https://www.digitalocean.com/community/tutorials/how-to-set-up-and-configure-an-openvpn-server-on-ubuntu-20-04
digitalocean.com How To Set Up and Configure an OpenVPN Server on Ubuntu 20.04 Jamon Camisso 43-55 minutes Introduction
A Virtual Private Network (VPN) allows you to traverse untrusted networks as if you were on a private network. It gives you the freedom to access the internet safely and securely from your smartphone or laptop when connected to an untrusted network, like the WiFi at a hotel or coffee shop.
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 untrusted networks.
OpenVPN is a full featured, open-source Transport Layer Security (TLS) VPN solution that accommodates a wide range of configurations. In this tutorial, you will set up OpenVPN on an Ubuntu 20.04 server, and then configure it to be accessible from a client machine.
Note: If you plan to set up an OpenVPN Server on a DigitalOcean Droplet, be aware that we, like many hosting providers, charge for bandwidth overages. For this reason, please be mindful of how much traffic your server is handling.
See this page for more info. Prerequisites
To follow this tutorial, you will need:
One Ubuntu 20.04 server with a sudo non-root user and a firewall enabled. To set this up, you can follow our Initial Server Setup with Ubuntu 20.04 tutorial. We will refer to this as the OpenVPN Server throughout this guide.
A separate Ubuntu 20.04 server set up as a private Certificate Authority (CA), which we will refer to as the CA Server throughout this guide. After executing the steps from the Initial Server Setup Guide on this server, you can follow steps 1 to 3 of our guide on How To Set Up and Configure a Certificate Authority (CA) on Ubuntu 20.04 to accomplish that.
Note: While it is technically possible to use your OpenVPN Server or your local machine as your CA, this is not recommended as it opens up your VPN to some security vulnerabilities. Per the official OpenVPN documentation, you should place your CA on a standalone machine that’s dedicated to importing and signing certificate requests. For this reason, this guide assumes that your CA is on a separate Ubuntu 20.04 server that also has a non-root user with sudo privileges and a basic firewall enabled.
In addition to that, you’ll need a client machine which you will use to connect to your OpenVPN Server. In this guide, we’ll call this the OpenVPN Client. For the purposes of this tutorial, it’s recommended that you use your local machine as the OpenVPN client.
With these prerequisites in place, you are ready to begin setting up and configuring an OpenVPN Server on Ubuntu 20.04.
Note: Please note that if you disable password authentication while configuring these servers, you may run into difficulties when transferring files between them later on in this guide. To resolve this issue, you could re-enable password authentication on each server. Alternatively, you could generate an SSH keypair for each server, then add the OpenVPN Server’s public SSH key to the CA machine’s authorized_keys file and vice versa. See How to Set Up SSH Keys on Ubuntu 20.04 for instructions on how to perform either of these solutions. Step 1 — Installing OpenVPN and Easy-RSA
The first step in this tutorial is to install OpenVPN and Easy-RSA. Easy-RSA is a public key infrastructure (PKI) management tool that you will use on the OpenVPN Server to generate a certificate request that you will then verify and sign on the CA Server.
To start off, update your OpenVPN Server’s package index and install OpenVPN and Easy-RSA. Both packages are available in Ubuntu’s default repositories, so you can use apt for the installation:
Next you will need to create a new directory on the OpenVPN Server as your non-root user called ~/easy-rsa:
Now you will need to create a symlink from the easyrsa script that the package installed into the ~/easy-rsa directory that you just created:
Note: While other guides might instruct you to copy the easy-rsa package files into your PKI directory, this tutorial adopts a symlink approach. As a result, any updates to the easy-rsa package will be automatically reflected in your PKI’s scripts.
Finally, ensure the directory’s owner is your non-root sudo user and restrict access to that user using chmod:
Once these programs are installed and have been moved to the right locations on your system, the next step is to create a Public Key Infrastructure (PKI) on the OpenVPN server so that you can request and manage TLS certificates for clients and other servers that will connect to your VPN. Step 2 — Creating a PKI for OpenVPN
Before you can create your OpenVPN server’s private key and certificate, you need to create a local Public Key Infrastructure directory on your OpenVPN server. You will use this directory to manage the server and clients’ certificate requests instead of making them directly on your CA server.
