CCNA Switching and Network Access Practice Question
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?
⚠ Common exam trap
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.
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
✓
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.
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
This is incorrect. On a Cisco switch, the 'switchport voice vlan' command is explicitly designed to be used on an access port. The switch uses CDP to inform the IP phone which VLAN to use for voice traffic; the phone then tags voice frames with that VLAN while the PC attached to the phone remains untagged on the access VLAN. Configuring the port as a trunk is neither required nor recommended, as a trunk would carry multiple VLANs and could complicate the access port design without providing any benefit for a single phone and PC.
- ✓
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.
- ✗
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?”
Visual reference
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
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.
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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.