I am interested in seeing if clients are connected to us on lets say port 63004. Now check_tcp works well to see if port is available. Unfortunatley I need to know if the port is in a LISTENING state or ESTABLISHED. is it possible to check if the state of the port is ESTABLISHED as we are in a listening state and await clients connecting to us
You probably have to write your own check script.
Something like this would work:
You should, of course, elaborate on the script, and make it something more robust than something slapped together in a couple minutes to answer a Serverfault question.