Specifications

Link Aggregation Overview
December 02, 2010 Page 5 of 23
•Becauseports1and2forboththeactorandpartneroperateinparallelwitheachother,rule3
issatisfiedfortheseports.
•Rule4issatisfied,regardlessofwhethersingleportLAGsareenabled,becausetherearetwo
aggregatableportpairingsbetweendevicesAandB.
Forthesereasons,
LAG1(lag.0.1)isformedusingactorandpartnerports1and2.
Actorports4‐8ondeviceAdirectlyconnecttopartnerports4‐8ondeviceC:
•Becauseallportsareoperatinginfull‐duplexmode,ruleoneissatisfiedforallfiveports.
• Investigatingportadminkeys,
weseethatports4‐6ondeviceAaresetto100(thesame
settingasallLAGportsonthedevice),whileports7and8ondeviceAaresetto300and400,
respectively.BecauseportadminkeysforallLAGsandthephysicalports4‐
6arethesame,
physicalports4‐6satisfyrule2.Becausetheadminkeysettingsforphysicalports7and8do
notagreewithanyLAGadminkeysettingonthedevice,ports7and8cannotbepartofany
LAG.
•Becauseports4‐6forboth
theactorandpartneroperateinparallelwitheachother,rule3is
satisfiedfortheseports.
•Rule4issatisfied,regardlessofwhethersingleportLAGisenabled,becausetherearethree
aggregatableportpairingsbetweendevicesAandC.
Forthesereasons,LAG2isformedusingactor
andpartnerports4‐6.
Attached Ports
OnceaLAGisformed,twostepsmusttakeplacebeforetrafficcanpassovertheLAG:
•Thedevicethatwillchoosewhichportstomovetotheattachedstatemustbeidentified
•TheprocessofmovingthechosenportstotheLACPattached statemusttakeplace
AsystemID,made
upofthedeviceMACaddressandthesystempriority,isassociatedwitheach
device.ThedevicewiththelowersystempriorityisinchargeofselectingtheLAGmembersto
movetotheattachedstate.Ifasystemprioritytieoccurs,thesystemwiththelowerMACaddress
valuebreaks
thetie.
OnlyLAGmemberswiththesameportspeedcanbemovedtotheattachedstate.Inacasewhere
multiplespeedsarepresentinaLAG,theLAGmemberwiththelowestportpriorityonthedevice
incharge,aswellasallothermemberswiththesameport
speedasthememberwiththelowest
portpriority,areselectedandmovedtotheattachedstate.UsingLAG2inFigure 1onpage 4asan
example,iftheLAG2memberportprioritiesaresetasshowninTable 1onpage 5,ports4and5
aremovedtotheattachedstate.
Note: Port speed is not a consideration in the forming phase for LAGs. LAG 2 contains 100Mbps
and 1Gb port members.
Table 1 LAG2 Port Priority Assignments
Port Number Port Speed Port Priority
4 100Mbps 200
5 100Mbps 300
61Gb 300