IGMP Leave Process

This section explores two types of leave process. The first leave process involves a single host leaving a multicast session while other hosts from the same VLAN are still receiving the multicast traffic. In the second example, the host is the last member to leave a multicast session.

The IGMP query router, MSFC, will send queries every 60 seconds to both VLAN 3 and VLAN 30 to check for members for the multicast group 239.1.1.1 (refer to Figure 9-6). As these queries are sent by the router to the switch, the switch forwards the queries to ports that are participating in the multicast session. Upon receiving the query message, the hosts will send back an IGMP membership report. The switch again intercepts these IGMP messages from the hosts and only forwards one membership report to the MSFC. A router does not need to receive membership reports from more than one host from a single VLAN for a multicast traffic. So long as there is one host, the multicast stream still needs to be forwarded to that interface. For this reason, the switch drops the other IGMP membership reports.