QNAP firmware: activating remote login
You can activate remote login (telnet and SSH) in the QNAP firmware by following these steps. First, click on Administration and enter the password (by default the user is admin and the password is also admin).
Then click on Remote login under System Tools.
Finally, enable telnet, leave the port they use (13131) and press apply.
Go back to the installing Debian on QNAP TS-209 page.