Understanding URLs, IP Addresses, Domain Names, DNS and the Domain Name Resolution Process

In this article the author, a senior architect, presents a comprehensive, easy‑to‑understand overview of URLs (also called domain names or Uniform Resource Locators), IP addresses, DNS, and the domain name resolution mechanism.

1. What is a URL? A URL is a human‑readable name that uniquely identifies a host on the Internet. It follows a hierarchical naming rule and is easier to remember than raw numeric IP addresses.

2. Why URLs are needed? IP addresses are difficult to memorize and most applications require a meaningful name rather than a numeric address. URLs solve both problems by providing memorable, hierarchical names that map to IP addresses.

3. URL structure

Host name

Organization name

Network name

Top‑level domain (TLD)

Example (illustrated in the original article):

主机名.机构名.网络名.顶级域名

4. DNS (Domain Name System) DNS is a distributed database that maps domain names to IP addresses. It was created to replace the cumbersome hosts.txt file used in the early ARPANET era.

5. DNS history and problems solved Before DNS, every host had to maintain a large, constantly updated hosts file, leading to scalability and conflict issues. DNS introduced a hierarchical, scalable solution.

6. DNS hierarchy

Root domain (represented by a dot ".") managed by InterNIC.

Top‑level domains (TLDs) – country code (ccTLD) and generic (gTLD).

Second‑level domains – registered by organizations (e.g., amazon.com).

Sub‑domains – further divisions within an organization.

7. Domain name servers DNS servers are distributed across the Internet. They include:

Root name servers (13 authoritative servers worldwide).

Top‑level domain servers that store records for second‑level domains.

Authoritative (authoritative) servers for each zone.

Local (recursive) DNS servers, often provided by ISPs, which cache results.

8. Domain name resolution process When a user enters a URL:

The local DNS server checks its cache for the IP address.

If not found, it queries a root server, which points to the appropriate TLD server.

The TLD server directs the query to the authoritative server for the domain.

The authoritative server returns the IP address, which the local server caches and returns to the client.

The article concludes that understanding these concepts helps readers with learning, interviews, and daily work involving network communication.