組播路由協(xié)議pim dm

1、PIM-DM 協(xié)議原理所謂PIM，即Protocol Independent Multicast，協(xié)議無關(guān)組播。其含義是在做RPF檢查以及特定的協(xié)議單播報文的時候利用已有的單播路由表，與具體采用何種單播路由協(xié)議獲得此單播路由無關(guān)；DM，即Dense Mode ，密集模式（用戶分布相對集中）。Page 2學(xué)習(xí)完此課程，您將會：掌握PIM-DM的基本原理掌握PIM-DM的工作機(jī)制掌握PIM-DM在IOS下的配置方法第1章 PIM概述第2章PIM-DM概述第3章PIM-DM協(xié)議機(jī)制第4章PIM-DM評價PIM概述協(xié)議無關(guān)組播PIMPIM（Protocol Independent Multicast）

2、稱為協(xié)議無關(guān)組播，表示組播依靠的單播路由可以由靜態(tài)路由、RIP、OSPF、IS-IS、BGP等提供，組播路由和單播路由協(xié)議無關(guān)，只要單播路由協(xié)議能產(chǎn)生所需路由表項，如：RPF檢查，即可。協(xié)議號：103PIM路由器組播地址為：224.0.0.13 PIM協(xié)議分為： PIM-DM（協(xié)議無關(guān)組播-密集模式） PIM-SM（協(xié)議無關(guān)組播-稀疏模式）PIM概述PIMv2報文頭格式071531版本 版本字段標(biāo)識版本信息，當(dāng)前為2 類型 0：Hello1：（僅用于SM）2：停止（僅用于SM）3：加入/剪枝4：Bootstrap（僅用于SM）5：Assert 6：嫁接（僅用于DM）7：嫁接回應(yīng)（僅用于DM）8

3、：候選RP公告（僅用于SM）版本類型保留校驗和第1章 PIM概述第2章 PIM-DM概述第3章 PIM-DM協(xié)議機(jī)制第4章 PIM-DM評價PIM-DM概述概述PIM-DM（Protocol Independent Multicast Dense Mode）稱為協(xié)議組播密集模式，屬于密集模式的組播路由協(xié)議，適用于小型網(wǎng)絡(luò)。協(xié)議假設(shè)：網(wǎng)絡(luò)中的每個子網(wǎng)都存在至少一個對組播源感的接收站點(diǎn)，因此組播數(shù)據(jù)包被擴(kuò)散到網(wǎng)絡(luò)中的所有點(diǎn)。PIM-DM對沒有組播數(shù)據(jù)轉(zhuǎn)發(fā)的分支進(jìn)行Prune剪枝操作， 只保留包含接收者的分支。為了使剪掉的有組播數(shù)據(jù)轉(zhuǎn)發(fā)需求的分支能夠重新接收組播數(shù)據(jù)流，剪掉的分支可以周期性地恢復(fù)成轉(zhuǎn)

4、發(fā)狀態(tài)。為了減少等待被剪掉的分支恢復(fù)成轉(zhuǎn)發(fā)狀態(tài)的延時時間，PIM-DM使用Graft嫁接機(jī)制主動恢復(fù)組播報文的轉(zhuǎn)發(fā)。PIM-DM概述概述（續(xù)）PIM-DM域中數(shù)據(jù)包的轉(zhuǎn)發(fā)路徑是“有源樹” 以“組播源”為根、組播組成員為的一棵樹 由于有源樹使用的是從組播源到接收者的最短路徑，因此也稱為最短路徑樹SPT（Shortest Path Tree）PIM-DM不依賴于特定的單播路由協(xié)議，而是使用現(xiàn)存的單播路由表進(jìn)行RPF檢查路由器收到組播數(shù)據(jù)的接口稱為上游接口，轉(zhuǎn)發(fā)組播數(shù)據(jù)的接口稱為下游接口第1章 PIM概述第2章 PIM-DM概述第3章 PIM-DM協(xié)議機(jī)制第4章 PIM-DM評價第3章 PIM-DM

5、協(xié)議機(jī)制第1節(jié) 鄰居發(fā)現(xiàn)第2節(jié)第3節(jié)第4節(jié)構(gòu)建SPT樹嫁接階段RPF檢查第5節(jié)Assert機(jī)制鄰居發(fā)現(xiàn)Hello報文 組播路由器需要使用Hello消息來發(fā)現(xiàn)鄰居，并維護(hù)鄰居關(guān)系 Hello報文格式：071531當(dāng)Hello報文選項類型（OptionType）1時，選項長度（OptionLength）2，選項值（Option Value）為Holdtime定時器。這個定時器指示在沒有進(jìn)一步收到PIMHello消息的情況下，接收方何時終止與方的鄰接關(guān)系。通過比較Hello消息上攜帶的優(yōu)先級（越高越好）和IP地址（越大越好），各路由器為多路由器網(wǎng)段指定路由器DR版本類型保留校驗和選項類型選項長度選項

