IPv6 (special unicast address)

IPv6 (special unicast address)

 IPv6 addresses have some unicast addresses that are used for special purposes. Here are the addresses:

typeNotation example
loopback address ::1
unspecified address ::
IPv4 compatible address ::/96
IPv4 mapped address ::FFFF:xyzw (xyzw is IPv4 address)
6to4 address 2002::/16

loopback address

 A loopback address is an address to send packets destined for itself. In IPv4, "" was used, but in IPv6, only the least significant bit is set to "1".


Display the Windows Vista command prompt.

Try to ping the loopback address "::1".


IPv6 is enabled by default, so you will get a Ping response.

unspecified address

 An address where all bits are "0", "0:0:0:0:0:0:0:0" (::), is defined as an unspecified address. An unspecified address indicates that the interface does not yet have an address.

 Indicates that the address has not yet been assigned when receiving an address assignment from the DHCPv6 server. This address is used when starting a node connection.

IPv4 compatible address

 An IPv4-compatible address is an address that two IPv6 hosts use to automatically create a tunnel when communicating over an IPv4 network.

The first 96 bits are "0", and the lower 32 bits use the IPv4 address as is.


For example, an IPv4-compatible address for the IPv4 address "" would be:

 200 (decimal) = C8 (hexadecimal)




IPv4 mapped address

 IPv4 mapped addresses are addresses used by IPv4 hosts that do not support IPv6. When an IPv6 host communicates with a host that only supports IPv4, the IPv6 host communicates using IPv4 mapped addresses.

6to4 address

 A 6to4 address is an address used when encapsulating an IPv6 datagram into an IPv4 datagram and connecting to an IPv6 network.

 A 6to4 address is generated with a prefix of "2002::/16" and a 48-bit prefix embedded with a 32-bit IPv4 address.