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OpenVPN - How to Set Up a Slackware Server and a Slackware Client

1. Introduction

1.1. OpenVPN(1)

OpenVPN is an open source software application that implements virtual private network (VPN) techniques for creating secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities. It uses a custom security protocol that utilizes SSL/TLS for key exchange. It is capable of traversing network address translators (NATs) and firewalls. It was written by James Yonan and is published under the GNU General Public License (GPL).

OpenVPN allows peers to authenticate each other using a pre-shared secret key, certificates, or username/password. When used in a multiclient-server configuration , it allows the server to release an authentication certificate for every client, using signature and Certificate authority. It uses the OpenSSL encryption library extensively, as well as the SSLv3/TLSv1 protocol, and contains many security and control features.

2. Scope and Objective

The objective of this how-to is to serve as a tutorial for the readers to set up a basic but functional Slackware VPN Server and Client over the Internet.

The emphasis of this tutorial is to provide you with a reliable method that you can easily follow to setup OpenVPN on Slackware Servers and Clients. Nevertheless the process is still not free from pitfalls and require some attention and determination to set up.

This document comprises of a selection of other similar tutorials found on the Internet. In particular the methods described here were extracted from References (2) and (3). However these were cutomised to satisfy the objective.

3. Installation

Openvpn is already installed on Slackware if a default installation was followed. If this was not the case, then it is available from the “n” directory of the Slackware DVD. Refer to other Slackware specific documents on how to go about this installation.

If you want to confirm that Openvpn is indeed installed, you can check it by listing the /var/log/packages/ directory:

# ls /var/log/packages/openvpn*
/var/log/packages/openvpn-2.2.2-i486-1

4. Requirements

A Server and a Client computers would be needed. They would have to be connected to the Internet on two different Routers and different Network Routes. For the purpose of this tutorial, specific details are defined in order to enhance the readability. Of course, you will probably have a different addresses, so you will need to amend accordingly.

4.1. Server DNS

A URL is normally used to address the Server. This is not mandatory and instead you may use only the Internet IP. However I recommend using a URL for the Server, especially if it is connected to a dynamic IP, which is typical for domestic Internet connections. The author is using noip2(4) as it is free upon subscription. Noip2 is available from http://slackbuilds.org.

4.2. Server details

hostname: server1
IP: 192.168.200.199/255.255.255.0
URL:  servervpn.no-ip.org
Network Interface: eth0

4.3. Client details

hostname: client1
IP: 192.168.1.234/255.255.255.0
Network Interface: wlan0

4.3 Administrator Rights

You will need to have administrator rights to set up the Openvpn. This applies to both the Server and the Client. In this tutorial, it will be assumed that all actions will be performed by the root user.

4.4 Possible Constraints and Possible Solutions for a WiFi equipped Client

The availability of two Routers might be challenging. Consider that interactive sessions on both the Server and Client will be needed before the VPN is set up. If the Client is equipped with a WiFi interface there might be some easy solutions that may be considered:

  1. Use a 3G smart phone's “Portable Wi-Fi Hot Spot” facility to connect the Client as the VPN Client. As 3G bandwidth is expensive you may want to minimise traffic. For example, you might want to switch off services that are not absolutely essential during the course of this exercise, such as ntpd, dropbox and tor.
  2. Connect the Client to another WiFi available in the vicinity of the Server. Some lucky people live in areas were benevolent neighbours provide them with openly accessible Internet WiFi. It is recommended to request permission before taking up this solution. In case that no such open service exists, you may find it appropriate to request a temporary password from a friendly neighbour for the private encrypted WiFi service.
  3. Nowadays, many governmental premises, such as libraries and Local Councils provide free WiFi service. Other places such as fast food outlets, pubs, cafés, etc. also provide free WiFi from their location to their valuable customers. You may access the Server via an available service such as SSH from a WiFi equipped Client. If this option is chosen for this solution, be aware that the Client may have to pass through some firewalls. Besides the VPN connection might be a breach of the terms of conditions that should be accepted before using the WiFi service.