6、值選項類型選項長度選項值第3章 PIM-DM協(xié)議機(jī)制第1節(jié) 鄰居發(fā)現(xiàn)第2節(jié) 構(gòu)建SPT樹第3節(jié)嫁接階段第4節(jié)RPF檢查第5節(jié)Assert機(jī)制構(gòu)建SPT樹擴(kuò)散組播源網(wǎng)絡(luò)中的每個路由器都會創(chuàng)建(S, G)表項組播報文接收者當(dāng)某組播源S開始向組播組G數(shù)據(jù)時，路由器接收到組播報文后，首先根據(jù)單播路由表進(jìn)行RPF檢查，如果檢查通過則創(chuàng)建一個（S，G）表項，然后將數(shù)據(jù)向網(wǎng)絡(luò)上所有下游PIM-DM節(jié)點(diǎn)轉(zhuǎn)發(fā)，這個過程稱為擴(kuò)散（Flooding）構(gòu)建SPT樹剪枝組播源組播報文接收者剪枝消息如果下游節(jié)點(diǎn)沒有組播組成員，則向上游節(jié)點(diǎn)發(fā)Prune剪枝消息，通知上游節(jié)點(diǎn)不用再轉(zhuǎn)發(fā)數(shù)據(jù)到該分支。上游節(jié)點(diǎn)收到Prune剪枝

7、消息后，就將相應(yīng)的接口從其組播轉(zhuǎn) 項（S，G）對應(yīng)的輸出接口列表中刪除，剪枝過程繼續(xù)直到PIM-DM中僅剩下了必要的分支，這就建立了一個以組播源S為根的SPTPIM Prune Delay on MultiaccessNetworksrtr-aS1S02Ill wait 3 secs to see if(S,G) Packetssomeone else wants (S,G)before I PruneInterface E0.4E01E0E0Join3Prunertr-brtr-cE1E1Receiver“rtr-b” is a leaf node without receivers. Se

8、nds Prune for (S,G).“rtr-a” schedules a Prune for (S,G) to occur in 3 seconds.123“rtr-c” hears Prune from “rtr-b”. Overrides with a Join.“rtr-a” hears Join and cancels Prune for (S,G).4PIM Prune Delay on MultiaccessNetworksWatch out for the ripple affect of this Delay!XXSourceXXPrunePrunePrunePrune3

9、 sec delay3 sec delay3 sec delay3 sec delaySource begins sending traffic, which is flooded everywhere.Leaf router has no receivers; sends prune, which ripples up the tree.Total time to prune back to source = 12 seconds!Process repeats three minutes later when prunes timeout!構(gòu)建SPT樹SPT樹形成組播源網(wǎng)絡(luò)中的每個路由器仍

10、然會保留(S, G)表項組播報文擴(kuò)散剪枝周期性進(jìn)行！ 每3分鐘重復(fù)一次。接收者第3章 PIM-DM協(xié)議機(jī)制第1節(jié) 鄰居發(fā)現(xiàn)第2節(jié) 構(gòu)建SPT樹第3節(jié) 嫁接階段第4節(jié) RPF檢查第5節(jié) Assert機(jī)制嫁接階段接收者嫁接組播源組播報文Graft嫁接消息接收者當(dāng)被剪枝的下游節(jié)點(diǎn)需要恢復(fù)到轉(zhuǎn)發(fā)狀態(tài)時，該節(jié)點(diǎn)使用Graft嫁接消息通知上游節(jié)點(diǎn)。Graft嫁接消息逐跳向組播源S傳遞，中間節(jié)點(diǎn)接收到Graft嫁接消息后回應(yīng)確認(rèn)嫁接階段新的SPT樹組播源組播報文接收者第3章 PIM-DM協(xié)議機(jī)制第1節(jié)第2節(jié)第3節(jié)鄰居發(fā)現(xiàn)構(gòu)建SPT樹嫁接階段第4節(jié) RPF檢查第5節(jié) Assert機(jī)制RPF檢查RPF檢查源15

11、1.10.3.21RPF檢查失敗報文從錯誤接口到來!組播報文利用單播路由表，可以是任何方式生成的路由表項：如果組播包到達(dá)接口是單播路由指示的通往組播源S的接口，就認(rèn)為這個組播包是從正確路徑來的第3章 PIM-DM協(xié)議機(jī)制第1節(jié)第2節(jié)第3節(jié)鄰居發(fā)現(xiàn)構(gòu)建SPT樹嫁接階段第4節(jié)RPF檢查第5節(jié) Assert機(jī)制Assert機(jī)制Router ARouter BRouter CRRREthernetSPTRRouter DAssertReceiverAssert報文選出一條最優(yōu)的路徑，獲勝路由器成為網(wǎng)絡(luò)中的各路由器通過該（S，G）項的上游鄰居，由它負(fù)責(zé)該（S，G）組播報文的轉(zhuǎn)發(fā)，而其他落選路由器則剪掉對

