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How to find remotely on which port the TFTP server is running on FreeBSD? The standard UDP port 69 is not listed amongst open ports when scan FreeBSD server with IP scanner.
That's not possible IMHO, it would be like hacking a server without logging to it. You could try exploit some vulnerability, but otherwise servers by design make discovering open ports for services as hard as they can. If they are set up properly even a simple IP scan should trigger safety measures and disconnect your IP.
netstat -an
?