What is DNS?

What is DNS?

What is DNS?

Before discussing about Domain Name Server: we are going to explain some factor and simple difference between Domain Name Server and Domain Name System.

Domain Name SystemsDomain Name Systems (DNS) is mechanisms that assign easy to remember names to IP address. Domain is a large group of computers on the Internet. Under this scheme each computer has an IP address and a domain name. Domains have been made on the base of organization type or geographical locations, e.g., the domain name google.com (where, com indicates that Google is a commercial organization).

The Domain Name System (DNS) associates various information with domain names; most importantly, it serves as the “phone book” for the Internet by translating human-readable computer hostnames, e.g.www.ecomputernotes.com, into IP addresses, e.g., which networking equipment needs to deliver information.

It also stores other information such as the list of mail servers that accept email for a given domain. In providing a worldwide keyword-based redirection service, the Domain Name System is an essential component of contemporary Internet use.

DNS makes it possible to assign Internet names to organizations independent of the physical routing hierarchy represented by the numerical IP address. Because of this, hyperlinks and Internet contact information can remain the same, whatever the current IP routing arrangements may be, and can take a human-readable form, which is easier to remember than the IP address

The Domain Name System distributes the responsibility for assigning domain names and mapping them to IP networks by allowing an authoritative name server for each domain to keep track of its own changes, avoiding the need for a central register to be continually consulted and updated.

At the request of Jon Postel, Paul Mockapetris invented the Domain Name system in 1983 and wrote the first implementation. The original specifications appear in RFC 882 and RFC 883. In November 1987, the publication of RFC 1034 and RFC 1035 updated the DNS specification and made RFC 882 and RFC 883 obsolete. Several more-recent RFCs have proposed various extensions to the core DNS protocols.

The Domain Name System consists of a hierarchical set of DNS servers. Each domain or sub domain has one or more authoritative DNS servers that publish information about that domain and the name servers of any domains “beneath” it. The hierarchy of authoritative DNS servers matches the hierarchy of domains. At the top of the hierarchy stand the root name servers: the servers to query when looking up a top-level domain name.

Domain names, arranged in a tree, cut into zones, each served by a name server.

A domain name usually consists of two or more parts which is conventionally written separated by dots, such as ecomputernotes.com.The rightmost label conveys the top-level domain for example, the address www.ecomputernotes.com has the top-level domain com.Each label to the left specifies a subdomain of the domain above it. For example: ecomputernotes.com comprises a subdomain of the com domain, and www. ecomputernotes.com comprises a subdomain of the domain ecomputernotes.com.

In theory, this subdivision can go down 127 levels. Each label can contain up to 63 characters. The whole domain name does not exceed a total length of 253 characters

A hostname refers to a domain name that has one or more associated IP addresses; ie: the ‘www. ecomputernotes.com’ and ‘ ecomputernotes.com’ domains are both hostnames, however, the ‘com’ domain is not.

Basically there are two types of top level domains

Non-geographical Domains.

Geographical Domains.

(a) Non-geographical domains are those which indicate the type of organization, e.g. www.yahoo.com in which com indicates that it is commercial type of organization.




(b) Geographical domains indicate the code for individual countries, e.g. www.yahoo.co.in.

Domain Name System

Here .in indicates that the network connection is in a country named India. Non-geographical Domains: Some examples are given below in reference of Non geographical and Geographical domains. Some of the standard non-geographical domains are:

Geographical Domains: The geographical based top level domains use two-letter country designations. Examples of geographical domains are listed below:

Each domain corresponds to a unique numeric IP address. Whenever we specify a DNS name like www.yahoo.com. This name is converted to its corresponding IP address and this IP address is used to locate the exact site on Internet.

Domain helps in locating a computer on Internet or in other words DNS is the way that Internet domain names are located and translated into Internet Protocol Addresses. A domain name is a meaningful and easy-to-remember for an Internet address.

A domain name is an identification label that defines a realm of administrative autonomy, authority, or control in the Internet, based on the Domain Name System (DNS).

