The l2-multicast fast-channel group-address command enables prompt join.
The undo l2-multicast fast-channel group-address command disables prompt join.
By default, prompt join is disabled.
l2-multicast fast-channel [ source-address source-address { SrcAddrMask | SrcAddrMaskLen } ] group-address group-address { GrpAddrMask | GrpAddrMaskLen }
undo l2-multicast fast-channel [ source-address source-address { SrcAddrMask | SrcAddrMaskLen } ] group-address group-address { GrpAddrMask | GrpAddrMaskLen }