To build a PKI directory on your OpenVPN server, you’ll need to populate a file called vars with some default values. First you will cd into the easy-rsa directory, then you will create and edit the vars file using nano or your preferred text editor.
Once the file is opened, paste in the following two lines:
~/easy-rsa/vars
set_var EASYRSA_ALGO "ec" set_var EASYRSA_DIGEST "sha512"
These are the only two lines that you need in this vars file on your OpenVPN server since it will not be used as a Certificate Authority. They will ensure that your private keys and certificate requests are configured to use modern Elliptic Curve Cryptography (ECC) to generate keys and secure signatures for your clients and OpenVPN server.
Configuring your OpenVPN & CA servers to use ECC means when a client and server attempt to establish a shared symmetric key, they can use Elliptic Curve algorithms to do their exchange. Using ECC for a key exchange is significantly faster than using plain Diffie-Hellman with the classic RSA algorithm since the numbers are much smaller and the computations are faster.
Background: When clients connect to OpenVPN, they use asymmetric encryption (also known as public/private key) to perform a TLS handshake. However, when transmitting encrypted VPN traffic, the server and clients use symmetric encryption, which is also known as shared key encryption.
There is much less computational overhead with symmetric encryption compared to asymmetric: the numbers that are used are much smaller, and modern CPUs integrate instructions to perform optimized symmetric encryption operations. To make the switch from asymmetric to symmetric encryption, the OpenVPN server and client will use the Elliptic Curve Diffie-Hellman (ECDH) algorithm to agree on a shared secret key as quickly as possible.
Once you have populated the vars file you can proceed with creating the PKI directory. To do so, run the easyrsa script with the init-pki option. Although you already ran this command on the CA server as part of the prerequisites, it’s necessary to run it here because your OpenVPN server and CA server have separate PKI directories:
Note that on your OpenVPN server there is no need to create a Certificate Authority. Your CA server is solely responsible for validating and signing certificates. The PKI on your VPN server is only used as a convenient and centralized place to store certificate requests and public certificates.
After you’ve initialized your PKI on the OpenVPN server, you are ready to move on to the next step, which is creating an OpenVPN server certificate request and private key. Step 3 — Creating an OpenVPN Server Certificate Request and Private Key
Now that your OpenVPN server has all the prerequisites installed, the next step is to generate a private key and Certificate Signing Request (CSR) on your OpenVPN server. After that you’ll transfer the request over to your CA to be signed, creating the required certificate. Once you have a signed certificate, you’ll transfer it back to the OpenVPN server and install it for the server to use.
To start, navigate to the ~/easy-rsa directory on your OpenVPN Server as your non-root user:
Now you’ll call the easyrsa with the gen-req option followed by a Common Name (CN) for the machine. The CN can be anything you like but it can be helpful to make it something descriptive. Throughout this tutorial, the OpenVPN Server’s CN will be server. Be sure to include the nopass option as well. Failing to do so will password-protect the request file which could lead to permissions issues later on.
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 directory, 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.
Output Common Name (eg: your user, host, or server name) [server]:
Keypair and certificate request completed. Your files are: req: /home/sammy/easy-rsa/pki/reqs/server.req key: /home/sammy/easy-rsa/pki/private/server.key
This will create a private key for the server and a certificate request file called server.req. Copy the server key to the /etc/openvpn/server directory:
After completing these steps, you have successfully created a private key for your OpenVPN server. You have also generated a Certificate Signing Request for the OpenVPN server. The CSR is now ready for signing by your CA. In the next section of this tutorial you will learn how to sign a CSR with your CA server’s private key. Step 4 — Signing the OpenVPN Server’s Certificate Request
In the previous step you created a Certificate Signing Request (CSR) and private key for the OpenVPN server. Now the CA server needs to know about the server certificate and validate it. Once the CA validates and relays the certificate back to the OpenVPN server, clients that trust your CA will be able to trust the OpenVPN server as well.
