Introduction
IP multicasting is one of the key technologies for the next generation of the Internet.Meantime, increasing network bandwidth makes applications such as video streaming more realistic, which then makes IP multicasting more important.
Although the basic notion of multicasting is common to both IPv4 and IPv6, IPv6 multicasting brings several new characteristics based on operational experiences gained from the IPv4 counterpart. For example, IPv6 explicitly limits the scope of a multicast address by using a fixed address field.
The notion of explicit multicast scoping (called administratively scoped multicast) was introduced in IPv4 multicasting subsequently. The IPv6 multicast scope can be regarded as a built-in extension of administrative scoping.
This topic discusses details about IPv6 multicasting, especially on multicast routing mechanisms. We first explain the basic technical background of IP multicasting, focusing on protocols specific to IPv6.
FIGURE 2-54
It includes both the host-to-router protocol and multicast routing protocols. We then describe the KAME kernel code that implements these standard protocols. Finally, we show some examples of IPv6 multicast operation using application programs provided in the KAME implementation.
IPv6 takes a similar approach on mapping an IPv4 multicast address to a Layer-2 multicast address. The exact mapping algorithm depends on the media type. In the case of Ethernet, the method of mapping an IPv6 multicast address to an Ethernet multicast address is to prepend the value of 0×3333 to the last four bytes of the IPv6 multicast address to form a 48-bit Ethernet multicast address. For example, the multicast address for DHCPv6 servers assigned by the IANA, ff05::1:3, is mapped into Ethernet MAC address 33-33-00-00-01-03 as shown in Figure 2-1.
