IPv6アドレスと概念

You've likely heard of IPv4, the internet's current addressing system. But IPv4 addresses are running out!

With billions of new devices connecting to the internet, we need a solution to keep everything connected. That's where IPv6 comes in.

IPv6 is the latest version of the Internet Protocol. It's designed to replace IPv4 and address its limitations, primarily the scarcity of available addresses.

• Vast Address Space: IPv6 uses 128-bit addresses, compared to IPv4's 32-bit. This means a practically infinite number of unique addresses.
• Improved Efficiency: Simplified header format, making routing more efficient.
• Enhanced Security: IPsec is built into IPv6, not an optional add-on.

An IPv6 address is 128 bits long, written in hexadecimal. It's divided into 8 groups of 16 bits each, separated by colons.

Each group is represented by four hexadecimal digits. For example:

This long format can be simplified, as we'll see next.

IPv6 addresses can often be shortened using two main rules:

1. Omit Leading Zeros: In each 16-bit block, leading zeros can be removed. E.g., 0db8 becomes db8.
2. Double Colon (::): A single :: can replace one or more consecutive blocks of zeros. This can only be used ONCE per address.

Let's compress our example address:

1. Remove leading zeros:

2. Use :: for consecutive zeros:

This makes addresses much easier to read!

IPv6 addresses have different purposes:

• Global Unicast Address (GUA): Publicly routable, unique across the internet. Similar to public IPv4.
• Link-Local Address (LLA): Used only for communication on a single network segment (link). Not routable.
• Unique Local Address (ULA): Private, routable only within an organization, not globally. Similar to private IPv4.
• Multicast Address: Used to send a single packet to multiple destinations simultaneously.

GUAs are the most common type, starting with 2 or 3 (e.g., 2001:db8::/32). They are globally unique and routable on the internet.

A typical GUA is composed of:

• Global Routing Prefix: Assigned by your ISP (e.g., /48 or /32).
• Subnet ID: Used by organizations to create subnets.
• Interface ID: Identifies a specific interface on a subnet.

Link-Local Addresses always start with fe80::/10. Every IPv6-enabled interface automatically configures one. They are essential for neighbor discovery and communication on the local link.

Let's see an example of how they appear on a Linux system:

IPv6 devices can automatically configure their own addresses using SLAAC. This means they don't always need a DHCP server.

SLAAC works by combining a prefix from a router advertisement (RA) with an interface identifier (often derived from the MAC address using EUI-64 or privacy extensions).

For stateful address assignment (like static IP or DNS server info), DHCPv6 can be used.

Since IPv4 and IPv6 aren't directly compatible, transition mechanisms are needed:

• Dual-Stack: Running both IPv4 and IPv6 on the same device simultaneously. This is the most common approach.
• Tunneling: Encapsulating IPv6 packets within IPv4 packets to traverse IPv4-only networks.
• Translation: Converting IPv6 packets to IPv4 and vice-versa (e.g., NAT64/DNS64).

We've covered the basics of IPv6!

• It solves IPv4 address exhaustion with 128-bit addresses.
• Addresses are written in hexadecimal and can be compressed.
• Key types include Global Unicast (public), Link-Local (local segment), and Unique Local (private).
• Devices can use SLAAC for automatic configuration.
• Dual-stack is a common transition method.

IPv6 is vital for the future of the internet!