication to fail.
C
The native VLAN on the trunk ports between the switch and the DHCP server is incorrectly set to VLAN 10.
Why wrong: The exhibit shows the access port is not a trunk, and even if there were uplink trunks, a native VLAN mismatch would cause spanning-tree issues or VLAN leakage, but not selectively prevent the phone from working while the PC functions.
D
The phone is manually configured to use VLAN 10 for voice traffic instead of VLAN 20.
Why wrong: By default, Cisco IP Phones use CDP to learn the voice VLAN from the switch. There is no indication of manual phone configuration, and if the phone were using VLAN 10, voice traffic would be untagged and would reach the network, which contradicts the symptom.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
VLAN 20 has not been created in the switch's VLAN database.
The PC obtains an IP address and can reach the network, indicating that the access VLAN (likely VLAN 1 or the native VLAN) is functioning. However, the phone displays 'Configuring IP' and never registers, which means it cannot obtain an IP address on its voice VLAN. The most likely cause is that VLAN 20, which is configured as the voice VLAN on the switchport, has not been created in the switch's VLAN database. Without the VLAN existing, the switch cannot forward traffic or DHCP requests for that VLAN, leaving the phone stuck in the IP configuration phase.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 switchport must be configured as a trunk to support voice VLANs.
Why it's wrong here
On a Cisco switch, the voice VLAN feature works perfectly on access ports using the 'switchport voice vlan' command. It is not necessary to configure the port as a trunk.
✓
VLAN 20 has not been created in the switch's VLAN database.
Why this is correct
The 'show vlan brief' output lists only VLANs 1 and 10. VLAN 20 does not exist, so the switch discards any tagged frames arriving on the port with VLAN ID 20, causing the phone's DHCP/TFTP communication to fail.
Clue confirmation
The clue words "most likely", "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The native VLAN on the trunk ports between the switch and the DHCP server is incorrectly set to VLAN 10.
Why it's wrong here
The exhibit shows the access port is not a trunk, and even if there were uplink trunks, a native VLAN mismatch would cause spanning-tree issues or VLAN leakage, but not selectively prevent the phone from working while the PC functions.
✗
The phone is manually configured to use VLAN 10 for voice traffic instead of VLAN 20.
Why it's wrong here
By default, Cisco IP Phones use CDP to learn the voice VLAN from the switch. There is no indication of manual phone configuration, and if the phone were using VLAN 10, voice traffic would be untagged and would reach the network, which contradicts the symptom.
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 20 has not been created in the switch's VLAN database.Correct answer▾
Why this is correct
The 'show vlan brief' output lists only VLANs 1 and 10. VLAN 20 does not exist, so the switch discards any tagged frames arriving on the port with VLAN ID 20, causing the phone's DHCP/TFTP communication to fail.
✗The switchport must be configured as a trunk to support voice VLANs.Wrong answer — click to see why▾
Why this is wrong here
Voice VLANs operate on access ports by tagging voice traffic while keeping PC traffic untagged in the data VLAN. A trunk is not required.
✗The native VLAN on the trunk ports between the switch and the DHCP server is incorrectly set to VLAN 10.Wrong answer — click to see why▾
Why this is wrong here
Native VLAN mismatches on trunks would affect both data and voice VLANs if both were allowed. The PC works, ruling out a general trunk issue.
✗The phone is manually configured to use VLAN 10 for voice traffic instead of VLAN 20.Wrong answer — click to see why▾
Why this is wrong here
The phone would work if it was sending voice traffic on the data VLAN (10), because VLAN 10 exists. The phone failing indicates a missing voice VLAN, not a misconfiguration on the phone.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between configuring a voice VLAN on an interface and actually creating that VLAN in the global VLAN database; candidates mistakenly assume that referencing a VLAN in interface configuration automatically creates it.
Trap categories for this question
Command / output trap
On a Cisco switch, the voice VLAN feature works perfectly on access ports using the 'switchport voice vlan' command. It is not necessary to configure the port as a trunk.
Detailed technical explanation
How to think about this question
When a Cisco IP Phone is connected to a switchport configured with 'switchport voice vlan 20', the switch uses CDP (Cisco Discovery Protocol) to inform the phone of the voice VLAN ID. The phone then tags its traffic with VLAN 20 and sends a DHCP request. If VLAN 20 is not created in the VLAN database, the switch drops all frames tagged with that VLAN, including DHCP discovery messages, because the VLAN is not active in the spanning-tree or forwarding table. This is a common misconfiguration where the VLAN is referenced in the interface configuration but not defined globally.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: VLAN 20 has not been created in the switch's VLAN database. — The PC obtains an IP address and can reach the network, indicating that the access VLAN (likely VLAN 1 or the native VLAN) is functioning. However, the phone displays 'Configuring IP' and never registers, which means it cannot obtain an IP address on its voice VLAN. The most likely cause is that VLAN 20, which is configured as the voice VLAN on the switchport, has not been created in the switch's VLAN database. Without the VLAN existing, the switch cannot forward traffic or DHCP requests for that VLAN, leaving the phone stuck in the IP configuration phase.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "never". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A user says the phone connected to a switch port works, but the attached PC does not get network access. What is the most likely switch-side issue?
medium
✓ A.The access VLAN for the PC is misconfigured
B.The voice VLAN should always match the access VLAN
C.PortFast blocks the PC from sending traffic
D.The phone requires the switch to be in trunk mode
Why A: An IP phone can use a voice VLAN while the attached PC uses the access VLAN. If the access VLAN is missing or wrong, the phone may still work while the PC fails.
Variation 2. A phone and a PC are attached to the same switchport. The intended data VLAN is VLAN 10, and the phone uses voice VLAN 20. The switchport currently has `switchport voice vlan 20` configured. The phone works, but the PC cannot reach the data network. Which command is most likely missing?
medium
A.switchport mode dynamic auto
B.switchport voice vlan 20
✓ C.switchport access vlan 10
D.spanning-tree guard root
Why C: When a Cisco IP phone and a PC share one port, the switchport often needs both a data VLAN and a voice VLAN. If the voice VLAN exists but the data access VLAN is wrong or missing, the phone can work while the PC fails.
Last reviewed: Jun 25, 2026
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