CCNA Switching and Network Access Practice Question
A phone and PC share one switchport. The phone registers successfully, but the workstation receives an address from the wrong subnet. Which explanation is strongest?
⚠ Common exam trap
Cisco often tests the misconception that if the phone works, the entire port configuration is correct, but the trap here is that the voice and data VLANs are independent, so a misconfigured access VLAN can still cause the PC to receive an incorrect IP address.
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 workstation is likely in the wrong data VLAN even though the phone is in the correct voice VLAN.
The phone and PC share a single switchport configured with separate voice and data VLANs. The phone successfully registers in the voice VLAN, but the workstation receives an IP address from the wrong subnet, indicating it is placed in an incorrect data VLAN. This typically occurs when the switchport's access VLAN (data VLAN) is misconfigured or mismatched with the workstation's expected subnet, while the voice VLAN (often using 802.1Q tagging) is correctly set for the phone.
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 workstation is likely in the wrong data VLAN even though the phone is in the correct voice VLAN.
Why this is correct
On a Cisco access port configured for voice, the switchport uses both an access VLAN (for the PC) and a separate voice VLAN (for the phone), and these are independent Layer 2 domains. If the phone registers, the voice VLAN, its SVI, and the DHCP scope for that subnet are working, but the PC remains dependent on the data/access VLAN's own SVI and DHCP service. Therefore a successful phone registration strongly suggests the data VLAN is misconfigured or mismatched with the PC's intended subnet.
- ✗
If the phone works, the data VLAN must also be correct automatically.
Why it's wrong here
The phone's successful IP connectivity is isolated to the voice VLAN; a Cisco IP phone tags its own frames with the voice VLAN ID while forwarding the PC's untagged frames into the access VLAN. The switch treats these as two separate broadcast domains, so registering on the voice side gives no assurance that the access VLAN has the correct configured VLAN ID, DHCP pool, or routing path. The phone can even work when the PC's data VLAN is entirely absent from the relevant SVI or trunk.
When this WOULD be correct
In a different scenario where a question states that both the phone and workstation are configured to use the same VLAN, and the phone registers successfully while the workstation fails to get an IP address, option B could be correct, indicating that the data VLAN is indeed functioning properly.
- ✗
The problem must be CAPWAP because phones require AP controllers.
Why it's wrong here
CAPWAP (Control and Provisioning of Wireless Access Points) is the UDP-based tunnelling protocol between lightweight APs and a wireless LAN controller, and it has no role in wired IP telephony on an Ethernet access port. A Cisco IP phone registers using SIP, SCCP, or similar signaling on the voice VLAN, not through CAPWAP, so invoking CAPWAP would be completely off-path. This scenario is purely a wired edge-switching problem involving VLAN placement and DHCP, not wireless controller operations.
When this WOULD be correct
In a different scenario where the question involves a wireless phone that connects to a network through an AP (Access Point) managed by a controller, and the question asks about issues related to phone registration and CAPWAP, this option could be correct if it were established that the phone's registration was failing due to CAPWAP misconfiguration.
- ✗
The phone registration proves that DHCP cannot be the issue for the PC.
Why it's wrong here
DHCP for the phone and for the PC run in different broadcast domains, so the phone obtaining an address proves nothing about the PC's DHCP request. A phone may register using a static IP, or its voice VLAN's DHCP server may have a valid lease pool while the data VLAN has no ip helper-address configured on its SVI. Thus the PC can still fail DHCP because it is assigned a bogus address, the wrong subnet, or no address at all despite the phone being fully registered.
When this WOULD be correct
In a different scenario, if a question states that both the phone and PC are on the same VLAN and the phone registers successfully while the PC fails to obtain an address, then this option could be correct, suggesting that DHCP is functioning properly for the phone but not for the PC due to other issues.
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.
✓The workstation is likely in the wrong data VLAN even though the phone is in the correct voice VLAN.Correct answer▾
Why this is correct
On a Cisco access port configured for voice, the switchport uses both an access VLAN (for the PC) and a separate voice VLAN (for the phone), and these are independent Layer 2 domains. If the phone registers, the voice VLAN, its SVI, and the DHCP scope for that subnet are working, but the PC remains dependent on the data/access VLAN's own SVI and DHCP service. Therefore a successful phone registration strongly suggests the data VLAN is misconfigured or mismatched with the PC's intended subnet.
✗If the phone works, the data VLAN must also be correct automatically.Wrong answer — click to see why▾
Why this is wrong here
This statement is incorrect because voice and data VLANs are independent on a switchport configured with separate VLANs. The phone successfully registering on the voice VLAN does not guarantee that the data VLAN is correctly configured; the PC could still be assigned to a different VLAN or subnet due to misconfiguration.
★ When this WOULD be the correct answer
In a different scenario where a question states that both the phone and workstation are configured to use the same VLAN, and the phone registers successfully while the workstation fails to get an IP address, option B could be correct, indicating that the data VLAN is indeed functioning properly.
Why candidates choose this
A student might think that if the phone works, the entire port configuration is correct, overlooking that the phone and PC use different VLANs. This confusion arises from not understanding that a single port can carry multiple VLANs with separate configurations.
✗The problem must be CAPWAP because phones require AP controllers.Wrong answer — click to see why▾
Why this is wrong here
CAPWAP (Control and Provisioning of Wireless Access Points) is a protocol used for wireless LAN controller and access point communication, not for wired switchport configuration. The scenario describes a wired phone and PC sharing a switchport, which is unrelated to wireless controllers.
★ When this WOULD be the correct answer
In a different scenario where the question involves a wireless phone that connects to a network through an AP (Access Point) managed by a controller, and the question asks about issues related to phone registration and CAPWAP, this option could be correct if it were established that the phone's registration was failing due to CAPWAP misconfiguration.
Why candidates choose this
Students might confuse the phone (IP phone) with a wireless access point, or think that any phone registration involves CAPWAP. However, IP phones typically use PoE and VLAN configuration on switches, not CAPWAP.
✗The phone registration proves that DHCP cannot be the issue for the PC.Wrong answer — click to see why▾
Why this is wrong here
The phone's successful registration does not rule out DHCP issues for the PC. The PC could be receiving an IP address from a DHCP server that is on the wrong subnet or VLAN, or the DHCP relay might be misconfigured for the data VLAN. The phone's DHCP success is independent of the PC's DHCP process.
★ When this WOULD be the correct answer
In a different scenario, if a question states that both the phone and PC are on the same VLAN and the phone registers successfully while the PC fails to obtain an address, then this option could be correct, suggesting that DHCP is functioning properly for the phone but not for the PC due to other issues.
Why candidates choose this
A student might assume that if DHCP works for one device on the same port, it should work for all devices. However, because the phone and PC are on different VLANs, they may use different DHCP servers or scopes, and the PC's DHCP request might be handled incorrectly.
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
Go deeper
Related to this question
Learn chapter
Interpreting Packet Capture Output for Layer 2/3 Troubleshooting
Key term
Switchport
A switchport is a physical or virtual interface on a network switch that connects devices like computers, printers, or other switches to a local area network.
Key term
IP address
An IP address is a unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
About these practice questions
This 200-301 question is part of Courseiva's 1,389-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.