The CTO of a company requires the support of a network consultant to deliver an MPLS solution without resigning to a certain degree of redundancy and scalability. Which solution effectively scales…

Question

Options

• AL2VPN with the broadcast traffic processed at the ingress PE.
• BL3VPN with direct LSP connectivity between all PEs.
• CL2VPN by encapsulating multiple frame formats with interworking.
• DL3VPN using a hierarchical topology of N-PEs and U-PEs.

• A
  12% (4)
• B
  21% (7)
• C
  3% (1)
• D
  64% (21)

Explanation

Option D is correct because L3VPN using a hierarchical topology of Network-facing PEs (N-PEs) and User-facing PEs (U-PEs) is specifically designed for massive scalability. U-PEs handle local customer aggregation and forward traffic to N-PEs, which carry the core routing intelligence - this separation of roles means you can add thousands of sites without burdening every PE with full routing tables across the network.

Why the distractors fail:

• A is wrong because processing broadcast traffic at the ingress PE in an L2VPN creates significant overhead and broadcast storms at scale - this limits scalability rather than enabling it.
• B is wrong because direct (full-mesh) LSP connectivity between all PEs grows at O(n²), meaning the number of tunnels explodes as sites are added - this approach collapses under hundreds or thousands of sites.
• C is wrong because L2VPN interworking (bridging different frame formats) solves an interoperability problem, not a scalability one; it adds complexity without addressing the scaling challenge.

Memory tip: Think of the N-PE/U-PE hierarchy like a corporate org chart - the U-PEs are frontline workers handling local tasks, while N-PEs are managers handling the big picture. You can hire thousands of frontline workers without each one needing a direct line to every other worker in the company.

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