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Linux: OpenVPN – Exhaustive write-up

How To Set Up an OpenVPN Server on Ubuntu 16.04
PostedMay 4, 2016 592.8k views VPN Ubuntu Ubuntu 16.04
Introduction

Want to access the Internet safely and securely from your smartphone or laptop when connected to an untrusted network such as the WiFi of a hotel or coffee shop? A Virtual Private Network (VPN) allows you to traverse untrusted networks privately and securely as if you were on a private network. The traffic emerges from the VPN server and continues its journey to the destination.

When combined with HTTPS connections, this setup allows you to secure your wireless logins and transactions. You can circumvent geographical restrictions and censorship, and shield your location and any unencrypted HTTP traffic from the untrusted network.

OpenVPN is a full-featured open source Secure Socket Layer (SSL) VPN solution that accommodates a wide range of configurations. In this tutorial, we’ll set up an OpenVPN server on a Droplet and then configure access to it from Windows, OS X, iOS and Android. This tutorial will keep the installation and configuration steps as simple as possible for these setups.
Prerequisites

To complete this tutorial, you will need access to an Ubuntu 16.04 server.

You will need to configure a non-root user with sudo privileges before you start this guide. You can follow our Ubuntu 16.04 initial server setup guide to set up a user with appropriate permissions. The linked tutorial will also set up a firewall, which we will assume is in place during this guide.

When you are ready to begin, log into your Ubuntu server as your sudo user and continue below.
Step 1: Install OpenVPN

To start off, we will install OpenVPN onto our server. OpenVPN is available in Ubuntu’s default repositories, so we can use apt for the installation. We will also be installing the easy-rsa package, which will help us set up an internal CA (certificate authority) for use with our VPN.

To update your server’s package index and install the necessary packages type:

sudo apt-get update
sudo apt-get install openvpn easy-rsa

The needed software is now on the server, ready to be configured.
Step 2: Set Up the CA Directory

OpenVPN is an TLS/SSL VPN. This means that it utilizes certificates in order to encrypt traffic between the server and clients. In order to issue trusted certificates, we will need to set up our own simple certificate authority (CA).

To begin, we can copy the easy-rsa template directory into our home directory with the make-cadir command:

make-cadir ~/openvpn-ca

Move into the newly created directory to begin configuring the CA:

cd ~/openvpn-ca

Step 3: Configure the CA Variables

To configure the values our CA will use, we need to edit the vars file within the directory. Open that file now in your text editor:

nano vars

Inside, you will find some variables that can be adjusted to determine how your certificates will be created. We only need to worry about a few of these.

Towards the bottom of the file, find the settings that set field defaults for new certificates. It should look something like this:
~/openvpn-ca/vars

. . .

export KEY_COUNTRY=”US”
export KEY_PROVINCE=”CA”
export KEY_CITY=”SanFrancisco”
export KEY_ORG=”Fort-Funston”
export KEY_EMAIL=”[email protected]”
export KEY_OU=”MyOrganizationalUnit”

. . .

Edit the values in red to whatever you’d prefer, but do not leave them blank:
~/openvpn-ca/vars

. . .

export KEY_COUNTRY=”US”
export KEY_PROVINCE=”NY”
export KEY_CITY=”New York City”
export KEY_ORG=”DigitalOcean”
export KEY_EMAIL=”[email protected]”
export KEY_OU=”Community”

. . .

While we are here, we will also edit the KEY_NAME value just below this section, which populates the subject field. To keep this simple, we’ll call it server in this guide:
~/openvpn-ca/vars

export KEY_NAME=”server”

When you are finished, save and close the file.
Step 4: Build the Certificate Authority

Now, we can use the variables we set and the easy-rsa utilities to build our certificate authority.

Ensure you are in your CA directory, and then source the vars file you just edited:

cd ~/openvpn-ca
source vars

You should see the following if it was sourced correctly:

Output
NOTE: If you run ./clean-all, I will be doing a rm -rf on /home/sammy/openvpn-ca/keys

Make sure we’re operating in a clean environment by typing:

./clean-all

Now, we can build our root CA by typing:

./build-ca

This will initiate the process of creating the root certificate authority key and certificate. Since we filled out the vars file, all of the values should be populated automatically. Just press ENTER through the prompts to confirm the selections:

