@tuxiqae Thanks for the pointer! I've also found a few blog posts and personal Nix modules/configurations implementing routers and firewalls with NixOS.
- https://s-n.me/building-a-nixos-router-for-a-uk-fttp-isp-the-basics
- https://codefionn.eu/blog/nixos-router-with-j4125-and-intel-i225/
- https://francis.begyn.be/blog/nixos-home-router
- https://github.com/NixRTR/nixos-router
- https://github.com/thelegy/nixos-nftables-firewall
- https://github.com/georgewhewell/nixos-host/tree/master/profiles/router
- https://github.com/LunNova/nixos-configs/tree/dev/hosts/router
If you have a fediverse account, you can quote this note from your own instance. Search https://hachyderm.io/users/joschi/statuses/115954961194478292 on your instance and quote it. (Note that quoting is not supported in Mastodon.)