Excerpt from Authorized Self-Study Guide Building Scalable Cisco Internetworks (BSCI), Third Edition.
By Diana Teare and Catherine Paquet Published by Cisco Press ISBN-10: 1-58705-223-7 ISBN-13: 978-1-58705-223-1

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This chapter introduces IPv6 and covers the following topics:

• Introducing IPv6

• IPv6 Addressing

• IPv6 Configuration and Using OSPF and Other Routing Protocols for IPv6

• Transitioning IPv4 to IPv6

IP Version 6 (IPv6) is a technology developed to overcome the limitations of the current standard, IP Version 4 (IPv4), which allows end systems to communicate and forms the foundation of the Internet as we know it today. One of the major shortcomings of IPv4 is its limited amount of address space. The explosion of new IP-enabled devices, the growth of undeveloped regions, and the rapid growth of other regions have fueled the need for more addresses. In the United States, the Department of Defense (DoD) is a primary driver for the adoption of IPv6 and has set a date of 2008 for all systems to be migrated to this new standard. Other potential IPv6 users include the National Research and Education Network (NREN), government agencies, enterprises, service providers, home networks, consumer appliances, distributed online gaming, and wireless services.

This chapter introduces IPv6 and the IPv6 addressing scheme. Routing protocols that support IPv6 are explored, and the details of Open Shortest Path First (OSPF) for IPv6 configuration are presented. The chapter concludes with a discussion of how IPv4 networks can be transitioned to IPv6.

Introducing IPv6

The ability to scale networks for future demands requires a limitless supply of IP addresses and improved mobility; IPv6 combines expanded addressing with a more efficient and feature-rich header to meet the demands. IPv6 satisfies the increasingly complex requirements of hierarchical addressing that IPv4 does not support.

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Note - IPv6 is defined in Requests for Comments (RFC) 2460, Internet Protocol, Version 6 (IPv6) Specification.

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This section introduces the key features and benefits of IPv6, and its addressing features. The Cisco IOS supports IPv6 in Release 12.2(2)T and later.

Features of IPv6

IPv6 is a powerful enhancement to IPv4 with features that better suit current and foreseeable network demands, including the following:

• Larger address space—IPv6 addresses are 128 bits, compared to IPv4's 32 bits. This larger address space provides several benefits, including: improved global reachability and flexibility; the ability to aggregate prefixes that are announced in routing tables; easier multihoming to several Internet service providers (ISPs); autoconfiguration that includes link-layer addresses in the IPv6 addresses for "plug and play" functionality and end-to-end communication without network address translation (NAT); and simplified mechanisms for address renumbering and modification.

• Simplified header—A simpler header provides several advantages over IPv4, including: better routing efficiency for performance and forwarding-rate scalability; no requirement for processing checksums; simpler and more efficient extension header mechanisms; and flow labels for per-flow processing with no need to examine the transport layer information to identify the various traffic flows.

• Support for mobility and security—Mobility and security help ensure compliance with mobile IP and IP security (IPsec) standards.

  Mobility enables people to move around in networks with mobile network devices, with many having wireless connectivity. Mobile IP is an Internet Engineering Task Force (IETF) standard available for both IPv4 and IPv6 that enables mobile devices to move without breaks in established network connections. Because IPv4 does not automatically provide this kind of mobility, supporting it requires additional configurations.

  In IPv6, mobility is built in, which means that any IPv6 node can use it when necessary. The routing headers of IPv6 make mobile IPv6 much more efficient for end nodes than mobile IPv4 does.

  IPsec is the IETF standard for IP network security, available for both IPv4 and IPv6. Although the functions are essentially identical in both environments, IPSec is mandatory in IPv6. IPSec is enabled and is available for use on every IPv6 node, making the IPv6 Internet more secure. IPSec also requires keys for each device, which implies global key deployment and distribution.

• Transition richness—There are a variety of ways to transition IPv4 to IPv6.

  One approach is to have a dual stack with both IPv4 and IPv6 configured on the interface of a network device.

  Another technique uses an IPv4 tunnel to carry IPv6 traffic. One implementation is IPv6-to-IPv4 (6-to-4) tunneling. This newer method (defined in RFC 3056, Connection of IPv6 Domains via IPv4 Clouds) replaces an older technique of IPv4-compatible tunneling (first defined in RFC 2893, Transition Mechanisms for IPv6 Hosts and Routers, which has been made obsolete by RFC 4213, Basic Transition Mechanisms for IPv6 Hosts and Routers).

  Cisco IOS Software Version 12.3(2)T (and later) also allows NAT protocol translation (NAT-PT) between IPv6 and IPv4, providing direct communication between hosts that are using the different protocol suites.