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Summary of Protocol Changes from IPv4 to IPv6

Updated: August 22, 2005

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

In response to concern about the finite number of IPv4 addresses, the Internet Engineering Task Force (IETF) developed a suite of protocols and standards known as Internet Protocol version 6 (IPv6). IPv6 was designed to replace IPv4, which is more than 20 years old. Because IPv6 is expected to become increasingly important as the Internet continues to grow, IPv6 functionality is included in the Microsoft® Windows®  XP and the Microsoft® Windows® Server 2003, Standard Edition; Windows® Server 2003, Enterprise Edition; Windows® Server 2003, Datacenter Edition; and Windows® Server 2003, Web Edition operating systems.

The Internet Protocol (IP) is the network-layer protocol used by TCP/IP for addressing and routing packets of data between hosts. The current version of the IP, IPv4, has remained primarily unchanged since RFC 791 was published in 1981. IPv4 is robust, easily implemented, and interoperable, and it scales well. However, continued dramatic growth of the Internet is pushing the limits of IPv4 design. Concerns with IPv4 include the scarcity of public IPv4 addresses for use on the Internet, the size and complexity of its backbone routing tables, and the need for simpler, more automatic configuration.

IPv6, previously named IP Next Generation (IPng), was developed primarily to allow for larger (128-bit) IP addresses. Additional enhancements include the following:

  • A more efficient routing infrastructure that allows backbone routers to maintain much smaller routing tables.

  • A new header format that reduces header overhead and provides more efficient processing at intermediate routers.

  • A simplified host configuration that uses both stateful and stateless address configuration.

  • Built-in security provided by Internet Protocol security (IPsec). (In IPv4, IPsec is optional.)

  • Better support for Quality of Service (QoS), which is the set of methods or processes that a service-based organization uses to maintain a specific level of quality.

  • A way to efficiently manage the interaction of neighboring nodes by using multicast and unicast messaging.

  • Extension headers for adding new features to IPv6.

Table G.1 lists pertinent IPv6 RFCs and serves as a useful reference to the source documents.

Table G.1 Summary of Useful Source Documents for Migrating from IPv4 to IPv6

Version Date RFC RFC Title


September, 1981

RFC 791

Internet Protocol

(Protocol specification)


January, 1995

RFC 1752

The Recommendation for the IP Next Generation Protocol

(Standards track for IPv6 General RFCs)


December, 1995

RFC 1883

Internet Protocol, Version 6 (IPv6) Specification

(Proposed standard — made obsolete by RFC 2460)


December, 1995

RFC 1886

DNS Extensions to support IP version 6

(IPv6 applications RFCs)


July, 1998

RFC 2373

RFC 35132

IP Version 6 Addressing Architecture

Internet Protocol Version 6 (IPv6) Addressing Architecture

(Standards track for IPv6 addressing RFCs)


December, 1998

RFC 24603

Internet Protocol, Version 6 (IPv6) Specification

(Standards track for the Network Layer RFCs and Internet drafts)

1 IPv5 was an experimental non-IP real-time stream protocol called ST, which was never widely used.

2 RFC  3513 supercedes RFC 2373; however Windows Server 2003 does not implement its changes with regard to site-local addresses.

3 In RFC 2460, Internet Protocol, Version 6 (IPv6) Specification, IPv6 is described as a connectionless, unreliable datagram protocol that is used primarily for addressing packets and routing them between hosts. Connectionless means that a session is not established before data exchange begins. Unreliable means that delivery is not guaranteed. IPv6, like IPv4, always makes a best-effort attempt to deliver a packet, but an IPv6 packet might be lost, delivered out of sequence, duplicated, or delayed. IPv6 itself does not attempt to recover from these types of errors; the acknowledgment of packet delivery and the recovery of lost packets is done by a higher-layer protocol, such as TCP. TCP performs reliably over both IPv4 and IPv6.

For more information about the design changes needed by IPv4 to accommodate the increasing demands of network traffic, see Introduction to IPv6 in Help and Support Center for Windows Server 2003. For more information about IPv6, see IPv6 features in Help and Support Center for Windows Server 2003.

For more information about RFCs, see

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