A Domain Name System assigns an alphabetic name to a numeric IP address and is made up of multiple Domain Name servers that enable IP address mapping for devices on the Internet (usually servers).

1. Domain Name System
Explained

2. Table of Contents
2
DNS
Uses of DNS
Types of DNS Servers
Steps in a DNS Lookup
Types of DNS Queries
DNS Protocol
DNS Master Files (Zone
Files)

3.  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 Internet’s 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 hosting is provided by web hosting companies.
The most reliable web hosting companies are usually referred to as the “Best Website Hosting Company”, the
“Best Windows Hosting Company”, the “Top Cloud Hosting Company” etc.
3
DNS

4. 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).
4
Uses of DNS

5. 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 hostname’s 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 hostname’s IP address to the DNS recursor, which
had made the request initially.
5
Types of DNS Servers

6. 6
1-800-123 -8156
Whoa!That’s a big number, aren’t
you proud?

7. 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 server’s response, which involves the address of a TLD DNS server. This Top Level Domain
DNS server stores its domain’s information.
 A request is made by the resolver to the TLD.
 The TLD server’s response contains the IP address that belongs to the domain’s 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 resolver’s 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.
7
Steps in a DNS Lookup

8. 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 client’s
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 isn’t 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.
8
Types of DNS Queries

9. 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 message’s type as well as other
information, such as if the nameserver is authoritative, the query is or isn’t 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 name’s resource records. When there are multiple IP
addresses associated with a domain name, then such a domain name may be present in multiple records.
9
DNS Protocol

10. A text file that is stored on a DNS nameserver and which specifies a single DNS zone’s DNS information is called a
DNS Master File.The data that a DNS Master File contains are mentioned below.
 GlobalTTL (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.
10
DNS Master Files (Zone Files)

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