The current IP multicast infrastructure in the Internet and many enterprise intranets is based on the Protocol Independent Multicast sparse mode (PIM-SM) protocol and Multicast Source Discovery Protocol (MSDP). These protocols are reliable, extensive, and efficient. However, they are bound to the complexity and functionality limitations of the Internet Standard Multicast (ISM) service model. For example, with ISM, the network must maintain knowledge about which hosts in the network are actively sending multicast traffic. With Source Specific Multicast (SSM), receivers provide this information through the source addresses relayed to the last hop routers by Internet Group Management Protocol Version 3 (IGMPv3), IGMP Version 3 lite (IGMP v3lite), or URL Rendezvous Directory (URD).
SSM is an incremental response to the issues associated with ISM and is intended to coexist in the network with the protocols developed for ISM. In general, SSM provides a more advantageous IP multicast service.
This chapter describes how an Internet service provider (ISP) customer within an interdomain multicast network implements SSM in its network using URD. This chapter begins by introducing the initial interdomain ISP topology and describing basic SSM operations (including SSM IP address range). There are three ways to implement SSM in an interdomain environment: using IGMPv3 host signaling, using IGMP v3lite host signaling, and using URD host signaling. Each of these possibilities is briefly described. This chapter then presents and discusses the recommended implementation solution: SSM using URD host signaling. This discussion includes benefits and ramifications of implementing SSM using URD host signaling, necessary prerequisites, and implementation process steps. This chapter concludes with a list of recommended and related documents.
The SSM solution presented in this chapter is based on an actual customer situation. This solution was tested and verified in a lab environment and has been deployed in the field. Alternative ways to implement SSM, such as with IGMPv3 and IGMP v3lite host signaling, are discussed but were not implemented in our lab environment.
The scope of this chapter is to describe basic design and deployment of SSM using URD. It does not discuss in detail the general operation of the protocols associated with developing interdomain multicast networks such as PIM-SM. For more information about PIM-SM, refer to Chapter 1, "IP Multicast Technology Overview."
Initial Interdomain Network Topology
The SSM network scenario used in this chapter is based on the hypothetical interdomain ISP network scenario described in Chapter 2, "Implementing Interdomain Multicast Using MSDP." Figure 6-1 shows the logical connections of the initial interdomain multicast network topology. Each ISP in Figure 6-1 has established Border Gateway Protocol (BGP) peering and its own autonomous system (AS). The design of each ISP multicast network topology depends on the individual requirements of the ISP.
Figure 6-1 Logical Connections of the Initial Interdomain Multicast Network Topology
The solution presented in this document is based on a hypothetical interdomain ISP environment. All the IP addresses and configuration in this document are provided for illustrative purposes only.