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Versions: 00 01 02 03 04 05 06 07 RFC 4443

Internet Draft                                     A. Conta, Transwitch
IPv6 Working Group                            S. Deering, Cisco Systems
11 July 2005                                      M. Gupta, Nokia (ed.)


               Internet Control Message Protocol (ICMPv6)
               for the Internet Protocol Version 6 (IPv6)
                             Specification

                   <draft-ietf-ipngwg-icmp-v3-07.txt>



Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   http://www.ietf.org/shadow.html.

   This internet draft will expire on Jan 11 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document describes the format of a set of control messages used
   in ICMPv6 (Internet Control Message Protocol).  ICMPv6 is the
   Internet Control Message Protocol for Internet Protocol version 6
   (IPv6).



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INTERNET-DRAFT           ICMPv6 (ICMP for IPv6)             11 July 2005


Table of Contents



   1. Introduction.....................................................3
   2. ICMPv6 (ICMP for IPv6)...........................................3
         2.1 Message General Format....................................3
         2.2 Message Source Address Determination......................5
         2.3 Message Checksum Calculation..............................6
         2.4 Message Processing Rules..................................6
   3. ICMPv6 Error Messages............................................9
         3.1 Destination Unreachable Message...........................9
         3.2 Packet Too Big Message...................................12
         3.3 Time Exceeded Message....................................13
         3.4 Parameter Problem Message................................14
   4. ICMPv6 Informational Messages...................................16
         4.1 Echo Request Message.....................................16
         4.2 Echo Reply Message.......................................17
   5. Security Considerations.........................................19
         5.1 Authentication and Confidentiality of ICMP messages......19
         5.2 ICMP Attacks.............................................19
   6. IANA Considerations.............................................21
         6.1 Procedure for new ICMPV6 Type and Code value assignments.22
         6.2 Assignments for this document............................22
   7. References......................................................23
         7.1 Normative................................................22
         7.2 Informative..............................................22
   8. Acknowledgments.................................................23
   9. Authors' Addresses..............................................23
   Appendix A - Changes since RFC 2463................................24





















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1. Introduction

   The Internet Protocol, version 6 (IPv6) uses the Internet Control
   Message Protocol (ICMP) as defined for IPv4 [RFC-792], with a number
   of changes.  The resulting protocol is called ICMPv6, and has an IPv6
   Next Header value of 58.

   This document describes the format of a set of control messages used
   in ICMPv6.  It does not describe the procedures for using these
   messages to chieve functions like Path MTU discovery; such procedures
   are described in other documents (e.g., [PMTU]).  Other documents may
   also introduce additional ICMPv6 message types, such as Neighbor
   Discovery messages [IPv6-DISC], subject to the general rules for
   ICMPv6 messages given in section 2 of this document.

   Terminology defined in the IPv6 specification [IPv6] and the IPv6
   Routing and Addressing specification [IPv6-ADDR] applies to this
   document as well.

   This document obsoletes RFC 2463 [RFC2463] and updates RFC 2780
   [RFC-2780].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC-2119].



2. ICMPv6 (ICMP for IPv6)

   ICMPv6 is used by IPv6 nodes to report errors encountered in
   processing packets, and to perform other internet-layer functions,
   such as diagnostics (ICMPv6 "ping").  ICMPv6 is an integral part of
   IPv6 and the base protocol (all the messages and behavior required by
   this specification) MUST be fully implemented by every IPv6 node.


2.1 Message General Format

   Every ICMPv6 message is preceded by an IPv6 header and zero or more
   IPv6 extension headers.  The ICMPv6 header is identified by a Next
   Header value of 58 in the immediately preceding header.  (NOTE: this
   is different than the value used to identify ICMP for IPv4.)








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   The ICMPv6 messages have the following general format:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     Code      |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                         Message Body                          +
      |                                                               |

   The type field indicates the type of the message. Its value
   determines the format of the remaining data.

   The code field depends on the message type. It is used to create an
   additional level of message granularity.

   The checksum field is used to detect data corruption in the ICMPv6
   message and parts of the IPv6 header.

