View source for RFC8883



Internet Engineering Task Force (IETF)                        T. Herbert
Request for Comments: 8883                                         Intel
Category: Standards Track                                 September 2020
ISSN: 2070-1721

  ICMPv6 Errors for Discarding Packets Due to Processing Limits

'''Abstract'''

Network nodes may discard packets if they are unable to process
protocol headers of packets due to processing constraints or limits.
When such packets are dropped, the sender receives no indication, so
it cannot take action to address the cause of discarded packets.
This specification defines several new ICMPv6 errors that can be sent
by a node that discards packets because it is unable to process the
protocol headers.  A node that receives such an ICMPv6 error may use
the information to diagnose packet loss and may modify what it sends
in future packets to avoid subsequent packet discards.

'''Status of This Memo'''

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF).  It represents the consensus of the IETF community.  It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG).  Further information on
Internet Standards is available in Section 2 of [[RFC7841|RFC 7841]].

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8883.

'''Copyright Notice'''

Copyright (c) 2020 IETF Trust and the persons identified as the
document authors.  All rights reserved.

This document is subject to [[BCP78|BCP 78]] and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document.  Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.  Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

1.  Introduction
  1.1.  Extension Header Limits
  1.2.  Aggregate Header Limits
  1.3.  Nonconformant Packet Discard
  1.4.  Terminology
2.  ICMPv6 Errors for Extension Header Limits
  2.1.  Format
  2.2.  Unrecognized Next Header Type Encountered by Intermediate
        Node (Code 5)
  2.3.  Extension Header Too Big (Code 6)
  2.4.  Extension Header Chain Too Long (Code 7)
  2.5.  Too Many Extension Headers (Code 8)
  2.6.  Too Many Options in Extension Header (Code 9)
  2.7.  Option Too Big (Code 10)
3.  ICMPv6 Error for Aggregate Header Limits
  3.1.  Format
  3.2.  Usage
4.  Operation
  4.1.  Priority of Reporting
  4.2.  Host Response
5.  Applicability and Use Cases
  5.1.  Reliability of ICMP
  5.2.  Processing Limits
    5.2.1.  Long Headers and Header Chains
    5.2.2.  At End Hosts
    5.2.3.  At Intermediate Nodes
6.  Security Considerations
7.  IANA Considerations
  7.1.  Parameter Problem Codes
  7.2.  Destination Unreachable Codes
  7.3.  ICMP Extension Object Classes and Class Sub-types
8.  References
  8.1.  Normative References
  8.2.  Informative References
Acknowledgments
Author's Address

== Introduction ==

This document specifies several new ICMPv6 errors that can be sent
when a node discards a packet due to it being unable to process the
necessary protocol headers because of processing constraints or
limits.  New ICMPv6 code points are defined to supplement those
defined in [[RFC4443]].  Six of the errors are specific to the
processing of extension headers; another error is used when the
aggregate protocol headers in a packet exceed the processing limits
of a node.

=== Extension Header Limits ===

In IPv6, optional internet-layer information is carried in one or
more IPv6 extension headers [[RFC8200]].  Extension headers are placed
between the IPv6 header and the upper-layer header in a packet.  The
term "header chain" refers collectively to the IPv6 header, extension
headers, and upper-layer headers occurring in a packet.  Individual
extension headers may have a maximum length of 2048 octets and must
fit into a single packet.  Destination Options and Hop-by-Hop Options
contain a list of options in type-length-value (TLV) format.  Each
option includes a length of the data field in octets: the minimum
size of an option (non-pad type) is two octets, and the maximum size
is 257 octets.  The number of options in an extension header is only
limited by the length of the extension header and the Path MTU from
the source to the destination.  Options may be skipped over by a
receiver if they are unknown and the Option Type indicates to skip
(first two high order bits are 00).

Per [[RFC8200]], except for Hop-by-Hop Options, extension headers are
not examined or processed by intermediate nodes.  However, in
deployed networks, many intermediate nodes do examine extension
headers for various purposes.  For instance, a node may examine all
extension headers to locate the transport header of a packet in order
to implement transport-layer filtering or to track connections to
implement a stateful firewall.

Destination hosts are expected to process all extension headers and
options in Hop-by-Hop and Destination Options.

