Internet Connection Sharing

The following example will describe how to share an active internet connection over a WiFi hotspot or alternatively via ethernet.

Share via WiFi

Usage

Share an existing internet connection of a wired interface eth0 using a wifi hotspot on wlan0 with the access point name MyAccessPoint.

nix shell nixpkgs#linux-wifi-hotspot
sudo create_ap wlan0 eth0 MyAccessPoint

Here eth0 is the ethernet interface connected to the internet, and wlan0 is the wifi interface to share the internet connection with a wifi hotspot. However, these names may not be the same on your system. To check the name of your hardware interface use the command ifconfig or ifconfig | grep ^[^:]*: It will list network adapters on your system. Then modify command accordingly sudo create_ap <wifiInterfaceName> <ethernetInterfaceName> MyAccessPoint <Password>

Configuration

Persistently share an existing internet connection of a wired interface eth0 using a wifi hotspot on wlan0 with the access point name My Wifi Hotspot. The network is protected with a simple WPA2 pre-shared key 12345678.

services.create_ap = {
  enable = true;
  settings = {
    INTERNET_IFACE = "eth0";
    WIFI_IFACE = "wlan0";
    SSID = "My Wifi Hotspot";
    PASSPHRASE = "12345678";
  };
};

Share via ethernet

Usage

Share an existing internet connection of a wireless interface wlan0 to clients connected on a ethernet device eth0. Make sure you've got TCP and UDP port 53 for the dnsmasq DHCP server opened in your Firewall.

# Setup ethernet device
ip link set up eth0
ip addr add 10.0.0.1/24 dev eth0

# Enable packet forwarding
sysctl net.ipv4.ip_forward=1

# Enable NAT for leaving packets
nft add table ip nat
nft add chain ip nat POSTROUTING { type nat hook postrouting priority 100 \; }
nft add rule nat POSTROUTING oifname wlan0 masquerade

# Start dnsmasq for DHCP
dnsmasq -d -i eth0 --dhcp-range=10.0.0.2,10.0.0.255,255.255.255.0,24h

To cleanup the configured interface run following commands

ip addr del 10.0.0.1/24 dev eth0
ip link set down eth0
# Get handle_number with: nft -a list table nat
nft delete rule nat POSTROUTING handle <handle_number>

Configuration

Persistently share an existing internet connection on interface `wlan0` to clients connected on an ethernet interface `eth0`. Tested where `wlan0` is a wireless interface, but it should work with a different ethernet interface as well. You do not need to manually open port 53.

# Set a static IP on the "downstream" interface
networking.interfaces."eth0" = {
  useDHCP = false;
  ipv4.addresses = [{
    address = "10.0.0.1";
    prefixLength = 24;
  }];
};
networking.firewall.extraCommands = ''
  # Set up SNAT on packets going from downstream to the wider internet
  iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE

  # Accept all connections from downstream. May not be necessary
  iptables -A INPUT -i enp2s0 -j ACCEPT
'';
# Run a DHCP server on the downstream interface
services.kea.dhcp4 = {
  enable = true;
  settings = {
    interfaces-config = {
      interfaces = [
        "eth0"
      ];
    };
    lease-database = {
      name = "/var/lib/kea/dhcp4.leases";
      persist = true;
      type = "memfile";
    };
    rebind-timer = 2000;
    renew-timer = 1000;
    subnet4 = [
      {
        id = 1;
        pools = [
          {
            pool = "10.0.0.2 - 10.0.0.255";
          }
        ];
        subnet = "10.0.0.1/24";
      }
    ];
    valid-lifetime = 4000;
    option-data = [{
      name = "routers";
      data = "10.0.0.1";
    }];
  };
};