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 1701
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 1701 -j ACCEPT # Ubuntu ufw ufw allow 1701/udp # firewalld firewall-cmd --permanent --add-port=1701/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=1701 action=accept place-before=0 comment="port 1701" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 1701 UDP" -Direction Inbound -Protocol UDP -LocalPort 1701 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 1701 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 1701 -j DROP ufw allow from 203.0.113.0/24 to any port 1701 proto udp /ip firewall filter add chain=input protocol=udp dst-port=1701 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=1701 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 ':1701 ' netstat -ano | findstr :1701 # Windows lsof -i :1701 # macOS