New to the domain name industry, or want to refresh your general knowledge about domain names ? I will try in this post to explain some basics of domain names to help you understand details involved. If you have been in the industry since 10 years, then this article is definitely not for you
What is a domain name ? (and what is not)
A Domain Name is the name used to identify resources belonging to the same authority on internet. It has been thought as an abstraction over IP addresses since it’s more readable, memorizable and easier to distinguish.
Often people do not make the difference between an URL, a Fully Qualified Domain Name and a Domain Name. I think this is the first step to understand the Domain Name System, so let’s define it.
Do not confuse it with …
A domain name is not an URL (Uniform Resource Protocol), and it’s not (exactly) a FQDN but it is a part of both of them.
An URL, as defined by the RFC 1738, is used to locate documents over the internet and is composed by the following parts:
The FQDN (Fully Qualified Domain Name) is a specific domain name that defines all its levels, and it’s used to identify a resource
But domain name is definitely not:
- a website
- a web hosting
- a mailbox
The domain names are obviously mostly present in all these services. But as described previously, they are used only to have an easily identifiable and memorizable name, and here are their unique roles.
Basically the domain name is composed in 2 parts, a name and an extension.
Notice: The term extension is not really accurate due to the hierarchical nature of the domain name system, (explained later on).
Now that we have a broad definition of a domain name, we will detail a little bit more deeply each of its components.
The Domain Name Data Structure
For me, the best way to describe the domain name is by defining its logical structure as UML, to transmit the big picture.
This data structure could be expressed in plain english this way:
- Domain has a name and belongs to a Top Level Domain
- Domain has 4 dates: the registration, the last update, the expiration and the release
- Domain has 4 contacts: the registrant, the administrative, technical and the billing
- Domain has many name servers (at least 2)
- Domain belongs to a sponsoring registrar
Again, these are general rules, you should bear in mind that each Registry
is responsible for its own rules. This structure is reflected in the
public whois results of generic domains, as you may figure out on the
whois of my
adlani.com domain if you execute the whois command
adlani.com or if you go to an online whois service like
A registrar is a service provider accredited with one or more registries, that registrants use to buy and manage domain names.
That sounds non trivial, let’s define some vocabulary to clarify it:
|Registry||Authority responsible in managing a Top Level Domain (ie. Verisign for .COM)|
|Registrar||Service Provider accredited with one or more registries|
|Registrant||Owner of registered domain names|
Most of the registries have a Registry/Registrar, which means you could not register a .fr domain name directly with AFNIC, but you have to go through an accredited registrar.
When you have registered the domain with a sponsoring registrar, its name is usually published in the whois.
More details about this subject will be provided on section “The Registry, the registrar and the registrant”.
The domain name should declare during the registration process several (2+) authoritative name servers so the registry shall delegate to them.
This set of name servers is here to ensure that even if one of them is inaccessible, the other(s) will take over by responding to the queries.
The role of the authoritative and the difference with the resolver will be described more precisely in the section “An hierarchical distributed system”.
In order to be contacted by your registrar, by the registry or by anyone else as required by ICANN, you are requested to fill in contact details of your domain.
There are 4 different kind of contacts
|Owner/Registrant||represents the legal owner of a Domain Name|
|Technical Contact||Person in charge of the technical aspect of the domain name (mainly name server)|
|Billing Contact||Financial Contact Person, not often used on principal tlds|
It is highly recommended to keep your domains up-to-date. In case of inaccurate whois report and if your registrar is not able to contact you, they will delete the domain name.
A Registered Name Holder’s willful provision of inaccurate or unreliable information, its willful failure promptly to update information provided to Registrar, or its failure to respond for over fifteen calendar days to inquiries by Registrar concerning the accuracy of contact details associated with the Registered Name Holder’s registration shall constitute a material breach of the Registered Name Holder-registrar contract and be a basis for cancellation of the Registered Name registration. Article 126.96.36.199 - ICANN Registrar Accreditation Agreement
ICANN requests its accredited registrars to apply the Whois Data Reminder Policy, which means:
At least annually, a registrar must present to the registrant the current Whois information, and remind the registrant that provision of false Whois information can be grounds for cancellation of their domain name registration. Registrants must review their Whois data, and make any corrections. Whois Data Reminder Policy - ICANN
The domain names are not sold for lifetime. It’s more like a rent, cause you register it for a defined period (usually between 1 and 10 years). At the end of this period you have the ability to renew it or not. The life cycle of domain names is mainly based on dates, that’s why there are several date fields published in the whois. I used “mainly” because domain names shall be deleted for non-compliance to the registry rules or following a court decision.
