The full name of VPN is "Virtual Private Network", which is translated as "Virtual Private Network ". As the name suggests, we can regard a virtual private network as an internal private line of an enterprise. It can establish a proprietary communication line between two or more enterprise intranets connected to the Internet in different places through special encrypted communication protocols, it is like setting up a leased line, but it does not need to lay physical lines such as optical cables. This is like applying for a leased line from the telecommunications board, but there is no need to pay for the laying of the line, or purchase a router or other hardware equipment. VPN technology was originally one of the most important technologies of routers. Currently, VPN functions are also supported in vswitches, firewall devices, Windows, and other software, the core of a VPN is to use a public network to establish a virtual private network. A Virtual Private Network (VPN) is defined as a temporary and secure connection through a public network (usually the internet). It is a secure and stable tunnel through a chaotic public network. A Virtual Private Network is an extension of the enterprise intranet. Virtual Private Network can help remote users, company branches, business partners and suppliers to establish trusted and secure connections with the company's Intranet, and ensure secure data transmission. A virtual private network can be used for the global Internet access of increasing mobile users to achieve secure connections. It can be used to implement virtual private lines for secure communication between enterprise websites, it is used to economically and effectively connect commercial partners and users to a secure, out-of-network virtual private network. PPTP is called Point to Point Tunneling Protocol-Point to Point tunnel Protocol, which is a type of VPN Protocol. 1, CentOS 5.3 pptp vpn Server installation 1, install related software 32-bit version: yum install-y ppp iptables wget http://up.2cto.com/2012/0320/20120320100657475.rar rpm-ivh pptpd-1.3.4-2.rhel5.i386.rpm 64-bit version: yum install-y ppp iptables wget http://up.2cto.com/2012/0320/20120320100710821.rar rpm-ivh pptpd-1.3.4-2.rhel5.x86_64.rpm 2. configuration file writing ①. configuration file/etc/ppp/options.ppt pd mv/etc/ppp/options.ppt pd/etc/ppp /options.ppt pd. bak vi/etc/ppp/ Options.ppt pd: name pptpd refuse-pap refuse-chap refuse-mschap require-mschap-v2 require-mppe-128 proxyarp lock nobsdcomp novj novjccomp nologfd idle 2592000 ms-dns 8.8.8.8 ms-dns 8.8.4.4 ②, configuration file/etc/ppp/chap- secrets mv/etc/ppp/chap-secrets/etc/ppp/chap-secrets.bak vi/etc/ppp/chap-secrets enter the following content # Secrets for authentication using CHAP # client server secret IP addresses myusername pptpd m Ypassword * Note: Here myusername and mypassword are the login username and password of pptp vpn ③, And the configuration file/etc/pptpd. conf mv/etc/pptpd. conf/etc/pptpd. conf. bak vi/etc/pptpd. enter the following content in conf: option/etc/ppp/options.ppt pd logwtmp localip 192.168.9.1 remoteip 192.168.9.11-30 Note: Assign 192.168.9.11 ~ IP address (4) between 192.168.9.30 and the configuration file/etc/sysctl. conf vi/etc/sysctl. conf: net. ipv4.ip _ forward = 1 save and run:/sbin/sysctl-p after exiting 3. start pptp vpn Server:/sbin/service pptpd start 4. start iptables: /sbin/service iptables start/sbin/iptables-t nat-a postrouting-o eth0-s 192.168.9.0/24-j MASQUERADE author banquet