On Sat, 12 Dec 2009, Richard Naylor wrote:
At 08:32 p.m. 12/12/2009, David wrote:
Today it is reasonable to assume DNS queries from ISP1's name servers (or address block in general) are probably from a client within the ISP1 network. With public DNS servers it gets a whole pile harder.
Well that's not always the case especially with outsourced DSL etc. I seem to also remember that the routing policy for Xtra's DNS servers was different from that of some of the DSL networks ( probably due to Xtra vs Telecom split ) at one point, though last time I looked they were fairly similar. I think the big advantage is that as long as the ISP's DNS is reliable and they don't start doing funny stuff like NXDOMAIN hijacking then customers will get a better experience by just leaving things on default and getting their settings automatically. Both Google and Opendns have their nearest servers hundreds of milliseconds away so people using them will get a worse experience, which should discourage people from using them.
Akamai does use DNS resolvers as a part of its CDN. Others tend to use anycast routing. It is more popular as it is more direct, rather than waiting on DNS responses and traffic hand offs. I wouldn't say Akamai is alone, but most newer CDNs use Anycast.
To tell the truth I got the opposite impression last time I looked at the top 20 vendors. A couple of them are using anycast but I got the impression that GSLB was preferred due to greater ability to fine-tune delivery and reduced build costs. Actually when it comes the CDNs the lack of choice in NZ is pretty bad[1]. AFAIK Citylink and Akamai are the only ones with any NZ based servers ( and Citylink has limited coverage) although I have heard some rumors. Anyway I'll make the assumption that everyone here checks their traffic sources regularly and if having (say) an EC2 node here would save you 6 figures per month you'd have already called Amazon and offered them a spare rackor two.. [1] - Not many in Australia either -- Simon Lyall | Very Busy | Web: http://www.darkmere.gen.nz/ "To stay awake all night adds a day to your life" - Stilgar | eMT.