Network+ (N10-009) · ELI Explains IP Addresses (book)
IPv4 and IPv6 Foundations
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In 30 seconds
This chapter covers the fundamental concepts every networking student needs before exploring specific address types.
The college version
IP Address
What It Is
A unique numerical identifier for each device on a network, enabling devices to find and communicate with each other.
What It Does
Routes data from source to correct destination, like a mailing address for digital traffic.
Where It Is Used
Every internet-connected device — phones, laptops, servers, TVs — has at least one IP address.
ELI Explains
An IP address is like your home's street address. When someone sends you a letter, they write your address. When a computer sends you a video, it uses your IP. Without addresses, nothing would know where to go.
A 10-Year-Old's Example
Your teacher calls your name to return your test. On a network, a server uses your device's IP to send a game to the right tablet — not your brother's.
Remember This
An IP address is a device's network identifier — without it, data has nowhere to go.
IPv4 Address Structure
What It Is
A 32-bit address written as four decimal numbers (0-255) separated by dots, like 192.168.1.1. Each number is 8 bits.
What It Does
Provides about 4.3 billion unique addresses organized so routers can find paths between networks.
Where It Is Used
Most internet traffic still uses IPv4. Home routers and websites continue supporting it.
ELI Explains
IPv4 is like a phone system with four parts written with dots. But it only has 4.3 billion numbers — less than one per person now, and everyone has multiple devices. The numbers ran out.
A 10-Year-Old's Example
If every house had a four-digit address, that works for a small town. With billions of houses, you need longer numbers. That's why IPv6 was invented.
Remember This
IPv4 uses 32-bit dotted-decimal addresses — about 4.3 billion total, no longer enough.
IPv6 Address Structure
What It Is
A 128-bit address written as eight groups of four hex digits separated by colons, like 2001:0db8::1, with zero-compression rules.
What It Does
Provides 340 undecillion addresses — effectively unlimited — plus native simplified headers and auto-configuration.
Where It Is Used
Modern OSes, mobile networks, and cloud providers increasingly use IPv6. Many carriers default to it.
ELI Explains
IPv6 is like giving every grain of sand on every beach its own postal code — with plenty left. It uses longer colon numbers instead of short dotted ones. A smarter system where devices configure themselves.
A 10-Year-Old's Example
If IPv4 is a two-digit locker number (99 lockers), IPv6 is giving every student in every school a unique code with so many digits you'll never run out.
Remember This
IPv6 uses 128-bit colon-hex addresses — the address space is effectively unlimited.
Why IPv6 Exists
What It Is
IPv6 was developed because 4.3 billion IPv4 addresses cannot support today's tens of billions of devices.
What It Does
Eliminates widespread NAT by giving every device a globally unique address, improving routing and auto-configuration.
Where It Is Used
IPv6 is the default on many mobile networks and cloud platforms. Adoption grows as IPv4 addresses become scarcer.
ELI Explains
Your town was built for 100 people with two-digit house numbers. Now 10,000 people live there — you need a new system. IPv6 is that new system, designed from the start for way more devices than we'll ever have.
A 10-Year-Old's Example
Your classroom has 30 desks numbered 1-30 — enough now. If every school merged into one giant room, you'd need longer numbers. IPv6 is that system, built before the merger.
Remember This
IPv6 exists because IPv4 ran out of addresses — not because IPv4 stopped working.
IPv4 vs IPv6
What It Is
IPv4: 32-bit dotted-decimal. IPv6: 128-bit colon-hexadecimal. Different header structures and feature sets.
What It Does
IPv4 relies on DHCP and NAT. IPv6 builds auto-configuration, larger payloads, and simplified routing into the protocol.
Where It Is Used
Most networks run both (dual-stack). IPv4 handles legacy; IPv6 provides future capacity during the ongoing migration.
ELI Explains
IPv4 and IPv6 are like two languages computers speak. IPv4 is older, needing tricks for many devices. IPv6 is newer, designed to handle everything naturally. They run side by side — one doesn't replace the other.
A 10-Year-Old's Example
Like having both an old landline and a smartphone. Both make calls, but the smartphone does more. Networks run IPv4 and IPv6 the same way — old and new together.
Remember This
IPv4 and IPv6 coexist — IPv6 is structurally different, not just longer addresses.
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