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LLDP Overview

The Link Layer Discovery Protocol (LLDP) is an industry-standard, vendor-neutral method to allow networked devices to advertise capabilities, identity, and other information onto a LAN. The Layer 2 protocol, detailed in IEEE 802.1AB-2005, replaces several proprietary protocols implemented by individual vendors for their equipment.

LLDP allows network devices that operate at the lower layers of a protocol stack (such as Layer 2 bridges and switches) to learn some of the capabilities and characteristics of LAN devices available to higher layer protocols, such as IP addresses. The information gathered through LLDP operation is stored in a network device and is queried with SNMP. Topology information can also be gathered from this database.

Some of the information that can be gathered by LLDP (only minimal information is mandatory) is:

  • System name and description

  • Port name and description

  • VLAN name and identifier

  • IP network management address

  • Capabilities of the device (for example, switch, router, or server)

  • MAC address and physical layer information

  • Power information

  • Link aggregation information

LLDP frames are sent at fixed intervals on each port 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.