Brocade 6910 Ethernet Access Switch Configuration Guide (Supporting R2.2.0.0) - Manual (Page 505)

Brocade 6910 Ethernet Access Switch Configuration Guide 449
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IGMP Snooping
• By default, the switch immediately enters into “multicast flooding mode” when a spanning tree
topology change occurs. In this mode, multicast traffic will be flooded to all VLAN ports. If many
ports have subscribed to different multicast groups, flooding may cause excessive loading on
the link between the switch and the end host. Flooding may be disabled to avoid this, causing
multicast traffic to be delivered only to those ports on which multicast group members have
been learned.
• When the spanning tree topology changes, the root bridge sends a proxy query to quickly
re-learn the host membership/port relations for multicast channels. The root bridge also sends
an unsolicited Multicast Router Discover (MRD) request to quickly locate the multicast routers
in this VLAN.
The proxy query and unsolicited MRD request are flooded to all VLAN ports except for the
receiving port when the switch receives such packets.
Example
The following example enables TCN flooding.
Console(config)#ip igmp snooping tcn-flood
Console(config)#
ip igmp snooping tcn-query-solicit
This command instructs the switch to send out an IGMP general query solicitation when a spanning
tree topology change notification (TCN) occurs. Use the no form to disable this feature.
Syntax
[no] ip igmp snooping tcn-query-solicit
Default Setting
Disabled
Command Mode
Global Configuration
Command Usage
• When the root bridge in a spanning tree receives a topology change notification for a VLAN
where IGMP snooping is enabled, it issues a global IGMP leave message (query solicitation).
When a switch receives this solicitation, it floods it to all ports in the VLAN where the spanning
tree change occurred. When an upstream multicast router receives this solicitation, it will also
immediately issues an IGMP general query.
• The ip igmp snooping tcn query-solicit command can be used to send a query solicitation
whenever it notices a topology change, even if the switch is not the root bridge in the spanning
tree.
Example
The following example instructs the switch to issue an IGMP general query whenever it receives a
spanning tree topology change notification.
Console(config)#ip igmp snooping tcn query-solicit
Console(config)#