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planktoscope/docs/remote_access.md
Romain Bazile 7e40661922 docs: small various updates
2021-01-21 13:23:44 +01:00

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Remote access via a standalone network

Setting up a Raspberry Pi as an access point in a standalone network (NAT)

This tutorial is adapted from a tutorial that you can find here.

In order to work as an access point, the Raspberry Pi will need to have access point software installed, along with DHCP server software to provide connecting devices with a network address.

To create an access point, we'll need DNSMasq and HostAPD. Install all the required software in one go with this command::

sudo apt install dnsmasq hostapd

Since the configuration files are not ready yet, turn the new software off as follows::

sudo systemctl unmask hostapd
sudo systemctl disable dnsmasq
sudo systemctl disable hostapd

Configuring HostAPD

Using a text editor edit the hostapd configuration file. This file won't exist at this stage so will be blank: sudo nano /etc/hostapd/hostapd.conf

#2.4GHz setup wifi 80211 b,g,n
interface=wlan0
driver=nl80211
ssid=RPiHotspotN
hw_mode=g
channel=8
wmm_enabled=0
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=1234567890
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP TKIP
rsn_pairwise=CCMP

#80211n - Change GB to your WiFi country code
country_code=GB
ieee80211n=1
ieee80211d=1

The interface will be wlan0 The driver nl80211 works with the Raspberry RPi 4, RPi 3B+, RPi 3 & Pi Zero W onboard WiFi but you will need to check that your wifi dongle is compatable and can use Access Point mode.

For more information on wifi dongles see elinux.org/RPi_USB_Wi-Fi_Adapters

The SSID is the name of the WiFi signal broadcast from the RPi, which you will connect to with your Tablet or phones WiFi settings. Channel can be set between 1 and 13. If you are having trouble connection because of to many wifi signals in your area are using channel 8 then try another channel. Wpa_passphrase is the password you will need to enter when you first connect a device to your Raspberry Pi's hotspot. This should be at least 8 characters and a bit more difficult to guess than my example. The country_code should be set to your country to comply with local RF laws. You may experience connection issues if this is not correct. Your country_code can be found in /etc/wpa_supplicant/wpa_supplicant.conf or in Raspberry Pi Configuration - Localisation settings

To save the config file press ctrl + O and to exit nano press ctrl + X.

Now the defaults file needs to be updated to point to where the config file is stored. In terminal enter the command sudo nano /etc/default/hostapd

Change #DAEMON_CONF="" to DAEMON_CONF="/etc/hostapd/hostapd.conf"

Check the DAEMON_OPTS="" is preceded by a #, so is #DAEMON_OPTS="".

And save.

DNSmasq configuration

Next dnsmasq needs to be configured to allow the Rpi to act as a router and issue ip addresses. Open the dnsmasq.conf file with sudo nano /etc/dnsmasq.conf

Go to the bottom of the file and add the following lines:

#AutoHotspot config
interface=wlan0
bind-dynamic 
server=8.8.8.8
domain-needed
bogus-priv
dhcp-range=192.168.50.150,192.168.50.200,12h

and then save ctrl + O and exit ctrl + X.

Configuring a static IP

We are configuring a standalone network to act as a server, so the Raspberry Pi needs to have a static IP address assigned to the wireless port. This documentation assumes that we are using the standard 192.168.x.x IP addresses for our wireless network, so we will assign the server the IP address 192.168.4.1. It is also assumed that the wireless device being used is wlan0.

To configure the static IP address, edit the dhcpcd configuration file with::

        sudo touch /etc/dhcpcd.conf
        chmod 777 /etc/dhcpcd.conf

Send the desired IP address to the end of the previous generated .conf::

        echo "interface wlan0" >> /etc/dhcpcd.conf
        echo "	static ip_address=192.168.4.1/24" >> /etc/dhcpcd.conf
        echo "	nohook wpa_supplicant" >> /etc/dhcpcd.conf

Now restart the dhcpcd daemon and set up the new wlan0 configuration::

        sudo service dhcpcd restart

Configuring the DHCP server (dnsmasq)

The DHCP service is provided by dnsmasq. By default, the configuration file contains a lot of information that is not needed, and it is easier to start from scratch. Rename this configuration file, and edit a new one::

        sudo mv /etc/dnsmasq.conf /etc/dnsmasq.conf.orig
        sudo touch /etc/dnsmasq.conf
        sudo chmod 777 /etc/dnsmasq.conf

Type or copy the following information into the dnsmasq configuration file and save it::

        sudo echo "interface=wlan0" >> /etc/dnsmasq.conf
        sudo echo "	dhcp-range=192.168.4.2,192.168.4.20,255.255.255.0,24h" >> /etc/dnsmasq.conf

So for wlan0, we are going to provide IP addresses between 192.168.4.2 and 192.168.4.20, with a lease time of 24 hours. If you are providing DHCP services for other network devices (e.g. eth0), you could add more sections with the appropriate interface header, with the range of addresses you intend to provide to that interface.

