Lenovo Flex System Fabric CN4093 User Manual

174 CN4093 Application Guide for N/OS 8.4
Bridge Protocol Data Units
TocreateaSpanningTree,theswitch generatesaconfigurationBridgeProtocol
DataUnit(BPDU),whichitthenforwardsoutofitsports.Allswitchesinthe Layer
2networkparticipatingintheSpanningTreegatherinformationaboutother
switchesinthenetwork throughanexchangeofBPDUs.
Abridgesends
BPDUpacketsataconfigurableregularinterval(2secondsby
default).TheBPDUisusedtoestablishapath,muchlikeahellopacketinIP
routing.BPDUscontaininformationaboutthetransmittingbridgeanditsports,
includingbridgeMACaddresses,bridgepriority,portpriority,and pathcost.Ifthe
ports
aretagged,eachportsendsoutaspecialBPDUcontainingthetagged
information.
ThegenericactionofaswitchonreceivingaBPDUistocomp arethereceived
BPDUtoitsownBPDUthatitwilltransmit.IfthepriorityofthereceivedBPDUis
betterthanitsownpriority,it
willreplaceitsBPDUwiththereceivedBPDU.Then,
theswitchaddsitsownbridgeIDnumberandincrementsthepathcostofthe
BPDU.Theswitchusesthisinformationtoblockany necessaryports.
Note: IfSTPisgloballydisabled,BPDUsfromexternaldeviceswilltransitthe
switchtransparently.If
STPisgloballyenabled,forportswhereSTPisturnedoff,
inboundBPDUswillinsteadbediscarded.
Determining the Path for Forwarding BPDUs
Whendeterminingwhichporttouseforforwardingandwhichporttoblock,the
CN4093usesinformationintheBPDU,includ ingeachbridgeID.Atechnique
basedonthe“lowestrootcost”isthencomputedtodeterminethemostefficient
pathforforwarding.
Bridge Priority
ThebridgepriorityparametercontrolswhichbridgeonthenetworkistheSTG
rootbridge.Tomakeoneswitchbecometherootbridge,configurethebridge
prioritylowerthanallotherswitchesandbridgesonyournetwork.Thelowerthe
value,thehigherthebridgepriority.Usethefollowingcommandto
configurethe
bridgepriority:
CN 4093(config)# spanning-tree stp <1‐128> bridge priority <0‐65535>

Lenovo Flex System Fabric CN4093 Specifications

General

Brand	Lenovo
Model	Flex System Fabric CN4093
Category	Switch
Language	English