LLDP
The LLDP ( L ink L ayer D iscovery P rotocol ) is a vendor-neutral Layer -2- protocol defined by the IEEE 802.1AB standard and offers the possibility to exchange information between neighboring devices.
A software component works on every device that supports LLDP, the so-called LLDP agent, which sends information about itself at periodic intervals and constantly receives information from neighboring devices. This happens completely independently of each other, which is why the LLDP is called a "one-way protocol" that does not establish communication with other devices.
The information received via the LLDP-DUs (Data Units) is stored locally on each device in a data structure, the Management Information Base (MIB). This information can then be accessed using SNMP . LLDP messages are sent in a layer 2 frame (OSI) to the multicast address "01: 80: C2: 00: 00: 0E" with the Ethertype "88-CC".
The LLDPDU consists of TLVs ( Type-Length-Value ). Each TLV has a type and, depending on the data (value), the corresponding length (length).
Application in the area of Voice over IP
LLDP-MED (Link Layer Discovery Protocol - Media Endpoint Devices) is an extension of LLDP, developed by TIA (ANSI / TIA-1057), in order to make VoIP end devices interoperable with other devices in the network (e.g. a PC ) to support.
LLDP-MED mainly focuses on the detection of devices such as IP telephones, which run between the network devices (switches, routers) and end devices.