Due to the variable lengths, high maximum lengths, or potential for a
denial-of-service attack of extension headers, many devices impose
operational limits on extension headers in packets they process.
[[RFC7045]] discusses the requirements of intermediate nodes that
discard packets because of unrecognized extension headers.  [[RFC8504]]
discusses limits that may be applied to the number of options in Hop-
by-Hop Options or Destination Options extension headers.  Both
intermediate nodes and end hosts may apply limits to extension header
processing.  When a limit is exceeded, the typical behavior is to
silently discard the packet.

This specification defines six Parameter Problem codes that may be
sent by a node that discards a packet due to the processing limits of
extension headers being exceeded.  The information in these ICMPv6
errors may be used for diagnostics to determine why packets are being
dropped.  Additionally, a source node that receives these ICMPv6
errors may be able to modify its use of extension headers in
subsequent packets sent to the destination in order to avoid further
occurrences of packets being discarded.

=== Aggregate Header Limits ===

Some hardware devices implement a parsing buffer of a fixed size to
process packets.  The parsing buffer is expected to contain all the
headers (often up to a transport-layer header for filtering) that a
device needs to examine.  If the aggregate length of headers in a
packet exceeds the size of the parsing buffer, a device will either
discard the packet or defer processing to a software slow path.  In
any case, no indication of a problem is sent back to the sender.

This document defines one code for ICMPv6 Destination Unreachable
that is sent by a node that is unable to process the headers of a
packet due to the aggregate size of the packet headers exceeding a
processing limit.  The information in this ICMPv6 error may be used
for diagnostics to determine why packets are being dropped.
Additionally, a source node that receives this ICMPv6 error may be
able to modify the headers used in subsequent packets to try to avoid
further occurrences of packets being discarded.

=== Nonconformant Packet Discard ===

The ICMP errors defined in this specification may be applicable to
scenarios in which a node is dropping packets outside the auspices of
any standard specification.  For instance, an intermediate node might
send a "Headers too long" code in a case where it drops a packet
because it is unable to parse deeply enough to extract the transport-
layer information needed for packet filtering.  Such behavior might
be considered nonconformant (with respect to [[RFC8200]], for
instance).

This specification does not advocate behaviors that might be
considered nonconformant.  However, packet discard does occur in real
deployments, and the intent of this specification is to provide
visibility as to why packets are being discarded.  In the spirit that
providing some reason is better than a silent drop, the sending of
ICMP errors is RECOMMENDED even in cases where a node might be
discarding packets per a nonconformant behavior.

=== Terminology ===

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[[BCP14|BCP 14]] [[RFC2119]] [[RFC8174]] when, and only when, they appear in all
capitals, as shown here.

== ICMPv6 Errors for Extension Header Limits ==

Six new codes are defined for the Parameter Problem type.

=== Format ===

The format of the ICMPv6 Parameter Problem message [[RFC4443]] for an
extension header limit exceeded error is:

 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 the invoking packet             |
+               as possible without the ICMPv6 packet           +
|              exceeding the minimum IPv6 MTU [[RFC8200]]         |

IPv6 Header Fields:
   Destination Address:
      Copied from the Source Address field of the invoking packet.

ICMPv6 Fields:
   Type:
      4  (Parameter Problem type)

   Code:
      (pertinent to this specification)

               +----+----------------------------------+
               | 5  | Unrecognized Next Header type    |
               |    | encountered by intermediate node |
               +----+----------------------------------+
               | 6  | Extension header too big         |
               +----+----------------------------------+
               | 7  | Extension header chain too long  |
               +----+----------------------------------+
               | 8  | Too many extension headers       |
               +----+----------------------------------+
               | 9  | Too many options in extension    |
               |    | header                           |
               +----+----------------------------------+
               | 10 | Option too big                   |
               +----+----------------------------------+

                                Table 1

   Pointer:
      Identifies the octet offset within the invoking packet where
      the problem occurred.

      The pointer will point beyond the end of the IPv6 packet if the
      field exceeding the limit is beyond what can fit in the maximum
      size of an ICMPv6 error message.  If the pointer is used as an
      offset to read the data in the invoking packet, then a node
      MUST first validate that the pointer value is less than the
      length of the invoking packet data.

=== Unrecognized Next Header Type Encountered by Intermediate Node ===
   (Code 5)

This code SHOULD be sent by an intermediate node that discards a
packet because it encounters a Next Header type that is unknown in
its examination.  The ICMPv6 Pointer field is set to the offset of
the unrecognized Next Header value within the original packet.

Note that this code is sent by intermediate nodes and SHOULD NOT be
sent by a final destination.  If a final destination node observes an
unrecognized header, then it SHOULD send an ICMP Parameter Problem
message with an ICMP Code value of 1 ("unrecognized Next Header type
encountered") as specified in [[RFC8200]].

