Domain Name System

  • Domain Name System (DNS) is a service which allows you to resolve hostname to and IP address and vice versa.
  • It is simply a service which maps domain name to IP and IP to name.

Example for understanding DNS

When dealing with the large networks, system administrators should be able to locate the resources with minimal searching without caring about the IP address. On the other hand end-users don’t care about the IP address. They just want to connect and access the resources in the easiest possible way.

Consider you are an employee of one company with 500 other employees. You all use computers. And also share data with each other over a network.

Now when you share a data, at system administrator’s point of view – each system must be connected in network and should have its own address. This address is nothing but IP (Internet Protocol) address – which is in numeric form obtained from some binary codes. Which is simply like or or like wise.

Now if you want to share a data with some users randomly everyday. You need to keep these IP address of the that particular computer, which in my sense is difficult. So to make it easier that you identify the computer name where you want to share the data, some simple name is supposed to be given.

But computer doesn’t understand simple English. Oh ho.. What to do now?

Here is a way:

DNS (Domain Name System) is the way which maps IP Address to Name and Name to IP.
So for particular IP Address particular Name would be given that will help you or any other user to identify the system to share data. And this is done only by DNS.

When you use browser for internet and here you go type any website say,

In actual it is the name or Domain Name you can easily type, which is mapped with the IP of that website

DNS Zones

  • DNS zone is a area where you will configure the DNS records for mapping the IP address to host name
  • It is a portion of  DNS name space over which specific DNS services has authority.
  • There are 3 zones available in DNS. viz, Primary zone, Secondary zone and Stub zone.

Primary Zone

  • Primary zones are database that store records for the DNS zone
  • It contains the primary copy of DNS database.
  • All records update happen in the Primary zone

Secondary Zone

  • Secondary zones are non-editable copies (read only) of DNS database
  • A secondary zone gets its database from the Primary zone created.

Stub zone

  • Stub zones are used for conditional forwarding.
  • Stub zones work like a Secondary zone and are non-editable copy of Primary zone
  • Stub zones are read only because the contain only 3 records: Name Server (NS), Start of Authority (SoA) and Glue Host (A)
  • It is called Glue host record because it is used for NS record to forward message saying there is no IP address.

DNS Records

Address Mapping Record (A Record)

  • ‘A’ record specifies IP address (IPv4) for a given host name.
  • ‘A’ records are used for conversion of domain names to corresponding IP Address

AAAA Record

  • ‘AAAA’ record (also called as quad-A record)specifies IP address (IPv6) for a given host name.
  • It works the same as A record. The only difference is the type of IP address

Pointer Record (PTR)

  • As opposed to A and AAAA record PTR record is used to map IP address to domain name
  • It looks for domain name based on the IP address

Canonical Name (CNAME)

  • CNAME records are used to create an alias of the existing domain names.
  • If any domain name length is longer and you want to give some alternate short name you can use CNAME for creating alias of that DNS record.

Mail Exchange Record (MX)

  • The MX records specifies the mail exchange for the specific DNS record.
  • In order to use specific domain name for the email system you can create MX record for email services using SMTP to route emails.

Name Server Record (NS)

  • NS records are used to specify the authorative name server for given host.

Start of Authority Record (SoA)

  • SoA record specifies the core information about the DNS zone.
  • Information includes primary name server, email of domain administrator, the domain serial number and TTL for refreshing the zone.

Text Record (TXT)

  • TXT records are the used to point the value, but these records are not used for redirecting any traffic.
  • These records are simple text records used for validating the domain names in case of cross platform (company name to register Microsoft/O365/Gmail domain).

Service Record (SRV)

  • The SRV record is a specification of data in DNS defining the location of service. (i.e. hostname and port number of servers for specified services).