Network devices are increasingly diverse, and their configurations are respectively complicate. Therefore, mutual discovery and interactions in information of system and configuration between devices of different manufacturers are necessary to facilitate management. LLDP (Link Layer Discovery Protocol ) is a neighbor discovery protocol defined in IEEE 802.1ab, which provides a discovery method in link layer network. By means of the LLDP technology, the system can quickly master the information of topology and its changes of the layer-2 network when the scale of network expands rapidly.
By means of LLDP, the LLDP information of the device, including the device information, system name, system description, port description, network management address and so on, can be sent in the form of standard TLV (Type Length Value) multicast message from the physical port to the directly-connected neighbor. If the neighbor enables LLDP too, then neighbor relations will be established between both sides. When the neighbor receives these messages, they are stored in the form of MIB in the SNMP MIB database, in order to be utilized by the network management system to search and analyze the two-layer topology and the problems in it of the current network.
The 4 work modes of LLDP are listed below:
- Transmit and Receive: the port transmits and receives LLDP messages.
- Receive only: the port only receives LLDP messages.
- Transmit only: the port only transmits LLDP messages.
- Not work: the port neither transmits nor receives LLDP messages.