Tip #813   Monitor open TCP connections

The command below will monitor open TCP connections:

watch -n 1 "netstat -tpanl | grep ESTABLISHED"

This will show connections by processes you can view, or if done as root ("sudo netstat") all processes.

Another option to perform the same task is:

sudo lsof -i -T -n

Again watch could be used with this, or adding -r as an option will make lsof refresh the output.