What is a Domain Name in DNS ?

Map Of Internet 1973

About

The term domain name is a name:

It's also known as domain, its short format.

Usage Example

This examples show how the domain name is used to define a host resource.

HostName

The Hostname is a domain name that identifies a host.

Example: host.example.com is a domain name

Email address

In the email address label@name, the domain name is the part after the arobase.

The domain portion identifies the point (node) to which the mail should be delivered:

Url

In a url: https://host/path?query#fragment, the domain name is the host part that identifies a HTTP server.

Name Example

With the following absolute name:

smtp.us.datacadamia.com.

You will read the name from right to left, with each level of the hierarchy divided by dots:

  • the invisible null character is the root (at the right of the point)
  • com, datacadamia, us and smtp are labels
  • com. is the Top Level domain
  • datacadamia is the apexLabel of the apex domain name datacadamia.com.
  • datacadamia.com. is a subdomain of com.
  • us.datacadamia.com. is a subdomain of datacadamia.com.
  • us.datacadamia.com. is the domain for the label smtp
  • Zone
    • smtp being the furthest left label may be the hostname (short) (if the resource is a host)
    • Except for the hostname, every section is called a zone zone, which defines a particular namespace:
      • us.datacadamia.com. is a zone
      • datacadamia.com. is a zone
      • com. is a zone

Syntax

Hierarchical Name

A domain name 1) is a succession of one or more labels separated by dots (known alas as the dot-atom form) that indicates the hierarchical structure (tree) of the namespace.

In a simplified way, a domain name looks like this:

[[.]label]*[.apexLabel][.tldLabel].rootLabel

where:

The domain is the namespace of the last label.

You can find the exact syntax at the end of this article as EBNF grammar

The label is zero to 63 octets in length. The domain name is the list of the labels on the path from the node to the root of the tree.

By convention, the labels that compose a domain name are printed or read left to right:

  • from the most specific (lowest, farthest from the root)
  • to the least specific (highest, closest to the root).

Text label Encoding

The text label encoding is ASCII. The international characters are supported via the punycode encoding.

Relative (Short) vs Absolute

A name has two kind of format:

Absolute

A complete/qualified domain name ends always with the root label of the namespace tree, and therefore the complete/qualified printed form ends with a dot.

An absolute domain name is more known as the fully qualified domain name (or FQDN)

For example, smtp.us.datacadamia.com.

Relative

A relative domain name represents the starting labels and should be completed by the local domain or zone.

For example, the “smtp” name used in the us.datacadamia.com. (domain or zone)

A relative name is also known as the short name

They are the names stored in DNS records.

Case

domain names can be written with arbitrary case, but domain name comparisons for all present domain functions are done in a case-insensitive manner

A node can be created with the label A or a, but they can't be sibling

Length Limitations

The total number of octets that represent a domain name (i.e., the sum of all label octets and label lengths) is limited to 255.

Zone

A domain name may also be logically an administrative unit and be therefore called a zone.

Storage

DNS record

A DNS name is an IP name stored in a DNS database. You will find the relative form in the first column of a DNS table.

In a DNS table, you would see:

NAME       TYPE   VALUE
--------------------------------------------------
bar        CNAME  foo.example.com.
foo        A      192.0.2.23

where

Host file

What is the hosts file ?

Hosting

See What is Hosting? (or hosted domains for HTTP, Email, )

Security

Subdomain TakeOver

Due to hosting, you may be at risk of a sub-domain takeover.

Registration

See Domain Registration and Ownership

Grammar

The exact definition of a domain name is given in the Rfc1024 - Preferred Name Syntax)

domain ::= subdomain | " "
subdomain ::= label | subdomain "." label
label ::= letter ( ( ldh-str ) let-dig )
ldh-str ::= let-dig-hyp | let-dig-hyp ldh-str
let-dig-hyp ::= let-dig | "-"
let-dig ::= letter | digit
letter ::= [A-Za-z]*
digit ::= [0-9]*

2)





Discover More
Map Of Internet 1973
AAAA DNS record

A AAAA DNS record maps a domain name to a IPV6 address
Map Of Internet 1973
DNS - Domain Name Space (NS)

The domain name space is a name space for a DNS name that shows: a tree structure (ie hierarchical) where the hierarchy levels are separated by the dot character . Each node on the tree corresponds...
Map Of Internet 1973
DNS - Record

A DNS record is a row in a DNS database. Example of a A record. where: api is a relative name IN is the INTERNET class (An other value is ANY) A is the A record 164.132.99.202 is the Ip address...
Map Of Internet 1973
DNS - nslookup command line

Nslookup is a DNS client program to query (ie lookup) domain name servers and get back DNS record information nslookuphost fileping Nslookup has two modes: The local DNS file is /etc/resolv.conf...
Map Of Internet 1973
DNS - rDNS - Reverse DNS (lookup|resolution) - from IP to name

A reverse dns lookup is a dns lookup that: query the PTR record with a reverse map name in order to get the DNS name (known also as the reverse DNS name) from a IP address forward dns lookup...
Map Of Internet 1973
DNS Alias record

An alias is a DNS record with a name that resolves directly to an ip_address. cnamenamenamean ip addressDNS resolverroundtripip_addressCNAME Before creating an ALIAS record, check there are no: ...
Map Of Internet 1973
DNS clients - A list of client that can query the DNS database

A DNS client is an application that calls the resolver to query name database in order to perform forward lookup (IP from name) or reverse lookup(Name from IP). This page lists this application
How to avoid SPAM with Postfix

An article on how to configure Postfix to avoid SPAM
Certificate Validity Period Not Before Not After Portecle
Identification Material - Certificate (or Public Key Certificate)

A certificate is a document which permits to define with certainty the owner of the private key (ensures that the party you are communicating with is whom you think.) because it's digitally signed A certificate...
Map Of Internet 1973
Network - (Internet) Apex Domain (also known as Zone domain)

An apex domain is the domain name that: is composed of the two top-level label of a name (the first being the top level domain) does not contain a subdomain For example: example.com is an apex domain....



Share this page:
Follow us:
Task Runner