翻译-字3000计算机应用文章．UnderstandingRapidSpanningTreeProtocol(802.1w)IntroductionThe802.1DSpanningTreeProtocol(STP)standardwasdesignedatatimewhentherecoveryofconnectivityafteranoutagewithinaminuteorsowasconsideredadequateperformance.WithwithroutedtheadventofLayer3switchinginLANenvironments,bridgingnowcompetes竞争solutionswhereprotocols,suchasOpenShortestPathFirst(OSPF)andEnhancedInteriorGatewayRoutingProtocol(EIGRP),areabletoprovideanalternatepathinlesstime.生成树协议标准是为了当一次连接中断后在一分钟快速快速恢复而设计优异的性能，随着三层交802.1D换机在局域网环境的推广，桥接技术因为能在较短时间内提供可替代路径，现在正和路由协议方案竞争起来，例如开放最短路径优先和增强内部网关协议，BackboneCiscoenhancedtheoriginal802.1DspecificationwithfeaturessuchasUplinkFast,,andPortFasttospeeduptheconvergencetimeofabridgednetwork.ThedrawbackisthatFastthesemechanismsareproprietaryandneedadditionalconfiguration.使收敛的速度加快，802.1D功能，思科通过uplinkBackboneFast和PortFast这些属性增强了原始的它的缺点是这些机制是专有的并需要额外配置RapidSpanningTreeProtocol(RSTP;IEEE802.1w)canbeseenasanevolutionofthe802.1Dstandardmorethanarevolution.The802.1Dterminologyremainsprimarilythesame.Mostparametershavebeenleftunchangedsousersfamiliarwith802.1Dcanrapidlyconfigurethenewprotocolcomfortably.Inmostcases,RSTPperformsbetterthanproprietaryextensionsofCiscowithoutanyadditionalconfiguration.802.1wcanalsorevertbackto802.1Dinordertointeroperatewithlegacybridgesonaper-portbasis.Thisdropsthebenefitsitintroduces.快速生成树协议可以被看成是标注的进化而不是革命。在中的术语仍然主要是相同的。大802.1802,1D多数参数都被保留不变，因此熟悉802.1D配置的用户可以迅速地与方便的配置新协议。大多数情况下，RSTP无需额外的配置表现的比思科特有的特性更好。当然802.1w也兼容802.1d这丢弃了它自己的优点。Theneweditionofthe802.1Dstandard,IEEE802.1D-2004,incorporatesIEEE802.1t-2001andIEEE802.1wstandards.新版本的802.1D标准IEEE802.1D-2004，兼容IEEE802.1t-2001和802.1w标准ThisdocumentprovidesinformationabouttheenhancementsaddedbyRSTPtotheprevious802.1Dstandard.这篇文档通过RSTP展示了比以前的802.1D的增强的特性信息。NewPortStatesandPortRoles新的端口状态和端口角色The802.1Disdefinedinthesefivedifferentportstates:802.1D定义了五种不同的端口状态?Disabled关闭?Listening监听?Learning学习?Blocking阻塞?Forwarding转发Thestateoftheportismixed,whetheritblocksorforwardstraffic,andtheroleitplaysintheactivetopology(rootport,designatedport,andsoon).Forexample,fromanoperationalpointofview,thereisnodifferencebetweenaportintheblockingstateandaportinthelisteningstate.BothdiscardframesanddonotlearnMACaddresses.Therealdifferenceliesintherolethespanningtreeassignstotheport.Itcansafelybeassumedthatalisteningportiseitherdesignatedorrootandisonitswaytotheforwardingstate.Unfortunately,onceintheforwardingstate,thereisnowaytoinferfromtheportstatewhethertheportisrootordesignated.Thiscontributestodemonstratethefailureofthisstate-basedterminology.RSTPdecouplestheroleandthestateofaporttoaddressthisissue.无论这些端口是阻塞还是转发流量的，端口的状态是混合的，并且它们在活动的拓扑变化中扮演着角色（例如根端口指定端口等等）。举个例子来说，从动态的观点来看，一个端口处于阻塞还是监听的状态并没有太大的差异，它们都丢弃帧并且不学习MAC地址。它们真正的不同点在于生成树分配给端口的角色。通常把监听状态的端口假设成指定端口或根端口是可行的，并且它中在变成转发状态，不幸的是，一旦变成转发状态，...