PIM-DM
涉及知识点：
*PIM DR的选择
*IGMP查询器的选择
*PIM前转器的选择
理论说明：
PIM DR的选择
因为在IGMP V1中不会选举IGMP查询器，如果在同一个多路网段上连接有多台路由器，那么就必须选择PIM DM来避免重复查询！此选举过程由PIM进行，AD越低越优，AD相同再比较metric,同样也是越低越优，还比较不出就将选择IP地址最高的为DR！
IGMP查询器的选择
查询器的选择是针对IGMP V2来说的。网络中拥有最低IP地址的路由器将被选举为IGMP查询器。
PIM前转器的选择
PIM前传器的选择是根据单播路由表条目来的，到组播源的路由的AD最小最优，AD相同就比较metric值，也是最小最优，如果metric值也相同就继续比较IP地址，IP地址则是越大越优！
实验证明：
实验基本配置如上图所示！
1 开启组播路由功能
（1）在每台路由器上开启组播路由功能
R1-R5：
R1(config)#ip multicast-routing
2 在接口上开启PIM Dense-Mode
说明：在全网所有路由器的所有接口上开启PIM，从而建立PIM邻居，要在所有接口开启是因为要让PIM自己决定该在什么接口转发组播，这样可以避免RPF检测失败，因为有可能只开部分接口，将导致接口不符合RPF接口而组播失败！
（1）在所有路由器的每个接口上开启PIM
R1(config)#int fa0/0
R1(config-if)#ip pim dense-mode
其他路由器接口同理！
3 查看PIM邻居
说明：相邻的两台路由器接口上开启PIM后，将成为PIM邻居
（1）查看R1的PIM邻居
R1#show ip pim neighbor
PIM Neighbor Table
Mode: B - Bidir Capable, DR - Designated Router, N - Default DR Priority,
S - State Refresh Capable
Neighbor Interface Uptime/Expires Ver DR
Address Prio/Mode
12.1.1.2 FastEthernet0/0 01:56:41/00:01:17 v2 1 / DR S
说明：可以看到R1的PIM邻居有R2，结果正常。因为双方的DR优先级相同，而R2的IP地址大于R1，所以在R1上看到R2为DR。
（2）查看R2的PIM邻居
R2#show ip pim neighbor
PIM Neighbor Table
Mode: B - Bidir Capable, DR - Designated Router, N - Default DR Priority,
S - State Refresh Capable
Neighbor Interface Uptime/Expires Ver DR
Address Prio/Mode
12.1.1.1 FastEthernet0/0 02:02:33/00:01:26 v2 1 / S
24.1.1.4 FastEthernet0/1 02:02:04/00:01:26 v2 1 / DR S
32.1.1.3 Serial1/0 02:02:14/00:01:41 v2 1 / S
（3）查看R3的PIM邻居
R3#show ip pim neighbor
PIM Neighbor Table
Mode: B - Bidir Capable, DR - Designated Router, N - Default DR Priority,
S - State Refresh Capable
Neighbor Interface Uptime/Expires Ver DR
Address Prio/Mode
32.1.1.2 Serial1/0 02:03:13/00:01:42 v2 1 / S
50.1.1.5 FastEthernet0/0 02:02:55/00:01:35 v2 1 / DR S
50.1.1.4 FastEthernet0/0 02:03:00/00:01:34 v2 1 / S
说明：结合R2和R3的输出可以看到DR的选举只在多路网络上才进行选举，R2和R3之前的串口是不选举的，同OSPF上选择DR一样！然后R5地址最大成为DR，R4也成为DR
4 将R5加入组224.2.2.2
说明：组成员要加入组，使用的协议为IGMP，而Cisco路由器开启PIM接口后，接口上将自动开启IGMP，所以R5在加入组时，无需额外开启IGMP而直接加入组224.2.2.2
（1）配置R5加入组224.2.2.2
R5(config)#int fa0/0
R5(config-if)#ip igmp join-group 224.2.2.2
5 测试组播通信
说明：在没有组播数据之前，也就无法确认组播源的位置，在没有组播源的情况下，组播树是不能建立的。在测试R1向组224.2.2.2发送组播流量时，只需要Ping224.2.2.2,只要数据包的目标地址为组播地址，就自动使用组播方式来传递。在R1上Ping组播，那么R1就是组播源
（1）从组播源R1上ping 224.2.2.2
R1#ping 224.2.2.2
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.2.2.2, timeout is 2 seconds:
Reply to request 0 from 50.1.1.5, 600 ms
说明：从回包中看出，已经收到组成员50.1.1.5的回包，说明组播成功被转发到组成员R5
6 查看IGMP查询器
（1）在R5上查看网络中的IGMP查询器
R5#show ip igmp interface fa0/0
FastEthernet0/0 is up, line protocol is up
Internet address is 50.1.1.5/24
