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Integrate OpenVPN on Linux

Using emnify, you can create a virtual private network (VPN) for your mobile IoT/M2M devices fitted with emnify SIMs. Data traffic is exchanged between the devices and the application server through an OpenVPN tunnel, enabling direct communication with the IPs of the mobile devices—no network address translation (NAT) applied.

The tunnel is established between the emnify Core Network and the customer's VPN gateway or server.

tip

The Cellular IoT University: Secure your devices with OpenVPN video provides a step-by-step walk-through.

Required preparation in the emnify Portal​

Any traffic exchanged with mobile devices is encrypted before being transmitted over the public internet, which adds an additional layer of security and privacy. No VPN software needs to be installed on the device, or there aren't any required configuration changes necessary. The default emnify APN also supports VPN flows.

Download the VPN configuration file​

warning

You can't use accounts with time-based one-time password (TOTP) MFA enabled to authenticate the OpenVPN tunnel. Email-based MFA doesn't affect OpenVPN.

For more information, see the MFA FAQ in the emnify Knowledge Base.

  1. Log in to your emnify account.

  2. Navigate to Integrations and find the Secure Connection section.

  3. Under OpenVPN, select Show instructions.

  4. Make sure you're on the Linux tab, then click Download client.conf.

    Select the desired region or choose Download all regions.

Once downloaded, store that file on your server in the folder /etc/openvpn.

Change the internet breakout region​

  1. Navigate to Device Policies in the emnify Portal.
  2. In the Service Policies section, select the policy assigned to the devices you want to secure and expand the policy details.
  3. Under Internet Breakout Region, set the service policy to a VPN breakout region (for example, eu-west-1 (VPN)).

Set up the OpenVPN client on Linux/Ubuntu​

Install the OpenVPN software​

First, install the OpenVPN package:

sudo apt-get install openvpn

Create credentials for authentication​

Once you install the software and download the configuration file, setting up authentication is next. Create a file called credentials.txt in the folder /etc/openvpn. You can use your user credentials to authenticate or use an application token (recommended).

Authentication with user credentials​

The content of the credentials.txt must be two lines. The first line is your username, and the second is your password.

username@domain.com
YourPassword
note

If you don't want to store your credentials, you can also choose to enter them each time the VPN tunnel is established. If you prefer that option, comment out the line auth-user-pass /etc/openvpn/credentials.txt in the client.conf file.

Authentication with an application token​

When you run the OpenVPN client on a VPN gateway or application server, using a dedicated application token is recommended. In this case, the first line in the credentials.txt file needs to contain your emnify organization identifier. Instead of the password on the second line, store the application token.

You can create application tokens in the emnify Portal. For instructions, see Application tokens.

Once created, copy the token into the credentials file. The content of the credentials file would then look like this:

orgId
ApplicationToken

When you log in to the emnify Portal, it shows this data under the VPN settings.

Protect the credentials file​

You should keep the credentials.txt file only readable by root and not by other server users. You can ensure this with the following commands:

sudo chown root:root /etc/openvpn/credentials.txt
sudo chmod 600 /etc/openvpn/credentials.txt

Start and monitor the OpenVPN connection​

Now you can start the VPN client by running:

sudo service openvpn start

The OpenVPN daemon logs into /var/log/syslog. If everything works, it looks like this:

Jul 12 17:53:55 openvpn-client ovpn-client[3027]: Data Channel Encrypt: Cipher 'BF-CBC' initialized with 128 bit key
Jul 12 17:53:55 openvpn-client ovpn-client[3027]: Data Channel Encrypt: Using 160 bit message hash 'SHA1' for HMAC authentication
Jul 12 17:53:55 openvpn-client ovpn-client[3027]: Control Channel: TLSv1, cipher TLSv1/SSLv3 DHE-RSA-AES256-SHA, 2048 bit RSA
Jul 12 17:53:55 openvpn-client ovpn-client[3027]: [openvpn.emnify.net] Peer Connection Initiated with [AF_INET]52.209.x.y:1194
Jul 12 17:53:57 openvpn-client ovpn-client[3027]: SENT CONTROL [openvpn.emnify.net]: 'PUSH_REQUEST' (status=1)
Jul 12 17:53:57 openvpn-client ovpn-client[3027]: PUSH: Received control message: 'PUSH_REPLY,route 10.64.0.1,topology net30,ping 1,ping-restart 5,route 10.x.y.z 255.255.128.0,ifconfig 10.64.0.224 10.64.0.225'
Jul 12 17:53:57 openvpn-client ovpn-client[3027]: TUN/TAP device tun0 opened
Jul 12 17:53:57 openvpn-client ovpn-client[3027]: /sbin/route add -net 10.64.0.1 netmask 255.255.255.255 gw 10.64.0.225
Jul 12 17:53:57 openvpn-client ovpn-client[3027]: /sbin/route add -net 10.x.y.z netmask 255.255.128.0 gw 10.64.0.225

Find the static private IP of your VPN client​

The emnify OpenVPN server allocates a static IP address to the tun interface of your VPN client. This IP also stays the same when your VPN client is reconnecting or if you move the tunnel to a different machine. So you can use it on your mobile devices to address your application. Nevertheless, you should never configure the IP directly on your devices but use a DNS to resolve it.

Once the tunnel is established, you can see that IP address on your tun interface. In this example, the IP address is 10.64.0.224:

ubuntu@openvpn-client:~$ ip a s tun0
14: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 100
    link/none 
    inet 10.64.0.224 peer 10.64.0.225/32 scope global tun0

Test successful data connectivity​

If the VPN tunnel is established successfully, you can connect directly to your mobile devices' private IP addresses.

For testing, you can choose any of your devices that are currently in an active data session.

  1. Log in to your emnify account.
  2. Navigate to Connected Devices and select one of your devices.
  3. Under Details, you can see if it's currently online and the IP address it has assigned.

Now you can ping that private IP address:

root@openvpn-client:~# ping 10.x.y.z
PING 10.x.y.z (10.x.y.z) 56(84) bytes of data.
64 bytes from 10.x.y.z: icmp_req=1 ttl=62 time=72 ms
64 bytes from 10.x.y.z: icmp_req=2 ttl=62 time=80 ms
64 bytes from 10.x.y.z: icmp_req=3 ttl=62 time=75 ms

For this to work, your device must run an IP stack responding to ICMP echo requests. This might differ for embedded devices that implement only partial IP stack functionality.

You can use any network protocol. For example, if your device runs an sshd daemon you can log into it via SSH.

Enable access for servers behind the VPN client​

If you have multiple servers behind your VPN gateway that need to communicate with your mobile device, you can apply masquerading using iptables to hide them behind the single IP address of your VPN client.

First, you need to enable IP forwarding on your VPN gateway (if it isn't already active):

  1. Open your /etc/sysctl.conf
  2. Set net.ipv4.ip_forward=1
  3. Load the configuration with sudo sysctl -p /etc/sysctl.conf

After, you need to enable masquerading for the tun interface by running:

sudo iptables -t nat -A POSTROUTING -o tun0 -j MASQUERADE

You can also forward connections coming to specific ports to an application server behind your VPN gateway by using DNAT. For example, to forward to an internal HTTP server at IP 192.168.100.21 use:

sudo iptables -t nat -A PREROUTING -i tun0 -p tcp --dport 80 -j DNAT --to-destination 192.168.100.21

To make these settings persistent, you can use the iptables-persistent package.

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