On the OpenVPN server, as your non-root user, use SCP or another transfer method to copy the server.req certificate request to the CA server for signing:
If you followed the prerequisite How To Set Up and Configure a Certificate Authority (CA) on Ubuntu 20.04 tutorial, the next step is to log in to the CA server as the non-root user that you created to manage your CA. You’ll cd to the ~/easy-rsa directory where you created your PK and then import the certificate request using the easyrsa script:
Output . . . The request has been successfully imported with a short name of: server You may now use this name to perform signing operations on this request.
Next, sign the request by running the easyrsa script with the sign-req option, followed by the request type and the Common Name. The request type can either be client or server. Since we’re working with the OpenVPN server’s certificate request, be sure to use the server request type:
In the output, you’ll be prompted to verify that the request comes from a trusted source. Type yes then press ENTER to confirm:
Output You are about to sign the following certificate. Please check over the details shown below for accuracy. Note that this request has not been cryptographically verified. Please be sure it came from a trusted source or that you have verified the request checksum with the sender.
Request subject, to be signed as a server certificate for 3650 days:
subject= commonName = server
Type the word 'yes' to continue, or any other input to abort. Confirm request details: yes . . . Certificate created at: /home/sammy/easy-rsa/pki/issued/server.crt
Note that if you encrypted your CA private key, you’ll be prompted for your password at this point.
With those steps complete, you have signed the OpenVPN server’s certificate request using the CA server’s private key. The resulting server.crt file contains the OpenVPN server’s public encryption key, as well as a signature from the CA server. The point of the signature is to tell anyone who trusts the CA server that they can also trust the OpenVPN server when they connect to it.
To finish configuring the certificates, copy the server.crt and ca.crt files from the CA server to the OpenVPN server:
Now back on your OpenVPN server, copy the files from /tmp to /etc/openvpn/server:
Now your OpenVPN server is nearly ready to accept connections. In the next step you’ll perform some additional steps to increase the security of the server. Step 5 — Configuring OpenVPN Cryptographic Material
For an additional layer of security, we’ll add an extra shared secret key that the server and all clients will use with OpenVPN’s tls-crypt directive. This option is used to obfuscate the TLS certificate that is used when a server and client connect to each other initially. It is also used by the OpenVPN server to perform quick checks on incoming packets: if a packet is signed using the pre-shared key, then the server processes it; if it is not signed, then the server knows it is from an untrusted source and can discard it without having to perform additional decryption work.
This option will help ensure that your OpenVPN server is able to cope with unauthenticated traffic, port scans, and Denial of Service attacks, which can tie up server resources. It also makes it harder to identify OpenVPN network traffic.
To generate the tls-crypt pre-shared key, run the following on the OpenVPN server in the ~/easy-rsa directory:
The result will be a file called ta.key. Copy it to the /etc/openvpn/server/ directory:
With these files in place on the OpenVPN server you are ready to create client certificates and key files for your users, which you will use to connect to the VPN. Step 6 — Generating a Client Certificate and Key Pair
Although you can generate a private key and certificate request on your client machine and then send it to the CA to be signed, this guide outlines a process for generating the certificate request on the OpenVPN server. The benefit of this approach is that we can create a script that will automatically generate client configuration files that contain all of the required keys and certificates. This lets you avoid having to transfer keys, certificates, and configuration files to clients and streamlines the process of joining the VPN.
We will generate a single client key and certificate pair for this guide. If you have more than one client, you can repeat this process for each one. Please note, though, that you will need to pass a unique name value to the script for every client. Throughout this tutorial, the first certificate/key pair is referred to as client1.