IGMP is enabled on interface
Current IGMP host version is 2
Current IGMP router version is 2
IGMP query interval is 60 seconds
IGMP querier timeout is 120 seconds
IGMP max query response time is 10 seconds
Last member query count is 2
Last member query response interval is 1000 ms
Inbound IGMP access group is not set
IGMP activity: 2 joins, 0 leaves
Multicast routing is enabled on interface
Multicast TTL threshold is 0
Multicast designated router (DR) is 50.1.1.5 (this system)
IGMP querying router is 50.1.1.3
Multicast groups joined by this system (number of users):
224.0.1.40(1) 224.2.2.2(1)
说明：与前面理论描述的一致，IP地址小的被设置为IGMP查询器！此处R3的地址为50.1.1.3，小于R4的50.1.1.4！
（2）改大R3fa0/0的接口地址为50.1.1.10，再看IGMP查询器是否改变为50.1.1.4
R3(config)#int fa0/0
R3(config-if)#ip ad 50.1.1.10 255.255.255.0
R5#show ip igmp interface fa0/0
FastEthernet0/0 is up, line protocol is up
Internet address is 50.1.1.5/24
IGMP is enabled on interface
Current IGMP host version is 2
Current IGMP router version is 2
IGMP query interval is 60 seconds
IGMP querier timeout is 120 seconds
IGMP max query response time is 10 seconds
Last member query count is 2
Last member query response interval is 1000 ms
Inbound IGMP access group is not set
IGMP activity: 2 joins, 0 leaves
Multicast routing is enabled on interface
Multicast TTL threshold is 0
Multicast designated router (DR) is 50.1.1.10
IGMP querying router is 50.1.1.4
Multicast groups joined by this system (number of users):
224.0.1.40(1) 224.2.2.2(1)
说明：可以看到IGMP查询器已经变为50.1.1.4，进一步证明了上面的理论！注意如果看不到现象就刷新下OSPF进程
7 查看PIM前传器
（1）把见面的IGMP查询地址恢复成原来的，再查看R3和R4到组播源的单播路由表
R3#show ip route
Gateway of last resort is not set
50.0.0.0/24 is subnetted, 1 subnets
C 50.1.1.0 is directly connected, FastEthernet0/0
32.0.0.0/24 is subnetted, 1 subnets
C 32.1.1.0 is directly connected, Serial1/0
24.0.0.0/24 is subnetted, 1 subnets
O 24.1.1.0 [110/2] via 50.1.1.4, 00:00:11, FastEthernet0/0
12.0.0.0/24 is subnetted, 1 subnets
O 12.1.1.0 [110/3] via 50.1.1.4, 00:00:11, FastEthernet0/0
R4#show ip route
Gateway of last resort is not set
50.0.0.0/24 is subnetted, 1 subnets
C 50.1.1.0 is directly connected, FastEthernet0/0
32.0.0.0/24 is subnetted, 1 subnets
O 32.1.1.0 [110/65] via 50.1.1.3, 00:00:32, FastEthernet0/0
[110/65] via 24.1.1.2, 00:00:32, FastEthernet0/1
24.0.0.0/24 is subnetted, 1 subnets
C 24.1.1.0 is directly connected, FastEthernet0/1
12.0.0.0/24 is subnetted, 1 subnets
O 12.1.1.0 [110/2] via 24.1.1.2, 00:00:32, FastEthernet0/1
说明：可以看到AD相同，R4到组播源的metric为2，R3为3，所以R4将被选为PIM前传器，最后结果将在R2组播路由表中体现出来
