Explain how DNS works and the Services Provided by DNS

Explain how DNS works and the Services Provided by DNS


Overview of How DNS Works:

The application will invoke the client side of DNS, specifying the hostname that needs to be translated.

DNS in the user’s host then takes over, sending a query message into the network.

This mapping is then passed to the invoking application.
▫ A simple design for DNS would have one DNS server that contains all the mappings.
▫ Although the simplicity of this design is attractive, it is inappropriate for today’s Internet, with its vast (and growing) number of hosts.

Services Provided by DNS:

The DNS is

(1) a distributed database implemented in a hierarchy of DNS servers.

(2) an application-layer protocol that allows hosts to query the distributed database. 

DNS provides a few other important services in addition to translating hostnames to IP addresses:

Host aliasing: A host with a complicated hostname can have one or more alias names. For example, a hostname such as relay1.west-coast.enterprise.com could have, say, two aliases such as enterprise.com and www.enterprise.com .

Mail server aliasing: For obvious reasons, it is highly desirable that e-mail addresses be mnemonic. For example, if Bob has an account with Yahoo Mail, Bob’s e-mail address might be as simple as [email protected].

Load distribution: DNS is also used to perform load distribution among replicated servers, such as replicated Web servers. Busy sites, such as cnn.com , are replicated over multiple servers, with each server running on a different end system and each having a different IP address.

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