What are the limitations of PPTP in pfSense
| PPTP is no longer considered a secure VPN technology because it relies upon MS-CHAPv2 which has been compromised. If you continue to use PPTP be aware that intercepted traffic can be decrypted by a third party, so it should be considered unencrypted. We advise migrating to another VPN type such as OpenVPN or IPsec.
More information on this can be found at https://isc.sans.edu/diary/End+of+Days+for+MS-CHAPv2/13807 and https://www.cloudcracker.com/blog/2012/07/29/cracking-ms-chap-v2/
There are two limitations of PPTP in pfSense, due to limitations in the NAT capabilities of pf.
1. If the PPTP server is enabled, no clients behind the firewall can connect to a PPTP server on the Internet if they have NAT applied to the same public IP used by the PPTP server on pfSense. If another public IP is available, it can be used to NAT the PPTP traffic destined for a specific remote server out that way. See this how-to.
2. Only one client can connect to a given PPTP server on the Internet simultaneously. 10 clients can connect to 10 different servers, but only a single simultaneous connection can exist to a single remote server.
In addition to these limitations on pfSense, PPTP in general has many limitations, especially from a security standpoint. As stated in the warning above, it should not be used no matter how strongly a client pushes to have it enabled.