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IPv6 Datagram Extension Headers
(Page 3 of 6)
Summary of IPv6 Extension Headers
Table 70
lists the different extension headers, showing its Next Header
value, length and defining RFC, and providing a brief description of
how each is used.
Table 70: IPv6 Extension Headers
Next Header
Value (decimal)
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Extension
Header Name
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Length
(bytes)
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Description
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Defining
RFC
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0
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Hop-By-Hop
Options
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Variable
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Defines an arbitrary set of options
that are intended to be examined by all devices on the path from the
source to destination device(s).
This is one of two extension headers used to define variable-format
options.
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2460
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43
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Routing
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Variable
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Defines a method
for allowing a source device to specify the route for a datagram. This
header type actually allows the definition of multiple routing types.
The IPv6 standard defines the Type 0 Routing extension header,
which is equivalent to the
loose source routing option in IPv4
and used in a similar way.
See below for the format of this extension header.
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2460
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44
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Fragment
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8
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When a datagram contains only
a fragment of the original message, this extension header is included.
It contains the Fragment Offset, Identification and More
Fragment fields that were removed from the main header.
See below for the format of this extension header, and the
topic on fragmentation and reassembly
for details on how the fields are used.
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2460
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50
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Encapsulating
Security Payload (ESP)
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Variable
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Carries encrypted
data for secure communications. This
header is described in detail in the section on IPSec.
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2406
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51
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Authentication
Header (AH)
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Variable
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Contains information used to
verify the authenticity of encrypted data. This
header is described in detail in the section on IPSec.
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2402
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60
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Destination
Options
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Variable
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Defines an
arbitrary set of options that are intended to be examined only by the
destination(s) of the datagram.
This is one of two extension headers used to define variable-format
options.
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2460
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Note that the Next Header
value of the IPv6 main header is 41; that of an IPv4 header is 4 (its
protocol number). Note that there is also a dummy extension
header called No Next Header that has a value of 59. This is
a placeholder that when found in the Next Header field indicates
that there is nothing after that extension header.
As I mentioned in the table, the
formats for several of the headers are provided in other topics. Two
of them I will describe here, however.
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Version 3.0 - Version Date: September 20, 2005
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