Link Layer Discovery Protocol

LLDP (Link Layer Discovery Protocol) is a vendor-neutral Layer 2 protocol that is defined by the IEEE 802.1AB standard and offers the possibility to share information between neighboring devices.

On any device that supports LLDP, operates a software component, called the LLDP agent that sends periodically information about yourself and constantly receives information from neighboring devices. This is done independently of each other, and therefore the LLDP is called a " one-way protocol ", which builds no communication to other devices.

The received information about the LLDP DU ( Data Units ) are locally stored on each device in a data structure, the Management Information Base (MIB). This information can then in turn be accessed by SNMP. LLDP messages are in a Layer 2 frame (OSI ) to the multicast address " 01:80: C2: 00:00:0 E" sent with the Ethertype " 88- CC".

The LLDPDU consists of TLVs (Type - Length-Value ). Each TLV has a type (type) depending on 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 ) to support interoperability of VoIP devices with other devices on the network (eg a PC).

LLDP -MED is mainly focused on the detection of devices such as IP phones, which run between the network devices (switches, routers ) and end devices.