How to Build OpenVPN Server on CentOS 6.x

How to Install, Setup, Config OpenVPN on CentOS 6.4 – In this page I write full tutorial to guide you installing OpenVPN on CentOS 6.x server. I will try all the steps to be as clear as possible. Do not hesitate to ask if you have any question. Previously: How to install PPTP on CentOS 6.x (the easiest way).

What you need?

1. A VPS or Dedicated server running CentOS 6.x
2. Proper knowledge to use Putty, SSH and common Unix command
3. Only for VPS based-on OpenVZ virtualization (other skip this): please enable TUN/TAP options in your VPS control panel (e.g: SolusVM).

OpenVZ VPS users only:

How to Install OpenVPN to Build CentOS VPN server

Prerequisite

Step 0 – Login to your server via SSH. You better login as root.
Step 1 – Now issue this first command syntax:

1	yum install gcc make rpm-build autoconf.noarch zlib-devel pam-devel openssl-devel -y

screenshot:

Step 2 – Now download LZO RPM and Configure RPMForge Repo. Use wget command:

1	wget http://openvpn.net/release/lzo-1.08-4.rf.src.rpm

screenshot:

Step 3 – Now add correct repo for your server:
CentOS 6 32-bit (x86):

1	wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.2-1.el6.rf.i686.rpm

CentOS 6 64-bit (x86_64):

1	wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm

screenshot:

How to know which one is your server? Issue this command:

1

uname -a

If you see “x86_64 GNU/Linux” at the end of the output line means your server is 64-bit. Otherwise if you see “i686 i386 GNU/Linux” or “x86 GNU/Linux” means your machine is 32-bit.

Step 4 – Then build the rpm package using this command:

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rpmbuild --rebuild lzo-1.08-4.rf.src.rpm rpm -Uvh lzo-*.rpm rpm -Uvh rpmforge-release*

hit enter for each line above.

Installing OpenVPN

Step 5 – Issue the special yum command:

1	yum install openvpn -y

screenshot

Step 6 – Copy the easy-rsa folder to /etc/openvpn/, use this command:

1	cp -R /usr/share/doc/openvpn-2.2.2/easy-rsa/ /etc/openvpn/

Step 7 – Now edit it:

1	nano /etc/openvpn/easy-rsa/2.0/vars

Edit this line:

1	export KEY_CONFIG='$EASY_RSA/whichopensslcnf $EASY_RSA'

replace it with:

1	export KEY_CONFIG=/etc/openvpn/easy-rsa/2.0/openssl-1.0.0.cnf

screenshot:

once done hit Control+O to save then Control+X to exit.
Step 8 – Create the certificate using these commands:

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cd /etc/openvpn/easy-rsa/2.0 chmod 755 * source ./vars ./vars ./clean-all

hit enter for each line.

Step 9 – It’s time to build necessary CA file:

1	./build-ca

screenshot:

Hint
Country Name: may be filled or press enter
State or Province Name: may be filled or press enter
City: may be filled or press enter
Org Name: may be filled or press enter
Org Unit Name: may be filled or press enter
Common Name: your server hostname
Email Address: may be filled or press enter
Step 10 – Time to build Key Server:

1	./build-key-server server

screenshot:

Hint:
Almost the same with ./build.ca but check the changes and additional
Common Name: server
A challenge password: leave
Optional company name: fill or enter
sign the certificate: y
1 out of 1 certificate requests: y
You can simply leave them blank. The only 2 required are sign the certificate (choose “y”) and 1 out of 1 certificate requests (choose “y”)
Step 11 – Now issue command below to build Diffie Hellman:

1	./build-dh

screenshot:

Step 12 – Create OpenVPN config file:

1	nano /etc/openvpn/server.conf

Step 13 – Now enter this value in that config file:

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port 1194 #- port proto udp #- protocol dev tun tun-mtu 1500 tun-mtu-extra 32 mssfix 1450 reneg-sec 0 ca /etc/openvpn/easy-rsa/2.0/keys/ca.crt cert /etc/openvpn/easy-rsa/2.0/keys/server.crt key /etc/openvpn/easy-rsa/2.0/keys/server.key dh /etc/openvpn/easy-rsa/2.0/keys/dh1024.pem plugin /usr/share/openvpn/plugin/lib/openvpn-auth-pam.so /etc/pam.d/login #- Comment this line if you are using FreeRADIUS #plugin /etc/openvpn/radiusplugin.so /etc/openvpn/radiusplugin.cnf #- Uncomment this line if you are using FreeRADIUS client-cert-not-required username-as-common-name server 10.8.0.0 255.255.255.0 push "redirect-gateway def1" push "dhcp-option DNS 8.8.8.8" push "dhcp-option DNS 8.8.4.4" keepalive 5 30 comp-lzo persist-key persist-tun status 1194.log verb 3

Save it once done. (Control+O then Control+X)

Step 14 – Lets start OpenVPN service on your server for the very first time:

1	service openvpn start

pic:

Step 15 – You’ll also need to enable IP forwarding in the file /etc/sysctl.conf. Open it and edit “net.ipv4.ip_forward” line to 1:

1	nano /etc/sysctl.conf

replace 0 with 1 in this line:

1	net.ipv4.ip_forward = 1

pic:

Hit Control+O to save then Control+X to exit nano.
Step 16 – Issue this command to load the change:

1

sysctl -p

Step 17 – Create new Linux username which can also be used to login to the VPN:

1	useradd username -s /bin/false

replace username with your own username.
Then also create its password:

1	passwd username

pic:

Step 18 – Now route some iptables.
Xen and KVM users use:

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

special for OpenVZ use these two instead:

1	iptables -t nat -A POSTROUTING -o venet0 -j SNAT --to-source 123.123.123.123

and

1	iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -j SNAT --to-source 123.123.123.123

Do not forget to replace 123.123.123.123 with your server IP. Pic:

Step 19 – Note: if you have CSF on the same server you need to open your OpenVPN port (Usually 1194) through the firewall and run the below commands for CSF:

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iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT iptables -A FORWARD -s 10.8.0.0/24 -j ACCEPT iptables -A FORWARD -j REJECT iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE iptables -t nat -A POSTROUTING -j SNAT --to-source 123.123.123.123

Step 20 – Now save that iptables rules:

1	service iptables save

Step 21 – Finally lets create a server.ovpn config file. To make it easy, you can simply create it on your local computer using Notepad (or any other simple text editor tool). Enter following in that file:

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client dev tun proto udp remote 123.123.123.123 1194 # - Your server IP and OpenVPN Port resolv-retry infinite nobind tun-mtu 1500 tun-mtu-extra 32 mssfix 1450 persist-key persist-tun ca ca.crt auth-user-pass comp-lzo reneg-sec 0 verb 3

Then save it with .ovpn extension. Save that file in the config directory of where you installed OpenVPN client in your computer. See screenshot:

Step 22 – That’s it. Now you can copy ca.crt file from /etc/openvpn/easy-rsa/2.0/keys/ directory and place it in your server’s document root (public_html).

1	cp /etc/openvpn/easy-rsa/2.0/keys/ca.crt /path/to/public/directory

example:

1	cp /etc/openvpn/easy-rsa/2.0/keys/ca.crt /var/www/servermom.com/public_html

Now you can download the ca.crt file from your browser by going to domain.com/ca.crt then save it to the same folder as .ovpn file you created earlier.
That’s it. Now you can login to your VPN using username and password you’ve created. ENJOY..