IPv6 Address Types: Unicast, Multicast, Anycast Guide

Three Categories of IPv6 Addresses

Unlike IPv4 which has unicast, broadcast, and multicast, IPv6 has three types:

Type	Delivery	IPv4 Equivalent
Unicast	One-to-one	Unicast
Multicast	One-to-many	Broadcast + Multicast
Anycast	One-to-nearest	No direct equivalent

There is no broadcast in IPv6. All one-to-many communication uses multicast.

Unicast Address Types

Global Unicast (GUA)

The equivalent of IPv4 public addresses. Globally routable and unique.

Prefix: 2000::/3 (addresses starting with 2 or 3)
Example: 2001:db8:1234:5678::1

Link-Local

Automatically assigned to every IPv6 interface. Only valid within a single network segment -- routers do not forward link-local traffic.

Prefix: fe80::/10
Example: fe80::1a2b:3c4d:5e6f:7890

Link-local addresses are essential for IPv6 operations: Neighbor Discovery, Router Advertisements, and routing protocol next-hops all use them.

Unique Local Address (ULA)

The IPv6 equivalent of RFC 1918 private addresses. Routable within your organization but not on the public internet.

Prefix: fc00::/7 (practically fd00::/8)
Example: fd12:3456:789a::1

Use ULA when you need stable internal addressing that does not depend on your ISP's prefix.

Loopback

::1/128  (equivalent to IPv4's 127.0.0.1)

Unspecified

::/128  (equivalent to IPv4's 0.0.0.0)

Multicast Addresses

All multicast addresses start with ff. The structure encodes the scope and group:

ff[flags][scope]::[group ID]

Address	Scope	Meaning
ff02::1	Link-local	All nodes on the link
ff02::2	Link-local	All routers on the link
ff02::1:ff00:0/104	Link-local	Solicited-node (for NDP)
ff05::2	Site-local	All routers in the site

Scope values: 1=interface, 2=link, 5=site, 8=organization, e=global.

Anycast Addresses

An anycast address is assigned to multiple interfaces (usually on different routers). Packets sent to an anycast address are delivered to the topologically nearest instance.

Common use: DNS root servers
  2001:503:ba3e::2:30  -> Multiple anycast instances worldwide
  Traffic goes to the nearest one

Anycast addresses look identical to unicast addresses -- the difference is in routing configuration, not address format.

Every Interface Has Multiple Addresses

A typical IPv6 interface has at least three addresses simultaneously:

eth0:
  fe80::1a2b:3c4d:5e6f:7890   (link-local, auto)
  2001:db8:1:1::100            (global unicast, SLAAC or DHCPv6)
  fd00:1:1::100                (ULA, if configured)

This multi-address design is fundamental to IPv6 and enables features like privacy extensions, address deprecation, and seamless renumbering.

IPv6 Address Types: Unicast, Multicast, Anycast