Luxul AMS-1208P, Quick Setup Manual

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UNDERSTANDING SPANNING TREE
The„Spanning„Tree„Protocol„(STP)„is„a„network„protocol„that„ensures„a„loop-free„topology„for„any„bridged„Ethernet„local„
area„network.„The„basic„function„of„STP„is„to„prevent„bridge„loops„and„the„resulting„broadcast„radiation.„Spanning„tree„
also„allows„a„network„design„to„include„spare„(redundant)„links„to„provide„automatic„backup„paths„if„an„active„link„fails,„
without„the„danger„of„bridge„loops,„or„the„need„for„manual„enabling/disabling„of„these„backup„links.
As„the„name„suggests,„Spanning„Tree„creates„a„tree„within„a„network„of„connected„Ethernet„switches,„and„disables„those„
links„that„are„not„part„of„the„spanning„tree,„leaving„a„single„active„path„between„any„two„network„nodes.
Eliminating Loops
If„your„switches„are„connected„in„a„loop„without„STP,„each„switch„would„infinitely„duplicate„the„first„broadcast„packet„it„
received„because„there’s„nothing„to„prevent„a„loop.
STP„prevents„loops„by„blocking„one„or„more„of„the„links.„If„one„of„the„links„in„use„goes„down,„then„it„would„fail„over„to„a„
previously-blocked„link.„How„spanning„tree„chooses„which„link„to„use„depends„entirely„on„the„topology„that„it„can„see.
The„idea„behind„a„spanning„tree„topology„is„that„bridges„can„discover„a„subset„of„the„topology„that„is„loop-free:„that’s„
the„tree.„STP„also„makes„certain„there„is„enough„connectivity„to„reach„every„portion„of„the„network„by„spanning„the„
entire„LAN.
Spanning Tree Configuration
Bridges„will„perform„the„spanning„tree„algorithm„when„they„are„first„connected„to„the„network„or„whenever„there„is„a„
topology„change.
When„a„bridge„hears„a„“configuration„message,”„it„will„begin„its„disruptive„spanning„tree„algorithm.„This„starts„with„the„
election„of„a„“root„bridge”„through„which„all„data„will„flow.
Next,„each„bridge„determines„the„shortest„path„to„the„root„bridge„so„that„it„knows„how„to„get„to„the„“center.”„A„second„
election„happens„on„each„LAN,„and„it„elects„the„designated„bridge,„or„the„bridge„that’s„closest„to„the„root„bridge.„The„
designated„bridge„will„forward„packets„from„the„LAN„toward„the„root„bridge.
The„final„step„for„an„individual„bridge„is„to„select„a„root„port.„This„simply„means„“the„port„that„I„use„to„send„data„towards„
the„root„bridge.”
c
n
NOTE: cEverycsinglecportconcacbridgec(evencthosecconnectedctocendpoints)cwillcparticipatecincthecspanningctreecunlesscacportcisc
configuredcasc“ignore.”
A„newly-connected„bridge„will„send„a„reconfiguration„message,„and„other„connected„devices„will„comply.„All„traffic„is„
stopped„for„30-50„seconds„while„the„spanning„tree„is„calculated.
Spanning tree drawbacks
One„drawback„of„STP„is„that„even„though„there„may„be„many„physical„or„equal-cost„multiple„paths„through„your„
network„from„one„node„to„another,„all„your„traffic„will„flow„along„a„single„path„defined„by„a„spanning„tree.„The„benefit„
of„this„is„that„traffic„loops„are„avoided,„but„the„cost„of„restricting„traffic„to„a„unique„path„means„blocking„alternative,„and„
sometimes„more„direct,„paths.„That„means„that„your„full„potential„network„capacity„can„never„be„realized.