IP多播技术介绍（三） 推荐

实例2：在帧中继的网络环境 拓扑图如下所示：



具体配置如下

R1#sh running-config Building configuration... Current configuration : 1718 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R1 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! ! ! ! ! ! ! interface FastEthernet0/0 ip address 10.1.1.1 255.255.255.0 ip pim dense-mode duplex half ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.305 point-to-point ip address 10.2.1.1 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 305 ! interface Serial1/0.309 point-to-point ip address 10.2.2.1 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 309 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.1.1.0 0.0.0.255 area 0 network 10.2.1.0 0.0.0.255 area 0 network 10.2.2.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 ! ! End ——————————————————————————————————————— R2#sh running-config Building configuration... Current configuration : 1819 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R2 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! ! ! ! ! interface FastEthernet0/0 no ip address shutdown duplex half ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.503 point-to-point ip address 10.2.1.2 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 503 ! interface Serial1/0.506 point-to-point ip address 10.2.4.2 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 506 ! interface Serial1/0.507 point-to-point ip address 10.2.5.2 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 507 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.2.1.0 0.0.0.255 area 0 network 10.2.4.0 0.0.0.255 area 0 network 10.2.5.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 ! ! End ——————————————————————————————————————— R3#sh running-config Building configuration... Current configuration : 1654 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R3 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! ! ! ! ! ! interface FastEthernet0/0 no ip address shutdown duplex half ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.903 point-to-point ip address 10.2.2.2 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 903 ! interface Serial1/0.906 point-to-point ip address 10.2.3.1 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 906 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.2.2.0 0.0.0.255 area 0 network 10.2.3.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 ! ! end ——————————————————————————————————————— R4#sh running-config Building configuration... Current configuration : 1718 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R4 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! ! ! ! interface FastEthernet0/0 ip address 10.1.2.1 255.255.255.0 ip pim dense-mode duplex full ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.605 point-to-point ip address 10.2.4.1 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 605 ! interface Serial1/0.609 point-to-point ip address 10.2.3.2 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 609 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.1.2.0 0.0.0.255 area 0 network 10.2.3.0 0.0.0.255 area 0 network 10.2.4.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 ! ! end ——————————————————————————————————————— R5#sh running-config Building configuration... Current configuration : 1554 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R5 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! ! ! interface FastEthernet0/0 ip address 10.1.2.25 255.255.255.0 ip pim dense-mode duplex full ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.705 point-to-point ip address 10.2.5.1 255.255.255.0 ip pim dense-mode frame-relay interface-dlci 705 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.1.2.0 0.0.0.255 area 0 network 10.2.5.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 ! ! end

配置完成后，同样打开组播测试工具，一个发送源，一个为接收成员。





Show ip mroute 查看组播路由表项。

R1#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:58:14/00:02:27, RP 0.0.0.0, flags: DCL Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.309, Forward/Dense, 00:57:11/00:00:00 Serial1/0.305, Forward/Dense, 00:57:12/00:00:00 FastEthernet0/0, Forward/Dense, 00:58:14/00:00:00 (*, 228.13.20.216), 00:41:26/stopped, RP 0.0.0.0, flags: DC Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: FastEthernet0/0, Forward/Dense, 00:16:33/00:00:00 Serial1/0.309, Forward/Dense, 00:41:26/00:00:00 Serial1/0.305, Forward/Dense, 00:41:26/00:00:00 (10.1.1.88, 228.13.20.216), 00:13:37/00:02:52, flags: T Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.305, Forward/Dense, 00:13:24/00:00:00 Serial1/0.309, Prune/Dense, 00:02:13/00:00:47 (*, 239.255.255.250), 00:57:33/00:02:27, RP 0.0.0.0, flags: DC Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.309, Forward/Dense, 00:57:12/00:00:00 Serial1/0.305, Forward/Dense, 00:57:13/00:00:00 FastEthernet0/0, Forward/Dense, 00:57:33/00:00:00

从上面状态可以看到，(10.1.1.88, 228.13.20.216)处于T（表示路由器是SPT中和一个有效成员）状态，在入站接口的RPF的nbr为0.0.0.0则说明所连接的设备为多播组的源。
在路由器R1上查看单播路由表，

