Question

The structure of Domain Name System (DNS) service is distributed. List reasons for this distributed service structure. Also, draw a diagram to show how IP address is resolved in DNS.

Answer 1

Domain name system

A domain name system (dns) is an internet service that translate domain name to IP Address.

• Domain Name System database is a database on the planet which receives the so many requests daily.There is no other database on the planet which is changed daily by millions of people. That is why DNS is an unique database.
• We need distributed system to name each connected node.
• Computer use IP addresses.and human can not remember IP address therefor we need unique names for each IP address but it is still not scalable so they have created name hierarchy.
• All the name in a given domain should be unique. Therefore there is a need of an entity which can control a list and ensure that no duplicate arise.
• For example .com domain can not contain a duplicate name. In network solution there is central database which contains the information about the owner and name server for each domain. This database is known as Whois database.
• Thats why DNS system is distributed

How IP address resolved in DNS

DNS can answer three types of queries that a user can make to a DNS server: recursive, iterative, and inverse. The client of a DNS server can be a resolver or another DNS server.

Clients

A DNS client is any machine issuing queries to a DNS server. The client hostname mayor may not be registered in a name server (DNS) database. Clients issue DNS requests (e.g hubpages.com)through processes called resolvers which resides in the client machines.

Resolver

The resolvers handle the process of mapping a symbolic name(e.g. hubpages.com) to an actual network address (66.111.109.13).

Root servers

When a DNS server processes a recursive query and that query cannot be resolved from local zone files, the query must be escalated to a root DNS server

DNS Zones

All DNS servers work together to resolve hierarchical names. If they already have information about a name(e.g. cnn.com), they simply fulfill the query for the client; otherwise, they query other DNS servers for the appropriate information.A DNS zone is a portion of the DNS namespace over which a specific DNS server has authority.

Below figure shows an example of both recursive and iterative queries. In this example, a user within his office is querying its DNS server for the IP address for hubpages.com. Here’s what happens to resolve the request: