How does Google Global Cache selects which cache to redirect a client?


Just wondering if anyone here I can discuss offline about Google Global Cache? I am interested in knowing how does the cache selection process takes place (i.e. how does Google know to which cache to redirect a client). I would also like to know what if I have 2 upstreams who both have GGCs installed in their network, how would the selection process takes place.

Thank you very much in advance.


Have you tried experimenting programmatically to determine if its
based on which DNS servers the client is using to resolve?