Moving the C Flag in EARO

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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶

This Internet-Draft will expire on 16 October 2025.¶

Copyright Notice

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

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 and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

Table of Contents

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].¶

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.¶

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)                  |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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.¶

Authors' Addresses