Operation Manual – Multicast
H3C S5600 Series Ethernet Switches
Chapter 4 PIM Configuration
4-11
2)
When the RP receives the register message, on one hand, it extracts the multicast
packet from the register message and forwards the multicast packet down the
RPT, and, on the other hand, it sends an (S, G) join message hop by hop toward
the multicast source. Thus, the routers along the path from the RP to the multicast
source constitute an SPT branch. Each router on this branch generates a (S, G)
entry in its forwarding table. The multicast source is the root, while the RP is the
leaf, of the SPT.
3) The subsequent multicast data from the multicast source travels along the
established SPT to the RP, and then the RP forwards the data along the RPT to
the receivers. When the multicast traffic arrives at the RP along the SPT, the RP
sends a register-stop message to the source-side DR by unicast to stop the
source registration process.
VI. Switchover from RPT to SPT
Initially, multicast traffic flows along an RPT from the RP to the receivers. Because the
RPT is not necessarily the tree that has the shortest path, upon receiving the first
multicast packet along the RPT, the receiver-side DR initiates an RPT-to-SPT
switchover process, as follows:
1) First, the receiver-side DR sends an (S, G) join message hop by hop to the
multicast source. When the join message reaches the source-side DR, all the
routers on the path have installed the (S, G) entry in their forwarding table, and
thus an SPT branch is established.
2)
Subsequently, the receiver-side DR sends a prune message hop by hop to the RP.
Upon receiving this prune message, the RP forwards it towards the multicast
source, thus to implement RPT-to-SPT switchover.
After the RPT-to-SPT switchover, multicast data can be directly sent from the source to
the receivers. PIM-SM builds SPTs through RPT-to-SPT switchover more economically
than PIM-DM does through the “flood and prune” mechanism.
VII. Assert
PIM-SM uses exactly the same assert mechanism as PIM-DM does. Refer to
Assert
.
4.2 Configuring PIM-DM
4.2.1 Enabling PIM-DM
With PIM-DM enabled, a router sends hello messages periodically to discover PIM
neighbors and processes messages from PIM neighbors. When deploying a PIM-DM
domain, you are recommended to enable PIM-DM on all interfaces of non-border
routers.
Follow these steps to enable PIM-DM: