tailieunhanh - The Illustrated Network- P46

The Illustrated Network- P46:In this chapter, you will learn about the protocol stack used on the global public Internet and how these protocols have been evolving in today’s world. We’ll review some key basic defi nitions and see the network used to illustrate all of the examples in this book, as well as the packet content, the role that hosts and routers play on the network, and how graphic user and command line interfaces (GUI and CLI, respectively) both are used to interact with devices. | CHAPTER 16 Multicast 419 Protocols for SourceSpecific Multicast Protocols for ReversePath Forwarding Protocols for Any-Source Multicast FIGURE Suite of multicast protocols showing how those for ASM SSM and RFP checks fit together and are used. receivers hosts . This eliminates much of the complexity of multicast mechanisms required in ASM and the use of MSDP. It also eliminates some of the scaling considerations associated with traffic on G groups. ASM and SSM are not protocols but service models. Most of what is described in this chapter applies to ASM the more general model . But keep in mind that SSM does away with many of the procedures covered in detail here that apply to ASM including RPs RPTs and MSDP. Figure shows the current suite of multicast protocols and how they all fit together. Multicast Source Discovery Protocol MSDP described in RFC 3618 is a mechanism to connect multiple PIM-SM domains usually each in an AS . Each PIM-SM domain can have its own independent RPs and these do not interact in any way so MSDP is not needed in SSM scenarios . The advantages of MSDP are that the RPs do not need any other resource to find each other and that domains can have receivers only and get content without globally advertising group membership. In addition MSDP can be used with protocols other than PIM-SM. 420 PART III Routing and Routing Protocols MSDP routers in a PIM-SM domain peer with their MSDP router peers in other domains. The peering session uses a TCP connection to exchange control information. Each domain has one or more of these connections in its virtual topology. This allows domains to discover multicast sources in other domains. If these sources are deemed of interest to receivers in another domain the usual source-tree mechanism in PIM-SM is used to deliver multicast content but now over an interdomain distribution tree. More details about MSDP are beyond the scope of this introductory chapter. Frames and Multicast Multicasting on a LAN is