Clarke Morledge, Williamsburg Macromedia User's Group, Feb 2003
Product Description
IPv6 Essentials, Second Edition provides a succinct, in-depth tour of all the new features and functions in IPv6. It guides you through everything you need to know to get started, including how to configure IPv6 on hosts and routers and which applications currently support IPv6. The new IPv6 protocols offers extended address space, scalability, improved support for security, real-time traffic support, and auto-configuration so that even a novice user can connect a machine to the Internet. Aimed at system and network administrators, engineers, network designers, and IT managers, this book will help you understand, plan for, design, and integrate IPv6 into your current IPv4 infrastructure.
Beginning with a short history of IPv6, author Silvia Hagen provides an overview of new functionality and discusses why we need IPv6. Hagen also shares exhaustive discussions of the new IPv6 header format and Extension Headers, IPv6 address and ICMPv6 message format, Security, QoS, Mobility and, last but not least, offers a Quick Start Guide for different operating systems. IPv6 Essentials, Second Edition also covers:
- In-depth technical guide to IPv6
- Mechanisms and Case Studies that show how to integrate IPv6 into your network without interruption of IPv4 services
- Routing protocols and upper layer protocols
- Security in IPv6: concepts and requirements. Includes the IPSEC framework and security elements available for authentication and encryption
- Quality of Service: covers the elements available for QoS in IPv6 and how they can be implemented
- Detailed discussion of DHCPv6 and Mobile IPv6
- Discussion of migration cost and business case
- Getting started on different operating systems: Sun Solaris, Linux, BSD, Windows XP, and Cisco routers
Whether you're ready to start implementing IPv6 today or are planning your strategy for the future, IPv6 Essentials, Second Edition will provide the solid foundation you need to get started.
"Silvia's look at IPv6 is always refreshing as she translates complex technology features into business drivers and genuine end-user benefits to enable building new business concepts based on end to end models." Latif Ladid, President IPv6 Forum, Chair EU IPv6 Task Force
From the Publisher
About the Author
In the networking industry since 1990, Silvia Hagen became a CNE (Certified Novell Engineer) and CNI (Certified Novell Instructor) in 1992. As a successful instructor, she has trained hundreds of system engineers. Today, Silvia is CEO of Sunny Connection AG in Switzerland and works as a senior consultant and analyst for many mid- and large-sized companies. Her expertise is in Directory Services and Protocol Analysis.
Excerpted from Ipv6 Essentials by Silvia Hagen. Copyright © 2002. Reprinted by permission. All rights reserved.
Protocol
This chapter explains the structure of the IPv6 header and compares it to the IPv4 header. It also discusses Extension headers,which are new in IPv6. The header structure of an IPv6 packet is specified in RFC 2460.The header has a fixed length of 40 bytes.The two fields for source and destination addresses each use 16 bytes (128 bits),so there are only 8 bytes for general header information.
General Header Structure
In IPv6,five fields from the IPv4 header have been removed:
•Header Length
•Identification
•Flags
•Fragment Offset
•Header Checksum
The Header Length field was removed because it is not needed in a header with a fixed length.In IPv4 the minimum header length is 20 bytes,but if options are added,it can be extended in 4-byte increments up to 60 bytes.
Therefore,with IPv4,the information about the total length of the header is important.In IPv6 options are defined by Extension headers (covered later in this chapter).
The Identification field,the Flags field,and the Fragment Offset field handle fragmentation of a packet in the IPv4 header.Fragmentation happens if a large packet has to be sent over a network that only supports smaller packet sizes.In that case, the IPv4 router splits the packet into smaller slices and forwards multiple packets.The destination host collects the packets and 12 | Chapter 2: The Structure of the IPv6 Protocol reassembles them.If only one packet is missing or has an error,the whole transmission has to be redone;this is very inefficient.In IPv6,a host learns the Path Maximum Transmission Unit (MTU)size through a procedure called Path MTU Discovery.If a sending IPv6 host wants to fragment a packet,it will use an Extension header to do so.IPv6 routers along the path of a packet do not provide fragmentation,as they did with IPv4.So the Identification, Flags,and Fragment Offset fields were removed from the IPv6 header and will be inserted as an Extension header,if needed.Extension headers are explained later in this chapter.
Path MTU Discovery is explained in Chapter 4.
The Header Checksum field was removed to improve processing speed.If routers do not have to check and update checksums,processing becomes much faster.Checksumming is done at the media access level,too,and the risk for undetected errors and misrouted packets is minimal.There is a checksum field at the transport layer (UDP and TCP).IP is a best-effort delivery protocol;it is the responsibility of upper layer protocols to insure
integrity.
The Type of Service field was replaced by the TrafficClass field.IPv6 has a different mechanism to handle preferences.Refer to Chapter 6 for more information.The Protocol Type and the Time-to-Live (TTL)fields were renamed and slightly modified.A Flow Label field was added.
The Fields in the IPv6 Header
By becoming familiar with the fields of the IPv6 header,you will better understand how IPv6 works.
For a detailed description of all the fields in an IPv4 header, refer to Novell ’s Guide to Troubleshooting TCP/IP (John Wiley &Sons)by Silvia Hagen and Stephanie Lewis.
Figure 2-1 provides an overview of the IPv6 header.The fields are discussed in detail in the following paragraphs.
Figure 2-1 shows that even though the header has a total size of 40 bytes, which is twice as long as a default IPv4 header,it has actually been streamlined because most of the header is taken by the two 16-byte IPv6 addresses. That leaves only 8 bytes for other header information.
Version (4 Bits)
This is a 4-bit field and contains the version of the protocol.In the case of IPv6,the number is 6.The version number 5 could not be used because it had already been assigned an experimental stream protocol (ST2,RFC 1819).
Traffic Class (1 Byte)
This field replaces the Type of Service field in IPv4.This field facilitates the handling of real-time data and any other data that requires special handling. This field can be used by sending nodes and forwarding routers to identify and distinguish between different classes or priorities of IPv6 packets.
RFC 2474,"Definition of the Differentiated Services Field (DS Field)in the IPv4 and IPv6 Headers,"explains how the Traffic Class field in IPv6 can be used.RFC 2474 uses the term DS Field to refer to the Type of Service field in the IPv4 header,as well as to the Traffic Class field in the IPv6 header. --This text refers to an out of print or unavailable edition of this title.