Output
Generating a 2048 bit RSA private key
………………………………………………………………………………+++
………………………….+++
writing new private key to ‘ca.key’
—–
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter ‘.’, the field will be left blank.
—–
Country Name (2 letter code) [US]:
State or Province Name (full name) [NY]:
Locality Name (eg, city) [New York City]:
Organization Name (eg, company) [DigitalOcean]:
Organizational Unit Name (eg, section) [Community]:
Common Name (eg, your name or your server’s hostname) [DigitalOcean CA]:
Name [server]:
Email Address [[email protected]]:

We now have a CA that can be used to create the rest of the files we need.
Step 5: Create the Server Certificate, Key, and Encryption Files

Next, we will generate our server certificate and key pair, as well as some additional files used during the encryption process.

Start by generating the OpenVPN server certificate and key pair. We can do this by typing:

Note: If you choose a name other than server here, you will have to adjust some of the instructions below. For instance, when copying the generated files to the /etc/openvpn directroy, you will have to substitute the correct names. You will also have to modify the /etc/openvpn/server.conf file later to point to the correct .crt and .key files.

./build-key-server server

Once again, the prompts will have default values based on the argument we just passed in (server) and the contents of our vars file we sourced.

Feel free to accept the default values by pressing ENTER. Do not enter a challenge password for this setup. Towards the end, you will have to enter y to two questions to sign and commit the certificate:

Output
. . .

Certificate is to be certified until May 1 17:51:16 2026 GMT (3650 days)
Sign the certificate? [y/n]:y

1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated

Next, we’ll generate a few other items. We can generate a strong Diffie-Hellman keys to use during key exchange by typing:

./build-dh

This might take a few minutes to complete.

Afterwards, we can generate an HMAC signature to strengthen the server’s TLS integrity verification capabilities:

openvpn –genkey –secret keys/ta.key

Step 6: Generate a Client Certificate and Key Pair

Next, we can generate a client certificate and key pair. Although this can be done on the client machine and then signed by the server/CA for security purposes, for this guide we will generate the signed key on the server for the sake of simplicity.

We will generate a single client key/certificate for this guide, but if you have more than one client, you can repeat this process as many times as you’d like. Pass in a unique value to the script for each client.

Because you may come back to this step at a later time, we’ll re-source the vars file. We will use client1 as the value for our first certificate/key pair for this guide.

To produce credentials without a password, to aid in automated connections, use the build-key command like this:

cd ~/openvpn-ca
source vars
./build-key client1

If instead, you wish to create a password-protected set of credentials, use the build-key-pass command:

cd ~/openvpn-ca
source vars
./build-key-pass client1

Again, the defaults should be populated, so you can just hit ENTER to continue. Leave the challenge password blank and make sure to enter y for the prompts that ask whether to sign and commit the certificate.
Step 7: Configure the OpenVPN Service

Next, we can begin configuring the OpenVPN service using the credentials and files we’ve generated.
Copy the Files to the OpenVPN Directory

To begin, we need to copy the files we need to the /etc/openvpn configuration directory.

We can start with all of the files that we just generated. These were placed within the ~/openvpn-ca/keys directory as they were created. We need to move our CA cert and key, our server cert and key, the HMAC signature, and the Diffie-Hellman file:

cd ~/openvpn-ca/keys
sudo cp ca.crt ca.key server.crt server.key ta.key dh2048.pem /etc/openvpn

Next, we need to copy and unzip a sample OpenVPN configuration file into configuration directory so that we can use it as a basis for our setup:

gunzip -c /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz | sudo tee /etc/openvpn/server.conf

Adjust the OpenVPN Configuration

Now that our files are in place, we can modify the server configuration file:

sudo nano /etc/openvpn/server.conf

Basic Configuration

First, find the HMAC section by looking for the tls-auth directive. Remove the “;” to uncomment the tls-auth line. Below this, add the key-direction parameter set to “0”:
/etc/openvpn/server.conf

tls-auth ta.key 0 # This file is secret
key-direction 0

Next, find the section on cryptographic ciphers by looking for the commented out cipher lines. The AES-128-CBC cipher offers a good level of encryption and is well supported. Remove the “;” to uncomment the cipher AES-128-CBC line:
/etc/openvpn/server.conf

cipher AES-128-CBC

Below this, add an auth line to select the HMAC message digest algorithm. For this, SHA256 is a good choice:
/etc/openvpn/server.conf

auth SHA256

Finally, find the user and group settings and remove the “;” at the beginning of to uncomment those lines:
/etc/openvpn/server.conf

user nobody
group nogroup

(Optional) Push DNS Changes to Redirect All Traffic Through the VPN

The settings above will create the VPN connection between the two machines, but will not force any connections to use the tunnel. If you wish to use the VPN to route all of your traffic, you will likely want to push the DNS settings to the client computers.