Domain names are used in various networking contexts and application-specific naming and addressing purposes. They are organized in subordinate levels (sub-domains) of the DNS root domain, which is nameless. The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains (gTLDs), such as the prominent domains com, net and org, and the country code top-level domains (ccTLDs).

Below these top level domains in the DNS hierarchy are the second-level and third-level domain names that are typically open for reservation by end-users that wish to connect local area networks to the Internet, run web sites, or create other publicly accessible Internet resources. The registration of these domain names is usually administered by domain name registrars who sell their services to the public.

Individual Internet host computers use domain names as host identifiers, or hostnames.

Hostnames are the leaf labels in the domain name system usually without further subordinate domain name space. Hostnames appear as a component in Uniform Resource Locators (URLs) for Internet resources such as web sites (e.g., en. wikipedia.org).

Domain names are also used as simple identification labels to indicate ownership or control of a resource. Such examples are the realm identifiers used in the Session Initiation Protocol (SIP), the Domain Keys used to verify DNS domains in e-mail systems, and in many other Uniform Resource Identifiers (URIs).

An important purpose of domain names is to provide easily recognizable and memorizable names to numerically addressed Internet resources. This abstraction allows any resource (e.g., website) to be moved to a different physical location in the address topology of the net1l1ork, globally or locally in an intranet. Such a move usually requires changing the IF addresses of a resource and the corresponding translation of this IP address to and from its domain name.

Parts of a domain name

A domain name consists of one or more parts, technically called labels that are conventionally concatenated, and delimited by dots, such as example.com.

The right-most label conveys the top-level domain; for example, the domain name www.example.com belongs to the top-level domain com.

The hierarchy of domains descends from the right to the left label in the name; each label to the left specifies a subdivision, or sub-domain of the domain to the right. For example: the label example specifies a sub-domain of the com domain, and www is a sub domain

of example .com. This tree of labels may consist of 127 levels. Each label may contain up to 63 ASCII characters. The fun domain name may not exceed a total length of 253 characters. In practice, some domain registries may have shorter limits.


A hostname is a domain name that has at least one IP addresses associated. For example, the domain names www.example.com and example.com are also hostl1ames, whereas the com domain is not.

Top-level domains

The top-level domains (TLDs) are the highest level of domain names of the Internet. They form the DNS root zone of the hierarchical Domain Name System. Every domain name ends in a top-level or first-level domain label.

When the Domain Name System was created in the 1980s, the domain name space was divided into two main groups of domains. The country code top-level domains (ccTLD) were primarily based on the two-character territory codes of IS0-3166 country abbreviations. In addition, a group of seven generic top-level domains (gTLD) was implemented which represented a set of categories of names and multi-organizations. These were the domains GOV, EDD, COM, MIL, ORG, NET, and INT.

Second-level and lower level domains

Below the top-level domains in the domain name hierarchy are the second-level domain (SLD) names. These are the names directly to the left of .com, .net, and the other top-level domains. As an example, in the domain en.wikipedia.org, wikipedia is the second-level domain.

Next are third-level domains, which are written immediately to the left of a second-level domain. There can be fourth and fifth-level domains, and so on, with virtually no limitation. An example of an operational domain name with four levels of domain labels is www.sos.state.oh.us.

The www preceding the domains is the host name of the World-Wide Web server. Each label is separated by a full stop (dot). ‘sos’ is said to be a sub-domain of ‘state.oh.us’, and ‘state’ a sub-domain of ‘oh.us’, etc. In general, sub-domains are domains subordinate to their parent domain. An example of very deep levels of sub-domain ordering is the IPv6 reverse resolution DNS zones, e.g.,, which is the reverse DNS resolution domain name for the IP address of a loop back interface, or the local host name.

Internationalized domain names

The character set allowed in the Domain Name System has prevented the representation of names and words of many languages in their native scripts or alphabets. ICANN has approved the Puny code-based Internationalized domain name (IDNA) system, which maps unicode strings into the valid DNS character set. Some registries have adopted IDNA.

