Given a ring topology, which loop prevention mechanism provides the fastest reconvergence time after a link failure?

Question

Options

• ARapid Per-VLAN Spanning Tree Protocol
• BResilient Ethernet Protocol
• CMultiple Spanning Tree Protocol
• DSpanning Tree Protocol

• A
  17% (7)
• B
  71% (29)
• C
  7% (3)
• D
  5% (2)

Explanation

Resilient Ethernet Protocol (REP) is purpose-built for ring topologies and achieves sub-50ms reconvergence by precomputing alternate paths and immediately unblocking a pre-designated port when a link failure is detected - no election or re-calculation delay is needed.

Why the distractors are wrong:

• A (Rapid PVST+): Faster than classic STP (typically 1–2 seconds), but not optimized for rings and carries per-VLAN overhead that slows reconvergence compared to REP.
• C (MST): Groups VLANs into instances for scalability, but convergence speed is comparable to RSTP - it offers no ring-specific optimization.
• D (STP): The slowest option, with convergence taking 30–50 seconds due to timer-based state transitions (listening → learning → forwarding).

Memory tip: Think "REP = Ring's Emergency Protocol" - it's the only one in the list designed for rings, so when you see "ring topology + fastest reconvergence," REP is always the answer. The STP family (STP, RSTP, PVST+, MST) was built for general Ethernet switching, not ring-specific recovery.

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