The fast leave function is configured using the igmp-snooping prompt-leave command (for Layer 2 multicast) or the igmp prompt-leave command (for Layer 3 multicast). If this function is not configured, the switch sends a Group-Specific Query message in response to an IGMP Leave message to check whether there are other users in the group specified in the Leave message. After fast leave is configured, the switch directly deletes the interface that receives the IGMP Leave message from the multicast forwarding entry, and does not check whether there are still users in the group.
        The fast leave function is applicable only to interfaces with only one user attached. If fast leave is configured on an interface connecting to multiple users, multicast traffic of all users under the interface is interrupted when one user switches to another channel.

I do not recommend the fast leave function.

Hehe.. ) Why ? )

Which device does the mechanism apply to? Routers or access devices?

This post relates to the access switches only (devices)