Internet Protocol version 6 (IPv6)

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Internet Protocol version 6 (IPv6)

IPv6 is defined in RFC 2460, "Internet Protocol, Version 6 (IPv6) Specification." IPv6 is a connectionless, unreliable datagram protocol used primarily for addressing and routing packets between hosts.

Connectionless means that a session is not established before exchanging data. Unreliable means that delivery is not guaranteed. IPv6 always makes a best-effort attempt to deliver a packet. An IPv6 packet might be lost, delivered out of sequence, duplicated, or delayed. IPv6 does not attempt to recover from these types of errors. The acknowledgment of packets delivered and the recovery of lost packets are done by a higher-layer protocol, such as TCP.

An IPv6 packet, also known as an IPv6 datagram, consists of an IPv6 header and an IPv6 payload, as shown in the following illustration.

The IPv6 header contains the following fields for addressing and routing.

IPv6 header field	Function
Source Address	The IPv6 address of the original source of the IPv6 packet.
Destination Address	The IPv6 address of the intermediate or final destination of the IPv6 packet.
Hop Limit	The number of network segments on which the packet is allowed to travel before being discarded by a router. The Hop Limit is set by the sending host and is used to prevent packets from endlessly circulating on an IPv6 internetwork. When forwarding an IPv6 packet, IPv6 routers are required to decrease the Hop Limit by 1 and to discard the IPv6 packet when the Hop Limit is 0.

Note

• IPv6 is a rapidly evolving standard. The RFCs referenced might have been made obsolete by newer RFCs.