trace a particular IP and port

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

You can use the default traceroute command for this purpose  then there will be nothing to install   traceroute -T -p 9100  lt IP address hostname gt    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  lt IP address hostname gt  9100

User · Answer

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

[linux] trace a particular IP and port

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