排除HSRP感知PIM故障
简介
本文档介绍如何对热备份路由器协议(HSRP)感知协议独立组播(PIM)功能以及可以使用该功能的场景进行故障排除。
解释
在需要冗余的环境中，HSRP正常运行。HSRP是一种经过验证的协议，它有效，但是当您有需要组播的客户端时，您如何处理？当活动路由器(AR)关闭时，什么触发组播以收敛？在本例中，使用拓扑1:
拓扑 1
这里需要注意的一点是，R3是PIM指定路由器(DR)，即使R2是HSRP AR。网络已使用开放最短路径优先(OSPF)建立，PIM和R1是IP地址为10.1.1.1的交汇点(RP)。R2和R3均收到互联网组管理协议(IGMP)报告，但只有R3发送PIM加入，因为它是PIM DR。R3向RP构建“*,G”：
R3#sh ip mroute 239.0.0.1
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
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 239.0.0.1), 02:54:15/00:02:20, RP 10.1.1.1, flags: SJC
Incoming interface: Ethernet0/0, RPF nbr 172.16.1.1
Outgoing interface list:
Ethernet0/2, Forward/Sparse, 00:25:59/00:02:20然后，从组播源ping 239.0.0.1，以构建S，G:
Sender#ping 239.0.0.1 re 3
Type escape sequence to abort.
Sending 3, 100-byte ICMP Echos to 239.0.0.1, timeout is 2 seconds:
Reply to request 0 from 10.0.0.10, 35 ms
Reply to request 1 from 10.0.0.10, 1 ms
Reply to request 2 from 10.0.0.10, 2 msS，G已经建立：
R3#sh ip mroute 239.0.0.1
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
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 239.0.0.1), 02:57:14/stopped, RP 10.1.1.1, flags: SJC
Incoming interface: Ethernet0/0, RPF nbr 172.16.1.1
Outgoing interface list:
Ethernet0/2, Forward/Sparse, 00:28:58/00:02:50
(192.168.1.10, 239.0.0.1), 00:02:03/00:00:56, flags: JT
Incoming interface: Ethernet0/0, RPF nbr 172.16.1.1
Outgoing interface list:
Ethernet0/2, Forward/Sparse, 00:02:03/00:02:50单播和组播拓扑当前不一致。这可能重要，也可能不重要。当R3发生故障时会发生什么情况？
R3(config)#int e0/2
R3(config-if)#sh
R3(config-if)#在R2上的PIM检测到R3已经消失并接管DR角色之前，不会收到对ping的应答。使用默认计时器时，需要60至90秒。
Sender#ping 239.0.0.1 re 100 ti 1
Type escape sequence to abort.
Sending 100, 100-byte ICMP Echos to 239.0.0.1, timeout is 1 seconds:
Reply to request 0 from 10.0.0.10, 18 ms
Reply to request 1 from 10.0.0.10, 2 ms....................................................................
.......
Reply to request 77 from 10.0.0.10, 10 ms
Reply to request 78 from 10.0.0.10, 1 ms
Reply to request 79 from 10.0.0.10, 1 ms
Reply to request 80 from 10.0.0.10, 1 ms您可以增加R2的DR优先级，使其成为DR。
R2(config-if)#ip pim dr-priority 50
*May 30 12:42:45.900: %PIM-5-DRCHG: DR change from neighbor 10.0.0.3 to 10.0.0.2 on interface Ethernet0/2HSRP感知PIM是使HSRP成为PIM DR的功能。它还会从虚拟IP发送PIM消息，在路由器具有通向虚拟IP(VIP)的静态路由时，此消息非常有用。 以下是思科对功能的描述：
HSRP感知PIM使组播流量能够通过HSRP AR转发，允许PIM利用HSRP冗余，避免潜在的重复流量，并启用故障转移，这取决于设备中的HSRP状态。PIM-DR与HSRP AR在同一网关上运行并维护mroute状态。