   ICMPv6 messages are grouped into two classes: error messages and
   informational messages.  Error messages are identified as such by
   having a zero in the high-order bit of their message Type field
   values.  Thus, error messages have message Types from 0 to 127;
   informational messages have message Types from 128 to 255.

   This document defines the message formats for the following ICMPv6
   messages:

        ICMPv6 error messages:

            1    Destination Unreachable      (see section 3.1)
            2    Packet Too Big               (see section 3.2)
            3    Time Exceeded                (see section 3.3)
            4    Parameter Problem            (see section 3.4)

            100  Private experimentation
            101  Private experimentation

            127  Reserved for expansion of ICMPv6 error messages











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        ICMPv6 informational messages:

            128  Echo Request                 (see section 4.1)
            129  Echo Reply                   (see section 4.2)

            200  Private experimentation
            201  Private experimentation

            255  Reserved for expansion of ICMPv6 informational messages


   Type values 100, 101, 200, and 201 are reserved for private
   experimentation.  These are not intended for general use.  It is
   expected that multiple concurrent experiments will be done with the
   same type values.  Any wide scale and/or uncontrolled usage should
   obtain real allocations as defined in section 6.

   Type value 255 is reserved for future expansion of the type value
   range if there should be a shortage in the future.  The details of
   this are left for future work.  One possible way of doing this that
   would not cause any problems with current implementations is if the
   type equals 255, use the code field for the new assignment.  Existing
   implementations would ignore the new assignments as specified in
   section 2.4, section (b).  The new messages using these expanded type
   values, could assign fields in the message body for it's code values.

   Sections 3 and 4 describe the message formats for the ICMPv6 error
   message types 1 through 4 and informational message types 128 and
   129.

   Inclusion of, at least, the start of the invoking packet is intended
   to allow the originator of a packet that has resulted in an ICMPv6
   error message to identify the upper-layer protocol and process that
   sent the packet.


2.2 Message Source Address Determination

   A node that originates an ICMPv6 message has to determine both the
   Source and Destination IPv6 Addresses in the IPv6 header before
   calculating the checksum.  If the node has more than one unicast
   address, it MUST choose the Source Address of the message as follows:

    (a) If the message is a response to a message sent to one of the
        node's unicast addresses, the Source Address of the reply MUST
        be that same address.

    (b) If the message is a response to a message sent to any other



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INTERNET-DRAFT           ICMPv6 (ICMP for IPv6)             11 July 2005


        address, such as
            - a multicast group address,
            - an anycast address implemented by the node, or
            - a unicast address which does not belong to the node
        the Source Address of the ICMPv6 packet MUST be a unicast
        address belonging to the node.  The address SHOULD be chosen
        according to the rules which would be used to select the source
        address for any other packet originated by the node, given the
        destination address of the packet, but MAY be selected in an
        alternative way if this would lead to a more informative choice
        of address which is reachable from the destination of the ICMPv6
        packet.


2.3 Message Checksum Calculation

   The checksum is the 16-bit one's complement of the one's complement
   sum of the entire ICMPv6 message starting with the ICMPv6 message
   type field, prepended with a "pseudo-header" of IPv6 header fields,
   as specified in [IPv6, section 8.1].  The Next Header value used in
   the pseudo-header is 58.  (NOTE: the inclusion of a pseudo-header in
   the ICMPv6 checksum is a change from IPv4; see [IPv6] for the
   rationale for this change.)

   For computing the checksum, the checksum field is first set to zero.


2.4 Message Processing Rules

   Implementations MUST observe the following rules when processing
   ICMPv6 messages (from [RFC-1122]):

    (a) If an ICMPv6 error message of unknown type is received at its
        destination, it MUST be passed to the upper-layer process that
        originated the packet that caused the error, where this can be
        identified (see Section 2.4(d)).

    (b) If an ICMPv6 informational message of unknown type is received,
        it MUST be silently discarded.

    (c) Every ICMPv6 error message (type < 128) MUST include as much of
        the IPv6 offending (invoking) packet (the packet that caused the
        error) as possible without making the error message packet
        exceed the minimum IPv6 MTU [IPv6].

