Transient Forwarding Anomalies and How to Find Them#

Roland Schmid; Tibor Schneider; Georgia Fragkouli; Laurent Vanbever (ETH Zurich)

• Why: Transient reachability violations during BGP re-convergence are exactly the class of event that makes a mockery of tight SLAs, and no existing method measures them accurately for all prefixes without perturbing the network. TRIX is a genuinely new inference approach to a problem you live with daily in WAN operations.
• What: TRIX infers transient violation times for BGP events from logged routing events or collected BGP messages, reconstructing network-wide reachability violations without active probing of every destination. Validated on a testbed with 12 real routers and a programmable switch: inferred violation times average within 13–25 ms of ground truth, and the approach scales to large networks (from abstract only).
• How: Key insight: you don't need to probe all destinations if you can reconstruct router-local forwarding state for all of them from available information. TRIX simulates the BGP control plane, models FIB-update rate, and combines per-router state with propagation delays — overcoming the fact that logged events are inaccurate in both content and timing of forwarding updates.
• Where applicable: Any BGP network with routing-event logging or route-collection infrastructure; the method is passive and doesn't worsen network performance. General technique, not operator-specific, though the 13–25 ms accuracy was established on a specific testbed configuration.