To understand domains, we need to first go over IP.
Every device connected to the internet (computers, smartphones, routers, etc.) has a unique IP address made up of a series of numbers.
IP addresses can be broadly classified by mutability into dynamic IPs and static IPs.

• Dynamic IP: an IP address that gets renewed at arbitrary points in time. The renewal interval isn't fixed. Applies to most internet connections.
• Static IP: an IP fixed to a connection line that never gets renewed. Provided as an add-on service, and suitable for cases like shopping malls or companies that need to run a system continuously.

Just as we look up an address to visit a place we want to go, visiting a website run on a particular server requires the IP that serves as that server's address.
Unfortunately, an IP consists of irregular numbers, which makes it somewhat difficult for people to remember easily. The domain exists to relieve this inconvenience.

A domain is divided into an SLD (subdomain), domain, and TLD (top-level domain). Information about a domain is primarily managed by each local DNS server, and ultimately managed by the Root DNS, which manages the TLD.

For more details on domains, refer to the earlier post URI? URL? URN? Distinguishing Resource Identifiers.

The actual IP of the site we commonly call Naver is 125.209.222.141. But none of us ever access Naver using that IP. Instead, we access it via the domain https://www.naver.com. The reason is simple: since the address itself contains the keyword naver, it's easy to remember.

A domain is an address made up of characters rather than numbers. Because it's made of characters, it's easy to give the address meaning. This makes it easier for users to remember the address, increasing its accessibility.
Connecting a desired IP to a created domain allows that IP to be accessed via the domain address as well. Depending on the domain provider, not only alphanumeric characters but also Unicode characters like Korean are supported, allowing for a distinctive address instead of a rigid IP.

This raises a question. We know that the IP 125.209.222.141 and the domain https://www.naver.com both point to Naver, but how does the internet actually know the link between the two addresses?

This can be understood by looking at how a domain works. Let's use accessing the domain blog.itcode.dev as an example.

1. An attempt is made to access blog.itcode.dev via HTTP communication.
2. Information about blog.itcode.dev is requested from the local DNS assigned to the network.
   • If the local DNS already holds information for that domain, it provides the information immediately.
3. If there's no information for blog.itcode.dev, the request is sent to the nearest Root DNS for that domain's information.
4. The Root DNS provides the local DNS with information about the DNS server that manages the .io TLD.
5. The local DNS requests the information from the TLD's DNS server that manages blog.itcode.dev.
6. The TLD DNS server provides information (such as the IP) for blog.itcode.dev.
7. Since the local DNS now knows the IP for blog.itcode.dev, it can use it to access the site.

Fundamentally, a domain must always be linked to a single IP. Thanks to this characteristic, a domain always returns one specific, fixed IP.