Sorry that I crash the party but things are quite different now. So, telnet is a technology that was common 20 years ago. You better use ssh/sshd for console access on your servers now.
Not sure if I need to explain the differences. Briefly, ssh is secure, at least a couple of order of magnitudes.
PS: and there is no difference between telneting+su and telneting+root, both credentials a transmitted in cleartext!