The link layer discovery protocol (LLDP) is an open and extendable part of the Internet protocol suite used in IEEE 802 to advertise a device’s identity and abilities, as well as other devices connected within the same network.
LLDP is mainly used in wired Ethernet-connected devices to facilitate management of network resources and simplify networking tasks for administrators in a multi-vendor network. The protocol’s multi-vendor support enables network discovery of devices and management tools like Simple Network Management Protocol (SNMP) in a network made up of devices from different manufacturers. LLDP makes it unnecessary to use a larger number of proprietary protocols to support a multi-vendor network or, on the other hand, limit oneself to the hardware of a single vendor.
On an interval schedule, an LLDP device sends its information in Ethernet frames. A frame starts with the required TLVs of Chassis ID, Port ID, and time-to-live (TTL). The frame contains the device’s destination MAC address as a multicast address that is not forwarded outside a network, assuming 802.1D compliance.
LLDP is also known as Station and Media Access Control Connectivity Discovery, as specified in IEEE 802.1AB. Similar proprietary protocols include Cisco Discovery Protocol (CDP), Extreme Discovery Protocol, Foundry Discovery Protocol (FDP), Microsoft's Link Layer Topology Discovery and Nortel Discovery Protocol (AKA SONMP).