Question 4. How does the Domain Name Server (DNS) redirect the requesting computer to another DNS?

Ans: See  Dr. Zulfiquar Ahmed, A Text Book on Cyber Law in Bangladesh, (Dhaka: National Law Book, 2009), pp. 17-19.
And read more for proper answering:
Every service provider has at least one DNS server, and usually provides many more. Medium sized businesses and organisations maintain their own email systems and other major services etc. will also typically have at least one DNS server for their network. DNS servers accept requests from programs and other domain name servers to provide mapping between domain names and IP addresses. When a request from a computer is made to resolve a URL to an IP address (And vice versa) a DNS server can do one of the following:

• It can answer the request with an IP address because it already knows the IP address for the requested domain. It gets this information from a resolution table that it constantly updates containing mappings of host domain names to IP addresses.
• If it doesn’t have the mapping, it can contact another DNS server and try to find the IP address for the name requested. Depending on the DNS configuration, it may have to do this multiple times in a hierarchal fashion eventually accessing the main DNS servers on the internet at the top of the ‘tree’.
• It may reply with the IP address of a more ‘distant’ DNS server that contains more table information relating to the requested URL and domain name, the requesting computer then using the more distant DNS server to query the address.
• It can return an error message because the requested domain name is invalid or does not exist, this typically being carried out as the DNS requests for information are reaching higher up the ‘tree’.

When a DNS server resolves a request, it caches the IP address it receives into a resolution table. For example, when a DNS server has made a request to a root DNS server for any .biz domain, it knows the IP address for a DNS server handling the .biz domain, so it doesn’t have to enquire to the root DNS servers again for that information and this then reduces traffic and request load.
More Read……………….
Domain Name System
Best Practices for Speeding Up Your Web Site
DNS security and performance considerations, and ISP alternatives
How Does DNS (Domain Name System) work?
DNS Server Overview
See  Dr. Zulfiquar Ahmed, A Text Book on Cyber Law in Bangladesh, (Dhaka: National Law Book, 2009), pp. 17-19.