D-Link DES-1228 - Manual (Page 48)

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'RouterPortPurgeInterval' time, the learnt router port entry will be
purged. Default is 125 seconds.
Leave Timer (0-25 sec): This is the interval after which a Leave
message is forwarded on a port. When a leave message from a host for
a group is received, a group-specific query is sent to the port on which
the leave message is received. A timer is started with a time interval
equal to IgsLeaveProcessInterval. If a report message is received
before above timer expires, the Leave message is dropped. Otherwise
the Leave message is either forwarded to the port. Default is 1 second.
To enable IGMP snooping for a given VLAN, select Enable and click
on the Apply button. Then press the Edit button under Router Port
Setting, and select the ports to be assigned for IGMP snooping for the
VLAN, and press Apply for changes to take effect.