CCNA Switching and Network Access Practice Question
Exhibit
Interface config: switchport mode access switchport access vlan 10 spanning-tree portfast
Exhibit: A switch interface connected to an IP phone and PC is configured as an access port in VLAN 10. The PC works, but the phone does not register. What additional configuration is most likely needed?
⚠ Common exam trap
Don't confuse portfast or trunk mode with the need for a voice VLAN. Focus on the specific requirements of IP phones.
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
✓
switchport voice vlan <voice-vlan-id>
An IP phone commonly requires a voice VLAN so tagged voice traffic is separated from the data VLAN used by the attached PC. Without a voice VLAN, the PC can still work on the access VLAN while the phone fails to register properly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
switchport trunk encapsulation dot1q
Why it's wrong here
This command sets the trunk encapsulation type to IEEE 802.1Q on a port, but it is only relevant on trunk ports that carry multiple VLANs. On an access port connected to an IP phone and PC, the port is not configured as a trunk; instead, the voice VLAN feature uses the phone's internal switch to tag only voice frames. Also, this command is not supported as a separate encapsulation configuration on modern Cisco switches because 802.1Q is the default and only trunking encapsulation.
When this WOULD be correct
In a scenario where the question involves a switch port configured as a trunk, and the requirement is to ensure proper encapsulation for multiple VLANs, this option would be correct. For example, if the question asked about a trunk port connecting to a router or another switch, specifying trunk encapsulation would be necessary.
- ✓
switchport voice vlan <voice-vlan-id>
Why this is correct
This command configures a dedicated voice VLAN on an access port connected to an IP phone. It allows the phone to tag voice traffic with the specified VLAN ID while the attached PC remains untagged in the access VLAN, enabling separate QoS policies and subnets for voice and data. This is the standard Cisco configuration for a single switchport carrying both phone and PC traffic.
- ✗
channel-group 1 mode active
Why it's wrong here
This command is used to configure EtherChannel using LACP active mode, which bundles multiple physical links into a single logical link for redundancy or bandwidth. It has no effect on voice VLAN configuration and does not influence how an IP phone classifies or tags voice traffic. Moreover, configuring 'channel-group' on a single access port without corresponding neighbor links would create a misconfiguration, and it certainly cannot replace the required voice VLAN command.
When this WOULD be correct
In a different scenario where the question involves configuring multiple switches for load balancing and redundancy, the option 'channel-group 1 mode active' would be correct if the exam asked about setting up an EtherChannel between two switches to aggregate bandwidth and ensure high availability.
- ✗
ip helper-address on the switchport
Why it's wrong here
The 'ip helper-address' command is configured on a Layer 3 interface such as a VLAN interface (SVI) or routed port to forward DHCP broadcasts to a DHCP server on another subnet. It is not applicable to a Layer 2 switchport, which does not process IP broadcast forwarding locally, and it would not separate voice and data traffic on a physical port. Even when applied to an SVI, it only aids DHCP relay, not voice VLAN tagging.
When this WOULD be correct
In a question where a network administrator is troubleshooting DHCP issues for multiple devices on a subnet, and the devices are unable to obtain IP addresses, the correct answer would involve configuring 'ip helper-address' on the switchport to direct DHCP requests to the appropriate server.
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.
✓switchport voice vlan <voice-vlan-id>Correct answer▾
Why this is correct
This command configures a dedicated voice VLAN on an access port connected to an IP phone. It allows the phone to tag voice traffic with the specified VLAN ID while the attached PC remains untagged in the access VLAN, enabling separate QoS policies and subnets for voice and data. This is the standard Cisco configuration for a single switchport carrying both phone and PC traffic.
✗switchport trunk encapsulation dot1qWrong answer — click to see why▾
Why this is wrong here
This option is incorrect because the question specifies an access port configuration, which does not require trunk encapsulation. Access ports do not use trunking protocols like dot1q, as they are meant for single VLAN traffic only.
★ When this WOULD be the correct answer
In a scenario where the question involves a switch port configured as a trunk, and the requirement is to ensure proper encapsulation for multiple VLANs, this option would be correct. For example, if the question asked about a trunk port connecting to a router or another switch, specifying trunk encapsulation would be necessary.
Why candidates choose this
Candidates may find this option tempting because they might associate VLAN configurations with trunking, especially if they have experience with mixed VLAN environments where trunking is common.
✗channel-group 1 mode activeWrong answer — click to see why▾
Why this is wrong here
This option is wrong because the channel-group command is used for configuring EtherChannel, which is not relevant to the issue of the IP phone not registering on an access port. The problem lies in the VLAN configuration for voice traffic, not in link aggregation.
★ When this WOULD be the correct answer
In a different scenario where the question involves configuring multiple switches for load balancing and redundancy, the option 'channel-group 1 mode active' would be correct if the exam asked about setting up an EtherChannel between two switches to aggregate bandwidth and ensure high availability.
Why candidates choose this
Candidates may find this option tempting because they might confuse the need for proper link configuration with the requirement for voice VLANs, thinking that channel aggregation could somehow resolve connectivity issues for devices on the same port.
✗ip helper-address on the switchportWrong answer — click to see why▾
Why this is wrong here
The 'ip helper-address' command is used to forward DHCP requests from clients to a DHCP server, but it does not address the registration issue of the IP phone in this scenario, which is related to VLAN configuration.
★ When this WOULD be the correct answer
In a question where a network administrator is troubleshooting DHCP issues for multiple devices on a subnet, and the devices are unable to obtain IP addresses, the correct answer would involve configuring 'ip helper-address' on the switchport to direct DHCP requests to the appropriate server.
Why candidates choose this
Candidates might choose this option because they associate 'ip helper-address' with network connectivity issues, mistakenly thinking it could resolve any problem related to device registration or connectivity.
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?”
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
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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.