There are many more options for dnsmasq; see the dnsmasq documentation for more details.

Reload dnsmasq to use the updated configuration::

        sudo systemctl reload dnsmasq

Configuring the access point host software (hostapd)

You need to edit the hostapd configuration file, located at /etc/hostapd/hostapd.conf, to add the various parameters for your wireless network. After initial install, this will be a new/empty file. ::

        sudo touch /etc/hostapd/hostapd.conf
        sudo chmod 777 /etc/hostapd/hostapd.conf

Add the information below to the configuration file. This configuration assumes we are using channel 7, with a network name of NameOfNetwork, and a password AardvarkBadgerHedgehog. Note that the name and password should not have quotes around them. The passphrase should be between 8 and 64 characters in length.

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)
  • ad = IEEE 802.11ad (60 GHz) (Not available on the Raspberry Pi)

!!! warning Make sure you define the wished name (ssid) of the future generated Wifi and its password (wpa_passphrase).

Set up your hoastapd.conf as follow ::

        sudo echo "interface=wlan0" >> /etc/hostapd/hostapd.conf
        sudo echo "driver=nl80211" >> /etc/hostapd/hostapd.conf
        sudo echo "ssid=NameOfNetwork" >> /etc/hostapd/hostapd.conf
        sudo echo "hw_mode=g" >> /etc/hostapd/hostapd.conf
        sudo echo "channel=7" >> /etc/hostapd/hostapd.conf
        sudo echo "wmm_enabled=0" >> /etc/hostapd/hostapd.conf
        sudo echo "macaddr_acl=0" >> /etc/hostapd/hostapd.conf
        sudo echo "auth_algs=1" >> /etc/hostapd/hostapd.conf
        sudo echo "ignore_broadcast_ssid=0" >> /etc/hostapd/hostapd.conf
        sudo echo "wpa=2" >> /etc/hostapd/hostapd.conf
        sudo echo "wpa_passphrase=YourPassword" >> /etc/hostapd/hostapd.conf
        sudo echo "wpa_key_mgmt=WPA-PSK" >> /etc/hostapd/hostapd.conf
        sudo echo "wpa_pairwise=TKIP" >> /etc/hostapd/hostapd.conf
        sudo echo "rsn_pairwise=CCMP" >> /etc/hostapd/hostapd.conf

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

        sudo chmod 777 /etc/default/hostapd

Find the line with #DAEMON_CONF, and replace it with this

        sudo echo 'DAEMON_CONF="/etc/hostapd/hostapd.conf"' >> /etc/default/hostapd

Start it up

Now enable and start hostapd

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

Do a quick check of their status to ensure they are active and running

        sudo systemctl status hostapd
        sudo systemctl status dnsmasq

Add routing and masquerade

Edit /etc/sysctl.conf and uncomment a line

        VAR=$(sudo grep -n -m 1 net.ipv4.ip_forward=1 /etc/sysctl.conf | sudo sed  's/\([0-9]*\).*/\1/')
        sudo sed -i "${VAR}s/# *//" /etc/sysctl.conf

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 and add this just above "exit 0" to install these rules on boot

        sudo chmod 777 /etc/rc.local
        sudo sed -i  '/exit 0/d' /etc/rc.local
        sudo echo "iptables-restore < /etc/iptables.ipv4.nat" >> /etc/rc.local
        sudo echo "exit 0" >> /etc/rc.local

Reboot and ensure it still functions.

Using a wireless device, search for networks. The network SSID you specified in the hostapd configuration should now be present, and it should be accessible with the specified password.

If SSH is enabled on the Raspberry Pi access point, it should be possible to connect to it from another Linux box (or a system with SSH connectivity present) as follows, assuming the pi account is present

        ssh pi@192.168.4.1

Most likely your password will be raspberry.

By this point, the Raspberry Pi is acting as an access point, and other devices can associate with it. Associated devices can access the Raspberry Pi access point via its IP address for operations such as rsync, scp, or ssh.