How to enable telnet on DNS-300
- Store your current config to XML file by Backup config menu
- Open XML file by simple text editor
- find tag <telnet>0</telnet> and replace 0 with 1
- don't touch anything else, otherwise DNS-300 don't allow to restore config back
- save XML file
- restore config from XML file by Restore config menu
- reboot DNS-300
Now you can use PuTTY to telnet to your DNS-300. Use your username and password to login. You can use command su and default root password to get root access.