R1#sh ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is not set 10.0.0.0/24 is subnetted, 7 subnets C 10.2.1.0 is directly connected, Serial1/0.305 O 10.1.2.0 [110/129] via 10.2.2.2, 00:50:00, Serial1/0.309 [110/129] via 10.2.1.2, 00:50:00, Serial1/0.305 C 10.2.2.0 is directly connected, Serial1/0.309 C 10.1.1.0 is directly connected, FastEthernet0/0 O 10.2.3.0 [110/128] via 10.2.2.2, 00:50:00, Serial1/0.309 O 10.2.4.0 [110/128] via 10.2.1.2, 00:50:00, Serial1/0.305 O 10.2.5.0 [110/128] via 10.2.1.2, 00:50:00, Serial1/0.305

去往10.1.2.0的路由有两条，其路径开销是相同的，这需要选择IP地址小的为最优路径。

R2#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:45:02/stopped, RP 0.0.0.0, flags: DCL Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.507, Forward/Dense, 00:43:47/00:00:00 Serial1/0.506, Forward/Dense, 00:43:50/00:00:00 Serial1/0.503, Forward/Dense, 00:44:01/00:00:00 (*, 228.13.20.216), 00:28:15/stopped, RP 0.0.0.0, flags: D Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.507, Forward/Dense, 00:28:15/00:00:00 Serial1/0.506, Forward/Dense, 00:28:15/00:00:00 Serial1/0.503, Forward/Dense, 00:28:15/00:00:00 (10.1.1.88, 228.13.20.216), 00:00:13/00:02:59, flags: T Incoming interface: Serial1/0.503, RPF nbr 10.2.1.1 Outgoing interface list: Serial1/0.506, Forward/Dense, 00:00:13/00:00:00 Serial1/0.507, Forward/Dense, 00:00:13/00:00:00

R3#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:49:49/stopped, RP 0.0.0.0, flags: DCL Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.906, Forward/Dense, 00:48:48/00:00:00 Serial1/0.903, Forward/Dense, 00:48:48/00:00:00 (*, 228.13.20.216), 00:32:46/stopped, RP 0.0.0.0, flags: D Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.906, Forward/Dense, 00:32:46/00:00:00 Serial1/0.903, Forward/Dense, 00:32:46/00:00:00 (10.1.1.88, 228.13.20.216), 00:02:36/00:00:23, flags: PT Incoming interface: Serial1/0.903, RPF nbr 10.2.2.1 Outgoing interface list: Serial1/0.906, Prune/Dense, 00:02:35/00:00:23, A

R4#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:48:55/00:02:47, RP 0.0.0.0, flags: DCL Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.605, Forward/Dense, 00:47:52/00:00:00 Serial1/0.609, Forward/Dense, 00:47:52/00:00:00 FastEthernet0/0, Forward/Dense, 00:48:55/00:00:00 (*, 228.13.20.216), 00:32:17/stopped, RP 0.0.0.0, flags: DC Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.609, Forward/Dense, 00:32:17/00:00:00 Serial1/0.605, Forward/Dense, 00:32:17/00:00:00 FastEthernet0/0, Forward/Dense, 00:32:17/00:00:00 (10.1.1.88, 228.13.20.216), 00:26:11/00:01:37, flags: PT Incoming interface: Serial1/0.605, RPF nbr 10.2.4.2 Outgoing interface list: FastEthernet0/0, Prune/Dense, 00:01:13/00:01:46 Serial1/0.609, Prune/Dense, 00:23:08/00:00:56, A (*, 239.255.255.250), 00:04:16/00:02:47, RP 0.0.0.0, flags: DC Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.609, Forward/Dense, 00:04:16/00:00:00 Serial1/0.605, Forward/Dense, 00:04:16/00:00:00 FastEthernet0/0, Forward/Dense, 00:04:16/00:00:00

