1. check the firewall on the server with
2. telnet server is normally disabled by default due to security issues ie plain text transmission.
You may need to install it
yum install telnetd
then go into /etc/xinetd.d and edit the telnet file, set 'disabled=no', restart xinetd service
You'll need to check /etc/hosts.allow,deny files as well.
Personally I wouldn't use a telnet server without a very good reason.
C:\>telnet xxx.xxx.xxx.xxx 23
Connecting to xxx.xxx.xxx.xxx 23....Could not open connection to the host, on port 21: Connect failed
is a typo; if you telnet to port 23, you won't get an err msg about port 21