so... we know that we can test that if a port is open on the firewall with: telnet SERVERIP PORT..but afaik there are services that can't be tested with telnet, because ex.: telnet doesn't know that protocol that the service is using, and telnet will report that the port is closed, but in reality the service is up&running. Q: first: was I correct about telnet? second: What to use for testing that a port is opened on a server? (so it's not blocked by a firewall) - are there any unix tools for this? 
What to use for firewall testing (port opened or not)
networking;firewall;ip;telnet
On the first question, maybe the service does not wait for interactive input. There could be other explanations, too. On the second,  nmap can be used to test the firewall. There are many options.Scan the first 1,000 ports (default):nmap -v -A -PN hostname.domainname.comOr perhaps a specific range:nmap -v -A -p 10000-11000 -PN hostname.domainname.com