Telnet is a service using which we can remotely communicate with server.However ssh is more secure alternative to it.Therefore we should disable this service by default.
Here is what you need to do if you are using redhat/centos 4,5.
This service is usually named as krb5-telnet.
You just need to edit file under /etc/xinetd.d/krb5-telnet.
Following is the content of file where telnet is disabled .
# cat /etc/xinetd.d/krb5-telnet
# default: off
# description: The kerberized telnet server accepts normal telnet sessions, \
# but can also use Kerberos 5 authentication.
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/kerberos/sbin/telnetd
log_on_failure += USERID
disable = yes
Just restart xinetd service.
Telnet should be disabled now.