Telnet in RHEL5

 First check whether telnet-server rpm in installed,

# rpm -q telnet-server
telnet-server-0.17-38.el5

If it is installed, then edit

# vi /etc/xinet.d/telnet
change the line disable = yes   to 
                disable = no

Then # service xinetd restart

Now We can able to telnet connection of linux system.

Note : It works for the system which is not protected with IPtables and Selinux

If you have iptables enabled. then please follow as below,

Make a rule to allow telnet from external clients

# iptables -I INPUT -p tcp --dport 23 -j ACCEPT 

# service iptables save

# service iptables restart

Just give following command and make sure that rule is saved.
# iptables -L

This rule is to allow request coming to port number 23 i.e. telnet connections from any client.