Which two fast reroute technologies provide the highest level of protected path coverage in a ring topology? (Choose two.)

Question

Options

• Aper-prefix LFA
• Bremote LFA
• Cautomatic protection switching
• DMPLS TE FRR
• Eper-link LFA

• A
  28% (9)
• B
  44% (14)
• D
  9% (3)
• E
  19% (6)

Explanation

Ring topologies present a specific coverage challenge for IP fast reroute. Per-link LFA (E) and per-prefix LFA (A) both fail in rings because the only available alternate next-hop typically traverses the same failed segment, meaning no loop-free alternate exists - coverage can be 0% in a simple ring. Remote LFA (rLFA, B) overcomes this by using MPLS tunnels to reach a 'PQ node' that is loop-free with respect to the destination, providing near-100% coverage even in rings where standard LFA fails entirely. Automatic Protection Switching (APS, C) - including ITU-T G.8032 Ethernet Ring Protection (ERP) and SONET/SDH ring protection - is purpose-built for ring topologies and achieves sub-50ms protection switching with guaranteed full coverage around the ring. MPLS TE FRR (D) provides excellent protection but requires a full MPLS TE infrastructure (RSVP-TE tunnels, headend/tailend LSRs) and is more complex to deploy; it is not ring-specific and is outperformed in ring scenarios by rLFA and APS in terms of simplicity and coverage guarantee.

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