If you have not already installed a TFTP server, you should do so:

# yum install tftp-server

Edit the /etc/xinetd.d/tftp file to set the disable parameter to no:

disable = no

and set the TFTP root to /tftpboot:

server_args             = -s /tftpboot

If the /tftpboot directory does not already exist, create it:

# mkdir /tftpboot

Restart the inetd server:

# service xinetd restart