I opened the port 4444 on a Debian 8 linux box (IP: 178.254.xxx.xxx) to let a program running on a remote CentOS machine (shared host) communicate with an application listening to this port.Unfortunately, connection to this port from the remote machine does not work:$ nc -zv  178.254.xxx.xxx 4444(times out eventually).By trying to connect from my local PC using cygwin I can verify that the port on the Debian box is actually open:$ nc -vz 178.254.xxx.xxx 4444Connection to 178.254.xxx.xxx 4444 port [tcp/*] succeeded!I guess that outbound connections are blocked on the CentOS side. It is a shared hosting machine, i.e., limited in its functionality anyways.How can I test positively that the port is blocked by firewall rules on the CentOS side?BTW: The Linux user on the remote machine is non-priviledged and has no access to iptables.
How to test whether an outbound network connection is blocked by a firewall
firewall;nc