=== Extension Header Too Big (Code 6) ===

An ICMPv6 Parameter Problem with code for "Extension header too big"
SHOULD be sent when a node discards a packet because the size of an
extension header exceeds its processing limit.  The ICMPv6 Pointer
field is set to the offset of the first octet in the extension header
that exceeds the limit.

=== Extension Header Chain Too Long (Code 7) ===

An ICMPv6 Parameter Problem with code for "Extension header chain too
long" SHOULD be sent when a node discards a packet with an extension
header chain that exceeds a limit on the total size in octets of the
header chain.  The ICMPv6 Pointer is set to the first octet beyond
the limit.

=== Too Many Extension Headers (Code 8) ===

An ICMPv6 Parameter Problem with code for "Too many extension
headers" SHOULD be sent when a node discards a packet with an
extension header chain that exceeds a limit on the number of
extension headers in the chain.  The ICMPv6 Pointer is set to the
offset of the first octet of the first extension header that is
beyond the limit.

=== Too Many Options in Extension Header (Code 9) ===

An ICMPv6 Parameter Problem with code for "Too many options in
extension header" SHOULD be sent when a node discards a packet with
an extension header that has a number of options that exceeds the
processing limits of the node.  This code is applicable for
Destination Options and Hop-by-Hop Options.  The ICMPv6 Pointer field
is set to the first octet of the first option that exceeds the limit.

=== Option Too Big (Code 10) ===

An ICMPv6 Parameter Problem with code for "Option too big" is sent in
two different cases: when the length of an individual Hop-by-Hop or
Destination Option exceeds a limit, or when the length or number of
consecutive Hop-by-Hop or Destination padding options exceeds a
limit.  In a case where the length of an option exceeds a processing
limit, the ICMPv6 Pointer field is set to the offset of the first
octet of the option that exceeds the limit.  In cases where the
length or number of padding options exceeds a limit, the ICMPv6
Pointer field is set to the offset of the first octet of the padding
option that exceeds the limit.

Possible limits related to padding include:

*  The number of consecutive PAD1 options in Destination Options or
   Hop-by-Hop Options is limited to seven octets [[RFC8504]].

*  The length of PADN options in Destination Options or Hop-by-Hop
   Options is limited seven octets [[RFC8504]].

*  The aggregate length of a set of consecutive PAD1 or PADN options
   in Destination Options or Hop-by-Hop Options is limited to seven
   octets.

== ICMPv6 Error for Aggregate Header Limits ==

One code is defined for the Destination Unreachable type for
aggregate header limits.

This ICMP error may be applied to other headers in a packet than just
the IPv6 header or IPv6 extension headers.  Therefore, a Destination
Unreachable type with a multi-part ICMPv6 message format is used in
lieu of the Parameter Problem type, which only indicates errors
concerning IPv6 headers.

=== Format ===

The error for aggregate header limits employs a multi-part ICMPv6
message format as defined in [[RFC4884]].  The extension object class
"Extended Information" is defined to contain objects for ancillary
information pertaining to an ICMP Destination Unreachable error.
Within this object class, the sub-type "Pointer" is defined, which
contains a Pointer field with similar semantics to the Pointer field
in ICMP Parameter Problem errors.

The format of the ICMPv6 message for an aggregate header limit
exceeded is:

 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             | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I
|    Length     |                  Unused                       | C
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ M
|                                                               | P
~                As much of the invoking packet                 ~
|              as possible without the ICMPv6 packet            |
|             exceeding the minimum IPv6 MTU [[RFC8200]]          |/
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/
|Version|       Reserved        |           Checksum            |\
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ E
|             Length            |   Class-Num   |   C-Type      | X
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ T
|                            Pointer                            | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/

IPv6 Header Fields:
   Destination Address:
      Copied from the Source Address field of the invoking packet.

ICMPv6 Fields:
   Type:
      1 -  Destination Unreachable

   Code: (pertinent to this specification)
      8 -  Headers too long

   Length:
      Length of the padded invoking packet data measured in 64-bit
      words.  The ICMP extension structure immediately follows the
      padded invoking packet data.

   Invoking Packet:
      Contains as much of the invoking packet as possible without the
      ICMPv6 packet exceeding the minimum IPv6 MTU.  The invoking
      packet data MUST be zero padded to the nearest 64-bit boundary
      [[RFC4884]].  If the original invoking packet did not contain 128
      octets, the invoking packet data MUST be zero padded to 128
      octets.

