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What is LLDP? - Benefits of Link Layer Discovery Protocol

What is LLDP?


The link layer discovery protocol (LLDP) is an open and extendable part of the Internet protocol suite used in IEEE 802 to advertise a device’s identity and abilities, as well as other devices connected within the same network.





LLDP


Link Layer Discovery Protocol


LLDP is mainly used in wired Ethernet-connected devices to facilitate management of network resources and simplify networking tasks for administrators in a multi-vendor network. The protocol’s multi-vendor support enables network discovery of devices and management tools like Simple Network Management Protocol (SNMP) in a network made up of devices from different manufacturers. LLDP makes it unnecessary to use a larger number of proprietary protocols to support a multi-vendor network or, on the other hand, limit oneself to the hardware of a single vendor.

LLDP is also known as Station and Media Access Control Connectivity Discovery, as specified in IEEE 802.1AB. Similar proprietary protocols include Cisco Discovery Protocol (CDP), Extreme Discovery Protocol, Foundry Discovery Protocol (FDP), Microsoft's Link Layer Topology Discovery and Nortel Discovery Protocol (AKA SONMP).

On an interval schedule, an LLDP device sends its information in Ethernet frames. A frame starts with the required TLVs of Chassis ID, Port ID, and time-to-live (TTL). The frame contains the device’s destination MAC address as a multicast address that is not forwarded outside a network, assuming 802.1D compliance.



Benefits of LLDP


  • Simplifies the use of network management tools in a multi-vendor environment.
  • Accurate discovery of physical network topologies that simplifies troubleshooting within enterprise networks.
     
  • Enables discovery of stations in multi-vendor environments.
     
  • Provides device capability and supports optional system name and description, and management address.
     
  • Provides information that can be used to detect duplex and speed mismatches.
     
  • Discover devices with misconfigured or unreachable IP addresses.


LLDP operating modes

An LLDP agent operatesbelow three modes:

  • Transmit-only mode: The agent can only transmit the information about the capabilities and the current status of the local system.

  • Receive-only mode: The agent can only receive the information about the capabilities and the current status of the remote systems.

  • Transmit and Receive mode: The agent can transmit the local system capabilities and status information and receive the remote system’s capabilities and status information.


LLDP timers

  • Hold timer refers to the time or duration that an LLDP device maintains the neighbor information before aging it. The default is 120 seconds. If the timer expires and no LLPD packet was received, the neighbor information will be discarded.
  • Frequency timer pertains to the interval at which the network devices sends LLDP updates to neighboring devices. The default is 30 seconds.
  • Reinit timer is the delay time for LLDP to initialize on any interface. The default is 2 seconds.

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