Domain Name System Explained

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Domain Name System Explained
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Table of Contents

• DNS
• Uses of DNS
• Types of DNS Servers
• Steps in a DNS Lookup

• Types of DNS Queries
• DNS Protocol
• DNS Master Files (Zone Files)

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DNS

• DNS is the abbreviation for Domain Name
  System (DNS). It is a decentralized naming
  system, which is hierarchical and is meant for
  resources (computers, services etc.) that are
  connected to the Internet or to a private
  network. Every device that is connected to the
  Internet has an IP (Internet Protocol) address
  that is unique. This IP address is used to find
  it. DNS refers to the Internets system for
  mapping names that are alphabetic to IP addresses
  that are numeric. It is a query/response
  protocol.
• A Domain Name System does away with the need for
  memorizing IP addresses. A DNS query is made each
  time that a web address is typed into a browser.
  The outcome leads to the IP address of the
  associated web server.
• In the context of web servers, these store the
  files of websites in order to make websites
  accessible over the Internet. Web hosting is the
  service through which these servers can be
  availed along with the essential technologies and
  services that keep websites accessible. Web
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  most reliable web hosting companies are usually
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  Company, the Best Windows Hosting Company, the
  Top Cloud Hosting Company etc.

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Uses of DNS

• DNS is mainly used for the following purposes-
• Converting hostnames to IP addresses.
• Converting IP addresses to hostnames (inverse or
  pointer query).
• Transferring information between DNS servers.
• For searching other names elements (mail
  exchange).

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Types of DNS Servers

• There are four types of DNS servers. These are
  mentioned below, in no particular order.
• DNS recursor- It is a server that is meant to
  receive client machines queries through
  applications (web browsers). It makes additional
  requests to satisfy the DNS query of the client.
• Root nameserver- It has to do with the initial
  step in translating or resolving host names into
  corresponding IP addresses.
• TLD nameserver- TLD is the abbreviation for Top
  Level Domain. This nameserver ensures the
  carrying out of the next step with regard to the
  search for a particular IP address. It hosts a
  hostnames last portion.
• Authoritative nameserver- It is involved in the
  final step of a nameserver query. If it has
  access to the record that has been requested, it
  will return the requested hostnames IP address
  to the DNS recursor, which had made the request
  initially.

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1-800-123 -8156

• Whoa! Thats a big number, arent you
  proud?

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Steps in a DNS Lookup

• The various steps that are involved in a DNS
  lookup are mentioned below.
• A user types a particular web address into a
  browser. A DNS recursive resolver receives the
  query via the Internet.
• A DNS root nameserver is queried by the resolver.
• The resolver receives the root servers response,
  which involves the address of a TLD DNS server.
  This Top Level Domain DNS server stores its
  domains information.
• A request is made by the resolver to the TLD.
• The TLD servers response contains the IP address
  that belongs to the domains nameserver.
• A query is sent by the recursive resolver to the
  nameserver of the domain.
• The IP address is returned from the nameserver to
  the resolver.
• The web browser receives the DNS resolvers
  response, which contains the IP address of the
  initially requested domain.
• The completion of the above-mentioned steps, with
  regard to the process of DNS lookup, returns the
  IP address. At this stage the browser is able to
  request for the web page. The IP address receives
  a request (HTTP) from the browser. The
  corresponding webpage, that is to be rendered in
  the browser, is returned by the server at that IP
  address.

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Types of DNS Queries

• A typical DNS lookup entails three types of
  queries. These are mentioned below.
• Recursive query- In this type of a query, a DNS
  server responds to the client based on the DNS
  clients requirement. This response contains
  either the resource record that has been
  requested or an error message for the record that
  the resolver is unable to find.
• Iterative query- In it, the DNS client lets a DNS
  server return the most appropriate answer. If
  there isnt a match for the query name, the
  queried DNS server returns a referral for a lower
  level of the domain namespace to a DNS server
  authoritative. Next a query is made by the DNS
  client to the referral address. This continues
  until a timeout occurs or an error happens.
• Non-recursive query- This usually takes place
  when a DNS server is queried by a DNS resolver
  client with regard to a record that is
  accessible. A DNS server usually caches DNS
  records to curtail additional bandwidth
  consumption as well as load on upstream servers.

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DNS Protocol

• Queries and replies are the two types of DNS
  messages that are used by the DNS protocol.
  Queries as well as the replies have a header
  along with four sections (question, answer,
  authority, additional space). Each of these
  sections is discussed in brief below.
• The header section- It is meant for
  identification. It serves the purpose of matching
  responses to queries.
• The flag field- This field has sections that
  consist of 1 or 4 bits and indicate a messages
  type as well as other information, such as if the
  nameserver is authoritative, the query is or
  isnt recursive, status etc.
• The question section- It contains the type of
  record that is being resolved as well as the
  domain name.
• The answer section- This section has the queried
  names resource records. When there are multiple
  IP addresses associated with a domain name, then
  such a domain name may be present in multiple
  records.

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DNS Master Files (Zone Files)

• A text file that is stored on a DNS nameserver
  and which specifies a single DNS zones DNS
  information is called a DNS Master File. The data
  that a DNS Master File contains are mentioned
  below.
• Global TTL (Time to Live)- The duration for
  keeping records in the local DNS cache.
• Start of Authority (SOA) record- The main
  authoritative nameserver for a zone.
• One or multiple resource records- Resource
  records store IP addresses and hostnames along
  with other information in DNS nameservers.

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