You can do this, uncomment a few directives that will configure client machines to redirect all web traffic through the VPN. Find the redirect-gateway section and remove the semicolon “;” from the beginning of the redirect-gateway line to uncomment it:
/etc/openvpn/server.conf

push “redirect-gateway def1 bypass-dhcp”

Just below this, find the dhcp-option section. Again, remove the “;” from in front of both of the lines to uncomment them:
/etc/openvpn/server.conf

push “dhcp-option DNS 208.67.222.222”
push “dhcp-option DNS 208.67.220.220”

This should assist clients in reconfiguring their DNS settings to use the VPN tunnel for as the default gateway.
(Optional) Adjust the Port and Protocol

By default, the OpenVPN server uses port 1194 and the UDP protocol to accept client connections. If you need to use a different port because of restrictive network environments that your clients might be in, you can change the port option. If you are not hosting web content your OpenVPN server, port 443 is a popular choice since this is usually allowed through firewall rules.
/etc/openvpn/server.conf

# Optional!
port 443

Often if the protocol will be restricted to that port as well. If so, change proto from UDP to TCP:
/etc/openvpn/server.conf

# Optional!
proto tcp

If you have no need to use a different port, it is best to leave these two settings as their default.
(Optional) Point to Non-Default Credentials

If you selected a different name during the ./build-key-server command earlier, modify the cert and key lines that you see to point to the appropriate .crt and .key files. If you used the default server, this should already be set correctly:
/etc/openvpn/server.conf

cert server.crt
key server.key

When you are finished, save and close the file.
Step 8: Adjust the Server Networking Configuration

Next, we need to adjust some aspects of the server’s networking so that OpenVPN can correctly route traffic.
Allow IP Forwarding

First, we need to allow the server to forward traffic. This is fairly essential to the functionality we want our VPN server to provide.

We can adjust this setting by modifying the /etc/sysctl.conf file:

sudo nano /etc/sysctl.conf

Inside, look for the line that sets net.ipv4.ip_forward. Remove the “#” character from the beginning of the line to uncomment that setting:
/etc/sysctl.conf

net.ipv4.ip_forward=1

Save and close the file when you are finished.

To read the file and adjust the values for the current session, type:

sudo sysctl -p

Adjust the UFW Rules to Masquerade Client Connections

If you followed the Ubuntu 16.04 initial server setup guide in the prerequisites, you should have the UFW firewall in place. Regardless of whether you use the firewall to block unwanted traffic (which you almost always should do), we need the firewall in this guide to manipulate some of the traffic coming into the server. We need to modify the rules file to set up masquerading, an iptables concept that provides on-the-fly dynamic NAT to correctly route client connections.

Before we open the firewall configuration file to add masquerading, we need to find the public network interface of our machine. To do this, type:

ip route | grep default

Your public interface should follow the word “dev”. For example, this result shows the interface named wlp11s0, which is highlighted below:

Output
default via 203.0.113.1 dev wlp11s0 proto static metric 600

When you have the interface associated with your default route, open the /etc/ufw/before.rules file to add the relevant configuration:

sudo nano /etc/ufw/before.rules

This file handles configuration that should be put into place before the conventional UFW rules are loaded. Towards the top of the file, add the highlighted lines below. This will set the default policy for the POSTROUTING chain in the nat table and masquerade any traffic coming from the VPN:

Note: Remember to replace wlp11s0 in the -A POSTROUTING line below with the interface you found in the above command.
/etc/ufw/before.rules

#
# rules.before
#
# Rules that should be run before the ufw command line added rules. Custom
# rules should be added to one of these chains:
# ufw-before-input
# ufw-before-output
# ufw-before-forward
#

# START OPENVPN RULES
# NAT table rules
*nat
:POSTROUTING ACCEPT [0:0]
# Allow traffic from OpenVPN client to wlp11s0 (change to the interface you discovered!)
-A POSTROUTING -s 10.8.0.0/8 -o wlp11s0 -j MASQUERADE
COMMIT
# END OPENVPN RULES

# Don’t delete these required lines, otherwise there will be errors
*filter
. . .

Save and close the file when you are finished.

