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 runWhen to Use This Command
- Enable LLDP on a switch to discover and display information about neighboring Cisco and third-party devices for network documentation and troubleshooting.
- Activate LLDP before configuring per-interface LLDP settings to ensure the protocol is globally available.
- Use LLDP to verify device capabilities, software versions, and VLAN assignments of connected switches and routers.
- Enable LLDP as a prerequisite for using CDP-like discovery in mixed-vendor environments where CDP is not supported.
Command Examples
Enabling LLDP Globally
Switch(config)# lldp runSwitch(config)#
No output is displayed upon successful execution. The command simply enables LLDP globally. Use 'show lldp' to verify the status.
Verifying LLDP Status After Enabling
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
The output confirms LLDP is active globally. 'Status: ACTIVE' indicates LLDP is enabled. The advertisement interval (30s) and hold time (120s) are default values. Reinitialization delay is the time before LLDP restarts on an interface after a configuration change.
Understanding the Output
The 'show lldp' command displays global LLDP status. 'Status: ACTIVE' means LLDP is enabled globally; 'INACTIVE' means it is disabled. The advertisement interval (default 30 seconds) controls how often LLDP packets are sent. The hold time (default 120 seconds) tells neighbors how long to keep the information before discarding it. The reinitialization delay (default 2 seconds) is the wait time before restarting LLDP on an interface after a change. In a real network, you should see ACTIVE; if not, use 'lldp run' to enable. Watch for mismatched timers that could cause premature neighbor loss.
CCNA Exam Tips
CCNA exam tip: 'lldp run' is a global configuration command; it must be entered in global config mode, not interface mode.
CCNA exam tip: LLDP is disabled by default on Cisco IOS; you must explicitly enable it with 'lldp run'.
CCNA exam tip: Unlike CDP which is Cisco proprietary, LLDP is IEEE 802.1AB standard and works with multi-vendor devices.
CCNA exam tip: The exam may test that 'lldp run' enables LLDP globally, but per-interface enablement with 'lldp transmit' and 'lldp receive' is also required for full operation.
Common Mistakes
Mistake: Forgetting to enter global configuration mode before typing 'lldp run'. Consequence: Command is rejected or applied incorrectly.
Mistake: Assuming LLDP is enabled by default. Consequence: Neighbor discovery fails until 'lldp run' is configured.
Mistake: Enabling LLDP globally but not enabling it on specific interfaces (using 'lldp transmit' and 'lldp receive'). Consequence: LLDP packets are not sent or received on those interfaces.
Related Commands
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 transmit
Enables LLDP transmission on an interface, allowing the device to advertise its identity and capabilities to neighboring LLDP-enabled devices.
show lldp neighbors
Displays information about directly connected LLDP-capable devices, including device ID, local interface, hold time, capability, and port ID, used to verify LLDP neighbor discovery and troubleshoot Layer 2 connectivity.
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