Cisco WS-2960-24LC-S Software Guide - Page 378
Configuring TCN-Related Commands, Controlling the Multicast Flooding Time After a TCN Event
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Configuring IGMP Snooping Chapter 18 Configuring IGMP Snooping and MVR Configuring TCN-Related Commands These sections describe how to control flooded multicast traffic during a TCN event: • Controlling the Multicast Flooding Time After a TCN Event, page 18-12 • Recovering from Flood Mode, page 18-12 • Disabling Multicast Flooding During a TCN Event, page 18-13 Controlling the Multicast Flooding Time After a TCN Event You can control the time that multicast traffic is flooded after a TCN event by using the ip igmp snooping tcn flood query count global configuration command. This command configures the number of general queries for which multicast data traffic is flooded after a TCN event. Some examples of TCN events are when the client changed its location and the receiver is on same port that was blocked but is now forwarding, and when a port went down without sending a leave message. If you set the TCN flood query count to 1 by using the ip igmp snooping tcn flood query count command, the flooding stops after receiving 1 general query. If you set the count to 7, the flooding until 7 general queries are received. Groups are relearned based on the general queries received during the TCN event. Beginning in privileged EXEC mode, follow these steps to configure the TCN flood query count: Step 1 Step 2 Command configure terminal ip igmp snooping tcn flood query count count Step 3 Step 4 Step 5 end show ip igmp snooping copy running-config startup-config Purpose Enter global configuration mode. Specify the number of IGMP general queries for which the multicast traffic is flooded. The range is 1 to 10. By default, the flooding query count is 2. Return to privileged EXEC mode. Verify the TCN settings. (Optional) Save your entries in the configuration file. To return to the default flooding query count, use the no ip igmp snooping tcn flood query count global configuration command. Recovering from Flood Mode When a topology change occurs, the spanning-tree root sends a special IGMP leave message (also known as global leave) with the group multicast address 0.0.0.0. However, when you enable the ip igmp snooping tcn query solicit global configuration command, the switch sends the global leave message whether or not it is the spanning-tree root. When the router receives this special leave, it immediately sends general queries, which expedite the process of recovering from the flood mode during the TCN event. Leaves are always sent if the switch is the spanning-tree root regardless of this configuration command. By default, query solicitation is disabled. 18-12 Catalyst 2960 Switch Software Configuration Guide OL-8603-04
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