Install OpenVPN services

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Note

• 30 Jul 2024: Updated for PEM pass phrase. "$" prompts changed to "#" when in root mode.
• 15 Jul 2023: Windows folder to contain config files revised.
• 26 Apr 2022: Cipher added.
• 18 Jan 2022: Installation procedures updated.
• 11 Apr 2018: Re-direct function added.
• 2 Sep 2018: Revised to suit Ubuntu 18.04 which requires a change of the network card device name.

Intro

OpenVPN enables remote client computers and smartphones to access VPN server's files and structure, and optionally re-direct clients' IP traffic through the VPN server.

Install VPN server for accessing file server

Switch to root:

$ sudo -s

Install openvpn and easy-rsa:

# apt-get install openvpn easy-rsa

Set up public key infrastructure:

# mkdir /etc/openvpn/easy-rsa/
# cp -r /usr/share/easy-rsa/* /etc/openvpn/easy-rsa/
# nano /etc/openvpn/easy-rsa/vars

Define in vars:

export KEY_COUNTRY="CN"
export KEY_PROVINCE="HK"
export KEY_CITY="HongKong"
export KEY_ORG="K C Tang Consultants Ltd"
export KEY_EMAIL="kctang@kctang.com.hk"
export KEY_OU=kctclVPN
export KEY_NAME=kctclVPN
# next line added to avoid error when building the certificate and key 
export KEY_ALTNAMES=kctclVPN

Generate master Certificate Authority (CA) certificate and key:

# cd /etc/openvpn/easy-rsa/
# source vars
# ./easyrsa init-pki
# ./easyrsa build-ca

Enter New CA Key Passphrase: <>

Re-enter New CA Key Passphrase: <>

Enter PEM pass phrase (if prompted): <>

Verifying - Enter PEM pass phrase (if prompted): <>

(last two lines added, 30/7/2024)

Enter Common Name: kctclVPN

Generate a key pair for the server:

# ./easyrsa gen-req kctclVPN nopass

Accept Common Name default [kctclVPN]: <enter key>

Generate Diffie Hellman parameters and generate certificate for the server

# ./easyrsa gen-dh
# ./easyrsa sign-req server kctclVPN

Check and confirm the Common Name: yes

Enter pass phrase (i.e. the PEM pass phrase if entered above, otherwise the CA Key Passphrase): <>

(last line revise to mention PEM pass phrase, 30/7/2024)

Copy certificates and keys generated in subdirectory pki/ to /etc/openvpn/:

# cp    pki/dh.pem    pki/ca.crt    pki/issued/kctclVPN.crt    pki/private/kctclVPN.key    /etc/openvpn/

Config server.conf:

# cd /
# cp    /usr/share/doc/openvpn/examples/sample-config-files/server.conf    /etc/openvpn/
# nano    /etc/openvpn/server.conf

Define as follows:

port 1194
proto udp
dev tun
# Enter the paths if files not in the same directory as the server.conf file
ca </path to file/>ca.crt
cert </path to file/>kctclVPN.crt
key </path to file/>kctclVPN.key
dh </path to file/>dh.pem # not dh2048.pem
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist /var/log/openvpn/ipp.txt
keepalive 10 120
tls-auth ta.key 0
cipher AES-256-GCM
user nobody
group nogroup
# last two lines added for linux system
persist-key
persist-tun
status /var/log/openvpn/openvpn-status.log
verb 3
explicit-exit-notify 1

(cipher added, 26 Apr 2022)

Generate ta.key for tls-auth:

# cd /etc/openvpn
# openvpn    --genkey    tls-auth    ta.key
$ openvpn --genkey secret ta.key # not --secret

Config sysctl.conf:

# nano /etc/sysctl.conf

Uncomment the following line to enable IP forwarding:

net.ipv4.ip_forward=1

Reload sysctl.conf:

# sysctl    -p    /etc/sysctl.conf

Start the server:

# systemctl    start    openvpn@server
# systemctl    status    openvpn@server

Check if OpenVPN created a tun0 interface:

# ifconfig tun0

Check syslog if tun0 does not appear:

# grep -i vpn /var/log/syslog

Exit from root:

# exit
$

Set the internet router to re-direct OpenVPN connections to server port 1194.

