LLDP-MED Not Providing Power/VLAN Info to IP Phones
Presenting Symptom
IP phones connected to a Cisco switch are not receiving power or correct VLAN information via LLDP-MED, resulting in phones not powering on or not being placed in the voice VLAN.
Network Context
A small branch office with a single Cisco Catalyst 2960-X switch running IOS 15.2. The switch connects to a Cisco 4321 ISR router for WAN. IP phones (Cisco 8845) are connected to access ports configured for voice VLAN 10. The switch uses LLDP-MED to provide power and VLAN info to phones. The network engineer observes that phones either do not power up or power up but remain in the default data VLAN instead of the voice VLAN.
Diagnostic Steps
Check LLDP status globally on the switch
show lldpGlobal LLDP Information: Status: ACTIVE LLDP advertisements are sent every 30 seconds LLDP hold time advertised: 120 seconds LLDP interface reinitialization delay: 2 seconds
If LLDP is not active globally, enable it with 'lldp run'. If active, proceed to check interface-level configuration.
Verify LLDP-MED configuration on the access port connected to the IP phone
show running-config interface GigabitEthernet0/1interface GigabitEthernet0/1 switchport mode access switchport access vlan 10 switchport voice vlan 10 spanning-tree portfast lldp med-tlv-select power-management lldp med-tlv-select network-policy ! (no lldp transmit or receive commands)
Look for 'lldp transmit' and 'lldp receive' under the interface. If missing, LLDP is not enabled on the port. Also check that 'lldp med-tlv-select' includes power-management and network-policy. If 'lldp med' is not present, LLDP-MED is not enabled.
Check LLDP neighbor details for the phone
show lldp neighbors GigabitEthernet0/1 detailLocal Intf: Gi0/1
Chassis id: xxxx.xxxx.xxxx
Port id: xxxx.xxxx.xxxx
Time To Live: 120
Port Description: IP Phone Port
System Name: IP Phone
System Description: Cisco IP Phone 8845
Enabled Capabilities: Telephone
Management Addresses:
IP: 10.1.1.2
Auto Negotiation - supported, enabled
Physical media capabilities: 1000baseT(FD), 100base-TX(FD), 100base-TX(HD), 10base-T(FD), 10base-T(HD)
Media Attachment Unit type: 16
Vlan ID: - not advertised
PoE Device Type: Type 2 PD
Power Request: 15400 mW, Power Available: 15400 mW
Network Policy: Voice VLAN 10, taggedIf the phone is not listed, LLDP is not working. If listed but 'Vlan ID' shows 'not advertised' or 'Network Policy' is missing, the switch is not sending LLDP-MED TLVs. Also check that 'PoE Device Type' and power info are present; if not, power negotiation is failing.
Check if LLDP-MED is enabled globally and on the interface
show lldp med interface GigabitEthernet0/1LLDP-MED is enabled on interface GigabitEthernet0/1 LLDP-MED capabilities: Capabilities, Network Policy, Power Management, Inventory LLDP-MED device type: Network Connectivity Device LLDP-MED fast start repeat count: 4
If LLDP-MED is not enabled, the switch will not send MED TLVs. Enable with 'lldp med' under the interface. Also verify that the device type is correct (Network Connectivity Device for switches).
Root Cause
LLDP-MED is not enabled on the switch access port. The interface configuration lacks the 'lldp transmit' and 'lldp receive' commands, and the 'lldp med' command is missing. Without LLDP-MED, the switch does not advertise power and voice VLAN information to the IP phone, causing the phone to either not power on or not switch to the voice VLAN.
Resolution
Verification
1. show lldp neighbors GigabitEthernet0/1 detail — Verify the phone appears with correct VLAN ID and power info. 2. show lldp med interface GigabitEthernet0/1 — Confirm LLDP-MED is enabled. 3. Check phone status: The phone should power on and display the correct voice VLAN (e.g., VLAN 10).
Prevention
1. Use a standard access port configuration template that includes 'lldp transmit', 'lldp receive', and 'lldp med' for all ports connecting to IP phones. 2. Enable LLDP globally by default on all switches. 3. Use Cisco Smartports or Auto Smartports to automatically apply LLDP-MED configuration when a phone is detected.
CCNA Exam Relevance
On the CCNA 200-301 exam, this scenario may appear as a troubleshooting question where you must identify why an IP phone is not receiving power or VLAN info. The exam tests knowledge of LLDP and LLDP-MED configuration, including the commands 'lldp run', 'lldp transmit', 'lldp receive', and 'lldp med'. A candidate must know that LLDP-MED is required for power negotiation and voice VLAN advertisement.
Exam Tips
Remember that LLDP-MED is a separate feature from basic LLDP; you must enable both LLDP and LLDP-MED on the interface.
The exam may show a configuration where 'lldp transmit' and 'lldp receive' are missing under the interface; that is a common misconfiguration.
Know that 'show lldp neighbors detail' displays LLDP-MED TLVs like Network Policy and Power; if these are missing, LLDP-MED is not enabled.
Commands Used in This Scenario
lldp receive
Enables LLDP reception on an interface, allowing the device to receive LLDP advertisements from neighboring devices for network discovery and topology mapping.
lldp run
Globally enables Link Layer Discovery Protocol (LLDP) on the switch, allowing it to advertise and receive device information from directly connected LLDP-capable neighbors.
lldp transmit
Enables LLDP transmission on an interface, allowing the device to advertise its identity and capabilities to neighboring LLDP-enabled devices.
show lldp neighbors detail
Displays detailed information about LLDP neighbors, including device capabilities, management addresses, and port descriptions, used for verifying Layer 2 topology and device discovery.
Test Your CCNA Knowledge
Practice with scenario-based questions to prepare for the CCNA 200-301 exam.
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