[2017年整理]网络设计 生成树协议.ppt

生成树协议STP(802.1D)协议原理RSTP(802.1W)协议原理MSTP(802.1S)协议原理STP的相关配置STP的保护措施1STP协议原理nSTP协议简介nBPDU报文结构n如何确定根桥n如何计算STP Path Costn如何确定端口角色n端口的状态迁移及定时器nMAC地址学习的生存周期nSTP的不足1STP协议简介lSTP都做了些什么？？？l1. STP在二层交换网络中选择一个根桥作为全部二层交换网络的逻辑中心（Root Bridge）l2. STP为全网中每一个参与STP运算的交换机计算到达根桥的最短距离（Path Cost)l3. 检测二层交换网络中存在的冗余链路，并把他们置于阻断/备份状态l4. 检测拓扑结构的变化并根据情况计算新的生成树1STP协议简介lSTP协议的结果是什么？è阻断了冗余链路，形成了以根桥为树根的树状拓扑结构RP – ROOT PORTSwitch A BID Switch A BID =0001 =0001 Switch C BID Switch C BID =1045 =1045 Switch B BID Switch B BID =0050=0050Switch D BID Switch D BID =0030=0030DP – DESIGNATED PORTDPRPDPRPDPDPAP – ALTERNATE PORTAP1STP协议简介l常用概念è根桥(Root Bridge)—桥ID最小的网桥。

其中桥ID是由网桥的优先级和网桥的MAC组成è根端口(Root Port)—这个端口到达根桥的路径是该端口所在网桥到达根桥的最佳路径全网中只有根桥是没有根端口的è指定端口(Designated Port)—每一个网段选择到根桥最近的网桥作为指定网桥，该网桥到这一网段的端口为指定端口è可选端口(Alternated Port)—既不是指定端口，也不是根端口的端口RP – ROOT PORTSwitch A Switch A BID =0001 BID =0001 Switch C Switch C BID =1045 BID =1045 Switch B Switch B BID =0050BID =0050 DP – DESIGNATED PORTDPRPDPRPDPDPAPAP Switch D Switch D BID =0030BID =0030 1BPDU报文结构（1）lSTP通过BPDU(Bridge Protocol Data Unit)报文来学习网络拓扑结构lBPDU报文的目标MAC地址为：01-80-C2-00-00-00.lBPDU报文在直连的两个网桥或多个网桥内交换，不能被转发。

没有运行STP协议的网桥将把BPDU报文当作普通业务报文转发BPDUBPDU Switch CSwitch CSwitch BSwitch BBPDUBPDU1BPDU报文结构（2）lDMA:目的MAC地址è目的地址是一个固定的桥的组播地址（0x0180c2000000）lSMA:源MAC地址è即发送该配置消息的桥MAC地址lL/T:帧长lLLC Header:固定的链路头lPayload:BPDU数据DMADMALLC HeaderLLC HeaderSMASMAL/TL/TPayloadPayload值值 域域占用字节占用字节协议协议IDID2 2协议版本协议版本BPDUBPDU类型类型标志位标志位根桥根桥IDID根路径开销根路径开销指定桥指定桥IDID指定端口指定端口IDIDMessage AgeMessage Age1 11 11 18 84 48 82 22 2Max AgeMax AgeHello TimeHello TimeForward DelayForward Delay2 22 22 21如何确定根桥（1）l根桥—BID（网桥ID）最小的网桥定为根桥lBID—网桥的优先级+网桥MAC。

