The Internet is made up of so many different services that it is easy to forget that they all individually matter for both speed and security when you are browsing the web. DNS is a service that generally works so well that most people, even technicians, don’t really think much about it anymore. Changing your DNS settings to use Google’s Public DNS servers may make your web browsing experience much better.
The first reason for this is that DNS servers are in fact servers so depending on the resources they have they may work better or worse. You really have no idea how good the DNS server your ISP uses is. It could be great, or it could be pegged out and barely able to keep up with the millions of requests it receives every minute. Since your computer has to query the DNS server every time you need to access a web page or web resource a small increase in speed may provide a marked improvement in performance.
Beyond speed if you use Google Public DNS you also don’t have to worry about your ISP redirecting you if you type in an address incorrectly. I was using Verizon FIOS and they started redirecting to their own Yahoo powered search page whenever I misspelled a web address. This was genuinely annoying and I would simply prefer to get a “not found” error rather than be redirected.
The final reason to use Google Public DNS is to try to prevent DNS Cache Poisoning or other DNS Hacking attacks. If you are traveling and connect to wireless networks and use the default DNS Server that DHCP Server provides you don’t know whether that DNS Server has been compromised.
To use Google’s Public DNS you just add 184.108.40.206 and 220.127.116.11 to your DNS record for either your computer, or your ISP router.
Check out more information here: https://developers.google.com/speed/public-dns/