So what is the role of FHR then? as per official Cert guide page 348 paragraph "PIM Shared and Source Path Trees", PIM SPT joins sent from RP to FHR not to the source..?
Look closely at the answer.
'Send join messages TOWARD a multicast source' - not '[...] TO multicast source'
You are right that RP join message will be send TO FHR but it is also correct that the join messages are sent TOWARDS source.
A is correct answer.
i tend to vote C as it's unconditional true. w/o this function receiver in PIM-SM never joins (*,G) & in turns never will receive (S,G). if u'll look here u'll not even find RP sending (S,G) pim-join toward source. but i need to lab it w/ wireshark...
labbed stuff. RP sends pim-join (S,G) toward SRC . reread answ C - in fact RP doesnt receive JOINS from receivers. it receives pim-join/prune from pim-neis instead. changed my vote to A
A. Send join messages toward a multicast source Shortest Path Tree (SPT).
The RP serves as a meeting point for sources and receivers in a multicast group. When a receiver wants to join a multicast group and receive traffic from a source, it sends a join message towards the RP. The RP is responsible for forwarding these join messages toward the source and building the optimal path known as the Shortest Path Tree (SPT), ensuring efficient multicast traffic distribution to the interested receivers.
Correct Answer: A
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-16/imc-pim-xe-16-book/imc-pim-allowrp.html#:~:text=.%20In%20a%20PIM,source%20and%20receiver.
A is the correct answer .
The RP receives PIM join from the LHR
The LHR receives IGMP join from the receiver
The RP receives PIM register from the FHR
https://docs.nvidia.com/networking-ethernet-software/knowledge-base/Configuration-and-Usage/Network-Configuration/Pim-Overview/#:~:text=First%20Hop%20Router%20(FHR),to%20an%20interested%20multicast%20receiver.
(RP) is used to establish communication between a source and the receivers in a multicast group using PIM protocols, so it sends join messages toward a multicast source using Protocol (PIM) to build the distribution tree for the multicast group SPT
Answer is B
An RP acts as the meeting place for sources and receivers of multicast data. In a PIM-SM network, sources must send their traffic to the RP. This traffic is then forwarded to receivers down a shared distribution tree
but what is a multicast source shortest path tree?
multicast source is the source of the traffic. SPT is describing the specific route/tree through the multicast network - there is no such thing as a multicast source SPT...
The answer is A because an RP does send a join message towards the source.
Note: The comments saying that IGMP operates at L2 are incorrect. IGMP and PIM are both L3 protocols and are carried in IP packets. Only IGMP Snooping, a switch feature, operates at L2.
A. incorrect because RP uses a shared tree and not SPT (shortes path tree)
B. incorrect because a shared tree is not always the shortest path between source and reciever
C. correct
D.incorrect because RP does not add any security
Disagree, RP uses SPT toward th FHR. and shared tree toward to receivers. find on Multicast on OCG. so A is CORRECT
C: NOT CORRECT because RP does not receive IGMP JOIN messages, that funcion is for LHR.
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