Wednesday, March 24, 2010

Achievement Unlocked

Working at Google is a lot of fun. The Nexus One is a very impressive phone and Android is a very cool platform to work with. Since I've been a big fan of Gmail, Google search, Blogger, YouTube, and many other Google products for years, it's really amazing to be working at the company that created all of that cool stuff, and to get to play with new features and new products before they are released to the public. The first week I really felt like I had unlocked an achievement in a videogame. It's very cool, and the free food is very tasty as well!

One fairly new Google service that not many people have heard of is Google Public DNS, which is a free public high-performance and secure DNS resolution service that you can use instead of the DNS resolver provided by your Internet provider. If you're not familiar with DNS, it's the service that translates the hostname that you type into your browser, for example "example.com", into a numeric IP address, such as 192.0.32.10 for example.com.

(BTW, Wikipedia's entry for DNS also uses example.com for its example hostname, but I hadn't read it when I wrote the previous sentence. I knew that "example.com" is officially reserved for the purpose of using as an example, and apparently so did the author of the Wikipedia entry!)

The IP address is what's used for the actual routing of data to the server, but hostnames are almost always used in URLs instead of IP addresses so that the URL will continue to point to the correct site no matter where the physical server is located. For a large site such as google.com, there are many thousands of web servers distributed across a number of data centers around the world with different IP addresses that all serve the same content. One of the features of DNS resolution is that the DNS server for a given domain can be configured to return different IP addresses depending on where the requesting server is physically located, so that requests to the actual web site will hopefully be routed to the nearest and least heavily loaded web servers.

Normally your computer will never perform the task of recursive DNS lookup directly (there are a few dozen root servers which in turn point to the DNS servers that are authoritative for a particular domain, and then you must query those servers to get the IP address of the full hostname), but will use a caching DNS server provided by your Internet provider, which will be typically be automatically configured for you by DHCP when you connect your computer to your router. The advantage of using a caching DNS server is that it saves a lot of time compared to querying the actual DNS servers, especially if it's a popular site and the answer is already in the cache.

The disadvantage of using your ISP's DNS server, as I discovered a few months ago, is that they can mess around with the DNS server to redirect you to a search page of their choosing if you look up a hostname that doesn't exist (rather than telling the browser that the hostname doesn't exist). Comcast turned that on a while back and I was really annoyed by that behavior. I tried running my own DNS server for a while, but that ended up slower than Comcast's DNS server, which I didn't like. I remembered hearing something about Google starting a DNS service, and sure enough, they had. I configured my Wi-Fi router to use 8.8.8.8 and 8.8.4.4 for DNS and now the websites I visit load more quickly with very little time spent in "Resolving host", and no redirect to some lame page I didn't want to go to if I mistype a URL with a hostname that doesn't exist.

One final point that I think is pretty neat: Google set up something called anycast routing for those two IP addresses (8.8.8.8 and 8.8.4.4) so that they will take you to the nearest Google public DNS server to your location anywhere in the world. Not only does that make DNS lookup even faster, but it's compatible with the geographic load-balancing I mentioned earlier, so when you look up google.com or some other site, the DNS server for that site will return the IP address nearest to the Google DNS server, which will hopefully also be near to you as well. You can read more about the performance and security improvements at the Google Public DNS site.

Next time I might talk about Google Web Toolkit, another cool product from Google that I have been meaning to play around with for some time now, since I'm intrigued by the concept, and since I'd much rather write an AJAX site in Java than JavaScript. I'll also continue with my series on OpenVMS, as well as any interesting Android adventures that I'm allowed to talk about.
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