Understanding The Differences: Domain, URL, and IP

Domains, URLs, and IP addresses, each play a unique role in the digital ecosystem. Understanding the differences between these components is crucial for anyone looking to grasp how the web operates. This article aims to demystify these concepts by explaining what a domain, a URL, and an IP address are, and why DNS resolvers are essential in translating fully qualified domain names (FQDNs) into IP addresses, while not functioning with URLs and IP addresses directly.

What is a Domain?

A domain is a human-readable address used to identify a location on the internet. Domains consist of a series of characters (letters and numbers) and are structured in levels, separated by dots. For example:

• Top-Level Domain (TLD): .com, .org, .net
• Second-Level Domain (SLD): example in example.com
• Subdomain: www in www.example.com

A full domain name might look like www.example.com.

What is a URL?

A URL (Uniform Resource Locator) is a complete address used to access a specific resource on the internet. It includes several components:

• Scheme: http:// or https://
• Domain: www.example.com
• Path: /page
• Port: :8080 (optional)
• Query String: ?id=123 (optional)
• Fragment: #section1 (optional)

Example of a URL: https://www.example.com/page?id=123#section1

What is an IP Address?

An IP address (Internet Protocol address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. IP addresses come in two versions:

• IPv4: 192.168.1.1
• IPv6: 2001:0db8:85a3:0000:0000:8a2e:0370:7334

Why DNS Resolvers Use Fully Qualified Domain Names (FQDNs)

What is a DNS Resolver?

A DNS resolver is a server on the internet that translates domain names (like www.example.com) into IP addresses (like 192.168.1.1). This process is essential because while humans use domain names to navigate the web, computers use IP addresses to communicate.

Why DNS Resolvers Use FQDNs and Not URLs or IPs:

1. FQDNs vs. URLs:
   • FQDN (Fully Qualified Domain Name) includes the complete domain hierarchy: subdomain.domain.tld (e.g., www.example.com).
   • URLs are more complex and include additional elements (scheme, path, query string) that are not relevant to the DNS resolution process.
   • DNS resolvers are designed to handle the domain part of the URL only, not the entire URL structure. The resolver’s job is to map the FQDN to an IP address, not to interpret paths, ports, or protocols.
2. FQDNs vs. IPs:
   • IP Addresses are already the end result of DNS resolution. DNS resolvers are unnecessary when you have an IP address because the translation step (domain to IP) is not required.
   • DNS resolvers function to convert FQDNs into IP addresses for routing purposes. If you already have an IP address, the role of the DNS resolver is bypassed.

Summary

• Domain: A human-readable name for a location on the internet.
• URL: A complete address for accessing a specific resource on the internet.
• IP Address: A numerical label used by computers to identify each other on the network.
• DNS Resolver: Translates FQDNs into IP addresses, essential for navigating the web.

DNS resolvers need FQDNs because their primary function is to map these names to IP addresses. URLs contain extraneous information not relevant to this process, and IP addresses do not need resolution.