LLDP (Link Layer Discovery Protocol)

how-lldp-works

LLDP (Link Layer Discovery Protocol)

LLDP (Link Layer Discovery Protocol) is a Standard Neighbour Discovery Protocol that is used by all vendors. Like all other Neighbour Discovery Protocols, LLDP works on Layer 2 (Data-link Layer). By using LLDP, directly connected neighbours are discovered.

To discover a neighbour device, LLDP must be enabled both on the discovering device and the discovered device.

With LLDP, ethernet devices advertise their identification, configuration etc. to the directly connected LLDP enabled devices.

As we mentioned before, there are many neighbour discovery protocol and they are vendor specific. To build a one common protocol, LLDP (Link Layer Discovery Protocol) is developed and it is used on all vendors’ devices. LLDP is independent from the brand of the device used.

Hello Timer is 30 seconds for LLDP and Dead Timer is 120 seconds.

LLDP has an extension version that provide end devices’s discovery. With this extention, LLDP discovers the endpoint PCs, IP Phone. This extended version of LLDP is LLDP-MED (Media Endpoint Discovery). We will talk about LLDP-MED, in the following articles. Here, in this article, our main focus is LLDP.

How LLDP Works?

As we have mentioned above, LLDP must be enabled on the devices firstly. After that, LLDP enabled devices send LLDP advertisements each other and the device information are stored in the MIB databases on the devices. Any Network Management Software gets this data by SNMP (Simple Network Management Protocol). And with this data, it builds the network map.

How LLDP Works, LLDP Mechanism
 

How LLDP Works, LLDP Mechanism
When the device receive a new information about the LLDP neightbour device, it stores this neighbour information in the MIB (Management Information Base). There are two MIB. LLDP Local System MIB and LLDP Remote System MIB. LLDP Local System MIB stores the information about the local device, the device’s own information. LLDP Remote System MIB stores the information gathered from the LLDP neightbour devices.

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Lesson tags: CDP, neighbor discovery, lldp
Back to: CCNA > Neighbor Discovery

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