- A
STP
Why wrong: STP is used to prevent network loops, not for VLAN assignment to endpoints.
- B
LLDP
LLDP-MED allows the switch to advertise the voice VLAN to the phone.
- C
RSTP
Why wrong: RSTP is a faster version of STP, not used for VLAN assignment.
- D
GVRP
Why wrong: GVRP (GARP VLAN Registration Protocol) is used for dynamic VLAN registration between switches, not for advertising VLAN information to endpoints like VoIP phones.
Question 324 of 1,020
220-1201 LLDP-MED Practice Question
This 220-1201 practice question tests your understanding of network protocols. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: lLDP-MED. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
During a network upgrade, a technician configures a new VoIP phone to use a dedicated VLAN for voice traffic. After connecting the phone to a switch port configured for voice VLAN, the phone powers on but cannot register with the call manager. The switch port is set to trunk mode. Which protocol is essential for the phone to obtain its VLAN assignment?
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
✓
LLDP
Link Layer Discovery Protocol (LLDP) is essential because it allows the switch to inform the VoIP phone of the configured voice VLAN ID. When a switch port is in trunk mode, the phone uses LLDP (specifically LLDP-MED) to learn which VLAN to tag its voice traffic with, enabling it to communicate with the call manager. Without LLDP, the phone would not know which VLAN to use and would fail to register.
Key principle: LLDP-MED
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
STP
- ✓
LLDP
Why this is correct
LLDP-MED allows the switch to advertise the voice VLAN to the phone.
Related concept
LLDP-MED
- ✗
RSTP
- ✗
GVRP
Why it's wrong here
GVRP (GARP VLAN Registration Protocol) is used for dynamic VLAN registration between switches, not for advertising VLAN information to endpoints like VoIP phones.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A+ candidates often confuse LLDP-MED with other protocols that manage VLANs between switches, such as GVRP, leading them to select GVRP instead of LLDP for endpoint VLAN assignment.
Detailed technical explanation
How to think about this question
CDP operates at Layer 2 and uses multicast frames to share information about directly connected Cisco devices. When a VoIP phone is connected to a trunk port, the switch sends a CDP message containing the voice VLAN ID (e.g., VLAN 10), and the phone then tags its packets with that VLAN. In real-world scenarios, if CDP is disabled globally or on the interface, the phone may default to the native VLAN or fail to obtain the correct voice VLAN, requiring manual configuration of the VLAN ID on the phone.
KKey Concepts to Remember
- LLDP-MED
- Voice VLAN
- Trunk Port
- VLAN Registration
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
LLDP-MED
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this 220-1201 question test?
Network Protocols — This question tests Network Protocols — LLDP-MED.
What is the correct answer to this question?
The correct answer is: LLDP — Link Layer Discovery Protocol (LLDP) is essential because it allows the switch to inform the VoIP phone of the configured voice VLAN ID. When a switch port is in trunk mode, the phone uses LLDP (specifically LLDP-MED) to learn which VLAN to tag its voice traffic with, enabling it to communicate with the call manager. Without LLDP, the phone would not know which VLAN to use and would fail to register.
What should I do if I get this 220-1201 question wrong?
Review lLDP-MED, then practise related 220-1201 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
LLDP-MED
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Last reviewed: Jul 4, 2026
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