H3C Technologies H3C S7500E Series Switches - Manual (Page 198)

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1: Vlan-interface100
Protocol: igmp, UpTime: 00:13:25, Expires: 00:03:25
The information on Switch B and Switch C is similar to that on Switch A.
# View the PIM routing table information on Switch D.
[SwitchD] display pim routing-table
Total 0 (*, G) entry; 1 (S, G) entry
(10.110.5.100, 232.1.1.1)
Protocol: pim-ssm, Flag: LOC
UpTime: 00:12:05
Upstream interface: Vlan-interface300
Upstream neighbor: NULL
RPF prime neighbor: NULL
Downstream interface(s) information:
Total number of downstreams: 1
1: Vlan-interface105
Protocol: pim-ssm, UpTime: 00:12:05, Expires: 00:03:25
Troubleshooting PIM Configuration
Failure of Building a Multicast Distribution Tree Correctly
Symptom
None of the routers in the network (including routers directly connected with multicast sources
and receivers) has multicast forwarding entries. That is, a multicast distribution tree cannot be
built correctly and clients cannot receive multicast data.
Analysis
z When PIM-DM runs on the entire network, multicast data is flooded from the first hop router
connected with the multicast source to the last hop router connected with the clients. When
the multicast data is flooded to a router, no matter which router is, it creates (S, G) entries
only if it has a route to the multicast source. If the router does not have a route to the
multicast source, or if PIM-DM is not enabled on the router’s RPF interface to the multicast
source, the router cannot create (S, G) entries.
z When PIM-SM runs on the entire network, and when a router is to join the SPT, the router
creates (S, G) entries only if it has a route to the multicast source. If the router does not
have a router to the multicast source, or if PIM-DM is not enabled on the router’s RPF
interface to the multicast source, the router cannot create (S, G) entries.
z When a multicast router receives a multicast packet, it searches the existing unicast routing
table for the optimal route to the RPF check object. The outgoing interface of this route will
act as the RPF interface and the next hop will be taken as the RPF neighbor. The RPF
interface completely relies on the existing unicast route, and is independent of PIM. The
RPF interface must be PIM-enabled, and the RPF neighbor must also be a PIM neighbor. If
PIM is not enabled on the router where the RPF interface or the RPF neighbor resides, the
establishment of a multicast distribution tree will surely fail, causing abnormal multicast
forwarding.
z Because a hello message does not carry the PIM mode information, a router running PIM is
unable to know what PIM mode its PIM neighbor is running. If different PIM modes are