    (d) In those cases where the internet-layer protocol is required to
        pass an ICMPv6 error message to the upper-layer process, the
        upper-layer protocol type is extracted from the original packet



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        (contained in the body of the ICMPv6 error message) and used to
        select the appropriate upper-layer process to handle the error.

        In the cases where it is not possible to retrieve the upper-
        layer protocol type from the ICMPv6 message, the ICMPv6 message
        is silently dropped after any IPv6-layer processing.  One
        example of such a case is an ICMPv6 message with unusually large
        amount of extension headers that does not have the upper-layer
        protocol type due to truncation of the original packet to meet
        the minimum IPv6 MTU [IPv6] limit.  Another example of such a
        case is an ICMPv6 message with ESP extension header where it is
        not possible to decrypt the original packet due to either
        truncation or the unavailability of the state necessary to
        decrypt the packet.

    (e) An ICMPv6 error message MUST NOT be originated as a result of
        receiving:

         (e.1) an ICMPv6 error message, or

         (e.2) an ICMPv6 redirect message [IPv6-DISC], or

         (e.3) a packet destined to an IPv6 multicast address (there are
               two exceptions to this rule: (1) the Packet Too Big
               Message - Section 3.2 - to allow Path MTU discovery to
               work for IPv6 multicast, and (2) the Parameter Problem
               Message, Code 2 - Section 3.4 - reporting an unrecognized
               IPv6 option (see section 4.2 of [IPv6]) that has the
               Option Type highest-order two bits set to 10), or

         (e.4) a packet sent as a link-layer multicast, (the exceptions
               from e.3 apply to this case too), or

         (e.5) a packet sent as a link-layer broadcast, (the exceptions
               from e.3 apply to this case too), or

         (e.6) a packet whose source address does not uniquely identify
               a single node -- e.g., the IPv6 Unspecified Address, an
               IPv6 multicast address, or an address known by the ICMP
               message originator to be an IPv6 anycast address.

    (f) Finally, in order to limit the bandwidth and forwarding costs
        incurred by originating ICMPv6 error messages, an IPv6 node MUST
        limit the rate of ICMPv6 error messages it originates.  This
        situation may occur when a source sending a stream of erroneous
        packets fails to heed the resulting ICMPv6 error messages.

        Rate-limiting of forwarded ICMP messages is out of scope of this



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        specification.

        A recommended method for implementing the rate-limiting function
        is a token bucket, limiting the average rate of transmission to
        N, where N can either be packets/second or a fraction of the
        attached link's bandwidth, but allowing up to B error messages
        to be transmitted in a burst, as long as the long-term average
        is not exceeded.

        Rate-limiting mechanisms which cannot cope with bursty traffic
        (e.g., traceroute) are not recommended; for example a simple
        timer-based implementation, allowing an error message every T
        milliseconds (even with low values for T), is not reasonable.

        The rate-limiting parameters SHOULD be configurable.  In the
        case of a token-bucket implementation, the best defaults depend
        on where the implementation is expected to be deployed (e.g., a
        high-end router vs. an embedded host).  For example, in a
        small/mid -sized device, the possible defaults could be B=10,
        N=10/s.

   NOTE: THE RESTRICTIONS UNDER (e) AND (f) ABOVE TAKE PRECEDENCE OVER
   ANY REQUIREMENT ELSEWHERE IN THIS DOCUMENT FOR ORIGINATING ICMP ERROR
   MESSAGES.

   The following sections describe the message formats for the above
   ICMPv6 messages.
























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INTERNET-DRAFT           ICMPv6 (ICMP for IPv6)             11 July 2005


3. ICMPv6 Error Messages

3.1 Destination Unreachable Message

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     Code      |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Unused                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +                as possible without the ICMPv6 packet          +
      |                exceeding the minimum IPv6 MTU [IPv6]          |

   IPv6 Fields:

   Destination Address

                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           1

   Code           0 - no route to destination
                  1 - communication with destination
                        administratively prohibited
                  2 - beyond scope of source address
                  3 - address unreachable
                  4 - port unreachable
                  5 - source address failed ingress/egress policy
                  6 - reject route to destination

   Unused         This field is unused for all code values.
                  It must be initialized to zero by the originator
                  and ignored by the receiver.
   Description

   A Destination Unreachable message SHOULD be generated by a router, or
   by the IPv6 layer in the originating node, in response to a packet
   that cannot be delivered to its destination address for reasons other
   than congestion.  (An ICMPv6 message MUST NOT be generated if a
   packet is dropped due to congestion.)

