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The CERN experiments' network journey to IPv6-only#

TNC26 (GÉANT research networking conference) digest Program Adjacent pick 8–12 June 2026

Abstract Slides

Tim Chown (Jisc)

  • Why: The best-documented large-scale argument that dual-stack is a waypoint, not a destination — with measured traffic shares to back it.
  • What: The WLCG (170 sites, 40 countries; LHCOPN private optical Tier-0/Tier-1 links, LHCONE L3VPN/VRF, NREN catch-all) IPv6 program: Phase 2 dual-stack is complete at data servers and 75% complete at worker nodes (ticket campaign running since December 2023); Phase 3 — removing IPv4 from WAN links — is underway, starting with CERN–Tier-1 LHCOPN links. Measured shares: >99.5% IPv6 on the KIT OPN link, >93% in FTS logs (including non-WLCG transfers), >99.9% of SciTags flows into RAL.
  • How: HEPiX IPv6 WG methodology — readiness/gap analysis (2011), dual-stack enable-and-prefer (2018–), then active IPv4 decommissioning on WANs, motivated by simpler operation, simpler security, no NAT.
  • Where applicable: Research-grid context, but the phased playbook and the "plan where and when you can turn off IPv4" message apply to any distributed infrastructure that has finished dual-stack and is wondering what's next.