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 2427
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 2427 -j ACCEPT # Ubuntu ufw ufw allow 2427/udp # firewalld firewall-cmd --permanent --add-port=2427/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=2427 action=accept place-before=0 comment="port 2427" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 2427 UDP" -Direction Inbound -Protocol UDP -LocalPort 2427 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 2427 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 2427 -j DROP ufw allow from 203.0.113.0/24 to any port 2427 proto udp /ip firewall filter add chain=input protocol=udp dst-port=2427 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=2427 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 ':2427 ' netstat -ano | findstr :2427 # Windows lsof -i :2427 # macOS