Question

I have an app running on port 9100 on a remote server serving http pages. After I ssh into the server I can curl localhost 9100 and I receive the response.

However I am unable to access the same app from the browser using http://ip:9100

I am also unable to telnet from my local PC. How do I debug it? Is there a way to traceroute a particular IP and port combination, to see where it is being blocked?

Any linux tools / commands / utilities will be appreciated.

Thanks,
Murtaza

Answer 1

Firstly, check the IP address that your application has bound to. It could only be binding to a local address, for example, which would mean that you’d never see it from a different machine regardless of firewall states.

You could try using a portscanner like nmap to see if the port is open and visible externally… it can tell you if the port is closed (there’s nothing listening there), open (you should be able to see it fine) or filtered (by a firewall, for example).