Specifications

How Do I Implement Neighbor Discovery?
October 15, 2008 Page 2 of 14
How Do I Implement Neighbor Discovery?
LLDP,EnterasysDiscoveryProtocol,andCiscoDiscoveryProtocolareenabledonEnterasys
devicesbydefault.Thoughallthreediscoveryprotocolscanrunsimultaneously,LLDPisthe
preferredprotocol.
Ifadevice,attachedtoaportthathasbeenenabledforneighbordiscovery,doesnotsupport
LLDPbutsupportsEnterasysDiscoveryProtocol
orCiscoDiscoveryProtocol,thenoneofthose
protocolsisusedinstead.
Understanding Neighbor Discovery
Asstatedpreviously,theneighbordiscoveryprotocolssupporttheLayer2processofnetwork
devicesadvertisingtheiridentitiesandcapabilitiesonaLANanddiscoveringthatinformation
abouttheirdirectlyconnectedneighbors.WhileEnterasysDiscoveryProtocolandCisco
DiscoveryProtocolarevendor‐specificprotocols,LLDPisanindustrystandard(IEEE802.1AB),

vendor‐neutralprotocol.
TheLLDP‐enableddeviceperiodicallyadvertisesinformationaboutitself(suchasmanagement
address,capabilities,media‐specificconfigurationinformation)inanLLDPDU(LinkLayer
DiscoveryProtocolDataUnit),whichissentinasingle802.3Ethernetframe(seeFigure 3onpage
6).AnLLDPDUconsistsofaset
ofTLV(type,length,andvalue)attributes.The information,
whichisextractedandtabula tedbyanLLDP‐enableddevice’speers,isrecordedinIEEE‐defined
managementinformationbase(MIB)modules,makingitpossiblefortheinformationtobe
accessedbyanetworkmanagementsystemusingamanagementprotocolsuchasSNMP.
The
informationisagedtoensurethatitiskeptuptodate.Portscanbeconfiguredtosendthis
information,receivethisinformation,orboth.
TheLLDPagentoperatesonlyinanadvertisingmode,andhencedoesnotsupportanymeansfor
solicitinginformationorkeepingstatebetweentwo
LLDPentities.
LLDPcanbeusedformanyadvancedfeaturesinaVoIPnetworkenvironment.Thesefeatures
includebasicconfiguration,networkpolicyconfiguration,locationidentification(includingfor
EmergencyCallService/E911),PoweroverEthernetmanagement,andinventorymanagement.
Tofulfilltheseneeds,thestandardprovidesextensionstoIEEE802.1ABthatarespecific
tothe
requirementsofmediaendpointdevicesinanIEEE802LAN.Interactionbehaviorbetweenthe
mediaendpointdevicesandtheLANinfrastructureelementsarealsodescribedwheretheyare
relevanttocorrectoperationormulti‐vendorinteroperability.Mediaendpointdevicesaddressed
include,butarenotlimitedto,IPphones,
IPvoice/mediagateways,IPmediaservers,andIP
communicationcontrollers.
Figure 1onpage3showsanexampleofLLDPcommunicationbetweendevices,doneviaLayer2
withLLDPDUpackets.ThecommunicationisonlybetweenLLDP‐enableddevices—the
informationisnotforwardedtootherdevices.