R5#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:47:01/00:02:39, RP 0.0.0.0, flags: DCL Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.705, Forward/Dense, 00:45:59/00:00:00 FastEthernet0/0, Forward/Dense, 00:47:01/00:00:00 (*, 228.13.20.216), 00:30:27/stopped, RP 0.0.0.0, flags: DC Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.705, Forward/Dense, 00:30:27/00:00:00 FastEthernet0/0, Forward/Dense, 00:30:27/00:00:00 (10.1.1.88, 228.13.20.216), 00:02:38/00:02:50, flags: T Incoming interface: Serial1/0.705, RPF nbr 10.2.5.2 Outgoing interface list: FastEthernet0/0, Forward/Dense, 00:02:25/00:00:00, A (*, 239.255.255.250), 00:02:25/00:02:34, RP 0.0.0.0, flags: DC Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.705, Forward/Dense, 00:02:27/00:00:00 FastEthernet0/0, Forward/Dense, 00:02:27/00:00:00 R4#sh ip pim neighbor PIM Neighbor Table Neighbor Interface Uptime/Expires Ver DR Address Prio/Mode 10.1.2.25 FastEthernet0/0 00:59:55/00:01:23 v2 1 / DR S 10.2.4.2 Serial1/0.605 00:59:22/00:01:24 v2 1 / S 10.2.3.1 Serial1/0.609 00:59:22/00:01:30 v2 1 / S

根据规则选择出DR。
6、PIM-SM（Protocol Independent Multicast Sparse Mode） PIM-SM使用了7种PIMV2消息：
l Hello
l Bootstrap（引导）
l Candidate-RP-Advertisement（候选RP宣告）
l Join/Prune（加入/剪除）
l Assert（声明）
l Register（注册）
l Register-Stop（注册终止）
Hello、Join/Prune、Assert这三种消息也在PIM-DM中使用，而另外四种消息上PIM-SM所独有的。正如PIM-DM中有两个独有的消息（Graft与Graft-ack）一样。
在 PIM-SM 域中，运行 PIM-SM 协议的路由器周期性的发送 Hello 消息，用以发现邻接的 PIM 路由器，并且负责在多路访问网络中进行 DR 的选举。这里，DR 负责为与其直连的组成员向组播树根节点的方向发送“加入/剪枝”消息，或是将直连组播源的数据发向组播分发树。
PIM-SM 通过建立组播分发树来进行组播数据包的转发。组播分发树分为两种：以组 G 的 RP 为根的共享树和以组播源为根的最短路径树。PIM-SM 通过显式的加入/剪枝机制来完成组播分发树的建立与维护。
PIM-SM 中还涉及到 RP 的选择机制。在 PIM-SM 域内配置了一个或多个候选自举路由器(Candidate-BSR)。使用一定的规则从中选出自举路由器 (BSR) 。PIM-SM 域中还配置有候选 RP 路由器(Candidate-RP)，这些候选 RP 将包含了它们地址及可以服务的组播组等信息的报文单播发送给自举路由器，再由 BSR 定期生成包括一系列候选 RP 以及相应的组地址的“自举”消息。“自举”消息在整个域中逐跳发送。路由器接收并保存这些“自举”消息。若 DR 从直连主机收到了 IGMP 加入报文后，如果它没有这个组的路由项，将使用 hash 算法将组地址映射到一个候选 RP。然后朝 RP 方向逐跳组播“加入/剪枝”消息。若 DR 从直连主机收到组播数据包，如果它没有这个组的路由项，也将使用 hash 算法将组地址映射到一个候选 RP，然后将组播数据封装在注册消息中单播发送到 RP。
在多路访问网络中，PIM-SM 还引入了以下机制：使用断言机制选举唯一的转发者，以防向同一网段重复转发组播数据包；使用加入/剪枝抑制机制减少冗余的加入/剪枝消息；使用剪枝否决机制否决不应有的剪枝行为。
共享树根植于多播网络中的一台路由器，PIM-SM称之为会聚点（rendezvous point RP）。在共享树建立之前，加入的路由器必须知道如何找到RP，路由器可以通过3种方法知道RP地址：
l 静态配置RP地址
l 使用Bootstrap自举协议来指定和宣告RP
l 以思科所私有Auto-RP协议来指定和宣告RP

