VPN on our VPS

For this article, we will use Ubuntu 16.04 and commands mostly related to deb based distros. OpenVPN installation: To install openvpn and easy-rsa we need to execute:
# apt update && apt upgrade 
# apt install easy-rsa openvpn -y
The first command will update VPS, second will install VPN server. 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). 1. To begin, we can copy the easy-rsa template directory into our home directory with the make-cadir command:

$ make-cadir ~/openvpn-ca
2. Move into the newly created directory to begin configuring the CA:

$ cd ~/openvpn-ca
3. 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:

. . .
export KEY_CITY="SanFrancisco"
export KEY_ORG="Fort-Funston"
export KEY_EMAIL="me@myhost.mydomain"
export KEY_OU="MyOrganizationalUnit"
. . .
Edit the values in red to whatever you'd prefer, but do not leave them blank:

. . .
export KEY_PROVINCE="Warsaw"
export KEY_CITY="Warsaw"
export KEY_ORG="ABC Hosting"
export KEY_EMAIL="admin@cba.pl"
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 a server in this guide:

export KEY_NAME="server"
When you are finished, save and close the file. To close and save in nano use: ctrl + o and hit enter to save current file and ctrl + x to exit the editor. 4. And how to 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:
NOTE: If you run
, 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:

Sample 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) [PL]:
State or Province Name (full name) [Warsaw]:
Locality Name (eg, city) [Warsaw]:
Organization Name (eg, company) [ABC Hosting]:
Organizational Unit Name (eg, section) [Community]:
Common Name (eg, your name or your server's hostname) [ABC Hosting CA]:
Name [server]:
Email Address [admin@cba.pl]:
We now have a CA that can be used to create the rest of the files we need. 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 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.
$ ./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:
Sample 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 key 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
5. We will need to 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. Next, we can begin configuring the OpenVPN service using the credentials and files we've generated. 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
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":
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:
cipher AES-128-CBC
Below this, add an auth line to select the HMAC message digest algorithm. For this, SHA256 is a good choice:
auth SHA256
Finally, find the user and group settings and remove the ";" at the beginning of to uncomment those lines:
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:
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:
push "dhcp-option DNS"
push "dhcp-option DNS"
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.
# Optional!
port 443
Often if the protocol will be restricted to that port as well. If so, change proto from UDP to TCP:
# 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:
cert server.crt
key server.key
When you are finished, save and close the file. 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:
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
Then we need to install iptables and adjust firewall rules:
# apt install iptables
To adjust rules execute following: # iptables -A INPUT -i eth0 -m state --state NEW -p udp --dport 1194 -j ACCEPT # iptables -A INPUT -i tun+ -j ACCEPT # iptables -A FORWARD -i tun+ -j ACCEPT # iptables -A FORWARD -i tun+ -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT # iptables -A FORWARD -i eth0 -o tun+ -m state --state RELATED,ESTABLISHED -j ACCEPT # iptables -t nat -A POSTROUTING -s -o eth0 -j MASQUERADE # iptables -A OUTPUT -o tun+ -j ACCEPT Also, please execute this to fix systemd service file for openvpn:
$ sudo sed -i 's/LimitNPROC=10 /#LimitNPROC=10 /' /lib/systemd/system/openvpn@.service
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
If everything went well, your output should look something that looks like this:
● openvpn@server.service - OpenVPN connection to server
   Loaded: loaded (/lib/systemd/system/openvpn@.service; disabled; vendor preset: enabled)
   Active: active (running) since Tue 2016-05-03 15:30:05 EDT; 47s ago
     Docs: man:openvpn(8)
  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/openvpn@server.service
           └─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 peer
May 03 15:30:05 openvpn2 ovpn-server[5856]: /sbin/ip route add via
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= 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:
4: tun0: POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP mtu 1500 qdisc noqueue state UNKNOWN group default qlen 100
    inet peer scope global tun0
       valid_lft forever preferred_lft forever
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:
. . .
# 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:
proto udp
Next, uncomment the user and group directives by removing the ";":
# 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:
# 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:
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:
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.
# 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:
# First argument: Client identifier

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:
$ scp sammy@openvpn_server_ip:client-configs/files/client1.ovpn ~/
Here are several tools for securely transferring files from the server to a local computer:
OVPN file can be used if GUI client for OpenVPN on Windows or Mac OS. Linus has Network Manager GUI that can work with .ovpn files.