The Point to Point Tunneling Protocol (PPTP) is a method for implementing virtual private networks. PPTP uses a control channel over TCP and a GRE tunnel operating to encapsulate PPP packets.(Source: Wikipedia)
The PPTP specification does not describe encryption or authentication features and relies on the Point-to-Point Protocol being tunneled to implement security functionality. However the most common PPTP implementation, shipping with the Microsoft Windows product families, implements various levels of authentication and encryption natively as standard features of the Windows PPTP stack. The intended use of this protocol is to provide security levels and remote access levels comparable with typical VPN products. (Source: Wikipedia)
Fulfilling Prerequisite
# aptitude install pptpd
OR
# apt-get install pptpd
Go to /etc/sysctl.conf and enable forwarding
# vi /etc/sysctl.conf
Check for below line if it is commented uncomment it and change value from 0 to 1 , else add it to sysctl.conf
net.ipv4.ip_forward=1
# iptables –t nat –A POSTROUTING –j MASQUERADE
Save the iptables configuration
# iptables-save
iptables –t nat –A POSTROUTING –j MASQUERADE
iptables-save
Configuring PPTP VPN
# vi /etc/pptpd.conf
localip 10.1.0.214
remoteip 192.168.101.234-245
# vi /etc/ppp/chap-secrets
user1 pptpd PASSWORD *
user2 pptpd PASSWORD *
user3 pptpd PASSWORD *
user4 pptpd PASSWORD *
user5 pptpd PASSWORD *
user6 pptpd PASSWORD *
user7 pptpd PASSWORD *
#/etc/init.d/pptpd stop
#/etc/init.d/pptpd start