Is it safe to open
Management interfaces give full control of the system. Make them reachable only from an admin network or VPN, change default credentials and keep the software patched.
How to open port 9090
Open to everyone
# Linux iptables iptables -A INPUT -p tcp --dport 9090 -j ACCEPT # Ubuntu ufw ufw allow 9090/tcp # firewalld firewall-cmd --permanent --add-port=9090/tcp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=tcp dst-port=9090 action=accept place-before=0 comment="port 9090" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 9090 TCP" -Direction Inbound -Protocol TCP -LocalPort 9090 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p tcp --dport 9090 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p tcp --dport 9090 -j DROP ufw allow from 203.0.113.0/24 to any port 9090 proto tcp /ip firewall filter add chain=input protocol=tcp dst-port=9090 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=tcp dst-port=9090 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 ':9090 ' netstat -ano | findstr :9090 # Windows lsof -i :9090 # macOS # test from another machine nc -vz example.com 9090