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 2727
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 2727 -j ACCEPT # Ubuntu ufw ufw allow 2727/udp # firewalld firewall-cmd --permanent --add-port=2727/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=2727 action=accept place-before=0 comment="port 2727" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 2727 UDP" -Direction Inbound -Protocol UDP -LocalPort 2727 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 2727 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 2727 -j DROP ufw allow from 203.0.113.0/24 to any port 2727 proto udp /ip firewall filter add chain=input protocol=udp dst-port=2727 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=2727 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 ':2727 ' netstat -ano | findstr :2727 # Windows lsof -i :2727 # macOS