An empirical evaluation of longitudinal anycast catchment stability#

Remi Hendriks, University of Twente (with Bernhard Degen, Bas Palinckx, Raffaele Sommese, Roland van Rijswijk-Deij)

• Why: Anyone running an anycast service (DNS, CDN edges, global ingress) needs to know how often to remap catchments — too rarely and traffic engineering is stale, too often and you burn effort. This replaces guesswork with six months of daily measurements.
• What: Daily Verfploeter catchment mappings on an industry-grade 32-PoP anycast testbed (20 countries, 6 continents) across IPv4 and IPv6 for six months (~3.5M responsive /24s, ~0.5M IPv6 /48s probed). Result: catchments are very stable short-term — 95% of prefixes route to the same PoP at one-week granularity, >99% day-to-day — and an IPv4 mapping stays valid roughly two months at a 10% error rate. But sudden routing events can shift catchments dramatically: in July, the Tokyo PoP lost most of its traffic to a Sydney PoP that expanded five-fold; north-eastern China switched to Frankfurt; Vietnamese addresses moved to Seoul.
• How: Active probing with one target per smallest propagated BGP prefix, using the USC/ISI and TUM IPv6 hitlists; stability measured across timescales from days to months.
• Where applicable: The recommendations (how frequently to run catchment analysis) apply to anycast operators generally, but absolute stability numbers come from a Vultr-hosted testbed — your mileage will vary with topology, peering, and remote-peering prevalence. The event-driven instability finding (plan for sudden shifts, not gradual drift) is the transferable lesson.