4A0-108 practice question 22 of 30

In Draft Rosen, a PE router encapsulates customer multicast packets into provider packets. What is the destination IP address of the provider packets sent on the I-PMSI?

Full set: 247 questions
Answer options
A: The destination group address of the customer packets.
B: The multicast group address configured for the I-PMSI. Correct answer
C: The system IP address of the receiving PE.
D: A multicast group address selected from the range of addresses specified in the I-PMSI configuration.
Correct Answer:
B. The multicast group address configured for the I-PMSI.
Explanation

In a Draft Rosen Multicast VPN (MVPN), the Inclusive Provider Multicast Service Interface (I-PMSI), also known as the Default Multicast Distribution Tree (Default-MDT), is used to flood customer multicast traffic to all PE routers participating in a specific VPN. To achieve this, a single, pre-configured multicast group address from the provider's address space is assigned to the I-PMSI for that VPN. When an ingress PE router receives a customer multicast packet, it encapsulates it into a provider packet (typically GRE). The destination IP address of this outer provider packet is set to the configured I-PMSI multicast group address, ensuring it is distributed through the provider's PIM-enabled core to all other PEs in the same MVPN.

Why Incorrect

A. The destination group address of the customer packets is the inner header's destination and is not used for routing across the provider core.
C. The system IP address of a receiving PE is a unicast address; an I-PMSI requires a point-to-multipoint transport using a multicast address.
D. A multicast group address selected from a range is a mechanism used for a Selective-PMSI (S-PMSI), not the all-encompassing I-PMSI.

References

1. RFC 6037: Cisco Systems' Solution for Multicast in BGP/MPLS IP VPNs.

Section 3, "Building the Default-MDT": "Each PE router that is a member of a given VRF is configured with a multicast address from the provider's address space. This address, called the 'Default-MDT group address', must be the same for all PE routers that are members of that VRF."

Section 4, "Sending Multicast Packets to Remote PE Routers": "When a PE router receives a multicast packet from a site, it encapsulates the packet... The destination address of the encapsulating... packet is the Default-MDT group address for the VRF."

2. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Services Guide, Release 21.10.R1.

Chapter: Multicast VPN, Section: Rosen MVPN: "The default-MDT uses a specific P-multicast group address to build a P-tunnel to flood C-multicast traffic for a specific MVPN... When C-multicast traffic is received on an ingress PE, the ingress PE encapsulates the C-multicast packets and forwards them over the P-network to the P-multicast group address of the default-MDT."

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