Since NixOS 25.05, scripted networking installs the default route from the
gateway interface's network-addresses-<iface>.service, matching the interface
via defaultGateway.interface or by subnet inclusion. Hetzner's off-subnet
point-to-point gateway (91.98.47.73/32 on eth0, gw 172.31.1.1) matched
neither with the bare-string form, so the 26.05 switch on 2026-08-03 left the
host with no default route and off the network (recovered via Hetzner rescue:
grubenv default back to the 24.11 generation).
With an explicit interface, the module installs both the gateway host route
and the default route from eth0's own unit:
ip -4 route replace 172.31.1.1 proto static dev eth0
ip -4 route replace default proto static dev eth0 via 172.31.1.1
Verified by nix eval of systemd.services.network-addresses-eth0.script.
nixpkgs: 50ab793 -> 531670d (nixos-26.05, was nixos-24.11 EOL)
sops-nix: 77c423a -> f140661 (master, buildGo125Module now builds on 26.05)
3-release channel jump (24.11 -> 25.05 -> 25.11 -> 26.05) to match the
orchestrator host and get CVE patches. 24.11 was EOL (2025-06-30).
Notable 26.05 changes reviewed: systemd Stage 1 boot (default, no config
change needed), dbus-broker default, bash nixos-rebuild removed (Python
rewrite mandatory; git present on host), MySQL 8.0 removed (not used as a
NixOS module). No system.rebuild/fileSystems/boot.initrd options in the
host config, so no config edits required.
