Which purpose of a dynamically created tunnel interface on the design of IPv6 multicast services Is true?

When a multicast source begins transmitting, the first-hop Designated Router automatically creates a dynamic tunnel interface toward the RP to encapsulate the initial multicast packets inside unicast PIM Register messages, registering the source with the RP and initiating shared or shortest-path tree setup. This tunnel is ephemeral - it exists only for the FHR-to-RP registration exchange and is removed once the RP issues a Register-Stop.

Multicast client (receiver) registration to the RP is handled by MLD (Multicast Listener Discovery) messages sent to the first-hop router, not by dynamically created tunnel interfaces.

The source itself does not create a tunnel to the RP - it simply sends multicast packets to its local DR, which acts on the source's behalf by creating the tunnel and sending Register messages.

The dynamic tunnel carries only PIM Register encapsulated traffic during the source registration phase; once the multicast distribution tree is established, traffic flows natively along that tree without using the tunnel.