Domain Name Registration

The right to use a domain name is delegated by domain name registrars who are accredited by the Internet Corporation for Assigned Names and Numbers (ICANN), the organization charged with overseeing the name and number systems of the Internet. In addition to ICANN, each top-level domain (TLD) is maintained and serviced technically by an administrative organization, operating a registry. A registry is responsible for maintaining the database of names registered within the TLD it administers. The registry receives registration information from each domain name registrar authorized to assign names in the corresponding TLD and publishes the information using a special service, the whois protocol.

Registries and registrars usually charge an annual fee for the service of delegating a domain name to a user and providing a default set of name servers. Often this transaction is termed a sale or lease of the domain name and the registrant may sometimes be called an “owner”, but no such legal relationship is actually associated with the transaction, only the exclusive right to use the domain name. More correctly, authorized users are known as “registrants” or as “domain holders”.

ICANN publishes the complete list of TLD registries and domain name registrars. Registrant information associated with domain names is maintained in an online database accessible with the WHOIS service. For most of the more than 240 country code top-level domains (ccTLDs), the domain registries maintain the WHOIS (Registrant, name servers, expiration dates, etc.) information.

Some domain name registries, often called network information centers (NIC), also function as registrars to end-users. The major generic top-level domain registries, such as for the COM, NET, ORG, INFO domains and others, use a registry-registrar model consisting of hundreds of domain name registrars (see lists at ICANN or VeriSign). In this method of management, the registry only manages the domain name database and the relationship with the registrars. The registrants (users of a domain name) are customers of the registrar, in some cases through additional layers of resellers.

In the process of registering a domain name and maintaining authority over the new name space created, registrars use several key pieces of information connected with a domain:

Administrative contact: A registrant usually designates an administrative contact to manage the domain name. The administrative contact usually has the highest level of control over a domain. Management functions delegated to the administrative contacts may include management of all business information, such as name’ of record, postal address, and contact information of the official registrant of the domain and the obligation to conform to the requirements of the domain registry in order to retain the right to use a domain name. Furthermore the administrative contact installs additional contact information for technical and billing functions.

Technical contact: The technical contact manages the name servers of a domain name. The functions of a technical contact include assuring conformance of the configurations of the domain name with the requirements of the domain registry, maintaining the domain zone records, and providing continuous functionality of the name servers (that leads to the accessibility of the domain name).

Billing contact: The party responsible for receiving billing invoices from the domain name registrar and paying applicable fees.

Name servers: Most registrars provide two or more name servers as part of the registration service. However, a registrant may specify its own authoritative name servers to host a domain’s resource records. The registrar’s policies govern the number of servers and the type of server information required. Some providers require a hostname and the corresponding IP address or just the hostname, which must be resolvable either in the new domain, or exist elsewhere. Based on traditional requirements (RFC 1034), typically a minimum of two servers is required.

Working of DNS

A DNS server is just a computer that is running DNS software. DNS software is generally made up of following elements


Name server

Database of resource records (RRs)

The actual name server responds to browser’s requests by supplying name to-address conversions. When it does not know the answer, the resolver will ask another name server for the information.

When you type a URL, your browser sends a request to the closest name server. If that server has ever filleted a request for the same host name (within a time period set by the administrator to prevent passing old information), it will locate the information in its cache and reply.

If the name server is unfamiliar with the domain name, the resolver will attempt to “solve” the problem by asking a server farther up the tree. If that does not work, the second server will ask yet another-until it finds one that knows. Once the information is located, it is passed back to your browser, and you can do your work. Usually this process occurs quickly but occasionally it takes an excruciatingly long time. In the worst cases, you will get a dialogue box that says the domain name doesn’t exist even though you know domain well it does.

This happens because the authoritative server is slow replaying to the first, and your computer gets tired of waiting so it times out (drops the connection). But if you try again, there is good chance it will work, because the authoritative server has enough time to reply, and your name server has stored the information in its cache.

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