   If the reason for the failure to deliver is lack of a matching entry
   in the forwarding node's routing table, the Code field is set to 0



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   (NOTE: this error can occur only in nodes that do not hold a "default
   route" in their routing tables).

   If the reason for the failure to deliver is administrative
   prohibition, e.g., a "firewall filter", the Code field is set to 1.

   If the reason for the failure to deliver is that the destination is
   beyond the scope of the source address, the Code field is set to 2.
   This condition can occur only when the scope of the source address is
   smaller than the scope of the destination address (e.g., when a
   packet has a link-local source address and a global-scope destination
   address) and the packet cannot be delivered to the destination
   without leaving the scope of the source address.

   If the reason for the failure to deliver can not be mapped to any of
   other codes, the Code field is set to 3.  The example of such cases
   are inability to resolve the IPv6 destination address into a
   corresponding link address, or a link-specific problem of some sort.

   One specific case in which a Destination Unreachable message with a
   code 3 is sent is in response to a packet received by a router from a
   point-to-point link, destined to an address within a subnet assigned
   to that same link (other than one of the receiving router's own
   addresses).  In such a case, the packet MUST NOT be forwarded back
   onto the arrival link.

   A destination node SHOULD originate a Destination Unreachable message
   with Code 4 in response to a packet for which the transport protocol
   (e.g., UDP) has no listener, if that transport protocol has no
   alternative means to inform the sender.

   If the reason for the failure to deliver is that packet with this
   source address is not allowed due to ingress or egress filtering
   policies, the Code field is set to 5.

   If the reason for the failure to deliver is that the route to the
   destination is a reject route, the Code field is set to 6.  This may
   occur if the router has been configured to reject all the traffic for
   a specific prefix.

   Codes 5 and 6 are more informative subsets of code 1.

   For security reasons, it is recommended that implementations SHOULD
   allow sending of ICMP destination unreachable messages to be
   disabled, preferably on a per-interface basis.






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   Upper layer notification

   A node receiving the ICMPv6 Destination Unreachable message MUST
   notify the upper-layer process if the relevant process can be
   identified (see section 2.4(d)).














































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3.2 Packet Too Big Message

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     Code      |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             MTU                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +               as possible without the ICMPv6 packet           +
      |               exceeding the minimum IPv6 MTU [IPv6]           |

   IPv6 Fields:

   Destination Address

                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           2

   Code           Set to 0 (zero) by the originator and ignored by the
                  receiver

   MTU            The Maximum Transmission Unit of the next-hop link.

   Description

   A Packet Too Big MUST be sent by a router in response to a packet
   that it cannot forward because the packet is larger than the MTU of
   the outgoing link.  The information in this message is used as part
   of the Path MTU Discovery process [PMTU].

   Originating a Packet Too Big Message makes an exception to one of the
   rules of when to originate an ICMPv6 error message, in that unlike
   other messages, it is sent in response to a packet received with an
   IPv6 multicast destination address, or a link-layer multicast or
   link-layer broadcast address.

   Upper layer notification

   An incoming Packet Too Big message MUST be passed to the upper-layer
   process if the relevant process can be identified (see section
   2.4(d)).




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INTERNET-DRAFT           ICMPv6 (ICMP for IPv6)             11 July 2005


3.3 Time Exceeded Message

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     Code      |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Unused                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +               as possible without the ICMPv6 packet           +
      |               exceeding the minimum IPv6 MTU [IPv6]           |

   IPv6 Fields:

   Destination Address
                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           3

   Code           0 - hop limit exceeded in transit

                  1 - fragment reassembly time exceeded

   Unused         This field is unused for all code values.
                  It must be initialized to zero by the originator
                  and ignored by the receiver.

   Description

   If a router receives a packet with a Hop Limit of zero, or a router
   decrements a packet's Hop Limit to zero, it MUST discard the packet
   and originate an ICMPv6 Time Exceeded message with Code 0 to the
   source of the packet.  This indicates either a routing loop or too
   small an initial Hop Limit value.