Get started by creating a directory structure within your home directory to store the client certificate and key files:
Since you will store your clients’ certificate/key pairs and configuration files in this directory, you should lock down its permissions now as a security measure:
Next, navigate back to the EasyRSA directory and run the easyrsa script with the gen-req and nopass options, along with the common name for the client:
Press ENTER to confirm the common name. Then, copy the client1.key file to the ~/client-configs/keys/ directory you created earlier:
Next, transfer the client1.req file to your CA Server using a secure method:
Now log in to your CA Server. Then, navigate to the EasyRSA directory, and import the certificate request:
Next, sign the request the same way as you did for the server in the previous step. This time, though, be sure to specify the client request type:
When prompted, enter yes to confirm that you intend to sign the certificate request and that it came from a trusted source:
Output Type the word 'yes' to continue, or any other input to abort. Confirm request details: yes
Again, if you encrypted your CA key, you’ll be prompted for your password here.
This will create a client certificate file named client1.crt. Transfer this file back to the server:
Back on your OpenVPN server, copy the client certificate to the ~/client-configs/keys/ directory:
Next, copy the ca.crt and ta.key files to the ~/client-configs/keys/ directory as well, and set the appropriate permissions for your sudo user:
With that, your server and client’s certificates and keys have all been generated and are stored in the appropriate directories on your OpenVPN server. There are still a few actions that need to be performed with these files, but those will come in a later step. For now, you can move on to configuring OpenVPN. Step 7 — Configuring OpenVPN
Like many other widely used open-source tools, OpenVPN has numerous configuration options available to customize your server for your specific needs. In this section, we will provide instructions on how to set up an OpenVPN server configuration based on one of the sample configuration files that is included within this software’s documentation.
First, copy the sample server.conf file as a starting point for your own configuration file:
Open the new file for editing with the text editor of your choice. We’ll use nano in our example:
We’ll need to change a few lines in this file. First, find the HMAC section of the configuration by searching for the tls-auth directive. This line will be enabled by default. Comment it out by adding a ; to the beginning of the line. Then add a new line after it containing the value tls-crypt ta.key only:
/etc/openvpn/server/server.conf
;tls-auth ta.key 0 # This file is secret tls-crypt ta.key
Next, find the section on cryptographic ciphers by looking for the cipher lines. The default value is set to AES-256-CBC, however, the AES-256-GCM cipher offers a better level of encryption, performance, and is well supported in up-to-date OpenVPN clients. We’ll comment out the default value by adding a ; sign to the beginning of this line, and then we’ll add another line after it containing the updated value of AES-256-GCM:
/etc/openvpn/server/server.conf
;cipher AES-256-CBC cipher AES-256-GCM
Right after this line, add an auth directive to select the HMAC message digest algorithm. For this, SHA256 is a good choice:
/etc/openvpn/server/server.conf
auth SHA256
Next, find the line containing a dh directive, which defines Diffie-Hellman parameters. Since we’ve configured all the certificates to use Elliptic Curve Cryptography, there is no need for a Diffie-Hellman seed file. Comment out the existing line that looks like dh dh2048.pem or dh dh.pem. The filename for the Diffie-Hellman key may be different than what is listed in the example server configuration file. Then add a line after it with the contents dh none:
/etc/openvpn/server/server.conf
;dh dh2048.pem dh none
Next, we want OpenVPN to run with no privileges once it has started, so we need to tell it to run with a user nobody and group nogroup. To enable this, find and uncomment the user nobody and group nogroup lines by removing the ; sign from the beginning of each line:
/etc/openvpn/server/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 your client and server, but will not force any connections to use the tunnel. If you wish to use the VPN to route all of your client traffic over the VPN, you will likely want to push some extra settings to the client computers.
To get started, find and uncomment the line containing push "redirect-gateway def1 bypass-dhcp". Doing this will tell your client to redirect all of its traffic through your OpenVPN Server. Be aware that enabling this functionality can cause connectivity issues with other network services, like SSH:
/etc/openvpn/server/server.conf
push "redirect-gateway def1 bypass-dhcp"
Just below this line, find the dhcp-option section. Again, remove the ; from the beginning of both of the lines to uncomment them:
/etc/openvpn/server/server.conf
push "dhcp-option DNS 208.67.222.222" push "dhcp-option DNS 208.67.220.220"
These lines will tell your client to use the free OpenDNS resolvers at the listed IP addresses. If you prefer other DNS resolvers you can substitute them in place of the highlighted IPs.
