Commonly used to provide remote access to mobile devices, Point-to-Point Tunneling Protocol (PPTP) uses TCP port 1723 for key exchange and IP protocol 47 (GRE) to encrypt data between peers.
Default Port:1723
nmap –Pn -sSV -p1723 <IP>
{% embed url="https://www.schneier.com/academic/pptp/" %}
{% embed url="https://github.com/moxie0/chapcrack" %}