CyberCertPrepNetwork FundamentalsSwitching & Routing BasicsEASYFree question
What is a voice VLAN, and how does a Cisco switch communicate voice VLAN information to a connected IP phone?
- A.A voice VLAN uses a higher VLAN ID than 1000; standard VLANs (1-1000) cannot carry voice traffic
- B.A voice VLAN is a separate physical switch dedicated to VoIP equipment; IP phones cannot share switch infrastructure with workstations
- C.A voice VLAN is configured on the IP phone itself; the switch passively forwards tagged voice frames without any VLAN configuration
- D.A voice VLAN is a dedicated VLAN for IP phone traffic tagged with 802.1Q for QoS treatment; Cisco switches advertise the voice VLAN to phones via CDP (Cisco Discovery Protocol) or LLDP-MED, telling the phone which VLAN to tag its traffic with
Why D is correct
Voice VLAN configuration on Cisco switches: 'switchport voice vlan <id>'. The switch sends CDP (or LLDP-MED) to the connected phone, informing it of the voice VLAN ID. The phone tags its RTP/SIP traffic with that VLAN and CoS (802.1p) priority 5 (voice) or 6 (signaling). The PC daisy-chained through the phone sends untagged traffic on the access VLAN. This allows QoS differentiation and security separation on a single physical cable. VLAN ID range 1-4094 applies equally to voice VLANs.
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