This will assist clients in reconfiguring their DNS settings to use the VPN tunnel 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 on your OpenVPN server, port 443 is a popular choice since it is usually allowed through firewall rules.
To change OpenVPN to listen on port 443, open the server.conf file and find the line that looks like this:
/etc/openvpn/server/server.conf
port 1194
Edit it so that the port is 443:
/etc/openvpn/server/server.conf
port 443
Oftentimes, the protocol is restricted to that port as well. If so, find the proto line below the port line and change the protocol from udp to tcp:
/etc/openvpn/server/server.conf
proto tcp
If you do switch the protocol to TCP, you will need to change the explicit-exit-notify directive’s value from 1 to 0, as this directive is only used by UDP. Failing to do so while using TCP will cause errors when you start the OpenVPN service.
Find the explicit-exit-notify line at the end of the file and change the value to 0:
/etc/openvpn/server/server.conf
explicit-exit-notify 0
If you have no need to use a different port and protocol, it is best to leave these settings unchanged. (Optional) Point to Non-Default Credentials
If you selected a different name during the ./easyrsa gen-req server command earlier, modify the cert and key lines in the server.conf configuration file so that they point to the appropriate .crt and .key files. If you used the default name, server, this is already set correctly:
/etc/openvpn/server/server.conf
cert server.crt key server.key
When you are finished, save and close the file.
You have now finished configuring your OpenVPN general settings. In the next step, we’ll customize the server’s networking options. Step 8 — Adjusting the OpenVPN Server Networking Configuration
There are some aspects of the server’s networking configuration that need to be tweaked so that OpenVPN can correctly route traffic through the VPN. The first of these is IP forwarding, a method for determining where IP traffic should be routed. This is essential to the VPN functionality that your server will provide.
To adjust your OpenVPN server’s default IP forwarding setting, open the /etc/sysctl.conf file using nano or your preferred editor:
Then add the following line at the bottom of the file:
/etc/sysctl.conf
net.ipv4.ip_forward = 1
Save and close the file when you are finished.
To read the file and load the new values for the current session, type:
Output net.ipv4.ip_forward = 1
Now your OpenVPN server will be able to forward incoming traffic from one ethernet device to another. This setting makes sure the server can direct traffic from clients that connect on the virtual VPN interface out over its other physical ethernet devices. This configuration will route all web traffic from your client via your server’s IP address, and your client’s public IP address will effectively be hidden.
In the next step you will need to configure some firewall rules to ensure that traffic to and from your OpenVPN server flows properly. Step 9 — Firewall Configuration
So far, you’ve installed OpenVPN on your server, configured it, and generated the keys and certificates needed for your client to access the VPN. However, you have not yet provided OpenVPN with any instructions on where to send incoming web traffic from clients. You can stipulate how the server should handle client traffic by establishing some firewall rules and routing configurations.
Assuming you followed the prerequisites at the start of this tutorial, you should already have ufw installed and running on your server. To allow OpenVPN through the firewall, you’ll need to enable masquerading, an iptables concept that provides on-the-fly dynamic network address translation (NAT) to correctly route client connections.
Before opening the firewall configuration file to add the masquerading rules, you must first find the public network interface of your machine. To do this, type:
Your public interface is the string found within this command’s output that follows the word “dev”. For example, this result shows the interface named eth0, which is highlighted below:
Output default via 159.65.160.1 dev eth0 proto static
When you have the interface associated with your default route, open the /etc/ufw/before.rules file to add the relevant configuration:
UFW rules are typically added using the ufw command. Rules listed in the before.rules file, though, are read and 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. Remember to replace eth0 in the -A POSTROUTING line below with the interface you found in the above command:
/etc/ufw/before.rules
*nat :POSTROUTING ACCEPT [0:0]
-A POSTROUTING -s 10.8.0.0/8 -o eth0 -j MASQUERADE COMMIT
*filter . . .
Save and close the file when you are finished.
