Brocade Communications Systems Brocate Ethernet Access Switch 6910 - Manual (Page 502)

452 Brocade 6910 Ethernet Access Switch Configuration Guide
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IGMP Snooping
23
Default Setting
300 seconds
Command Mode
Global Configuration
Example
The following shows how to configure the time out to 400 seconds:
Console(config)#ip igmp snooping router-port-expire-time 400
Console(config)#
ip igmp snooping tcn-flood
This command enables flooding of multicast traffic if a spanning tree topology change notification
(TCN) occurs. Use the no form to disable flooding.
Syntax
[no] ip igmp snooping tcn-flood
Default Setting
Disabled
Command Mode
Global Configuration
Command Usage
• When a spanning tree topology change occurs, the multicast membership information learned
by the switch may be out of date. For example, a host linked to one port before the topology
change (TC) may be moved to another port after the change. To ensure that multicast data is
delivered to all receivers, by default, a switch in a VLAN (with IGMP snooping enabled) that
receives a Bridge Protocol Data Unit (BPDU) with the TC bit set (by the root bridge) will enter
into “multicast flooding mode” for a period of time until the topology has stabilized and the
new locations of all multicast receivers are learned.
• If a topology change notification (TCN) is received, and all the uplink ports are subsequently
deleted, a time out mechanism is used to delete all of the currently learned multicast
channels.
• When a new uplink port starts up, the switch sends unsolicited reports for all current learned
channels out through the new uplink port.
• 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.