ICMP Extension Fields:
   Version:
      2 -  per [[RFC4884]]

   Reserved:
      0

   Checksum:
      The one's complement checksum of the ICMP extension [[RFC4884]]

   Length:
      8 -  length of the object header and Pointer field

   Class-Num:
      4 -  Extended Information

   C-Type:
      1 -  Pointer

   Pointer:
      Identifies the octet offset within the invoking packet where a
      limit was exceeded.

      The pointer will point beyond the end of the invoking packet
      data if the field exceeding the limit is beyond what can fit in
      the maximum size of an ICMPv6 error message with the ICMP
      extension.  If the pointer is used as an offset to read the
      data in the invoking packet, then a node MUST first validate
      that the pointer value is less than the length of the invoking
      packet data.

=== Usage ===

An ICMPv6 Destination Unreachable error with code for "Headers too
long" SHOULD be sent when a node discards a packet because the
aggregate length of the headers in the packet exceeds the processing
limits of the node.  The Pointer in the extended ICMPv6 structure is
set to the offset of the first octet that exceeds the limit.

This error is sent in response to a node dropping a packet because
the aggregate header chain exceeds the processing limits of a node.
The aggregate header chain may be composed of protocol headers other
than an IPv6 header and IPv6 extension headers.  For instance, in the
case of a node parsing a UDP encapsulation protocol, the
encapsulating UDP header would be considered to be in the aggregate
header chain.

As noted in Section 4.1, the ICMPv6 Destination Unreachable error
with code for "Headers too long" has the lowest precedence of the
ICMP errors discussed in this specification.  If a packet contains an
error corresponding to a Parameter Problem code, then a node SHOULD
send the Parameter Problem error instead of sending the ICMPv6
Destination Unreachable error with code for "Headers too long".

== Operation ==

Nodes that send or receive ICMPv6 errors due to header processing
limits MUST comply with ICMPv6 processing as specified in [[RFC4443]].

=== Priority of Reporting ===

More than one ICMPv6 error may be applicable to report for a packet.
For instance, the number of extension headers in a packet might
exceed a limit, and the aggregate length of protocol headers might
also exceed a limit.  Only one ICMPv6 error SHOULD be sent for a
packet, so a priority is defined to determine which error to report.

The RECOMMENDED reporting priority of ICMPv6 errors for processing
limits is listed from highest to lowest priority:

1.  Existing ICMP errors defined in [[RFC4443]].

2.  "Unrecognized Next Header type encountered by intermediate node"

3.  "Extension header too big"

4.  "Option too big" for length or number of consecutive padding
    options exceeding a limit.

5.  "Option too big" for the length of an option exceeding a limit.

6.  "Too many options in an extension header"

7.  "Extension header chain too long" headers exceeding a limit.

8.  "Too many extension headers"

9.  "Headers too long"

=== Host Response ===

When a source host receives an ICMPv6 error for a processing limit
being exceeded, it SHOULD verify the ICMPv6 error is valid and take
appropriate action as suggested below.

The general validations for ICMP as described in [[RFC4443]] are
applicable.  The packet in the ICMP data SHOULD be validated to match
the upper-layer process or connection that generated the original
packet.  Other validation checks that are specific to the upper
layers may be performed and are out of the scope of this
specification.

The ICMPv6 error SHOULD be logged with sufficient detail for
debugging packet loss.  The details of the error, including the
addresses and the offending extension header or data, should be
retained.  This, for instance, would be useful for debugging when a
node is misconfigured and unexpectedly discarding packets or when a
new extension header is being deployed.

A host MAY modify its usage of protocol headers in subsequent packets
to avoid repeated occurrences of the same error.

For ICMPv6 errors caused by extension header limits being exceeded:

*  An error SHOULD be reported to an application if the application
   enabled extension headers for its traffic.  In response, the
   application may terminate communications if extension headers are
   required, stop using extension headers in packets to the
   destination indicated by the ICMPv6 error, or attempt to modify
   its use of headers or extension headers to avoid further packet
   discards.

*  A host system SHOULD take appropriate action if it is creating
   packets with extension headers on behalf of the application.  If
   the offending extension header is not required for communication,
   the host may either stop sending it or otherwise modify its use in
   subsequent packets sent to the destination indicated in the ICMPv6
   error.

