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1、生成樹協(xié)議SpanningTreeProtocolObjectivesRedundanttopologiesSpanningTreeProtocol冗余(Redundancy)冗余網(wǎng)絡拓撲確保網(wǎng)絡持續(xù)工作,避免單點故障Redundantnetworkingtopologiesaredesignedtoensurethatnetworkscontinuetofunctioninthepresenceofsinglepointsoffailure.冗余拓撲(RedundantTopologies)冗余拓撲(RedundantTopologies)1.冗余拓撲的目標
2、是為了避免網(wǎng)絡出現(xiàn)單點故障Agoalofredundanttopologiesistoeliminatenetworkoutagescausedbyasinglepointoffailure.2.所有的網(wǎng)絡需要冗余來提高可靠性Allnetworksneedredundancyforenhancedreliability.簡單的冗余交換拓撲(SimpleRedundantSwitchedTopology)簡單的冗余交換拓撲(SimpleRedundantSwitchedTopology)1.冗余拓撲消除了單點故障Redundanttopologieselim
3、inatesinglepointsoffailure.2.交換機對不知道地址的幀進行泛洪Switcheswillfloodframesforunknowndestinations.3.交換機對廣播和組播也進行泛洪。Broadcastsandmulticastsarealsoflooded.4.冗余交換拓撲或許會帶來廣播風暴、多幀拷貝以及MAC地址表不穩(wěn)定的問題Aredundantswitchedtopologymaycausebroadcaststorms,multipleframecopies,andMACaddresstableinstabilitypro
4、blems.廣播風暴(BroadcastStorm)多幀傳輸(MultipleFrameTransmissions)在冗余交換網(wǎng)絡中,對終端設備來講,收到多幀相同數(shù)據(jù)是可能的。Inaredundantswitchednetworkitispossibleforanenddevicetoreceivemultipleframes.創(chuàng)建邏輯無環(huán)路拓撲(Creatingalogicalloopfreetopology)1.冗余增加了可靠性,但是同時將物理環(huán)路帶進網(wǎng)絡。Reliabilityisincreasedbyredundancy.redundancyconn
5、ectionsintroducephysicalloopsintothenetwork.2.解決辦法就是創(chuàng)建邏輯無環(huán)路拓撲,同時保留物理環(huán)存在Thesolutionistoallowphysicalloops,butcreatealoopfreelogicaltopology.3.無環(huán)路拓撲稱為樹,并且是可擴展的樹。Theloopfreelogicaltopologycreatediscalledatree.Itisaspanningtreebecausealldevicesinthenetworkarereachableorspanned.4.創(chuàng)建無環(huán)路拓撲
6、的算法稱為生成樹算法。Thealgorithmusedtocreatethisloopfreelogicaltopologyisthespanning-treealgorithm.STP術語(STPTerms)1.橋ID(BridgeID)2.開銷(Cost)3.橋協(xié)議數(shù)據(jù)單元(BPDU)橋ID(BridgeID)1.BID用來識別每一個交換機/網(wǎng)橋。2.BID用來確定網(wǎng)絡的中心,在STP中稱為根橋。3.優(yōu)先級默認為32768TheBIDconsistsofabridgeprioritythatdefaultsto32768開銷(Cost)最短路徑是cost累
7、加,而cost是基于鏈路的速率的。Shortestpathisbasedoncumulativelinkcosts.Linkcostsarebasedonthespeedofthelink.橋協(xié)議數(shù)據(jù)單元(BPDU)1.交換機發(fā)送的創(chuàng)建邏輯無環(huán)路的數(shù)據(jù)包稱為BPDUThemessagethataswitchsends,allowingtheformationofaloopfreelogicaltopology,iscalledaBridgeProtocolDataUnit(BPDU).2.BPDU在阻塞的接口上也可以接收,這確保如果鏈路或設備出現(xiàn)問題,新的生成
8、樹會被計算BPDUscontinuet