   An ICMPv6 Time Exceeded message with Code 1 is used to report
   fragment reassembly timeout, as specified in [IPv6, Section 4.5].

   Upper layer notification

   An incoming Time Exceeded message MUST be passed to the upper-layer
   process if the relevant process can be identified (see section
   2.4(d)).




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3.4 Parameter Problem Message

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     Code      |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Pointer                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +               as possible without the ICMPv6 packet           +
      |               exceeding the minimum IPv6 MTU [IPv6]           |

   IPv6 Fields:

   Destination Address

                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           4

   Code           0 - erroneous header field encountered

                  1 - unrecognized Next Header type encountered

                  2 - unrecognized IPv6 option encountered

   Pointer        Identifies the octet offset within the
                  invoking packet where the error was detected.

                  The pointer will point beyond the end of the ICMPv6
                  packet if the field in error is beyond what can fit
                  in the maximum size of an ICMPv6 error message.

   Description

   If an IPv6 node processing a packet finds a problem with a field in
   the IPv6 header or extension headers such that it cannot complete
   processing the packet, it MUST discard the packet and SHOULD
   originate an ICMPv6 Parameter Problem message to the packet's source,
   indicating the type and location of the problem.

   Codes 1 and 2 are more informative subsets of Code 0.

   The pointer identifies the octet of the original packet's header



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   where the error was detected.  For example, an ICMPv6 message with
   Type field = 4, Code field = 1, and Pointer field = 40 would indicate
   that the IPv6 extension header following the IPv6 header of the
   original packet holds an unrecognized Next Header field value.

   Upper layer notification

   A node receiving this ICMPv6 message MUST notify the upper-layer
   process if the relevant process can be identified (see section
   2.4(d)).









































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INTERNET-DRAFT           ICMPv6 (ICMP for IPv6)             11 July 2005


4. ICMPv6 Informational Messages

4.1 Echo Request Message

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     Code      |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Identifier          |        Sequence Number        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Data ...
      +-+-+-+-+-

   IPv6 Fields:

   Destination Address

                  Any legal IPv6 address.

   ICMPv6 Fields:

   Type           128

   Code           0

   Identifier     An identifier to aid in matching Echo Replies
                  to this Echo Request.  May be zero.

   Sequence Number

                  A sequence number to aid in matching Echo Replies
                  to this Echo Request.  May be zero.

   Data           Zero or more octets of arbitrary data.

   Description

   Every node MUST implement an ICMPv6 Echo responder function that
   receives Echo Requests and originates corresponding Echo Replies.  A
   node SHOULD also implement an application-layer interface for
   originating Echo Requests and receiving Echo Replies, for diagnostic
   purposes.

   Upper layer notification

   Echo Request messages MAY be passed to processes receiving ICMP
   messages.



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4.2 Echo Reply Message

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     Code      |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Identifier          |        Sequence Number        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Data ...
      +-+-+-+-+-

   IPv6 Fields:

   Destination Address

                  Copied from the Source Address field of the invoking
                  Echo Request packet.

   ICMPv6 Fields:

   Type           129

   Code           0

   Identifier     The identifier from the invoking Echo Request message.

   Sequence       The sequence number from the invoking Echo Request
   Number         message.

   Data           The data from the invoking Echo Request message.

   Description

   Every node MUST implement an ICMPv6 Echo responder function that
   receives Echo Requests and originates corresponding Echo Replies.  A
   node SHOULD also implement an application-layer interface for
   originating Echo Requests and receiving Echo Replies, for diagnostic
   purposes.

   The source address of an Echo Reply sent in response to a unicast
   Echo Request message MUST be the same as the destination address of
   that Echo Request message.

   An Echo Reply SHOULD be sent in response to an Echo Request message
   sent to an IPv6 multicast or anycast address.  In this case, the
   source address of the reply MUST be a unicast address belonging to
   the interface on which the Echo Request message was received.



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   The data received in the ICMPv6 Echo Request message MUST be returned
   entirely and unmodified in the ICMPv6 Echo Reply message.

