Should have put a disclaimer that my employer operates/owns a CDN (not that I'm directly involved).
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.
I agree with Simon, there are some very clear benefits to using DNS alongside anycast. Control is a huge problem with anycast: it's all or nothing and you are not always sure what you're going to get before you start advertising. Load-balancing is not possible among the sites, only within them. If we are discussing popularity, it's fair to say that Akamai are by far the most popular and will be impacted. NZ ISP who host Akamai servers could also be negatively impacted. I wanted to ensure people are aware of the issues associated with using a third-party resolver and may even take the opportunity to have a good look at their current resolvers to ensure they are performing. The issue Google are highlighting as the "most dominant cause of DNS latency" is cache miss. How many of us have really looked at the hit/miss ratio in BIND or considered how load-balancing/anycasting to DNS resolvers can reduce the hit rate? Is anyone implementing BIND forwarding to try and obtain a larger cache? For example, if you have anycast resolvers deployed around your network they will maintain their own local cache - by setting forward-only and then directing the query traffic to site-wide caches which do full recursion at the head of the network you get the benefit of local caching and load balancing and (hopefully) an increase the hit rate within your network. In the case of the Google DNS service, the product manager says "We are continuing to work with other companies and individuals on possible solutions. " to the problem of CDN GSLB. (full txt here: http://groups.google.com/group/public-dns-discuss/msg/1bb9feb0922ff585 ). I'm not holding my breath. -d