The Disputed Internet: Quantifying Fragmentation in the IPv6 Internet#

Authors: Vivian Band (University of Glasgow), Romain Fontugne (IIJ Research Laboratory)

• Why: As your dual-stack footprint grows, IPv6 reachability is not a clean mirror of IPv4 — peering disputes (the Cogent–Hurricane Electric case being the exemplar) fragment the IPv6 topology. Anyone running IPv6-only or IPv6-preferred infrastructure should understand this failure mode.
• What: Quantifies IPv6 fragmentation via BGP-measured reachability differences between large transit providers, and uses forward DNS data to estimate the impact on popular website reachability. Findings: IPv6 fragmentation is substantial relative to the unified IPv4 topology, is worsening over time, and an increasing number of popular sites are partially reachable in IPv6. IPv4 fallback currently masks the user-facing impact. (from abstract only)
• How: BGP-based reachability comparison across large transits in both protocols, plus forward-DNS-based estimation of popular-site impact.
• Where applicable: Global Internet; most relevant if you operate or depend on IPv6-heavy paths. The mitigating reality today is happy-eyeballs-style fallback, so treat this as a structural risk to monitor rather than a current outage driver.