Knowledge Base

A light weight approach to validating network port connectivity

If it becomes necessary to validate, particularly in a clustered environment whether Causal Cluster or High Availability, whether or not 1 instance can talk to another instance on a given port one can use linux command netcat.

To validate connectivity and that the hostname/port is not being filtered out as a result of a firewall or other establish 2 terminal sessions.

  • From the first terminal session run from the linux command line/prompt

$ nc -l -p 5000

and to which this will start up a process on the host listening for traffic on port 5000. If the connection is possible then your terminal window will advance to the next line and simply await messages from another nc command.

If the port number is already in use by another linux process you will encounter error message

nc: Address already in use

  • From the second terminal session run from the linux command line/prompt

$ nc -v <hostname> 5000

replacing <hostname> with the internal IP address/hostname of the first terminal session. This command will make a connection to the <hostname> and port 5000. If the connection is successful then your terminal window will report the following and focus will advance to the next line:

Connection to <hostname> 5000 port [tcp/*] succeeded!

From here if you enter text, for example Hello, upon hitting return/enter you should then see the text on the first terminal window. And provided you see the text on the first terminal window connectivity has been successfully proved/established.

If the connection is not successful you may receive error messages similar to:

nc: getaddrinfo: Temporary failure in name resolution
nc: connection refused