Порт 1723 (PPTP)

TCP port 1723 is the standard port for Point-to-Point Tunneling Protocol (PPTP), a method for implementing virtual private networks (VPNs). PPTP, developed by Microsoft in the late 1990s, creates a tunnel over a TCP/IP network to encapsulate PPP (Point-to-Point Protocol) frames, allowing remote clients to securely connect to a private network. The protocol uses TCP port 1723 for connection management and control, while GRE (Generic Routing Encapsulation, protocol 47) handles the actual data transfer. The client initiates a TCP connection to the server on port 1723. Once the connection is established, PPTP uses this channel to negotiate encryption and authentication parameters. After the negotiation, GRE is used to encapsulate the PPP frames, providing a secure channel for data transmission. PPTP authenticates users using various methods, including Password Authentication Protocol (PAP), Challenge-Handshake Authentication Protocol (CHAP), and Microsoft CHAP (MS-CHAP).

## Firewall Recommendations

Due to the inherent security weaknesses of PPTP, it is generally recommended to block TCP port 1723 and GRE protocol 47 unless absolutely necessary. If PPTP must be used, it should be replaced with a more secure VPN protocol such as OpenVPN, IPsec, or WireGuard. If blocking is not possible, ensure that strong passwords are used, and consider implementing multi-factor authentication. Monitor network traffic for suspicious activity, and keep the PPTP server software up to date with the latest security patches. It is crucial to understand that even with these measures, PPTP remains a high-risk protocol and should be avoided whenever possible. Consider using a modern VPN solution that offers better security features and encryption algorithms.