IPv6: The Future Is Already Here

In 2011, IPv4 addresses ran out. Today they're bought on the secondary market for $50+ each. Meanwhile, every smartphone could be assigned as many IPv6 addresses as there are atoms in the universe - with plenty left over.

• **Mobile networks:** LTE/5G operators are massively switching to IPv6-only with NAT64. iPhone and Android have supported it for years
• **Cloud providers:** AWS, GCP give IPv6 for free, and are starting to charge for IPv4 (~$4/month per address)
• **Home IoT:** Smart devices get global addresses - you can connect directly without complex NAT configurations

Предварительные знания

• IP Addresses: the postal codes of the internet

IPv6 Address Format

**IPv6** solves the main problem of IPv4 - address exhaustion. IPv4's 32 bits give 4.3 billion addresses. IPv6's 128 bits give **340 undecillion** (3.4×10³⁸) - more than the number of atoms in a human body.

**Scale:** If IPv6 addresses were handed out at 1 billion per second, the supply would run out in 10⁷ TRILLION years. The universe is ~14 billion years old.

IPv6 addresses can be **abbreviated** using two rules:

IPv6 Address Types

IPv6 has three address types: **Unicast** (one recipient), **Multicast** (group of recipients), **Anycast** (nearest in a group). **Broadcast is absent** - replaced by multicast.

**Fun fact:** In IPv6, every interface has **multiple addresses** simultaneously: link-local (mandatory), global (usually), temporary (for privacy).

Key IPv6 ranges:

Link-Local Addresses

**Link-Local** (fe80::/10) - addresses that work only within a single network segment. They are **automatically** created on every IPv6 interface without any configuration.

**Privacy:** EUI-64 allows tracking a device by its MAC. Modern OSes use **Privacy Extensions** - a random Interface ID that changes periodically.

Link-Local is used for service protocols:

When specifying a link-local address in commands, a **zone ID** (interface index) is required, because the same address can exist on different interfaces:

Global Unicast and Address Assignment

**Global Unicast Address (GUA)** - routable internet addresses (2000::/3). In IPv6, there are three ways to obtain a GUA: **SLAAC**, **DHCPv6**, and **manual configuration**.

**SLAAC vs DHCP:** SLAAC doesn't provide DNS and other options. The O (Other) flag in RA tells the host to use DHCPv6 for DNS. The M (Managed) flag tells the host to get its address via DHCPv6.

Before using an address, the host verifies its uniqueness:

IPv6 adoption: Google sees ~45% of traffic over IPv6, in some countries (India, Germany) - over 60%. Mobile networks (LTE/5G) are often IPv6-only with NAT64.

Key Ideas

• **128 bits** vs IPv4's 32. Address written in hex, 8 groups of 4 characters. Abbreviated via :: and omitting leading zeros
• **Link-local (fe80::/10)** is created automatically on every interface. Used for NDP, Router Discovery, as default gateway
• **SLAAC** - getting an address without a DHCP server. Router announces prefix, host generates Interface ID itself
• **Dual-stack** and **Happy Eyeballs** ensure smooth transition. IPv6 preferred, IPv4 as fallback

Related Topics

IPv6 changes familiar concepts:

• IP Addressing — IPv6 extends IPv4 concepts: more addresses, but same subnetting principles
• NAT — IPv6 makes NAT unnecessary - every device gets a global address

Вопросы для размышления

• Why is the transition to IPv6 taking decades, even though the protocol has existed since 1998?
• How will application architecture change when NAT becomes a thing of the past?
• Why do some consider EUI-64 a privacy threat?

Связанные уроки

• arch-01-binary