Leaving A Multicast Group; Immediate Leave; Igmp Configurable-Leave Timer; Igmp Report Suppression - Cisco Catalyst 2360 Software Configuration Manual

Chapter 15

Configuring IGMP Snooping

Leaving a Multicast Group

The router sends periodic multicast general queries, and the switch forwards these queries through all
ports in the VLAN. Interested hosts respond to the queries. If at least one host in the VLAN wishes to
receive multicast traffic, the router continues forwarding the multicast traffic to the VLAN. The switch
forwards multicast group traffic only to those hosts listed in the forwarding table for that IP multicast
group maintained by IGMP snooping.
When hosts want to leave a multicast group, they can silently leave, or they can send a leave message.
When the switch receives a leave message from a host, it sends a group-specific query to learn if any
other devices connected to that interface are interested in traffic for the specific multicast group. The
switch then updates the forwarding table for that MAC group so that only those hosts interested in
receiving multicast traffic for the group are listed in the forwarding table. If the router receives no
reports from a VLAN, it removes the group for the VLAN from its IGMP cache.

Immediate Leave

Immediate Leave is only supported on IGMP Version 2 hosts.
The switch uses IGMP snooping Immediate Leave to remove from the forwarding table an interface that
sends a leave message without the switch sending group-specific queries to the interface. The VLAN
interface is pruned from the multicast tree for the multicast group specified in the original leave message.
Immediate Leave ensures optimal bandwidth management for all hosts on a switched network, even
when multiple multicast groups are simultaneously in use.
Note You should only use the Immediate Leave feature on VLANs where a single host is connected to each
port. If Immediate Leave is enabled in VLANs where more than one host is connected to a port, some
hosts might inadvertently be dropped.
For configuration steps, see the

IGMP Configurable-Leave Timer

You can configure the time that the switch waits after sending a group-specific query to determine if
hosts are still interested in a specific multicast group. The IGMP leave response time can be configured
from 100 to 5000 milliseconds. The timer can be set either globally or on a per-VLAN basis. The VLAN
configuration of the leave time overrides the global configuration.
For configuration steps, see the

IGMP Report Suppression

IGMP report suppression is supported only when the multicast query has IGMPv1 and IGMPv2 reports.
Note
This feature is not supported when the query includes IGMPv3 reports.
OL-19808-01
"Enabling IGMP Immediate Leave" section on page
"Configuring the IGMP Leave Timer" section on page
Catalyst 2360 Switch Software Configuration Guide
Understanding IGMP Snooping
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