HP 6125G HP 6125G & 6125G/XG Blade Switches IP Multicast Configuration - Page 124

Figure 44 SPT building in PIM-SSM As shown in Figure 44, Host B and Host C are multicast information receivers. They send IGMPv3 report messages to the respective DRs to express their interest in the information about the specific multicast source S. After receiving a report message, the DR first determines whether the group address in this message falls into the SSM group range and then does the following: • If the group address in the message does fall into the SSM group range, the DR sends a subscribe message for channel subscription hop by hop toward the multicast source S. An (S, G) entry is created on all routers on the path from the DR to the source. An SPT is thereby built in the network, with the source S as its root and receivers as its leaves. This SPT is the transmission channel in PIM-SSM. • If the group address in the message does not fall into the SSM group range, the receiver-side DR follows the PIM-SM process. The receiver-side DR sends a (*, G) join message to the RP, and the source-side DR registers the multicast source. Relationships among PIM protocols In a PIM network, PIM-DM cannot run together with PIM-SM or PIM-SSM. However, PIM-SM and PIM-SSM can run together. When they run together, which one is chosen for a receiver trying to join a group depends, as shown in Figure 45. 113