在拓扑1中，HSRP向客户端运行，因此，尽管此功能听起来很适合，但在组播融合中却无济于事。在R2上配置此功能：
R2(config-if)#ip pim redundancy HSRP1 hsrp dr-priority 100
R2(config-if)#
*May 30 12:48:20.024: %PIM-5-DRCHG: DR change from neighbor 10.0.0.3 to 10.0.0.2 on interface Ethernet0/2R2现在是PIM DR，R3现在在接口E0/2上看到两个PIM邻居：
R3#sh ip pim nei e0/2
PIM Neighbor Table
Mode: B - Bidir Capable, DR - Designated Router, N - Default DR Priority,
P - Proxy Capable, S - State Refresh Capable, G - GenID Capable
Neighbor Interface Uptime/Expires Ver DR
Address Prio/Mode
10.0.0.1 Ethernet0/2 00:00:51/00:01:23 v2 0 / S P G
10.0.0.2 Ethernet0/2 00:07:24/00:01:23 v2 100/ DR S P GR2现在拥有S、G，您可以看到它是断言赢家，因为R3以前是LAN网段的组播转发器。
R2#sh ip mroute 239.0.0.1
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
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 239.0.0.1), 00:20:31/stopped, RP 10.1.1.1, flags: SJC
Incoming interface: Ethernet0/0, RPF nbr 192.0.2.1
Outgoing interface list:
Ethernet0/2, Forward/Sparse, 00:16:21/00:02:35
(192.168.1.10, 239.0.0.1), 00:00:19/00:02:40, flags: JT
Incoming interface: Ethernet0/0, RPF nbr 192.0.2.1
Outgoing interface list:
Ethernet0/2, Forward/Sparse, 00:00:19/00:02:40, A当R2的LAN接口关闭时会发生什么情况？R3能否成为DR?它能以多快的速度收敛？
R2(config)#int e0/2
R2(config-if)#shHSRP在R3上更改为活动，但PIM DR角色在PIM查询间隔过期(3x hello)之前不会收敛。
*May 30 12:51:44.204: HSRP: Et0/2 Grp 1 Redundancy "hsrp-Et0/2-1" state Standby -> Active
R3#sh ip pim nei e0/2
PIM Neighbor Table
Mode: B - Bidir Capable, DR - Designated Router, N - Default DR Priority,
P - Proxy Capable, S - State Refresh Capable, G - GenID Capable
Neighbor Interface Uptime/Expires Ver DR
Address Prio/Mode
10.0.0.1 Ethernet0/2 00:04:05/00:00:36 v2 0 / S P G
10.0.0.2 Ethernet0/2 00:10:39/00:00:36 v2 100/ DR S P G
R3#
*May 30 12:53:02.013: %PIM-5-NBRCHG: neighbor 10.0.0.2 DOWN on interface Ethernet0/2 DR
*May 30 12:53:02.013: %PIM-5-DRCHG: DR change from neighbor 10.0.0.2 to 10.0.0.3 on interface Ethernet0/2
*May 30 12:53:02.013: %PIM-5-NBRCHG: neighbor 10.0.0.1 DOWN on interface Ethernet0/2 non DR当PIM收敛发生时，您会丢失大量数据包：
Sender#ping 239.0.0.1 re 100 time 1
Type escape sequence to abort.
Sending 100, 100-byte ICMP Echos to 239.0.0.1, timeout is 1 seconds:
Reply to request 0 from 10.0.0.10, 5 ms
Reply to request 0 from 10.0.0.10, 14 ms...................................................................
