Basics of Domain Name System

This article gives you a basic yet good understanding of Domain Name System (DNS).

What is a Domain Name?

Computers communicate by using IP addresses to contact each other as we use a phone number to dial a phone number if we wish to call someone. Domain names on the internet are much like entries in a phone book. The phone book tells people looking for a business what the entries are just as a domain tells people (i.e. their computers) that a domain is hosted on the server.


A domain name usually consists of two or more parts (technically labels), separated by dots. For example:

  • The rightmost label conveys the top-level domain.
  • Each label to the left specifies a subdivision or subdomain of the domain above it.
  • A hostname refers to a domain name that has one or more associated IP addresses.

For example, the and domains are both hostnames.

domain name system



Domain Name System

The Domain Name System consists of a hierarchical set of DNS servers. Each domain or subdomain has one or more authoritative DNS servers that publish information about that domain and the nameservers 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 nameservers: the servers to query when looking up (resolving) a top-level domain name (TLD). Iterative and recursive queries:

  • An iterative query is one where the DNS server may provide a partial answer to the query (or give an error). DNS servers must support non-recursive queries.
  • A recursive query is one where the DNS server will fully answer the query (or give an error). DNS servers are not required to support recursive queries and both the resolver (or another DNS acting recursively on behalf of another resolver) negotiate use of recursive service using bits in the query headers.


DNS Propagation means time for any DNS changes to transmit across the Internet. Please remember that DNS changes in general can take up to 24-48 hours to fully propagate.


Root Domain

The root domain (also sometimes referred to as the “parent,” “naked,” or “apex” domain) is the primary entry for the domain without any subdomains. The NAME field typically remains blank as this would define a subdomain. This type of record should usually be an A record, with the value set to the destination IP address.


CNAME Records (Canonical Name) are used to define an alias hostname. A CNAME record takes this format:      IN     CNAME

This defines as an alias for the host whose canonical (standard) name is

A Record

A record means Address Record, assigns an IP address to a domain or subdomain name.

That way, users that try to go to will get to the right IP address. An A record or “Address Record” maps a hostname to a 32-bit IPv4 address. An “A” Record takes this format (example):

Name                                  TTL     TYPE    DATA   43200   A       IP Address

MX Record

An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain.

A zone can have one or more Mail Exchange (MX) records. These records point to hosts that accept mail messages on behalf of the host. A host can be an ‘MX’ for itself. MX records need not point to a host in the same zone. An ‘MX’ record takes this format: 14400 IN MX 0

The ‘MX’ preference numbers nn (value 0 to 65535) signify the order in which mailers select ‘MX’ records when they attempt mail delivery to the host. The lower the ‘MX’ number, the higher the host is in priority.

PTR Record / Pointer Record

Maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the domain that corresponds to an IP address implements reverse DNS lookup for that address. For example, at the time of writing, has the IP address, but a PTR record maps to its canonical name.

NS Record or “Name Server Record”

Maps a domain name to a list of DNS servers authoritative for that domain. Example:

SOA Record or “Start of Authority Record”

It specifies the DNS server providing authoritative information about an Internet domain, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.

TXT Record

The TXT Record allows an administrator to insert arbitrary text into a DNS record. For example, this record is used to implement the Sender Policy Framework and DomainKeys specifications.

For more details please see the knowledgeable.

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