show lldp neighbors
Displays a summary of directly connected networking equipment using the Link Layer Discovery Protocol (LLDP - IEEE 802.1AB). This is the vendor-neutral, open-standard alternative to CDP. If a Cisco switch is plugged into a Juniper router or an HP server, LLDP is the tool used to map the connection.
CCNA Exam Gotchas
Disabled by Default
Unlike CDP, which is blaring by default the second you turn on a Cisco switch, LLDP is disabled by default on Cisco IOS.
If you type show lldp neighbors on a fresh switch, it will throw an error. You must first enter Global Configuration mode and type the master command lldp run to start the protocol.
Granular Transmit vs Receive
A unique feature of LLDP heavily tested on the exam is its directionality. You can configure an interface to listen for LLDP packets from a neighbor, but refuse to send any of its own data back.
This is done at the interface level using lldp transmit and lldp receive. (If you want to disable it entirely on a port, you must negate both: no lldp transmit & no lldp receive).