PPTP is a tunneling protocol, not a complete VPN protocol itself. Although encryption and authentication are handled through the Point-to-Point Protocol (PPP), PPP does not include a routing mechanism to direct the packet to its destination.

PPTP establishes a TCP connection with the VPN server through port 1723, and uses Generic Routing Encapsulation (GRE) to repackage the PPPIP packet. Use Microsoft Point-to-Point Encryption (MPPE) to encrypt these packets, it uses RSARC4 stream cipher, and the maximum key size is 128 bits.

Authentication is usually implemented using the MS-CHAP (currently using v2) protocol. (AEP-TLS can be used more securely, but this requires the implementation of a server certificate system, which largely negates the advantages of PPTP.)

The Point-to-Point Tunneling Protocol (PPTP) is used to protect the connection between your device and the VPN server. PPTP is one of the oldest VPN protocols. It has been plagued by many security issues and is now considered obsolete.

Nevertheless, it is widely compatible with a large number of traditional software and hardware, easy to set up, lightweight features, and the high cost of upgrading the old PPTP corporate intranet VPN system for enterprises, means that the protocol can still be widely used in 2021 .

What is the VPN protocol?

The VPN protocol mixes transmission protocols and encryption standards. It can establish a secure connection between your device and the VPN server, and encrypt the data when it is transmitted between these servers.

The VPN protocol should provide three points:

• Authentication-Prevent unauthorized users from connecting to the VPN server.

• Confidentiality-the use of encryption to ensure that no one can access ("sniff") the content of information packets sent through the VPN network.

• Integrity-check whether the transmitted data has been tampered with in any way.