Network Working Group           A. Conta (Digital Equipment Corporation)
INTERNET-DRAFT                        S. Deering (Xerox PARC)
                                            February 1995                 |

            ICMP
               Internet Control Message Protocol (ICMPv6)
               for the Internet Protocol Version 6 (IPv6)
                     draft-ietf-ipngwg-icmp-01.txt                        |
                             Specification

                    <draft-ietf-ipngwg-icmp-02.txt>

Status of this Memo

   This document is an Internet  Draft.   Internet  Drafts  are  working
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   Distribution of this memo is unlimited.

Abstract

   This document specifies a set of Internet  Control  Message  Protocol
   (ICMP)  messages  for  use  with  version  6 of the Internet Protocol
   (IPv6).  The  Internet  Group  Management  Protocol  (IGMP)  messages
   specified  in  RFC-1112 have been merged into ICMP, for IPv6, and are
   included in this document.

Table of Contents

1. Introduction........................................3                  |
2. ICMP ICMPv6 (ICMP for IPv6.......................................3                  | 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.....................8
3. ICMP ICMPv6 Error Messages.................................7                  | Messages..............................10
      3.1 Destination Unreachable Message..............7                  | Message.............10
      3.2 Packet Too Big Message.......................8                  | Message......................12
      3.3 Time Exceeded Message........................9                  | Message.......................13
      3.4 Parameter Problem Message...................11                  | Message...................14
4. ICMP ICMPv6 Informational Messages........................12                  | Messages......................16
      4.1 Echo Request Message........................12                  | Message........................16
      4.2 Echo Reply Message..........................13                  | Message..........................17
      4.3 Group Membership Messages...................15                  | Messages...................18
5. References.........................................16                  | References.........................................19
6. Acknowledgements...................................17                  | Acknowledgements...................................20
7. Security Considerations............................17                  |
8. Considerations............................20
Authors' Addresses.................................17                  | Addresses....................................21

1.   Introduction                                                         |

   The Internet Protocol, version 6 (IPv6) is a new version of IP.  IPv6
   uses the Internet Control Message Protocol (ICMP) as defined for IPv4
   [RFC-792], with a number of changes.  The Internet  Group  |  Membership                                                             |
   Protocol  (IGMP)  specified for IPv4 [RFC-1112] has also been revised
   and has been absorbed into ICMP for IPv6. The resulting  protocol  is
   called ICMPv6, and has an IPv6 Next Header value 58.

   This document describes the format of a set of control messages  used
   in ICMP
   for IPv6.  ICMPv6.   It  does  not  describe  the procedures for using these  |
   messages to achieve functions like Path MTU  discovery  or  multicast  |
   group  membership maintenance; such procedures are described in other  |
   documents (e.g., [RFC-1112, RFC-1191]).   Other  documents  may  also  |
   introduce additional ICMP ICMPv6 message types, such as Neighbor Discovery  |
   messages  [IPv6-DISC],  subject  to  the  general  rules  for ICMP  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.

2.   ICMP   ICMPv6 (ICMP for IPv6

   IPv6 ICMP IPv6)

   ICMPv6 is  used  by  IPv6  nodes  to  report  errors  encountered  in
   processing  packets,  and  to perform other internet-layer functions,
   such  as  diagnostics (ICMP  (ICMPv6  "ping")  and   multicast                        |   membership
   reporting.  IPv6 ICMP   ICMPv6  is  an  integral  part of IPv6 and MUST be fully
   implemented by every IPv6 node.

   ICMP

2.1  Message General Format

   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 IPv6 ICMP  |  ICMPv6
   messages:                                                              |
        ICMP

        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)             |
        ICMP

        ICMPv6 informational messages:                                      |

          128  Echo Request                 (see section 4.1)             |
          129  Echo Reply                   (see section 4.2)             |
          130  Group Membership Qeury Query       (see section 4.3)             |
          131  Group Membership Report      (see section 4.3)             |
          132  Group Membership Termination (see section 4.3)             |

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

   The IPv6 ICMP 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 is the 16-bit one's complement of the  one's  complement
   sum of the IPv6 Source Address, the IPv6 Destination Address (the final destination, if a Routing Header is  being  used),  | the IPv6
   Payload Length, the Next Header type that identifies IPv6  |
   ICMP(<TBD>), ICMPv6 (value  =
   58),  and  the entire  ICMP ICMPv6 message starting with the  ICMP  | ICMPv6 message
   type. For                                                      |
   computing the checksum, the checksum field is set to zero.
   (NOTE: the inclusion of the IPv6 header fields in the  ICMP  checksum  |
   is a change from IPv4; see [IPv6] for the rationale for this change.)  |
   Implementation Notes:                                                  |

