An enterprise company needs to transport multicast traffic between its hub-and-spoke WAN routers over an MPLS Layer 3 VPN provider that does not currently support multicast. Which option describes how

Question

Options

• AUse MSDP over the WAN.
• BEnable multicast routing on the WAN physical and tunnel interfaces.
• CCreate multicast-enabled GRE tunnels over the WAN between the hub-and-spoke routers.
• DProvide an Internet link to each site and use DMVPN over the Internet.

• A
  25% (14)
• B
  7% (4)
• C
  55% (30)
• D
  13% (7)

Explanation

When an MPLS L3 VPN provider does not support native multicast (mVPN/Multicast VPN), the most cost-effective solution is to create GRE (Generic Routing Encapsulation) tunnels between the hub and spoke routers. GRE tunnels encapsulate multicast packets inside unicast GRE headers, allowing them to traverse the provider network as ordinary unicast traffic. PIM and multicast routing run over these tunnels, making multicast appear to work end-to-end. This avoids the cost of upgrading the provider or adding Internet links. MSDP (Option A) is used for inter-domain RP discovery, not for crossing non-multicast networks. Option B fails because the provider infrastructure still cannot forward multicast. Option D (DMVPN over Internet) would work but requires provisioning and paying for separate Internet links at every site, making it less cost-effective.

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