nixos-config/machines/shinobu/services/router/default.nix

# Home network configuration
#            (2.5GbE clients)
#                  | |
#     +----------+ +----------+
#     |          | | | |      | (1GbE clients)
#     |          | | | |     +|-|-|-|-|+
# +---+----+   +-+-+-+-+-+   |5 4 3 2 1|
# |upstream|   | 1 2 3 4 |   |TL-SG105 |
# +--------+   | shinobu |   +---------+
#              +---------+
#
# It consists of shinobu 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 (for now) from a PŸUR “WLAN-Kabelbox” (Compal CH7467CE).
# Sadly, I could not enable bridge mode on it, so the packets now go through (at least) four layers of NAT:
# device → NAT on shinobu (→ NAT on plastic router → PŸUR CGNAT) → NAT on VPN
#
# Because the switch only supports GbE,
# the two clients I currently have with support for 2.5GbE are connected
# directly to the two remaining network interfaces on shinobu.
# Once I have more devices with support for 2.5GbE
# or I find a good deal on a matching switch,
# I will change this.
#
# 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
  cfg = import ./common.nix;
in
{
  imports = [
    ./dnsmasq.nix
    ./nft.nix
    ./wlan.nix
  ];

  boot.kernel.sysctl = {
    "net.ipv4.conf.all.forwarding" = true;
    "net.ipv6.conf.all.forwarding" = true;
  };

  environment.systemPackages = with pkgs; [
    ethtool
  ];

  sops.secrets.wg-upstream-private-key = {
    owner = config.users.users.systemd-network.name;
    sopsFile = ../../secrets.yaml;
  };

  networking.useDHCP = false;

  systemd.network = {
    enable = true;
    # not all interfaces need to be up
    wait-online.extraArgs = [ "--any" ];
    netdevs = {
      br-lan = {
        netdevConfig = {
          Name = "br-lan";
          Kind = "bridge";
        };
      };
      wg-upstream = {
        netdevConfig = {
          Kind = "wireguard";
          Name = "wg-upstream";
        };
        wireguardConfig = {
          PrivateKeyFile = config.sops.secrets.wg-upstream-private-key.path;
          FirewallMark = 51820;
        };
        wireguardPeers = lib.singleton {
          wireguardPeerConfig = with cfg.wg-upstream; {
            Endpoint = endpoint.full;
            PublicKey = publicKey;
            AllowedIPs = [ "0.0.0.0/0" "::0/0" ];
            PersistentKeepalive = 25;
          };
        };
      };
    };
    networks = {
      wan = {
        name = "enp1s0";
        DHCP = "ipv4";
        networkConfig = {
          IPv6AcceptRA = "yes";
        };
        dhcpV4Config = {
          UseDNS = "no";
        };
        ipv6AcceptRAConfig = {
          # Only use RA
          DHCPv6Client = false;
          UseDNS = "no";
        };
      };
      lan1 = {
        name = "enp2s0";
        bridge = [ "br-lan" ];
      };
      lan2 = {
        name = "enp3s0";
        bridge = [ "br-lan" ];
      };
      lan3 = {
        name = "enp4s0";
        bridge = [ "br-lan" ];
      };
      br-lan = {
        name = "br-lan";
        domains = [ cfg.domain ];
        address = [ "10.80.1.1/24" "fd00:80:1::1/64" ];
      };
      wg-upstream = {
        name = "wg-upstream";
        address = cfg.wg-upstream.addresses;
        routingPolicyRules = [
          {
            routingPolicyRuleConfig = {
              Family = "both"; # default is only ipv4
              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
          # LAN (v4)
          {
            routingPolicyRuleConfig = {
              To = "10.80.1.0/24";
              Priority = 9;
            };
          }
          # LAN (v6)
          {
            routingPolicyRuleConfig = {
              To = "fd00:80:1::/64";
              Priority = 9;
            };
          }
          # wg-home
          {
            routingPolicyRuleConfig = {
              To = "10.80.0.0/24";
              Priority = 9;
            };
          }
          # VPN bypass
          {
            routingPolicyRuleConfig = {
              Family = "both"; # welcome in the year 2023, where ipv4 is the default
              FirewallMark = cfg.vpnBypassFwMark;
              Priority = 9;
            };
          }
          # plastic router
          {
            routingPolicyRuleConfig = {
              To = "192.168.0.0/24";
              Priority = 9;
            };
          }
        ];
        routes = [
          {
            routeConfig = {
              Gateway = "0.0.0.0"; # point-to-point connection
              Table = 51820;
            };
          }
          {
            routeConfig = {
              Gateway = "::";
              Table = 51820;
            };
          }
        ];
      };
    };
  };
  services.resolved.enable = false;
}