10G Core Routing Switch User Manual
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sent. When the RP receives the packets sent to multicast group G, the packets will be sent to leaf routers along the
path built and then reach the hosts. In this way, an RP-rooted tree (RPT) is built as shown in the following figure.
Figure
RPT schematic diagram
II. Multicast source registration
When multicast source S sends a multicast packet to the multicast group G, the PIM-SM multicast router directly
connected to S will encapsulate the received packet into a registration packet and send it to the corresponding RP in
unicast form. If there are multiple PIM-SM multicast routers on a network segment, the Designated Router (DR) will be
responsible for sending the multicast packet.
Preparations before Configuring PIM-SM
I. Configuring candidate RPs
In a PIM-SM network, multiple RPs (candidate-RPs) can be configured. Each Candidate-RP (C-RP) is responsible for
forwarding multicast packets with the destination addresses in a certain range. Configuring multiple C-RPs is to
implement load balancing of the RP. These C-RPs are equal. All multicast routers calculate the RPs corresponding to
multicast groups according to the same algorithm after receiving the C-RP messages that the BSR advertises.
It should be noted that one RP can serve multiple multicast groups or all multicast groups. Each multicast group can
only be uniquely correspondent to one RP at a time rather than multiple RPs.
II. Configuring BSRs
The BSR is the management core in a PIM-SM network. Candidate-RPs send announcement to the BSR, which is
responsible for collecting and advertising the information about all candidate-RPs. It should be noted that there can be
only one BSR in a network but you can configure multiple candidate-BSRs. In this case, once a BSR fails, you can switch
over to another BSR. A BSR is elected among the C-BSRs automatically. The C-BSR with the highest priority is elected as
the BSR. If the priority is the same, the C-BSR with the largest IP address is elected as the BSR.
III. Configuring static RP
The router that serves as the RP is the core router of multicast routes. If the dynamic RP elected by BSR mechanism is
invalid for some reason, the static RP can be configured to specify RP. As the backup of dynamic RP, static RP improves
network robusticity and enhances the operation and management capability of multicast network.