Is it safe to open
Open only what you need, to the addresses that need it.
How to open port 3702
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 3702 -j ACCEPT # Ubuntu ufw ufw allow 3702/udp # firewalld firewall-cmd --permanent --add-port=3702/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=3702 action=accept place-before=0 comment="port 3702" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 3702 UDP" -Direction Inbound -Protocol UDP -LocalPort 3702 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 3702 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 3702 -j DROP ufw allow from 203.0.113.0/24 to any port 3702 proto udp /ip firewall filter add chain=input protocol=udp dst-port=3702 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=3702 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 ':3702 ' netstat -ano | findstr :3702 # Windows lsof -i :3702 # macOS