|Registration date||Date the domain name was registered with the registry|
|Last update date||Date the registry received the last update (UPDATE, TRADE, RENEW)|
|Expiration date||Date the domain will not be active anymore|
|Release date||Date the registrant will have no more chance to renew it and will be publicly available|
Domain Name Life Cycle
A domain name is considered as available if no one has already registered it and if the naming convention of the registry allows it.
As soon as a domain registration has been executed, it becomes registered
A registered domain, will be displayed as taken until the deletion by the registry, which happens after the expiration, following a court decision or if the domain has broken some registry rules.
At the registration, the registrant has to choose the duration of the initial period. This period can go from 1 to 10 years selectable by year.
Once registration done, the domain name is the property of the registrant and is managed through the registrar.
During this period, the following actions are possible:
|NS Update||Change his authoritative name servers|
|Contact Update||Update the administrative, billing or technical contact|
|Domain Trade||Change the owner of the domain|
|Domain Transfer||Transfer the domain name to another registrar|
At the end of this period, you will be sent a reminder by the registrar to renew your domain name before the expiration date. If no action has been taken the domain is entering the Auto Renew Grace Period
Auto Renew Grace period
During this, the domain name is still active at the registry during 30 days (auto renewed). The registrant has still the ability to renew it or to let the domain expire.
This procedure has been put in place to prevent renewals issues during absence without cut of service. But after this period, the registrar will ask the registry to delete this domain which leads to the redemption period.
During the Redemption Period, the domain name is de-activated from the root zone. That is to say, any service attached to this domain name will stop working immediately.
The aim of this period is to allow the domain name registrant, if he missed
all the registrar’s reminders, to detect that his domain has expired and to let
him reactivate it. he’s the only one able to renew it.
After this period the domain is to be deleted.
At the end of the redemption period, a pending delete status will automatically be applied on the domain. At this step, no registrar shall be able to act on the domain, neither reactivate it. It will be dropped from the registy database in the 5 coming days.
After that, the domain becomes available again.
An hierarchical distributed naming system
A domain name is composed by one or more parts separated by dots (.).
Those parts represent the different levels in the hierarchical tree, and each one
is an independent zone in the tree structured name space.
To represent this tree, the domain name shall be read part by part from right to left.
www.example.com. should be interpreted like
.com.example.www and represented as following:
This representation could be simplified to:
|Layer 1||Top Level Domain||com, net, org, fr, de, nl, eu, asia|
|Layer 2||Second Level Domain||co.uk, com.es, google.com, mit.edu|
|Layer 3+||Third Level Domain||www.google.com, mail.google.com, amazon.co.uk|
You understand better now why I’ve said previously that the terminology of “extension” was not really appropriated: the domain name string shall be read from right to left.
It is said as distributed because of the fact that each domain (each element in each layers) is managed in an independent zone file hosted on several authoritative name servers.
A name server is a program able to translate domain names into IP addresses. This process is named domain name resolution. A name server can also be Authoritative or Recursive (sometimes both but it’s not recommended)
Authoritative Name Servers
Authoritative name servers are responsible for providing the official response for the zones they are currently hosting. They are declared during the domain name registration process and are (usually) published in the whois record. They are usually provided by the registrar for free with the domain name registration, but you can also subscribe to professional DNS service or use your own ones.
Recursive Name Servers
Recursive Name Servers, also referred as DNS or Resolvers, are the tools able to convert the URL you’ve entered in your browser to addresses understandable by machines. They are querying step by step all the authoritative name servers from the domain hierarchy. That’s where the recursive comes from.
The results provided by the authoritative name servers, during the Time To Live value (TTL is available on
all the DNS resource records), will be cached by the resolvers for performance matter.
The following video is the best illustration of how a DNS resolution is done.
Top-level, Second Level domains
You’ve probably already heard (or will) hear about all those words making part of the domain name industry vocabulary: Top Level Domains, Second Level Domain, and TLDs.