Bootstrap协议
要运行Bootstrap协议，必须在网络中指派C-BSR(候选引导路由器)和C-RP（候选聚合点），通常情况下，一般将同一组路由器同时配置为C-BSR和C-RP，通过IP地址（环回接口）来区分C-BSR和C-RP。
首先要从C-BSR中选出BSR，每一个C-BSR都分配有0~255的优先级（默认为0）和一个BSR IP地址，当路由器配置成C-BSR时，会启动一个130秒的引地定时器并侦听Bootstrap消息。
Bootstrap消息的作用是宣告发起路由器的优先级和BSR IP地址，当C-BSR收到Bootstrap消息后，会将自己的优先级与发起路由器的优先级进行对比，如果发起路由器的优先级较高，由接收路由器会重置自己的引导计时器并继续侦听。如果接收路由器的优先级较高，则将自己宣称为BSR并开始每隔60秒发送一条Bootstrap消息。如两者的优先级相等，则BSR IP地址较高的路由器为BSR。
当C-BSR的130秒引导计时器到期时，该路由器将认定网络中无BSR，则将自己宣称为BSR，并开始每隔60秒发送Bootstrap消息。
Bootstrap消息使用全部PIM路由器地址224.0.0.13,且TTL设为1。当PIM路由器接收到一条Bootstarp消息后，会通过所有接口（接收到该消息的接口除外）向外发送该消息的复本。该处理过程不仅可以将保证Bootstrap消息泛洪到整个多播源，还可保证每台PIM路由器都能接收到一份消息复本并知道哪台路由器是BSR。
每台C-RP都会分配一个RP IP地址和一个0~255之间的优先级，可以将路由器配置为某些特定多播组的C-RP，也可配置为所有多播组的C-RP，当通过接收到的Bootstrap消息知道了BSR之后，C-RP就开始向BSR单播发送Candidate-RP-Advertisement（候选RP宣告）消息，这些消息中包含了发起路由器的RP地址、组地址（发起路由器是该组的候选RP）及其优先级。
BSR将所有有C-RP的优先级及相关的多播组都编译成RP-set，并通过Bootstrap消息在整个PIM域中宣告该RP-set。此外，Bootstrap消息中还包括一个8bit的hash掩码。所有路由器都会收到此消息。
当某台路由器接收到IGMP消息或PIM join消息而要加入某共享树时，需要检查接收自BSR的RP-set。
l 如果该多播组只有一个C-RP，由该路由器被选为RP
l 如果该多播组拥有多个C-RP，且优先级不同，则优先级最低的路由器将成为RP
l 如果该多播组拥有多个C-RP，且优先级相同，则需要运行hash函数。函数输出值最大的C-RP将成为RP。
l 如果多个C-RP的hash函数输出值相同，则IP地址最大的C-RP将成为RP。
Auto-RP协议
此协议是思科专有的协议，Auto-RP协议与Bootstrap协议类似，需要在PIM-SM环境中指派C-RP，并通过指派的IP地址（环回地址）来标识C-RP，还需要指定一个或多个RP映射代理，其作用与BSR相似。RP映射代理是直接指派的，RP映射代理是将多播映射到RP，而不是宣告RP-set以及在整个多播域中发布选举进程。其使用两个保留地址224.0.1.39和224.0.1.40。当路由器被配置为一个或多个多播组的C-RP时，它会在RP-Announce（RP通告）消息中宣告自己是这些多播组的C-RP，并每隔60秒将这些消息多播到保留的Cisco-RP-Announce地址224.0.1.39.PIM域中已配置的RP映射代理将侦听该地址，并从接收到的全部RP-Announce消息中为该多播组选出一个RP（该多播组的所有C-RP中IP地址最大者将成为RP）。
映射代理在RP-Discovery（RP发现）消息中宣告完整的group-to-RP映射表，并以60秒为间隔将这些消息多播到保留的Cisoco-RP-Discovery地址224.0.1.40.所有思科PIM-SM路由器会侦听该地址，因面可以掌握每个多播组的RP情况。

