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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  Internet Control Message Protocol (ICMP/ICMPv4 and ICMPv6)
                9  ICMP Message Types and Formats
                     9  ICMP Version 6 (ICMPv6) Error Message Types and Formats

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ICMPv6 Time Exceeded Messages
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ICMP Version 6 (ICMPv6) Informational Message Types and Formats
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ICMPv6 Parameter Problem Messages
(Page 3 of 3)

Parameter Problem Message Interpretation Codes and The Pointer Field

The Pointer field, which was only 8 bits wide in ICMPv4, has been widened to 32 bits in ICMPv6, to provide more flexibility in isolating the error. The Code value is also used somewhat differently in ICMPv6 than it was in the ICMPv4 version of this message type. In ICMPv4, the Pointer was used only when the Code field was 0, and other code values indicated other problem categories for which the Pointer field did not make sense. In ICMPv6, the Pointer field is used with all Code types, to indicate the general nature of what the problem is. This means the Pointer field tells the recipient of the Parameter Problem where in the message the problem happened, and the Code field tells it what the nature of the problem is. The following table shows the three Code values and provides a brief explanation of each:


Table 107: ICMPv6 Parameter Problem Message Interpretation Codes

Code Value

Message Subtype

Description

0

Erroneous Header Field Encountered

The Pointer field points to a header that contains an error or otherwise could not be processed.

1

Unrecognized Next Header Type Encountered

Recall that in IPv6 a datagram can have multiple headers, each of which contains a Next Header field that points to the next header in the datagram. This code indicates that the Pointer field points to a Next Header field containing an unrecognized value.

2

Unrecognized IPv6 Option Encountered

The Pointer field points to an IPv6 option that was not recognized by the processing device.


Key Concept: The ICMPv6 Parameter Problem message is a generic error message that can be used to convey an error of any type in an IP datagram. The Pointer field is used to indicate to the recipient of the message where the problem was in the original datagram.


 


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ICMPv6 Time Exceeded Messages
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ICMP Version 6 (ICMPv6) Informational Message Types and Formats
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