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3.1. Addresses without a special prefix

3.1.1. Localhost address

This is a special address for the loopback interface, similiar to IPv4 with its "". With IPv6, the localhost address is:


or compressed:


Packets with this address as source or destination should never leave the sending host.

3.1.2. Unspecified address

This is a special address like "any" or "" in IPv4 . For IPv6 it's:




These addresses are mostly used/seen in socket binding (to any IPv6 address) or routing tables.

Note: the unspecified address cannot be used as destination address.

3.1.3. IPv6 address with embedded IPv4 address

There are two addresses which contain an IPv4 address. IPv4-mapped IPv6 address

IPv4-only IPv6-compatible addresses are sometimes used/shown for sockets created by an IPv6-enabled daemon, but only binding to an IPv4 address.

These addresses are defined with a special prefix of length 96 (a.b.c.d is the IPv4 address):


or in compressed format


For example, the IPv4 address looks like this:

::ffff: IPv4-compatible IPv6 address

Used for automatic tunneling (RFC 2893 / Transition Mechanisms for IPv6 Hosts and Routers), which is being replaced by 6to4 tunneling.


or in compressed format


  Published under the terms of the GNU General Public License Design by Interspire