Enabling Fast Leave

For setup, refer to Figure IGMP- Topology 1.

When the fast (immediate) leave setting is enabled, the device removes an interface from the forwarding-table entry without first sending IGMP Group-Specific queries to the interface. The interface is pruned from the multicast tree for the multicast group specified in the IGMP leave message. The immediate leave setting ensures optimal bandwidth management for hosts on a switched network, even when multiple multicast groups are being used simultaneously.

When fast leave is disabled and one host sends a leave group message, the routing device first sends a group query to determine if another receiver responds. If no receiver responds, the routing device removes all hosts on the interface from the multicast group.

Immediate leave is disabled by default for both IGMP version 2 and IGMP version 3. For this device, the default IGMP version is 2, so by default, fast leave is disabled.

  1. Execute the following commands to enable Fast (Immediate) Leave in the Router.

    Type the following:

    • Enter the Global Configuration Mode.
    iS5comm# configure terminal
    • Enter the Interface Configuration mode for VLAN 2.
    iS5comm(config)# interface vlan 2
    • Enable Fast Leave.
    iS5comm(config-if)# ip igmp immediate-leave
    • Exit the Interface Configuration Mode.
    iS5comm(config-if)# end
  2. View the configuration using the following command.

    Type the following:

    iS5comm# show ip igmp interface vlan2
    IGMP is globally enabled
    vlan2, line protocol is up
    Internet Address is 12.0.0.1/8
    IGMP is disabled on interface
    Current IGMP router version is 2
    IGMP rate limit for joins packets is 0
    IGMP query interval is 125 seconds
    Last member query response interval is 10 seconds
    IGMP max query response time is 100 seconds
    Robustness value is 2
    IGMP querying router is 12.0.0.1 (this system) 
    Fast leave is enabled on this interface
    No multicast groups joined
    Checksum errors: 0, Packet length errors: 0
    Packets with Local IP as source: 0, Source subnet check failures: 0
    Query from non-querier: 0
    Report version mismatch: 0, Query version mismatch:  0
    Unknown IGMP message type: 0
    Invalid V1 reports: 0, Invalid V2 reports: 0, Invalid v3 reports: 0
    Packets dropped due to router-alert check: 0
    Reports in SSM range: 0
    Invalid Reports in SSM range: 0
    IGMP Global rate limit for joins packets : 0
Parent topic: Configuring IGMP