Reachable
The TCP path is externally reachable. If the app still fails, investigate the application layer, authentication, hostname or client configuration.
Live connection diagnosis
TCP Port Checker
Test one TCP port from outside your network. A positive result is verified reachability; a negative result continues into diagnosis.
TCP reachability check
Verify whether one TCP port on this connection can accept a connection from the public internet.
Detected public IPChecking…
IP version—
Network—
The public IP shown here is detected from this browser request. External probes are restricted to that same public IP.
A port result should start a diagnosis, not end it
A successful connection is strong positive evidence that the public TCP path reaches a listening service. A failed connection is not a precise cause by itself. Continue with local-service, forwarding and WAN/public-IP checks before changing router settings.
Not reachable
The path failed. Confirm the service works locally, then inspect port forwarding, firewall rules and upstream NAT.
CGNAT
A failed port alone does not prove CGNAT. Compare the router WAN IPv4 with the public IPv4 using the dedicated check.
Frequently asked questions
What does reachable mean?
Connection Vitals established a TCP connection from outside your network to the detected public IP and selected port.
Does not reachable mean my firewall is definitely blocking it?
No. A failed TCP connection can be caused by the service not listening, router forwarding, a firewall, upstream NAT, CGNAT or another path problem.
Can I scan another person’s server?
No. The public probe is intentionally restricted to the public IP detected from your own browser request.
Use a service-specific check when the port has context
A bare TCP result is more useful when paired with the application state that should be listening.
qBittorrent listening port
Check the incoming peer port while qBittorrent is actually running.
RDP / TCP 3389
Check reachability without confusing an open socket with a successful RDP login.
Minecraft Java
Check the server TCP endpoint while the Java server is running.
Why is the port unreachable?
Work through listener, NAT, forwarding, firewall and binding in order.