We need to tell UFW to allow forwarded packets by default as well. To do this, we will open the /etc/default/ufw file:

sudo nano /etc/default/ufw

Inside, find the DEFAULT_FORWARD_POLICY directive. We will change the value from DROP to ACCEPT:
/etc/default/ufw

DEFAULT_FORWARD_POLICY=”ACCEPT”

Save and close the file when you are finished.
Open the OpenVPN Port and Enable the Changes

Next, we’ll adjust the firewall itself to allow traffic to OpenVPN.

If you did not change the port and protocol in the /etc/openvpn/server.conf file, you will need to open up UDP traffic to port 1194. If you modified the port and/or protocol, substitute the values you selected here.

We’ll also add the SSH port in case you forgot to add it when following the prerequisite tutorial:

sudo ufw allow 1194/udp
sudo ufw allow OpenSSH

Now, we can disable and re-enable UFW to load the changes from all of the files we’ve modified:

sudo ufw disable
sudo ufw enable

Our server is now configured to correctly handle OpenVPN traffic.
Step 9: Start and Enable the OpenVPN Service

We’re finally ready to start the OpenVPN service on our server. We can do this using systemd.

We need to start the OpenVPN server by specifying our configuration file name as an instance variable after the systemd unit file name. Our configuration file for our server is called /etc/openvpn/server.conf, so we will add @server to end of our unit file when calling it:

sudo systemctl start openvpn@server

Double-check that the service has started successfully by typing:

sudo systemctl status openvpn@server

If everything went well, your output should look something that looks like this:

Output
● [email protected] – OpenVPN connection to server
Loaded: loaded (/lib/systemd/system/[email protected]; disabled; vendor preset: enabled)
Active: active (running) since Tue 2016-05-03 15:30:05 EDT; 47s ago
Docs: man:openvpn(8)
https://community.openvpn.net/openvpn/wiki/Openvpn23ManPage
https://community.openvpn.net/openvpn/wiki/HOWTO
Process: 5852 ExecStart=/usr/sbin/openvpn –daemon ovpn-%i –status /run/openvpn/%i.status 10 –cd /etc/openvpn –script-security 2 –config /etc/openvpn/%i.conf –writepid /run/openvpn/%i.pid (code=exited, sta
Main PID: 5856 (openvpn)
Tasks: 1 (limit: 512)
CGroup: /system.slice/system-openvpn.slice/[email protected]
└─5856 /usr/sbin/openvpn –daemon ovpn-server –status /run/openvpn/server.status 10 –cd /etc/openvpn –script-security 2 –config /etc/openvpn/server.conf –writepid /run/openvpn/server.pid

May 03 15:30:05 openvpn2 ovpn-server[5856]: /sbin/ip addr add dev tun0 local 10.8.0.1 peer 10.8.0.2
May 03 15:30:05 openvpn2 ovpn-server[5856]: /sbin/ip route add 10.8.0.0/24 via 10.8.0.2
May 03 15:30:05 openvpn2 ovpn-server[5856]: GID set to nogroup
May 03 15:30:05 openvpn2 ovpn-server[5856]: UID set to nobody
May 03 15:30:05 openvpn2 ovpn-server[5856]: UDPv4 link local (bound): [undef]
May 03 15:30:05 openvpn2 ovpn-server[5856]: UDPv4 link remote: [undef]
May 03 15:30:05 openvpn2 ovpn-server[5856]: MULTI: multi_init called, r=256 v=256
May 03 15:30:05 openvpn2 ovpn-server[5856]: IFCONFIG POOL: base=10.8.0.4 size=62, ipv6=0
May 03 15:30:05 openvpn2 ovpn-server[5856]: IFCONFIG POOL LIST
May 03 15:30:05 openvpn2 ovpn-server[5856]: Initialization Sequence Completed

You can also check that the OpenVPN tun0 interface is available by typing:

ip addr show tun0

You should see a configured interface:

Output
4: tun0: mtu 1500 qdisc noqueue state UNKNOWN group default qlen 100
link/none
inet 10.8.0.1 peer 10.8.0.2/32 scope global tun0
valid_lft forever preferred_lft forever

If everything went well, enable the service so that it starts automatically at boot:

sudo systemctl enable openvpn@server

Step 10: Create Client Configuration Infrastructure

Next, we need to set up a system that will allow us to create client configuration files easily.
Creating the Client Config Directory Structure

Create a directory structure within your home directory to store the files:

mkdir -p ~/client-configs/files

Since our client configuration files will have the client keys embedded, we should lock down permissions on our inner directory:

chmod 700 ~/client-configs/files

Creating a Base Configuration

Next, let’s copy an example client configuration into our directory to use as our base configuration:

cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf ~/client-configs/base.conf

Open this new file in your text editor:

nano ~/client-configs/base.conf

Inside, we need to make a few adjustments.