Extend to re-direct clients' IP traffic through VPN server

(section added 5 April 2018)

Define optionally in server.conf to re-direct clients' IP traffic such as web browsing and DNS lookups to go through the VPN server, i.e. the clients will appear to use the IP of the VPN server instead of the actual IP of the clients for internet traffic:

Config server.conf:

$ sudo nano /etc/openvpn/server.conf

Define by uncommenting the following line:

push "redirect-gateway def1 bypass-dhcp"

Some guide suggests to add the following, but this results in email server not working: (10 April 2018)

push "dhcp-option DNS 10.8.0.1"

Some other guides suggest to uncomment the following, this works: (10 April 2018)

push "dhcp-option DNS 208.67.222.222"
push "dhcp-option DNS 208.67.220.220"

However, it is found that it still works when the above two lines are left commented. Therefore, the only line needing change is the 'redirect-gateway' line. (2 Sep 2018)

Execute to restart the service:

$ sudo systemctl restart openvpn@server

Execute to see the network card device names:

$ ip route

Find the output line beginning with "default", e.g.:

default via 192.168.0.1 dev enp4s0 proto static metro 100

The name "enp4s0" after the word "dev" is the default network card device name. Previously, the default name is "eth0", but this has been changed after Ubuntu 16.04.

(2 Sep 2018)

Execute with the default name inserted after "-o":

$ sudo iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o enp4s0 -j MASQUERADE

Note that the iptables configuration will be lost after reboot.

Store the current iptables configurations:

$ sudo sh -c "iptables-save > /etc/iptables.up.rules"

View and remove any configurations no longer applicable:

$ sudo nano /etc/iptables.up.rules

Do the same whenever the iptables configurations have been changed.

Config file for use on reboot:

$ sudo nano /etc/network/interfaces

Define to reuse the stored configurations:

auto lo
iface lo inet loopback
post-up iptables-restore < /etc/iptables.up.rules

Generate files for each Windows client

Switch to root:

$ sudo -s

Generate a certificate and private key for each client user of <username>:

# cd /etc/openvpn/easy-rsa/
# ./easyrsa gen-req <username> nopass
# ./easyrsa sign-req client <username>

Check and confirm the Common Name: yes

Enter Passphrase as previously defined: <>

Copy or move client's certificate and key to a Samba directory, which is for temporary use only: to enable emailing:

# cd    /etc/openvpn/easy-rsa/
# cp    pki/ca.crt    pki/issued/<username>.crt    pki/private/<username>.key    /<Samba directory>/
# cd    /etc/openvpn/
# cp    ta.key    /<Samba directory>/ 

Change the owners of the files:

# cd    /<Samba directory>
# chown    nobody:nogroup    ca.crt ta.key    <username>.crt    <username>.key
# chmod    644    ca.crt    ta.key    <username>.crt    <username>.key

Create a <username>.txt under the Samba directory and define it to contain:

client
dev tun
proto udp
remote kctang.com.hk 1194
resolv-retry infinite
nobind
persist-key
persist-tun
mute-replay-warnings
ca ca.crt
cert <\\path\\><username>.crt
key <\\path\\><username>.key
remote-cert-tls server
tls-auth ta.key 1
cipher AES-256-GCM
auth-nocache
verb 3

(cipher added, 26 Apr 2022)

Specify path in Windows format if ca.crt, ta.key, <username>.crt, and <username>.key are to be saved in a folder different from <username>.txt.

Change filename from <username>.txt to <username>.ovpn. Creating as a txt file first permits editing by the usual text processors. Watch out that the line breaks are using Windows' linebreak code.

E-mail ca.crt, ta.key, <username>.crt, <username>.key, and <username>.ovpn files to the client computer.

Remove the files:

# rm    ca.crt    ta.key <username>.crt    <username>.key    <username>.ovpn

Exit from root:

# exit
$

Install on Windows client computer

Download and install the latest OpenVPN Windows Installer.

An OpenVPN GUI icon should appear at the bottom system tray, with no connection yet.

Save ca.crt, ta.key, <username>.crt, <username>.key, and <username>.ovpn files (emailed from the server) under:

• C:\Program Files\OpenVPN\config-auto\ (for use as a service)

or

• C:\Program Files\OpenVPN\config\ (for use with GUI).

(revised 15 Jul 2023)

Run on Windows client as a service

• Right-click OpenVPN GUI icon on Desktop.
• Click Run this program as an administrator > Yes.

Or

• Click the OpenVPN GUI icon on the bottom system tray to connect or right-click the icon and click Connect.

Map drive for quick access

• Open file manager and enter \\10.8.0.1 to access the vpn server.
• Right-click the desired folder.
• Click Map network drive.
• Choose a drive name to represent the folder.
• Click Finish.

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