apt-get install pptpd
nano /etc/pptpd.conf
localip 10.0.0.1 remoteip 10.0.0.100-200
Setup authentication
adding users and passwords. Simply add them to /etc/ppp/chap-secrets
nano /etc/ppp/chap-secrets
Add DNS Servers
nano /etc/ppp/pptpd-options
ms-dns 8.8.8.8 ms-dns 8.8.4.4
service pptpd restart
Setup Forwarding
nano /etc/sysctl.conf net.ipv4.ip_forward = 1 sysctl -p
Create a NAT rule for iptables
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
Preserving Iptables Rules
https://pupli.net/2017/12/22/set-up-openconnect-vpn-server-ocserv-on-ubuntu-16-04-17-10-with-lets-encrypt
References
https://www.digitalocean.com/community/tutorials/how-to-setup-your-own-vpn-with-pptp