来自youtube

1）进入xshell运行脚本：

yum install wget
wget https://git.io/vpnsetup-centos -O vpnsetup.sh && sudo sh vpnsetup.sh

2）安装完成后屏幕会给出取得L2TP登陆信息；样式如下：

Server IP: xxx.xx.xx.xx
IPsec PSK: xxxx
Username: xxxx
Password: xxxx

到这一步填写到windows的VPN连接似乎就可以了。

3）修改修改ipsec配置文件，vi /etc/ipsec.conf

在config setup中添加一句：nat_traversal=yes，充许传透nat建立l2tp连接；

4）配置iptables，安装iptables服务

yum install -y iptables
yum install -y iptables-services
iptables -P INPUT ACCEPT
iptables -F
iptables -F
iptables -X
iptables -Z

5）保存重启iptables

service iptables save
systemctl restart iptables

6）检查 iptables、ipsec、xl2tpd 三个服务是否是正常开启状态

systemctl status iptables
systemctl status ipsec
systemctl status xl2tpd

设置开机自启

systemctl enable ipsec
systemctl enable xl2tpd

重启

systemctl restart iptables
systemctl restart ipsec
systemctl restart xl2tpd

启动

systemctl start iptables
systemctl start ipsec
systemctl start xl2tpd