Names

Overview

People remember names, not numbers. DNS (Domain Name System) is the internet's directory that translates human-friendly names like example.com into the IP addresses machines actually use to connect. This lesson introduces domain names and the naming structure DNS is built on.

Learning objectives

• Explain why DNS exists and the problem it solves.
• Describe the hierarchical structure of domain names.
• Identify the parts of a fully qualified domain name.

Core concept

DNS maps domain names to IP addresses (and other records), so you can type a name instead of memorizing an address. Names are organized as a hierarchy, read right to left:

• Root — the implicit top of the tree (a trailing dot, usually omitted).
• Top-level domain (TLD) — .com, .org, .net, country codes like .uk.
• Second-level domain — the registered name, e.g. example in example.com.
• Subdomain / host — optional labels to the left, e.g. www in www.example.com.

A complete name like www.example.com. is a fully qualified domain name (FQDN) — it specifies the exact position in the hierarchy.

How it works

The hierarchy is what makes DNS scalable and distributed: no single server holds every name. Instead, authority is delegated down the tree — the root points to TLD servers, which point to the servers authoritative for each registered domain, which answer for their own subdomains. Reading a name right to left mirrors this delegation: .com first, then example, then www.

Practical example

In mail.example.com: .com is the TLD, example is the registered second-level domain, and mail is a host/subdomain within it. The same registered domain can host many names — www.example.com, mail.example.com, shop.example.com — each potentially pointing to a different server, all managed under the one example.com domain.

Cybersecurity relevance

Domain names are central to security. Attackers register look-alike domains (typosquatting, e.g. examp1e.com) for phishing, and rely on DNS to point victims at malicious servers. Understanding name structure helps analysts spot suspicious domains, and subdomain enumeration is a common reconnaissance step in authorized testing. Because so much depends on DNS, it is both a defensive monitoring point and an attack target.

Common mistakes

• Reading names left to right for hierarchy — the hierarchy actually runs right to left (TLD is rightmost).
• Confusing the registered domain with the full hostname — example.com is the domain; www.example.com is a host within it.
• Assuming a name maps to exactly one server — one domain can have many hosts and addresses.

Key takeaways

• DNS translates human-readable domain names into IP addresses machines use.
• Domain names are hierarchical, read right to left: root → TLD → second-level domain → subdomain/host.
• An FQDN specifies a name's exact place in the hierarchy; authority is delegated down the tree, keeping DNS distributed.

Check your understanding

• In shop.example.co.uk, which label is the TLD and which is the registered domain area?
• Why does the hierarchical, delegated design let DNS scale to the entire internet?