Consolidated Platform Configuration Guide, Cisco Ios Release 15.2(4)E (Catalyst 2960-X Switches - Cisco Catalyst 2960 series Configuration Manual

Example: Configuring a Host Statically to Join a Group, on page 162
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 wants 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
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.
Immediate Leave is only supported on IGMP version 2 hosts. IGMP version 2 is the default version for the
switch.
You should use the Immediate Leave feature only on VLANs where a single host is connected to each
Note
port. If Immediate Leave is enabled on VLANs where more than one host is connected to a port, some
hosts may be dropped inadvertently.
Related Topics
Enabling IGMP Immediate Leave , on page 135
Example: Enabling IGMP Immediate Leave, on page 162
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 32767 milliseconds.
Related Topics
Configuring the IGMP Leave Timer , on page 137

Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)

Information About IGMP Snooping and MVR
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