http://www.360doc.com/content/14/0304/09/15165033_357558764.shtml
. apt-get update; apt-get install pptpd
. vim /etc/pptpd.conf # 修改客户端 ip 范围
. vim /etc/ppp/options # 修改 ms-dns
. vim /etc/ppp/chap-secrets # 添加用户名密码
. sysctl -w net.ipv4.ip_forward=
vim /etc/sysctl.conf # 开启 ip_forward
. iptables -t nat -A POSTROUTING -s 192.168.0.0/ -j MASQUERADE # 地址伪装