L2 neighbors (LLDP)

What it does: reads a switch's LLDP-MIB over SNMP and lists its neighbors — for each of the switch's ports, the connected device's system name, port, and chassis ID. This is the 'who's plugged into which port' map that ICMP/ARP discovery can't give you.

Safe to run: yes, read-only SNMP.

Reading results: point it at a SWITCH (with SNMP v2c enabled) — a plain host almost never runs an LLDP agent, so its remote table is empty. Empty results usually mean LLDP is off on the device, the LLDP-MIB isn't supported, or the community/port is wrong. (CDP is Cisco-proprietary and not in a standard MIB; modern Cisco/Arista/Juniper gear all also speak LLDP, which is what this uses.)