350-501 Question #69: Real Exam Question with Answer & Explanation

Question

Which two steps must a service provider consider when adding multicast support to the existing MPLS L3VPN? (Choose two.)

Options

• AUsing SSM for data MDT helps to minimize the number of group addresses needed in the core
• BUsing default MDT results in a reduction of multicast routing states in the core
• CAll PEs must be configured as RPs inside of each customer VRF to minimize impact of the RPF
• DBandwidth may be wasted on PEs as a result of only using the default MDT
• EForwarding customer multicast traffic only via the default MDT optimizes PE utilization

Explanation

When adding multicast support to MPLS L3VPNs, service providers must consider that using the default MDT reduces core multicast routing states by aggregating customer traffic, but relying solely on it can lead to wasted bandwidth on PEs that receive traffic for groups without local receivers.

Common mistakes.

• A. While SSM (Source-Specific Multicast) can improve efficiency and reduce PIM state complexity by removing RP dependency, its primary benefit is not 'minimizing the number of group addresses needed in the core,' as customer group addresses are determined by the customer, and SSM merely changes how they are handled.
• C. It is not a requirement for all PEs to be configured as RPs (Rendezvous Points) for every customer VRF; typically, a few RPs are strategically placed for scalability and redundancy, and having all PEs as RPs for all VRFs would increase complexity.
• E. Forwarding all customer multicast traffic exclusively over the default MDT does not optimize PE utilization; instead, it can lead to inefficient utilization and wasted bandwidth because PEs will receive traffic for groups without local receivers, increasing processing load and unnecessary traffic.

Concept tested. MPLS L3VPN Multicast (MVPN) - MDTs

Reference. https://www.cisco.com/c/en/us/td/docs/ios/mvpn/configuration/guide/mvpn_c/mvpn_mdt.html

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