4A0-108 practice question 3 of 30

Which of the following is NOT a characteristic of Draft Rosen?

Full set: 247 questions
Answer options
A: PIM in the VRF.
B: PIM in the service provider's core network.
C: GRE encapsulation for multicast data traffic.
D: MPLS encapsulation for multicast data traffic. Correct answer
Correct Answer:
D. MPLS encapsulation for multicast data traffic.
Explanation

Draft Rosen, also known as PIM/GRE MVPN, is a traditional architecture for providing multicast services over an MPLS VPN backbone. A core characteristic of this model is the use of Generic Routing Encapsulation (GRE) to tunnel customer multicast data packets across the service provider's core network. The provider core itself uses PIM to build Multicast Distribution Trees (MDTs) that carry this GRE-encapsulated traffic between PE routers. Customer VRFs also run their own instances of PIM to manage multicast state within the VPN. MPLS encapsulation for multicast data traffic is a feature of Next-Generation MVPN (NG-MVPN) architectures (defined in RFC 6513/6514), not the original Draft Rosen model.

Why Incorrect

A. PIM in the VRF is a fundamental component, used to learn about customer multicast sources and receivers and to build customer-specific multicast trees.
B. PIM is required in the service provider's core to establish the default and data MDTs that transport the encapsulated customer multicast traffic between PE routers.
C. GRE is the specified encapsulation method in Draft Rosen for tunneling customer multicast packets across the provider's IP/MPLS core network.

References

1. Nokia 7750 SR OS Layer 3 Services Guide, Release 22.10.R1, Section: "MVPN Overview". The document states, "Draft Rosen Layer 3 MVPNs use PIM to create and signal the provider tunnels, and GRE to encapsulate the multicast traffic." This explicitly confirms the use of PIM in the core and GRE encapsulation. It also describes the requirement for PIM within the VRF instance.

2. RFC 6513: Multicast in MPLS/BGP IP VPNs, Section 1: "Introduction". This document, which defines Next-Generation MVPN, contrasts the new framework with the older method. It states that the prior art (Draft Rosen) "requires the use of PIM in the SP network" and "uses GRE encapsulation for the C-multicast data packets". It then introduces the use of MPLS P-tunnels (such as P2MP LSPs) as a key feature of the new framework, distinguishing it from Draft Rosen.

3. RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs), Section 11: "Multicast". This RFC describes the foundational principles of Draft Rosen MVPN. It details the creation of a "Default MDT" for each VPN in the provider core using PIM and the encapsulation of customer multicast packets (C-packets) inside provider packets (P-packets) for transport across these tunnels.

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