IPv6 Address Format & Types

The experience of IPv4 revealed that the scalability of a network layer protocol heavily depends on its addressing architecture. The designers of IPv6 therefore spent a lot of effort defining its addressing architecture RFC 3513. IPv6 supports unicast, multicast and anycast addresses.


As with IPv4, an IPv6 unicast address is used to identify one data link layer interface on a host. If a host has several data link layer interfaces (such as an Ethernet interface and a WiFi interface), then it needs several IPv6 addresses. An IPv6 unicast address is composed of three parts:

  1. A global routing prefix that is assigned to the Internet Service Provider that owns this block of addresses
  2. A subnet identifier that identifies a customer of the ISP
  3. An interface identifier that identifies a particular interface on an end-system

As described in the previous lesson, IPv6 addresses are divided into eight 16-bit groups separated by colons. Each group is represented by four hexadecimal digits.

In general, an IPv6 unicast address is structured as shown in the figure below:

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