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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 Go

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 [edit] Google even covers this in their Public DNS FAQ: http://code.google.com/speed/public-dns/faq.html#cdn http://code.google.com/speed/public-dns/faq.html#cdn. They offer 31 different locations, while Akamai may offer thousands of nodes (I can't find hard numbers, but they refer to 1,200+ points of presence here http://www.akamai.com/hdonline http://www.akamai.com/hdonline and 1,000 networks here http://www.akamai.com/html/technology/edgeplatform.html http://www.akamai.com/html/technology/edgeplatform.html). You're basically constraining yourself to a small subset of at least Akamai's CDN by using Google Public DNS.

ComputerGuru 15y ago
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.
michaelcampbell 15y ago
> 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?
- ComputerGuru 15y ago
  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.

ComputerGuru 15y ago

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.

michaelcampbell 15y ago

> 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?

ComputerGuru 15y ago
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.