Towards an IPv6-only WLCG: More successes in reducing IPv4

¹ University of Nebraska-Lincoln (UNL), 1400 R St, Lincoln, NE 68588, USA
² European Organization for Nuclear Research (CERN), CH-1211 Geneva 23, Switzerland
³ UKRI STFC Rutherford Appleton Laboratory (RAL), Harwell Campus, Didcot OX11 0QX, UK
⁴ Energy Sciences Network (ESnet), Lawrence Berkeley National Laboratory, Berkeley CA 94720, USA
⁵ Jisc, Portwall Lane, Bristol BS1 6NB, UK
⁶ Institute of Physics, Academy of Sciences of the Czech Republic, Prague 8, Czech Republic
⁷ Fermi National Accelerator Laboratory (FNAL), P.O. Box 500, Batavia IL 60510, USA
⁸ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
⁹ Karlsruhe Inst. of Technology, Hermann-v-Helmholtz-Pl. 1, D-76344 Egg.-Leopoldshafen, Germany
¹⁰ Brookhaven National Laboratory (BNL), 98 Rochester St., Upton NY 11973, USA
¹¹ University of Michigan Physics, 450 Church St, Ann Arbor, MI 48109, USA
¹² Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, D-22607 Hamburg, Germany
¹³ INFN, Sezione di Milano, via G. Celoria 16, I-20133 Milan, Italy
¹⁴ Imperial College London, South Kensington Campus, London SW7 2AZ, UK

^* e-mail: david.kelsey@stfc.ac.uk

Published online: 7 October 2025

Abstract

The Worldwide Large Hadron Collider Computing Grid (WLCG) community’s deployment of dual-stack IPv6/IPv4 on its worldwide storage infrastructure has been very successful. Dual-stack is not, however, a viable longterm solution; the HEPiX IPv6 Working Group has focused on studying where and why IPv4 is still being used, and how to flip such traffic to IPv6. The agreed end goal is to turn IPv4 off and run IPv6-only over the wide-area network to simplify both operations and security management.

This paper reports our work since the CHEP2023 conference. Firstly, we present our campaign to deploy IPv6 on CPU services and Worker Nodes, with a deadline of end of June 2024. Then, the WLCG Data Challenge (DC24) performed in February 2024 was an excellent opportunity to observe the percentage of data transfers carried by IPv6. We observed the predominance of IPv6 in data transfers during DC24 and were able to understand yet more reasons for the use of IPv4 and areas for remedial action.

The paper ends with the working group’s plans for moving WLCG to “IPv6- only”. One aspect of this is the possible automated use of IPv6-only clients configured with a customer-side translator, or CLAT, together with a deployment of NAT64 using what is often known as “IPv6-Mostly”, enabling IPv6-only sites to connect to non-WLCG IPv4-only services.