March 20, 2007

Transition IPv6 seamlessly in embedded systems

Here's an overview of IPv6 and an introduction to possible transition methods, complete with the implications of transition on an embedded system.

By Christian E. Legare, Micrium

IPv6 Overview
IPv6 was designed to be an evolutionary step from IPv4. It was not a design goal to take a radical step away from IPv4. Functions that work in IPv4 were maintained in IPv6, and those that didn't work were removed. The changes from IPv4 to IPv6 fall primarily into the following categories:

• Expanded Routing and Addressing Capabilities--IPv6 increases the IP address size from 32 bits to 128 bits, to support more levels of addressing hierarchy and a much greater number of addressable nodes, and simpler auto-configuration of addresses.
• The scalability of multicast routing is improved by adding a "scope" field to multicast addresses.
• Header Format Simplification--Some IPv4 header fields have been dropped or made optional, to reduce the common-case processing cost of packet handling and to keep the bandwidth cost of the IPv6 header as low as possible despite the increased size of the addresses. Even though the IPv6 addresses are four times longer than the IPv4 addresses, the IPv6 header is only twice the size of the IPv4 header.
• Improved Support for Options--Changes in the way IP header options are encoded allows for more efficient forwarding, less stringent limits on the length of options, and greater flexibility for introducing new options in the future.
• Quality-of-Service Capabilities--A new capability is added to enable the labeling of packets belonging to particular traffic "flows" for which the sender requests special handling, such as non-default quality of service or "real-time" service.
• Authentication and Privacy Capabilities--IPv6 includes the definition of extensions, which provide support for authentication, data integrity, and confidentiality. This is included as a basic element of IPv6 and will be included in all implementations.

The IPv6 protocol consists of two parts, the basic IPv6 header and IPv6 extension headers.

IPv6--Unique aspects
IPv6 solves Internet scaling challenges, provides a flexible transition mechanism for the current Internet, and meets the needs of such new markets as mobile personal computing devices, networked entertainment, and device control. This article summarizes a variety of IPv6 key issues while focusing on the use of the dual stack in embedded systems where resources are often limited. IPv6 is designed with a rich set of seamless transitions methods. Specific mechanisms (embedded IPv4 addresses, pseudo-checksum rules etc.) are built into IPv6 to support transition and compatibility with IPv4. It was designed to permit a gradual deployment.

IPv6 supports large hierarchical addresses, which allow the Internet to continue to grow and provide new routing capabilities not built into IPv4. It features anycast addresses, which can be used for policy route selection and has scoped multicast addresses, which provide improved scalability over IPv4 multicast. It also features local use address mechanisms, which provide the ability for "plug and play" installation. IPv6 provides a platform for new Internet functionality. This includes support for real-time flows, provider selection, host mobility, end-to-end security, auto-configuration, and auto-reconfiguration.

IPv6 can be installed as a normal software upgrade in Internet devices. It is interoperable with the current IPv4. Its deployment strategy was designed to not have any D-day. IPv6 is designed to run well on high performance networks (e.g., ATM, MPLS) and at the same time is still efficient for low bandwidth networks (e.g., wireless). In addition, it provides a platform for new internet functionality that will be required in the near future.

Key issues
There are several key issues that should be considered when reviewing the design of the next generation Internet protocol. Some are very straightforward while others are less obvious. For example, the protocol must be able to support large global networks and there must be a clear way to transition the current large installed base of IPv4 systems. It doesn't matter how good a new protocol is if there isn't a practical way to transition the current operational systems running IPv4 to the new protocol.

Growth
Growth is the basic issue for a next generation IP. Initially, IPv4 was designed to serve the computer market, the driver of the growth of the Internet. Its focus is to connect computers together in the large business, government, and university education markets. The computer market, however, will not drive the next phase of growth. Running all services (real-time and non real-time) on one network, mobile devices, Internet games and multimedia is the driving force behind IPv6.

At some point in the next few years the Internet will require new version of the Internet protocol. Two factors are driving this: routing and addressing. Global Internet routing based on the 32-bit addresses of IPv4 is becoming increasingly strained. IPv4 addresses do not provide enough flexibility to construct efficient hierarchies that can be aggregated. The deployment of Classless Inter-Domain Routing is extending the life of IPv4 routing by a number of years, and the effort required to manage the routing will continue to increase. Even if IPv4 routing can be scaled to support a full IPv4 Internet, the Internet will eventually run out of network numbers. There is no question that an IPv6 is needed--only a question of when.

As soon as the financial incentive is significant enough, IPv6 networks will start to be implemented, just as today, we are seeing the implementation of VoIP systems. It is predicted that the transition from our all IPv4 Internet to an all IPv6 Internet will last for approximately 35 years.