First, locate the remote directive. This points the client to our OpenVPN server address. This should be the public IP address of your OpenVPN server. If you changed the port that the OpenVPN server is listening on, change 1194 to the port you selected:
~/client-configs/base.conf

. . .
# The hostname/IP and port of the server.
# You can have multiple remote entries
# to load balance between the servers.
remote server_IP_address 1194
. . .

Be sure that the protocol matches the value you are using in the server configuration:
~/client-configs/base.conf

proto udp

Next, uncomment the user and group directives by removing the “;”:
~/client-configs/base.conf

# Downgrade privileges after initialization (non-Windows only)
user nobody
group nogroup

Find the directives that set the ca, cert, and key. Comment out these directives since we will be adding the certs and keys within the file itself:
~/client-configs/base.conf

# SSL/TLS parms.
# See the server config file for more
# description. It’s best to use
# a separate .crt/.key file pair
# for each client. A single ca
# file can be used for all clients.
#ca ca.crt
#cert client.crt
#key client.key

Mirror the cipher and auth settings that we set in the /etc/openvpn/server.conf file:
~/client-configs/base.conf

cipher AES-128-CBC
auth SHA256

Next, add the key-direction directive somewhere in the file. This must be set to “1” to work with the server:
~/client-configs/base.conf

key-direction 1

Finally, add a few commented out lines. We want to include these with every config, but should only enable them for Linux clients that ship with a /etc/openvpn/update-resolv-conf file. This script uses the resolvconf utility to update DNS information for Linux clients.
~/client-configs/base.conf

# script-security 2
# up /etc/openvpn/update-resolv-conf
# down /etc/openvpn/update-resolv-conf

If your client is running Linux and has an /etc/openvpn/update-resolv-conf file, you should uncomment these lines from the generated OpenVPN client configuration file.

Save the file when you are finished.
Creating a Configuration Generation Script

Next, we will create a simple script to compile our base configuration with the relevant certificate, key, and encryption files. This will place the generated configuration in the ~/client-configs/files directory.

Create and open a file called make_config.sh within the ~/client-configs directory:

nano ~/client-configs/make_config.sh

Inside, paste the following script:
~/client-configs/make_config.sh

#!/bin/bash

# First argument: Client identifier

KEY_DIR=~/openvpn-ca/keys
OUTPUT_DIR=~/client-configs/files
BASE_CONFIG=~/client-configs/base.conf

cat ${BASE_CONFIG} \
<(echo -e '‘) \
${KEY_DIR}/ca.crt \
<(echo -e '\n‘) \
${KEY_DIR}/${1}.crt \
<(echo -e '\n‘) \
${KEY_DIR}/${1}.key \
<(echo -e '\n‘) \
${KEY_DIR}/ta.key \
<(echo -e '‘) \
> ${OUTPUT_DIR}/${1}.ovpn

Save and close the file when you are finished.

Mark the file as executable by typing:

chmod 700 ~/client-configs/make_config.sh

Step 11: Generate Client Configurations

Now, we can easily generate client configuration files.

If you followed along with the guide, you created a client certificate and key called client1.crt and client1.key respectively by running the ./build-key client1 command in step 6. We can generate a config for these credentials by moving into our ~/client-configs directory and using the script we made:

cd ~/client-configs
./make_config.sh client1

If everything went well, we should have a client1.ovpn file in our ~/client-configs/files directory:

ls ~/client-configs/files

Output
client1.ovpn

Transferring Configuration to Client Devices

We need to transfer the client configuration file to the relevant device. For instance, this could be your local computer or a mobile device.

While the exact applications used to accomplish this transfer will depend on your choice and device’s operating system, you want the application to use SFTP (SSH file transfer protocol) or SCP (Secure Copy) on the backend. This will transport your client’s VPN authentication files over an encrypted connection.