2.2  Message Source Address Determination

   A node that sends an ICMP 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  address, addresses, the Source Address of the reply must be  |
       that same address.                                                  |

  (b)  If the message is a response to a message sent to a multicast  |  or
       anycast  group  in which the node is a member, the Source Address
       of the  | reply must be a unicast address belonging to the interface
       on  | which the multicast packet was received.                            |

  (c)  If the message is a response to a message sent to an address that
       does  not  belong  to the node, the Source Address should be that
       unicast address belonging to the node that will be  most  helpful
       in  diagnosing  the  error.  For  example,  if  the  message is a
       response to a  packet  forwarding  action  that  cannot  complete
       successfully,  the  Source  Address  should  be a unicast address
       belonging to the interface on which the packet forwarding failed.

  (d)  Otherwise, the node's routing table must be examined to determine  |
       which  interface  will  be  used  to  transmit the message to its  |
       destination, and a unicast address belonging  to  that  interface  |
       must be used as the Source Address of the message.                  |

2.3  Message Checksum Calculation

   An illustration of the IPv6 and ICMPv6 header fields fetched  into  a
   pseudo-header for calculating the ICMPv6 checksum is:

      From the IPv6 Header:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                         Source Address                        +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                      Destination Address                      +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     zero      | Next Hdr = 58 |         Payload Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      From the ICMPv6 Header and 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 = zero         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                         Message Body                          +
      |                                                               |

   An illustration of the IPv6, IPv6 Hop-by-Hop Jumbo Payload Option and
   ICMPv6  headers  fields  fetched into a pseudo-header for calculating
   the ICMPv6 checksum in case of a Jumbo Payload (IPv6  packet  payload
   longer than 65535 octets) is:

      From the IPv6 Header:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                         Source Address                        +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                      Destination Address                      +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     zero      | Next Hdr = 58 |             zero              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      From the IPv6 Hop-by-Hop Jumbo Payload Option Extension Header:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Payload Length                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      From the ICMPv6 Header and 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 = zero         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                         Message Body                          +
      |                                                               |
   The ICMPv6 checksum calculation rules are:

  (a)  If the packet contains a Routing header, the Destination  Address
       used  in  the pseudo-header is that of the final destination.  At
       the originating system, that address will be in the last  element
       of  the Routing header; at the recipient(s), that address will be
       in the Destination Address field of the IPv6 header.

  (b)  The Next Header value in the pseudo-header identifies the  ICMPv6
       protocol (e.g., 58). It will differ from the Next Header value in
       the IPv6 header if there are additional headers between the  IPv6
       header and the ICMPv6 header.

  (c)  The Payload Length used in the pseudo-header is the length of the
       ICMPv6  message,  including  the  ICMPv6 header.  It will be less
       than the Payload Length in the IPv6 header or in  the  IPv6  Hop-
       by-Hop  Jumbo  Payload  Option  header  if  there  are additional
       headers  between  the  IPv6  header  and   the   ICMPv6   header,
       respectively  the  IPv6  Hop-by-Hop  Jumbo  Option Header and the
       ICMPv6 Header.

  (d)  For computing the checksum, the checksum field is set to zero.

       (NOTE: the inclusion of the IPv6  header  fields  in  the  ICMPv6
       checksum  is a change from IPv4; see [IPv6] for the rationale for
       this change.)

2.4  Message Processing Rules

   Implementations MUST observe  the  following  rules  when  processing IPv6
   ICMP
   ICMPv6 messages (from [RFC-1122]):

  (a)  If an IPv6 ICMP ICMPv6 error message of unknown type is received,  it  MUST
       be passed to the upper layer.

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

  (b)

  (c)  Every IPv6 ICMP ICMPv6 error message (the first  four  messages  in  the
       above  list) (type < 128) includes as much  of  the
       IPv6  offending  (invoking)  packet  (the  packet that causes the
       error) as will fit without making the error message packet exceed
       576 octets.