Next, you need to tell UFW to allow forwarded packets by default as well. To do this, open the /etc/default/ufw file:
Inside, find the DEFAULT_FORWARD_POLICY directive and change the value from DROP to ACCEPT:
/etc/default/ufw
DEFAULT_FORWARD_POLICY="ACCEPT"
Save and close the file when you are finished.
Next, 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.
In case you forgot to add the SSH port when following the prerequisite tutorial, add it here as well:
Note: If you are using a different firewall or have customized your UFW configuration, you may need to add additional firewall rules. For example, if you decide to tunnel all of your network traffic over the VPN connection, you will need to ensure that port 53 traffic is allowed for DNS requests, and ports like 80 and 443 for HTTP and HTTPS traffic respectively. If there are other protocols that you are using over the VPN then you will need to add rules for them as well.
After adding those rules, disable and re-enable UFW to restart it and load the changes from all of the files you’ve modified:
Your server is now configured to correctly handle OpenVPN traffic. With the firewall rules in place, we can start the OpenVPN service on the server. Step 10 — Starting OpenVPN
OpenVPN runs as a systemd service, so we can use systemctl to manage it. We will configure OpenVPN to start up at boot so you can connect to your VPN at any time as long as your server is running. To do this, enable the OpenVPN service by adding it to systemctl:
Then start the OpenVPN service:
Double check that the OpenVPN service is active with the following command. You should see active (running) in the output:
Output ● openvpn-server@server.service - OpenVPN service for server Loaded: loaded (/lib/systemd/system/openvpn-server@.service; enabled; vendor preset: enabled) Active: active (running) since Wed 2020-04-29 15:39:59 UTC; 6s ago Docs: man:openvpn(8) https://community.openvpn.net/openvpn/wiki/Openvpn24ManPage https://community.openvpn.net/openvpn/wiki/HOWTO Main PID: 16872 (openvpn) Status: "Initialization Sequence Completed" Tasks: 1 (limit: 1137) Memory: 1.0M CGroup: /system.slice/system-openvpn\x2dserver.slice/openvpn-server@server.service └─16872 /usr/sbin/openvpn --status /run/openvpn-server/status-server.log --status-version 2 --suppress-timestamps --c> . . . . . . Apr 29 15:39:59 ubuntu-20 openvpn[16872]: Initialization Sequence Completed
We’ve now completed the server-side configuration for OpenVPN. Next, you will configure your client machine and connect to the OpenVPN Server. Step 11 — Creating the Client Configuration Infrastructure
Creating configuration files for OpenVPN clients can be somewhat involved, as every client must have its own config and each must align with the settings outlined in the server’s configuration file. Rather than writing a single configuration file that can only be used on one client, this step outlines a process for building a client configuration infrastructure which you can use to generate config files on-the-fly. You will first create a “base” configuration file then build a script which will allow you to generate unique client config files, certificates, and keys as needed.
Get started by creating a new directory where you will store client configuration files within the client-configs directory you created earlier:
Next, copy an example client configuration file into the client-configs directory to use as your base configuration:
Open this new file using nano or your preferred text editor:
Inside, locate the remote directive. This points the client to your OpenVPN server address — the public IP address of your OpenVPN server. If you decided to change the port that the OpenVPN server is listening on, you will also need to change 1194 to the port you selected:
~/client-configs/base.conf
. . .
remote your_server_ip 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 ; sign at the beginning of each line:
~/client-configs/base.conf
user nobody group nogroup
Find the directives that set the ca, cert, and key. Comment out these directives since you will add the certs and keys within the file itself shortly:
~/client-configs/base.conf
;ca ca.crt ;cert client.crt ;key client.key
Similarly, comment out the tls-auth directive, as you will add ta.key directly into the client configuration file (and the server is set up to use tls-crypt):
~/client-configs/base.conf
;tls-auth ta.key 1
Mirror the cipher and auth settings that you set in the /etc/openvpn/server/server.conf file:
~/client-configs/base.conf
cipher AES-256-GCM auth SHA256
Next, add the key-direction directive somewhere in the file. You must set this to “1” for the VPN to function correctly on the client machine:
~/client-configs/base.conf
key-direction 1
Finally, add a few commented out lines to handle various methods that Linux based VPN clients will use for DNS resolution. You’ll add two similar, but separate sets of commented out lines. The first set is for clients that do not use systemd-resolved to manage DNS. These clients rely on 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
Now add another set of lines for clients that use systemd-resolved for DNS resolution:
~/client-configs/base.conf
; script-security 2 ; up /etc/openvpn/update-systemd-resolved ; down /etc/openvpn/update-systemd-resolved ; down-pre ; dhcp-option DOMAIN-ROUTE .
