How to find out why the port is not available?

nmap 178.208.83.17 Starting Nmap Nmap scan report for s13.h.mchost.ru (178.208.83.17) Host is up ( latency). Not shown: 989 closed ports PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 80/tcp open http 81/tcp filtered hosts2-ns 179/tcp filtered bgp 443/tcp open https 777/tcp filtered multiling-http 873/tcp open rsync 3333/tcp filtered dec-notes 5666/tcp open nrpe 8888/tcp open sun-answerbook