Cisco Catalyst 2950 Command Reference Manual page 182

ip igmp snooping source-only-learning
The aging time only affects the forwarding-table entries that the switch learns by using the source-only
learning method. If the aging time is too long or is disabled, the forwarding table is filled with unused
multicast addresses that the switch learned by using source-only learning or by using the IGMP join
messages. When the switch receives traffic for new IP multicast groups, it floods the packet to all ports
in the same VLAN. This unnecessary flooding can impact switch performance.
To disable the aging of the forwarding-table entries, enter the ip igmp snooping source-only-learning
age-timer 0 global configuration command. If aging is disabled and you want to delete multicast
addresses that the switch learned by using source-only learning, re-enable aging of the forwarding-table
entries. The switch can now age out the multicast addresses that were learned by the source-only learning
method and that re not in use.
If you disable source-only learning, the aging time has no effect on the switch.
Examples
This example shows how to disable source-only learning:
Switch(config)# no ip igmp snooping source-only-learning
This example shows how to enable source-only learning:
Switch(config)# ip igmp snooping source-only-learning
This example shows how to set the aging time as 1200 seconds (20 minutes):
Switch(config)# ip igmp snooping source-only-learning age-timer 1200
This example shows how to disable aging of the forward-table entries:
Switch(config)# ip igmp snooping source-only-learning age-timer 0
You can verify your settings by entering the show running-config | include source-only-learning
privileged EXEC command.
Related Commands Command
ip igmp snooping
show running-config | include
source-only-learning
Catalyst 2950 and Catalyst 2955 Switch Command Reference
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Chapter 2
Description
Globally enables IGMP snooping. IGMP snooping must be globally
enabled in order to be enabled on a VLAN.
Displays the configuration information running on the switch. For
syntax information, select Cisco IOS Configuration Fundamentals
Command Reference for Release 12.1 > Cisco IOS File
Management Commands > Configuration File Commands.
Catalyst 2950 and 2955 Cisco IOS Commands
OL-10102-01