9. Discuss the significance of DNS.
The DNS translates Internet domain and host
names to IP addresses. DNS automatically converts the names we type in our Web
browser address bar to the IP addresses of Web servers hosting those sites.
DNS implements a distributed database to store this name and address information for all public hosts on the Internet. DNS assumes IP addresses do not change (are statically assigned rather than dynamically assigned).
The DNS database resides on a hierarchy of
special database servers. When clients like Web browsers issue requests
involving Internet host names, a piece of software called the DNS resolver
(usually built into the network operating system) first contacts a DNS server
to determine the server's IP address. If the DNS server does not contain the
needed mapping, it will in turn forward the request to a different DNS server
at the next higher level in the hierarchy. After potentially several forwarding
and delegation messages are sent within the DNS hierarchy, the IP address for
the given host eventually arrives at the resolver, that in turn completes the
request over Internet Protocol.
DNS additionally includes support for caching
requests and for redundancy. Most network operating systems support
configuration of primary, secondary, and tertiary DNS servers, each of which
can service initial requests from clients. Internet Service Providers (ISPs)
maintain their own DNS servers and use DHCP to automatically configure clients,
relieving most home users of the burden of DNS configuration.
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