[linux] trace a particular IP and port

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

You can use the default traceroute command for this purpose, then there will be nothing to install.

traceroute -T -p 9100 <IP address/hostname>

The -T argument is required so that the TCP protocol is used instead of UDP.

In the rare case when traceroute isn't available, you can also use ncat.

nc -Czvw 5 <IP address/hostname> 9100

tcptraceroute   xx.xx.xx.xx 9100

if you didn't find it you can install it

yum -y install tcptraceroute 

or

aptitude -y install tcptraceroute 

you can use tcpdump on the server to check if the client even reaches the server.

  tcpdump -i any tcp port 9100

also make sure your firewall is not blocking incoming connections.

EDIT: you can also write the dump into a file and view it with wireshark on your client if you don't want to read it on the console.

2nd Edit: you can check if you can reach the port via

 nc ip 9100 -z -v

from your local PC.

it can be done by using this command: tcptraceroute -p destination port destination IP. like: tcptraceroute -p 9100 10.0.0.50 but don't forget to install tcptraceroute package on your system. tcpdump and nc by default installed on the system. regards