This guide describes IPv6 features that affect TCP/IP in areas such as address configuration and resolution, route discovery, and security.

Expanded Addressing Capabilities

IPv6 increases the IP address size from 32 bits to 128 bits to support more levels of addressing hierarchy, a much greater number of addressable nodes, and simpler autoconfiguration of addresses. The scalability of multicast routing is improved by adding a scope field to multicast addresses. A new type of address called anycast address is defined and used to send a packet to any one of a group of nodes.

See Overview of TCP/IP Routing for a detailed description of IPv6 addressing conventions.

Header Format Simplification

Some IPv4 header fields have been dropped or moved to optional extension headers to reduce the common-case processing cost of packet handling and to limit the added bandwidth cost of the IPv6 header (beyond the long addresses). Fragmentation and reassembly are limited to the source and destination nodes.

Improved Support for Extensions and Options

Optional Internet-layer information is encoded in separate headers, called extension headers, which can be placed between the IPv6 header and the upper-layer header in the packet. An IPv6 packet can carry zero, one, or more extension headers.

Changes in the way IP header options are encoded allow for more efficient forwarding, less stringent limits on the length of options, and greater flexibility for introducing new options in the future.

These headers increase and enhance the current capability of IP. For example, IPv6 has the ability to support datagrams (packets) larger than 65535 bytes, referred to as Jumbograms. This is accomplished through the use of the Jumbo Payload Hop-by-Hop option. IPv6 also provides greater network security through the use of the Authentication Headers (AH) and Encapsulating Security Payload (ESP) headers.

IP Security

IPv6 uses IP Security (IPsec) to enable the TCP/IP network provider to secure network traffic and communicate with other endpoints. IPsec provides security services by enabling a host to select required security protocols, determine the algorithms used for the service, and put in place any cryptographic keys required to provide the requested service. IPsec supports encrypted and authenticated datagrams through the use of ESP headers for the encryption and AH for the authentication. You establish encryption with keys that are either pre-shared or negotiated using the IKEv2 protocol.

IPsec and its policies are administered by Security Center. Refer to the MCP Security Overview and Implementation Guide and the Security Center Help for additional information.

Status information can be retrieved using the following Operations Interface (OI) commands:

For more information on the TCPIP OPTION and TCPIP STATUS commands, see Operating TCP/IP Software. For more information on the TCPIP DEBUG command, see Troubleshooting TCP/IP Installation and Configuration Problems.

ICMPv6 Messages

The IPv6 version of ICMP (ICMPv6) is supported and implemented by every IPv6 node. ICMPv6 messages are one of two types: error messages or informational messages. All ICMPv6 messages have three fields that are common to all messages (type, code, and checksum), and a variable-length field that varies based on the message type.

ICMPv6 supports the following error and information types:

ICMPv6 supports the following new Multicast Listener Discovery (MLD) message types:

ICMPv6 supports the following new Neighbor Discovery message types:

Automatic Stateless Address Configuration and Duplicate Address Detection

To simplify host configuration, IPv6 supports automatic stateless address configuration. This enables hosts on a link to automatically configure themselves with IPv6 addresses for the link and with addresses 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. This feature allows an IPv6-enabled node to be added to a network and, without any configuration, be able to communicate with other destinations in the network.

Before an address is permanently assigned to an interface, it is verified to ensure that it is not already in use by another interface on the link using duplicate address detection. For information on specifying automatic stateless address configuration and duplicate address detection, see “Assigning IPv6 Addresses” and “Specifying Autoconfiguration for a Network Interface” in Operating TCP/IP Software.

IPv6 Neighbor Discovery

IPv6 discovers and records information about neighbor nodes on the local link. This enables nodes to determine which neighbors are reachable and to find routers that are able to forward packets for them. It is the primary means of discovering IPv6 routing information.

Neighbor Discovery provides the following as part of the base protocol set:

These features are described in more detail in IPv6 Neighbor Discoveryand in Using Neighbor Discovery. For information on using Neighbor Discovery, see Specifying Neighbor Discovery Options.

Multicast Listener Discovery V1

Multicast listener discovery allows IPv6 routers to discover nodes on its link that want to receive multicast packets and to discover which multicast addresses are of interest to its neighboring nodes. This information is used by IPv6 routers to deliver multicast information to the links on which there are listening nodes.

To receive multicast input, an application must specify the multicast IP address for which it intends to receive multicast input, and the TCP/IP initialization file must be configured with the link-layer multicast address.

To specify multicast listener discovery report intervals and retry limits, see Specifying the Unsolicited Report Options for Multicast Listener Discovery .