How Do URLs Turn Into IP Addresses? A Simple Q&A on DNS and Domain Names

Preface

Today we will walk through a plain‑language article about URL , IP address , domain name , DNS , and domain name resolution using a simple Q&A format to help readers understand for study, interviews, and work.

1. A Question

Before raising the question, note the following:

All data on the Internet is stored on hosts (servers).

Every host on the Internet has a unique IP address.

Communication between any two hosts is performed via IP addresses.

Considering the simplest communication between two hosts – browsing – we ask: the Internet uses IP for host communication, yet we only type a URL, not an IP. How does the system find the correct host?

Therefore, there must be a mechanism that resolves a URL into an IP address, and this mechanism is the main thread of the article.

2. URL

1. What is a URL?

A URL, also called a domain name or Uniform Resource Locator, is the name used by Internet users to identify a host. The name is unique and hierarchical, often reflecting the host’s account, function, nature, region, or organization, making it easy to remember.

The URL (Uniform Resource Locator) indicates the server and specific page location of an Internet host. Its composition rules and examples are shown below.

Feature: URL naming follows Internet domain rules, is easy to manage, and is bound to an IP address so that when a user accesses a domain, the URL can be efficiently mapped to the IP address by the domain name server.

2. What problems does a URL solve?

The URL / domain name / URL solves two problems:

Problem 1: IP addresses are the uniform addressing method for all hosts, but they are hard to remember because they are just numbers.

Problem 2: Application‑level software typically does not use IP addresses directly; users must input a meaningful hostname to access a host.

3. URL structure composition

The naming of host names (i.e., URLs/domain names) follows rules set by the Internet’s “name management authority”, the Domain Name System (DNS). The composition is:

hostname.organization.network.top‑level domain

In the Internet, a host’s domain name consists of all its hierarchical domain levels and its own name, separated by dots. The rightmost part is the top‑level domain, the leftmost part is the host’s own name.

Below we will detail the DNS system, including the problems it solved, its history, hierarchy, top‑level domains, name servers, and the resolution process.

3. DNS (Domain Name System)

1. What is DNS?

DNS

(Domain Name System) is a distributed database that provides the mapping between domain names and IP addresses.

2. DNS history

3. What problems does DNS solve?

Before DNS, each host’s hosts file recorded all hostnames and their IP addresses. The file had to be regularly updated and synchronized, which became difficult as the number of hosts grew, leading to conflicts. In 1983 DNS was created to replace the hosts file.

4. DNS hierarchy

DNS is a hierarchical tree. Each level is a domain with the following meanings:

A domain represents a region or scope.

Each domain can contain many hosts.

Every host has its own domain, though not necessarily a domain name address.

Domain name length is generally limited to 63 characters, with a maximum of 255 characters for the full name.

Allowed characters are letters (case‑insensitive), digits, and hyphens (not at the start or end).

The server that holds a domain is called a name server and maps the domain to an IP address.

While domain names solve the memorization problem, actual communication still requires IP addresses; DNS therefore efficiently maps domain names to IP addresses.

5. Name servers

Name servers form the distributed network of DNS. Their main function is to provide mutual mapping services between domain names and IP addresses for internal and external hosts.

A client sends a domain name to its local DNS server; the server returns the corresponding IP address. If the local server cannot resolve the name, it follows the standard DNS resolution flow to query higher‑level servers.

4. Domain name resolution process

The process of obtaining an IP address from a domain name involves several key components, illustrated below.

Root name servers

: The highest‑level servers (13 IPv4 servers) that know the addresses of top‑level domain servers. Top‑level domain servers: Manage second‑level domains under each TLD. Authoritative name servers: Provide DNS query services for a specific zone. Local DNS server: Usually provided by the ISP; it receives the user’s query first.

One picture to understand the whole process

Using an example of accessing a news website, the following steps occur:

1. The user enters the website URL in a browser; the computer sends a query to the local DNS server.

2. The local DNS server checks its cache for the IP address; if not found, it queries a root name server.

3. The root server points the local server to the appropriate .com top‑level domain server.

4. The .com server directs the request to the domain’s authoritative server.

5. The authoritative server returns the IP address; the local DNS server caches it and sends it back to the user.

Conclusion

This article uses plain language and visual diagrams to explain the principles of URLs, domain names, IP addresses, DNS, and the resolution process, helping readers learn and remember these core networking concepts.