LLDP works on a simple principle: The so-called LLDP agent runs on all devices with LLDP support. On the one hand, this software component sends information to all interfaces of the device at regular intervals. This is done using either Unicast or Multicast, depending on the destination addresses, which you can configure as required. On the other hand, the LLDP agent is continuously receiving information from neighboring devices. The transmission and reception of the respective data packets is handled independently from each other.
The data packets being sent and received contain information such as the name and the description of the device, the ID and description of ports, the IP address or MAC address of the device, the specific capabilities of the device (e.g., in terms of switching and routing), VLAN identifiers and vendor-specific details. In this case, LLDP defines basic information that a data packet must always include, as well as optional additional information.
The individual devices store the information received locally in a data structure, the so-called MIB (Management Information Base). An MIB therefore contains data from its own LLDP agent and of the detected, direct neighbor agent.
The information exchange provides a continuing identification of the devices within the network, because the devices normally send packets cyclically (i.e. in configurable intervals). Furthermore, the devices also inform their network neighbors when changes occur on the device or in its network connection.
For the actual device identification process it is crucial that each connection point in the topology is clearly identified as a "Media Service Access Point" (MSAP). An MSAP is composed of a device ID (Chassis ID) and a port identification (Port ID). The unique identification or assignment of devices is therefore based on the fact that each MSAP in the monitored network topology may occur only once.
The Administrator can query and capture the data reported by the devices via a central network management software on his computer, where the query of the individual MIBs is performed using the SNMP protocol. The management software thus documents the entire topology of the network and allows automatic display of this topology along with a graphic representation of the current diagnostic data.
In LANconfig, LLDP is enabled under .
