Moving the C Flag in EARO
draft-ietf-6lo-updating-rfc-8928-00

6lo                                                           P. Thubert
Internet-Draft                                                          
Updates: 8928 (if approved)                                    A. Rashid
Intended status: Standards Track                                  P Bari
Expires: 16 October 2025                                   14 April 2025

                       Moving the C Flag in EARO
                  draft-ietf-6lo-updating-rfc-8928-00

Abstract

   This document updates RFC 8928, “Address-Protected Neighbor Discovery
   for Low-Power and Lossy Networks” (AP-ND), by explicitly specifying
   the bit position for the “C” flag and registering it with IANA.  This
   clarification ensures consistent implementation and interoperability
   of the AP-ND protocol, which protects against address theft and
   impersonation attacks in Low-Power and Lossy Networks (LLNs).  This
   update provides a precise definition of the “C” flag’s bit position,
   enabling correct deployment and verification of AP-ND’s security
   features.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 16 October 2025.

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   Please review these documents carefully, as they describe your rights

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   and restrictions with respect to this document.  Code Components
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  References  . . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Updating RFC 8928 . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Bit Position of the "C" Flag  . . . . . . . . . . . . . .   5
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The classical Neighbor Discovery (IPv6 ND) Protocol [RFC4861]
   [RFC4862] was defined for serial links and shared transit media such
   as Ethernet at a time when broadcast was cheap on those media while
   memory for neighbor cache was expensive.  It was thus designed as a
   reactive protocol that relies on caching and multicast operations for
   the Address Resolution (AR, aka Address Discovery or Address Lookup)
   and Duplicate Address Detection (DAD) of IPv6 unicast addresses.
   Those multicast operations typically impact every node on-link when
   at most one is really targeted, which is a waste of energy, and imply
   that all nodes are awake to hear the request, which is inconsistent
   with power saving (sleeping) modes.

   Low-Power Personal Area Networks (LoWPANs) require an optimized IPv6
   Neighbor Discovery due to resource constraints and high multicast
   overhead.  To address this, 6LoWPAN ND [RFC6775], [RFC8505],
   [RFC8929], [RFC9685], [I-D.ietf-6lo-prefix-registration] introduces a
   unicast, anycast, and multicast Address Registration (AR) mechanism
   as well as a Prefix Registration (PR) mechanism.  Staring with
   [RFC8505], the registration mechanism uses the Extended Address
   Registration Option (EARO), significantly reducing reliance on
   multicast for Duplicate Address Detection (DAD).  In these networks,
   the 6LoWPAN Border Router (6LBR) serves as a central repository for
   registered addresses. 6LoWPAN ND is being generalized to NBMA
   networks as Subnet Neighbor Discovery (SND), see
   [I-D.ietf-6man-ipv6-over-wireless].

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   For enhanced security, [RFC8505] introduces a Registration Ownership
   Verifier (ROVR) in the EARO.  Building on this, the
   "Address-Protected Neighbor Discovery for LLNs" [RFC8928], protects
   the ownership of unicast IPv6 addresses registered with [RFC8505].
   In this framework, a node auto-configures a public/private key pair
   and signs its address registrations, enabling the first-hop router
   (6LoWPAN Router (6LR)) to validate registrations and perform source
   address verification.

   However, the “Address-Protected Neighbor Discovery for Low-Power and
   Lossy Networks” [RFC8928] (AP-ND), initially defined the “C” flag in
   EARO, later on [RFC9685] defined the P-Field in bits 2 and 3 of the
   EARO flags 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 flag avoiding 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 for IP version 6 [RFC4861]

   *  IPv6 Stateless Address Autoconfiguration [RFC4862]

   *  Neighbor Discovery Optimization for IPv6 over Low-Power Wireless
      Personal Area Networks (6LoWPANs) [RFC6775]

   *  Registration Extensions for IPv6 over Low-Power Wireless Personal
      Area Network (6LoWPAN) Neighbor Discovery [RFC8505]

   *  IPv6 Backbone Router [RFC8929]

   *  Address-Protected Neighbor Discovery for Low-Power and Lossy
      Networks [RFC8928]

   *  Listener Subscription for IPv6 Neighbor Discovery Multicast and
      Anycast Addresses [RFC9685]

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2.3.  Acronyms

   This document uses the following abbreviations:

   6LN:  6LoWPAN Node
   6LBR:  6LoWPAN Border Router
   6LR:  6LoWPAN Router
   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 Personal Area Network (IEEE Std. 802.15.4)
      [IEEE802154]
   NDP:  Neighbor Discovery Protocol
   ROVR:  Registration Ownership Verifier
   SND:  Subnet Neighbor Discovery
   TID:  Transaction ID

3.  Updating RFC 8928

   The "Address-Protected Neighbor Discovery for Low-Power and Lossy
   Networks" [RFC8928] was defined to protect the ownership of unicast
   IPv6 addresses that are registered with [RFC8505].  In [RFC8928], the
   "C" flag is shown in the EARO flags field at bit position 3 (as
   depicted in Figure 1 of [RFC8928]); however, it does not explicitly
   specify the bit number and 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.

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

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

   Option Fields of interest for this specification:

   *Type:*  33

   *Length:*  Defined in [RFC8505] and copied in the "EARO Length" field
      in the associated Crypto-ID Parameters Option (CIPO).

   *Status:*  Defined in [RFC8505].

   *Opaque:*  Defined in [RFC8505].

   *R (Reserved):*  1-bit unsigned integer.  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 P-Field

   *I, R, T:*  Defined in [RFC8505].

   *TID and Registration Lifetime:*  Defined in [RFC8505].

   *Registration Ownership Verifier (ROVR):*  When the "C" flag is set,
      this field contains a Crypto-ID.

4.  IANA Considerations

4.1.  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.  IANA is
   requested to make an addition to the "Address Registration Option
   Flags" [IANA.ICMP.ARO.FLG] registry under the heading "Internet
   Control Message Protocol version 6 (ICMPv6) Parameters" as indicated
   in Table 1:

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

                  Table 1: Bit Position of the "C" Flag

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5.  Acknowledgments

   Many thanks to Dave Thaler and Dan Romascanu for their early INT-DIR
   review.

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>.

   [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>.

   [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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   [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>.

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>.

   [I-D.ietf-6lo-prefix-registration]
              Thubert, P., "IPv6 Neighbor Discovery Prefix
              Registration", Work in Progress, Internet-Draft, draft-
              ietf-6lo-prefix-registration-07, 25 March 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-6lo-
              prefix-registration-07>.

   [I-D.ietf-6man-ipv6-over-wireless]
              Thubert, P. and M. Richardson, "Architecture and Framework
              for IPv6 over Non-Broadcast Access", Work in Progress,
              Internet-Draft, draft-ietf-6man-ipv6-over-wireless-07, 23
              November 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-6man-ipv6-over-wireless-07>.

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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