问题：

[多选] Which three statements are true about IP multicast configuration?（）

A . PIM sparse - dense mode and PIM dense mode require an RP on the network.
B . PIM sparse mode and PIM dense mode require an RP on the network.
C . PIM sparse mode interfaces are always added to the multicast routing table in a router.
D . PIM sparse mode and PIM sparse - dense mode require an RP on the network.
E . PIM dense mode interfaces are always added to the multicast routing table in a router.
F . PIM sparse - dense mode acts as PIM dense mode if an RP is not known.