Here is an example SFTP command using our client1.ovpn example. This command can be run from your local computer (OS X or Linux). It places the .ovpn file in your home directory:

sftp sammy@openvpn_server_ip:client-configs/files/client1.ovpn ~/

Here are several tools and tutorials for securely transferring files from the server to a local computer:

WinSCP
How To Use SFTP to Securely Transfer Files with a Remote Server
How To Use Filezilla to Transfer and Manage Files Securely on your VPS

Step 12: Install the Client Configuration

Now, we’ll discuss how to install a client VPN profile on Windows, OS X, iOS, and Android. None of these client instructions are dependent on one another, so feel free to skip to whichever is applicable to you.

The OpenVPN connection will be called whatever you named the .ovpn file. In our example, this means that the connection will be called client1.ovpn for the first client file we generated.
Windows

Installing

The OpenVPN client application for Windows can be found on OpenVPN’s Downloads page. Choose the appropriate installer version for your version of Windows.

Note
OpenVPN needs administrative privileges to install.

After installing OpenVPN, copy the .ovpn file to:

C:\Program Files\OpenVPN\config

When you launch OpenVPN, it will automatically see the profile and makes it available.

OpenVPN must be run as an administrator each time it’s used, even by administrative accounts. To do this without having to right-click and select Run as administrator every time you use the VPN, you can preset this, but this must be done from an administrative account. This also means that standard users will need to enter the administrator’s password to use OpenVPN. On the other hand, standard users can’t properly connect to the server unless the OpenVPN application on the client has admin rights, so the elevated privileges are necessary.

To set the OpenVPN application to always run as an administrator, right-click on its shortcut icon and go to Properties. At the bottom of the Compatibility tab, click the button to Change settings for all users. In the new window, check Run this program as an administrator.

Connecting

Each time you launch the OpenVPN GUI, Windows will ask if you want to allow the program to make changes to your computer. Click Yes. Launching the OpenVPN client application only puts the applet in the system tray so that the VPN can be connected and disconnected as needed; it does not actually make the VPN connection.

Once OpenVPN is started, initiate a connection by going into the system tray applet and right-clicking on the OpenVPN applet icon. This opens the context menu. Select client1 at the top of the menu (that’s our client1.ovpn profile) and choose Connect.

A status window will open showing the log output while the connection is established, and a message will show once the client is connected.

Disconnect from the VPN the same way: Go into the system tray applet, right-click the OpenVPN applet icon, select the client profile and click Disconnect.
OS X

Installing

Tunnelblick is a free, open source OpenVPN client for Mac OS X. You can download the latest disk image from the Tunnelblick Downloads page. Double-click the downloaded .dmg file and follow the prompts to install.

Towards the end of the installation process, Tunnelblick will ask if you have any configuration files. It can be easier to answer No and let Tunnelblick finish. Open a Finder window and double-click client1.ovpn. Tunnelblick will install the client profile. Administrative privileges are required.

Connecting

Launch Tunnelblick by double-clicking Tunnelblick in the Applications folder. Once Tunnelblick has been launched, there will be a Tunnelblick icon in the menu bar at the top right of the screen for controlling connections. Click on the icon, and then the Connect menu item to initiate the VPN connection. Select the client1 connection.
Linux
Installing

If you are using Linux, there are a variety of tools that you can use depending on your distribution. Your desktop environment or window manager might also include connection utilities.

The most universal way of connecting, however, is to just use the OpenVPN software.

On Ubuntu or Debian, you can install it just as you did on the server by typing:

sudo apt-get update
sudo apt-get install openvpn

On CentOS you can enable the EPEL repositories and then install it by typing:

sudo yum install epel-release
sudo yum install openvpn

Configuring

Check to see if your distribution includes a /etc/openvpn/update-resolv-conf script:

ls /etc/openvpn

Output
update-resolve-conf

Next, edit the OpenVPN client configuration file you transfered:

nano client1.ovpn

Uncomment the three lines we placed in to adjust the DNS settings if you were able to find an update-resolv-conf file:
client1.ovpn

script-security 2
up /etc/openvpn/update-resolv-conf
down /etc/openvpn/update-resolv-conf

If you are using CentOS, change the group from nogroup to nobody to match the distribution’s available groups:
client1.ovpn

group nobody

Save and close the file.

