For SSH to be truly effective, using insecure connection
protocols, such as Telnet and FTP, should be prohibited. Otherwise,
a user's password may be protected using SSH for one session, only
to be captured later while logging in using Telnet.
Some services to disable include:
To disable insecure connection methods to the system, use the
command line program chkconfig, the
ncurses-based program ntsysv, or the
Services Configuration Tool (redhat-config-services) graphical application. All
of these tools require root level access.
For more information on runlevels and configuring services with
chkconfig, ntsysv, and the Services
Configuration Tool, refer to the chapter titled Controlling Access to Services in the Red Hat Enterprise Linux System Administration