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400-007 · Question #144
400-007 Question #144: Real Exam Question with Answer & Explanation
The correct answer is A: first-hop router registration to the RP. In IPv6 PIM-SM, a dynamically created tunnel interface is used by the first-hop router to encapsulate and send PIM Register messages to the RP when a new multicast source is detected.
Question
Which purpose of a dynamically created tunnel interface on the design of IPv6 multicast services Is true?
Options
- Afirst-hop router registration to the RP
- Bmulticast client registration to the RP
- Cmulticast source registration to the RP
- Dtransport of all IPv6 multicast traffic
Explanation
In IPv6 PIM-SM, a dynamically created tunnel interface is used by the first-hop router to encapsulate and send PIM Register messages to the RP when a new multicast source is detected.
Common mistakes.
- B. Multicast client (receiver) registration to the RP is handled by MLD (Multicast Listener Discovery) messages sent to the first-hop router, not by dynamically created tunnel interfaces.
- C. The source itself does not create a tunnel to the RP - it simply sends multicast packets to its local DR, which acts on the source's behalf by creating the tunnel and sending Register messages.
- D. The dynamic tunnel carries only PIM Register encapsulated traffic during the source registration phase; once the multicast distribution tree is established, traffic flows natively along that tree without using the tunnel.
Concept tested. IPv6 PIM-SM dynamic tunnel interface for FHR RP registration
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