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Catalyst 3560 Switch Software Configuration Guide
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Chapter 23 Configuring IGMP Snooping and MVR
Configuring IGMP Snooping
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 “Enabling IGMP Immediate Leave” section on page 23-10.

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 “Configuring the IGMP Leave Timer” section on page 23-11.

IGMP Report Suppression

Note IGMP report suppression is supported only when the multicast query has IGMPv1 and IGMPv2 reports.
This feature is not supported when the query includes IGMPv3 reports.
The switch uses IGMP report suppression to forward only one IGMP report per multicast router query
to multicast devices. When IGMP router suppression is enabled (the default), the switch sends the first
IGMP report from all hosts for a group to all the multicast routers. The switch does not send the
remaining IGMP reports for the group to the multicast routers. This feature prevents duplicate reports
from being sent to the multicast devices.
If the multicast router query includes requests only for IGMPv1 and IGMPv2 reports, the switch
forwards only the first IGMPv1 or IGMPv2 report from all hosts for a group to all the multicast routers.
If the multicast router query also includes requests for IGMPv3 reports, the switch forwards all IGMPv1,
IGMPv2, and IGMPv3 reports for a group to the multicast devices.
If you disable IGMP report suppression, all IGMP reports are forwarded to the multicast routers. For
configuration steps, see the “Disabling IGMP Report Suppression” section on page 23-15.
Configuring IGMP Snooping
IGMP snooping allows switches to examine IGMP packets and make forwarding decisions based on
their content. These sections contain this configuration information:
• Default IGMP Snooping Configuration, page 23-7
• Enabling or Disabling IGMP Snooping, page 23-7
• Setting the Snooping Method, page 23-8
• Configuring a Multicast Router Port, page 23-9
• Configuring a Host Statically to Join a Group, page 23-10
• Enabling IGMP Immediate Leave, page 23-10