Start with local service
Verify that the service is listening on the correct interface and port. A process limited to 127.0.0.1 is not reachable from the local network. Test locally first, then from another device on the LAN.
Control the firewall
Allow only the port and protocol needed, ideally for the expected sources. Do not disable the firewall entirely for an extended test. Check the system firewall and the router firewall separately.
NAT and redirection
The redirect should target the stable local address of the correct device and use TCP or UDP depending on the service. Behind two routers, each tier must be processed or removed by a simpler architecture.
Detect CGNAT and test carefully
If the WAN address of the box differs from the public address, an operator translation can block incoming connections. Test from a controlled outside network, without unnecessarily publishing an administrative or unupdated service.
Frequently asked questions
Is a port test site enough?
It only indicates whether a connection is successful at the time of the test. The service must be started and the test must use the correct protocol.
Does UPnP replace a secure configuration?
No. It automates some openings, but needs to be understood, limited, and disabled when not needed.
Reference sources
To be explored next
Published and verified by the VoirMonIP.com team on July 15, 2026.