Specifications

Link Aggregation Overview
December 02, 2010 Page 3 of 23
Link Aggregation Overview
Thissectionprovidesanoverviewoflinkaggregationconfiguration.
LACP Operation
InordertoallowLACPtodeterminewhetherasetoflinksconnecttothesamedevice,andto
determinewhetherthoselinksarecompatiblefromthepointofviewofaggregation,itis
necessarytobeabletoestablish:
•Agloballyuniqueidentifierforeachdevicethatparticipatesinli nk
aggregation.
•Ameansofidentifyingthesetofcapabilitiesassociatedwitheachportandwitheach
aggregator,asunderstoodbyagivendevice.
•AmeansofidentifyingaLAGanditsassociatedaggregator.
Foreachaggregatableportinthedevice,LACP:
• Maintainsconfigurationinformation(reflectingtheinherentpropertiesoftheindividuallinks
as
wellasthoseestablishedbynetworkadministration)tocontrolaggregation.
•Exchangesconfigurat ioninformationwithotherdevicestoallocatethelinktoaLAG.
• AttachestheporttotheaggregatorusedbytheLAG,anddetachestheportfromthe
aggregatorwhenitisnolongerusedbytheLAG.
•Usesinformationfrom
thepartnerdevice’slinkaggregationcontrolentitytodecidewhether
toaggregateports.
TheoperationofLACPinvolvesthefollowingactivities:
•Checkingthatcandidatelinkscanactuallybeaggregated.
• ControllingtheadditionofalinktoaLAGandthe creationofthegroupifnecessary.
• Monitoringthestatusofaggregatedlinks
toensurethattheaggregationisstillvalid.
•RemovingalinkfromaLAGifitsmembershipisnolongervalid,andremovingthegroupifit
nolongerhasanymemberlinks.
How a LAG Forms
LAGsformautomaticallywithLACPenabledonthedevice.Therearefourcriteriaforforminga
LAG.Bothactorandpartnerportsmust:
1. Operateinfullduplexmode.
2. HavematchinglocalLAGandphysicalportadminkeysforthedevicecontrollingLAG
formation.
3. OperateinparallelinthataLAGcanhave
onlytwodevicesassociatedwithit.
4. ConsistoftwoormorephysicalactortopartnerportpairingsunlessthesingleportLAG
featureisenabled.
Note: A given link is allocated to, at most, one LAG at a time. The allocation mechanism attempts to
maximize aggregation, subject to management controls.