Cisco配置PIM-DMPIM-DM介绍 PIM-DM（Protocol Independent Multicast-

PIM简介

PIM是Protocol Independent Multicast（协议无关组播）的简称，表示可以利用静态路由或者任意单播路由协议（包括RIP、OSPF、IS-IS、BGP等）所生成的单播路由表为IP组播提供路由。组播路由与所采用的单播路由协议无关，只要能够通过单播路由协议产生相应的组播路由表项即可。PIM借助RPF（Reverse Path Forwarding，逆向路径转发）机制实现对组播报文的转发。当组播报文到达本地设备时，首先对其进行RPF检查：若RPF检查通过，则创建相应的组播路由表项，从而进行组播报文的转发；若RPF检查失败，则丢弃该报文。

根据实现机制的不同，PIM分为以下两种模式：

PIM-DM（Protocol Independent Multicast-Dense Mode，协议无关组播—密集模式）
PIM-SM（Protocol Independent Multicast-Sparse Mode，协议无关组播—稀疏模式）

PIM-DM简介

PIM-DM属于密集模式的组播路由协议，使用“推（Push）模式”传送组播数据，通常适用于组播组成员相对比较密集的小型网络。

PIM-DM的基本原理如下：

PIM-DM假设网络中的每个子网都存在至少一个组播组成员，因此组播数据将被扩散（Flooding）到网络中的所有节点。然后，PIM-DM对没有组播数据转发的分支进行剪枝（Prune），只保留包含接收者的分支。这种“扩散—剪枝”现象周期性地发生，被剪枝的分支也可以周期性地恢复成转发状态。
当被剪枝分支的节点上出现了组播组的成员时，为了减少该节点恢复成转发状态所需的时间，PIM-DM使用嫁接（Graft）机制主动恢复其对组播数据的转发。

一般说来，密集模式下数据包的转发路径是有源树（Source Tree，即以组播源为“根”、组播组成员为“枝叶”的一棵转发树）。由于有源树使用的是从组播源到接收者的最短路径，因此也称为最短路径树（Shortest Path Tree，SPT）。

实验拓扑

R1的环回接口模拟组播源
R5模拟一台主机加组238.1.1.10

基础配置

R1

R1#configure terminal 
R1(config)#interface lo0
R1(config-if)#ip address 11.1.1.1 255.255.255.0
R1(config-if)#no shutdown 

R1(config-if)#interface eth0/0
R1(config-if)#ip address 12.1.1.1 255.255.255.0
R1(config-if)#no shutdown 

R1(config-if)#interface eth 0/1
R1(config-if)#ip address 13.1.1.1 255.255.255.0
R1(config-if)#no shutdown

R2

R2#configure terminal 
R2(config)#interface eth 0/0
R2(config-if)#ip address 12.1.1.2 255.255.255.0
R2(config-if)#no shutdown 

R2(config-if)#interface eth 0/1
R2(config-if)#ip address 100.1.1.2 255.255.255.0
R2(config-if)#no shutdown

R3

R3#configure terminal 
R3(config)#interface eth0/0
R3(config-if)#ip address 13.1.1.3 255.255.255.0
R3(config-if)#no shutdown 

R3(config-if)#interface eth0/1
R3(config-if)#ip address 100.1.1.3 255.255.255.0
R3(config-if)#no shutdown

R4

R4#configure terminal 
R4(config)#interface eth 0/0
R4(config-if)#ip address 100.1.1.4 255.255.255.0
R4(config-if)#no shutdown 

R4(config-if)#interface eth0/1
R4(config-if)#ip address 45.1.1.4 255.255.255.0
R4(config-if)#ip address 45.1.1.4 255.255.255.0
R4(config-if)#no shutdown

R5

R5#configure terminal 
R5(config)#interface eth0/0
R5(config-if)#ip address 45.1.1.5 255.255.255.0
R5(config-if)#no shutdown

配置IGP

组播要能正常通需要先配置单播。我们配置OSPF

R1

R1的环回接口一定要宣告，因为该接口是组播源，后面要对其进行RPF校验

R1(config)#router ospf 1
R1(config-router)#network 11.1.1.0 0.0.0.255 area 0
R1(config-router)#network 12.1.1.0 0.0.0.255 area 0
R1(config-router)#network 13.1.1.0 0.0.0.255 area 0

