In this article we show you how to install and properly configure a PPTP VPN server in RHEL/CentOS linux. With this VPN you’ll have access to transfering your data encrypted and using a ethernet interface that uses your Server IP address. This tunneling technology is compatible with several devices like desktop operating systems, mobile phones and tablets.
First need enable tun module (tunelling kernel module):

# echo 'modprobe tun' >> /etc/rc.modules
# chmod +x /etc/rc.modules

At next boot will be loaded tun module in kernel
Make sure you begin with a clean install by removing any previously installed packages:

yum remove -y pptpd ppp
iptables --flush POSTROUTING --table nat
iptables --flush FORWARD
rm -rf /etc/pptpd.conf
rm -rf /etc/ppp

Installation procedure

First, install the poptop package from sourceforge:

rpm -Uhv
yum -y install make libpcap iptables gcc-c++ logrotate tar cpio perl pam tcp_wrappers dkms kernel_ppp_mppe ppp pptpd

Now, we need to enable IP forwading, set internal IP addresses and point the DNS Servers that will be used by the pptp server:

mknod /dev/ppp c 108 0
echo 1 > /proc/sys/net/ipv4/ip_forward
echo "mknod /dev/ppp c 108 0" >> /etc/rc.local
echo "echo 1 > /proc/sys/net/ipv4/ip_forward" >> /etc/rc.local
echo "localip" >> /etc/pptpd.conf
echo "remoteip" >> /etc/pptpd.conf
echo "ms-dns" >> /etc/ppp/options.pptpd
echo "ms-dns" >> /etc/ppp/options.pptpd

Then, create your users credentials for the PPTP server. This credentials will be used to log in to the PPTP server on every client/device you connect from:

nano /etc/ppp/chap-secrets

Your chap-secrets file should look like this:

# Secrets for authentication using CHAP
# client server secret IP addresses
yourusername pptpd yourpassword *

Save and close the file.
Next, you need to add the following iptables rules in order to open the correct ports and properly forward the data packets:

# VPN rules (pptpd)
iptables -A INPUT -i eth0 -p tcp --dport 1723 -j ACCEPT
iptables -A INPUT -i eth0 -p gre -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -p tcp -s -j TCPMSS --syn --set-mss 1356

Save and restart your iptables firewall:

service iptables save
service iptables restart

Make sure you load your iptables after every reboot:

chkconfig iptables on
chkconfig pptpd on

And finally, restart iptables and pptpd services:

service iptables start
service pptpd start

That is it.
Note: pptp is unsecure. Not to use it in the production machine. This article written only education purpose.
Also check out How to install and configure the OpenVPN server on CentOS 6.4 Linux