   Upper layer notification

   Echo Reply messages MUST be passed to the process that originated an
   Echo Request message. An Echo Reply message MAY be passed to
   processes that did not originate the Echo Request message.











































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   Note that there is no limitations on the amount of data that can be
   put in Echo Request and Echo Reply Messages.


5. Security Considerations

5.1 Authentication and Confidentiality of ICMP messages

   ICMP protocol packet exchanges can be authenticated using the IP
   Authentication Header [IPv6-AUTH] or IP Encapsulating Security
   Payload Header [IPv6-ESP].  Confidentiality for the ICMP protocol
   packet exchanges can be achieved using IP Encapsulating Security
   Payload Header [IPv6-ESP].

   [SEC-ARCH] describes the IPsec handling of ICMP traffic in detail.

5.2 ICMP Attacks

   ICMP messages may be subject to various attacks.  A complete
   discussion can be found in the IP Security Architecture [IPv6-SA].  A
   brief discussion of such attacks and their prevention is as follows:

   1. ICMP messages may be subject to actions intended to cause the
      receiver to believe the message came from a different source than
      the message originator. The protection against this attack can be
      achieved by applying the IPv6 Authentication mechanism [IPv6-AUTH]
      to the ICMP message.

   2. ICMP messages may be subject to actions intended to cause the
      message or the reply to it go to a destination different than the
      message originator's intention.  The protection against this
      attack can be achieved by using the Authentication Header
      [IPv6-AUTH] or the Encapsulating Security Payload Header
      [IPv6-ESP].  Authentication Header provides the protection against
      change for the source and the destination address of the IP
      packet.  Encapsulating Security Payload Header does not provide
      this protection but the ICMP checksum calculation includes the
      source and the destination addresses and the Encapsulating
      Security Payload Header protects the checksum.  Therefore, the
      combination of ICMP checksum and the Encapsulating Security
      Payload Header provides the protection against this attack.  The
      protection provided by the Encapsulating Security Payload Header
      will not be as strong as the protection provided by the
      Authentication Header.

   3. ICMP messages may be subject to changes in the message fields, or
      payload.  The authentication [IPv6-AUTH] or encryption [IPv6-ESP]
      of the ICMP message is a protection against such actions.



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   4. ICMP messages may be used as attempts to perform denial of service
      attacks by sending back to back erroneous IP packets.  An
      implementation that correctly followed section 2.4, paragraph (f)
      of this specifications, would be protected by the ICMP error rate
      limiting mechanism.

   5. The exception number 2 of rule e.3 in section 2.4 gives the
      opportunity to a malicious node to cause a denial of service
      attack to a multicast source.  A malicious node can send a
      multicast packet with an unknown destination option marked as
      mandatory with the IPv6 source address of a valid multicast
      source.  A large number of destination nodes will send ICMP
      Parameter Problem Message to the multicast source causing a denial
      of service attack.  The way multicast traffic is forwarded by the
      multicast routers does require the malicious node to be part of
      the correct multicast path i.e. near to the multicast source.
      This attack can only be avoided by securing the multicast traffic.
      The multicast source should be careful while sending multicast
      traffic with the destination options marked as mandatory because
      they can cause a denial of service attack to themselves if the
      destination option is unknown to a large number of destinations.

   6. As the ICMP messages are passed to the upper-layer processes, it
      is possible to perform attacks on the upper layer protocols (e.g.,
      TCP) with ICMP [TCP-attack].  It is recommended for the upper
      layers to perform some form of validation of ICMP messages (using
      the information contained in the payload of the ICMP message)
      before acting upon them.  The actual validation checks are
      specific to the upper layers and are out of the scope of this
      spec.  Protecting the upper layer with IPsec mitigates these
      attacks.

      ICMP error messages signal network error conditions that were
      encountered while processing an internet datagram.  Depending on
      the particular scenario, the error conditions being reported might
      or might not get solved in the near term.  Therefore, reaction to
      ICMP error messages may depend not only on the error type and
      code, but also on other factors such as the time the error
      messages are received, previous knowledge of the network error
      conditions being reported, and knowledge of the network scenario
      in which the receiving host is operating.










