生成樹協(xié)議原理與應(yīng)用

第1頁生成樹協(xié)議原理與應(yīng)用第2頁生成樹綜述生成樹協(xié)議的產(chǎn)生背景LAN1LAN2存在單點故障冗余的設(shè)計又會帶來環(huán)路,導(dǎo)致廣播風(fēng)暴第3頁生成樹綜述生成樹協(xié)議的分類生成樹協(xié)議的分類，按照產(chǎn)生的時間先后順序為STP、RSTP、MSTP生成樹協(xié)議所遵循的IEEE標(biāo)準(zhǔn)三種生成樹所遵循的IEEE標(biāo)準(zhǔn)分別為STP-IEEE802.3d，RSTP-IEEE802.3W，MSTP-IEEE802.3S第4頁STP概述STP是怎樣的一個協(xié)議呢?通過阻斷冗余鏈路將一個有環(huán)路的橋接網(wǎng)絡(luò)修剪成一個無環(huán)路的樹型拓?fù)浣Y(jié)構(gòu),這樣既解決了環(huán)路問題，又能在某條活動(active)的鏈路斷開時,通過激活被阻斷的冗余鏈路重新修剪拓?fù)浣Y(jié)構(gòu)以恢復(fù)網(wǎng)絡(luò)的連通.

LAN1LAN2該鏈路處于阻塞狀態(tài)該鏈路重新被激活第5頁STP工作原理基本思想:在網(wǎng)橋之間傳遞配置消息(BPDU),網(wǎng)橋利用收到的配置消息做以下工作:從網(wǎng)絡(luò)中的所有網(wǎng)橋中,選出一個作為根網(wǎng)橋(root)計算本網(wǎng)橋到根網(wǎng)橋的最短路徑網(wǎng)橋選擇一個根端口,該端口給出的路徑是此網(wǎng)橋到根橋的最短路徑選擇除根端口之外的轉(zhuǎn)發(fā)端口（指定端口）第6頁配置消息介紹配置消息也被稱做橋協(xié)議數(shù)據(jù)單元(BPDU)主要內(nèi)容包括:根網(wǎng)橋的Identifier(RootID)從本網(wǎng)橋到根網(wǎng)橋的最小路徑開銷(RootPathCost)發(fā)送該配置消息的網(wǎng)橋的Identifier發(fā)送該配置消息的網(wǎng)橋的指定端口的Identifier即(RootID,RootPathCost,BridgeID,PortID)第7頁配置消息格式字節(jié)數(shù)

