10.3 Link Layer Discovery Protocol (LLDP) Explained
Key Concepts of LLDP
Link Layer Discovery Protocol (LLDP) is a vendor-neutral protocol used by network devices to advertise their identity, capabilities, and neighbors on a local area network. Key concepts include:
- LLDP Advertisements: Messages sent by devices to advertise their presence and capabilities.
- Neighbor Discovery: The process of discovering and identifying adjacent devices.
- TLVs (Type-Length-Value): Informational elements within LLDP packets that convey specific details about the device.
- LLDPDU (LLDP Data Unit): The format of the LLDP packet containing TLVs.
- LLDP Timers: Parameters that control the frequency and duration of LLDP advertisements.
LLDP Advertisements
LLDP advertisements are periodic messages sent by network devices to inform adjacent devices about their presence and capabilities. These messages help in building a topology map of the network.
Example: A MikroTik switch sends LLDP advertisements every 30 seconds to its directly connected devices. These advertisements include information such as the switch's MAC address, IP address, and port number.
Neighbor Discovery
Neighbor Discovery is the process by which network devices identify and learn about adjacent devices. This information is crucial for network management and troubleshooting.
Example: When a MikroTik router receives an LLDP advertisement from a switch, it records the switch's details in its neighbor table. This allows the router to know which switch is connected to which port.
TLVs (Type-Length-Value)
TLVs are informational elements within LLDP packets that convey specific details about the device. Common TLVs include the Chassis ID, Port ID, and Time to Live (TTL).
Example: In an LLDP packet, the Chassis ID TLV might contain the MAC address of the sending device, while the Port ID TLV might contain the port number from which the packet was sent.
LLDPDU (LLDP Data Unit)
LLDPDU is the format of the LLDP packet containing TLVs. It is structured to ensure that all necessary information about the device is conveyed efficiently.
Example: An LLDPDU from a MikroTik switch includes multiple TLVs such as the Chassis ID, Port ID, and System Name. This comprehensive information helps in accurately mapping the network topology.
LLDP Timers
LLDP Timers control the frequency and duration of LLDP advertisements. These parameters include the Transmission Interval, Hold Time, and Re-initialization Delay.
Example: On a MikroTik switch, the Transmission Interval is set to 30 seconds, meaning LLDP advertisements are sent every 30 seconds. The Hold Time is set to 120 seconds, ensuring that neighbor information is retained for 120 seconds before being discarded.