Link Layer Discovery Protocol: Difference between revisions

Revision as of 17:24, 24 November 2021

Revision as of 19:51, 24 November 2021

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''Media Endpoint Discovery'' is an enhancement of LLDP, known as '''LLDP-MED''', that provides the following facilities:

* Auto-discovery of LAN policies (such as VLAN, [[802.1q|Layer 2 Priority]] and [[Differentiated services]] (Diffserv) settings) enabling [[plug and play]] networking.

* Device ___location discovery to allow the creation of ___location databases and, in the case of [[Voice over Internet Protocol]] (VoIP), [[Enhanced 911]] services.

* Extended and automated power management of [[Power over Ethernet]] (PoE) endpointsend points.

* Inventory management, allowing network administrators to track their network devices, and determine their characteristics (manufacturer, software and hardware versions, serial or asset number).

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== System Capability Codes ==

{| class="wiki tablewikitable"

|+

!Code

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LLDP information is sent by devices from each of their interfaces at a fixed interval, in the form of an [[Ethernet frame]]. Each frame contains one LLDP Data Unit (LLDPDU). Each LLDPDU is a sequence of [[type–length–value]] (TLV) structures.

The Ethernet frame used in LLDP typically has its destination [[MAC address]] set to a special [[multicast address]] that [[802.1D]]-compliant bridges do not forward. Other multicast and unicast destination addresses are permitted. The [[Ether TypeEtherType]] field is set to 0x88cc.

Each LLDP frame starts with the following mandatory TLVs: ''Chassis ID'', ''Port ID'', and ''Time-to-Live''. The mandatory TLVs are followed by any number of optional TLVs. The frame ends with a special TLV, named ''end of LLDPDU'' in which both the ''type'' and ''length'' fields are 0.

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Accordingly, an Ethernet frame containing an LLDPDU has the following structure:

{| class="wiki tablewikitable" style="text-align: center;"

|+ LLDP Ethernet frame structure

|-

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! Destination MAC

! Source MAC

! [[Ether typeEthertype]]

! Chassis ID TLV

! Port ID TLV