Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureHard
A network engineer is configuring an access layer switch for a new office floor. The switch needs to support Voice over IP (VoIP) phones, which are daisy-chained behind desktop computers. To ensure optimal voice quality, the VoIP phones must receive an IP address from a specific VLAN (VLAN 10 for voice) and prioritize their traffic. The desktop computers connected to the phones should receive an IP address from a different VLAN (VLAN 20 for data). Which feature allows the switch to automatically assign the phone to the voice VLAN and the PC to the data VLAN on a single port?
- AVLAN Trunking Protocol (VTP)
- BPort Security
- CVoice VLAN
- DDynamic ARP Inspection (DAI)
Show answer & explanationAnswer & explanation
Correct answer: C. Voice VLAN
The Voice VLAN feature on Cisco switches allows a single switch port to carry traffic for both a VoIP phone and a data device (like a PC) connected in series. The switch automatically identifies the VoIP phone (often via its OUI or CDP/LLDP) and places its traffic into a dedicated voice VLAN, while the data traffic from the PC remains in the native (data) VLAN. This simplifies deployment and ensures QoS for voice.
Why the other options are wrong
- A. VLAN Trunking Protocol (VTP) is used to propagate VLAN configurations across switches but does not dynamically assign devices to specific VLANs on access ports.
- B. Port Security restricts MAC addresses on a port but does not differentiate between voice and data traffic or assign VLANs dynamically based on device type.
- D. Dynamic ARP Inspection (DAI) is a security feature that validates ARP packets and prevents ARP spoofing, not for assigning VLANs to devices.
Voice VLAN
A Cisco Catalyst switch feature that allows a single access port to carry traffic for both a voice device (VoIP phone) and a data device (PC) by placing them into separate VLANs.
- Uses CDP or LLDP to detect VoIP phones.
- Assigns phone to a dedicated voice VLAN.
- PC traffic remains in the native data VLAN.
- Ensures QoS for voice traffic.
Memory trick: VLANs: Organizing devices for network efficiency.