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Understanding IGMP Snooping
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 blade servers on a switched network,
even when multiple multicast groups are simultaneously in use.
You should only use the Immediate Leave feature on VLANs where a single blade server is connected
Note
to each port. If Immediate Leave is enabled in VLANs where more than one blade server is connected
to a port, some blade servers 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.
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 blade servers 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 blade servers 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
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
22-6
"Enabling IGMP Immediate Leave" section on page
"Configuring the IGMP Leave Timer" section on page
"Disabling IGMP Report Suppression" section on page
Chapter 22
Configuring IGMP Snooping and MVR
22-11.
22-16.
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OL-8915-03
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