5. Creating a Public Key Infrastructure (PKI) using the easy-rsa Scripts

The PKI may be created on any computer with an Openvpn installation, but it is probably more sensible to be done on the Server. In any case, in this tutorial it will be assumed that this is the case.

The easy-rsa scripts referred to in this chapter reside in the /usr/doc/ directory.

It is not recommended to use this directory to create the PKI. This directory may be overwritten by an Openvpn package upgrade, and some files that will be created, should kept secret as otherwise the security of the created VPN would be compromised.

Copy the whole easy-rsa directory to root's home directory.

# cp -r /usr/doc/openvpn-2.2.2/easy-rsa /root 
# cd /root/easy-rsa/2.0/

Find the vars file. As a minimum it is recommended to edit the following:

KEY_COUNTRY
KEY_PROVINCE
KEY_ORG
KEY_EMAIL

The purpose of this recommendation is to assure consistency in the default values of some following steps that need to be followed. You should not be really worried about the exact meaning or the correctness of the chosen entries as the actual values will have no bearing on the success or failure of this exercise.

The following is my complete vars file. You may note some additional entries that were entered. Most of these are meant to enhance the range of default values that will be immediately available, thus increasing the chances of a successful creation of the PKI.

# easy-rsa parameter settings 

# NOTE: If you installed from an RPM, 
# don't edit this file in place in 
# /usr/share/openvpn/easy-rsa -- 
# instead, you should copy the whole 
# easy-rsa directory to another location 
# (such as /etc/openvpn) so that your 
# edits will not be wiped out by a future 
# OpenVPN package upgrade. 

# This variable should point to 
# the top level of the easy-rsa 
# tree. 
export EASY_RSA="`pwd`" 

# 
# This variable should point to 
# the requested executables 
# 
export OPENSSL="openssl" 
export PKCS11TOOL="pkcs11-tool" 
export GREP="grep" 


# This variable should point to 
# the openssl.cnf file included 
# with easy-rsa. 
export KEY_CONFIG=`$EASY_RSA/whichopensslcnf $EASY_RSA` 

# Edit this variable to point to 
# your soon-to-be-created key 
# directory. 
# 
# WARNING: clean-all will do 
# a rm -rf on this directory 
# so make sure you define 
# it correctly! 
export KEY_DIR="$EASY_RSA/keys" 

# Issue rm -rf warning 
echo NOTE: If you run ./clean-all, I will be doing a rm -rf on $KEY_DIR 

# PKCS11 fixes 
export PKCS11_MODULE_PATH="dummy" 
export PKCS11_PIN="dummy" 

# Increase this to 2048 if you 
# are paranoid.  This will slow 
# down TLS negotiation performance 
# as well as the one-time DH parms 
# generation process. 
export KEY_SIZE=2048 

# In how many days should the root CA key expire? 
export CA_EXPIRE=3650 

# In how many days should certificates expire? 
export KEY_EXPIRE=3650 

# These are the default values for fields 
# which will be placed in the certificate. 
# Don't leave any of these fields blank. 
export KEY_COUNTRY="MT" 
export KEY_PROVINCE="Malta" 
export KEY_CITY="Valletta" 
export KEY_ORG="ABCDEF Co. Ltd." 
#export KEY_EMAIL="me@myhost.mydomain" 
export KEY_EMAIL=support@abcdef.com 
export KEY_CN=server1 
export KEY_NAME=server1 
export KEY_OU="" 
export PKCS11_MODULE_PATH=changeme 
export PKCS11_PIN=1234 

Source the vars file:

# source ./vars
NOTE: If you run ./clean-all, I will be doing a rm -rf on /root/easy-rsa/2.0/keys

Proceed like this:

# ./clean-all
# ./build-ca
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) [MT]: 
State or Province Name (full name) [Malta]: 
Locality Name (eg, city) [Valletta]: 
Organization Name (eg, company) [ABCDEF Co. Ltd.]: 
Organizational Unit Name (eg, section) []: 
Common Name (eg, your name or your server's hostname) [server1]: 
Name [server1]: 
Email Address [support@abcdef.com]: 

Hint: The less information you enter, the less likely it will cause you problems later on.

