Is it safe to open
SIP and VoIP ports are scanned constantly by toll-fraud bots looking for weak extensions. Allow only your provider's IP addresses on the firewall where possible, use long SIP passwords, fail2ban, and disable SIP ALG on the router.
How to open port 1720
Open to everyone
# Linux iptables iptables -A INPUT -p tcp --dport 1720 -j ACCEPT # Ubuntu ufw ufw allow 1720/tcp # firewalld firewall-cmd --permanent --add-port=1720/tcp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=tcp dst-port=1720 action=accept place-before=0 comment="port 1720" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 1720 TCP" -Direction Inbound -Protocol TCP -LocalPort 1720 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p tcp --dport 1720 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p tcp --dport 1720 -j DROP ufw allow from 203.0.113.0/24 to any port 1720 proto tcp /ip firewall filter add chain=input protocol=tcp dst-port=1720 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=tcp dst-port=1720 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 ':1720 ' netstat -ano | findstr :1720 # Windows lsof -i :1720 # macOS # test from another machine nc -vz example.com 1720