1220 CHAPTER 73: MLD CONFIGURATIONAs shown in Figure 354, the network comprises two IPv6 multicast sources, Source1 (S1) and Source 2 (S2), both of which can send IPv6 multicast data to IPv6multicast group G. Host B is interested only in the IPv6 multicast data that Source1 sends to G but not in the data from Source 2.Figure 354 Flow paths of source-and-group-specific multicast trafficIn the case of MLDv1, Host B cannot select IPv6 multicast sources when it joinsIPv6 multicast group G. Therefore, IPv6 multicast streams from both Source 1 andSource 2 will flow to Host B whether it needs them or not.When MLDv2 is running on the hosts and routers, Host B can explicitly express itsinterest in the IPv6 multicast data Source 1 sends to G (denoted as (S1, G)), ratherthan the IPv6 multicast data Source 2 sends to G (denoted as (S2, G)). Thus, onlyIPv6 multicast data from Source 1 will be delivered to Host B.MLD stateA multicast router running MLDv2 maintains the multicast address state permulticast address per attached subnet. The multicast address state consists of thefollowing:■ Filter mode: The router keeps tracing the Include or Exclude state.■ List of sources: The router keeps tracing the newly added or deleted IPv6multicast source.■ Timers: Filter timer (the time the router waits before switching to the Includemode after an IPv6 multicast address times out), source timer (for sourcerecording), and so on.Receiver host state listeningBy listening to the state of receiver hosts, a multicast router running MLDv2records and maintains information of hosts joining the source group on theattached subnet.MLD Message Types The following descriptions are based on MLDv2 messages.Source 2ReceiverHost AHost BHost CPackets (S1,G)Packets (S2,G)Source 1
