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raspberry_pi_router.md

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Assumption

You have Raspian installed on your Pi and that its primary LAN (eth0) is configured to use DHCP. It will likely get its address information from your Internet modem/routers. I assume you can connect to it over eth0.

Install dnsmasq

From the command line, run sudo apt install dnsmasq to install dnsmasq. Stop it, for now, with sudo systemctl stop dnsmasq

Static IP for eth1

Now set a static IP address for the second ethernet connection (eth1). Edit /etc/dhcpcd.conf with sudo nano /etc/dhcpcd.conf. Go to the end of the file and edit it so that it looks like the following:

interface eth1
    static ip_address=192.168.7.1/24

Configure dnsmasq

Discard the old conf file and create a new configuration:

sudo mv /etc/dnsmasq.conf /etc/dnsmasq.conf.orig
sudo nano /etc/dnsmasq.conf

Add these lines:

interface=eth1
dhcp-range=192.168.7.100,192.168.7.120,255.255.255.0,24h

This will define a new DHCP range 192.168.7.x which will be administered by the Pi via eth1.

Now start dnsmasq with sudo systemctl start dnsmasq

Note

To see clients connected to eth1 use cat /var/lib/misc/dnsmasq.leases

The output will be something like

574256399 00:10:a7:0c:a2:c1 192.168.7.109 rpi3a 01:00:10:a7:0c:a2:c1

IP forwarding

Edit /etc/sysctl.conf with sudo nano /etc/sysctl.conf and this add line (for persistence)

net.ipv4.ip_forward=1

Activate forwarding now with sudo sysctl -w net.ipv4.ip_forward=1

Add a masquerade for outbound traffic on eth0

sudo iptables -t nat -A  POSTROUTING -o eth0 -j MASQUERADE

Save the iptables rule.

sudo sh -c "iptables-save > /etc/iptables.ipv4.nat"

Edit /etc/rc.local with sudo nano /etc/rc.local and add this just above "exit 0" to install these rules on boot.

iptables-restore < /etc/iptables.ipv4.nat

Now the router is working. Connect a wired device to the eth1 network. From that device you will have access to the network attached to eth0 and eth1 and if eth0's network has Internet, you will get Internet access as well.

Now add a third network over Wi-Fi!

Static IP for wlan0

Now set a static IP address for the Wi-Fi (wlan0). Edit /etc/dhcpcd.conf with sudo nano /etc/dhcpcd.conf. Go to the end of the file and add these lines:

interface wlan0
    static ip_address=192.168.17.1/24
    nohook wpa_supplicant

This will give it a static address of 192.168.17.1

Now restart the DHCP server with sudo service dhcpcd restart

Install hostapd

sudo apt install hostapd
sudo systemctl stop hostapd

Edit the dnsmasq.conf file with sudo nano /etc/dnsmasq.conf and add

interface=wlan0
dhcp-range=192.168.17.100,192.168.17.120,255.255.255.0,24h

Reload the configuration file with sudo systemctl reload dnsmasq

Configure hostapd

To use the 5 GHz band, you can change the operations mode from hw_mode=g to hw_mode=a. Possible values for hw_mode are:

  • a = IEEE 802.11a (5 GHz)
  • b = IEEE 802.11b (2.4 GHz)
  • g = IEEE 802.11g (2.4 GHz)

Edit sudo nano /etc/hostapd/hostapd.conf and add these line:

interface=wlan0
driver=nl80211
ssid=PiNet
hw_mode=g
channel=7
wmm_enabled=0
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=raspberry
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

PiNet will be the network SSID and the password will be raspberry. Change accordingly.

We now need to tell the system where to find this configuration file.

Edit this file sudo nano /etc/default/hostapd and find the line with #DAEMON_CONF, and replace it with this:

DAEMON_CONF="/etc/hostapd/hostapd.conf"

Now enable and start hostapd:

sudo systemctl unmask hostapd
sudo systemctl enable hostapd
sudo systemctl start hostapd

You will now have a PiNet Wi-Fi network which has access to the network on eth0

General note

If things aren't working as expected after you configured routing with eth1 or after you added Wi-Fi support, then a good old fashioned reboot will likely fix the problem. Or in the words of the TV show 'IT Crowd', "Have you tried turning it off and on again?"