# ./build-key-server server1

Do not enter a challenge password or company name when prompted.

Generating a 2048 bit RSA private key 
........................+++ 
................................................+++ 
writing new private key to 'server1.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) [MT]: 
State or Province Name (full name) [Malta]: 
Locality Name (eg, city) [Valletta]: 
Organization Name (eg, company) [ABCDEF Co. Ltd.]: 
Organizational Unit Name (eg, section) []: 
Common Name (eg, your name or your server's hostname) [server1]: 
Name [server1]: 
Email Address [support@abcdef.com]: 

Please enter the following 'extra' attributes 
to be sent with your certificate request 
A challenge password []: 
An optional company name []: 
Using configuration from /root/easy-rsa/2.0/openssl-1.0.0.cnf 
Check that the request matches the signature 
Signature ok 
The Subject's Distinguished Name is as follows 
countryName           :PRINTABLE:'MT' 
stateOrProvinceName   :PRINTABLE:'Malta' 
localityName          :PRINTABLE:'Valletta' 
organizationName      :PRINTABLE:'ABCDEF Co. Ltd.' 
commonName            :PRINTABLE:'server1' 
name                  :PRINTABLE:'server1' 
emailAddress          :IA5STRING:'support@abcdef.com' 
Certificate is to be certified until Jan 18 19:37:43 2023 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 
# ./build-dh
This is going to take a long time 
..................+........................................................................................................... 
.................................................................
# ./build-key client1

Do not enter a challenge password or company name when prompted.

Generating a 2048 bit RSA private key 
...............................................................................................+++ 
..+++ 
writing new private key to 'client1.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) [MT]: 
State or Province Name (full name) [Malta]: 
Locality Name (eg, city) [Valletta]: 
Organization Name (eg, company) [ABCDEF Co. Ltd.]: 
Organizational Unit Name (eg, section) []: 
Common Name (eg, your name or your server's hostname) [client1]: 
Name [server1]: 
Email Address [support@abcdef.com]: 

Please enter the following 'extra' attributes 
to be sent with your certificate request 
A challenge password []: 
An optional company name []: 
Using configuration from /root/easy-rsa/2.0/openssl-1.0.0.cnf 
Check that the request matches the signature 
Signature ok 
The Subject's Distinguished Name is as follows 
countryName           :PRINTABLE:'MT' 
stateOrProvinceName   :PRINTABLE:'Malta' 
localityName          :PRINTABLE:'Valletta' 
organizationName      :PRINTABLE:'ABCDEF Co. Ltd.' 
commonName            :PRINTABLE:'client1' 
name                  :PRINTABLE:'server1' 
emailAddress          :IA5STRING:'support@abcdef.com' 
Certificate is to be certified until Jan 18 19:42:33 2023 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 
# openvpn --genkey --secret /root/easy-rsa/2.0/keys/ta.key

6. Setting up the Server

Copy the following files generated by the easy-rsa scripts to their respective directories in the /etc/openvpn/ directory:

# cp /root/easy-rsa/2.0/keys/{ca.crt,server1.crt,dh2048.pem} \
> /etc/openvpn/certs/
# cp /root/easy-rsa/2.0/keys/{server1.key,ta.key} \
> /etc/openvpn/keys/

Restrict the permission of /etc/openvpn/keys/

# chmod 700 /etc/openvpn/keys

On the Server machine copy the sample server.conf onto the openvpn's configuration directory.