12、應(yīng)的接口以轉(zhuǎn)發(fā)信息。選取原則： Metric值：路由器上到組播源的cost值；如果Metric值相同，則比較接口上IP地址：IP地址大的優(yōu)先。第1章PIM概述第2章PIM-DM概述第3章PIM-DM協(xié)議機(jī)制第4章 PIM-DM評價PIM-DM評價PIM-DM對于小型網(wǎng)絡(luò)來說非常有效優(yōu)勢: 易于配置 實現(xiàn)機(jī)制簡單（擴(kuò)散剪枝嫁接）潛在問題.擴(kuò)散剪枝過程不夠高效復(fù)雜的Assert機(jī)制和數(shù)據(jù)平面混合導(dǎo)致網(wǎng)絡(luò)內(nèi)部的所有路由器上都有(S, G)表項存在不支持共享樹PIM Dense Mode Implementation andTroubleshooting© 2002, Cisco Syste

13、ms, Inc.s.Dense Mode IP Multicast Protocols v1.1-28ObjectivesUpon completion of this section, you will beable to: Configure PIM DM on Cisco routers Troubleshoot basic IP multicast problems in PIM DMPIM DM Configuration Commandsrouter(config)# Enables multicast routing.router(config-if)# Enables PIM

14、dense mode on an interface.PIM DM Configuration ExampleE1E0 Simple to configure One global command One command per interfaceS0Finding PIM Neighborsrouter# Displays information about interfaces configured for PIMrouter# Lists the PIM neighbors discovered by the Cisco IOS softwarerouter# Queries what

15、neighboring multicast routers are peering withthe local routerPIM DM (*,G) State Rules(*,G) created automatically When 1st (S,G) for group is created (S,G) must always have a parent (*,G) When a directly connected member joins the group(*,G) reflect PIM neighbor adjacency IIF = NULL OIL = all interf

16、aceswith PIM-DM neighbors orwith directly connected hosts or manually configuredPIM DM (S,G) State Rules(S,G) created by multicast data arrivalParent (*,G) created (if does not exist)IIF = RPF interface in direction of source OIL = Copy of OIL from (*,G) minus IIFInterfaces in OIL initially “Forward

17、”Go to “Pruned” state when Prune rcvd“Forward” interface timers never expire “Pruned” interface timers expire in 3 minutesPIM DM State FlagsDC L P TJ= Dense Mode= Directly Connected Host= Local (Router is member)= Pruned (All interfaces in OIL = Prune)= Forwarding via SPTIndicates at least one packe

18、t was forwarded= Join SPTAlways on in (*,G) entry in PIM DM Basically meaningless in PIM DMShow ip pim NeighborShow ip pim InterfaceMrinfoUsed to query a peering router about multicast informationExample shown is from the Cisco internal network on a remote office router; when no arguments are given,

19、 the router queries itselfChecking Underlying Unicast Topologyrouter# Displays how IP multicast routing does Reverse PathForwarding (RPF)router# Displays the current state of the routing tableShow ip rpfShow ip RouteChecking the Group Staterouter# Displays multicast-related information about an inte

20、rfacerouter# Displays the multicast groups that are directly connected tothe router and that were learned via IGMPshow ip igmp Interfaceshow ip igmp GroupsInspecting Multicast Routing Tablerouter(config)#Displays the contents of the IP multicast routing table Summary - displays a one-line, abbreviat

21、ed summary of each entry in the IP multicast routing table Count - displays statistics about the group and source, including number of packets, packets per second, average packet size, and bits per second Active - displays the rate that active sources are sending to multicast groups. Active sources

22、are those sending at a rate of kbps or higher. The kbps argument defaults to 4 kbpsshow ip mroute Summaryshow ip mrouteshow ip mroute Countshow ip mroute ActiveBasic Debugging of IP Multicastrouter# Displays changes to the IP multicast routing tablerouter# Displays IP multicast packets received and

23、transmittedrouter# Displays PIM packets received and transmitted as well as PIMrelated eventsDebug ip mroutingDebug ip mpacketDebug ip pimDebug ip pim (cont.)Debug ip pim (cont.)SummaryAfter completing this section, you should beable to: Configure PIM DM on Cisco routers Troubleshoot basic IP multicast problems in PIM DMReview Questions1.List the basic Cisco IOS commands for inspecting PIMconfiguration on ro