When using PIM-SM in SSM mode, which event triggers the creation of a shortest-path tree?
A.
Multicast traffic received at the receiver’s designated router (DR).
B.
An IGMPv3 report received at the receiver’s designated router (DR).
C.
Multicast traffic received at the rendezvous point (RP).
D.
An IGMPv3 report received at the source’s designated router (DR).
http://www.juniper.net/techpubs/en_US/junos14.2/topics/topic-map/mcast-ssm.html
In a PIM SSM-configured network, a host subscribes to an SSM channel (by means of IGMPv3), announcing a desire to join group G and source S (see Figure 1). The directly connected PIM sparse-mode router, the receiver’s DR, sends an (S,G) join message to its RPF neighbor for the source. Notice in Figure 1 that the RP is not contact
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http://www.juniper.net/techpubs/en_US/junos14.2/topics/topic-map/mcast-ssm.html
PIM SSM builds shortest-path trees (SPTs) rooted at the source immediately because in SSM, the router closest to the interested receiver host is informed of the unicast IP address of the source for the multicast traffic. That is, PIM SSM bypasses the RP connection stage through shared distribution trees, as in PIM sparse mode, and goes directly to the source-based distribution tree.
Correct seems B choise
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