Exam 350-401 topic 1 question 223 discussion

From Cisco Document, matches A exactly https://www.cisco.com/c/en/us/td/docs/ios/12_4t/ip_mcast/configuration/guide/mctmsdp.html#wp1054452 Benefits of Using MSDP to Interconnect Multiple PIM-SM Domains •Allows a rendezvous points (RP) to dynamically discover active sources outside of its domain.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-3s/asr903/imc-pim-xe-3s-asr903-book/imc_msdp.pdf Page 2 : Benefits of Using MSDP to Interconnect Multiple PIM-SM Domains • Allows a rendezvous point (RP) to dynamically discover active sources outside of its domain

If you read the Link that was shared by Daaid, https://www.cisco.com/c/en/us/td/docs/ios/12_4t/ip_mcast/configuration/guide/mctmsdp.html#wp1054452 And ten we review The Answers in reverse order. D is Correct - MSDP messages are used to advertise Active sources but this doesn't addrress the "Interconnect" part of the question. C is also correct. According to this document MSDP does require BGP or MBGP but this is a requirement of MSDP and again doesn't address the "Interconnect" issue. B is wrong - MSDP uses SA messages to advertise active sources, not to request a list of sources. A is also Correct and this directly addresses the issue of Interconnecting Multiple PIM-SM Domains

I don't know , both A and C could be correct..... This is a tough one, the dfference may be in wording...

The only required task to use MSDP to interconnect multiple PIM-SM domains is configuring an MSDP Peer. "All MSDP peers must be configured to run BGP before being configured for MSDP." The other statements are correct! https://www.cisco.com/c/en/us/td/docs/ios/12_4t/ip_mcast/configuration/guide/mctmsdp.html#wp1054697

Based on this IP Multicast Guide from Cisco the answer is C Prerequisites for Using MSDP to Interconnect Multiple PIM-SM Domains. Before you configure MSDP, the addresses of all MSDP peers must be known in Border Gateway Protocol (BGP) https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-16/imc-pim-xe-16-book/imc-msdp-im-pim-sim.html

Prerequisites for Using MSDP to Interconnect Multiple PIM-SM Domains. Before you configure MSDP, the addresses of all MSDP peers must be known in Border Gateway Protocol (BGP) https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-16/imc-pim-xe-16-book/imc-msdp-im-pim-sim.html

it´s A MSDP (Multicast Source Discovery Protocol) facilitates the interconnection of multiple PIM-SM (Protocol Independent Multicast - Sparse Mode) domains. It enables rendezvous points (RPs) in different PIM-SM domains to exchange information about active multicast sources. This allows an RP in one domain to dynamically discover active sources in other domains, facilitating efficient multicast traffic forwarding across domain boundaries.

The correct answer is: A. MSDP allows a rendezvous point to dynamically discover active sources outside of its domain. MSDP enables multiple PIM-SM domains to exchange information about active multicast sources, allowing each domain's Rendezvous Point (RP) to dynamically discover sources located in other domains. This facilitates interdomain multicast communication by allowing multicast traffic from sources in one domain to be distributed to receivers in other domains.

answer is clearly A

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-16/imc-pim-xe-16-book/imc-msdp-im-pim-sim.html#GUID-56896581-339B-407F-9CE2-00566608F35E

MSDP depends on BGP or multiprotocol BGP (MBGP) for interdomain operation. We recommended that you run MSDP on RPs sending to global multicast groups.

SA Request Messages SA request messages are used to request a list of active sources for a specific group. These messages are sent to an MSDP SA cache that is maintains a list of active (S, G) pairs in its SA cache. Join latency can be reduced by using SA request messages to request the list of active sources for a group instead of having to wait up to 60 seconds for all active sources in the group to be readvertised by originating RPs. https://www.cisco.com/c/en/us/td/docs/ios/12_4t/ip_mcast/configuration/guide/mctmsdp.html

Pay attention to the Question: "How is MSDP used"? it does not ask 'WHAT(protocol) is MSDP DEPENDS'

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-16/imc-pim-xe-16-book/imc-msdp-im-pim-sim.html according to the link, I paste somet content here: 1. Allows a rendezvous point (RP) to dynamically discover active sources outside of its domain. ==> matches option A 2. SA request messages are used to request a list of active sources for a specific group. ==> matches option B 3. MSDP depends on BGP or multiprotocol BGP (MBGP) for interdomain operation. We recommended that you run MSDP on RPs sending to global multicast groups. ==> matches option C 4. SA messages are used to advertise active sources in a domain. ==> it's SA message, not all 4 types of MSDP messages, so it's wrong Is there any possibility that the question asked you to select an INCORRECT option?

Multicast Source Discovery Protocol- MSDP, If listeners exist, it triggers a PIM join into the source domain towards the data source. In a peering relationship, one MSDP peer listens for new TCP connections on the well-known port 639.

Nope, C: Prerequisites for Using MSDP to Interconnect Multiple PIM-SM Domains Before you configure MSDP, the addresses of all MSDP peers must be known in Border Gateway Protocol (BGP).