IPv6 features

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

IPv6 features

The following are the features of the IPv6 protocol:

  • New header format

  • Large address space

  • Efficient and hierarchical addressing and routing infrastructure

  • Stateless and stateful address configuration

  • Built-in security

  • Better support for quality of service (QoS)

  • New protocol for neighboring node interaction

  • Extensibility

The following sections discuss each of these new features in detail.

New header format

The IPv6 header has a new format that is designed to minimize header overhead. This is achieved by moving both nonessential fields and option fields to extension headers that are placed after the IPv6 header. The streamlined IPv6 header provides more efficient processing at intermediate routers.

IPv4 headers and IPv6 headers are not interoperable and the IPv6 protocol is not backward compatible with the IPv4 protocol. A host or router must use an implementation of both IPv4 and IPv6 in order to recognize and process both header formats. The new IPv6 header is only twice as large as the IPv4 header, even though IPv6 addresses are four times as large as IPv4 addresses.

For more information, see Internet Protocol version 6 (IPv6).

Large address space

IPv6 has 128-bit (16-byte) source and destination addresses. Although 128 bits can provide over 3.4×1038 possible combinations, the large address space of IPv6 has been designed to allow for multiple levels of subnetting and address allocation from the Internet backbone to the individual subnets within an organization.

Although only a small percentage of possible addresses are currently allocated for use by hosts, there are plenty of addresses available for future use. With a much larger number of available addresses, address-conservation techniques, such as the deployment of NATs, are no longer necessary.

For more information, see IPv6 Addressing.

Efficient and hierarchical addressing and routing infrastructure

IPv6 global addresses used on the IPv6 portion of the Internet are designed to create an efficient, hierarchical, and summarizable routing infrastructure that addresses the common occurrence of multiple levels of Internet service providers. On the IPv6 Internet, backbone routers have much smaller routing tables.

For more information, see Unicast IPv6 addresses.

Stateless and stateful address configuration

To simplify host configuration, IPv6 supports both stateful address configuration, such as address configuration in the presence of a DHCP server, and stateless address configuration (address configuration in the absence of a DHCP server). With stateless address configuration, hosts on a link automatically configure themselves with IPv6 addresses for the link (link-local addresses) and with addresses that are derived from prefixes advertised by local routers. Even in the absence of a router, hosts on the same link can automatically configure themselves with link-local addresses and communicate without manual configuration.

For more information, see IPv6 address autoconfiguration.

Built-in security

Support for IPSec is an IPv6 protocol suite requirement. This requirement provides a standards-based solution for network security needs and promotes interoperability between different IPv6 implementations.

For more information, see Security features for IPv6.

Better support for quality of service (QoS)

New fields in the IPv6 header define how traffic is handled and identified. Traffic identification, by using a Flow Label field in the IPv6 header, allows routers to identify and provide special handling for packets that belong to a flow. A flow is a series of packets between a source and destination. Because the traffic is identified in the IPv6 header, support for QoS can be easily achieved even when the packet payload is encrypted with IPSec.

New protocol for neighboring node interaction

The Neighbor Discovery protocol for IPv6 is a series of Internet Control Message Protocol for IPv6 (ICMPv6) messages that manage the interaction of neighboring nodes (that is, nodes on the same link). Neighbor Discovery replaces Address Resolution Protocol (ARP), ICMPv4 Router Discovery, and ICMPv4 Redirect messages with efficient multicast and unicast messages and provides additional functionality.

For more information, see Neighbor Discovery (ND).


IPv6 can be extended for new features by adding extension headers after the IPv6 header. Unlike the IPv4 header, which can only support 40 bytes of options, the size of IPv6 extension headers is only constrained by the size of the IPv6 packet.