nixos-config/machines/fuuko/services/router.nix

# Home network configuration
#
#     +----------+ +------+
#     |          | |      | ( clients )
#     |          | |     +|-|-|-|-|+
# +---+----+   +-+-+-+   |5 4 3 2 1|
# |upstream|   |fuuko|   |TL-SG105 |
# +--------+   +-----+   +---------+
#
# It consists of fuuko as a router (this configuration),
# connected to a TP-LINK TL-SG105E “smart managed” (i.e., it can do VLANs) 5-port switch.
# The upstream comes from some plasic Huawei router/AP I don’t control.
#
# fuuko has two physical network interfaces,
# because remote unlocking (which requires network in initrd) is hard with VLANs.
#
# Wireless is configured by providing the whole hostapd configuration file as a secret.
# Once nixpkgs PR 222536 is merged, I will migrate to using the NixOS module.
# Thanks to Intel’s wisdom, it’s not possible to use 5GHz in AP mode.
{ config, lib, pkgs, ... }:
let
  domain = "home.sbruder.de";
in
{
  sops.secrets.wg-mullvad-private-key = {
    owner = config.users.users.systemd-network.name;
    sopsFile = ../secrets.yaml;
  };
  sops.secrets.hostapd-config = {
    sopsFile = ../secrets.yaml;
  };

  boot.kernel.sysctl = {
    "net.ipv4.conf.all.forwarding" = true;
  };

  networking = {
    # networkd handles this
    useDHCP = false;
    # networkd didn’t work that well for this
    nat = {
      enable = true;
      enableIPv6 = true;
      externalInterface = "wg-mullvad";
      internalInterfaces = [ "br-lan" ];
      internalIPv6s = [ "fd00:80:1::/64" ];
    };
  };

  systemd.network = {
    enable = true;
    netdevs = {
      br-lan = {
        netdevConfig = {
          Name = "br-lan";
          Kind = "bridge";
        };
      };
      wg-mullvad = {
        netdevConfig = {
          Kind = "wireguard";
          Name = "wg-mullvad";
        };
        wireguardConfig = {
          PrivateKeyFile = config.sops.secrets.wg-mullvad-private-key.path;
          FirewallMark = 51820;
        };
        wireguardPeers = lib.singleton {
          wireguardPeerConfig = {
            Endpoint = "185.65.134.86:51820";
            PublicKey = "xpZ3ZDEukbqKQvdHwaqKMUhsYhcYD3uLPUh1ACsVr1s=";
            AllowedIPs = [ "0.0.0.0/0" "::0/0" ];
            PersistentKeepalive = 25;
          };
        };
      };
    };
    networks = {
      wan = {
        name = "enp8s0";
        networkConfig = {
          # Upstream provides no IPv6 :(
          # If this is not set, it waits and fails systemd-networkd-wait-online
          LinkLocalAddressing = "no";
          IPv6AcceptRA = "no";
        };
        DHCP = "ipv4";
        dhcpV4Config = {
          UseDNS = "no";
        };
      };
      lan = {
        name = "enp9s0";
        bridge = [ "br-lan" ];
      };
      br-lan = {
        name = "br-lan";
        domains = [ domain ];
        address = [ "10.80.1.1/24" "fd00:80:1::1/64" ];
      };
      wg-mullvad = {
        name = "wg-mullvad";
        address = [ "10.66.208.88/32" "fc00:bbbb:bbbb:bb01::3:d057/128" ];
        dns = [ "10.64.0.1" ];
        routingPolicyRules = [
          {
            routingPolicyRuleConfig = {
              FirewallMark = 51820;
              InvertRule = "yes";
              Table = 51820;
              Priority = 10;
              #SuppressPrefixLength = 0; # can’t be used here (forwarding does not work with it)
            };
          }
          # FIXME: those two shouldn’t be necessary
          # It should automatically detect those routes existing and prioritise them
          {
            routingPolicyRuleConfig = {
              To = "10.80.0.0/24";
              Priority = 9;
            };
          }
          {
            routingPolicyRuleConfig = {
              To = "10.80.1.0/24";
              Priority = 9;
            };
          }
        ];
        routes = [
          {
            routeConfig = {
              Gateway = "0.0.0.0"; # point-to-point connection
              Table = 51820;
            };
          }
          {
            routeConfig = {
              Gateway = "::";
            };
          }
        ];
      };
    };
  };
  services.resolved.enable = false;

