My problem was low download speed from Mac App Store. I changed my DNS configuration to Google DNS 126.96.36.199 and it started to download over 10x faster with the same WiFi. How is this actually possible?
It can indirectly.
Example, downloading a file from Akamai. You're in Germany say. DNS A resolves you to a French node, connection is good, download is fast. DNS B resolves you to a US node, connection is poor, download is significantly slower.
Slow DNS queries themselves wont slow your download speed, but will cause pages to wait longer before starting to download.
3Note that it is more likely that your local ISP's DNS will resolve Akamai to the address in France, and Google's DNS resolves it to the US address, because for DNS-based anycast the location of the DNS server that performs the recursive resolution is what counts. Dec 16, 2015 at 9:12
4@SimonRichter actually the google DNS service goes to great lengths to resolve local IPs. They even send your country in the query to the upstream servers.– JosefDec 16, 2015 at 9:56
It has some effect, but not that much.
A DNS does nothing more (in this case) than translating an domainname to an IP. They do this really really fast, often under 5ms. Changing to another DNS could be benchmarked to notice a change in timing, but we're talking milliseconds here. The changes for that part will be minimal.
The difference is in where the DNS points to. If one DNS points you to a server on the other side of the planet for a resource, that'll result in a slow download. If the other DNS points you to a server nearby, that'll download a lot faster.
Using AppStore or iTunes on OS X the DNS settings do have a major effect on my download speeds, i.e. 500kbps vs. 50Mbps; this is roughly a factor of 100. Does Apple utilize that many requests during a single download? I am getting the same results on WiFi and cable. To bring it back to the original question; how is this possible?– benApr 16, 2016 at 19:58
Keeping in mind DNS is cached on the client, how could it be possible? Perhaps the DNS is putting you to the wrong (read: far away) resource– JonathanJul 11, 2017 at 1:00
Okay so I’m not going to get too technical here. Your ISP is purposely redirecting your DNS queries to servers that are otherwise undesirable for the customer due to latency derived from the distance of the physical network. I.E. www.Google.com resolves to Server_A (California) and Server_B (Atlanta) if you are located in Oregon than you would naturally presume your ISP would send you to the closest server. This is not what occurs in practice, your ISP is a business, and therefor must constantly be dynamically changing the network to best utilize the available resources. This can often include purposely redirecting you to slower DNS servers, usually owned by the ISP itself, this then allows them a layered approach of throttling network traffic at the session layer (OSI Model) without telling the customer, because at the physical and network layers the connection to the network is unchanged. But if you own the DNS SERVER you can direct your customers traffic to throttle or tier your profits.
This does directly affect your download speed because in the modern age download links contain multiple mirrors per file resource, if the ISP is sending you to Germany to download a file also located in California than your connection speed will suffer greatly!