IPv6 Unicast Addresses

Like in the world of IPv4, a unicast transmission represents data meant for a single destination address only. However, IPv6 uses a few different types of unicast addresses for different purposes. These include global, site-local, link-local, and IPv4-mapped IPv6 addresses. Each is outlined below.

Global Unicast Address. Very similar in function to an IPv4 unicast address such as, these addresses include a global routing prefix, a subnet ID, and an interface ID as outlined earlier.

Site-Local Unicast Address. Very similar in function to the IPv4 private address space that includes ranges like, these addresses are meant for internal communications and are not routable on the public Internet. Site-local addresses start with the prefix FEC0::/10, and then include the appropriate subnet ID and interface ID as outlined earlier.

Link-Local Unicast Address. For certain communications that are meant to stay within a given broadcast domain, IPv6 uses link-local addresses. These addresses are used for features like stateless autoconfiguration, which will be looked at shortly. Link-local addresses start with the prefix FE80::/10, and then include an interface ID. Note that since these addresses never communicate outside of their local subnet, the subnet ID is not included.

IPv4-mapped IPv6 Address. For environments that are transitioning between IPv4 and IPv6, IPv6 provides another type of unicast address known as an IPv4-mapped IPv6 address. This addressing method is used on systems running both an IPv4 and IPv6 protocol stack. When used, a system will include its current 32-bit IPv4 address in the low-order bits of an IPv6 address, preceded by 16 bits set to FFFF, and the remaining bits set to 0. For example, a host with the IPv4 address would use the address of 0:0:0:0:0:FFFF:

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of 2000Trainers.com. He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.