== Applicability and Use Cases ==

=== Reliability of ICMP ===

ICMP is fundamentally an unreliable protocol and, in real deployment,
it may consistently fail over some paths.  As with any other use of
ICMP, it is assumed that the errors defined in this document are only
the best effort to be delivered.  No protocol should be implemented
that relies on reliable delivery of ICMP messages.  If necessary,
alternative or additional mechanisms may be employed to augment the
processes used to deduce the reason that packets are being discarded.
For instance, ICMP error messages may be correlated with information
attained through Packetization Layer Path MTU Discovery (PLPMTUD)
[[RFC4821]] or Happy Eyeballs for IPv6 [[RFC8305]].  Details of the
interaction with alternative mechanisms are out of scope of this
specification.

=== Processing Limits ===

This section discusses the trends and motivations of processing
limits that warrant ICMP errors.

==== Long Headers and Header Chains ====

The trend towards longer and more complex headers and header chains
needing to be processed by end nodes, as well as intermediate nodes,
is driven by:

*  Increasing prevalence of deep packet inspection in middleboxes.
   In particular, many intermediate nodes now parse network-layer
   encapsulation protocols or transport-layer protocols.

*  Deployment of routing headers.  For instance, [[RFC8754]] defines an
   extension header format that includes a list of IPv6 addresses
   which may consume a considerable number of bytes.

*  Development of in situ OAM headers that allow a rich set of
   measurements to be gathered in the data path at the cost of
   additional header overhead, which may be significant [OAM-IPV6].

*  Other emerging use cases of Hop-by-Hop and Destination Options.

==== At End Hosts ====

End hosts may implement limits on processing extension headers as
described in [[RFC8504]].  Host implementations are usually software
stacks that typically don't have inherent processing limitations.
Limits imposed by a software stack are more likely to be for denial-
of-service mitigation or performance.

==== At Intermediate Nodes ====

Hardware devices that process packet headers may have limits as to
how many headers or bytes of headers they can process.  For instance,
a middlebox hardware implementation might have a parsing buffer that
contains some number of bytes of packet headers to process.  Parsing
buffers typically have a fixed size such as 64, 128, or 256 bytes.
In addition, hardware implementations (and some software
implementations) often don't have loop constructs.  Processing of a
TLV list might be implemented as an unrolled loop so that the number
of TLVs that can be processed is limited.

== Security Considerations ==

The security considerations for ICMPv6 described in [[RFC4443]] are
applicable.  The ICMP errors described in this document MAY be
filtered by firewalls in accordance with [[RFC4890]].

In some circumstances, the sending of ICMP errors might conceptually
be exploited as a means to covertly deduce the processing
capabilities of nodes.  Accordingly, an implementation SHOULD allow a
configurable policy to withhold sending of the ICMP errors described
in this specification in environments where the security of ICMP
errors is a concern.

== IANA Considerations ==

=== Parameter Problem Codes ===

IANA has assigned the following codes in the "Type 4 - Parameter
Problem" registry within the ICMPv6 Parameters registry [IANA-ICMP]:

             +======+==================================+
             | Code | Name                             |
             +======+==================================+
             | 5    | Unrecognized Next Header type    |
             |      | encountered by intermediate node |
             +------+----------------------------------+
             | 6    | Extension header too big         |
             +------+----------------------------------+
             | 7    | Extension header chain too long  |
             +------+----------------------------------+
             | 8    | Too many extension headers       |
             +------+----------------------------------+
             | 9    | Too many options in extension    |
             |      | header                           |
             +------+----------------------------------+
             | 10   | Option too big                   |
             +------+----------------------------------+

                               Table 2

=== Destination Unreachable Codes ===

IANA has assigned the following code in the "Type 1 - Destination
Unreachable" registry within the ICMPv6 Parameters registry
[IANA-ICMP]:

                     +======+==================+
                     | Code | Name             |
                     +======+==================+
                     | 8    | Headers too long |
                     +------+------------------+

                               Table 3

=== ICMP Extension Object Classes and Class Sub-types ===

IANA has assigned the following Class value in the "ICMP Extension
Object Classes and Class Sub-types" registry within the ICMP
Parameters registry [IANA-ICMPEXT]:

               +=============+======================+
               | Class Value | Class Name           |
               +=============+======================+
               | 4           | Extended Information |
               +-------------+----------------------+

                              Table 4

IANA has created a sub-type registry for the "Extended Information"
ICMP extension object class.  The registration procedure for this
registry is "Standards Action".  The sub-type value of 0 is reserved;
values greater than zero may be assigned.