Save and close the file when you are finished.
Later in Step 13 - Installing the Client Configuration step of this tutorial you will learn how to determine how DNS resolution works on Linux clients and which section to uncomment.
Next, we’ll create a script that will compile your base configuration with the relevant certificate, key, and encryption files and then place the generated configuration in the ~/client-configs/files directory. Open a new file called make_config.sh within the ~/client-configs directory:
Inside, add the following content:
~/client-configs/make_config.sh
Save and close the file when you are finished.
Before moving on, be sure to mark this file as executable by typing:
This script will make a copy of the base.conf file you made, collect all the certificate and key files you’ve created for your client, extract their contents, append them to the copy of the base configuration file, and export all of this content into a new client configuration file. This means that, rather than having to manage the client’s configuration, certificate, and key files separately, all the required information is stored in one place. The benefit of using this method is that if you ever need to add a client in the future, you can run this script to quickly create a new config file and ensure that all the important information is stored in a single, easy-to-access location.
Please note that any time you add a new client, you will need to generate new keys and certificates for it before you can run this script and generate its configuration file. You will get some practice using this script in the next step. Step 12 — Generating Client Configurations
If you followed along with the guide, you created a client certificate and key named client1.crt and client1.key, respectively, in Step 6. You can generate a config file for these credentials by moving into your ~/client-configs directory and running the script you made at the end of the previous step:
This will create a file named client1.ovpn in your ~/client-configs/files directory:
Output client1.ovpn
You need to transfer this file to the device you plan to use as the client. 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 device’s operating system and your personal preferences, a dependable and secure method is 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 which you can run from your local computer (macOS or Linux). This will copy the client1.ovpn file we’ve created in the last step to your home directory:
Here are several tools and tutorials for securely transferring files from the OpenVPN 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 13 — Installing the Client Configuration
This section covers how to install a client VPN profile on Windows, macOS, Linux, iOS, and Android. None of these client instructions are dependent on one another, so feel free to skip to whichever is applicable to your device.
The OpenVPN connection will have the same name as whatever you called the .ovpn file. In regards to this tutorial, this means that the connection is named client1.ovpn, aligning with the first client file you generated. Windows
Installing
Download the OpenVPN client application for Windows from 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 locate the profile and make it available.
You must run OpenVPN 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 must preset this 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 you can connect and disconnect the VPN 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 your 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. macOS
Installing
Tunnelblick is a free, open source OpenVPN client for macOS. 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. Answer I have configuration files 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 the Tunnelblick icon 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 client1 menu item to initiate the VPN connection. If you are using custom DNS settings with Tunnelblick, you may need check “Allow changes to manually-set network settings” in the advanced configuration dialog. 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:
On CentOS you can enable the EPEL repositories and then install it by typing: Configuring Clients that use systemd-resolved
First determine if your system is using systemd-resolved to handle DNS resolution by checking the /etc/resolv.conf file:
Output
. . .
nameserver 127.0.0.53 options edns0
If your system is configured to use systemd-resolved for DNS resolution, the IP address after the nameserver option will be 127.0.0.53. There should also be comments in the file like the output that is shown that explain how systemd-resolved is managing the file. If you have a different IP address than 127.0.0.53 then chances are your system is not using systemd-resolved and you can go to the next section on configuring Linux clients that have an update-resolv-conf script instead.
To support these clients, first install the openvpn-systemd-resolved package. It provides scripts that will force systemd-resolved to use the VPN server for DNS resolution.
