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rfc:std:std89

Network Working Group A. Conta Request for Comments: 4443 Transwitch Obsoletes: 2463 S. Deering Updates: 2780 Cisco Systems Category: Standards Track M. Gupta, Ed.

                                                       Tropos Networks
                                                            March 2006
             Internet Control Message Protocol (ICMPv6)
      for the Internet Protocol Version 6 (IPv6) Specification

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

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).

Conta, et al. Standards Track [Page 1] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

Table of Contents

 1. Introduction ....................................................2
 2. ICMPv6 (ICMP for IPv6) ..........................................3
    2.1. Message General Format .....................................3
    2.2. Message Source Address Determination .......................5
    2.3. Message Checksum Calculation ...............................5
    2.4. Message Processing Rules ...................................5
 3. ICMPv6 Error Messages ...........................................8
    3.1. Destination Unreachable Message ............................8
    3.2. Packet Too Big Message ....................................10
    3.3. Time Exceeded Message .....................................11
    3.4. Parameter Problem Message .................................12
 4. ICMPv6 Informational Messages ..................................13
    4.1. Echo Request Message ......................................13
    4.2. Echo Reply Message ........................................14
 5. Security Considerations ........................................15
    5.1. Authentication and Confidentiality of ICMP Messages .......15
    5.2. ICMP Attacks ..............................................16
 6. IANA Considerations ............................................17
    6.1. Procedure for New ICMPV6 Type and Code Value Assignments ..17
    6.2. Assignments for This Document .............................18
 7. References .....................................................19
    7.1. Normative References ......................................19
    7.2. Informative References ....................................19
 8. Acknowledgements ...............................................20
 Appendix A - Changes since RFC 2463................................21

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 achieve functions like Path MTU discovery; these
 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.

Conta, et al. Standards Track [Page 2] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 This document obsoletes RFC 2463 [RFC-2463] 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.  (This is
 different from the value used to identify ICMP for IPv4.)
 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 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.

Conta, et al. Standards Track [Page 3] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 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
    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.  They 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 values 127 and 255 are reserved for future expansion of the type
 value range if there is 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 that if
 the type equals 127 or 255, the code field should be used for the new
 assignment.  Existing implementations would ignore the new
 assignments as specified in Section 2.4, (b).  The new messages using
 these expanded type values could assign fields in the message body
 for its 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.

Conta, et al. Standards Track [Page 4] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 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
     address, such as
  1. a multicast group address,
  2. an anycast address implemented by the node, or
  3. a unicast address that 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 that would be used to select the source address for any
    other packet originated by the node, given the destination address
    of the packet.  However, it MAY be selected in an alternative way
    if this would lead to a more informative choice of address
    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, and 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.  (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]):

Conta, et al. Standards Track [Page 5] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 (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 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 (contained in
     the body of the ICMPv6 error message) and used to select the
     appropriate upper-layer process to handle the error.
     In 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 an 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 is an ICMPv6 message with
     an ESP extension header for which 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 the following:
     (e.1) An ICMPv6 error message.
     (e.2) An ICMPv6 redirect message [IPv6-DISC].
     (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).
     (e.4) A packet sent as a link-layer multicast (the exceptions
           from e.3 apply to this case, too).

Conta, et al. Standards Track [Page 6] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

     (e.5) A packet sent as a link-layer broadcast (the exceptions
           from e.3 apply to this case, too).
     (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
     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 be either 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 that 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-size 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.

Conta, et al. Standards Track [Page 7] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

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.

Conta, et al. Standards Track [Page 8] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 (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 cannot be mapped to any of
 other codes, the Code field is set to 3.  Example of such cases are
 an 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 is sent
 with a code 3 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 the 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.

Conta, et al. Standards Track [Page 9] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 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)).

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 as to when to originate an ICMPv6 error message.  Unlike other
 messages, it is sent in response to a packet received with an IPv6
 multicast destination address, or with a link-layer multicast or
 link-layer broadcast address.

Conta, et al. Standards Track [Page 10] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 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)).

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 if 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].

Conta, et al. Standards Track [Page 11] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 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)).

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.

Conta, et al. Standards Track [Page 12] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 Codes 1 and 2 are more informative subsets of Code 0.
 The pointer identifies the octet of the original packet's header
 where the error was detected.  For example, an ICMPv6 message with a
 Type field of 4, Code field of 1, and Pointer field of 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)).

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.

Conta, et al. Standards Track [Page 13] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 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.

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.

Conta, et al. Standards Track [Page 14] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 Sequence Number
                The sequence number from the invoking Echo Request
                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.
 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.
 Note that there is no limitation 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 the IP Encapsulating Security
 Payload Header [IPv6-ESP].
 [SEC-ARCH] describes the IPsec handling of ICMP traffic in detail.

Conta, et al. Standards Track [Page 15] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

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 these attacks and their prevention follows:
 1. ICMP messages may be subject to actions intended to cause the
    receiver to believe the message came from a different source from
    that of 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 to go to a destination different from
    that of 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].  The Authentication Header provides the protection
    against change for the source and the destination address of the
    IP packet.  The 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 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 protects against such actions.
 4. ICMP messages may be used to attempt denial-of-service attacks by
    sending back to back erroneous IP packets.  An implementation that
    correctly followed Section 2.4, paragraph (f), of this
    specification, would be protected by the ICMP error rate limiting
    mechanism.
 5. The exception number 2 of rule e.3 in Section 2.4 gives a
    malicious node the opportunity 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 an ICMP Parameter Problem
    Message to the multicast source, causing a denial-of-service
    attack.  The way multicast traffic is forwarded by the multicast
    routers requires that the malicious node be part of the correct

Conta, et al. Standards Track [Page 16] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

    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 that the upper
    layers 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 specification.
    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 at which 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.

