NS (Domain Name System or Service or Server), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to198.105.232.4.

             The Domain Name System (DNS) is a hierarchical naming system built on a distributed database for computers, services, or any resource connected to the Internet or a private network. Most importantly, it translates domain names meaningful to humans into the numerical identifiers associated with networking equipment for the purpose of locating and addressing these devices worldwide.
             Domain Name System is used to map IP address to host name and host name to IP Address. It organizes the name in hierarchical order. The root domain is repressed by a dot (.) or a Full Qualify Domain Name (FQDN) is identified by a dot in the last.
 
DNS Resolvers
DNS works in a client/server fashion. DNS servers respond to requests from DNS clients called resolvers. ISPs and other organizations set up local DNS resolvers as well as servers. Most DNS servers also act as resolvers, routing requests up the tree to higher-level DNS servers, and also delegating requests to other servers. DNS servers eventually return the requested mapping (either address-to-name or name-to-address) to the resolver.
 
DNS Records
DNS records or Zone files are used for mapping URLs to an IPs. Located on servers called the DNS servers, these records are typically the connection of your website with the outside world. Requests for your website are forwarded to your DNS servers and then get pointed to the Web Servers that serve the website or to Email servers that handle the incoming email.
DNS Records Types:-
This List of DNS record types provides an overview of types of resource records (database records) stored in the zone files of the Domain Name System (DNS). The DNS implements a distributed, hierarchical, and redundant database for information associated with Internet domain names and addresses. In these domain servers, different record types are used for different purposes.
The below DNS records are mostly used in all DNS Configurations. Now we will see each one with examples
 
Type
Value (decimal)
Defining RFC
Description
Function
 
A
 
1
 
RFC 1035
 
address record
Returns a 32-bit IPv4 address, most commonly used to map hostnames to an IP address of the host, but also used for DNSBLs, storing subnet masks in RFC 1101, etc.
AAAA
28
RFC 3596
IPv6 address
record
Returns a 128-bit IPv6 address, most commonly used to map hostnames to an IP address of the host.
CNAME
5
RFC 1035
Canonical name
record
Alias of one name to another: the DNS lookup will continue by retrying the lookup with the new name.
MX
15
RFC 1035
Mail exchange
record
Maps a domain name to a list of message transfer agents for that domain
 
PTR
 
12
 
RFC 1035
 
pointer record
Pointer to a canonical name. Unlike a CNAME, DNS processing does NOT proceed, just the name is returned. The most common use is for implementing reverse DNS lookups, but other uses include such things as DNS-SD.
NS
2
RFC 1035
name server
record
Delegates a DNS zone to use the given authoritative name servers
 
SOA
 
6
 
RFC 1035
 
start of authority
record
Specifies authoritative information about a DNS zone, including the primary name server, the email of the domain administrator, the domain serial number, and several timers relating to
 
SRV
 
33
 
RFC 2782
 
Service locator
Generalized service location record, used for newer protocols instead of creating protocol-specific records such as MX.
 
 
 
TXT
 
 
 
16
 
 
 
RFC 1035
 
 
 
Text record
Originally for arbitrary human-readable text in a DNS record. Since the early 1990s, however, this record more often carries machine-readable data, such as specified by RFC 1464, opportunistic encryption, Sender Policy Framework (although this provisional use of TXT records is deprecated in favor of SPF records), Domain Keys, DNS-SD, etc.
 
NAPTR
 
35
 
RFC 3403
Naming Authority Pointer
Allows regular expression based rewriting of domain names which can then be used as URIs, further domain names to lookups, etc

Name Space

The domain name space consists of a tree of domain names. Each node or leaf in the tree has zero or more resource records, which hold information associated with the domain name. The tree sub-divides into zones beginning at the root zone. A DNS zone may consist of only one domain, or may comprise many domains and sub-domains, depending on the administrative authority delegated to the manager.
             DNS is the name service provided by the Internet for TCP/IP networks. DNS is broken up into domains, a logical organization of computers that exist in a larger network. The domains exist at different levels and connect in a hierarchy that resembles the root structure of a tree.
DOMAIN NAME REGISTRATION
The right to use a domain name is delegated by domain name registrars which 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.
         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.)
DNS ZONE
Zones are name space area represented by a FQDN in other words information about records of the resource within your DNS domain in stored in a zone file and this zone file exists on the hard drive of one of your name space server. General there is two types: - (1) Forward lookup zone (2) Reverse lookup zone.
 
Zone Categories
Zone in divided in three categories
  1. Primary Zone: - A primary zone server is the master server of that zone. It includes all the records.
  2. Secondary Zone: -This are called backup zone server and contains the copiers of master sever records.
  3. Stub Zone: -Stub zone one mini zone that contains few records that host for master zone. It is similar to the secondary zone but it contains only following records.
  • SOA(Start Of Authority)Record
  • NS (Name Space) Record
  • Host (A) Records
 
DNS Delegation
It is process of Transferring authority a zone from one server to another server.
Likewise, an organization administering a domain can divide it into sub domains. Each of those sub domains can be delegated to other organizations. This means that an organization becomes responsible for maintaining all the data in that sub domain. It can freely change the data, and even divide up its sub domain into more sub domains and delegate those. The parent domain retains only pointers to sources of the sub domain's data so that it can refer queries there.

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