Troubleshooting Pim Configuration - HP 4800G Series Configuration Manual

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
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.
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.
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.
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 enabled on the RPF
1-54