Many of us use public DNS servers like Google Public DNS and Open DNS for faster web browsing and other benefits. But in some cases your ISP's DNS server is much faster. Weblog Digital Inspiration illustrates why and when this might be.Photo by dawning.ca
It's all about your IP address. As Digital Inspiration explains, all of the major websites use Content Delivery Networks like Amazon and Akamai to serve up the content. A CDN looks up your computer's IP address to direct you to the nearest server, but because a public DNS server masks your IP address, the CDN might serve you content from a server that's actually not the closest one to you. Your download speeds will thus be slower than if you were using your ISP's DNS server. (It's also likely that any unmetered content your ISP offers won't be recognised as such.)
Google's DNS server information page acknowledges this issue:
Note, however, that because nameservers geolocate according to the resolver's IP address rather than the user's, Google Public DNS has the same limitations as other open DNS services: that is, the server to which a user is referred might be farther away than one to which a local DNS provider would have referred. This could cause a slower browsing experience for certain sites
How to tell if you should use your ISP's DNS server or a public one? Digital Inspiration recommends (and provides instructions for) using the dig tool and an IP geo-location app to find out if the CDN servers you're accessing are near you ... or on a different continent. You can also use previously mentioned Namebench to find the fastest DNS server for you. And if you heavily use your ISP's own software mirrors, gaming servers or other unmetered options, stick with the recommended settings.
Have any DNS-related tips or want to share your results? Let's hear them in the comments.
Before Changing DNS Servers to Open DNS or Google DNS, Read This! [Digital Inspiration]