Top Level Domain
A top level domain, TLD, is the domain name just under the ROOT of the domain name system. In other words it’s the “extension” of your domain name (com, net, de, nl,…).
The TLDs are delegated directly from the root zone by IANA (who is responsible of it). An up-to-date list of all the existing TLDs is available on IANA’s website here
There are 4 different types of TLDs existing: Generic, Country Code, Sponsored, Infrastructure
|Generic TLD (gTLDs)||The generic TLDs, also known as gTLDs, are the most famous since some of them were part of the initial release and usually are not restricted.||com, net, org, info, ...|
|Country Code TLD (ccTLDs)||The ccTLDs, are the Top Level Domains allocated to a country based on the 2 letters version of its [ISO 3166-1 code](http://en.wikipedia.org/wiki/ISO_3166-1).||fr, de, us, nl, es, ...|
|Infrastructure TLD||The infrastructure TLDs are reserved by IANA for technical purpose and contains only the .arpa top level domain. For more information about the arpa zone, please refer to the documentation available on IANA's website||.arpa|
|Sponsored TLD||The sponsored TLDs, considered also has a sub category of the gTLDs, are specialized in the specific community.||coop, museum, edu, aero|
Second Level Domain
Usually called second-level domains, they are registered with your Domain Name Registrar. The second level domain are composed with a name/label and a TLD.
Example: anouar.im, google.com, …
Other cases of SLD offer the registration of third level domains as a specialized alternative to TLDs for their customers.
- uk: Because of the registration restriction on the TLD
- .co.uk - general use
- .gov.uk - government
- .ltd.uk - limited companies
- .me.uk - general use -fr: To provide additional categories
- .assoc.fr - association use
- .tm.fr - trademarks use
Some are just provided by private companies owning short second level
domain such as
It permits to override the limitation on some top level domains:
The Registry, the registrar and the registrant
reg·is·try /ˈrejəstrē/ Noun
- A place or office where registers or records are kept
The registry is the authority responsible of managing a Top Level Domain (ie. Verisign for .COM).
In a more traditional market, the registry could be compared to wholesaler.
Each registry fixes its own rules. This is the reason why I’ve said previously that the elements shall vary from a registry to another.
Some examples of naming convention rules could be:
- minimum 3 letters
- minimum registration period of 2 years
- maximum registration period of 10 years
- no sexual or pornographic connotation
- maximum 10 domains per registrant
- registrant living in a certain country
- should not be a reserved domain
The accreditation rules are also fixed by the registry and define the mandatory steps needed to be an official registrar. An example of those steps could be:
- to be ICANN accredited
- to credit an account with a certain amount
- to have authoritative name server in a certain country
- to pass a MCQ on the management rules of the registry
- to pass a technical test to validate API calls
All registrars are required to be accredited with the registry in order to resell domain names.
reg·is·trar /ˈrejəsträr/ Noun
- An official responsible for keeping a register or official records.
An accredited registrar is a Service Provider allowed to sell the TLDs provided by a registry.
More basically, if a customer wants to register a domain name the registrar, being an authorized retailer, can provide it from the registry.
As an intermediate between the registry and the registrant, registrars have to handle at the same time a B2C and B2B relationship.
The B2C being between it and the registrant, to whom it offers a web interface to order and manage his domain names.
The B2B being between it and the registry, whom it communicates with over APIs to automate the provisioning,
reg·is·trant /ˈrejəstrənt/ Noun
- A person who registers.
A registrant is an individual or an organization that owns a domain name. The registrant can be yourself or your company when you register your own domain name.
- DNS Glossary: Men & Mice DNS Glossary
- RFC 1034: DOMAIN NAMES - CONCEPTS and FACILITIES
- RFC 1035: DOMAIN NAMES - IMPLEMENTATION and SPECIFICATION
- RFC 3172: Management Guidelines & Operational Requirements for the ARPA
- RFC 1738: Uniform Resource Locators
- ICANN: Internet Corporation for Assigned Names and Numbers
- IANA: The Internet Assigned Numbers Authority
- Root zone DB: Root Zone Database
I hope you enjoyed this post. If you’d like to discuss feel please feel free to a comment below or to drop me an email.