# macOS 26.2 stops self-assigning IPv4 on Thunderbolt RDMA interfaces > The claim is that from macOS 26.2 the Thunderbolt RDMA member interfaces stay without an IPv4 address until something assigns one, so JACCL has no IPv4-mapped GID to pair with and fails at RTR. Parent: [Mac local LLMs: Clusters, RDMA, exo and ds4](https://llms-explorer.com/tree/mac-local-llms-clusters-rdma-exo-ds4/) · 1 facets · 18 facts · page: https://llms-explorer.com/tree/macos-26-2-stops-self-assigning-ipv4-on-thunderb/ ## Facts - The claim is that from macOS 26.2 the Thunderbolt RDMA member interfaces stay without an IPv4 address until something assigns one, so JACCL has no IPv4-mapped GID to pair with and fails at RTR. — [source](https://github.com/exo-explore/exo/issues/1390) - The exo console error for this case is `ValueError: [jaccl] Changing queue pair to RTR failed with errno 22`, printed on each runner start; the dashboard shows `preparing` then `failed` in sequence for a tensor-sharded, MLX RDMA instance on 2 or more Macs. — [source](https://github.com/exo-explore/exo/issues/1390) - The same log shows `Fast synch flag: 1` just before the error, so the failure happens during JACCL group creation, not in a fence wait. — [source](https://github.com/exo-explore/exo/issues/1390) - The reporter's `sw_vers`-style output was macOS 26.2, build 25C56. A second user wrote that their two Studios went from macOS 15.7 to 26.2 and that the OS had created a bridge device so the individual Thunderbolt interfaces were not available; running exo's `tmp/` network script, which sets up a location without the bridge, made RDMA work. — [source](https://github.com/exo-explore/exo/issues/1390) - A third user ran the script, rebooted and re-pulled the source and then everything worked; that user drafted a troubleshooting text listing three options: enable DHCP on each interface, assign and route addresses manually, or run the script. — [source](https://github.com/exo-explore/exo/issues/1390) - A reporter suggested that exo should check whether the interfaces are in a bridge and either warn or disable the MLX RDMA button; a maintainer agreed that UI and documentation changes could help. — [source](https://github.com/exo-explore/exo/issues/1390) - Two different causes give the same errno 22: no IPv4 on a member interface (the 26.2 case) and interfaces enslaved to a bridge, which the 15.7-to-26.2 user hit. The sources do not separate them by symptom. — [source](https://github.com/exo-explore/exo/issues/1390) - Exo issue 1390 still showed state Open when fetched on 2026-10-04, so the exo project had not closed the gap in the app. — [source](https://github.com/exo-explore/exo/issues/1390) - Whether macOS 26.2 changed behaviour or the interfaces never self-assigned: the maintainer says "after macOS 26.2 they do not self-assign by default"; one reporter says the OS created a bridge when upgrading from 15.7. No Apple release note or document is cited by anyone. — [source](https://github.com/exo-explore/exo/issues/1390) - Whether the change is a link-local (IPv4LL) policy change in 26.2, a service-order or bridge-creation change, or both. — source: `asserted` - Whether later 26.x builds (the cluster in exo issue 1847 ran 26.3 on DHCP link-local ports) restored self-assignment. — source: `asserted` - The exo errno 22 failure is printed as `ValueError: [jaccl] Changing queue pair to RTR failed with errno 22` and the dashboard shows preparing then failed. — [source](https://github.com/exo-explore/exo/issues/1390) - The first reporter ran macOS 26.2 build 25C56. — [source](https://github.com/exo-explore/exo/issues/1390) - A user upgraded from macOS 15.7 to 26.2 found an OS-created bridge device and fixed RDMA by using exo's `tmp/` script to build a location without the bridge. — [source](https://github.com/exo-explore/exo/issues/1390) - A user's troubleshooting draft offers three options: DHCP per interface, manual address plus route per interface, or the exo script. — [source](https://github.com/exo-explore/exo/issues/1390) - A reporter proposed an exo check for bridged interfaces that warns or disables the MLX RDMA option. — [source](https://github.com/exo-explore/exo/issues/1390) - Exo issue 1390 was still Open on 2026-10-04. — [source](https://github.com/exo-explore/exo/issues/1390) - No cited source ties the no-self-assign behaviour to an Apple document or release note; it rests on a maintainer statement. — source: `asserted`