（2）查看R2的组播路由表
R2#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,
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
(*, 224.2.2.2), 00:00:06/stopped, RP 0.0.0.0, flags: D
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Serial1/0, Forward/Dense, 00:00:06/00:00:00
FastEthernet0/1, Forward/Dense, 00:00:06/00:00:00
FastEthernet0/0, Forward/Dense, 00:00:06/00:00:00
(12.1.1.1, 224.2.2.2), 00:00:06/00:02:56, flags: T
Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/1, Forward/Dense, 00:00:08/00:00:00
Serial1/0, Prune/Dense, 00:00:08/00:02:54, A
(*, 224.0.1.40), 02:33:09/00:02:57, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/1, Forward/Dense, 02:32:40/00:00:00
Serial1/0, Forward/Dense, 02:32:51/00:00:00
FastEthernet0/0, Forward/Dense, 02:33:09/00:00:00
说明1：可以看到在（12.1.1.1，24.2.2.2）条目的出口上，fa0/1为转发状态，s1/0为修剪状态，所以R4被选为了PIM前传器，这就证明了前面的理论！
说明2：在PIM-DM模式中同样也有（*，G）的记录，创建（*，G）是为了作为（S,G)的“父”数据结构
8 改变PIM的前传器
说明：根据前面的理论，要想改变PIM的前传器，在相同AD下只需要改变其metric值，这里我们先把其metric也设为一样，再改变R3fa0/0的地址为50.1.1.10
（1）改变R3接口s0/0的cost值，并查看R3到组播源R1的metric
R3(config)#int s1/0
R3(config-if)#ip ospf cost 1
R3#show ip route
Gateway of last resort is not set
50.0.0.0/24 is subnetted, 1 subnets
C 50.1.1.0 is directly connected, FastEthernet0/0
32.0.0.0/24 is subnetted, 1 subnets
C 32.1.1.0 is directly connected, Serial1/0
24.0.0.0/24 is subnetted, 1 subnets
O 24.1.1.0 [110/2] via 50.1.1.4, 00:00:11, FastEthernet0/0
[110/2] via 32.1.1.2, 00:00:11, Serial1/0
12.0.0.0/24 is subnetted, 1 subnets
O 12.1.1.0 [110/2] via 32.1.1.2, 00:00:11, Serial1/0
说明：可以看到metric改为和R4一样了，都为2！
（2）在R2查看PIM前传器结果
R2#show ip mroute
(12.1.1.1, 224.2.2.2), 00:00:04/00:02:55, flags: T
Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/1, Forward/Dense, 00:00:06/00:00:00
Serial1/0, Prune/Dense, 00:00:05/00:02:54
说明：可以看到结果任然没有改变，虽然R3到组播源的metric和R4一样了，但是R4的IP地址任然大于R3！
（3）改变R3的IP地址为50.1.1.10，并查看前传器结果
R3(config)#int fa0/0
R3(config-if)#ip ad 50.1.1.10 255.255.255.0
R2#show ip mroute
(12.1.1.1, 224.2.2.2), 00:00:04/00:02:55, flags: T
Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/1, Prune/Dense, 00:00:05/00:02:54
Serial1/0, Forward/Dense, 00:00:05/00:00:00
说明：可以看到前传器已经改变！至此，前面的理论已经证明完毕！
补充PIM-DM知识点
1 如果一个路由器有5个接口，其中一个为组播源接口，一个连接了组成员接口，在PIM DM中，这些没有连接组成员的接口也为被放在出口中，也就是说出口记录了4个，实际上只用了1个，这样有点浪费资源了！还是上面的实验，我们查看R2的组播路由表：
R2#show ip mroute
(12.1.1.1, 224.2.2.2), 00:00:04/00:02:55, flags: T
Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/1, Prune/Dense, 00:00:05/00:02:54
Serial1/0, Forward/Dense, 00:00:05/00:00:00
说明：可以看到被修剪的接口依然放在了出口，如果是PIM-SM就不会！