install pptp
$ sudo apt-get instal pptp
insert line in /etc/pptpd.conf
localip 192.168.0.1 remoteip 192.168.0.2-10
dns setting
insert line into /etc/ppp/options.pptpd
ms-dsn 8.8.8.8
add account
insert line into /etc/ppp/chap-secrets user-account <tab> pptp <tab> password <tab> *
nat setting
/etc/sysctl.conf net.ipv4.ip_forward = 1
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
iptables -t nat -A POSTROUTING -s 10.8.0.0/255.255.255.0 -o eth0 -j MASQUERADE