Some infos About PPTP :
1) Basic : Point-to-Point Tunneling Protocol - Wikipedia, the free encyclopedia
2) Advance : http://www.ietf.org/rfc/rfc2637.txt


First you must install PPTP server. You must be sudoer.

Code:

# sudo apt-get install pptpd

And then you must edit config file

Code:

# sudo nano /etc/pptpd.conf

And then you must choose IP address for your server(using localip SERVER_IP) and then address range for clients(using remoteip). use invalid IP addresses for local and remote (10.0.0.0/24, 172.16.0.0/12, 192.168.0.0/16)

Code:

For example :
localip 10.0.0.1
remoteip 10.0.0.2-100

Ctrl+O then Enter finally Ctrl+X

and then you must select primary and secondary DNS servers :

Code:

# sudo nano /etc/ppp/pptpd-options

What is DNS ?
Basic : http://en.wikipedia.org/wiki/Domain_Name_System
Advance : http://www.ietf.org/rfc/rfc1035.txt

Code:

For example:
ms-dns 8.8.8.8 #google dns server
ms-dns 4.2.2.4 #sun's

An then you must add some usernames and passwords :

Code:

# sudo nano /etc/ppp/chap-secrets

for example :

Code:

# client        server  secret                  IP addresses
test pptpd test *

Ctrl+O then Enter finally Ctrl+X

client : Username
server : pptpd for this
secret : Password
IP addresses : to restrict this client to a special IP range

And then you must start the server :

Code:

# /etc/init.d/pptpd restart

And then you must enable port forwarding for IPV4

Code:

# sudo nano /etc/sysctl.conf

Than Uncommment this line :

Code:

net.ipv4.ip_forward=1

Ctrl+O then Enter finally Ctrl+X

Then you must load new configs :

Code:

# sudo sysctl -p

Finally you must add forwarding rule to iptable(linux's firewall)

Code:

# sudo nano /etc/rc.local

Add this rule to forward incoming packet through eth0:

Code:

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

Ctrl+O then Enter finally Ctrl+X