After receiving the leave message, the querier sends a configurable number of IGMP
group-specific queries to the group that the host is leaving. Both the destination address field
and the group address field of the message are the address of the multicast group that is being
One of the remaining members (if any on the subnet) in the group should send a report within
the maximum response time advertised in the group-specific queries.
If the querier receives a report for the group before the maximum response timer expires, it
maintains the memberships for the group. Otherwise, the querier assumes that the local subnet
has no member hosts for the group and stops maintaining the memberships for the group.
IGMPv3 is based on and is compatible with IGMPv1 and IGMPv2. It enhances the control
capabilities of hosts and the query and report capabilities of IGMP routers.
Enhancements in control capability of hosts
IGMPv3 introduced two source filtering modes (Include and Exclude). These modes allow a host to
receive or reject multicast data from the specified multicast sources. When a host joins a multicast
group, one of the following occurs:
If the host expects to receive multicast data from specific sources like S1, S2, ..., it sends a
report with the Filter-Mode denoted as "Include Sources (S1, S2, ...)."
If the host expects to reject multicast data from specific sources like S1, S2, ..., it sends a report
with the Filter-Mode denoted as "Exclude Sources (S1, S2, ...)."
As shown in
Both of these sources can send multicast data to the multicast group G. Host B wants to receive the
multicast data addressed to G from Source 1 but not from Source 2.
Figure 35 Flow paths of source-and-group-specific multicast traffic
In IGMPv1 or IGMPv2, Host B cannot select multicast sources when it joins the multicast group G.
The multicast streams from both Source 1 and Source 2 flow to Host B whether or not it needs them.
In IGMPv3, Host B can explicitly express that it needs to receive multicast data destined to the
multicast group G from Source 1 but not from Source 2.
Enhancements in query and report capabilities
IGMPv3 introduces IGMP group-and-source queries and IGMP reports carrying group records.
Query message carrying the source addresses
35, the network has two multicast sources: Source 1 (S1) and Source 2 (S2).