I run into this issue occasionally and just looking for suggestions on how others solved it. I would like to monitor ports on a large number of systems and would like to determine which systems are listening on specific ports. I know there are heavy-weight apps that provide this such as HP ovo but I am looking for some light-weight open source options. I believe a syn scan will be sufficient for my purpose but I have not used any tools previously or not sure if their is a way to use default system tools or commands for this. Also for the those that have used syn scanning, does anyone run into issues due to simulating a syn attack in any of your networks?
Before you relpy, please do not recommend ping as it does not provide the functionality that I am looking for. Also, telnet will not provide this functionality because I do not what to have to script any break out or termination sequences for various connections (ie sendmail - port 25).
Thanks all for your feedback.
I was not aware for nmap. This looks like a great tool.
I love the simplicity of the python script also.
I believe lsof is for the local system, meaning that it must be installed on the local system to gather info which may not be effective for monitoring a large number of systems. Plus, one will have to handle remote login access to run the command.