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352-001 · Question #469

What is a characteristic of DMVPN as related to IP multicast?

The correct answer is A. The RP should be placed either in the core network or on the DMVPN headend.. In DMVPN, the hub is the central forwarding point for all spoke traffic, making the hub or core network the correct placement for the multicast Rendezvous Point.

Designing Network Services

Question

What is a characteristic of DMVPN as related to IP multicast?

Options

  • AThe RP should be placed either in the core network or on the DMVPN headend.
  • BWhen the multicast source is at a spoke, the data flows directly towards the spokes that want to
  • CMulticast on DMVPN is similar in behavior to the broadcast multi-access network.
  • DThe RP is typically placed at the spoke router.

How the community answered

(46 responses)
  • A
    70% (32)
  • B
    15% (7)
  • C
    4% (2)
  • D
    11% (5)

Why each option

In DMVPN, the hub is the central forwarding point for all spoke traffic, making the hub or core network the correct placement for the multicast Rendezvous Point.

AThe RP should be placed either in the core network or on the DMVPN headend.Correct

DMVPN uses a hub-and-spoke NBMA topology where multicast traffic from spokes travels through the hub router. Placing the RP at the hub or in the core network ensures that PIM register messages and shared-tree joins are anchored at a centrally reachable point. This avoids suboptimal multicast paths and ensures all spokes can reach the RP reliably.

BWhen the multicast source is at a spoke, the data flows directly towards the spokes that want to

In DMVPN, multicast sourced from a spoke does not flow directly to other spokes - it traverses the hub router, particularly in Phase 1 and for multicast replication in Phase 2 and 3.

CMulticast on DMVPN is similar in behavior to the broadcast multi-access network.

DMVPN is a Non-Broadcast Multi-Access (NBMA) network, not a broadcast multi-access network, so its multicast behavior differs fundamentally from a standard Ethernet LAN segment.

DThe RP is typically placed at the spoke router.

Placing the RP at a spoke is poor design because all multicast registrations and shared-tree traffic must still traverse the hub to reach that spoke RP, creating suboptimal and fragile paths.

Concept tested: DMVPN multicast RP placement in hub-and-spoke topology

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipidr/configuration/xe-16/idr-xe-16-book/idr-dmvpn.html

Topics

#DMVPN#IP multicast#RP placement#hub-and-spoke

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