  (c)

  (d)  In those cases where the Internet layer is  required  to  pass  a  |
       IPv6  ICMP
       ICMPv6  error  message to the transport layer, the IPv6  | Transport                                                          |
       Protocol is extracted from the original header (contained in       |  the
       body  of  the IPv6 ICMP  ICMPv6  error  message)  and  used  to  select the
       appropriate transport protocol entity to handle the error.

  (d)

  (e)  An IPv6 ICMP ICMPv6  error  message  MUST  NOT  be  sent  as  a  result  of
       receiving:

          (d.1.)an IPv6 ICMP

       (e.1)  an ICMPv6 error message, or                            |
          (d.2.)a

       (e.2)  a  packet  destined  to  an  IPv6  multicast  address  (an  |
              exception  to  this  rule  is the Packet Too Big Message -
              Section 3.2 - to allow Path MTU discovery to work for IPv6
              multicast), or

          (d.3.)                                                          |

       (e.3)  a packet sent as a link-layer  multicast,  (the  exception  |
              from d.2. e.2. applies to this case too) too), or                    |

          (d.4.)

       (e.4)  a packet sent as a link-layer  broadcast,  (the  exception  |
              from d.2. e.2., applies to this case too) too), or                    |

          (d.5.)a

       (e.5)  a packet whose source address does not uniquely identify a
              single  node  -- e.g., the IPv6 Unspecified Address, or an
              IPv6 multicast address, or an IPv6 anycast address.

       (e)

  (f)  Finally, to each sender of an erroneous data packet, an IPv6 node
       MUST  limit  the  rate of ICMP ICMPv6 error messages sent, in order to  |
       limit the bandwidth and forwarding costs incurred  by  the the  |  error
       messages  when  a generator of erroneous packets does  | not respond
       to those error messages by ceasing its  | transmissions.  There  are
       a variety of ways of implementing  | the rate-limiting function, for
       example:                      |

          (e.1.)Timer-based

       (f.1)  Timer-based  -  for  example,   limiting   the   rate   of  |
              transmission  of  error  messages to a given source, or to  |
              any source, to at most once every T milliseconds.          |

          (e.2.)Bandwidth-based

       (f.2)  Bandwidth-based - for example, limiting the rate at  |  which
              error  messages  are  sent  from a particular interface  | to
              some fraction F of the attached link's bandwidth.       |

       The limit parameters (e.g., T or F in the above examples)  | MUST be
       configurable  for  the  node,  with  a conservative  | default value
       (e.g., T = 1 second, NOT 0 seconds, or F =  2  |  percent,  NOT  100
       percent).                                    |

   The following sections describe the message  formats  for  the  above
   IPv6 ICMP
   ICMPv6 messages.

3.   ICMP   ICMPv6 Error Messages

3.1.

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 will fit without ICMP ICMPv6 packet           +
      |
      |                       exceeding 576 octets                    |
      +                                                               +
      |                                                               |                                                               |

   IPv6 Fields:                                                              |

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

IPv6 ICMP

   ICMPv6 Fields:                                                         |

   Type           1                                                       |

   Code           0 - no route to destination                             |
                  1 - communication with destination                      |
                        administratively prohibited                       |
                  2 - not a neighbor
                  3 - address unreachable                                 |
                  4 - port unreachable                                    |

   Unused         This field is unused for all code values.
                  It must be initialized to zero by the sender
                  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.  (If   (An  ICMPv6  message  MUST  NOT be generated if a
   packet is dropped due to congestion, no ICMP  |
   error message is generated.) 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
   (NOTE: this error can occur only  in  |  routers  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 next destination
   address  in  the  Routing  header is not a neighbor of the processing
   node but the "strict" bit is set for  that  address,  then  the  Code
   field is set to 2.

   If there is any other  reason  for  the  failure  to  deliver,  e.g.,  |
   inability   to   resolve   the   IPv6   destination  address  into  a  |
   corresponding link address, or a link-specific problem of some  sort,  |
   then the Code field is set to 3.                                       |

   A destination node SHOULD send 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.                                |

   Upper layer notification                                                  |

   A node receiving the ICMP  ICMPv6  Destination  Unreachable  message  MUST
   notify  | the upper layer.                                                       |

3.2.                                                                      |

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 will fit without ICMP ICMPv6 packet           +
      |
      |                       exceeding 576 octets                    |
      +                                                               +
      |                                                               |                                                               |

   IPv6 Fields:                                                              |

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

IPv6 ICMP

   ICMPv6 Fields:                                                         |

   Type           2                                                       |

   Code           0

   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 [RFC-1191].  |

   Sending a Packet Too Big Message makes an exception  to  one  of  the
   rules  of  |  when to send an ICMP 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  | link-
   layer broadcast address.                                                     |

   Upper layer notification

   An incoming Packet Too Big message MUST be passed to the  transport upper layer.