Reply to request 68 from 10.0.0.10, 10 ms
Reply to request 69 from 10.0.0.10, 2 ms
Reply to request 70 from 10.0.0.10, 1 msHSRP知道PIM在这方面没有真正帮助。如果改为使用拓扑2，则此命令非常有用：
拓扑 2
路由器R5已添加，而接收方位于R5后面。R5不与R2和R3运行路由，只与RP和组播源处的静态路由点运行：
R5(config)#ip route 10.1.1.1 255.255.255.255 10.0.0.1
R5(config)#ip route 192.168.1.0 255.255.255.0 10.0.0.1如果没有HSRP感知PIM，反向路径转发(RPF)检查将失败，因为具有物理地址的PIM对等体，但R5在网段上看到三个邻居，其中一个是VIP:
R5#sh ip pim nei
PIM Neighbor Table
Mode: B - Bidir Capable, DR - Designated Router, N - Default DR Priority,
P - Proxy Capable, S - State Refresh Capable, G - GenID Capable
Neighbor Interface Uptime/Expires Ver DR
Address Prio/Mode
10.0.0.2 Ethernet0/0 00:03:00/00:01:41 v2 100/ DR S P G
10.0.0.1 Ethernet0/0 00:03:00/00:01:41 v2 0 / S P G
10.0.0.3 Ethernet0/0 00:03:00/00:01:41 v2 1 / S P GR2是在正常情况下转发组播的路由器，因为它是通过活动路由器的HSRP状态转发PIM DR:
R2#sh ip mroute 239.0.0.1
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
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 239.0.0.1), 00:02:12/00:02:39, RP 10.1.1.1, flags: S
Incoming interface: Ethernet0/0, RPF nbr 192.0.2.1
Outgoing interface list:
Ethernet0/2, Forward/Sparse, 00:02:12/00:02:39尝试从源执行ping操作：
Sender#ping 239.0.0.1 re 3
Type escape sequence to abort.
Sending 3, 100-byte ICMP Echos to 239.0.0.1, timeout is 2 seconds:
Reply to request 0 from 198.51.100.10, 1 ms
Reply to request 1 from 198.51.100.10, 2 ms
Reply to request 2 from 198.51.100.10, 2 msping工作，R2具有S、G:
R2#sh ip mroute 239.0.0.1
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
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 239.0.0.1), 00:04:18/00:03:29, RP 10.1.1.1, flags: S
Incoming interface: Ethernet0/0, RPF nbr 192.0.2.1
Outgoing interface list:
Ethernet0/2, Forward/Sparse, 00:04:18/00:03:29
(192.168.1.10, 239.0.0.1), 00:01:35/00:01:24, flags: T
Incoming interface: Ethernet0/0, RPF nbr 192.0.2.1
Outgoing interface list:
Ethernet0/2, Forward/Sparse, 00:01:35/00:03:29当R2发生故障时会发生什么情况？
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#int e0/2
R2(config-if)#sh
R2(config-if)#Sender#ping 239.0.0.1 re 200 ti 1
Type escape sequence to abort.
Sending 200, 100-byte ICMP Echos to 239.0.0.1, timeout is 1 seconds:
Reply to request 0 from 198.51.100.10, 9 ms
Reply to request 1 from 198.51.100.10, 2 ms
Reply to request 1 from 198.51.100.10, 11 ms....................................................................
......................................................................
............................................................
ping超时，因为当R5的PIM加入进入时，R3不会意识到它必须处理加入。
*May 30 13:20:13.236: PIM(0): Received v2 Join/Prune on Ethernet0/2 from 10.0.0.5, not to us
*May 30 13:20:32.183: PIM(0): Generation ID changed from neighbor 10.0.0.2结果是，PIM冗余命令也必须在辅助路由器上配置，以便处理PIM加入到VIP。
R3(config-if)#ip pim redundancy HSRP1 hsrp dr-priority 10配置完后，将处理传入的加入。R3触发R5发送新的加入，因为GenID在PIM hello中设置为新值。
*May 30 13:59:19.333: PIM(0): Matched redundancy group VIP 10.0.0.1 on Ethernet0/2 Active, processing the Join/Prune, to us
*May 30 13:40:34.043: PIM(0): Generation ID changed from neighbor 10.0.0.1在此配置后，PIM DR角色的收敛速度与HSRP允许的速度一样快。此场景中使用双向转发检测(BFD)。
结论
了解HSRP感知PIM的关键概念是：
- 最初，AR上的PIM冗余配置使其成为DR。
- PIM冗余也必须在辅助路由器上配置，否则，它无法处理PIM加入到VIP。
- PIM DR角色在PIM呼叫超时之前不会收敛。辅助路由器处理Joins，因此组播会收敛。
要点
当HSRP LAN上有接收器时，此功能不起作用，因为DR角色在PIM邻接过期之前不会移动。
相关信息
修订历史记录
| 版本 | 发布日期 | 备注 |
|---|---|---|
1.0 |
02-Jun-2022 |
初始版本 |
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