l网桥的优先级为可配置，缺省值为32768l在缺省情况下，根桥将由MAC地址最小的网桥担任1如何确定根桥（2）Switch A BID =0001 Switch A BID =0001 Switch C BID =1045 Switch C BID =1045 Switch B BID =0050Switch B BID =0050I’m the Root Switch I’m the Root Switch I’m the Root Switch I’m the Root Switch Switch D BID =0030Switch D BID =0030I’m the Root Switch I’m the Root Switch I’m the Root Switch I’m the Root Switch 1如何确定根桥（3）Switch A BID =0001 Switch A BID =0001 Switch C BID =1045 Switch C BID =1045 Switch B BID =0050Switch B BID =0050I’m the Root Switch I’m the Root Switch I’m the Root Switch I’m the Root Switch Switch D BID =0030Switch D BID =0030I’m the Root Switch I’m the Root Switch BPDU: Root Switch= 1045BPDU: Root Switch= 1045BPDU:BPDU: Root Switch= 0001 Root Switch= 0001BPDU: Root Switch= 0030BPDU: Root Switch= 0030BPDU: Root Switch = 0050BPDU: Root Switch = 0050BPDU: Root Switch = 0030BPDU: Root Switch = 0030BPDU: Root Switch = 1045BPDU: Root Switch = 1045BPDU: Root Switch = 0050BPDU: Root Switch = 0050BPDU: Root Switch = 0001BPDU: Root Switch = 0001I’m the Root Switch I’m the Root Switch BPDU: Root Switch = 1045BPDU: Root Switch = 1045BPDU: Root Switch = 0050BPDU: Root Switch = 00501如何确定根桥（4）Switch A BID =0001 Switch A BID =0001 Switch C BID =1045 Switch C BID =1045 Switch B BID =0050Switch B BID =0050I’m the Root Switch I’m the Root Switch Root Switch =0001 Root Switch =0001 Switch D BID =0030Switch D BID =0030I’m the Root SwitchI’m the Root Switch Root Switch = 0001 Root Switch = 0001 1如何确定根桥（5）BPDU: Root Switch = 0001BPDU: Root Switch = 0001BPDU: Root Switch = 0001BPDU: Root Switch = 0001Switch A BID =0001 Switch A BID =0001 Switch C BID =1045 Switch C BID =1045 Switch B BID =0050Switch B BID =0050I’m the Root Switch I’m the Root Switch Root Switch =0001 Root Switch =0001 Switch D BID =0030Switch D BID =0030I’m the Root Switch I’m the Root Switch BPDU: Root Switch= 0001BPDU: Root Switch= 0001BPDU:BPDU: Root Switch= 0001 Root Switch= 0001BPDU: Root Switch= 0030BPDU: Root Switch= 0030BPDU: Root Switch = 0001BPDU: Root Switch = 0001BPDU: Root Switch = 0030BPDU: Root Switch = 0030BPDU: Root Switch = 0001BPDU: Root Switch = 0001BPDU: Root Switch = 0001BPDU: Root Switch = 0001BPDU: Root Switch = 0001BPDU: Root Switch = 0001Root Switch = 0001 Root Switch = 0001 1如何确定根桥（6）Switch A BID =0001 Switch A BID =0001 Switch C BID =1045 Switch C BID =1045 Switch B BID =0050Switch B BID =0050I’m the Root Switch I’m the Root Switch Root Switch =0001 Root Switch =0001 Switch D BID =0030Switch D BID =0030Root Switch = 0001Root Switch = 0001Root Switch = 0001 Root Switch = 0001 1如何计算STP Path CostlPath Cost的两种定义标准SpeedLink type802.1D cost802.1t cost10MbpsHalf Duplex1002,000,000Full Duplex951,999,999Aggregated link901,000,000100MbpsHalf Duplex19200,000Full Duplex18199,999Aggregated Link15100,0001000MbpsFull Duplex420,000Aggregated Link310,0001如何决定BPDU配置消息的优劣l比较RID(Root Bridge ID)，确定网络同步。

lRID相同，比较Path Cost（到根桥距离），越小越优lRID/Path Cost相同，比较指定桥的BID (Designated Bridge ID)，越小越优lRID/Path Cost/DBID相同，比较指定端口的ID (Designated Port ID)，越小越优哪边更优？BPDUBPDU1BPDU交换过程Switch A BID =0001 Switch A BID =0001 Switch C BID =1045 Switch C BID =1045 Switch B BID =0050Switch B BID =0050Switch D BID =0030Switch D BID =00302 Gig Aggregated2 Gig AggregatedPath cost = Path cost = 3 31 Gig1 GigPath Cost = Path Cost = 4 41 Gig1 GigPath Cost = Path Cost 。