Configuring IP Multicast 765The following table summarizes the equivalent CLI commands for this feature.Protocol Independent MulticastProtocol Independent Multicast-Dense Mode (PIM-DM) protocol is a simple, protocol-independentmulticast routing protocol. It uses an existing Unicast routing table and a Join/Prune/Graft mechanismto build a tree. PIM-DM creates source-based shortest-path distribution trees that make use of RPF. Itcannot be used to build a shared distribution tree, as is the case in PIM-SM. PIM-DM assumes thatwhen a sender starts sending data, all downstream routers and hosts want to receive a multicastdatagram. PIM-DM initially floods multicast traffic throughout the network. Routers that do not haveany downstream neighbors prune back the unwanted traffic. In addition to PRUNE messages, PIM-DMmakes use of graft and assert messages. Graft messages are used whenever a new host wants to join thegroup. Assert messages are used to shutoff duplicate flows on the same multi-access network.There are two versions of PIM-DM. Version 2 doesn’t use the IGMP message; instead, it uses a messagethat is encapsulated in IP package, with protocol number 103. In Version 2, Hello message is introducedin place of query message.PIM-DM is appropriate for:• Densely distributed receivers• Few senders -to- many receivers (due to frequent flooding)• High volume of multicast traffic• Constant stream of trafficProtocol Independent Multicast-Sparse Mode ( PIM-SM) is used to efficiently route multicast traffic tomulticast groups that may span wide area networks and where bandwidth is a constraint. PIM-SM usesshared trees by default and implements source-based trees for efficiency. This data threshold rate is usedto toggle between trees. PIM-SM assumes that no hosts want the multicast traffic unless they specificallyask for it. It creates a shared distribution tree centered on a defined rendezvous point (RP) from whichsource traffic is relayed to the receivers. Senders first send the multicast data to the RP, which in turnsends the data down the shared tree to the receivers. Shared trees centered on a RP do not necessarilyprovide the shortest/optimal path. In such cases, PIM-SM provides a means to switch to more efficientsource-specific trees.The PIM menu page contains links to web pages that define and display PIM-DM and PIM-SMparameters and data. Only one PIM protocol can be enabled on the switch at a time. To display the PIMpage, click IPv4 Multicast →PIM or IPv6 Multicast →PIM in the tree view.Following are the web pages accessible from this menu page:Table 12-31. IPv6 MLD Membership Detailed Information CommandCLI Command Descriptionshow ipv6 mld-proxy groups detail Displays information about multicast groups that MLD Proxyreported.
