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.
nixos-infect emitted defaultGateway6.address="" and ipv6.routes=[{address="";
prefixLength=128}] for this v4-only Hetzner instance, so network-addresses-eth0.service
failed at boot ("ip route add /128 ... any valid prefix is expected rather than /128").
The box has no real IPv6 (link-local only, kernel-managed), so remove the empty IPv6
gateway, address, and route. IPv4 unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Port from terraform-hetzner branch. Adds the Hetzner cc-ci flake host with
all 3 root authorized keys so nixos-rebuild doesn't lock out SSH access.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>