If you run PIM-SM in a multicast network, you need to build a multicast forwarding tree between the multicast source and the receiver to enable the receiver to receive the multicast effect, so what are the following options for the correct tree sketch for the build?

In Protocol Independent Multicast - Sparse Mode (PIM-SM), two types of multicast distribution trees are used.
1. Shared Tree (RPT): Initially, receivers join a shared tree rooted at a central point called the Rendezvous Point (RP). PIM Join messages from the receiver's designated router (DR) travel towards the RP, building the RPT. This is described in option B.
2. Shortest Path Tree (SPT): When a source sends traffic, its DR registers with the RP. The RP then builds a source-rooted SPT back to the source to receive the traffic natively. This is described in option A. For efficiency, a receiver's DR can also initiate a switchover from the RPT to a direct SPT from the source to the receiver.

C. This statement is incomplete. It correctly identifies the RPT as a tree type used in PIM-SM but fails to specify which network elements it connects.
D. This is incorrect. The tree between the RP and the receiver is the RPT (Shared Tree). The SPT is built from the multicast source to the receiver, not from the RP.

1. RFC 7761, "Protocol Independent Multicast - Sparse Mode (PIM-SM)", Section 4.1, "PIM-SM Trees". "PIM-SM uses two types of trees: a source-rooted Shortest Path Tree (SPT) and a shared Rendezvous Point Tree (RPT)."

2. Huawei HedEx Documentation, NE40E, NE9000, etc. Configuration Guide - IP Multicast, "PIM Configuration", Section "PIM-SM Principles". This section details the RPT and SPT setup processes, including source registration and receiver joins.