Chapter 22
| Multicast Filtering Commands
IGMP Snooping
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ip igmp snooping
router-port-expire-
time
This command configures the querier time out. Use the no form to restore the
default.
Syntax
ip igmp snooping router-port-expire-time seconds
no ip igmp snooping router-port-expire-time
seconds - The time the switch waits after the previous querier stops before
it considers it to have expired. (Range: 1-65535;
Recommended Range: 300-500)
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information learned by the switch may be out of date.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.
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