HP Cisco Catalyst Blade Switch 3020 Cisco Catalyst Blade Switch 3020 for HP So - Page 379

Leaving a Multicast Group, Immediate Leave, IGMP Configurable-Leave Timer

Page 379 highlights

Chapter 18 Configuring IGMP Snooping and MVR Understanding 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 blade servers respond to the queries. If at least one blade server 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 blade servers listed in the forwarding table for that IP multicast group maintained by IGMP snooping. When blade servers 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 blade server, 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 blade servers 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 blade servers 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 blade server is connected 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 "Enabling IGMP Immediate Leave" section on page 18-10. 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 18-11. OL-8915-01 Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide 18-5

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18-5
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
OL-8915-01
Chapter 18
Configuring IGMP Snooping and MVR
Understanding 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 blade servers respond to the queries. If at least one blade server 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 blade servers listed in the forwarding
table for that IP multicast group maintained by IGMP snooping.
When blade servers 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 blade server, 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 blade servers
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 blade servers 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 blade server is connected
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
“Enabling IGMP Immediate Leave” section on page 18-10
.
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 18-11
.