Planet XGS3-24042 User Manual download pdf (Page 409)

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48.2.4 PIM-DM Troubleshooting

In configuring and using PIM-DM Protocol, PIM-DM Protocol might not operate normally caused by physical

connection or incorrect configuration. Therefore, the user should pay attention to the following issues:

 To assure that physical connection is correct

 To assure the Protocol of Interface and Link is UP (use show interface command)

 To assure PIM Protocol is enabled in Global Mode (use ipv6 pim multicast-routing )

 Enable PIM-DM Protocol on the interface (use ipv6 pim dense-mode command)

 Multicast Protocol requires RPF Check using Unicast routing; therefore the correctness of Unicast

routing must be assured beforehand

If all attempts including Check are made but the problems on PIM-DM can’t be solved yet, then use debug

commands such as debug pim please, and then copy DEBUG information in 3 minutes and send to

Technology Service Center.

48.3 PIM-SM

48.3.1 Introduction to PIM-SM

PIM-SM（Protocol Independent Multicast, Sparse Mode）is Protocol Independent Multicast Sparse Mode. It is

a Multicast Routing Protocol in Sparse Mode and mainly used in big scale network with group members

distributed relatively sparse and wide-spread. Unlike the Flooding & Prune of Dense Mode, PIM-SM Protocol

assumes no host needs receiving Multicast data packets. PIM-SM router transmits Multicast Data Packets to

a host only if it presents explicit requirement.

By setting RP (Rendezvous Point) and BSR (Bootstrap Router), PIM-SM announce Multicast packet to all

PIM-SM routers and establish RPT (RP-rooted shared tree) based on RP using Join/Prune message of

routers. Consequently the network bandwidth occupied by data packets and message control is cut down and

the transaction cost of routers decreases. Multicast data get to the network segment where the Multicast

group members are located along the shared tree flow. When the data traffic reaches a certain amount,

Multicast data stream can be switched to the shortest path tree SPT based on the source to reduce network

delay. PIM-SM doesn’t rely on any specific Unicast Routing Protocol but make RPF Check using existing

Unicast routing table.

1. PIM-SM Working Principle

The central working processes of PIM-SM are: Neighbor Discovery, Generation of RP Shared Tree (RPT),

Multicast source registration, SPT Switch, etc. We won’t describe the mechanism of Neighbor Discovery here

since it is same as that of PIM-DM.

(1) Generation of RP Shared Tree (RPT)

When a host joins a Multicast Group G, the leaf router that is connected to this host directly finds out

through IGMP message that there is a receiver of Multicast Group G, then it works out the

corresponding Rendezvous Point RP for Multicast Group G, and send join message to upper lever

nodes in RP direction. Every router on the way from the leaf router to RP will generate a (*, G) table

entry, where a message from any source to Multicast group applies to this entry. When RP receives

the message sent to Multicast Group G, the message will get to the leaf router along the set up path

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