Although best practice is to have redundant DNS servers, not every small business has the luxury of being able to afford a second server. There are however cases when the server is down but users need to get online and work (or look up ways to solve the server’s issues). Fortunately Google has provided a solution in the form of a pair of publicly accessible DNS servers. While these servers will NOT provide address resolution for local LAN devices such as file shares, printers or local e-mail systems, they do allow for name resolution for any public site on the Internet.
The process is as simple as opening the IP setting for a system’s LAN card and entering the IP address of one of the public DNS server, 184.108.40.206 or 220.127.116.11.
For more details look at Google’s instruction page at https://developers.google.com/speed/public-dns/docs/using