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IP Addressing, DNS & Domain Names

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Lesson

IP Addressing, DNS & Domain Names

IPv4 vs IPv6, the DNS hierarchy, and the rules that govern domain names.

IP Addressing, DNS & Domain Names

Internet Protocol (IP)

An IP address identifies a device so data can be routed to it. There are two versions in use today.

	IPv4	IPv6
Size	32-bit	128-bit
Format	Four 8-bit numbers separated by periods — `191.57.126.0`	Eight groups of four hex digits
Range	`0.0.0.0` to `255.255.255.255`	340 undecillion addresses
Capacity	~4.3 billion unique addresses (running out)	Effectively unlimited
Extras	Organisations get assigned IP blocks	Built-in security (IPsec), auto-configuration, supports IoT & 5G

IPv6 adoption keeps growing: around 47% of Google traffic now travels over IPv6 (2025).

IP Addressing, DNS & Domain Names

The Domain Name System (DNS)

The DNS is a hierarchical, distributed system that translates human-readable domain names (e.g. example.com) into numeric IP addresses (e.g. 192.0.2.1). It is the “phone book” of the Internet.

DNS hierarchy

Root — represented by .; the starting point for all DNS lookups.
Top-Level Domain (TLD) — .com, .org, .net, .edu, .gov, .io, .ai, .app.
Second-Level Domain (SLD) — example.com, registered by individuals or organisations.
Subdomain — mail.example.com, blog.example.com, api.example.com.

DNS resolution in five steps

User types a domain name.
Resolver checks its cache.
Root server is contacted.
TLD server is contacted.
IP address is returned.

IP Addressing, DNS & Domain Names

Domain Naming Rules

Rule	Detail
Max length	255 characters for the full domain; 63 per label
Allowed characters	Letters A–Z, digits 0–9, hyphens (`-`)
No leading/trailing hyphen	Cannot begin or end with a hyphen
No spaces	Spaces are not permitted anywhere
Case insensitive	`EXAMPLE.com` = `example.com` = `Example.COM`
Label count	Typically 2–5 labels separated by periods
Trademark	Trademark owners get domain preference rights

TLD categories

Generic TLDs — .com, .org, .net, .info, .biz
Sponsored TLDs — .edu, .gov, .mil, .int, .aero
Country code (ccTLD) — .my, .uk, .us, .jp, .de, .au
New generic TLDs — .io, .ai, .app, .dev, .tech
Infrastructure TLD — .arpa (internal DNS use only)