I currently have a VPS in a data center, I asked the admin to open a port to install a ftp server. It opened port 3345, at first I tought the port is not forwarded correctly, because I ran nmap as this :
nmap 194.110.xxx.xx Starting Nmap 6.00 ( http://nmap.org ) at 2013-12-17 14:33 EET Nmap scan report for host-194-110-xxx-xx(194.110.xxx.xx) Host is up (0.0022s latency). Not shown: 995 closed ports PORT STATE SERVICE 21/tcp open ftp 80/tcp open http 443/tcp filtered https 3306/tcp open mysql 3389/tcp open ms-wbt-server
But when trying to connect with the client it works ok. Why nmap is not reporting that the port 3345 is open ?