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Tip of the Day
Language: Web Development
Expertise: Beginner
Mar 18, 1997

How does DNS work?

Question:
How does DNS work?

Answer:
Domain Name Service (DNS) is a service that is contained in the TCP/IP protocol suite 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 a request is received. The name server stores and updates the DNS information; i.e. name to IP address maps.

It is a safe practice to implement primary and secondary DNS servers in WAN environments. These two name servers keep copies of the names database. Whenever a change is made on the primary server, the secondary server receives an update. This fault-tolerant setup ensures that DNS services continue 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, the following would occur:

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

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

Primary:        dns1.xxx.xxx.xxx
Secondary:      dns2.xxx.xxx.xxx
A query is sent to the primary DNS server with a question that means "How do I reach "Sunrise"?"

c. The primary DNS name server, dns1, then looks up "Sunrise" in its names table and responds with Sunrise's IP address; in our example it is 135.200.56.90. This response is the answer to the DNS query. If the host name was not found 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, the secondary server dns2 would have responded to the request.

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