PPTP

download pptpd for redhat based 64bit
http://poptop.sourceforge.net/yum/stable/packages/pptpd-1.4.0-1.el6.x86_64.rpm

download pptpd for redhat based 32bit
http://poptop.sourceforge.net/yum/stable/packages/pptpd-1.4.0-1.el6.i686.rpm

OS: CentOS 6 64bit
VPN server:  192.168.0.2
VPN client IP: 192.168.10.10 - 192.168.10.70
VPN username: vpnuser
Password: myVPN$99

1. Install ppp via yum:

$ yum install ppp -y

2. Download and install pptpd (the daemon for point-to-point tunneling). You can find the correct package at this website http://poptop.sourceforge.net/yum/stable/packages/  OR go above link at top of page:

$ cd /usr/local/src $ wget http://poptop.sourceforge.net/yum/stable/packages/pptpd-1.3.4-2.el6.x86_64.rpm $ rpm -Uhv pptpd-1.3.4-2.el6.x86_64.rpm

3. Once installed, open /etc/pptpd.conf using text editor and add following line:

localip 192.168.10.1 //your ip remoteip 192.168.10.10-70 //ip for remote distribution

4. Open /etc/ppp/options.pptpd and add  authenticate method, encryption and DNS resolver value:

require-mschap-v2 require-mppe-128 ms-dns 8.8.8.8

5. create user to access the VPN server. Open /etc/ppp/chap-secrets and add the user as below:

vpnuser pptpd myVPN$99 *

The format is: [username] [space] [server] [space] [password] [space][IP addresses]

6. We need to allow IP packet forwarding for this server. Open /etc/sysctl.conf via text editor and change line below:

net.ipv4.ip_forward = 1

7. Run following command to take effect on the changes:

$ sysctl -p

8. Allow IP masquerading in IPtables by executing following line:

$ iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE $ service iptables save $ service iptables restart

Update: Once you have done with step 8, check the rules at /etc/sysconfig/iptables. Make sure that the POSTROUTING rules is above any REJECT rules.
9. Turn on the pptpd service at startup and reboot the server:

$ chkconfig pptpd on $ init 6

Once the server is online after reboot, you should now able to access the PPTP server from the VPN client. >> monitor /var/log/messages for ppp and pptpd related log

If you would also like your PPTP clients to talk to each other, add the following iptables rules:

iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -I INPUT -s 10.0.0.0/8 -i ppp0 -j ACCEPT
iptables -A FORWARD --in-interface eth0 -j ACCEPT