6. IANA Considerations

6.1. Procedure for New ICMPV6 Type and Code Value Assignments

 The IPv6 ICMP header defined in this document 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".

Conta, et al. Standards Track [Page 17] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

    The "reclaimable in the future" tag will be removed when an RFC is
    published that documents 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-3978] are not considered 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 has updated assignments located at:
    http://www.iana.org/assignments/icmpv6-parameters
 The IANA has reassigned ICMPv6 type 1 "Destination Unreachable" code
 2, which was unassigned in [RFC-2463], to:
       2 - Beyond scope of source address
 The IANA has assigned 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 has assigned the following new type values:
       100  Private experimentation
       101  Private experimentation
       127  Reserved for expansion of ICMPv6 error messages
       200  Private experimentation
       201  Private experimentation

Conta, et al. Standards Track [Page 18] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

       255  Reserved for expansion of ICMPv6 informational messages

7. References

7.1. Normative References

 [IPv6]       Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.
 [IPv6-DISC]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461, December
              1998.
 [RFC-792]    Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.
 [RFC-2463]   Conta, A. and S. Deering, "Internet Control Message
              Protocol (ICMPv6) for the Internet Protocol Version 6
              (IPv6) Specification", RFC 2463, December 1998.
 [RFC-1122]   Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.
 [RFC-2119]   Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC-3978]   Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
              3978, March 2005.

7.2. Informative References

 [RFC-2780]   Bradner, S. and V. Paxson, "IANA Allocation Guidelines
              For Values In the Internet Protocol and Related
              Headers", BCP 37, RFC 2780, March 2000.
 [IPv6-ADDR]  Hinden, R. and S. Deering, "Intpernet Protocol Version 6
              (IPv6) Addressing Architecture", RFC 3513, April 2003.
 [PMTU]       McCann, J., Deering, S., and J. Mogul, "Path MTU
              Discovery for IP version 6", RFC 1981, August 1996.
 [IPv6-SA]    Kent, S. and R. Atkinson, "Security Architecture for the
              Internet Protocol", RFC 2401, November 1998.
 [IPv6-AUTH]  Kent, S., "IP Authentication Header", RFC 4302, December
              2005.

Conta, et al. Standards Track [Page 19] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

 [IPv6-ESP]   Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
              4203, December 2005.
 [SEC-ARCH]   Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.
 [TCP-attack] Gont, F., "ICMP attacks against TCP", Work in Progress.

8. Acknowledgements

 The document is derived from previous ICMP documents 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.

Conta, et al. Standards Track [Page 20] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

Appendix A - Changes since RFC 2463

 The following changes were made from RFC 2463:
  1. Edited the Abstract to make it a little more elaborate.
  1. Corrected typos in Section 2.4, where references to sub-bullet e.2

were supposed to be references to e.3.

  1. Removed the Timer-based and the Bandwidth-based methods from the

example rate-limiting mechanism for ICMP error messages. Added

   Token-bucket based method.
  1. 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.
  1. 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).
  1. Added description of Time Exceeded Code 1 (fragment reassembly

timeout).

  1. 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).
  1. Reserved some ICMP type values for experimentation.
  1. Added a NOTE in Section 2.4 that specifies ICMP message processing

rules precedence.

  1. Added ICMP REDIRECT to the list in Section 2.4, (e) of cases in

which ICMP error messages are not to be generated.

  1. Made minor editorial changes in Section 2.3 on checksum

calculation, and in Section 5.2.

  1. Clarified in Section 4.2, regarding the Echo Reply Message; the

source address of an Echo Reply to an anycast Echo Request should

   be a unicast address, as in the case of multicast.

Conta, et al. Standards Track [Page 21] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

  1. Revised the Security Considerations section. Added the use of the

Encapsulating Security Payload Header for authentication. Changed

   the requirement of an option of "not allowing unauthenticated ICMP
   messages" to MAY from SHOULD.
  1. Added a new attack in the list of possible ICMP attacks in Section

5.2.

  1. Separated References into Normative and Informative.
  1. 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.
  1. Added a procedure for new ICMPv6 Type and Code value assignments in

the IANA Considerations section.

  1. Replaced word "send" with "originate" to make it clear that ICMP

packets being forwarded are out of scope of this specification.

  1. Changed the ESP and AH references to the updated ESP and AH

documents.

  1. Added reference to the updated IPsec Security Architecture

document.

  1. Added a SHOULD requirement for allowing the sending of ICMP

destination unreachable messages to be disabled.

  1. Simplified the source address selection of the ICMPv6 packet.
  1. Reorganized the General Message Format (Section 2.1).
  1. Removed the general packet format from Section 2.1. It refers to

Sections 3 and 4 for packet formats now.

  1. Added text about attacks to the transport protocols that could

potentially be caused by ICMP.

Conta, et al. Standards Track [Page 22] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

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.
 Tropos Networks
 555 Del Rey Avenue
 Sunnyvale, CA 94085
 Phone: +1 408-331-6889
 EMail: mukesh.gupta@tropos.com

Conta, et al. Standards Track [Page 23] RFC 4443 ICMPv6 (ICMP for IPv6) March 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

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 Intellectual Property Rights or other rights that might be claimed to
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 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 The IETF invites any interested party to bring to its attention any
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 this standard.  Please address the information to the IETF at
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Acknowledgement

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 Administrative Support Activity (IASA).

Conta, et al. Standards Track [Page 24]

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