域2Protocolid1Version1Messagetype1Flags8Rootid4RootPathCost8Bridgeid2Portid2Messageage2Maximumtime2Hellotime2ForwarddelayDMASMAL/TLLCHeaderPayloadDMA:目的MAC地址配置消息的目的地址是一個固定的組播地址(0x0180c2000000)SMA:源MAC地址即發(fā)送該配置消息的橋MAC地址L/T:幀長LLCHeader:配置消息固定的鏈路頭Payload:BPDU數(shù)據(jù)第8頁如何利用配置消息工作?主要工作有:選擇根橋RootID:最優(yōu)配置消息的RootID計算到根橋的最短路徑開銷RootPathCost:如果自己是根橋,則最短路徑開銷為0,否則為它所收到的最優(yōu)配置消息的RootPathCost與收到該配置消息的端口開銷之和.更新配置消息:更新RootID、RootPathCost等參數(shù)，交換機繼續(xù)廣播發(fā)送新配置信息。選擇根端口RootPort:如果自己是根橋,則根端口為0,否則根端口為收到最優(yōu)配置消息的那個端口選擇指定端口:包括在生成樹上處于轉(zhuǎn)發(fā)狀態(tài)的其他端口從指定端口發(fā)送更優(yōu)的配置消息第9頁如何確定最優(yōu)的配置消息配置消息的優(yōu)先級比較原則:假定有兩條配置消息C1和C2,則:如果C1的RootID小于C2的RootID,則C1優(yōu)于C2如果C1和C2的RootID相同,但C1的RootPathCost小于C2,則C1優(yōu)于C2如果C1和C2的RootID和RootPathCost相同,但C1的發(fā)送網(wǎng)橋ID小于C2,則C1優(yōu)于C2如果C1和C2的RootID、RootPathCost和發(fā)送網(wǎng)橋ID相同,但C1的發(fā)送網(wǎng)橋的PortID小于C2,則C1優(yōu)于C2第10頁配置消息處理示例一根據(jù)收到的配置消息,選舉了根橋（橋ID=23）,更新自己的配置消息為(23,15,50)接收到最優(yōu)配置消息的端口為根端口，選擇Port4為根端口用自己更新后的配置消息與從Port1、Port2、Port3上收到的配置消息比較，比較結(jié)果:自己的配置消息優(yōu)于從Port1、Port2收到的配置消息，從Port3上收到的配置消息優(yōu)于自己的配置消息，因此將Port1、Port2置為指定端口,將Port3置為阻塞端口從Port1和Port2發(fā)送新的配置消息(23,15,50)port1port2port3port4BridgeID=5032，0，3223，18，2023，14，8023，14，70BlockingRootDesignateDesignate23，15，5023，15，50第11頁鏈路故障處理示例Port4的配置消息生存期(MessageAge達(dá)到MaxAge)超時了，則拋棄該配置信息，重新進行生成樹計算，選擇Port3為新的根端口，而該網(wǎng)橋的配置信息沒有發(fā)生變化，仍為(23,15,50)port1port2port3port4BridgeID=5032，0，3223，18，2023，14，8023，14，70BlockingDesignateDesignate23，15，5023，15，50RootRoot第12頁鏈路故障處理示例Port3的配置消息生存期也超時了，則拋棄該配置信息，重新進行生成樹計算，選擇Port2為新的根端口，該網(wǎng)橋的配置信息變?yōu)?23,19,50)port1port2port3port4BridgeID=5032，0，3223，18，2023，14，8023，14，70RootDesignate23，19，50DesignateRoot第13頁臨時環(huán)路的問題當(dāng)拓?fù)浣Y(jié)構(gòu)發(fā)生變化，新的配置消息要經(jīng)過一定的時延才能傳播到整個網(wǎng)絡(luò)，在所有網(wǎng)橋收到這個變化的消息之前：若舊拓?fù)渲刑幱谵D(zhuǎn)發(fā)狀態(tài)的端口還沒發(fā)現(xiàn)自己應(yīng)該在新的拓?fù)渲型Ｖ罐D(zhuǎn)發(fā)，則可能存在臨時的環(huán)路若舊的拓?fù)浣Y(jié)構(gòu)中阻塞的端口還沒有發(fā)現(xiàn)自己應(yīng)該在新的拓?fù)浣Y(jié)構(gòu)中開始轉(zhuǎn)發(fā)，則可能造成網(wǎng)絡(luò)暫時失去連通性第14頁如何避免臨時環(huán)路問題端口由阻塞狀態(tài)進入轉(zhuǎn)發(fā)狀態(tài)時，要經(jīng)過一定時間的延時，這個時間起碼是配置消息傳播到整個網(wǎng)絡(luò)所需最大時間的兩倍ForwardDelay：配置消息傳播到整個網(wǎng)絡(luò)的最大時延設(shè)計中間狀態(tài)，處于中間狀態(tài)的端口只是學(xué)習(xí)站點的地址信息，但不轉(zhuǎn)發(fā)數(shù)據(jù)；端口從阻塞狀態(tài)經(jīng)過ForwardDelay的延時后進入中間狀態(tài)；再經(jīng)過ForwardDelay的延時后才能進入轉(zhuǎn)發(fā)狀態(tài)。第15頁端口狀態(tài)端口狀態(tài)端口能力Disabled不收發(fā)任何報文Blocking不接收或轉(zhuǎn)發(fā)數(shù)據(jù)，接收但不發(fā)送BPDU，不進行地址學(xué)習(xí)Listening不接收或轉(zhuǎn)發(fā)數(shù)據(jù)，接收并發(fā)送BPDU，不進行地址學(xué)習(xí)Learning不接收或轉(zhuǎn)發(fā)數(shù)據(jù)，接收并發(fā)送BPDU，開始地址學(xué)習(xí)Forwarding接收并轉(zhuǎn)發(fā)數(shù)據(jù)，接收并發(fā)送BPDU，進行地址學(xué)習(xí)第16頁端口狀態(tài)遷移(1)端口enabled(2)端口disabled(3)端口被選為根端口或指定端口DisabledListeningBlockingLearningForwarding(4)端口被選為備用端口（阻塞）(5)ForwardDelay延時（1）（2）（5）（1，2）（4）（5）（1，2）（3）（4）（4）（1，2）（1，2）第17頁MAC地址信息的生存期拓?fù)涓淖儠r仍然存在的問題拓?fù)浣Y(jié)構(gòu)改變會使站點在生成樹中的相對位置發(fā)生移動，那么網(wǎng)橋原來學(xué)習(xí)到的MAC地址信息就可能變得不正確在生成樹協(xié)議中地址有兩個生存期：拓?fù)浞€(wěn)定的時候用較長的生存期拓?fù)涓淖兊臅r候用較短的生存期網(wǎng)絡(luò)拓?fù)浒l(fā)生改變的時候，并不是所有的網(wǎng)橋能夠發(fā)現(xiàn)這一變化，所以需要把拓?fù)涓淖兊男畔⑼ㄖ秸麄€網(wǎng)絡(luò)。第18頁拓?fù)涓淖兿⒌膫鞑?234455拓?fù)涓淖兺ㄖ⑼負(fù)涓淖儜?yīng)答消息拓?fù)涓淖兿W1SW2SW3Root第19頁STP回顧STP工作原理配置消息（BPDU）的報文格式配置消息（BPDU）的處理各種端口狀態(tài)之間的轉(zhuǎn)換第20頁MSTP簡介MSTP是在傳統(tǒng)的STP、RSTP的基礎(chǔ)上發(fā)展而來的新的生成樹協(xié)議，本身就包含了RSTP的快速Forwarding機制。MSTP是基于實例來進行無環(huán)拓?fù)溆嬎悖缺苊饬谁h(huán)路的產(chǎn)生，也能讓相同vlan間的通訊不受影響。第21頁MSTP相關(guān)概念instance:一臺交換機的一個或多個vlan的集合MSTRegion:有著相同instance配置的交換機組成的域，這些交換機運行獨立的生成樹（IST，internalspanning-tree）CST（commonspanningtree）:不同MSTregion之間運行的生成樹。第22頁MSTPregion的劃分MST配置名稱（name）：最長可用32個字節(jié)長的字符串來標(biāo)識MSTPregion。MSTrevisionnumber：用一個16bit長的修正值來標(biāo)識MSTPregion。MSTinstance—vlan的對應(yīng)表：每臺交換機都最多可以新增64個instance，instance0是強制存在的，用戶還可以按需要分配1-4094個vlan屬于不同的instance（0－64），未分配的vlan缺省就屬于instance0。

