Fixing the C-Flag in EARO

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Table of Contents

1. Introduction

The “Address-Protected Neighbor Discovery for Low-Power and Lossy Networks” (AP-ND) [RFC8928] , initially 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.¶

3. Updating RFC 8928

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. Moreover, figure 1 of this I-D replaces the Figure 1 [RFC8928].¶

   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).¶

F:

1-bit flag. It MUST be set to zero by the sender and MUST be ignored by the receiver[I-D.ietf-6lo-prefix-registration].¶

Prefix Length:

8-bit unsigned integer. It MUST be set to zero by the sender and MUST be ignored by the receiver [I-D.ietf-6lo-prefix-registration]¶

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 an address is unicast, multicast, or anycast. Used to transport the RATInd in different protocols. All values registry are defined in Table 2 of [RFC9685].¶

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 falg. Set if the next octet is used as a TID. Defined in [RFC8505].¶

TID and Registration Lifetime:

8-bit unsigned integer that tracks transactions for registrations. It's 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, used to verify who "owns" a registered IPv6 address [RFC8505]. When the C-flag is set, this field contains a Crypto-ID [RFC8928].¶

Authors' Addresses