Question:
How does DNS work?

Answer:
Domain Name Service (DNS) is a service that is contained in the TCP/IP protocolsuite and provides a way of mapping IP addresses to names; for instance,135.200.56.90 to sunrise.mktg.starwars.com.

DNS relies on a Name Server to provide the IP address information when arequest is received. The name server stores and updates the DNSinformation; i.e. name to IP address maps.

It is a safe practice to implement primary and secondary DNS servers in WANenvironments. These two name servers keep copies of the names database.Whenever a change is made on the primary server, the secondary serverreceives an update. This fault-tolerant setup ensures that DNS servicescontinue to be provided if ever the primary name server were to go down.

When a node on a network requests a service, telnet for instance, thefollowing would occur:

a. The hosts initiates the telnet request to sunrise.mktg.startwars.com bytypically typing::telnet sunrise

b. We assume that the host has been configured with the following DNS nameserver IP address information:

Primary:        dns1.xxx.xxx.xxxSecondary:      dns2.xxx.xxx.xxx

A query is sent to the primary DNS server with a question that means “How doI reach “Sunrise”?”

c. The primary DNS name server, dns1, then looks up “Sunrise” in its namestable and responds with Sunrise’s IP address; in our example it is135.200.56.90.This response is the answer to the DNS query. If the host name was notfound in the names table, an appropriate “host not found” reply will be sent.

d. The network node then establishes a telnet session with the host.

e. If the primary DNS server dns1 was inactive for any reason, thesecondary server dns2 would have responded to the request.