3.3.

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 will fit without ICMP ICMPv6 packet           +
      |
      |                       exceeding 576 octets                    |
      +                                                               +
      |                                                               |                                                               |

   IPv6 Fields:                                                              |

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

IPv6 ICMP

   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 sender            |
                  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 discards MUST discard the packet
   and
   sends send an IPv6 ICMP ICMPv6 Time Exceeded message with Code 0 to the source source of
   the  packet.   This  indicates  either a routing loop or too small an
   initial Hop Limit value.

   The router sending an ICMPv6 Time Exceeded message with Code 0 SHOULD
   consider  the  receiving  interface of the packet as the interface on
   which  the  packet  forwarding  failed  in  following  rule  (d)  for
   selecting the Source Address of the packet.  This indicates either a  routing  |
   loop or too small an initial                                           |
   Hop Limit value. message.

   IPv6 systems are expected to avoid fragmentation by implementing Path
   MTU  discovery.   However,  IPv6  defines an end-to-end fragmentation
   function  for  backwards  compatibility  with  existing  higher-layer  |
   protocols.    All   IPv6  implementations  are  required  to  support  |
   reassembly                                                             | of IPv6 fragments.  There MUST be  a  reassembly  timeout.
   The  reassembly  timeout  SHOULD be a fixed value.  It is recommended
   that this value lie between 60  and  120  seconds.   If  the  timeout
   expires,  the  partially-reassembled packet MUST be discarded. If the
   fragment        | with offset zero was received, received during  the  reassembly  time,
   the destination host SHOULD also send an IPv6 ICMP ICMPv6 Time Exceeded message
   with Code 1 to the source of the  | fragment.                                                              |

   Upper layer notification

   An incoming Time Exceeded message MUST be passed to the  transport upper layer.

3.4.                                                                      |

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 will fit without ICMP ICMPv6 packet           +
      |
      |                       exceeding 576 octets                    |
      +                                                               +
      |                                                               |                                                               |
   IPv6 Fields:                                                              |

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

IPv6 ICMP

   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 ICMP       | ICMPv6
                  packet if the field in error is beyond what can fit     |
                  in the 576-byte limit of an ICMP 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 send  an  |
   ICMP
   ICMPv6  Parameter  Problem message to the packet's source, indicating
   the  | type and location of the problem.                                      |

   The pointer identifies the octet of the  original  datagram's  header
   where  the  error  was  detected. For example, an ICMPv6 message with
   Type field = 4, Code field = 1, and Pointer field = 48 would indicate
   that  the  IPv6  extension  header  following  the IPv6 header of the
   original datagram is holds an unrecognized Next Header field value.

   Upper layer notification

   A node receiving this ICMP ICMPv6 message MUST notify the upper layer.

4.                                                                        |
     ICMP   ICMPv6 Informational Messages                                          |

4.1.

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.                                 |
                                                                          |
IPv6 ICMP

   ICMPv6 Fields:

   Type           128                                                     |

   Code           0

   Identifier     If code = 0, an identifier to aid in matching           |
                  Echo Replies to this Echo Request.  May be zero.        |

   Sequence Number
                  If code = 0, a sequence number to aid in matching       |
   Number
                  Echo Replies to this Echo Request.  May be zero.        |

   Data           If code = 0, zero or more octets of arbitrary data.     |

   Description

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

   Upper layer notification                                                  |

   A node receiving this ICMP ICMPv6 message MAY notify the upper layer.         |

4.2.                                                                      |

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.                                    |

IPv6 ICMP

   ICMPv6 Fields:                                                         |

   Type           129                                                     |

   Code           0

   Identifier     If code = 0, the identifier from the invoking           |
                  Echo Request message.                                   |

   Sequence       If code = 0, the sequence number from the invoking      |
   Number         Echo Request message.                                   |

   Data           If code = 0, the data from the invoking                 |
                  Echo Request message                                    |

