How is MSDP used to interconnect multiple PIM-SM domains?

Question

Exhibit

Options

• AMSDP depends on BGP or multiprotocol BGP for mterdomam operation
• BMSDP SA request messages are used to request a list of active sources for a specific group
• CMSDP allows a rendezvous point to dynamically discover active sources outside of its domain
• DMSDP messages are used to advertise active sources in a domain

• A
  11% (3)
• B
  79% (22)
• C
  4% (1)
• D
  7% (2)

Explanation

MSDP and Interconnecting PIM-SM Domains

Why B is Correct: MSDP SA (Source Active) Request messages serve the specific function of allowing a Rendezvous Point (RP) to request a list of active sources for a particular multicast group from a peer RP in another domain - this is the precise mechanism that enables inter-domain multicast source discovery.

Why the Distractors Are Wrong:

• Option A is misleading - while MSDP peers are often established between BGP neighbors for practicality, MSDP does not depend on BGP to function; peering can be configured independently.
• Option C describes a general benefit of MSDP but does not explain the specific mechanism (SA Request messages) used to interconnect domains - it's too vague to be the best answer.
• Option D describes SA advertisements (unsolicited broadcasts of active sources), which is a related but distinct function from the SA Request process that specifically enables inter-domain operation.

Memory Tip: Think of SA Request messages as a "Source Wanted" ad - when an RP doesn't know about active sources in another domain, it requests that information specifically. The keyword "request" signals the active inter-domain query mechanism that makes MSDP work across boundaries.

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