# cp /usr/doc/openvpn-2.2.2/sample-config-files/server.conf \
> /etc/openvpn/

Edit the following lines of /etc/openvpn/server.conf

From these lines:

ca ca.crt
cert server.crt
key server.key  # This file should be kept secret


dh dh1024.pem
;tls-auth ta.key 0 # This file is secret

;user nobody 
;group nobody

To

ca /etc/openvpn/certs/ca.crt 
cert /etc/openvpn/certs/server1.crt 
key /etc/openvpn/keys/server1.key #This file should be kept secret

dh /etc/openvpn/certs/dh2048.pem

tls-auth /etc/openvpn/keys/ta.key 0 # This file is secret

user nobody 
group nobody

Note that comments in server.conf may be either start with # or ; In order to help you with entering parameters, the former are used to comment out text while the latter are for commented out configuration lines.

Copy the rc.openvpn-server listed hereunder and place under /etc/rc.d/

#!/bin/sh 
# 
# /etc/rc.d/rc.openvpn-server 
# 
# Start/stop/restart the openvpn server. 
# 
# To make OpenVPN start automatically at boot, make this 
# file executable:  chmod 755 /etc/rc.d/rc.openvpn-server 
# 

ovpn_start() { 
  if [ -x /usr/sbin/openvpn -a -r /etc/openvpn/server.conf ]; then 
    echo "Starting OpenVPN:  /usr/sbin/openvpn server.conf" 
    /usr/sbin/openvpn /etc/openvpn/server.conf & 
  fi 
} 

ovpn_stop() { 
  killall openvpn 
} 

ovpn_restart() { 
  ovpn_stop 
  sleep 2 
  ovpn_start 
} 

case "$1" in 
'start') 
  ovpn_start 
  ;; 
'stop') 
  ovpn_stop 
  ;; 
'restart') 
  ovpn_restart 
  ;; 
*) 
  echo "Usage: $0 {start|stop|restart}" 
esac

Then give it executable permissions:

# chmod 755 /etc/rc.d/rc.openvpn-server

7. Port Forwarding

You will need to forward traffic from the port you have chosen for Openvpn to be routed to the Server. To accomplish this you will need to provide your Server with a fixed IP and you will need to configure your router. You may use netconfig, wicd or network-manager to set the fixed IP on Slackware. Then you also need to consult the documentation provided with your router to set up the selected IP address reserved for the Server, and the port forwarding. For our default Openvpn set up, the UDP Port would be 1194.

In case if you have misplaced such documentation, you may search on the Internet on how this may be achieved. A good place to start is http://portforward.com/. Astute readers are warned that typical port scanning tools like nmap might not be able to detect your open ports at this stage.

8. Setting up the Client

On the client machine perform the following instructions to set it up.

# cp /usr/doc/openvpn-2.2.2/sample-config-files/client.conf \
> /etc/openvpn/

Edit the following lines of /etc/openvpn/client.conf

remote my-server-1 1194

;user nobody 
;group nobody 

ca ca.crt 
cert client.crt 
key client.key 

;tls-auth ta.key 1

to the following lines:

remote servervpn.no-ip.org 1194

user nobody 
group nobody 

ca /etc/openvpn/certs/ca.crt 
cert /etc/openvpn/certs/client1.crt 
key /etc/openvpn/keys/client1.key 

tls-auth /etc/openvpn/keys/ta.key 1

Note that comments in client.conf may be either # or ; The former are used to comment out text while the latter are for commented out configuration lines. This should help you a lot in the configuration process.

You will need the following files that were generated by the easy-rsa scripts:

ca.crt
client1.crt
client1.key
ta.key

Place these files as indicated in client.conf. So ca.crt and client1.crt go under /etc/openvpn/certs/ while client1.key and ta.key go under /etc/openvpn/keys/

Copy the following rc.openvpn-client listed hereunder and place under /etc/rc.d/

#!/bin/sh 
# 
# /etc/rc.d/rc.openvpn-client 
# 
# Start/stop/restart the openvpn client. 
# 

ovpn_start() { 
  if [ -x /usr/sbin/openvpn -a -r /etc/openvpn/client.conf ]; then 
    echo "Starting OpenVPN:  /usr/sbin/openvpn client.conf" 
    /usr/sbin/openvpn /etc/openvpn/client.conf & 
  fi 
} 

ovpn_stop() { 
  killall openvpn 
} 

ovpn_restart() { 
  ovpn_stop 
  sleep 2 
  ovpn_start 
} 
 
case "$1" in 
'start') 
  ovpn_start 
  ;; 
'stop') 
  ovpn_stop 
  ;; 
'restart') 
  ovpn_restart 
  ;; 
*) 
  echo "Usage: $0 {start|stop|restart}" 
esac

