IGMPv2 Leave Process

IGMPv2 Leave Process
IGMPv2 implemented the capability for hosts to remove themselves from the multicast group
immediately (in a matter of seconds) instead of the router having to wait up to three minutes.
The process is known as the IGMP Leave process. The two new additions of the Leave and
600 Chapter 19  Understanding and Configuring Multicast Operation
Group-Specific messages work together to enable a host to remove itself from the multicast
group immediately without interrupting the state of the interface on the multicast router.
Figure 19.10 depicts how the IGMPv2 Leave process works. First, Host A sends a Leave message
to the all multicast routers address (224.0.0.2), expressing the intent to withdraw from the
multicast group. Because Router 1 doesn’t know how many hosts on the segment belong to
group 224.2.155.145, it must send a Group-Specific Query to see whether any hosts remain
members of the group. If no responses are received, the router disables multicast forwarding out
of the interface for the 224.2.155.145 group. If any hosts respond to the query, the router leaves
the interface status quo. In the figure, you can see that Host B responds because it is still participating
in the group 224.2.155.145. Hence, the interface is left active for that group.