PPTP
What is Port 1723?
Port 1723 is used by the Point-to-Point Tunneling Protocol (PPTP), one of the earliest VPN protocols developed by Microsoft in the 1990s. PPTP creates a VPN tunnel by encapsulating PPP frames within GRE (Generic Routing Encapsulation) packets, using port 1723 for the control channel. PPTP was built into every version of Windows since Windows 95 and was the most common VPN protocol for years due to its ease of setup. However, PPTP's encryption (MPPE based on MS-CHAPv2) has been completely broken by security researchers. Tools exist to crack PPTP authentication in minutes. Despite being deprecated for security use, PPTP is still encountered in legacy systems and environments where security is not the primary concern.
Common Uses
- Legacy VPN connections in older systems
- Simple VPN setup where security is not critical
- Backward compatibility with Windows NT/2000 era systems
- Testing and educational environments
Technical Details
Copy-paste commands to check port 1723 (PPTP) from your terminal
Test connectivity
nc -zv example.com 1723
curl -v --max-time 5 http://example.com:1723/
telnet example.com 1723
nmap -p 1723 -sV example.com
(echo > /dev/tcp/example.com/1723) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 1723/tcp
sudo iptables -A INPUT -p tcp --dport 1723 -j ACCEPT
sudo firewall-cmd --permanent --add-port=1723/tcp && sudo firewall-cmd --reload
Security Considerations
PPTP is cryptographically broken and should never be used for securing sensitive data. MS-CHAPv2 authentication can be cracked to a single DES key, and the MPPE encryption it provides is therefore compromised. Migrate all PPTP VPNs to IKEv2/IPSec, OpenVPN, or WireGuard. If PPTP must remain temporarily, limit access and plan for rapid migration.
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