IANA has assigned the following sub-type within the "Sub-types -
Class 4 - Extended Information" registry within the ICMP Parameters
registry:

                       +=======+=============+
                       | Value | Description |
                       +=======+=============+
                       | 1     | Pointer     |
                       +-------+-------------+

                               Table 5

== References ==

=== Normative References ===

[IANA-ICMP]
           IANA, "Internet Control Message Protocol version 6
           (ICMPv6) Parameters",
           <https://www.iana.org/assignments/icmpv6-parameters/>.

[IANA-ICMPEXT]
           IANA, "Internet Control Message Protocol (ICMP)
           Parameters",
           <https://www.iana.org/assignments/icmp-parameters/>.

[[RFC2119]]  Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", [[BCP14|BCP 14]], [[RFC2119|RFC 2119]],
           DOI 10.17487/RFC2119, March 1997,
           <https://www.rfc-editor.org/info/rfc2119>.

[[RFC4443]]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
           Control Message Protocol (ICMPv6) for the Internet
           Protocol Version 6 (IPv6) Specification", [[STD89|STD 89]],
           [[RFC4443|RFC 4443]], DOI 10.17487/RFC4443, March 2006,
           <https://www.rfc-editor.org/info/rfc4443>.

[[RFC4884]]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
           "Extended ICMP to Support Multi-Part Messages", [[RFC4884|RFC 4884]],
           DOI 10.17487/RFC4884, April 2007,
           <https://www.rfc-editor.org/info/rfc4884>.

[[RFC7045]]  Carpenter, B. and S. Jiang, "Transmission and Processing
           of IPv6 Extension Headers", [[RFC7045|RFC 7045]],
           DOI 10.17487/RFC7045, December 2013,
           <https://www.rfc-editor.org/info/rfc7045>.

[[RFC8174]]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
           2119 Key Words", [[BCP14|BCP 14]], [[RFC8174|RFC 8174]], DOI 10.17487/RFC8174,
           May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[[RFC8200]]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
           (IPv6) Specification", [[STD86|STD 86]], [[RFC8200|RFC 8200]],
           DOI 10.17487/RFC8200, July 2017,
           <https://www.rfc-editor.org/info/rfc8200>.

=== Informative References ===

[OAM-IPV6] Bhandari, S., Brockners, F., Pignataro, C., Gredler, H.,
           Leddy, J., Youell, S., Mizrahi, T., Kfir, A., Gafni, B.,
           Lapukhov, P., Spiegel, M., Krishnan, S., Asati, R., and M.
           Smith, "In-situ OAM IPv6 Options", Work in Progress,
           Internet-Draft, draft-ietf-ippm-ioam-ipv6-options-03, 18
           September 2020, <https://tools.ietf.org/html/draft-ietf-
           ippm-ioam-ipv6-options-03>.

[[RFC4821]]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
           Discovery", [[RFC4821|RFC 4821]], DOI 10.17487/RFC4821, March 2007,
           <https://www.rfc-editor.org/info/rfc4821>.

[[RFC4890]]  Davies, E. and J. Mohacsi, "Recommendations for Filtering
           ICMPv6 Messages in Firewalls", [[RFC4890|RFC 4890]],
           DOI 10.17487/RFC4890, May 2007,
           <https://www.rfc-editor.org/info/rfc4890>.

[[RFC8305]]  Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
           Better Connectivity Using Concurrency", [[RFC8305|RFC 8305]],
           DOI 10.17487/RFC8305, December 2017,
           <https://www.rfc-editor.org/info/rfc8305>.

[[RFC8504]]  Chown, T., Loughney, J., and T. Winters, "IPv6 Node
           Requirements", [[BCP220|BCP 220]], [[RFC8504|RFC 8504]], DOI 10.17487/RFC8504,
           January 2019, <https://www.rfc-editor.org/info/rfc8504>.

[[RFC8754]]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
           Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
           (SRH)", [[RFC8754|RFC 8754]], DOI 10.17487/RFC8754, March 2020,
           <https://www.rfc-editor.org/info/rfc8754>.

Acknowledgments

The author would like to thank Ron Bonica, Bob Hinden, Nick Hilliard,
Michael Richardson, Mark Smith, Suresh Krishnan, and Ole Tran for
their comments and suggestions that improved this document.

Author's Address

Tom Herbert
Intel
Santa Clara, CA
United States of America

Email: tom@quantonium.net

[[Category:Standards Track]]