I'm behind fairly restrictive firewall regarding ports, that can be used for connecting outside. I'm also running service on my remote box, and I want to connect to it.
Problem is, that I'm unable to find out which ports I can access, so I don't know where I can bind the service. (The typical unrestricted ports like 80 and 443 are already used on given machine).
I tried to run
nmap -sS behind firewall to scan all TCP ports and wireshark on the second machine to determine SYNs that I receive, but I can see false positives (when I listen with
netcat on given port and try to connect, it fails).
Is there any tool that can serve my purpose?