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Most of the information found here is an amalgamation from these tutorials: https://www.digitalocean.com/community/tutorials/how-to-set-up-and-configure-an-openvpn-server-on-centos-8 and https://vitux.com/how-to-install-openvpn-on-almalinux-8-centos-8-or-rocky-linux-8/ and https://openvpn.net/community-resources/how-to/ https://kifarunix.com/assign-static-ip-addresses-for-openvpn-clients/ https://www.paulligocki.com/auto-connect-openvpn-client-startup-raspian/

About OpenVPN and Easy-RSA

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DEVICE=$(ip route | awk '/^default via/ {print $5}')
sudo firewall-cmd --permanent --direct --passthrough ipv4 -t nat -A POSTROUTING -s 10.8.0.0/24 -o $DEVICE -j MASQUERADE

Be sure to reload firewalld so that all your changes take effect:

sudo firewall-cmd --reload

The commands with the --permanent flag will ensure that the rules will persist across reboots. The firewall-cmd --reload command makes sure that all the outstanding changes to the firewall are applied. With the firewall rules in place, we can start the OpenVPN service on the server.

Starting OpenVPN

OpenVPN runs as a systemd service, so we can use systemctl for managing 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:

sudo systemctl -f enable openvpn-server@server.service

Then start the OpenVPN service:

sudo systemctl start openvpn-server@server.service

Double check that the OpenVPN service is active with the following command. You should see active (running) in the output:

sudo systemctl -f enable openvpn-server@server.service
Created symlink /etc/systemd/system/multi-user.target.wants/openvpn-server@server.service → /usr/lib/systemd/system/openvpn-server@.service.
[mtb@sierra easy-rsa]$ sudo systemctl start openvpn-server@server.service
[mtb@sierra easy-rsa]$ sudo systemctl status openvpn-server@server.service
● openvpn-server@server.service - OpenVPN service for server
   Loaded: loaded (/usr/lib/systemd/system/openvpn-server@.service; enabled; vendor prese>
   Active: active (running) since Mon 2022-07-25 09:37:32 UTC; 25s ago
     Docs: man:openvpn(8)
           https://community.openvpn.net/openvpn/wiki/Openvpn24ManPage
           https://community.openvpn.net/openvpn/wiki/HOWTO
 Main PID: 2127755 (openvpn)
   Status: "Initialization Sequence Completed"
    Tasks: 1 (limit: 49268)
   Memory: 1.0M
   CGroup: /system.slice/system-openvpn\x2dserver.slice/openvpn-server@server.service
           └─2127755 /usr/sbin/openvpn --status /run/openvpn-server/status-server.log --s>

Jul 25 09:37:32 sierra openvpn[2127755]: Could not determine IPv4/IPv6 protocol. Using AF>
Jul 25 09:37:32 sierra openvpn[2127755]: Socket Buffers: R=[212992->212992] S=[212992->21>
Jul 25 09:37:32 sierra openvpn[2127755]: UDPv4 link local (bound): [AF_INET][undef]:1194
Jul 25 09:37:32 sierra openvpn[2127755]: UDPv4 link remote: [AF_UNSPEC]
Jul 25 09:37:32 sierra openvpn[2127755]: GID set to nobody
Jul 25 09:37:32 sierra openvpn[2127755]: UID set to nobody
Jul 25 09:37:32 sierra openvpn[2127755]: MULTI: multi_init called, r=256 v=256
Jul 25 09:37:32 sierra openvpn[2127755]: IFCONFIG POOL: base=10.8.0.4 size=62, ipv6=0
Jul 25 09:37:32 sierra openvpn[2127755]: IFCONFIG POOL LIST
Jul 25 09:37:32 sierra openvpn[2127755]: Initialization Sequence Completed
lines 1-23/23 (END)

We’ve now completed the server-side configuration for OpenVPN. Next, you will configure your client machine and connect to the OpenVPN Server.

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:

mkdir -p ~/client-configs/files

Next, copy an example client configuration file into the client-configs directory to use as your base configuration:

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

Open this new file using vi or your preferred text editor:

vi ~/client-configs/base.conf

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:

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

Be sure that the protocol matches the value you are using in the server configuration:

proto udp

Next, uncomment the user and group directives by removing the ; sign at the beginning of each line:

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

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:

# 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

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):

# If a tls-auth key is used on the server
# then every client must also have the key.
;tls-auth ta.key 1

Mirror the cipher and auth settings that you set in the /etc/openvpn/server/server.conf file:

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:

key-direction 1

Finally, add a few commented out lines. Although you can include these directives in every client configuration file, you only need to enable them for Linux clients that ship with an /etc/openvpn/update-resolv-conf file. This script uses the resolvconf utility to update DNS information for Linux clients.

; 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, uncomment these lines from the client’s configuration file after it has been generated.

Save and close the file when you are finished.

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:

vi ~/client-configs/make_config.sh

Inside, add the following content:

#!/bin/bash
 
# First argument: Client identifier
 
KEY_DIR=~/client-configs/keys
OUTPUT_DIR=~/client-configs/files
BASE_CONFIG=~/client-configs/base.conf
 
cat ${BASE_CONFIG} \
<(echo -e '<ca>') \
${KEY_DIR}/ca.crt \
<(echo -e '</ca>\n<cert>') \
${KEY_DIR}/${1}.crt \
<(echo -e '</cert>\n<key>') \
${KEY_DIR}/${1}.key \
<(echo -e '</key>\n<tls-crypt>') \
${KEY_DIR}/ta.key \
<(echo -e '</tls-crypt>') \
> ${OUTPUT_DIR}/${1}.ovpn

Save and close the file when you are finished.

