This chapter offered an introduction to multicast building blocks and protocols. It covered historical developments in addition to modern multicasting approaches, LAN/WAN issues, dense/sparse subscriber distribution, interdomain/intradomain architectures, and a comparison of link/network/application layer issues. Note that essentially all the routing packages discussed in Chapter 2, "User-Space Routing Software," are incapable of dealing with multicast signaling, with the exception of XORP PIM and generic MBGP hooks in Zebra/Quagga. The user-space daemons mrouted and pimd add DVMRP and PIM-SM routing capabilities to the UNIX operating systems.

All discussed UNIX kernels natively support IGMPv1/v2; IGMPv3 packages and patches are available, too. IGMPv3 is closely connected to SSM receiver operation.

A lot of development work focuses on the area of SSM, reliable multicast, multicast security, and DoS issues. SSM is a PIM extension to increase one-to-many communication efficiency without the involvement of RPs. Modern interarea multicast approaches are based on a combination of MSDP, BGMP, and MBGP; eventually, however, one single protocol will prevail.

Note that this chapter really just introduced the concept of interdomain multicasting; a thorough discussion of interdomain multicast signaling protocols goes beyond the scope of this book.