CCNA Switching and Network Access Practice Question
Exhibit
SW1# show running-config interface gigabitEthernet 1/0/1 Building configuration... Current configuration : 150 bytes ! interface GigabitEthernet1/0/1 switchport mode access switchport access vlan 10 no shutdown end SW1# show interfaces gigabitEthernet 1/0/1 switchport Name: Gi1/0/1 Switchport: Enabled Administrative Mode: static access Operational Mode: static access Administrative Trunking Encapsulation: negotiate Operational Trunking Encapsulation: native Negotiation of Trunking: Off Access Mode VLAN: 10 (VLAN0010) Trunking Native Mode VLAN: 1 (default) Administrative Native VLAN tagging: enabled Voice VLAN: none
Refer to the exhibit. A network administrator connects an IP phone to interface GigabitEthernet1/0/1 on a Cisco Catalyst switch. The PC connected through the phone works normally on the data VLAN, but the phone cannot obtain an IP address and fails to register with the call server. Which action will resolve the problem?
⚠ Common exam trap
Cisco often tests the distinction between 'switchport access vlan' (for data) and 'switchport voice vlan' (for voice), and the trap here is that candidates may confuse which VLAN is assigned to which device, or incorrectly think trunking is required for a phone connection.
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
✓
Add 'switchport voice vlan 20' on interface GigabitEthernet1/0/1.
The PC works on the data VLAN, but the phone cannot obtain an IP address, indicating the phone is not receiving the correct VLAN assignment. The phone should be placed in the voice VLAN (VLAN 20) using the 'switchport voice vlan 20' command, which allows the switch to tag the phone's traffic with VLAN 20 via CDP/LLDP, enabling it to get an IP from the voice VLAN DHCP server.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure 'switchport trunk allowed vlan 10,20' on interface Gi1/0/1 and change the switchport mode to trunk.
Why it's wrong here
Changing the interface to trunk mode with 'switchport mode trunk' and permitting VLANs 10 and 20 modifies the port to carry multiple VLANs using 802.1Q tagging. However, the PC connecting through the phone is not trunk-aware; it expects untagged frames on the access VLAN, and trunk mode does not define an access VLAN for the PC. This would break PC connectivity because the phone would either bridge untagged data incorrectly or the PC would receive frames on the native VLAN, causing misrouting or dropped traffic.
- ✓
Add 'switchport voice vlan 20' on interface GigabitEthernet1/0/1.
Why this is correct
The 'switchport voice vlan 20' command is the correct Cisco IOS configuration for a voice-enabled access port. It leaves VLAN 10 as the default access VLAN for PC data (untagged) while defining VLAN 20 as the voice VLAN for the IP phone. The phone discovers VLAN 20 via CDP or LLDP and tags its voice frames with 802.1Q, keeping voice and data in separate Layer 2 domains and subnets.
- ✗
Issue 'switchport access vlan 20' and 'switchport voice vlan 10' on interface Gi1/0/1.
Why it's wrong here
This configuration swaps the intended VLAN roles: VLAN 20 becomes the access VLAN for PC data, and VLAN 10 is set as the voice VLAN for the phone. The phone would then tag voice frames with VLAN 10 while the PC remains untagged in VLAN 20, meaning voice traffic traverses the wrong subnet and likely cannot reach the call control server. Additionally, the phone's untagged traffic (if it falls back) would be placed in VLAN 20, compounding the misconfiguration.
- ✗
Enable 'switchport port-security mac-address sticky' on the interface and manually add the phone’s MAC address to the access VLAN.
Why it's wrong here
Port security with sticky MAC addresses only restricts which source MAC addresses are allowed to send frames on the interface; it does not influence VLAN assignment or configure a voice VLAN. Manually adding the phone's MAC address to the access VLAN does not create a separate voice VLAN or tell the phone to tag traffic. The phone would continue to send voice as untagged data in the access VLAN, defeating the purpose of separating voice and data traffic.
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.
✓Add 'switchport voice vlan 20' on interface GigabitEthernet1/0/1.Correct answer▾
Why this is correct
The 'switchport voice vlan 20' command is the correct Cisco IOS configuration for a voice-enabled access port. It leaves VLAN 10 as the default access VLAN for PC data (untagged) while defining VLAN 20 as the voice VLAN for the IP phone. The phone discovers VLAN 20 via CDP or LLDP and tags its voice frames with 802.1Q, keeping voice and data in separate Layer 2 domains and subnets.
✗Configure 'switchport trunk allowed vlan 10,20' on interface Gi1/0/1 and change the switchport mode to trunk.Wrong answer — click to see why▾
Why this is wrong here
A trunk port does not provide the voice VLAN advertisement mechanism to the phone; the PC would need to send tagged frames, which typical endpoint NICs do not do.
✗Issue 'switchport access vlan 20' and 'switchport voice vlan 10' on interface Gi1/0/1.Wrong answer — click to see why▾
Why this is wrong here
The phone requires access to VLAN 20 for voice services, and the PC must remain in VLAN 10 for data; this configuration does the opposite, failing to meet the requirement.
✗Enable 'switchport port-security mac-address sticky' on the interface and manually add the phone’s MAC address to the access VLAN.Wrong answer — click to see why▾
Why this is wrong here
The phone still cannot learn the voice VLAN; port security does not provide a DHCP address or make the switch advertise VLAN 20 to 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?”
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
DHCP
Dynamic Host Configuration Protocol (DHCP) automatically assigns IP addresses and network settings to devices on a network, so they can communicate without manual configuration.
Key term
Cisco Discovery Protocol
A proprietary Layer 2 network protocol used by Cisco devices to discover information about directly connected neighbor devices.
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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.