PIM-SM路由器加入/剪除
在PIM-SM网络环境中，当PIM-SM DR从某台主机接收到IGMP成员关系报告消息，想加入到某个多播组时，首先检查其多播组是否已经存在在该多播组的路由表项，如果存在，那么接收到该IGMP消息的接口将被加入到路由表项中作为出站接口。无需再做其它操作。如果多播表中无相应的表项，那就需要为该多播组创建一个新的（*,G）表项，并加入出站接口。之后该路由器会查找group-to-RP映射列表中的该多播组，查询单播路由表以找到去往特定RP的路由，并将去住RP的上行接口加入到入站的接口中。之后，该路由器将通过上行出接口向224.0.0.13发出一条join/prune消息，该消息中包含了将要加入的多播组的地址和RP地址，消息中的剪除字段为空。此外还设置两个标记（WC-bit和RPT-bit标记）。
当上游路由器接收到join/prune消息后，会执行下面4种操作中的一种：
l 如果该路由器不是RP路由器，但位于共享树上，那么该路由器会将接收到的join/prune消息的接口加入到该多播组的出站接口列表中
l 如果该路由器不是RP路由器，且不位于共享树上，那么该路由器将创建一个（*,G）表项。并沿着RP的方向向上游邻居发送自己的join/prune消息。
l 如果该路由器是RP，且路由表中已经存在该多播的路由表项，那么该路由器会将接收到的join/prune消息的接口加入到该多播组的出站接口列表
l 如果该路由器是RP，但其路由表项中没有该多播的路由表项，那么该路由器将创建一个（*.G）表项，并将接收到的join/prune消息的接口加入到该多播组的出站接口列表中。
多播树建立之后，路由器就开始周期性（默认为60秒）地向上游发送join/prune消息以保持激活。如果在保持时间（是join/prune消息间隔的3倍，默认为3分钟）内PIM路由器没有从下游邻居接收到join/prune消息，则将邻居从其多播组表项的出站接口列表中剪除。
剪除过程与加入过程是一样的。
源注册
在共享树环境中，多播树的根是核心路由器或聚合点，而不是源，那么多播源如何将多播分组分发给RP。
当PIM-SM路由器首次接收到其直连多播源的多播分组时，会在其group-to-RP映射表中查找目的多播组的RP。确定了多播组的RP之后，路由器将多播分组封装在PIM Register（注册）消息中，并将该消息发送给RP，需要注意的是，Register消息以单播方式发送到RP地址的。



RP接收到Register消息后，就将多播分组解封装出来，如果其多播路由表中已存在该多播组的路由表项，则在其出站接口列表中的所有接口上转发该多播包。



如果需要将大量的多播分组传送到RP，那么继续将多播分组封装到Register消息中再传送到RP，效率非常低下，因而RP在其多播表中创建一个（S,G）表项，并通过多播传送一条join/prune消息来建立一个去住源DR的SPT，这条消息中包含了多播源地址，WC-bit=0且RPT-bit＝0,表示该路径是有源SPT，而不是共享SPT。



建立了SPT之后，RP就可以通过该多播树接收多播流量。此时，路由器需要向多播源的DR发送一条register-stop（消息终止）消息，告诉DR停止在Register消息中发送多播分组。



如果多播源开始向RP发送多播流量的时候没有组成员，那么RP将不构建SPT，而是向多播源的DR发送一条Register stop消息，让其停止在Register 消息中发送被封装的多播分组。RP有该多播组的（*,G）表项，当有组成员加入时，RP就可以启动SPT。
注册抑制（Register Suppression）机制是用来阻止DR持续不断的向失效RP发送数据包，当DR接收到Register stop消息后，会启动注册抵制定时器（60s）,该路由器会现次通过Register消息发送多播分组。但是在这之前的5s,DR会发送一条携带Null-register（空注册）bit标记的Register消息，如果消息触发了一条来自RP的Register stop消息，那么会重置注册抑制定时器。
实例1：静态配置RP 实验拓扑图如下所示：



