A post at TUAW today recommends you change your DNS provider to a service like Google DNS for faster performance. If you are located outside the US — like I am and like most APC readers are — this is a bad idea. I only discovered why after experiencing slow download speeds for several months.
Like other tech enthusiasts I jumped on the opportunity to switch my computer’s domain name server settings away from my ISP’s defaults to — I assumed — the much larger and faster Google DNS servers at 188.8.131.52 and 184.108.40.206 when they were first announced.
If you’re not familiar with what exactly DNS servers do they translate the web address you type into your browser into the actual IP address of the internet server you’re connecting to at the other end. For example a DNS server will convert “apcmag.com” typed into your browser address bar into “220.127.116.11” which is the IP address of our server at Macquarie Telecom’s datacentre.
DNS servers can be one cause (among many) of slowness in your web browsing if your ISP’s DNS server is overloaded and responding slowly — you may experience a delay of seconds each time you go to a web address that your computer hasn’t seen recently (and therefore has to connect to a DNS server to find out the correlating IP address).
This is one of the problems that third-party public DNS providers like Google DNS and OpenDNS are supposed to fix — faster more reliable lookups.
However it was Simon Hackett CEO of Internode who I bumped into at a function who warned me off using third party DNS servers located overseas such as Google DNS or OpenDNS. (By the way if I’ve got any of the technical details wrong in this article it’s much more likely to be my fault than Simon’s…!)
The key reason they’re bad is that they stuff up your computer’s ability to find the closest Akamai server to you. Akamai is the worldwide system which places massive file servers inside ISP data centres worldwide — so that when you download a big file like a Windows or Mac OS X update or a TV show or movie from iTunes it downloads from a server that’s very close to you and therefore pumps down your line as fast as your ADSL2+ can handle. (The primary selling point of Akamai is that it avoids server overload when everyone tries to download something at once but a secondary selling point is that you’re downloading a file from a local server inside your ISP or at least in your country so that the trip between the file server and you is as short/fast as possible.)
If you use a US-based DNS server your closest Akamai cache will instead be chosen as being in the US and you’ll get crummy download speeds as your file trickles over the international link.
In my case this meant that iTunes downloads were coming down at a couple of hundred kilobytes per second rather than the 1.9MB/s I was accustomed to before I changed my DNS servers to Google DNS and OpenDNS.
Don’t get me wrong — there are some distinct advantages to using reliable servers from companies that specialise in providing DNS like much faster refresh of their DNS records when new domains are registered or websites change their IP addresses DNS-level blocking of known phishing sites and so on.
But when they claim you’ll get faster speed by using them they’re conveniently forgetting to mention that if you’re not located in the US they could badly slow down your speed when downloading from distributed caches like Akamai.
Admittedly part of the problem is the design of Akamai — it is to an extent a ‘hack’ of the DNS system (not in the illegal sense; but in the sense that they’re using the DNS system in a way it was not quite designed for initially.) I have contacted Akamai’s senior PR people twice and asked if they’re investigating any way of mitigating the problem when people use DNS servers outside their local geography but I haven’t heard back.
Of course if Google DNS OpenDNS or other public DNS providers put servers into Australia the problem would be largely gone. But until they do my advice is to stick with the DNS provided by your ISP. To their credit OpenDNS is reasonably up-front
about this problem (though it’s not something they advertise on
their homepage so most users wouldn’t be aware of it.)
UPDATE: Phil Sweeney from Whirlpool reminded me that using a third-party DNS service can also screw up your ISP’s quota free downloads. For example iiNet provides unmetered downloads from Apple’s iTunes Store which is great if you like to buy TV series and rent/buy movies on iTunes. However if you change your DNS to OpenDNS or Google DNS you’ll be pulling the content from an Akamai server overseas rather than the one in iiNet’s network that is designated for free downloads. As a result you will be charged for those downloads.