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6. IANA Considerations

6.1 Procedure for new ICMPV6 Type and Code value assignments

   The IPv6 ICMP header [ICMPV6] contains the following fields that
   carry values assigned from IANA-managed name spaces: Type and Code.
   Code field values are defined relative to a specific Type value.

   Values for the IPv6 ICMP Type fields are allocated using the
   following procedure:

   1. The IANA should allocate and permanently register new ICMPv6 type
      codes from IETF RFC publication.  This is for all RFC types
      including standards track, informational, and experimental status
      that originate from the IETF and have been approved by the IESG
      for publication.

   2. IETF working groups with working group consensus and area director
      approval can request reclaimable ICMPV6 type code assignments from
      the IANA.  The IANA will tag the values as "reclaimable in
      future".

      The "reclaimable in the future" tag will be removed when an RFC is
      published documenting the protocol as defined in 1).  This will
      make the assignment permanent and update the reference on the IANA
      web pages.

      At the point where the ICMPv6 type values are 85% assigned, the
      IETF will review the assignments tagged "reclaimable in the
      future" and inform the IANA which ones should be reclaimed and
      reassigned.

   3. Requests for new ICMPv6 type value assignments from outside the
      IETF are only made through the publication of an IETF document,
      per 1) above.   Note also that documents published as "RFC Editor
      contributions" [RFC 3667] are not considered to be IETF documents.

   The assignment of new Code values for the Type values defined in this
   document require standards action or IESG approval.  The policy for
   assigning Code values for new IPv6 ICMP Types not defined in this
   document should be defined in the document defining the new Type
   values.

6.2 Assignments for this document

   The following should update the assignments located at:

      http://www.iana.org/assignments/icmpv6-parameters



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   The IANA is requested to reassign ICMPv6 type 1 "Destination
   Unreachable" code 2, that was unassigned in [RFC-2463], to:

          2 - beyond scope of source address

   The IANA is requested to assign the following two new codes values
   for ICMPv6 type 1 "Destination Unreachable":

           5 - source address failed ingress/egress policy
           6 - reject route to destination

   The IANA is requested to assign the following new type values:

           100  Private experimentation
           101  Private experimentation

           200  Private experimentation
           201  Private experimentation

           255  Reserved for expansion

7. References

7.1 Normative

   [IPv6]       Deering, S., R. Hinden, "Internet Protocol, Version 6,
                Specification", RFC2460, December 1998.

   [IPv6-DISC]  Narten, T., E. Nordmark, W. Simpson, "Neighbor Discovery
                for IP Version 6 (IPv6)", RFC2461, December, 1998.

   [RFC-792]    Postel, J., "Internet Control Message Protocol", STD 5,
                RFC792, September 1981.

   [RFC-2463]   Conta, A., S. Deering, "Internet Control Message
                Protocol (ICMPv6) for the Internet Protocol Version 6
                (IPv6) Specification", RFC2463, December, 1998.

   [RFC-1122]   Braden, R., "Requirements for Internet Hosts -
                Communication Layers", STD 5, RFC1122, August 1989.

   [RFC-2119]   Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP14, RFC2119, March 1997.


7.2 Informative

   [RFC-2780]   Bradner, S., V. Paxson, "IANA Allocation Guidelines For



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                Values In the Internet Protocol and Related Headers",
                RFC 2780, March 2000.

   [IPv6-ADDR]  Hinden, R., S. Deering, "IP Version 6 Addressing
                Architecture", RFC2373, July 1998.

   [PMTU]       McCann, J., S. Deering, J. Mogul, "Path MTU Discovery
                for IP version 6", RFC1981, August 1996.

   [IPv6-SA]    Kent, S., R. Atkinson, "Security Architecture for the
                Internet Protocol", RFC1825, November 1998.

   [IPv6-AUTH]  Kent, S., "IP Authentication Header", draft-ietf-ipsec-
                rfc2402bis-11.txt, work in progress.

   [IPv6-ESP]   Kent, S., "IP Encapsulating Security Payload (ESP)",
                draft-ietf-ipsec-esp-v3-10.txt, work in progress.

   [SEC-ARCH]   Kent, S., K. Seo, "Security Architecture for the
                Internet Protocol", draft-ietf-ipsec-rfc2401bis-05.txt,
                work in progress.

   [TCP-attack] Gont, F., "ICMP attacks against TCP", draft-gont-tcpm-
                icmp-attacks-03.txt, work in progress.

8. Acknowledgments

   The document is derived from previous ICMP drafts of the SIPP and
   IPng working group.

   The IPng working group and particularly Robert Elz, Jim Bound, Bill
   Simpson, Thomas Narten, Charlie Lynn, Bill Fink, Scott Bradner,
   Dimitri Haskin, Bob Hinden, Jun-ichiro Itojun Hagino, Tatuya Jinmei,
   Brian Zill, Pekka Savola, Fred Templin and Elwyn davies (in
   chronological order) provided extensive review information and
   feedback.

   Bob Hinden was the document editor for this document.













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9. Authors' Addresses

   Alex Conta
   Transwitch Corporation
   3 Enterprise Drive
   Shelton, CT 06484
   USA
   Email: aconta@txc.com

   Stephen Deering
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134-1706
   USA

   Mukesh Gupta (ed.)
   Nokia
   313 Fairchild Drive
   Mountain View, CA 94043
   US
   Phone: +1 650-625-2264
   Email: mukesh.k.gupta@nokia.com


Appendix A - Changes since RFC 2463


   The following changes were made from RFC 2463:

    - Edited the Abstract to make it a little more elaborate.

    - Corrected typos in section 2.4, where references to sub-bullet e.2
      were supposed to be references to e.3.

    - Removed the Timer-based and the Bandwidth-based methods from the
      example rate-limiting mechanism for ICMP error messages.  Added
      Token-bucket based method.

    - Added specification that all ICMP error messages shall have
      exactly 32 bits of type-specific data, so that receivers can
      reliably find the embedded invoking packet even when they don't
      recognize the ICMP message Type.

    - In the description of Destination Unreachable messages, Code 3,
      added rule prohibiting forwarding of packets back onto point-to-
      point links from which they were received, if their destination
      addresses belong to the link itself ("anti-ping-ponging" rule).




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    - Added description of Time Exceeded Code 1 (fragment reassembly
      timeout).

    - Added "beyond scope of source address", "source address failed
      ingress/egress policy", and "reject route to destination" messages
      to the family of "unreachable destination" type ICMP error
      messages (section 3.1).

    - Reserved some ICMP type values for experimentation.

    - Added a NOTE in section 2.4, that specifies ICMP message
      processing rules precedence.

    - Added ICMP REDIRECT to the list in Section 2.4 e) of cases in
      which ICMP error messages are not to be generated.

    - Made minor editorial changes in Section 2.3 on checksum
      calculation, and in Section 5.2.

    - Clarified in section 4.2, regarding the Echo Reply Message, that
      the source address of an Echo Reply to an anycast Echo Request
      should be a unicast address, as in the case of multicast.

    - Revised the Security Considerations section.  Added the use of
      Encapsulating Security Payload Header for authentication.  Changed
      the requirement of an option of "not allowing unauthenticated ICMP
      messages" to MAY from SHOULD.

    - Added a new attack in the list of possible ICMP attacks in section
      5.2.

    - Separated References into Normative and Informative.

    - Added reference to RFC-2780 "IANA Allocation Guidelines For Values
      In the Internet Protocol and Related Headers".  Also added a note
      that this document updates RFC-2780.

    - Added a procedure for new ICMPv6 Type and Code value assignments
      in the IANA Consideration section.

    - Replaced word "send" with "originate" to make it clear that ICMP
      packets being forwarded are out of scope of this specification.

    - Changed the ESP and AH references to the updated ESP and AH
      drafts.

    - Added reference to the updated IPsec Security Architecture draft.




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    - Added a SHOULD requirement for allowing the sending of ICMP
      destination unreachable messages to be disabled.

    - Simplified the source address selection of the ICMPv6 packet.

    - Reorganized the General Message Format (section 2.1).

    - Removed the general packet format from section 2.1.  It refers to
      section 3 and 4 for packet formats now.

    - Added text about attacks to the transport protocols that could
      potentially be caused by ICMP.

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   This document and the information contained herein are provided on an
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   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE



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   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
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Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




































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