H3C Technologies H3C S3100V2 Series Switches - Manual (Page 31)

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Configuring fast leave processing
The fast leave processing feature allows the switch to process IGMP leave messages in a fast way. With
the fast leave processing feature enabled, when receiving an IGMP leave message on a port, the switch
immediately removes that port from the outgoing port list of the entry in the forwarding table for the
indicated group. Then, when receiving IGMP group-specific queries for that multicast group, the switch
will not forward them to that port.
In VLANs where only one host is attached to each port, fast leave processing helps improve bandwidth
and resource usage. However, if fast leave processing is enabled on a port to which more than one host
is attached, when one host leaves a multicast group, the other hosts attached to the port and interested
in the same multicast group will fail to receive multicast data for that group. If the function of dropping
unknown multicast traffic is already enabled on the switch or in the VLANs, the fast leave processing
function should not be enabled.
Configuring fast leave processing globally
Follow these steps to configure fast leave processing globally:
To do... Use the command... Remarks
Enter system view system-view —
Enter IGMP snooping view igmp-snooping —
Enable fast leave processing fast-leave [ vlan vlan-list ]
Required
Disabled by default
Configuring fast leave processing on a port or a group of ports
Follow these steps to configure fast leave processing on a port or a group of ports:
To do... Use the command... Remarks
Enter system view system-view —
interface interface-type interface-number Enter Ethernet interface/Layer 2
aggregate interface view or port
group view
port-group manual port-group-name
Required
Use either approach
Enable fast leave processing igmp-snooping fast-leave [ vlan vlan-list ]
Required
Disabled by default
Disabling a port or a group of ports from changing into
dynamic router ports
The following problems exist in a multicast access network:
• Upon receiving an IGMP general query or a PIM Hello message from a connected host, a switch
port becomes a dynamic router port. Before its timer expires, this dynamic router port will receive all
multicast packets within the VLAN it belongs to and forward them to the host, affecting normal
multicast reception of the host.
• In addition, the IGMP general query or PIM Hello message sent from the host affects the multicast
routing protocol state on Layer 3 devices, such as the IGMP querier or DR election, and might further
cause network interruption.