Why are My iTunes Downloads so Slow?

I am using hsd1.ca.comcast.net. (67.215.65.132, my ISP's default DNS server). I'll try adding some static routes to iTune's download servers for my geo (Sunnyvale, CA) and report my findings.

However, I don't see how changing DNS servers will help me unless my iTunes client is doing multiple DNS lookups (i.e. many, many, many times) per download, which it is not (I monitored iTunes and my ATV with netstat). What is your theory of operation for why a different DNS server will improve download speeds by an order of magniture? I know you reported that changing your DNS server(s) improved your download speeds, but can you explain why?

-Matt

@ulf76: Your logic makes no sense. Changing DNS servers works if you cannot make a connection at all (due to lookup failures), but it has nothing to do with bandwidth. The computer looks up a given address once, then caches the result. It's not a constant process with each data packet.

That said, Apple is obviously throttling downloads. Performance has become much worse in the past few months, especially this last week for me. I can download a 3 Gb game from Steam in 20 minutes, yet it takes 4 hours to download a single, 1.4 Gb TV episode from Apple. Ouch.

Rassilon:

I get your logic about the DNS connection not needing to be queried continuously, but clearly something about DNS servers is going on here. Apple's download system may be

Considerably more complex than we understand.

One more data point: I was on Open DNS and Fios for years, and iTunes downloads were almost always fast. Speeds were noticeably better around the time of the North Carolina data center completion. When I posted the other day here, an iTunes movie rental was agonizingly slow, and after trying numerous things, switching from Open DNs to my default Verizon DNS settings was like turning on a lightbulb.

Like was mentioned earlier in the thread its not so much "DNS" as it is how the CDN (Content Delivery Network) providers respond to queries from anycast DNS services such as OpenDNS, Google, Dyn etc... Not all CDN's are a problem, but Akamai is (Which Apple uses). In simple terms the CDN looks looks at the DNS query for location (not the end user's location). It then uses serves the request for content from the distribution point closest to the point where that DNS query came from. Unfortunately, when using anycast DNS, you sometimes do not end up using a DNS server that is geographically close to you. It may end up across the country or further. On the other hand you may randomly get great download speeds if you end up with a geographically close DNS server that in turn points the CDN to serve you from a closer distribution point. It also explains why most people get great download speeds when using their ISP's DNS servers because you always get referred to a close distribution point. If you are using your ISP's DNS servers and getting poor download speeds, it is highly unlikely it is a DNS issue. The DNS providers and the CDN's know this is an issue and look to be trying to solve it. Hopefully this at least helps explain the issue.

There are many articles on this. I linked to a few earlier in the thread and below are a few more.

http://www.labnol.org/internet/changing-dns-servers/18996/

http://apcmag.com/why-using-google-dns-opendns-is-a-bad-idea.htm

Thank you, HM801. That makes sense, though if Apple is using the wrong server, that is entirely their fault. I only use my ISP's DNS, and that places me about 2 miles from my home.

In this case Apple has offloaded their frontend content delivery (iTunes movies, music, tv shows etc...) to Akamai (http://www.akamai.com). The issue is actually between Akamai and the Anycast DNS providers. I guess Apple could use a different CDN and I actually think they may also use Limelight??. I have read that Apple may build its own private CDN like Netflix ( http://www.forbes.com/sites/ericsavitz/2012/06/05/netflix-shifts-traffic-to-its- own-cdn-akamai-limelight-shrs-hit/ and http://techcrunch.com/2012/06/04/netflix-open-connect/ ).

Here is maybe a better explanation than mine

http://00f.net/2012/02/22/akamai-vs-public-dns-servers/

I changed my DNS to a static setting like you suggested and it didn't make any difference...

My guess is that Apple has grown too popular for their own good. By allowing streaming to millions of devices, any data center will have a difficult time keeping up with demand.

By way of confirmation, it is 6 months since my first remarks and nothing changes.

Right now I'm in the midst of a 7 hour download of an HD movie. I have a slow connection ( 2.5 Mbps }but this works out at about 0.7.

Naturally, Apple TV is out of the question.

Meanwhile Netflix streams away - no hesitation and an acceptable quality.

I only resort to itunes when I can't get a movie my wife wants any other way.

Apple is very arrogant. The always kiss you off regardless of who is at fault.

I do understand how DNS works, and I was also confused about why changing your DNS server might affect download speeds. On the surface of it, it shouldn't -- it doesn't matter how quickly I look up your address, if the road to get to you is slow, I should have slow performance.

Then I remembered something I read about Google and YouTube bandwidth -- and it boils down to this:

* Google (YouTube), Apple, and other providers of big content (or CDNs) may have reached an arrangement with your ISP to offer a more direct connection to their content, perhaps over dedicated links that reach more directly to the content servers.

* The easiest way to inform your computer about this more direct link is to send you an address specially for the purpose -- if you are on Verizon FiOS, then the Verizon DNS servers will send you the correct address for Verizon's fast connection to Apple.

* If you don't use Verizon's DNS, but, for example, use 8.8.8.8 (Google), there is no way that Google would know or should ever send you the specific Verizion-Apple IP address.

I had a similar configuration myself and after removing the 8.8.8.8 Google DNS and using the default Verizon DNS, I went from 300kbps to 6mbs.

So you can stop yelling at each other, you're both right: DNS can't actually make a difference in download speed, but it could send you to a private wormhole-type IP address that actually gives you much faster download speeds because of the physical topology of the network and agreements between carriers and Apple to facilitate faster speeds. Which, at least in my case, it seems to do.

I saw nobody yelling, Pacobo, and we already had a nice explanation. What I don't understand is why anyone would use Google's DNS service at all. It serves no useful purpose, and only exists to give Google even more access to your personal life. By using a third-party DNS, you voluntarily tell Google everywhere you're going, and when. This is dangerous.

For what it's worth, I use my phone company's DNS, which is located a few miles from my Vermont home. Sadly, this has no bearing on Apple's broken system. It still claims that itunes.apple.com is hosted in Australia. Only off by 15000 miles ...

thanks pacobo. i had my dns set to google (8.8.8.8) and i changed it to my local isp dns and that did the trick. was wondering what was going on when it said my movie was going to take 3 hours to download. paused my download, changed the dns, and now it says 10mins!

Thanks ccmoon007 your advice was helpful 😉

Hello- I rent films from iTunes once a month or so and usually have decent download speeds about 1 meg a second but tonight it was about 10% of that so I paused the download and rebooted my mac and unplugged my Airport Extreme and Cable Modem. When I replugged and restarted the download in iTunes My download initial recovered to the 1 meg a second but within a few minutes began to fluctuate between .1 meg a sec to 1+ meg a second. No doubt maintainance somewhere in itunes delivery method as speedtest.net shows no loss of my cable modems bandwidth.😟