Fault Symptom
PIM-SM is configured on the network; Router C functions as the static RP; Switch C functions as the receiver's DR.
The receiver's DR initiates the generation of an SPT. After the SPT is set up, it is found that users cannot watch the programs of certain IPTV channels.
Fault Analysis
1. According to the network topology, there are equal-cost routes. One route passes through Router A, and the other route passes through Router B. Router C functions as the RP, and there is only one hop between Router A to Router C. Therefore, there are complete (S, G) and (*, G) entries on Router A.
When Switch C sends Join messages to trigger the establishment of the SPT, some of the Join messages may be sent to Router B. In this case, when the first (S, G) Join message reaches Switch C along the SPT, Switch C sends Prune messages along the RPT to the RP.
2. Run the debugging pim join-prune command on Router B to view debugging information. It is found that Router B receives Join messages from Switch C, creates (S, G) entries, and sends them to Router D.
<HUAWEI> debugging pim join-prune
*6.575255524 DeviceB PIM/8/EVENT:Public:PIM-SM: Upstream (221.1.1.192, 224.1.1.58) FSM transited from NotJoined to Joined, JoinDesired == True. (S13328)
*6.575255524 DeviceB PIM/8/ROUT:Public:PIM-SM: Deleting iif 221.1.1.38 from (221.1.1.192, 224.1.1.58). (S011943)
*6.575255524 DeviceB PIM/8/ROUT:Public:PIM-SM: Adding iif 221.1.1.38 to (221.1.1.192, 224.1.1.58). (S012275)
*6.575255524 DeviceB PIM/8/JP:Public:PIM ver 2 JP sending 221.1.1.38 -> 224.0.0.13 on GigabitEthernet2/0/0 (P011934)
*6.575255524 DeviceB PIM/8/JP:Public:Upstream 221.1.1.37, Groups 1, Holdtime 210 (P011698)
*6.575255524 DeviceB PIM/8/JP:Public:Group: 224.1.1.58/32 --- 1 joins 0 prunes (P011734)
*6.575255524 DeviceB PIM/8/JP:Public:Join: 221.1.1.192/32 S (P011757)
3. View debugging information on Router D in the same manner. It is found that Router D receives Join messages and sends them to the upstream device. Router D, however, does not receive any (S, G) Join messages from the peer device within 210 seconds. Therefore, the multicast route is pruned.
<HUAWEI> debugging pim join-prune
*6.574204484 DeviceD PIM/8/ROUT:Public:PIM-SM: Adding iif 221.1.1.69 to (221.1.1.175, 224.1.1.2). (S012275)
*6.574204484 DeviceD PIM/8/JP:Public:PIM ver 2 JP sending 221.1.1.69 -> 224.0.0.13 on GigabitEthernet6/0/0 (P011934)
*6.574204484 DeviceD PIM/8/JP:Public:Upstream 221.1.1.70, Groups 1, Holdtime 210 (P011698)
*6.574204484 DeviceD PIM/8/JP:Public:Group: 224.1.1.2/32 --- 1 joins 0 prunes (P011734)
*6.574204484 DeviceD PIM/8/JP:Public:Join: 221.1.1.175/32 S (P011757)
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*6.574314704 DeviceD PIM/8/JP:Public:Upstream 221.1.1.70, Groups 1, Holdtime 210 (P011698)
*6.574314704 DeviceD PIM/8/JP:Public:Group: 224.1.1.58/32 --- 0 joins 1 prunes (P011734)
*6.574314704 DeviceD PIM/8/JP:Public:Prune: 221.1.1.192/32 S (P011780)
4. Check the configurations of the upstream device. It is found that PIM is not enabled on the interfaces of Switch B. As a result, the Join messages from the downstream device cannot be sent to the multicast source. 210 seconds later, the (S, G) entry on Router D expires and the entry is thus deleted.
Procedure
1. After PIM is enabled on the interfaces of Switch B, the services run normally. The fault is thus rectified.
Summary
If there are multiple equal-cost routes between the receiver's DR and multicast source, you need to enable the multicast protocol on each device along each route.
