Domain Name System
Published: 2023-05-28 18:11:58

**DNS (Domain Name System)** provides a simple way for us to communicate with devices on the internet without remembering complex numbers. Much like every house has a unique address for sending mail directly to it, every computer on the internet has its own unique address to communicate with it called an **IP address**. 

An IP address looks like the following 104.26.10.229, 4 sets of digits ranging from 0 - 255 separated by a period. When you want to visit a website, it's not exactly convenient to remember this complicated set of numbers, and that's where DNS can help.

Now, let us talk about Domain Hierarchy. The DNS follows the following hierarchy - 


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/0lpd4nenrqreo0ar8b3c.jpg)

- **TLD (Top-Level Domain)**

> A TLD is the most righthand part of a domain name. So, for example, the dev.to TLD is .to. There are two types of TLD, **gTLD (Generic Top Level)** and **ccTLD (Country Code Top Level Domain)**. 

> Historically, a gTLD was meant to tell the user the domain name's purpose; for example, a .com would be for commercial purposes, .org for an organization, .edu for education and .gov for government. And a ccTLD was used for geographical purposes, for example, .ca for sites based in Canada, .co.uk for sites based in the United Kingdom and so on. Due to such demand, there is an influx of new gTLDs ranging from .online , .club , .website , .biz and so many more.

- **Second-Level Domain**

> Taking dev.to as an example, the .to part is the TLD, and dev is the Second Level Domain. When registering a domain name, the second-level domain is limited to **63 characters** + the TLD and can only use a-z 0-9 and hyphens (cannot start or end with hyphens or have consecutive hyphens).

- **Subdomain**

> A subdomain sits on the left-hand side of the Second-Level Domain using a period to separate it; for example, in the name admin.dev.to the admin part is the subdomain. 

> A subdomain name has the same creation restrictions as a Second-Level Domain, being limited to 63 characters and can only use a-z 0-9 and hyphens (cannot start or end with hyphens or have consecutive hyphens). You can use multiple subdomains split with periods to create longer names, such as jupiter.servers.dev.to. But the length must be kept to **253 characters or less**. There is no limit to the number of subdomains you can create for your domain name.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/dg6mubgzlofbphelcmmh.png)

Now, let us talk about DNS Record Types. DNS isn't just for websites though, and multiple types of DNS record exist. We'll go over some of the most common ones that you're likely to come across.

- **A Record**

> These records resolve to IPv4 addresses, for example 104.26.10.229

- **AAAA Record**

> These records resolve to IPv6 addresses, for example 2606:4700:20::681a:be5

- **CNAME Record**

> These records resolve to another domain name. A common example is when you have both example.com and www.example.com pointing to the same application and hosted by the same server.

- **MX Record**

> These records resolve to the address of the servers that handle the email for the domain you are querying. These records also come with a priority flag. This tells the client in which order to try the servers, this is perfect for if the main server goes down and email needs to be sent to a backup server.

- **TXT Record**

> TXT records are free text fields where any text-based data can be stored. TXT records have multiple uses, but some common ones can be to list servers that have the authority to send an email on behalf of the domain (this can help in the battle against spam and spoofed email). They can also be used to verify ownership of the domain name when signing up for third party services.