Fixing the C-Flag in EARO

Introduction The Address-Protected Neighbor Discovery for Low-Power and Lossy Networks (AP-ND) 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 defined the C-flag in the EARO in bit position 3; later 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 which depicts the location of the C-flag. This specification updates by repositioning the C-flag as bit 1 of the EARO flags field, thereby preventing conflicts.

Terminology

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 when, and only when, they appear in all capitals, as shown here.

References This document uses terms and concepts that are discussed in:

Neighbor Discovery for IP version 6
IPv6 Stateless Address Autoconfiguration
Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)
Registration Extensions for IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor Discovery
IPv6 Backbone Router
Address-Protected Neighbor Discovery for Low-Power and Lossy Networks
Listener Subscription for IPv6 Neighbor Discovery Multicast and Anycast Addresses

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
CIPO:: Crypto-ID Parameters 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)
NDP:: Neighbor Discovery Protocol
RATInd:: Registered Address Type Indicator
ROVR:: Registration Ownership Verifier
TID:: Transaction ID

Updating RFC 8928 incorrectly refers to the Extended Address Registration Option (EARO) as the Enhanced Address Registration Option. This specification corrects this terminology throughout the document. In , the C-flag is specified in the EARO flags field at bit position 3 (as depicted in the Figure 1 of ); however, fails to register its position with IANA. Later, 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 . To resolve the conflict, this specification updates by repositioning the C-flag to bit 1 of the EARO flags field, thereby avoiding the overlapping definitions. replaces Figure 1 in in the case of an EARO used in an NS message.

Extended Address Registration Option (EARO) Format for use in NS messages 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) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ replaces Figure 1 in 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.

Extended Address Registration Option (EARO) Format for use in NA messages 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 ... | (64, 128, 192, or 256 bits) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option fields of interest for this specification:

Type:: 33
Length:: Defined in and copied in the "EARO Length" field in the associated Crypto-ID Parameters Option (CIPO).
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 .
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 between 16 and 120, both included. 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 .
Status:: 6-bit unsigned integer. Indicates the status of a registration in the NA response. The field MUST be set to 0 in NS messages unless the registration is for a prefix, in which case the F flag is set and the prefix length is provided. For use in NA messages only. The Status field is defined in and resized by . The values for the Status field are available in
Opaque:: 8-bit field opaque to ND. It MUST be set to 0 when not used. Defined in .
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 . 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 .
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 .
R:: 1-bit flag. Registering Node sets the R-flag to request reachability services for the Registered Address from a Routing Registrar. Defined in .
T:: 1-bit flag. Set if the next octet is used as a TID. Defined in .
TID and Registration Lifetime:: 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 .
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 .
Registration Ownership Verifier (ROVR):: Variable length field, used to verify who "owns" a registered IPv6 address . When the C-flag is set, this field contains a Crypto-ID .

Security Considerations This specification does not introduce any new security considerations beyond those already discussed in and .

IANA Considerations

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

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