注：instance0所對應(yīng)的生成樹稱為CIST（CommonInstanceSpanningTree）第23頁MSTPregion的劃分MSTPBPDU里面包含MST配置名稱、MSTrevisionnumber、MSTinstance—vlan的對應(yīng)表，如果在一個端口上收到的BPDU里面MST配置信息與本地的一致，那么就可以認(rèn)為該端口上所連接的交換機與本交換機處于同一個MSTRegion,運行相同的IST。第24頁MSTP運行示例-IST完成了如上的配置之后，經(jīng)過BPDU的交流，IST就生成了，而各個instance也生成了獨立的生成樹(MSTI)SW1SW2SW3首先劃分MSTregion,三臺交換機上分別創(chuàng)建了vlan10,20,其中vlan10屬于instance1，vlan20屬于instance2，配置如下：spanning-mstconfigrationinstance1vlan10instance2vlan20nametest(名稱自定義，但必須保持一致)可選配置revision1（號碼必須保持一致）可選配置配置三臺交換機上各實例的優(yōu)先級SW1spanning-treeinstance0priority4096SW1spanning-treeinstance1priority4096SW1spanning-treeinstance2priority8192SW2spanning-treeinstance0priority8192SW2spanning-treeinstance1priority8192SW2spanning-treeinstance2priority4096SW3上保持默認(rèn)的優(yōu)先級配置即32768第25頁MSTP運行示例-ISTinstace0的拓?fù)淝闆rSW1SW3SW2instace0所對應(yīng)的生成樹稱為CIST(CommonInstanceSpanningTree)選舉根橋：SW1具有最高優(yōu)先級4096選為根橋，SW2和SW3更新自己的配置消息。SW2（4096,1,8192）SW3（4096,1,32768）選舉根端口：SW1是根橋，無根端口，其他交換機根據(jù)收到的最優(yōu)配置信息的端口，設(shè)置根端口選舉指定端口：根橋上的所有端口都為指定端口，在其他交換機上,比較在除根端口以外的其他端口上所收到的配置信息與自己的配置信息，如果自己的配置信息優(yōu)于所接收到的配置信息，那么這個端口將被置為指定端口，否則被置為阻塞端口根端口指定端口阻塞端口112221第26頁MSTP運行示例-IST配置驗證SW1#shspanning-treemst0######MST0vlansmapped:1-9,11-19,21-4094BridgeAddr:00d0.f8ff.a1a6Priority:4096TimeSinceTopologyChange:0d:0h:4m:37sTopologyChanges:0DesignatedRoot:100000D0F8FFA1A6RootCost:0RootPort:0CistRegionRoot:100000D0F8FFA1A6CistPathCost:0SW1#shspanning-treeintf0/1######MST0vlansmapped:1-9,11-19,21-4094PortState:forwardingPortPriority:128PortDesignatedRoot:100000D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:100000D0F8FFA1A6PortDesignatedPort:8001PortForwardTransitions:1PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPortSW1#shspanning-treeintf0/2######MST0vlansmapped:1-9,11-19,21-4094PortState:forwardingPortPriority:128PortDesignatedRoot:100000D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:100000D0F8FFA1A6PortDesignatedPort:8002PortForwardTransitions:1PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPort第27頁MSTP運行示例-IST配置驗證SW2#shspanning-treemst0######MST0vlansmapped:1-9,11-19,21-4094BridgeAddr:00d0.f8b3.1f3cPriority:8192TimeSinceTopologyChange:0d:0h:5m:46sTopologyChanges:0DesignatedRoot:100000D0F8FFA1A6RootCost:0RootPort:Fa0/1CistRegionRoot:100000D0F8FFA1A6CistPathCost:200000SW2#shspanning-treeintf0/1######MST0vlansmapped:1-9,11-19,21-4094PortState:forwardingPortPriority:128PortDesignatedRoot:100000D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:100000D0F8FFA1A6PortDesignatedPort:8002PortForwardTransitions:2PortAdminPathCost:0PortOperPathCost:200000PortRole:rootPortSW2#shspanning-treeintf0/2######MST0vlansmapped:1-9,11-19,21-4094PortState:forwardingPortPriority:128PortDesignatedRoot:100000D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:200000D0F8B31F3CPortDesignatedPort:8002PortForwardTransitions:3PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPort第28頁MSTP運行示例-IST配置驗證SW3#shspanning-treemst0######MST0vlansmapped:1-9,11-19,21-4094BridgeAddr:00d0.f88c.17dcPriority:32768TimeSinceTopologyChange:0d:0h:7m:11sTopologyChanges:0DesignatedRoot:100000D0F8FFA1A6RootCost:0RootPort:Fa0/1CistRegionRoot:100000D0F8FFA1A6CistPathCost:200000SW3#shspanning-treeintf0/1######MST0vlansmapped:1-9,11-19,21-4094PortState:forwardingPortPriority:128PortDesignatedRoot:100000D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:100000D0F8FFA1A6PortDesignatedPort:8001PortForwardTransitions:4PortAdminPathCost:0PortOperPathCost:200000PortRole:rootPortSW3#shspanning-treeintf0/2######MST0vlansmapped:1-9,11-19,21-4094PortState:discardingPortPriority:128PortDesignatedRoot:100000D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:200000D0F8B31F3CPortDesignatedPort:8002PortForwardTransitions:4PortAdminPathCost:0PortOperPathCost:200000PortRole:alternatePort第29頁MSTP運行示例-ISTinstace1的拓?fù)淝闆rSW1SW3SW2根端口指定端口阻塞端口112221第30頁MSTP運行示例-IST配置驗證SW1#shspanning-treemst1

