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How to create a OpenVPN VPN Server on CentOS 6 64bit.

First let's prepare your vps. Type in the following on ssh.
yum update -y
Now you are ready to continue on the next steps.
Step 1:
You need to check if you have tun/tap enabled, and you need to download/install all the dependencies and openvpn it'self
cat /dev/net/tun
If you get "cat: /dev/net/tun: File descriptor in bad state" then you are all set! If not then ask your host to enable tun!
Step 2:
Now you need to install openvpn and it's dependencies. Run each of these commands ;
yum install gcc make rpm-build autoconf.noarch zlib-devel pam-devel openssl-devel iptables

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

rpmbuild --rebuild lzo-1.08-4.rf.src.rpm

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

rpm -Uvh lzo-*.rpm

rpm -Uvh rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm

yum install openvpn
Step 3:
Now you need to change some files, copy directories, and generate the SSL keys for your server. Execute the following commands:
cp -r /usr/share/doc/openvpn-2.2.2/easy-rsa/ /etc/openvpn/

cp -irv /etc/openvpn/easy-rsa/2.0/openssl-1.0.0.cnf /etc/openvpn/easy-rsa/2.0/openssl.cnf

cd /etc/openvpn/easy-rsa/2.0

chmod 755 *

source ./vars


Step 4: 
In the following step you can put whatever you like for certificate details, but leave the password blank by entering "." when prompted.

./build-key-server server

Step 5:
Now you need to create the openvpn server config file, run the following:
*To save and exit the server.conf file we press [ESC] and type: :x
cd /etc/openvpn

vi server.conf
local x.x.x.x #- change it with your server ip address
port 1194
proto udp
dev tun
tun-mtu 1500
tun-mtu-extra 32
mssfix 1450
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
push "redirect-gateway def1"
push "dhcp-option DNS"
push "dhcp-option DNS"
keepalive 5 30
status server-tcp.log
verb 3
Step 6:
Check your OpenVPN server is working, and configure some few extra bits for firewall, ipforwarding, auto startup, etc
*If you see “Initialization Sequence Completed.” then all is good! Press [CTRL+z] to exit.
openvpn /etc/openvpn/server.conf
Step 7:
type the following ;
chkconfig openvpn on

chkconfig iptables on
Step 8:
Now change up the iptables for the VPN to work.
*Again, press [ESC] to exit text mode and save/exit with :x
vi /etc/sysctl.conf
Change the line: net.ipv4.ip_forward = 0 TO 1
Comment out this line: # net.ipv4.tcp_syncookies = 1
After type the following to save :
sysctl -p
Step 9:
We will use SNAT instead of MASQUERADE to forward data via iptables.
Remember to replace x.x.x.x with your server IP
iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT

iptables -A FORWARD -s -j ACCEPT

iptables -t nat -A POSTROUTING -s -j SNAT --to x.x.x.x

service iptables save
Step 10:
You need to create a client config file for your VPN clients
Create a config file named NameOfVPN.ovpn and put it in your %programfiles%/OpenVPN/Config/NameOfDir/
The ovpn config file should contain the following, replace x.x.x.x with your VPN IP.
You will also need to copy the Server CA (Certificate Authority) crt file to each of your clients!
Download ca.crt from /etc/openvpn/easy-rsa/2.0/keys and put in %programfiles%/OpenVPN/Config/NameOfDir/
dev tun
proto udp
remote x.x.x.x 1194 #- your OPENVPN server ip and port
resolv-retry infinite
tun-mtu 1500
tun-mtu-extra 32
mssfix 1450
ca ca.crt
verb 3
Step 11:
Make your vpn tunnel start upon boot (adds the command to rc.local)
echo openvpn /etc/openvpn/server.conf >> /etc/rc.d/rc.local

openvpn /etc/openvpn/server.conf
Final step 12:
Your VPS will need to get rebooted so type the following;
Useful Commands:
To create a new user we type: (replace openvpn with the username)
useradd openvpn -s /bin/false
To create the password we type
passwd openvpn
To Delete a user type
userdel openvpn

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