Fixing the C-Flag in EARO
draft-ietf-6lo-updating-rfc-8928-03

6lo                                                           P. Thubert
Internet-Draft                                                          
Updates: 8928 (if approved)                                    A. Rashid
Intended status: Standards Track                     Politecnico di Bari
Expires: 18 November 2025                                    17 May 2025

                       Fixing the C-Flag in EARO
                  draft-ietf-6lo-updating-rfc-8928-03

Abstract

   This document updates RFC 8928, “Address-Protected Neighbor Discovery
   for Low-Power and Lossy Networks” (AP-ND), by updating the bit
   position for the C-flag in the Extended Address Registration Option
   (EARO) and registering it with IANA.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 18 November 2025.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     2.2.  References  . . . . . . . . . . . . . . . . . . . . . . .   2
     2.3.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Updating RFC 8928 . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Bit Position of the C-flag  . . . . . . . . . . . . . . .   6
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The Address-Protected Neighbor Discovery for Low-Power and Lossy
   Networks (AP-ND) [RFC8928] defined the C-flag in EARO.  It is used to
   indicate that the Registration Ownership Verifier (ROVR) field
   contains a Crypto-ID and that the 6LoWPAN Node (6LN) may be
   challenged for ownership of the registered address.  Initially
   [RFC8928] defined the C-flag in the EARO in bit position 3; later
   [RFC9685] defined the P-field in bits 2 and 3 of the EARO flags field
   with proper IANA registration, causing an overlap with Figure 1 of
   [RFC8928] which depicts the location of the C-flag.

   This specification updates [RFC8928] by repositioning the C-flag as
   bit 1 of the EARO flags field, thereby preventing conflicts.

2.  Terminology

2.1.  Requirements Language

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

2.2.  References

   This document uses terms and concepts that are discussed in Neighbor
   Discovery (ND) for IPv6 [RFC4861], [RFC4862] and Subnet ND [RFC6775],
   [RFC8505] [RFC8928], [RFC8929] [RFC9685], and
   [I-D.ietf-6lo-prefix-registration].

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2.3.  Acronyms

   This document uses the following abbreviations:

   *6LN:*  6LoWPAN Node
   *AP-ND:*  Address-Protected Neighbor Discovery
   *ARO:*  Address Registration Option
   *DAD:*  Duplicate Address Detection
   *EARO:*  Extended Address Registration Option
   *LLN:*  Low-Power and Lossy Network
   *LoWPAN:*  Low-Rate Wireless Personal Area Network (IEEE Std.
      802.15.4) [IEEE802154]
   *ND:*  Neighbor Discovery
   *RATInd:*  Registered Address Type Indicator
   *ROVR:*  Registration Ownership Verifier
   *TID:*  Transaction ID

3.  Updating RFC 8928

   [RFC8928] incorrectly refers to the Extended Address Registration
   Option (EARO) as the Enhanced Address Registration Option.  This
   specification corrects this terminology throughout the document.

   In [RFC8928], the C-flag is specified in the EARO flags field at bit
   position 3 (as depicted in the Figure 1 of [RFC8928]); however,
   [RFC8928] fails to register its position with IANA.  Later, [RFC9685]
   defined the P-field in bits 2 and 3 of the EARO flags field and
   obtained proper IANA registration, but this introduced an overlap
   with the representation in [RFC8928].  To resolve the conflict, this
   specification updates [RFC8928] by repositioning the C-flag to bit 1
   of the EARO flags field, thereby avoiding the overlapping
   definitions.

   Figure 1 below replaces Figure 1 in [RFC8928] in the case of an EARO
   used in an NS 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      |     Length    |F|Prefix Length|    Opaque     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |r|C| P | I |R|T|     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...            Registration Ownership Verifier (ROVR)           ...
     |                  (64, 128, 192, or 256 bits)                  |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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      Figure 1: Extended Address Registration Option (EARO) Format for
                             use in NS messages

   Figure 2 below replaces Figure 1 in [RFC8928] in the case of an EARO
   used in an NA message.  The difference between the two formats is in
   the usage of bits 16 to 23.

      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      |     Length    | r |  Status   |    Opaque     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |r|C| P | I |R|T|     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...            Registration Ownership Verifier (ROVR)           ...
     |                  (64, 128, 192, or 256 bits)                  |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 2: Extended Address Registration Option (EARO) Format for
                             use in NA messages

   Option fields of interest for this specification:

   *Type:*  33

   *Length:*  Defined in [RFC8505].

   *F:*  1-bit flag; set to 1 to indicate that the sender expects other
      routers to forward packets to self when the packets are sourced
      within the registered prefix.  For use in NS messages only
      [I-D.ietf-6lo-prefix-registration].

   *Prefix Length*  7-bit integer.  This field contains a prefix length
      expressed in bits if the P-field is set to 3 and the EARO is
      placed in an NS message.  In that case, the value MUST be at least
      16 and at most 120.  The field contains a Status if the EARO is
      placed in an NA message regardless of the setting of the P-flag.
      In all other cases, it is reserved, so it MUST be set to 0 by the
      sender and ignored by the receiver.  For use in NS messages only
      [I-D.ietf-6lo-prefix-registration].

   *Status:*  6-bit unsigned integer.  This field is used in NA(EARO)

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      response messages only to indicate the status of a registration.
      This field is defined in [RFC8505] and resized by [RFC9010].  The
      values for the Status field are available in [IANA.ICMP.ARO.STAT].
      This field MUST be set to 0 in NS(EARO) messages unless the
      registration is for a prefix, in which case the F-flag is set and
      the prefix length is provided.

