Why do you think iTunes would care what DNS server you are using? I'm genuinely curious, as I would think that the DNS lookups are abstracted by the OS, and even if they were not, I cannot see how using a different (esp. a better performing) DNS server would hinder iTunes performance — especially since the original DNS isn't provided by Apple or anything.
CDNs often rely on your DNS info to determine which node is closest to you and, thus, which node should offer the best performance.
Using a central DNS like Google's can do two things:
1) Break locality. Using 8.8.8.8 may cause CDNs to potentially direct you to a node that's nowhere near your actual physical location
2) Aggregate traffic on a node. The more people using 8.8.8.8 for DNS, the more people who may land on the CDN nodes associated with 8.8.8.8's location and thus that node may be more loaded than the one closer to you
That completely slipped my mind. You are, of course, correct.
An alternative suggestion here is to use Comcast's 75.75.75.75 IP address; while it may seem static, it's actually an anycast address, and will resolve to the nearest node.
One thing many people forget when choosing a DNS server is that it's not just the ping time that counts - the time it takes the server to reply to the actual DNS request is what matters.
e.g. while 75.75.75.75 for me (Comcast Chicago) is a 15ms trip and 8.8.8.8 is a 28ms ping, the lookup on the former (dig x.com @dns_ip) can reach 120ms while on Google's DNS it never exceeds ~35ms.
> CDNs often rely on your DNS info to determine which node is closest to you and, thus, which node should offer the best performance.
Why do they do this? Wasn't DNS SUPPOSED to be something that wasn't in any way tied to locality? Are CDN's just using the side effect/fact of life that they happened to fall out that way, because it's easier?
Pretty much, yes. But it's not just easier, it's also simpler. If you do the distribution at the DNS level (which is pretty much as low as you can go), you don't have to deal with the much messier geo-distribution on a higher level.