Before moving on, be sure to mark this file as executable by typing:

chmod 700 ~/client-configs/make_config.sh

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.

Generating Client Configurations

If you followed along with the guide, you created a client certificate and key named foxtrot.crt and foxtrot.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:

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

This will create a file named foxtrot.ovpn in your ~/client-configs/files directory:

ls files
foxtrot.ovpn

You need to transfer this file to the device you plan to use as the client.

Installing the Client Configuration

This section covers how to install a client VPN profile on macOS, Linux, and 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 foxtrot.ovpn, aligning with the first client file you generated.

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 foxtrot.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.

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 update
sudo apt install openvpn

Copy

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

sudo yum install epel-release
sudo yum install openvpn

Copy

Configuring

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

ls /etc/openvpn

Copy

Outputupdate-resolv-conf

Next, edit the OpenVPN client configuration file you transfered:

vi client1.ovpn

Copy

If you were able to find an update-resolv-conf file, 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.

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

sudo openvpn --config foxtrot.ovpn

Copy

This should connect you to your VPN.

Automatic client start

To ensure that OVPN starts on boot with the proper configuration, move the foxtrot.ovpnfile to /etc/openvpn/client/client.conf and make sure the permissions are set to 600 and owned by root.

Raspberry Pi

How to have an OpenVPN client connect on system Startup. How to set up a persistant OpenVPN client connection on Raspian.

Ensure *.conf file is located in /etc/openvpn/
*.ovpn files will not work, they will need to be renamed to *.conf.
Renaming a ovpen file to conf is ok and does work.

Edit /etc/default/openvpn

• Ensure a similar line below exist.

• Ensure the value does not have an extension.

• Ensure the value matches the certificate name.

AUTOSTART=”ClientName”

Example: Lets say there is a client certificate called LocationB and the config/settings file is called LocationB.ovpn.
Copy LocationB.ovpn into /etc/openvpn/LocationB.conf
Then add a line into /etc/default/openvpn
AUTOSTART=”LocationB”

Client Fixed IP addresses

OpenVPN clients will be assigned a dynamic IP address when connecting unless we force a static configuration.

OpenVPN has the ability to assign clients specific IP addresses from the IP pool defined. To achieve this, it uses three types of client IP address selection algorithms. These include, in the order in which they are used;

1. Use of --client-connect script. This involves execution of the specified script that generates file containing static IP addresses on the server when a client connects. This method is usually the first choice to be considered.

2. Use of --client-config-dir. This involves the use of a file which contains static IP addresses for the clients as per their client certificate common name (CN) (second choice).

3. Use of --ifconfig-pool for the allocation for dynamic IP (last choice).

For more information, consult man openvpn.

In this guide, we are going to use the second option, where by we will configure our OpenVPN server to read a specific file, that contains the client common names and mapped IP addresses. This ensures that, a connecting client is assigned static IP address based on the common name defined on their client certificate.

Create a File to Store Static IP addresses

The use of the client-config-dir option, requires that the static IP addresses to be assigned to connecting clients be stored in a file that can be read by OpenVPN server.

Therefore, open the OpenVPN server configuration file, /etc/openvpn/server/server.conf, and set your path to static IP assignment file as the value for the client-config-dir parameter.

vi /etc/openvpn/server/server.conf

...
# EXAMPLE: Suppose you want to give
# Thelonious a fixed VPN IP address of 10.9.0.1.
# First uncomment out these lines:
client-config-dir /etc/openvpn/ccd
...

In this demo, we set the path to store static/fixed IP addresses assignment file to, /etc/openvpn/ccd.

mkdir /etc/openvpn/ccd
chown root:openvpn /etc/openvpn/ccd
chmod 750 /etc/openvpn/ccd

Assign Static IP Addresses to OpenVPN Clients

For every OpenVPN client that you want to assign static IP address to, you need to extract the common name from that specific client certificate.

In our demo, we have the OpenVPN client jujitsu. To extract the common names from the clients certificate, use openssl command as shown below. Be sure to replace the clients certificates.

openssl x509 -subject -noout -in ~/client-configs/keys/jujitsu.crt

subject=CN = jujitsu

Once you have the common name for the client, you can then assign static IP addresses using the ifconfig-push option. For example, to assign the client using the certificate with jujitsu as common name an IP address, 10.8.0.50, this is how the assignment is done;

echo "ifconfig-push 10.8.0.50 255.255.255.0" > /etc/openvpn/ccd/jujitsu

Set the proper file permissions:

chown root:openvpn /etc/openvpn/ccd/*
chmod 640 /etc/openvpn/ccd/*

Note that, how you assign the static IP addresses depends on the topology you configured your OpenVPN server. In our, case, we set the topology to subnet;

# Network topology
...
topology subnet

Restart OpenVPN Server;

systemctl restart openvpn-server@server

Be sure to always check the logs;

tail -f /var/log/openvpn/openvpn.log