Tham khảo tài liệu 'routing6', công nghệ thông tin, chứng chỉ quốc tế phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Operation of Protocol Independent Multicast Sparse Mode PIM-SM 489 Notice that three of the messages Hello Join Prune and Assert also are used by PIM-DM There are four messages unique to PIM-SM just as there are two messages Graft and Graft-Ack used only by PIM-DM Several functions are common to PIM-SM and PIM-DM Neighbor discovery through exchange of Hello messages Recalculation of the RPF interface when the unicast routing table changes Election of a designated router on multiaccess networks The use of Prune Overrides on multiaccess networks Use of Assert messages to elect a designated forwarder on multiaccess networks These functions are all described in the PIM-DM section and so are not described again here Unlike PIM-DM PIM-SM uses explicit joins making the creation of both shared and source-based multicast trees more efficient Finding the Rendezvous Point As you have already learned a shared tree is rooted at a router somewhere in the multicast internetwork rather than at the source CBT calls this router the core and PIM-SM calls it the rendezvous point RP Before a shared tree can be established the joining routers must know how to find the RP The router can learn the address of the RP in three ways The RP address can be statically configured on all routers An open-standard bootstrap protocol can be used to designate and advertise the RP The Cisco-proprietary Auto-RP protocol can be used to designate and advertise the RP The use of all three methods is demonstrated in Chapter 6 As with static routes statically configuring RP addresses on all routers has the advantage of providing very specific control of the internetwork but at the cost of high administrative overhead Static RP configuration is generally only feasible on small multicast internetworks The Bootstrap Protocol The bootstrap protocol first supported in Cisco IOS Software Release 11 3T is essentially the same protocol used by CBT to advertise core routers with a few changes in message names and .