Then give it executable permissions:

# chmod +x /etc/rc.d/rc.openvpn-client

9. Testing the VPN

On the Server:

# /etc/rc.d/rc.openvpn-server start

On the Client:

# /etc/rc.d/rc.openvpn-client start

On both you should see a new network interface called tun0. On the Server, I obtained the following:

# ifconfig tun0 
tun0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST>  mtu 1500 
        inet 10.8.0.1  netmask 255.255.255.255  destination 10.8.0.2 
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 100  (UNSPEC) 
        RX packets 0  bytes 0 (0.0 B) 
        RX errors 0  dropped 0  overruns 0  frame 0 
        TX packets 0  bytes 0 (0.0 B) 
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0 

Similarly on the Client:

# ifconfig tun0 
tun0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST>  mtu 1500 
        inet 10.8.0.6  netmask 255.255.255.255  destination 10.8.0.5 
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 100  (UNSPEC) 
        RX packets 0  bytes 0 (0.0 B) 
        RX errors 0  dropped 0  overruns 0  frame 0 
        TX packets 0  bytes 0 (0.0 B) 
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Naturally you can ping the Server from Client (or vice versa):

For example, from the Client:

# ping -c 3 10.8.0.1
PING 10.8.0.1 (10.8.0.1) 56(84) bytes of data. 
64 bytes from 10.8.0.1: icmp_req=1 ttl=64 time=2888 ms 
64 bytes from 10.8.0.1: icmp_req=2 ttl=64 time=1997 ms 
64 bytes from 10.8.0.1: icmp_req=3 ttl=64 time=1324 ms 

--- 10.8.0.1 ping statistics --- 
3 packets transmitted, 3 received, 0% packet loss, time 1999ms 
rtt min/avg/max/mdev = 1324.475/2070.293/2888.429/640.527 ms, pipe 3

To start the openvpn service automatically on boot-up from the Server, include these lines in /etc/rc.d/rc.local

# Start the OpenVPN Server
if [ -x /etc/rc.d/rc.openvpn-server ]; then 
  /etc/rc.d/rc.openvpn-server start 
fi

10. IP Routing

Up to now we have created a tunnel device on both the Server and the Client called tun0 which is visible only to these two machines. However more work is needed to route the Client's connection via tun0 and then to the WAN that is connected to the Server.

10.1 Server Configuration

Enable IP forwarding:

# chmod +x /etc/rc.d/rc.ip_forward
# /etc/rc.d/rc.ip_forward start

IP forwarding is now enabled and will be enabled also after you reboot.

Make a directory called ccd in /etc/openvpn

# mkdir /etc/openvpn/ccd/

Create a file with the same name of the client (in this case client1) and enter the following line in /etc/openvpn/ccd/client1

iroute 192.168.1.0 255.255.255.0

Replace 192.168.1.0 255.255.255.0 by the Network Route of your Client.

Similarly edit /etc/openvpn/server.conf with the following lines:

push "route 192.168.200.0 255.255.255.0"

client-config-dir ccd 
route 192.168.1.0 255.255.255.0 

push "redirect-gateway def1 bypass-dhcp"

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

Naturally replace 192.168.200.0 255.255.255.0 with the Server's Network Route, and 192.168.1.0 255.255.255.0 with the Client's Network Route.

208.67.222.222 and 208.67.220.220 are the OpenDNS IP addresses. Up to now the DNS push configuration has not been successful. You can either use the original Client DNS servers or else you may edit /etc/resolv.conf manually. However it is still worth trying to use the DNS servers listed by the Client, I find that they are generally still be available from the Server's Network, so you would not need to do anything.

