Chapter 27
IPv6
Protocol
TCP/IP Protocol Suite
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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OBJECTIVES:
 To give the format of an IPv6 datagram composed of a base
header and a payload.
 To discuss different fields used in an IPv6 datagram based
header and compare them with the fields in IPv4 datagram.
 To show how the options in IPv4 header are implemented using
the extension header in IPv6.
 To show how security is implemented in IPv6.
 To discuss three strategies used to handle the transition from
IPv4 to IPv6: dual stack, tunneling, and header translation.
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Chapter
Outline
TCP/IP Protocol Suite
27.1 Introduction
27.2
Packet Format
27.3
Transition to IPv6
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27-1 INTRODUCTION
In this introductory section, we discuss two topics:
rationale for a new protocol and the reasons for
delayed adoption.
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Topics Discussed in the Section
 Rationale for Change
 Reason for Delay in Adoption
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27-2 PACKET FORMAT
The IPv6 packet is shown in Figure 27.1. Each
packet is composed of a mandatory base header
followed by the payload. The payload consists of two
parts: optional extension headers and data from an
upper layer. The base header occupies 40 bytes,
whereas the extension headers and data from the
upper layer contain up to 65,535 bytes of
information.
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Topics Discussed in the Section
 Base Header
 Flow Label
 Comparison between IPv4 and IPv6 Headers
 Extension Headers
 Comparison between IPv4 and IPv6 Options
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Figure 27.1
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IPv6 datagram
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Figure 27.2
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Format of the base header
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Figure 27.3
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Extension header format
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Figure 27.4
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Extension header types
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Figure 27.5
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Hop-by-hop option header format
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Figure 27.6
Action
2 bits
C
1 bit
The format of the option in a hop-by-hop option header
Type
5 bits
Action: if the option not recognized
00 Skip this option
01 Discard datagram, no more action
10 Discard datagram and send ICMP message
11 Discard datagram send ICMP message if not multicast
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00000 Pad1
Type
00001 PadN
00010 Jumbo payload
C: Change in option value
0 Does not change in transit
1 May be changed in transit
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Figure 27.7 Pad1
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Figure 27.8
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PadN
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Figure 27.9
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Jumbo payload
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Figure 27.10
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Source routing
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Figure 27.11 Source routing example
Source: A
Destination: R1
Left: 3
R2
R3
B
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Source: A
Destination: R2
Left: 2
R1
R3
B
Source: A
Destination: R3
Left: 1
R1
R2
B
Source: A
Destination: B
Left: 0
R1
R2
R3
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Figure 27.12
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Fragmentation
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Figure 27.13
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Authentication
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Figure 27.14
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Calculation of authentication data
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Figure 27.15
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Encrypted security payload
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27-3 TRANSITION FROM IPv4 TO IPv6
Because of the huge number of systems on the
Internet, the transition from IPv4 to IPv6 cannot
happen suddenly. It will take a considerable amount
of time before every system in the Internet can move
from IPv4 to IPv6. The transition must be smooth to
prevent any problems between IPv4 and IPv6
systems. Three strategies have been devised by the
IETF to help the transition (see Figure 27.16).
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Topics Discussed in the Section
 Dual Stack
 Tunneling
 Header Translation
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Figure 27.16
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Three transition strategies
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Figure 27.17
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Dual stack
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Figure 27.18
Tunneling strategy
IPv4 header
IPv6 header
Payload
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Figure 27.19
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Header translation strategy
IPv6 header
IPv4 header
Payload
Payload
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