My school has a firewall which limits most outgoing ports. There're only
TCP/21 allowed. Is there's a way to find out all the outgoing port allowed by the firewall?
My current idea: open all TCP ports with
nc on a remote server, then use
nmap to scan which ports are accessible. But how do I do if I don't have a remote server? or is there a public server that opens all the ports for this kind of tests?
For those who are concerning that I'm breaching the school's rules, I think it's not a big deal to do that. Suppose I was establishing a service in external host and wish it to be accessible by the school network, I would be willing to know which ports I could use for this service. I was not breaking anything. I believe doing it is 100% legal.