ICMP Extension Header Length Field
draft-ietf-intarea-icmp-exten-hdr-len-01

INTAREA Group                                                  R. Bonica
Internet-Draft                                          Juniper Networks
Updates: RFC 4884 (if approved)                                    X. He
Intended status: Standards Track                           China Telecom
Expires: 20 December 2025                                         X. Min
                                                         ZTE Corporation
                                                              T. Mizrahi
                                                                  Huawei
                                                            18 June 2025

                   ICMP Extension Header Length Field
                draft-ietf-intarea-icmp-exten-hdr-len-01

Abstract

   The ICMP Extension Structure does not have a length field.
   Therefore, unless the length of the Extension Structure can be
   inferred from other data in the ICMP message, the Extension Structure
   must be the last item in the ICMP message.

   This document defines a length field for the ICMP Extension
   Structure.  When length information is provided, receivers can use it
   to parse ICMP messages.  Specifically, receivers can use length
   information to determine the offset at which the item after the ICMP
   Extension Structure begins.

Status of This Memo

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   This Internet-Draft will expire on 20 December 2025.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to 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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   2
   3.  The ICMP Extension Structure  . . . . . . . . . . . . . . . .   3
   4.  Backwards Compatibility . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The ICMP Extension Structure [RFC4884] does not have a length field.
   Therefore, unless the length of the Extension Structure can be
   inferred from other data in the ICMP message, the Extension Structure
   must be the last item in the ICMP message.

   This document defines a length field for the ICMP Extension
   Structure.  When length information is provided, receivers can use it
   to parse ICMP messages.  Specifically, receivers can use length
   information to determine the offset at which the item after the ICMP
   Extension Structure begins.

   New implementations SHOULD always include the length field, even
   though it is not needed when the ICMP message ends with an ICMP
   Extension Structure.

2.  Conventions and Definitions

   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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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3.  The ICMP Extension Structure

   Figure 1 depicts the ICMP 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Version|  Rsvd |     Length    |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: ICMP Extension Header

   Version: 4 bits

   *  Defined in [RFC4884]

   Reserved (Rsvd): 4 bits

   *  Defined in [RFC4884]

   Length: 8 bits

   *  This field represents the length of the ICMP Extension Structure,
      including all options and optional padding, but excluding the ICMP
      Extension Header.  The length is measured in 4-byte words.  Legacy
      implementations set this field to 0.

   Checksum: 16 bits

   *  Defined in [RFC4884]

   The ICMP Extension Structure MUST be zero-padded so that it ends on a
   4-byte boundary.

4.  Backwards Compatibility

   Legacy implementations set the length field to 0.  When the length
   field is set to 0, it conveys no information and cannot be used to
   parse the ICMP packet.

   In these cases, one of the following statements MUST be true:

   *  The ICMP Extension Structure is the final item in the ICMP packet.

   *  The length of the ICMP Extension Structure can be inferred from
      other fields in the packet.

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   Legacy implementation that do not recognize the ICMP Extension Header
   length field MUST NOT process ICMP messages in which the ICMP
   Extension structure may be followed by something else.  This is
   because they will not be able to parse the message correctly.

5.  IANA Considerations

   This document requires no IANA actions.

6.  Security Considerations

   This document introduces no security vulnerabilities.  However, it
   does inherit security considerations from [RFC4884].

7.  Acknowledgements

   Thanks to Tom Herbert and Michael Welzl for their review and helpful
   suggestion.

8.  Normative References

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

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

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

Authors' Addresses

   Ron Bonica
   Juniper Networks
   United States of America
   Email: rbonica@juniper.net

   Xiaoming He
   China Telecom
   China
   Email: hexm4@chinatelecom.cn

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   Xiao Min
   ZTE Corporation
   China
   Email: xiao.min2@zte.com.cn

   Tal Mizrahi
   Huawei
   Israel
   Email: tal.mizrahi.phd@gmail.com

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