If you go into the /etc/dhcp directory you will see a file called dhclient.conf
somewhere (anywhere really), in the file put the following line:prepend domain-name-servers 184.108.40.206;
if you want just your custom dns server:
supersede domain-name-servers 220.127.116.11;
This will put the 18.104.22.168 dns server at the top of the list of dns servers in the /etc/resolv.conf file, in addition the to usual ones that the dhcp server gave to your computer.
Of course for your network you will probably replace 22.214.171.124 with the ip address of another dns server (unless you really want to use one of google's dns servers).
In fedora you have to go to /etc/sysconfig/network-scripts/, and find the file for your network device (something like ifcfg-ethX, where X is a number usually 0).
change the line PEERDNS=yes to =no.