95
As shown in
, the network has two multicast sources, Source 1 (S1) and Source 2 (S2).
Both of them can send multicast data to multicast group G. Host B is interested in the multicast data
that the source 1 sends to G but not in the data from the source 2.
Figure 34 Flow paths of source-and-group-specific multicast traffic
In IGMPv1 or IGMPv2, Host B cannot select multicast sources when it joins multicast group G. The
multicast streams from both the source 1 and the source 2 flow to Host B whether or not it needs
them.
When IGMPv3 runs between the hosts and routers, Host B can explicitly express that it needs to
receive the multicast data that Source 1 sends to multicast group G (denoted as (S1, G)). It also can
explicitly express that it does not want to receive the multicast data that Source 2 sends to multicast
group G (denoted as (S2, G)). As a result, Host B receives only multicast data from Source 1
Enhancements in query and report capabilities
1.
Query message carrying the source addresses
IGMPv3 supports general queries (feature of IGMPv1), group-specific queries (feature of
IGMPv2), and group-and-source-specific queries.
{
A general query does not carry a group address or a source address
{
A group-specific query carries a group address, but no source address
{
A group-and-source-specific query carries a group address and one or more source
addresses.
2.
Reports containing multiple group records
Unlike an IGMPv1 or IGMPv2 report message, an IGMPv3 report message is destined to
224.0.0.22 and contains one or more group records. Each group record contains a multicast
group address and a multicast source address list.
Group records fall into the following categories:
{
IS_IN
—The source filtering mode is Include. The report sender requests the multicast data
from only the sources defined in the specified multicast source list.
{
IS_EX
—The source filtering mode is Exclude. The report sender requests the multicast
data from any sources but those defined in the specified multicast source list.
{
TO_IN
—The filtering mode has changed from Exclude to Include.
{
TO_EX
—The filtering mode has changed from Include to Exclude.
{
ALLOW
—The Source Address fields contain a list of additional sources from which the
receiver wants to obtain data. If the current filtering mode is Include, these sources are
added to the multicast source list. If the current filtering mode is Exclude, these sources are
deleted from the multicast source list.
