Networking – Connection Refused from Localhost to Localhost: Troubleshooting Guide

linux-networkingnetcatnetworking

I started a tcp listener using nc -l 127.0.0.1 900 and then attempted to connect to it using nc 127.0.0.1 900 when I got the connection refused error. The same happens when connecting using telnet. ufw is disabled. I don't understand how this could happen. Please throw some light onto this issue.
Thanks in advance.

Best Answer

Some versions of nc has strange behavior, related with specifying of listening port and listening address. Try to run nc with -v (verbosity) option:

~# nc -v -l 127.0.0.1 900
listening on 0.0.0.0:36915 ...
^C

~# nc -v -l 127.0.0.1 -p 900
listening on 0.0.0.0:900 ...
^C

Other way to troubleshoot similar issues is checking of the listened sockets:

~# ss -tlnp | grep nc
LISTEN     0      1            *:43395   *:*      (("nc",pid=2210,fd=3))
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