Question

A service provider runs PIM Sparse Mode with a statically configured RP. A directly connected multicast source begins streaming to group 239.10.10.10. The first-hop router (FHR) receives the source's traffic on a LAN interface, but downstream receivers report they are not getting the stream even though they have sent IGMP joins toward the RP. On the FHR you observe the (S,G) entry has the 'Registering' flag set and a Register-Encapsulation tunnel interface is present. What is the FHR doing at this stage of PIM-SM operation?

Accepted Answer

Encapsulating the source's multicast packets in PIM Register unicast messages and sending them to the RP

Answer

Flooding the multicast traffic natively out all PIM-enabled interfaces until it receives a prune

Answer

Building the shortest-path tree directly to each receiver, bypassing the RP

Answer

Sending PIM Assert messages to elect itself as the designated forwarder for the source subnet