This is how I would answer this: The computer checks it's DNS records and does not have it correct one. It then requests the record from the router. The router doesn't know so it goes to the ISP for the DNS record. The ISP doesn't know so it asks the ROOT SERVER for the correct NAME SERVER. Your ISP asks the NAME SERVER for the DNS record. When your ISP has the record it passes it to your router which in turn passes it to you computer. Now you computer has the IP address of the site it wants to visit.