Thursday, December 9, 2010

iTunes download slow

Trying to download a movie or song and iTunes says it'll take 9hours on your 24mbps connection?
Check your DNS server, if it's google (8.8.8.8 or 8.8.4.4), try changing it back to your ISP DNS, flush your cache, and restart iTunes. I did, and it solved my download problem instantly.

The problem seems to be with the way DNS resolvers return hosts when using a CDN(Content distribution network, like Akamai). iTunes uses a CDN to serve data from closer sources to you, but when using the Google DNS, the Google DNS may return a different CDN host for the iTunes data, then your local ISP (who may even cache the iTunes data). So the returned CDN host from Google could be anywhere in the world.

Google is aware of the issue, but there isn't much they can do about it at the moment since it's a limitation in the DNS protocol.