   *Opaque:*  8-bit field opaque to ND.  It MUST be set to 0 when not
      used.  Defined in [RFC8505].

   *r (reserVed):*  1-bit reserved field.  It MUST be set to zero by the
      sender and MUST be ignored by the receiver.

   *C:*  1-bit flag, moved from its position in Figure 1 of [RFC8928].
      It is set to indicate that the ROVR field contains a Crypto-ID and
      that the 6LN MAY be challenged for ownership.

   *P:*  2-bit field for Registered Address Type Indicator (RATInd).
      Indicates whether the registered address is unicast, multicast, or
      anycast, or derived from the unicast prefix that is being
      registered.  Used to transport the RATInd in different protocols.
      The values for the RATInd field are available in
      [IANA.ICMP.ARO.P-FIELD].

   *I:*  2-bit integer field that helps to decide how to use the 8-bit
      Opaque field.  When 0, it means the Opaque field has info about
      the default routing path.  Other values are reserved.  Defined in
      [RFC8505].

   *R:*  1-bit flag.  Registering Node sets the R-flag to request
      reachability services for the Registered Address from a Routing
      Registrar.  Defined in [RFC8505].

   *T:*  1-bit flag.  Set if the next octet is used as a TID.  Defined
      in [RFC8505].

   *TID (Transaction ID):*  8-bit unsigned integer that tracks
      transactions for registrations.  It is incremented with each new
      transaction and ignored unless the T-flag is set.  Defined in
      [RFC8505].

   *Registration Lifetime:*  16-bit integer representing the lifetime in
      minutes of the Registered Address.  Zero indicates the
      registration has ended, and the associated state MUST be removed.
      Defined in [RFC8505].

   *Registration Ownership Verifier (ROVR):*  Variable length field,

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      used to verify who "owns" a registered IPv6 address [RFC8505].
      When the C-flag is set, this field contains a Crypto-ID [RFC8928].

4.  Security Considerations

   This specification does not introduce any new security considerations
   beyond those already discussed in [RFC8928] and [RFC8505].

5.  IANA Considerations

5.1.  Bit Position of the C-flag

   This specification updates the location of the C-flag introduced in
   [RFC8928] to position it as bit 1 in the EARO flags field.  IANA is
   requested to reference this RFC in addition to [RFC8928] when
   updating the "Address Registration Option Flags" [IANA.ICMP.ARO.FLG]
   registry under the heading "Internet Control Message Protocol version
   6 (ICMPv6) Parameters" as specified in Table 1:

            +---------------+---------+-----------------------+
            | ARO flag      | Meaning | Reference             |
            +---------------+---------+-----------------------+
            | 1 (suggested) | C-Flag  | RFC This and RFC 8928 |
            +---------------+---------+-----------------------+

                    Table 1: Bit Position of the C-flag

6.  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/info/rfc2119>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.

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   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <https://www.rfc-editor.org/info/rfc6775>.

   [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/info/rfc8174>.

   [RFC8505]  Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Neighbor
              Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
              <https://www.rfc-editor.org/info/rfc8505>.

   [RFC8928]  Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik,
              "Address-Protected Neighbor Discovery for Low-Power and
              Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November
              2020, <https://www.rfc-editor.org/info/rfc8928>.

   [RFC9010]  Thubert, P., Ed. and M. Richardson, "Routing for RPL
              (Routing Protocol for Low-Power and Lossy Networks)
              Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021,
              <https://www.rfc-editor.org/info/rfc9010>.

   [RFC9685]  Thubert, P., Ed., "Listener Subscription for IPv6 Neighbor
              Discovery Multicast and Anycast Addresses", RFC 9685,
              DOI 10.17487/RFC9685, November 2024,
              <https://www.rfc-editor.org/info/rfc9685>.

   [I-D.ietf-6lo-prefix-registration]
              Thubert, P., "IPv6 Neighbor Discovery Prefix
              Registration", Work in Progress, Internet-Draft, draft-
              ietf-6lo-prefix-registration-10, 17 April 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-6lo-
              prefix-registration-10>.

   [IANA.ICMP.ARO.FLG]
              IANA, "IANA Registry for the Address Registration Option
              Flags", IANA, https://www.iana.org/assignments/icmpv6-
              parameters/icmpv6-parameters.xhtml#icmpv6-adress-
              registration-option-flags.

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   [IANA.ICMP.ARO.STAT]
              IANA, "IANA Registry for the Address Registration Option
              Status Value", IANA, https://www.iana.org/assignments/
              icmpv6-parameters/icmpv6-parameters.xhtml#address-
              registration.

   [IANA.ICMP.ARO.P-FIELD]
              IANA, "IANA Registry for the Address Registration Option
              Status Value", IANA, https://www.iana.org/assignments/
              icmpv6-parameters/icmpv6-parameters.xhtml#p-field-values.

7.  Informative References

   [IEEE802154]
              IEEE standard for Information Technology, "IEEE Std
              802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
              and Physical Layer (PHY) Specifications for Low-Rate
              Wireless Personal Area Networks".

   [RFC8929]  Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli,
              "IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929,
              November 2020, <https://www.rfc-editor.org/info/rfc8929>.

Authors' Addresses

   Pascal Thubert
   06330 Roquefort-les-Pins
   France
   Email: pascal.thubert@gmail.com

   Adnan Rashid
   Politecnico di Bari
   Via Edoardo Orabona 4
   70126 Bari
   Italy
   Email: adnan.rashid@poliba.it

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