Caching servers in Local ISPs !!

[itpp2012]

You don't need to do anything with a dns that is only local to the clients
served by the ISP.

Suppose I am in Africa;
Question to my ISP: I'd like to go to new-york
ISP: new-york is located in south-Africa

Suppose I am in the US;
Question to my ISP: I'd like to go to new-york
ISP: new-york is located in the US

The DNS is just a pointer, where ever you have an edge server make the dns
name point to it, when not point the dns to origin.
Every ISP client gets the DNS servers from their ISP, its really simple.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,249997,250957#msg-250957