Now, you can connect to the VPN by just pointing the openvpn command to the client configuration file:

sudo openvpn –config client1.ovpn

This should connect you to your server.
iOS

Installing

From the iTunes App Store, search for and install OpenVPN Connect, the official iOS OpenVPN client application. To transfer your iOS client configuration onto the device, connect it directly to a computer.

Completing the transfer with iTunes will be outlined here. Open iTunes on the computer and click on iPhone > apps. Scroll down to the bottom to the File Sharing section and click the OpenVPN app. The blank window to the right, OpenVPN Documents, is for sharing files. Drag the .ovpn file to the OpenVPN Documents window.

iTunes showing the VPN profile ready to load on the iPhone

Now launch the OpenVPN app on the iPhone. There will be a notification that a new profile is ready to import. Tap the green plus sign to import it.

The OpenVPN iOS app showing new profile ready to import

Connecting

OpenVPN is now ready to use with the new profile. Start the connection by sliding the Connect button to the On position. Disconnect by sliding the same button to Off.

Note
The VPN switch under Settings cannot be used to connect to the VPN. If you try, you will receive a notice to only connect using the OpenVPN app.

The OpenVPN iOS app connected to the VPN
Android

Installing

Open the Google Play Store. Search for and install Android OpenVPN Connect, the official Android OpenVPN client application.

The .ovpn profile can be transferred by connecting the Android device to your computer by USB and copying the file over. Alternatively, if you have an SD card reader, you can remove the device’s SD card, copy the profile onto it and then insert the card back into the Android device.

Start the OpenVPN app and tap the menu to import the profile.

The OpenVPN Android app profile import menu selection

Then navigate to the location of the saved profile (the screenshot uses /sdcard/Download/) and select the file. The app will make a note that the profile was imported.

The OpenVPN Android app selecting VPN profile to import

Connecting

To connect, simply tap the Connect button. You’ll be asked if you trust the OpenVPN application. Choose OK to initiate the connection. To disconnect from the VPN, go back to the OpenVPN app and choose Disconnect.

The OpenVPN Android app ready to connect to the VPN
Step 13: Test Your VPN Connection

Once everything is installed, a simple check confirms everything is working properly. Without having a VPN connection enabled, open a browser and go to DNSLeakTest.

The site will return the IP address assigned by your internet service provider and as you appear to the rest of the world. To check your DNS settings through the same website, click on Extended Test and it will tell you which DNS servers you are using.

Now connect the OpenVPN client to your Droplet’s VPN and refresh the browser. The completely different IP address of your VPN server should now appear. That is now how you appear to the world. Again, DNSLeakTest’s Extended Test will check your DNS settings and confirm you are now using the DNS resolvers pushed by your VPN.
Step 14: Revoking Client Certificates

Occasionally, you may need to revoke a client certificate to prevent further access to the OpenVPN server.

To do so, enter your CA directory and re-source the vars file:

cd ~/openvpn-ca
source vars

Next, call the revoke-full command using the client name that you wish to revoke:

./revoke-full client3

This will show some output, ending in error 23. This is normal and the process should have successfully generated the necessary revocation information, which is stored in a file called crl.pem within the keys subdirectory.

Transfer this file to the /etc/openvpn configuration directory:

sudo cp ~/openvpn-ca/keys/crl.pem /etc/openvpn

Next, open the OpenVPN server configuration file:

sudo nano /etc/openvpn/server.conf

At the bottom of the file, add the crl-verify option, so that the OpenVPN server checks the certificate revocation list that we’ve created each time a connection attempt is made:
/etc/openvpn/server.conf

crl-verify crl.pem

Save and close the file.

Finally, restart OpenVPN to implement the certificate revocation:

sudo systemctl restart openvpn@server

The client should now longer be able to successfully connect to the server using the old credential.

To revoke additional clients, follow this process:

Generate a new certificate revocation list by sourcing the vars file in the ~/openvpn-ca directory and then calling the revoke-full script on the client name.
Copy the new certificate revocation list to the /etc/openvpn directory to overwrite the old list.
Restart the OpenVPN service.

This process can be used to revoke any certificates that you’ve previously issued for your server.
Conclusion

Congratulations! You are now securely traversing the internet protecting your identity, location, and traffic from snoopers and censors.

To configure more clients, you only need to follow steps 6, and 11-13 for each additional device. To revoke access to clients, follow step 14.

By: Justin Ellingwood
Found on Digital Ocean’s community forums

Category: Linux | Comments Off

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