Netgear XCM8806 Chassis User Manual - Page 728

NETGEAR 8800 User Manual Note: This feature is supported at and above the license level listed for this feature in the license tables in Appendix A, XCM8800 Software Licenses. PIM-DM routers perform reverse path multicasting (RPM). However, instead of exchanging its own unicast route tables for the RPM algorithm, PIM-DM uses the existing unicast routing table for the reverse path. As a result, PIM-DM requires less system memory. PIM-DM with State Refresh The PIM-DM State Refresh feature keeps the PIM-DM prune state from timing out by periodically sending a state refresh control message down the source tree. These control messages reset the prune hold time timer on each pruned interface and prevent the bandwidth waste that occurs with each prune, time-out, and flood cycle. When a topology change occurs, the PIM-DM State Refresh feature improves network convergence. For example, suppose that an S, G entry on S5 in Figure 82 is removed due to non-availability of a route. Without PIM-DM State Refresh, multicast traffic is blocked for minutes (due to a time-out on the upstream routers). In the meantime if an IGMP member or a PIM-DM neighbor joins S5, there is no way to pull traffic down immediately because S5 does not have any S, G information. State refresh control messages solve this problem by indicating S, G state information periodically to all downstream routers. When S5 receives a state refresh from S3, it scans the S, G information and all pending requests from PIM-DM neighbors and IGMP members. If there are pending requests for the group in the state refresh message, S5 can immediately send a graft message upstream to circumvent the upstream timers and pull multicast traffic to its members and neighbors. To enable, configure, and disable the PIM-DM State Refresh feature, use the following commands: configure pim state-refresh {vlan} [ | all] [on | off] configure pim state-refresh timer origination-interval configure pim state-refresh timer source-active-timer configure pim state-refresh ttl PIM Sparse Mode Unlike PIM-DM, Protocol-Independent Multicast - Sparse Mode (PIM-SM) is an explicit join and prune protocol, which means that multicast receivers, and the routers that support them, must join multicast groups before they receive multicast traffic. When all receivers on a network branch leave a multicast group, that branch is pruned so that the multicast traffic does not continue to consume bandwidth on that branch. PIM-SM supports shared trees as well as shortest path trees (SPTs). PIM-SM is beneficial for large networks that have group members that are sparsely distributed. 728 | Chapter 27. Multicast Routing and Switching