PPTP

PPTP, or Point-to-Point Tunneling Protocol, is a VPN protocol used to create secure connections over the Internet by encapsulating PPP frames within IP packets. It was designed to provide a simple, widely supported method for establishing private networks over public networks and has been implemented in many operating systems and devices.

Technically, PPTP uses a control channel over TCP to manage the tunnel (commonly TCP port 1723) and encapsulates user data using the Generic Routing Encapsulation (GRE) protocol. Authentication is typically performed using MS-CHAP v2, and data encryption, when enabled, relies on MPPE (Microsoft Point-to-Point Encryption) with 40- or 128-bit keys. The combination of these components allows point-to-point connections to be established between a client and a server and for traffic to be carried securely within the GRE tunnel.

Security and evaluation: PPTP has been the subject of extensive security analysis and is generally considered to have several weaknesses. The MS-CHAP v2 authentication mechanism has known vulnerabilities that can facilitate password-guessing attacks, and the MPPE encryption employed by PPTP is regarded as weak by modern standards. GRE itself can be susceptible to certain network-level attacks. As a result, PPTP is commonly described as deprecated for VPN deployments in favor of more secure protocols.

Usage and status: Introduced by Microsoft in the 1990s, PPTP was once widely used due to ease of configuration and broad support. Today, many organizations prefer L2TP/IPsec, OpenVPN, or WireGuard for stronger security, and PPTP remains primarily for legacy or compatibility purposes.