Which two statements about RPF checks in Multicast Source Discovery Protocol (MSDP) are true? (Choose two)

Question

Options

• ARPF check should be done against the route to the source of the corresponding PIM-SM domain.
• BChecking session advertisement (SA) messages causes messages looping.
• CThe RPF check ensures that there is a working redundancy for anycast RPs.
• DRPF check should be done against the route to the RP of the PIM-SM domain that originated the SA.
• EIt prevents message looping, and session advertisement (SA) messages must be RPF checked.

• A
  11% (5)
• B
  4% (2)
• C
  7% (3)
• D
  78% (36)

Explanation

SA Message Receipt SA messages are only accepted from the MSDP RPF peer that is in the best path back toward The same SA message arriving from other MSDP peers must be ignored or SA loops can occur. Deterministically selecting the MSDP RPF peer for an arriving SA message requires knowledge of the MSDP topology. However, MSDP does not distribute topology information in the form of routing updates. MSDP infers this information by using (M)BGP routing data as the best approximation of the MSDP topology for the SA RPF check mechanism. An MSDP topology, therefore, must follow the same general topology as the BGP peer topology. Besides a few exceptions (such as default MSDP peers and MSDP peers in MSDP mesh groups), MSDP peers, in general should also be (M)BGP peers. Rule 1 of RPF checking in MSDP is applied when the sending MSDP peer is also an i(M)BGP peer. When Rule 1 is applied, the RPF check proceeds as follows: The peer searches the BGP Multicast Routing Information Base (MRIB) for the best path to the RP that originated the SA message. If a path is not found in the MRIB, the peer then searches the Unicast Routing Information Base (URIB). If a path is still not found, the RPF check fails. If the previous search succeeds (that is, the best path is found), the peer then determines the address of the BGP neighbor for this best path, which will be the address of the BGP neighbor that sent the peer the path in BGP update messages.

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