Public DNS services, like OpenDNS or Google DNS, may offer more reliable and faster lookups than the DNS server of your ISP but in some cases, you may get much better download speeds if you continue to stick to your ISP’s DNS server.
You know about Content Delivery Networks like Amazon, Akamai, etc. that have data centers located across the globe and they serve content from the one that’s closest to you geographically. A site like Adobe hosts its files on Akamai so when you download that 1 GB Photoshop installer from Adobe.com, the file will be served to you from the Akamai data center that’s nearest to you.
A CDN uses your computer’s IP Address to determine your current location and then redirects you to the server that’s nearest to you. However, if you use a public DNS service, the CDN may not get to know your accurate location as your IP address is masked by the public DNS Service. The CDN could therefore serve content from a server that’s not closest to you and hence it will take more time to download files.
A recent story published in The Economist discusses this problem in much greater detail.
Are CDNs serving you content through the shortest path?
Considering the fact that all major websites – from Microsoft to CNN to YouTube – use CDNs for delivering content, it is important to know if your are getting served from the nearest located server. How do you find that out?
Step 1: Download the Dig tool and run it against a domain (like trials.adobe.com).
C:\labnol>dig trials.adobe.com A trials.adobe.com. 687 IN CNAME trials.adobe.com.edgesuite.net. a1326.g.akamai.net. 20 IN A <strong><span style="color: #ff0000;">220.127.116.11</span></strong> a1326.g.akamai.net. 20 IN A <strong><span style="color: #ff0000;">18.104.22.168</span></strong>
Once you have the IP Addresses, you can find the server’s physical location using this online tool. If you are in India and request a file through Adobe (Akamai CDN), it should be served from their data-center in Asia and not the one in North America.
22.214.171.124 MY <span style="color: #ff0000;">Malaysia</span> Simpang Tiga TMnet Telekom Malaysia 126.96.36.199 MY <span style="color: #ff0000;">Malaysia</span> Simpang Tiga TMnet Telekom Malaysia
When I asked OpenDNS about this issue, their representative told me that it is something ‘fixable’ and that they’re working on a solution where the DNS Server itself passes on the client’s location to the CDN.
Unless this happens, as Atul Chitnis rightly points out, non-ISP DNS services “kill the benefits of CDNs like Akamai.”