A receiver on VLAN100 joins multicast group 239.10.10.10 on a PIM sparse-mode network where an RP is configured. What PIM message does the first-hop multicast-capable router send toward the RP to build the rendezvous-point tree?

When a host (receiver) on a PIM sparse-mode network wants to receive multicast traffic for a specific group (G), its first-hop router sends an IGMP Join message to the router. This first-hop router then originates a PIM Join message for (,G) – meaning "any source, this group" – and sends it toward the Rendezvous Point (RP). This PIM Join message builds the shared tree (RPT) from the receiver's first-hop router all the way to the RP, allowing multicast traffic to flow from the RP down to the receiver. PIM Register messages are sent by the first-hop router of a source to the RP to encapsulate and tunnel initial multicast data. PIM Prune messages are used to stop receiving traffic for a specific group or source. PIM Hello messages are used between PIM neighbors to establish and maintain adjacencies.