Zte ZXR10 5900E Series - STP Configuration Examples

Chapter5STPConguration
Note:
BridgesinanMSTareamushhavesameMSTcongID.T wo
bridgeswithsameMSTcongIDareprobablyindifferentMST
area.Forexample,iftwobridgeswiththesameMSTcong
IDareconnectedthroughtheLANofanotherMSTarea,they
shouldbelongtodifferentMSTarea.
MSTareamayhavedifferentspanningtreestructures:Inter-
nalSpanningTree(IST),MST1,MST2andMSTn.EachMSTi
canberegardedasanMSTI.Thebridgeforwardstheframe
withthedesignatedVIDbasedonthepathtowhichtheVID
corresponds.ThemappingbetweenVIDandMSTIisshown
bytheMSTCongID.ThespanningtreestructureofMSTIis
decidedbypriorityparametersconguredbythesystem.
3.MSTInstance
MSTbridgemustsupporttwokindsofinstancesthatisIST
instanceandmultipleMSTinstances.Bydefault,ISTrunsin
anarea.AlltheVLANsareconguredtotheISTbydefault.
ISTconnectsalltheswitchesinthearea.ISTisresponsible
forcommunicationwithotherMSTareasandSSTareasout-
sidethearea.MSTinstancedoesnotsendtheBPDUpacket
independently.Spanningtreeinformationisincludedinthe
M-record,andtransmittedaspartoftheISTBPDUinsidethe
area.
4.CIST
internalISTandexternalCSTofeachMSTareajointlycon-
stituteCommonandInternalSpanningTree(CIST).Itmeans
thatCISTissameasISTinsidetheMSTarea,andCSToutside
theMSTarea.
5.ISTRegionRoot
EachMSTareahasanISTRegionRootswitchwhichhasmin-
imumoverheadfromtheCSTRootpath.WhenCISTRootis
inacertainMSTarea,theCISTRootistheISTRegionRoot
ofthisMSTarea.AftertheISTRegionRootisselected,other
portstowardstheCISTRootintheareawillbeblocked.
6.MSTBPDU
MSTIinsidetheMSTareadoesnotcommunicatewiththeout-
side,whiletheISTexchangesBPDUpacketswiththeoutside.
InsidetheareaMSTIdoesnotsendBPDUpacketsindepen-
dently.MSTBPDUpacketsaresentbytheISTincludesMSTI
information.MSTIusesaagtoshowthereisneedtosend
theMSTBPDUpacket.ISTisresponsibleforsendingpackets.
AllMSTIsthatneedtosendBPDUpacketsplacetheirinforma-
tionintheM-recordstructurewhichissentaspartoftheIST
BPDU.
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