R2

network 0.0.0.0 0.0.0.0：这里的 IP 地址和反掩码都是 0.0.0.0，表示匹配所有接口，也就是说将所有接口都启用 OSPF

R2(config)#router ospf 1
R2(config-router)#network 0.0.0.0 0.0.0.0 area 0

R3

R3(config)#router ospf 1
R3(config-router)#network 0.0.0.0 0.0.0.0 area 0

R4

R4(config)#router ospf 1
R4(config-router)#network 0.0.0.0 0.0.0.0 area 0

R5

R5模拟一台主机，这里我们配置一个默认路由

R5(config)#ip route 0.0.0.0 0.0.0.0 45.1.1.4

组播配置

启用组播路由功能

在所有路由器(R1, R2, R3, R4)上执行如下命令

(config)#ip multicast-routing

运行PIM-DM

R1 配置

运行ip pim dense-mode 在接口上开启组播路由协议

R1(config)#interface eth 0/0
R1(config-if)#ip pim dense-mode 

R1(config-if)#interface eth 0/1
R1(config-if)#ip pim dense-mode 

R1(config-if)#interface lo0
R1(config-if)#ip pim dense-mode

R2配置

R2(config)#interface range eth0/0-1
R2(config-if-range)#ip pim dense-mode

R3配置

R3(config)#interface range eth0/0-1  
R3(config-if-range)#ip pim dense-mode

R4配置

R4(config)#interface range eth0/0-1
R4(config-if-range)#ip pim dense-mode

让R5模拟加组

加入到238.1.1.10组播组。

R5(config)#interface eth0/0
R5(config-if)#ip igmp join-group 238.1.1.10

加组操作后在R4上查看下面有哪些组。

R4#show ip igmp group
IGMP Connected Group Membership
Group Address    Interface                Uptime    Expires   Last Reporter   Group Accounted
238.1.1.10       Ethernet0/1              00:01:21  00:02:09  45.1.1.5        
224.0.1.40       Ethernet0/0              00:03:58  00:02:21  100.1.1.4

查看路由

我们查看下R1,R2, R3的组播路由表, 发现此时没有关于238.1.1.10的组播路由

R3#show 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, E - Extranet,
       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, 
       G - Received BGP C-Mroute, g - Sent BGP C-Mroute, 
       N - Received BGP Shared-Tree Prune, n - BGP C-Mroute suppressed, 
       Q - Received BGP S-A Route, q - Sent BGP S-A Route, 
       V - RD & Vector, v - Vector, p - PIM Joins on route, 
       x - VxLAN group
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
 Timers: Uptime/Expires
 Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 224.0.1.40), 00:07:14/00:02:39, RP 0.0.0.0, flags: DCL
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list:
    Ethernet0/1, Forward/Dense, 00:07:14/stopped
    Ethernet0/0, Forward/Dense, 00:07:14/stopped

只有R4的组播路由表里面有

R4#show 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, E - Extranet,
       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, 
       G - Received BGP C-Mroute, g - Sent BGP C-Mroute, 
       N - Received BGP Shared-Tree Prune, n - BGP C-Mroute suppressed, 
       Q - Received BGP S-A Route, q - Sent BGP S-A Route, 
       V - RD & Vector, v - Vector, p - PIM Joins on route, 
       x - VxLAN group
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
 Timers: Uptime/Expires
 Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 238.1.1.10), 00:03:33/00:02:53, RP 0.0.0.0, flags: DC
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list:
    Ethernet0/1, Forward/Dense, 00:03:33/stopped
    Ethernet0/0, Forward/Dense, 00:03:33/stopped

(*, 224.0.1.40), 00:06:11/00:02:04, RP 0.0.0.0, flags: DCL
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list:
    Ethernet0/0, Forward/Dense, 00:06:11/stopped

如果此时我们在R1上ping238.1.1.10后路由表会发生变化，产生该组播的相关路由。

# ping指定源为lo0

R1#ping 238.1.1.10 source loopback 0
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 238.1.1.10, timeout is 2 seconds:
Packet sent with a source address of 11.1.1.1 

Reply to request 0 from 45.1.1.5, 3 ms
Reply to request 0 from 45.1.1.5, 5 ms

再查看下组播路由表,发现此时出现了(S, G)路由。(注： (11.1.1.1, 238.1.1.10)为(S, G)路由。)

R1#show 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, E - Extranet,
       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, 
       G - Received BGP C-Mroute, g - Sent BGP C-Mroute, 
       N - Received BGP Shared-Tree Prune, n - BGP C-Mroute suppressed, 
       Q - Received BGP S-A Route, q - Sent BGP S-A Route, 
       V - RD & Vector, v - Vector, p - PIM Joins on route, 
       x - VxLAN group
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
 Timers: Uptime/Expires
 Interface state: Interface, Next-Hop or VCD, State/Mode

(*, 238.1.1.10), 00:00:41/stopped, RP 0.0.0.0, flags: D
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list:
    Ethernet0/1, Forward/Dense, 00:00:41/stopped
    Ethernet0/0, Forward/Dense, 00:00:41/stopped

(11.1.1.1, 238.1.1.10), 00:00:41/00:02:42, flags: T
  Incoming interface: Loopback0, RPF nbr 0.0.0.0
  Outgoing interface list:
    Ethernet0/0, Prune/Dense, 00:00:41/00:02:18
    Ethernet0/1, Forward/Dense, 00:00:41/stopped

(*, 224.0.1.40), 00:16:53/00:02:18, RP 0.0.0.0, flags: DCL
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list:
    Ethernet0/1, Forward/Dense, 00:10:30/stopped
    Ethernet0/0, Forward/Dense, 00:16:53/stopped

所以在PIM-DM中是先有组播流量然后才有组播路由表项。原因是第一个包先往下推（除了收到包的其他接口都会往外发数据）然后拉上来形成了路由表。后面的流量再发的话就会利用路由表

Cisco配置PIM-DM