Specifications

Why Would I Use Link Aggregation in My Network
December 02, 2010 Page 2 of 23
Why Would I Use Link Aggregation in My Network
Theconceptofgroupingmultipleportsintoasinglelinkisnotanewidea.Cabletronʹs
SmartTrunk,CiscoʹsInterSwitchLinktrunking,andAdaptecʹsDuralinkarepreviousexamples.
Theproblemwiththeseoldermethods,fromthenetworkadministratorspointofview,isthat
theyareproprietary.Administratorswho
wantedtoimplementfasterlogicallinksfacedmajor
problemsiftheyalsowanted,orneeded,touseadifferentbrandofnetworkinghardware.Link
aggregationisstandardsbasedallowingforinteroperabilitybetweenmultiplevendorsinthe
network.
Olderimplementationsrequiredmanualconfiguration.WithLACP,ifasetoflinkscan
aggregate,
theywillaggregate.LACP’sabilitytoautomaticallyaggregatelinksrepresentsatimesaverforthe
networkadministratorwhowillnotberequiredtomanuallyconfiguretheaggregates.However,
manualoverridesareprovidedforwhentheadministratorneedstocustomize.Linkaggregation
alsoprovidesforrapidconfigurationandreconfigurationwhenthereare
changesinthephysical
connections.Linkaggregationwillautomaticallyandquicklyconvergethenewconfiguration.
Thisconvergencetypicallyoccursinonesecondorless.
Linkaggregationisacosteffectivewaytoimplementincreasedbandwidth.Amajorbenefitof
linkaggregationistheabilitytoincrementallyaddbandwidthinalinear
fashion.Withoutlink
aggregation,ifthereisaneedtoincreasethebandwidthfora100Mbpspipe,theonlychoiceisan
exponentialupgradetoa1000Mbpspipe.Ifthereisaneedfora300Mb pspipe,aggregatingthree
100Mbpsportsisbothlessexpensive,becauseaforklifthardwareupgrade
isavoided,andmakes
formoreefficientuseofthesystemportsthatarealreadyavailable.
Thephysicallinkswithintheaggregatecanserveasredundantbackupstooneanother.Sinceonly
asingleMACaddressrepresentingtheentireaggregateispresentedtotheMACclient,thefailure
ofanylink
withintheaggregateistransparent.Failoverishandledwithinthelinkaggregation
sublayer.
How Can I Implement Link Aggregation
Toimplementlinkaggregation:
•EnableLACPonthenetworkdevice
• Optionallysetanon‐defaultsystempriorityforthedevice
• Optionallychangetheadministrativelyassignedkeyforeachportonthedevice
• OptionallyenablesingleportLAGsonthedevice
•EnableLACPportstateonS‐Series,B5,andC5platforms
• OptionallychangeLAG
parametersoneachport
• OptionallychangehowflowswillbehavewhenchangestakeplacetotheLAG
• OptionallychangetheloadbalancingbehaviorforflowsovertheLAG
• OptionallyassignstaticportstoaLAGwhenthepartnerdeviceonlysupportsanon‐LACP
methodofaggregation