Next you will have to configure some iptables NAT forwarding on the Server (only). You can do this by first flushing the iptables:

# iptables -F

And then:

# iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

On Slackware, such a line may be included in /etc/rc.d/rc.firewall and /etc/rc.d/rc.inet2 will run it each time you reboot the Server if the former has executable permissions. You do not have to include anything in /etc/rc.d/rc.local.

The exact lines which you need to include depend on whether you already entered your own iptables filter chains and rules, but I will assume that that this is not the case.

As already explained, as a minimum you only need to enter the following lines in /etc/rc.d/rc.firewall

#!/bin/sh
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

If on the other hand you would like a better firewall and you are at least moderately confident with iptables, I propose the following script to be included in your /etc/rc.d/rc.firewall. The comments in the script should help you understand the impact they will have on the Server.

#!/bin/sh 
# Start/stop/restart the firewall 
# A VPN server iptable filter rules 
 
IPT=/usr/sbin/iptables # This will provide some portability 

firewall_start() { 

  # flush the iptables 
  $IPT -F 

  # policies 
  $IPT -P OUTPUT ACCEPT 
  $IPT -P INPUT DROP 
  $IPT -P FORWARD DROP 
  $IPT -N SERVICES # services is a custom chain 

  # allowed inputs 
  #$IPT -A INPUT -i lo -j ACCEPT # Uncomment if the Server is a desktop 
  $IPT -A INPUT -j SERVICES # Append the services chain to the input 

  # allowed forwards 
  $IPT -A FORWARD -i eth0 -o tun0 -m state --state ESTABLISHED,RELATED -j ACCEPT 
  $IPT -A FORWARD -s 10.8.0.0/24 -o eth0 -j ACCEPT 

  # masquerade the openvpn network 
  $IPT -t nat -A POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -o eth0 -j MASQUERADE 

  # allow responses 
  $IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT 

  # allow services 

  # allow vpn on the default udp port 1194 
  $IPT -A SERVICES -p udp --dport 1194 -j ACCEPT 

  # allow sshd on the default tcp port 22 
  $IPT -A SERVICES -p tcp --dport 22 -j ACCEPT 

} 

firewall_stop() { 

  # polcies (permissive) 
  $IPT -P INPUT ACCEPT 

  # flush the iptables 
  $IPT -F 

  # delete the services custom chain 
  $IPT -X SERVICES 
} 

case "$1" in 
'start') 
  firewall_start 
  ;; 
'stop') 
  firewall_stop 
  ;; 
'restart') 
  firewall_stop 
  firewall_start 
  ;; 
*) 
  echo "Usage $0 start|stop|restart" 
esac

Give the firewall rc script executable permission:

# chmod +x /etc/rc.d/rc.firewall

and start it:

# /etc/rc.d/rc.firewall start

Now you will you need to do is to restart the OpenVPN service on the Server and restart the Client connection.

11. Firewalls

In the previous chapter we referred to a firewall you may include to protect your Openvpn Server. However this chapter refers to firewalls on the Client LAN that may block the VPN connection by blocking traffic on UDP port 1194.

In order to penetrate through the Client firewall your may want to try changing the port to 443 - normally reserved for https. Using TCP instead of UDP will also help. To make these change you will need to amend /etc/openvpn/server.conf of the Server, from

port 1194
proto udp

to:

port 443
proto tcp

and /etc/openvpn/client.conf of the Client, from

proto udp

remote servervpn.no-ip.org 1194

to:

proto tcp

remote servervpn.no-ip.org 443

The Server's firewall script would also need to be modified. Change these lines:

# allow vpn on the default udp port 1194 
$IPT -A SERVICES -p udp --dport 1194 -j ACCEPT 

to:

# allow vpn on the custom tcp port 443 
$IPT -A SERVICES -p tcp --dport 443 -j ACCEPT 

You also have to modify your Router's port forwarding to TCP port 443.

12. References


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