Although it is well-known that pptp is not secure and is subject to many forms of attacks, the reality is that a lot of legacy and embedded devices use pptp. I argue that if it is being used for routing or remote access or over an already secure connection (eg. another VPN like ikev2) then this is still acceptable. Or in a LANor in a public environment where no private data is exchanged. However, if the nature of the data is extremely sensitive, you should do whatever........
Remember that control connections are established on port 1723 and then actual data is transferred over GRE protocol 47.
If you have a NAT setup this will work without special forwarding or accepting of GRE packets (normally if you are not blocking outgoing connections and accepting established and related connections).
The below two commands will get things going so PPTP and GRE work
We first load the ip_nat_pptp module which allows PPTP to work with........