Exam 350-401 Topic 2 Question 1125 Discussion

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 maintains a list of active (S, G) pairs in its SA cache -> Answer C is correct.
SA response messages are sent by the MSDP peer in response to an SA request message. SA response messages contain the IP address of the originating RP and one or more (S, G) pairs of the active sources in the originating RP's domain that are stored in the cache -> Answer D is not correct as it should be "SA response messages are used to advertise active sources in a domain" (not MSDP messages).
Reference: 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
Note:
After a large PIM-SM network is divided into multiple PIM-SM domains, a mechanism is required to enable user hosts in a PIM-SM domain to receive multicast data from sources in another PIM- SM domain.
Multicast Source Discovery Protocol (MSDP) provides such a mechanism. It interconnects multiple PIM-SM domains to implement inter-domain multicast. RPs in PIM-SM domains set up MSDP peer relationships. By sending Source Active (SA) messages, the MSDP peers send the (S, G) information from the RP to which the source registers to the RPs in another PIM-SM domain.

Reference: https://support.huawei.com/enterprise/en/doc/EDOC1000027471?section=j009 Note: A benefit of using MSDP to interconnect multiple PIM-SM domains is to allow a rendezvous point (RP) to dynamically discover active sources outside of its domain.