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Juniper JN0-650 Exam - Topic 7 Question 9 Discussion
Topic #: 7
You are troubleshooting a multicast deployment in a network. Some multicast groups operate in PIM-ASM mode and others operate in PIM-SSM mode. While troubleshooting, you note the following:
- The network uses IGMPv2 for some segments and IGMPv3 for others.
- For group 232.1.1.1, receivers know the exact source IP of the multicast sender
- For group 239.10.10.10. receivers do not know the source address in advance.
Which two statements correctly describe the operational differences between these two modes in Junos OS? (Choose two.)
Junos OS 24.4 handles multicast traffic using two distinct models based on whether the source is known in advance.
Knowledge and Sources (Option A): PIM-ASM (Any Source Multicast) is designed for 'many-to-many' communication where receivers join a group ($*,G$) and rely on a Rendezvous Point (RP) to discover active sources. In contrast, PIM-SSM (Source-Specific Multicast) is for 'one-to-many' scenarios where receivers must already know the exact source IP ($S,G$) before joining.
Protocol and RP Logic (Option D): PIM-SSM bypasses the RP entirely. It relies on IGMPv3 messages from the host, which explicitly include both the source address and the group address. This allows the last-hop router to build a Shortest Path Tree (SPT) directly toward the source immediately.
Register Process (Option B): While PIM-ASM does use registers, it is the First-Hop Router (Designated Router on the source segment) that sends the register to the RP, not the receiver's DR.
RP Role (Option C): This is exactly backwards; PIM-ASM requires an RP for source discovery, whereas PIM-SSM does not use one at all.
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