CCNP Infrastructure Practice Question
A network administrator is configuring a Cisco Catalyst switch to assign a voice VLAN to IP phones and a data VLAN to connected PCs on the same port. The phones are Cisco and use CDP to communicate VLAN information. Which configuration should be applied to the switch port?
⚠ Common exam trap
The trap here is thinking that a trunk port is required to carry both voice and data VLANs; in reality, an access port with a voice VLAN handles both, with the phone tagging voice traffic.
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
✓
Configure the port as an access port in the data VLAN and enable the voice VLAN with the 'switchport voice vlan' command.
The correct configuration is to set the port as an access port in the data VLAN and then specify the voice VLAN using the 'switchport voice vlan' command. This allows the switch to use CDP to inform the IP phone of the voice VLAN, so the phone tags its voice traffic with the appropriate VLAN ID while the PC's data traffic remains untagged in the access VLAN. This is the Cisco best practice for connecting IP phones and PCs to the same switch port.
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 the port as an access port in the data VLAN and enable the voice VLAN with the 'switchport voice vlan' command.
Why this is correct
This configuration allows the switch port to carry data traffic for the PC in the access VLAN (untagged) and voice traffic for the phone in the voice VLAN (tagged with 802.1Q). The 'switchport voice vlan' command instructs the switch to use CDP to tell the phone which VLAN to use for voice. This is the standard and recommended method for connecting Cisco IP phones and PCs on the same port.
- ✗
Configure the port as a dynamic auto port and set the voice VLAN to be negotiated via DTP.
Why it's wrong here
DTP is used to negotiate trunking, not voice VLAN assignment. Voice VLANs are communicated via CDP or LLDP-MED, not DTP. Setting the port to dynamic auto would not automatically assign a voice VLAN; it would attempt to form a trunk. This is not the correct method for voice VLAN configuration and could lead to unexpected trunking behavior.
- ✗
Configure the port as a private VLAN host port and map the voice VLAN as a secondary VLAN.
Why it's wrong here
Private VLANs are used for layer 2 isolation between ports, not for voice VLAN assignment. Mapping a voice VLAN as a secondary VLAN is not a supported or practical configuration for IP telephony. This approach would not provide the necessary connectivity for the phone or PC and is unrelated to the standard voice VLAN feature.
- ✗
Configure the port as a trunk with native VLAN for data and allow the voice VLAN.
Why it's wrong here
While a trunk port can carry both voice and data VLANs, it is not the recommended configuration for connecting an IP phone and PC. A trunk would require the phone to tag data traffic or the PC to be on a separate VLAN, which complicates the setup. The standard Cisco approach is to use an access port with a voice VLAN, which simplifies configuration and leverages CDP for automatic voice VLAN assignment.
Visual reference
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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