IPv6 address types

In this course, we will see the different types of IPv6 addresses. Feel free to read this course on Introduction to IPv6 addresses if you need a refresher.

IPv6 addressing

As a reminder, IPv6 addresses are encoded on 128 bits and thus allow to identify individual interfaces and sets of interfaces of a device.

Note that IPv6 addresses of all types are assigned to interfaces, not nodes. That is, hosts, Layer Three switches and routers.

Since each interface therefore belongs to a single node, then any of the Unicast addresses of that node’s interfaces can be used as an identifier for the node.

The same interface can therefore be assigned several IPv6 addresses of any type. Here is the example below, the IPv6 configuration of a host:

IPv6 address types

Indeed, in communication, there are three main categories of different types of IPv6 addresses:

  • Unicast ;
  • Anycast ;
  • And multicast.

The different types of IPv4 addresses

Unicast addresses

A unicast address therefore specifies a single interface. A packet sent to a unicast address destination then goes from a host to the destination host.

Unicast addresses therefore have two types of regular addresses and two special Unicast addresses.

Regular Unicast address types :

  • Link-local address

Link-local addresses are therefore designed to be used on a single local link (local network).

Link-local addresses are thus automatically configured on all interfaces, and the prefix used for a link-local address is fe80::/10.

Packets forwarded on one router to a destination on another network do not use link-local addresses.

  • Global address

Unlike link-local addresses, global addresses are designed to be used on any network.

The prefix used for a global address thus begins with the binary 001.

Special Unicast address types:

  • Address not specified

The unspecified address is therefore 0:0:0:0:0:0:0:0 and also abbreviated with a colon (::).

In fact, the unspecified address indicates the absence of an address and can never be assigned to a host.

It can thus be used by an IPv6 host to which no address has yet been assigned.

For example, when the host sends a packet to find out if an address is being used by another node, the host uses the unspecified address as the source address.

  • Loopback address

The loopback address is 0:0:0:0:0:0:0:1 and in abbreviation the loopback address is ::1.

It is therefore an address used by a node to send a packet to itself.

This is the equivalent of the localhost address in IPv4 addressing.

Anycast address

An IPv6 anycast address is therefore an address that is assigned to multiple interfaces, usually belonging to different nodes. Where a packet sent to an anycast address is routed to the nearest interface with that address.

Anycast addresses, when used as part of a route sequence, allow a node to select which of several ISPs it wishes to forward its traffic.

These anycast addresses can be used as intermediate addresses in an IPv6 routing header, so that a packet is delivered by a particular provider or sequence of providers.

However, you can also use anycast addresses to identify the set of routers attached to a particular subnet or the set of routers allowing access to a particular routing domain.

Multicast address

The multicast address specifies a set of interfaces, possibly at several locations.

It is, in fact, an identifier for a group of interfaces. An interface can thus belong to any number of multicast groups.

The prefix used for a multicast address is therefore ff. If a packet is sent to a multicast address, a copy of the packet is also sent to each member of the group.

IPv6 address types

Address typesPrefixIPv4 equivalence
Site-local unicastFEC0::/10
Not specified::/1280.0.0.0
GlobalEverything else
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Adam Guipelbé

Ingénieur Systèmes et Réseaux

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