hping and firewall testing

["Doug Fox" <dfox168 () hotmail com>]

hping2 is a feature rich utility.  However it is new to me.  Could you some 
please tell me which syntax(es) could I do to test our firewall externally?

I am trying to use HPING to find out the firewall which nmap and nessus 
could not find.

The nmap syntax is nmap -v -sT sV -P0 -O.

Any suggestions/comments/advise are much appreciated.

Many thanks!

DF