A trading firm steers market-data over app-route policy with strict loss and latency limits, preferring fiber color gold, but during congestion no tunnel of any color meets the SLA class for 30 seconds. Sessions must continue on the tunnel closest to meeting the SLA rather than drop until quality recovers. Which fallback behavior when no tunnel meets the SLA class keeps market-data flowing?

Backup SLA preferred-color logic preserves strict loss and latency limits while preferring gold fiber when it meets the SLA. If no tunnel of any color meets the class for 30 seconds, the best-tunnel fallback keeps sessions established on the tunnel whose measured metrics are closest to the SLA, so market-data continues until quality recovers. The least-loaded fallback bases forwarding on utilization, not SLA proximity, and could send sensitive data over an empty but high-delay or lossy path. The silver preferred-color configuration retains best-tunnel continuity, but the scenario does not identify silver transport, so that preference cannot implement the stated gold-to-any-color policy. The gold preference with best-tunnel fallback and relaxed limits preserves continuity, but changing the limits makes noncompliant loss or latency appear acceptable and violates the requirement for strict assurance. Exam caveat: distinguish the closest-to-SLA fallback from the least-loaded choice, the unsupported silver preference, and relaxed thresholds; each changes a different part of the policy. Practical check: inspect live policy and SLA history to confirm gold is selected while compliant, the closest-to-SLA tunnel carries market-data during a prolonged violation without session reset, and strict loss and latency thresholds remain unchanged.