   Description

   Every node MUST implement an ICMP  ICMPv6  Echo  responder  function  that         |
   receives  Echo Requests and sends corresponding Echo Replies.  A node
   SHOULD also implement an application-layer interface for sending 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 address.  The source address of the reply
   MUST be a unicast address belonging to the  interface  on  which  the
   multicast Echo Request message was received.                       |

   The data received in the ICMP ICMPv6 Echo Request message MUST be returned  |
   entirely  and unmodified in the ICMP ICMPv6 Echo Reply message, unless the  |
   Echo Reply would exceed  the  MTU  of  the  path  back  to  the  Echo  |
   requester, in which case the data is truncated to fit that path MTU.   |

   Upper layer notification

   Echo Reply messages MUST be passed  to  the ICMP  ICMPv6  user  interface,
   unless the corresponding Echo Request originated in the IP layer.

4.3.                                                                      |

4.3  Group Membership Messages                                            |

   The ICMP ICMPv6 Group Membership Messages have the following 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             |   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |
      |     Maximum Response Delay    |          Unused               |   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                          Multicast                            |
      +                                                               +
      |                           Address                             |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IPv6 Fields:                                                              |

   Destination Address                                                    |
                  In a Group Membership Query message, the multicast      |
                  address of the group being queried, or the Link-Local   |
                  All-Nodes multicast address.                            |

                  In a Group Membership Report or a Group Membership      |
                  Termination message, the multicast address of the       |
                  group being reported or terminated.                     |

   Hop Limit      1                                                       |

IPv6 ICMP

   ICMPv6 Fields:

   Type           130 - Group Membership Query                            |
                  131 - Group Membership Report                           |
                  132 - Group Membership Termination                      |

   Code           0                                                       |

   Maximum Response Delay                                                 |
                  In Query messages, the maximum time that responding     |
                  Report messages may be delayed, in milliseconds.        |

                  In Report and Termination messages, this field is       |
                  is initialized to zero by the sender and ignored by
                  receivers.

   Unused         Initialized to zero by the sender; ignored by receivers.

   Multicast Address
                  The address if of the multicast group about which the
                  message is being sent.  In Query messages, the Multicast
                  Address field may be zero, implying a query for all
                  groups.

   Description

   The ICMP ICMPv6 Group Membership messages are used to  convey  information  |
   about                                                                  |  multicast  group  membership  from  nodes to their neighboring
   routers.  The details of their usage is given in [RFC-1112].

5.   References                                                           |

     [IPv6]R.

     [IPv6]S.  Deering,  R.  Hinden,  "Internet Protocol  Protocol,  Version 6 Specification",        |
          February 1995                                                   |   6,
     [IPv6-ADDR]
          R.  Hinden,  "IP  Next  Generation  Addressing  Architecture",  |
          February 1995                                                   |
     [IPv6-DISC]
          W. A. Simpson, "IPv6 Neighbor Discovery", February 1995         |
     [RFC-792]                                                            |
          J. Postel, "Internet Control Message Protocol", RFC 792.        |

     [RFC-1112]                                                           |
          S. Deering, "Host Extensions for IP Multicasting", RFC 1112.    |

     [RFC-1122]                                                           |
          R. Braden, "Requirements for Internet  Hosts  -  Communication  |
          Layers", RFC 1122.                                              |

     [RFC-1191]                                                           |
          J. Mogul and S. Deering, "Path MTU Discovery", RFC 1191.        |

6.   Acknowledgements                                                     |

   The document is derived from previous ICMP drafts  of  the "ICMP and IGMP  for  SIPP"  document
   published  as  a  draft by Ramesh Govindan  SIPP  and Steve Deering in March
   1994.
   IPng working group.

   The IPng working group and particularly Robert Elz, Jim  Bound,  and  Bill  |
   Simpson
   Simpson,  Thomas  Narten,  Charlie Lynn, Bill Fink, and Scott Bradner
   (in chronological order) provided extensive  review  information  and
   feedback.            |

7.   Security Considerations                                              |

   Security considerations are not discussed in this memo.

Authors' Addresses:

   Alex Conta                            Stephen Deering
   Digital Equipment Corporation         Xerox Palo Alto Research Center
   110 Spitbrook Rd                      3333 Coyote Hill Road
   Nashua, NH 03062                      Palo Alto, CA 94304
   +1-603-881-0744                       +1-415-812-4839

   email: conta@zk3.dec.com              email: deering@parc.xerox.com