IPv4-Compatible IPv6 Address

IPv4-Compatible IPv6 Address
As a transition mechanism, the IPv4-compatible IPv6 address is used to tunnel IPv6 packets over
an IPv4 infrastructure, without the need to preconfigure tunnels through the IPv4 network. This
address type embeds an IPv4 address in the low-order 32 bits. It pads all 96 high-order bits with
0s. It is used between two interfaces that support both the IPv4 and IPv6 protocol stacks, but are
separated by devices that support only IPv4, and the format is 0:0:0:0:0:0:A.B.C.D, or ::A.B.C.D,
where A.B.C.D is the IPv4 unicast address. Nodes that are assigned IPv4-compatible IPv6
addresses perform automatic tunneling. Whenever a node with one of these addresses sources or
receives an IPv6 packet whose next hop is over an IPv4 interface, it must encapsulate the IPv6
packet within an IPv4 packet before sending it out. Conversely, these nodes must be prepared to
accept IPv4 packets with IPv6 packets encapsulated within. In addition to the information found
in RFC 3513, RFC 2893 gives additional details concerning IPv4-compatible IPv6 addresses.