{
  # Make sure that the firewall is enabled, even if it's the default.
  networking.firewall.enable = true;

  programs.ssh.knownHosts = {
    build01 = {
      hostNames = [ "build01.nix-community.org" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIElIQ54qAy7Dh63rBudYKdbzJHrrbrrMXLYl7Pkmk88H";
    };
    build02 = {
      hostNames = [ "build02.nix-community.org" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMm3/o1HguyRL1z/nZxLBY9j/YUNXeNuDoiBLZAyt88Z";
    };
    build03 = {
      hostNames = [ "build03.nix-community.org" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFiozp1A1+SUfJQPa5DZUQcVc6CZK2ZxL6FJtNdh+2TP";
    };
    build04 = {
      hostNames = [ "build04.nix-community.org" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAINvzMJfCiVKGfEjCfBZqDD7Kib5y+2zz04YI8XrCZ68O";
    };
    darwin02 = {
      hostNames = [ "darwin02.nix-community.org" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICJqwpMUEl1/iwrBakeDb1rlheXlE5mfDLICVz8w6yi6";
    };
    darwin03 = {
      hostNames = [ "darwin03.nix-community.org" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKX7W1ztzAtVXT+NBMITU+JLXcIE5HTEOd7Q3fQNu80S";
    };
    aarch64-nixos-community = {
      hostNames = [ "aarch64.nixos.community" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMUTz5i9u5H2FHNAmZJyoJfIGyUm/HfGhfwnc142L3ds";
    };
    hetzner-storage-box = {
      hostNames = [ "[u348918.your-storagebox.de]:23" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIICf9svRenC/PLKIL9nk6K/pxQgoiFC41wTNvoIncOxs";
    };
    web01 = {
      hostNames = [ "web01.nix-community.org" ];
      publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIBlk4GXei97txlkLtRQDblje0YXZxQnu5w7rVSBPzYRl";
    };
  };

  services.openssh = {
    hostKeys = [
      { path = "/etc/ssh/ssh_host_ed25519_key"; type = "ed25519"; }
    ];
  };

  # Ban brute force SSH
  services.fail2ban.enable = true;
}