具体配置如下：

R1#sh running-config Building configuration... Current configuration : 1757 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R1 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! interface FastEthernet0/0 ip address 10.1.1.1 255.255.255.0 ip pim sparse-mode duplex half ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.305 point-to-point ip address 10.2.1.1 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 305 ! interface Serial1/0.309 point-to-point ip address 10.2.2.1 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 309 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.1.1.0 0.0.0.255 area 0 network 10.2.1.0 0.0.0.255 area 0 network 10.2.2.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ip pim rp-address 10.224.1.1 ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 login ! ! end R1# R2#sh running-config Building configuration... Current configuration : 1858 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R2 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! interface FastEthernet0/0 no ip address shutdown duplex half ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.503 point-to-point ip address 10.2.1.2 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 503 ! interface Serial1/0.506 point-to-point ip address 10.2.4.2 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 506 ! interface Serial1/0.507 point-to-point ip address 10.2.5.2 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 507 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.2.1.0 0.0.0.255 area 0 network 10.2.4.0 0.0.0.255 area 0 network 10.2.5.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ip pim rp-address 10.224.1.1 ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 login ! ! end R3#sh running-config Building configuration... Current configuration : 1788 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R3 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! ! ! ! interface Loopback0 ip address 10.224.1.1 255.255.255.255 ! interface FastEthernet0/0 no ip address shutdown duplex half ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.903 point-to-point ip address 10.2.2.2 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 903 ! interface Serial1/0.906 point-to-point ip address 10.2.3.1 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 906 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.2.2.0 0.0.0.255 area 0 network 10.2.3.0 0.0.0.255 area 0 network 10.224.1.1 0.0.0.0 area 0 ! ip classless no ip http server no ip http secure-server ! ! ip pim rp-address 10.224.1.1 ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 login ! ! end R4#sh running-config Building configuration... Current configuration : 1766 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R4 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! ! ! ! ! interface FastEthernet0/0 ip address 10.1.2.1 255.255.255.0 ip pim sparse-mode ip cgmp duplex full ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.605 point-to-point ip address 10.2.4.1 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 605 ! interface Serial1/0.609 point-to-point ip address 10.2.3.2 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 609 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.1.2.0 0.0.0.255 area 0 network 10.2.3.0 0.0.0.255 area 0 network 10.2.4.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ip pim rp-address 10.224.1.1 ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 login ! ! End R5#sh running-config Building configuration... Current configuration : 1601 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R5 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! ip subnet-zero ip cef ! ! ! ! ip multicast-routing ! ! ! interface FastEthernet0/0 ip address 10.1.2.25 255.255.255.0 ip pim sparse-mode ip cgmp duplex full ! interface Serial1/0 no ip address encapsulation frame-relay serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/0.705 point-to-point ip address 10.2.5.1 255.255.255.0 ip pim sparse-mode frame-relay interface-dlci 705 ! interface Serial1/1 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/2 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Serial1/3 no ip address shutdown serial restart-delay 0 no dce-terminal-timing-enable ! interface Ethernet2/0 no ip address shutdown duplex half ! interface Ethernet2/1 no ip address shutdown duplex half ! interface Ethernet2/2 no ip address shutdown duplex half ! interface Ethernet2/3 no ip address shutdown duplex half ! router ospf 10 log-adjacency-changes network 10.1.2.0 0.0.0.255 area 0 network 10.2.5.0 0.0.0.255 area 0 ! ip classless no ip http server no ip http secure-server ! ! ip pim rp-address 10.224.1.1 ! logging alarm informational ! ! ! ! control-plane ! ! ! ! ! ! gatekeeper shutdown ! ! line con 0 exec-timeout 0 0 stopbits 1 line aux 0 stopbits 1 line vty 0 4 login ! ! end R5#

