Answer:

Firstly, to permit public network traffic to reach your Cloud Server you need to add a Cloud IP (Public IP) to your server.

For security reasons, by default we do not have automatic rules permitting traffic to flow from your Cloud Server's Public IP to its Private IP address.  To permit network traffic to 'flow' from the public IP / port to a private IP / port of your Cloud Server, you need to apply one or more Network Access Groups (NAG), which results in 'forwarding' rules being created to permit traffic.

By default, we have defined several pre-defined NAG's such as Remote Access, Web Access, Database Access, etc that contain pre-defined Network Access Rules (NAR) to cover the most common TCP/IP protocols and ports.

Finally, you will need to ensure that the software firewall within your Cloud Server is enabled to allow traffic on the port number you wish to accept it on.  Refer to these operating system specific guides:

CentOS: http://wiki.centos.org/HowTos/Network/IPTables

Ubuntu: https://help.ubuntu.com/8.04/serverguide/C/firewall.html

Debian: http://wiki.debian.org/Firewalls

Windows Server 2008: http://technet.microsoft.com/en-us/library/cc732283(WS.10).aspx