######MST1vlansmapped:10BridgeAddr:00d0.f8ff.a1a6Priority:4096TimeSinceTopologyChange:0d:0h:5m:0sTopologyChanges:0DesignatedRoot:100100D0F8FFA1A6RootCost:0RootPort:0SW1#shspanning-treeintf0/1######MST1vlansmapped:10PortState:forwardingPortPriority:128PortDesignatedRoot:100100D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:100100D0F8FFA1A6PortDesignatedPort:8001PortForwardTransitions:1PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPortSW1#shspanning-treeintf0/2######MST1vlansmapped:10PortState:forwardingPortPriority:128PortDesignatedRoot:100100D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:100100D0F8FFA1A6PortDesignatedPort:8002PortForwardTransitions:1PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPort第31頁MSTP運行示例-IST配置驗證SW2#shspanning-treemst1

######MST1vlansmapped:10BridgeAddr:00d0.f8b3.1f3cPriority:8192TimeSinceTopologyChange:0d:0h:15m:15sTopologyChanges:0DesignatedRoot:100100D0F8FFA1A6RootCost:200000RootPort:Fa0/1SW2#shspanning-treeintf0/1######MST1vlansmapped:10PortState:forwardingPortPriority:128PortDesignatedRoot:100100D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:100100D0F8FFA1A6PortDesignatedPort:8002PortForwardTransitions:2PortAdminPathCost:0PortOperPathCost:200000PortRole:rootPortSW2#shspanning-treeintf0/2######MST1vlansmapped:10PortState:forwardingPortPriority:128PortDesignatedRoot:100100D0F8FFA1A6PortDesignatedCost:200000PortDesignatedBridge:200100D0F8B31F3CPortDesignatedPort:8002PortForwardTransitions:3PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPort第32頁MSTP運行示例-IST配置驗證SW3#shspanning-treemst1

######MST1vlansmapped:10BridgeAddr:00d0.f88c.17dcPriority:32768TimeSinceTopologyChange:0d:0h:16m:45sTopologyChanges:0DesignatedRoot:100100D0F8FFA1A6RootCost:200000RootPort:Fa0/1SW3#shspanning-treeintf0/1######MST1vlansmapped:10PortState:forwardingPortPriority:128PortDesignatedRoot:100100D0F8FFA1A6PortDesignatedCost:0PortDesignatedBridge:100100D0F8FFA1A6PortDesignatedPort:8001PortForwardTransitions:4PortAdminPathCost:0PortOperPathCost:200000PortRole:rootPortSW3#shspanning-treeintf0/2######MST1vlansmapped:10PortState:discardingPortPriority:128PortDesignatedRoot:100100D0F8FFA1A6PortDesignatedCost:200000PortDesignatedBridge:200100D0F8B31F3CPortDesignatedPort:8002PortForwardTransitions:4PortAdminPathCost:0PortOperPathCost:200000PortRole:alternatePort第33頁MSTP運行示例-ISTinstace2的拓?fù)淝闆rSW1SW3SW2根端口指定端口阻塞端口112221第34頁MSTP運行示例-IST配置驗證SW1#shspanning-treemst2

######MST2vlansmapped:20BridgeAddr:00d0.f8ff.a1a6Priority:8192TimeSinceTopologyChange:0d:0h:5m:4sTopologyChanges:0DesignatedRoot:100200D0F8B31F3CRootCost:200000RootPort:Fa0/2SW1#shspanning-treeintf0/1######MST2vlansmapped:20PortState:forwardingPortPriority:128PortDesignatedRoot:100200D0F8B31F3CPortDesignatedCost:200000PortDesignatedBridge:200200D0F8FFA1A6PortDesignatedPort:8001PortForwardTransitions:2PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPortSW1#shspanning-treeintf0/2######MST2vlansmapped:20PortState:forwardingPortPriority:128PortDesignatedRoot:100200D0F8B31F3CPortDesignatedCost:0PortDesignatedBridge:100200D0F8B31F3CPortDesignatedPort:8001PortForwardTransitions:1PortAdminPathCost:0PortOperPathCost:200000PortRole:rootPort第35頁MSTP運行示例-IST配置驗證SW2#shspanning-treemst2

######MST2vlansmapped:20BridgeAddr:00d0.f8b3.1f3cPriority:4096TimeSinceTopologyChange:0d:0h:15m:16sTopologyChanges:0DesignatedRoot:100200D0F8B31F3CRootCost:0RootPort:0SW2#shspanning-treeintf0/1######MST2vlansmapped:20PortState:forwardingPortPriority:128PortDesignatedRoot:100200D0F8B31F3CPortDesignatedCost:0PortDesignatedBridge:100200D0F8B31F3CPortDesignatedPort:8001PortForwardTransitions:2PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPortSW2#shspanning-treeintf0/2######MST2vlansmapped:20PortState:forwardingPortPriority:128PortDesignatedRoot:100200D0F8B31F3CPortDesignatedCost:0PortDesignatedBridge:100200D0F8B31F3CPortDesignatedPort:8002PortForwardTransitions:1PortAdminPathCost:0PortOperPathCost:200000PortRole:designatedPort第36頁MSTP運行示例-IST配置驗證SW3#shspanning-treemst2######MST2vlansmapped:20BridgeAddr:00d0.f88c.17dcPriority:32768TimeSinceTopologyChange:0d:0h:16m:47sTopologyChanges:0DesignatedRoot:100200D0F8B31F3CRootCost:200000RootPort:Fa0/2SW3#shspanning-treeintf0/1######MST2vlansmapped:20PortState:discardingPortPriority:128PortDesignatedRoot:100200D0F8B31F3CPortDesignatedCost:200000PortDesignate