如同上面的实验一样，打开组播工具，进行发送和接收，使用show查查看其状态。

R1#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:30:15/00:02:44, RP 10.224.1.1, flags: SJCL Incoming interface: Serial1/0.309, RPF nbr 10.2.2.2 Outgoing interface list: FastEthernet0/0, Forward/Sparse, 00:26:08/00:02:44 (*, 228.13.20.216), 00:06:29/stopped, RP 10.224.1.1, flags: SJCF Incoming interface: Serial1/0.309, RPF nbr 10.2.2.2 Outgoing interface list: FastEthernet0/0, Forward/Sparse, 00:06:29/00:02:40 (10.1.1.88, 228.13.20.216), 00:06:29/00:03:26, flags: FT Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.305, Forward/Sparse, 00:06:22/00:03:03 (*, 239.255.255.250), 00:29:34/00:02:42, RP 10.224.1.1, flags: SJC Incoming interface: Serial1/0.309, RPF nbr 10.2.2.2 Outgoing interface list: FastEthernet0/0, Forward/Sparse, 00:26:48/00:02:42 R2#sh ip mroute 228.13.20.216 IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 228.13.20.216), 00:07:10/stopped, RP 10.224.1.1, flags: SP Incoming interface: Serial1/0.506, RPF nbr 10.2.4.1 Outgoing interface list: Null (10.1.1.88, 228.13.20.216), 00:07:10/00:03:25, flags: T Incoming interface: Serial1/0.503, RPF nbr 10.2.1.1 Outgoing interface list: Serial1/0.507, Forward/Sparse, 00:07:10/00:03:12 R3#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:31:22/00:03:28, RP 10.224.1.1, flags: SJCL Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.906, Forward/Sparse, 00:25:18/00:03:07 Serial1/0.903, Forward/Sparse, 00:25:47/00:03:28 (*, 228.13.20.216), 00:08:05/00:03:17, RP 10.224.1.1, flags: S Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.903, Forward/Sparse, 00:08:05/00:03:17 (10.1.1.88, 228.13.20.216), 00:08:05/00:02:55, flags: PT Incoming interface: Serial1/0.903, RPF nbr 10.2.2.1 Outgoing interface list: Null (*, 239.255.255.250), 00:25:47/00:03:02, RP 10.224.1.1, flags: S Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial1/0.906, Forward/Sparse, 00:03:15/00:03:02 Serial1/0.903, Forward/Sparse, 00:25:47/00:02:30 R4#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:32:06/00:02:50, RP 10.224.1.1, flags: SJCL Incoming interface: Serial1/0.609, RPF nbr 10.2.3.1 Outgoing interface list: FastEthernet0/0, Forward/Sparse, 00:02:04/00:01:25 Serial1/0.605, Forward/Sparse, 00:24:34/00:03:12 (*, 228.13.20.216), 00:08:44/00:02:51, RP 10.224.1.1, flags: SP Incoming interface: Serial1/0.609, RPF nbr 10.2.3.1 Outgoing interface list: Null (*, 239.255.255.250), 00:31:21/00:02:54, RP 10.224.1.1, flags: SJC Incoming interface: Serial1/0.609, RPF nbr 10.2.3.1 Outgoing interface list: FastEthernet0/0, Forward/Sparse, 00:03:59/00:01:28 R5#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement, U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel, z - MDT-data group sender, Y - Joined MDT-data group, y - Sending to MDT-data group Outgoing interface flags: H - Hardware switched, A - Assert winner Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 224.0.1.40), 00:32:47/00:02:06, RP 10.224.1.1, flags: SJPCL Incoming interface: FastEthernet0/0, RPF nbr 10.1.2.1 Outgoing interface list: Null (*, 228.13.20.216), 00:09:29/stopped, RP 10.224.1.1, flags: SJPC Incoming interface: FastEthernet0/0, RPF nbr 10.1.2.1 Outgoing interface list: Null (10.1.1.88, 228.13.20.216), 00:09:28/00:02:57, flags: JT Incoming interface: Serial1/0.705, RPF nbr 10.2.5.2 Outgoing interface list: FastEthernet0/0, Forward/Sparse, 00:09:28/00:02:07, A (*, 239.255.255.250), 00:32:06/00:02:09, RP 10.224.1.1, flags: SJPC Incoming interface: FastEthernet0/0, RPF nbr 10.1.2.1 Outgoing interface list: Null R5#sh ip route 10.224.1.1 Routing entry for 10.224.1.1/32 Known via "ospf 10", distance 110, metric 66, type intra area Last update from 10.1.2.1 on FastEthernet0/0, 00:33:44 ago Routing Descriptor Blocks: * 10.1.2.1, from 10.2.3.1, 00:33:44 ago, via FastEthernet0/0 Route metric is 66, traffic share count is 1 R5#sh ip route 10.1.1.0 Routing entry for 10.1.1.0/24 Known via "ospf 10", distance 110, metric 129, type intra area Last update from 10.2.5.2 on Serial1/0.705, 00:33:55 ago Routing Descriptor Blocks: * 10.2.5.2, from 10.2.2.1, 00:33:55 ago, via Serial1/0.705 Route metric is 129, traffic share count is 1 R4#sh ip pim interface Address Interface Ver/ Nbr Query DR DR Mode Count Intvl Prior 10.1.2.1 FastEthernet0/0 v2/S 1 30 1 10.1.2.25 10.2.4.1 Serial1/0.605 v2/S 1 30 1 0.0.0.0 10.2.3.2 Serial1/0.609 v2/S 1 30 1 0.0.0.0

未完等续。。。。