LLDP – Link Layer Discovery Protocol

LLDP – Link Layer Discovery Protocol is an industry-standard, vendor-neutral method to allow networked devices to advertise capabilities, identity, and other information onto a LAN. LLDP is Layer 2 protocol described in IEEE 802.1AB-2005 standard. It replaces several proprietary protocols implemented by individual vendors for their equipment like the most known protocol of this kind, CDP – Cisco Discovery Protocol.

LLDP allows network devices like bridges and switches that operate at the lower layers of OSI model to learn some of the capabilities and characteristics of LAN devices available to higher layer protocols, such as IP addresses. The information that they get through LLDP operation is stored in a network device and is queried with SNMP. Topology information can also be gathered from this database.

If you are interested in the Cisco proprietary solution for LLDP functionality check out CDP:

Some of the information that can be shown by LLDP:

  • System name and description
  • Port name and description
  • VLAN name and identifier
  • IP network management address
  • Capabilities of the device
  • MAC address and physical layer information
  • Power information
  • Link aggregation information

LLDP frames are sent at intervals on each port on the device that runs LLDP. LLDP protocol data units (LLDP PDUs) are sent inside Ethernet frames and identified by their destination Media Access Control (MAC) address (01:80:C2:00:00:0E) and Ethertype (0x88CC). Mandatory information supplied by LLDP is chassis ID, port ID, and a time-to-live value for this information.

LLDP is a powerful way to allow Layer 2 devices to gather details about other network-attached devices.


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