  services.dnsmasq = {
    enable = true;

    settings = {
      bogus-priv = true; # do not forward revese lookups of internal addresses
      domain-needed = true; # do not forward names without domain
      interface = "br-lan"; # only respond to queries from lan
      no-hosts = true; # do not resolve hosts from /etc/hosts
      no-resolv = true; # only use explicitly configured resolvers

      cache-size = 10000;

      inherit domain;

      # Allow resolving the router
      interface-name = [
        "${config.networking.hostName}.${domain},br-lan"
        "${config.networking.hostName},br-lan"
      ];

      # DHCPv4
      dhcp-range = [
        "10.80.1.20,10.80.1.150,12h" # DHCPv4
        "fd00:80:1::,ra-stateless,ra-names" # SLAAC (for addresses) / DHCPv6 (for DNS)
      ];
      dhcp-option = [
        "option:router,10.80.1.1"
        "option6:dns-server,fd00:80:1::1"
      ];

      # Despite its name, the switch does not have a “smart” configuration,
      # that would allow me to tell it not to get DHCP from wan,
      # but from lan instead.
      # So it has to use static configuration.
      host-record = "switchviech,switchviech.${domain},10.80.1.19";
      server = [
        "10.64.0.1" # mullvad DNS, should be fastest overall
        #"9.9.9.9" # dns.quad9.net
        #"2620:fe::fe"
      ];
    };
  };
  systemd.services.dnsmasq.after = [ "systemd-networkd.service" ];

  services.prometheus.exporters.dnsmasq = {
    enable = true;
    listenAddress = config.sbruder.wireguard.home.address;
    leasesPath = "/var/lib/dnsmasq/dnsmasq.leases";
  };

  networking.firewall.allowedUDPPorts = [ 53 67 ];
  networking.firewall.allowedTCPPorts = [ 53 ];

  # Wireless
  boot.kernelModules = [ "nl80211" ];

  environment.systemPackages = with pkgs; [
    iw
    wirelesstools
  ];

  # The service is mostly taken from nixpkgs pr 222536.
  systemd.services.hostapd = {
    path = with pkgs; [ hostapd ];
    after = [ "sys-subsystem-net-devices-wlp7s0.device" ];
    bindsTo = [ "sys-subsystem-net-devices-wlp7s0.device" ];
    wantedBy = [ "multi-user.target" ];

    serviceConfig = {
      ExecStart = "${pkgs.hostapd}/bin/hostapd ${config.sops.secrets.hostapd-config.path}";
      Restart = "always";
      ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
      RuntimeDirectory = "hostapd";

      # Hardening
      LockPersonality = true;
      MemoryDenyWriteExecute = true;
      DevicePolicy = "closed";
      DeviceAllow = "/dev/rfkill rw";
      NoNewPrivileges = true;
      PrivateUsers = false; # hostapd requires true root access.
      PrivateTmp = true;
      ProtectClock = true;
      ProtectControlGroups = true;
      ProtectHome = true;
      ProtectHostname = true;
      ProtectKernelLogs = true;
      ProtectKernelModules = true;
      ProtectKernelTunables = true;
      ProtectProc = "invisible";
      ProcSubset = "pid";
      ProtectSystem = "strict";
      RestrictAddressFamilies = [
        "AF_INET"
        "AF_INET6"
        "AF_NETLINK"
        "AF_UNIX"
      ];
      RestrictNamespaces = true;
      RestrictRealtime = true;
      RestrictSUIDSGID = true;
      SystemCallArchitectures = "native";
      SystemCallFilter = [
        "@system-service"
        "~@privileged"
        "@chown"
      ];
      UMask = "0077";
    };
  };
}