One that package is installed, configure the client to use it, and to send all DNS queries over the VPN interface. Open the client’s VPN file:
Now uncomment the following lines that you added earlier:
client1.ovpn
script-security 2 up /etc/openvpn/update-systemd-resolved down /etc/openvpn/update-systemd-resolved down-pre dhcp-option DOMAIN-ROUTE .
Configuring Clients that use update-resolv-conf
If your system is not using systemd-resolved to manage DNS, check to see if your distribution includes an /etc/openvpn/update-resolv-conf script instead:
Output update-resolv-conf
If your client includes the update-resolv-conf file, then edit the OpenVPN client configuration file that you transferred earlier:
Uncomment the three lines you added to adjust the DNS settings:
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 directive from nogroup to nobody to match the distribution’s available groups:
client1.ovpn
group nobody
Save and close the file.
Connecting
Now, you can connect to the VPN by just pointing the openvpn command to the client configuration file:
This should connect you to your VPN.
Note: If your client uses systemd-resolved to manage DNS, check the settings are applied correctly by running the systemd-resolve --status command like this:
You should see output like the following:
Output Link 22 (tun0) . . . DNS Servers: 208.67.222.222 208.67.220.220 DNS Domain: ~.
If you see the IP addresses of the DNS servers that you configured on the OpenVPN server, along with the ~. setting for DNS Domain in the output, then you have correctly configured your client to use the VPN server’s DNS resolver. You can also check that you are sending DNS queries over the VPN by using a site like DNS leak test.com. 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.
The process of completing the transfer with iTunes is 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. You will receive 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.
You can transfer the .ovpn profile 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 FILE 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 /storage/emulated/0/openvpn) and select your .ovpn file. Tap the IMPORT button to finish importing this profile.
The OpenVPN Android app selecting VPN profile to import
Connecting Once the profile is added, you will see a screen like this:
The OpenVPN Android app with new profile added
To connect, tap the toggle button close to the profile you want to use. You’ll see real time stats of your connection and traffic being routed through your OpenVPN server: The OpenVPN Android app connected to the VPN
To disconnect, just tap the toggle button on the top left once again. You will be prompted to confirm that you want to disconnect from your VPN. Step 14 — Testing Your VPN Connection (Optional)
Note: This method for testing your VPN connection will only work if you opted to route all your traffic through the VPN in Step 7 when you edited the server.conf file for OpenVPN.
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. A completely different IP address (that of your VPN server) should now appear, and this is 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 15 — Revoking Client Certificates
Occasionally, you may need to revoke a client certificate to prevent further access to the OpenVPN server.
To do so, follow the example in the prerequisite tutorial on How to Set Up and Configure a Certificate Authority on Ubuntu 20.04 under the Revoking a Certificate section.
Once you have revoked a certificate for a client using those instructions, you’ll need to copy the generated crl.pem file to your OpenVPN server in the /etc/openvpn/server directory:
Next, open the OpenVPN server configuration file:
At the bottom of the file, add the crl-verify option, which will instruct the OpenVPN server to check the certificate revocation list that we’ve created each time a connection attempt is made:
/etc/openvpn/server/server.conf
crl-verify crl.pem
Save and close the file.
Finally, restart OpenVPN to implement the certificate revocation:
The client should no longer be able to successfully connect to the server using the old credential.
To revoke additional clients, follow this process:
Revoke the certificate with the ./easyrsa revoke client_name command
Generate a new CRL
Transfer the new crl.pem file to your OpenVPN server and copy it to the /etc/openvpn/server/ directory to overwrite the old list.
Restart the OpenVPN service.
You can use this process to revoke any certificates that you’ve previously issued for your server. Conclusion
You should now have a fully operational virtual private network running on your OpenVPN Server. You can browse the web and download content without worrying about malicious actors tracking your activity.
There are several steps you could take to customize your OpenVPN installation even further, such as configuring your client to connect to the VPN automatically or configuring client-specific rules and access policies. For these and other OpenVPN customizations, you should consult the official OpenVPN documentation.
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 15.