Is it safe to open
VPN ports are meant to be open. Use modern protocols (WireGuard, IKEv2), strong keys, and keep the VPN software up to date.
How to open port 1723
Open to everyone
# Linux iptables iptables -A INPUT -p tcp --dport 1723 -j ACCEPT # Ubuntu ufw ufw allow 1723/tcp # firewalld firewall-cmd --permanent --add-port=1723/tcp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=tcp dst-port=1723 action=accept place-before=0 comment="port 1723" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 1723 TCP" -Direction Inbound -Protocol TCP -LocalPort 1723 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p tcp --dport 1723 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p tcp --dport 1723 -j DROP ufw allow from 203.0.113.0/24 to any port 1723 proto tcp /ip firewall filter add chain=input protocol=tcp dst-port=1723 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=tcp dst-port=1723 action=drop
If the server is behind a router, you also need a port forward (dst-nat). Behind ISP CGNAT (100.64.0.0/10 on the WAN) forwarding will not help: you need a public IP or a VPN.
What is listening
Check on the server
# what listens on the port ss -lntup | grep ':1723 ' netstat -ano | findstr :1723 # Windows lsof -i :1723 # macOS # test from another machine nc -vz example.com 1723