You will have to select one server to be responsible for handling out IPs to others and authenticating all of your servers into your VPN. This will become your PPTP Server.

On CentOS 6 x64:

rpm -i http://poptop.sourceforge.net/yum/stable/rhel6/pptp-release-current.noarch.rpm
yum -y install pptpd

On Ubuntu 12.10 x64:

apt-get install pptpd

Now you should edit /etc/pptpd.conf and add the following lines:

localip 10.0.0.1
remoteip 10.0.0.100-200

Where localip is IP address of your server and remoteip are IPs that will be assigned to clients that connect to it.

Next, you should setup authentication for PPTP by adding users and passwords. Simply add them to /etc/ppp/chap-secrets :

Where client is the username, server is type of service – pptpd for our example, secret is the password, and IP addresses specifies which IP address may authenticate. By setting ‘*’ in IP addresses field, you specify that you would accept username/password pair for any IP.

ms-dns 8.8.8.8
ms-dns 8.8.4.4

Now you can start PPTP daemon:

service pptpd restart

Verify that it is running and accepting connections:

It is important to enable IP forwarding on your PPTP server. This will allow you to forward packets between public IP and private IPs that you setup with PPTP. Simply edit /etc/sysctl.conf and add the following line if it doesn’t exist there already:

net.ipv4.ip_forward = 1

To make changes active, run sysctl -p

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE && iptables-save

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

iptables --table nat --append POSTROUTING --out-interface ppp0 -j MASQUERADE
iptables -I INPUT -s 10.0.0.0/8 -i ppp0 -j ACCEPT
iptables --append FORWARD --in-interface eth0 -j ACCEPT

Now your PPTP server also acts as a router.

If you would like to restrict which servers can connect to your droplets, you can setup an iptables rule that restricts TCP connects to port 1723.

On your client servers, install PPTP client:

yum -y install pptp

modprobe ppp_mppe

Create a new file /etc/ppp/peers/pptpserver and add the following lines, replacing name and password with your own values:

pty "pptp 198.211.104.17 --nolaunchpppd"
name box1
password 24oiunOi24
remotename PPTP
require-mppe-128

Where 198.211.104.17 is the public IP address of our PPTP server, with username ‘box1’ and password ‘24oiunOi24’ that we specified /etc/ppp/chap-secrets file on our PPTP server.

Now we can ‘call’ this PPTP server, since this is a point-to-point protocol. Whichever name you gave your peers file in/etc/ppp/peers/ should be used in this next line. Since we called our file pptpserver:

pppd call pptpserver

You should see successful connection from PPTP server logs:

On your PPTP client, setup routing to your private network via ppp0 interface:

ip route add 10.0.0.0/8 dev ppp0

Your interface ppp0 should come up on PPTP client server, and can be checked by running ifconfig

Now you can ping your PPTP server and any other clients that are connected to this network:

We can add our second PPTP client to this network:

yum -y install pptp
modprobe ppp_mppe

Add to /etc/ppp/peers/pptpserver (replacing with your own name and password values):

pty "pptp 198.211.104.17 --nolaunchpppd"
name box2
password 239Aok24ma
remotename PPTP
require-mppe-128

Now run on your second client the following:

pppd call pptpserver
ip route add 10.0.0.0/8 dev ppp0

You can also ping the first client, as packets would go through the PPTP server and be routed using the iptables rules we’ve placed earlier:

This setup allows you to create your own virtual private network:

If you wanted to have all of your devices communicating securely on one network, this is a quick way of implementing it.

You can use it with Nginx, Squid, MySQL, and any other application you can think of.

Since traffic is 128-bit encrypted, it is less CPU-intensive than OpenVPN, and still provides an added level of security to your traffic.