Link Layer Discovery Protocol: Difference between revisions

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{{short description|Protocol used by network devices for advertising their identity}}

{{Redirect|LLDP|the lyingleft lateral decubitus position|DecubitusLying (position)}}

{{IPstack}}

{{Internet protocol suite|link=LLDP}}

The '''Link Layer Discovery Protocol''' ('''LLDP''') is a vendor-neutral [[link layer]] protocol used by network devices for advertising their identity, capabilities, and neighbors on an [[IEEE 802]] local area network, principally [[wired Ethernet]].<ref>{{cite web

The '''Link Layer Discovery Protocol''' ('''LLDP''') is a vendor-neutral [[link layer]] protocol used by [[network devicesdevice]]s for advertising their identity, capabilities, and neighbors on ana [[IEEElocal 802area network]] localbased areaon network[[IEEE 802]] technology, principally [[wired Ethernet]].<ref>{{cite web

|title=802.1AB-REV - Station and Media Access Control Connectivity Discovery

|url=http://www.ieee802.org/1/pages/802.1AB-rev.html

|publisher=IEEE

|accessdateaccess-date=2009-10-17

}}</ref> The protocol is formally referred to by the IEEE as ''Station and Media Access Control Connectivity Discovery'' specified in '''IEEE 802.1AB''' andwith additional support in '''IEEE 802.3 section 6 clause 79'''.<ref>{{cite web|url=https://standards.ieee.org/standardieee/802_1AB-2009-Cor2-2015802.html1AB/6047/|title=IEEE standard 802.1AB-20092016 - IEEE Standard for Local and metropolitan area networks - Station and Media Access Control (Cor2Connectivity 2015)Discovery}}</ref>

LLDP performs functions similar to several [[proprietary protocol]]s, such as [[Cisco Discovery Protocol]], [[Foundry Discovery Protocol]], [[Nortel Discovery Protocol]] and [[Link Layer Topology Discovery]].

==Information gathered==

Information gathered with LLDP can be stored in the device [[Managementmanagement information base|management information database]] (MIB) and queried with the [[Simple Network Management Protocol]] (SNMP) as specified in RFC{{IETF RFC|2922}}. The topology of an LLDP-enabled network can be discovered by ''crawling'' the hosts and querying this database. Information that may be retrieved include:

* System name and description

* [[Port (computer networking)|Port]] name and description

* [[VLAN]] name

* IP management address

* System capabilities ([[Network switch|switching]], [[routing]], etc.)

* [[Medium access control|MAC]]/[[PHY]] information

* [[Power over Ethernet|MDI power]]

* [[Link aggregation]]

==Applications==

The Link Layer Discovery Protocol may be used as a component in [[network management]] and [[network monitoring]] applications.

{{expand section|date=December 2018}}

The Link Layer Discovery Protocol may be used as a component in network management and monitoring applications.

One such example is its use in [[data center bridging]] requirements. The '''{{visible anchor|'''Data Center Bridging Capabilities Exchange Protocol}}'''}} (DCBX) is a discovery and capability exchange protocol that is used for conveying capabilities and configuration of the above features between neighbors to ensure consistent configuration across the network.<ref>{{cite web

|title=DCB Capabilities Exchange Protocol Base Specification, Rev 1.01

|url=http://www.ieee802.org/1/files/public/docs2008/az-wadekar-dcbx-capability-exchange-discovery-protocol-1108-v1.01.pdf

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}}</ref>

LLDP is used to advertise [[power over Ethernet]] capabilities and requirements and negotiate power delivery.

===Media endpoint discovery extension {{anchor|LLPD-MED}} ===

''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 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) end pointsendpoints.

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

The LLDP-MED protocol extension was formally approved and published as the standard ANSI/TIA-1057 by the [[Telecommunications Industry Association]] (TIA) in April 2006.<ref name="tia1057">{{cite web

| url=http://www.tiaonline.org/standards/technology/voip/documents/ANSI-TIA-1057_final_for_publication.pdf

| title=ANSI/TIA-1057 standard

| archive-url = https://web.archive.org/web/20101008234510/https://tiaonline.org/standards/technology/voip/documents/ANSI-TIA-1057_final_for_publication.pdf

| archive-date = 2010-10-08

}}</ref>

== System Capability Codes ==

{| class="wikitable"

|+

!Code

!Capability

|-

|B

|Bridge (Switch)

|-

|C

|DOCSIS Cable Device

|-

|O

|Other

|-

|P

|Repeater

|-

|R

|Router

|-

|S

|Station

|-

|T

|Telephone

|-

|W

|WLAN Access Point

|}

==Frame structure==

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-valuetype–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.<ref group=note>IEEE 802.1AB-2009 suggests three such addresses, 01:80:c2:00:00:0e, 01:80:c2:00:00:03 and 01:80:c2:00:00:00.</ref> Other multicast and unicast destination addresses are permitted. The [[EtherType]] 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 optionally ends with a special TLV, named ''end of LLDPDU'' in which both the ''type'' and ''length'' fields are 0.<ref>IEEE 802.1AB-2016 chapter 8.4</ref>

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

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! Time to live TLV

! Optional TLVs

! Optional End of LLDPDU TLV

! [[Frame check sequence]]

|-

|

| align="left" | {{MACaddr|01:80:c2:00:00:0e}},&nbsp;or<br /> {{MACaddr|01:80:c2:00:00:03}},&nbsp;or<br /> {{MACaddr|01:80:c2:00:00:00}}

| Station's address

| 0x88CC

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{| class="wikitable"

|+ TLV type values<ref>IEEE 802.1AB ''8.4 Basic TLV Format''</ref>

! TLV type !! TLV name !! Usage in LLDPPDULLDPDU

|-

| 0 || End of LLDPDU || MandatoryOptional

|-

| 1 || Chassis ID || Mandatory

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|}

According to IEEE Std 802.1AB, §9.6.1.3, "The Organizationally Unique Identifier shall contain the organization's OUI as defined in IEEE Std 802-2001." Each organization is responsible for managing theirits subtypes.

==Media endpoint discovery extension {{anchor|LLPD-MED}} ==

''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 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) end points.

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

The LLDP-MED protocol extension was formally approved and published as the standard ANSI/TIA-1057 by the [[Telecommunications Industry Association]] (TIA) in April 2006.<ref name="tia1057">{{cite web

| url=http://www.tiaonline.org/standards/technology/voip/documents/ANSI-TIA-1057_final_for_publication.pdf

| title=ANSI/TIA-1057 standard

| format=PDF

}}</ref>

==See also==

* [[OpenLLDP]]

==Notes==

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*[https://www.eetimes.com/document.asp?doc_id=1272069 Tutorial on the Link Layer Discovery Protocol] on [[EE Times]]

* [http://www.ieee802.org/1/pages/802.1ab.html 802.1AB - Station and Media Access Control Connectivity Discovery] on [[IEEE 802.1]]

*[https://wikigitlab.com/wireshark.org/wireshark/-/wikis/LinkLayerDiscoveryProtocol Link Layer Discovery Protocol] on The [[Wireshark]] Wiki

[[Category:Computer networks]]

[[Category:Device discovery protocols]]

[[Category:Ethernet standards]]

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[[Category:Link protocols]]

[[Category:Logical link control]]

[[Category:Network protocols]]