| Internet-Draft | IPv6 ND Unicast Lookup | September 2021 |
| Thubert & Levy-Abegnoli | Expires 31 March 2022 | [Page] |
This document updates RFC 8505 in order to enable unicast address lookup from a 6LoWPAN Border Router acting as an Address Registrar.¶
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/.¶
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This Internet-Draft will expire on 31 March 2022.¶
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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[RFC8505] defines the Routing Registrar and extends [RFC6775] to use a 6LoWPAN Border Router (6LBR) as a central service for Address Registration and duplicate detection amongst Routing Registrars and possibly individual Nodes that access it directly.¶
[RFC8929] introduces the Backbone Router (6BBR) as a Routing Registrar that performs IPv6 ND [RFC4861] [RFC4862] proxy operation between IPv6 Nodes on a federating Backbone Link and Registering Nodes attached to a LowPower Lossy Networks (LLNs) that register their addresses to the 6BBR. The federated links form a Multilink Subnet (MLSN).¶
The 6BBRs may exchange Extended Duplicate Address Messages (EDAR and EDAC) [RFC8505] to register the proxied addresses on behalf of the Registering Nodes to the 6LBR. The Registration Ownership Verifier (ROVR) field in the EDAR and EDAC messages is used to correlate attempts to register the same address and to detect duplications. The ROVR can also be used as a proof-of-ownership (see [RFC8928]) to protect the Registered address against theft and impersonation attacks (more in [I-D.bi-savi-wlan]). Conflicting registrations to different 6BBRs for the same Registered address are resolved using the TID field, which creates a temporal order and enables to recognize the freshest registration.¶
With [RFC8929], the Link Layer address (LLA) that the 6BBR advertises for a Registered address on behalf of the Registered Node over the Backbone can belong to the Registering Node; in that case, the 6BBR acts as a Bridging Proxy and bridges the unicast packets. Alternatively, the LLA can be that of the 6BBR on the Backbone interface, in which case the 6BBR acts as a Routing Proxy, that receives the unicast packets at Layer-3 and routes them. The 6BBR signals that LLA in a Source LLA Option (SLLAO) in the EDAR messages to the 6LBR, and the 6LBR responds with a Target LLA Option (TLLAO) that indicates the LLA associated to the current registration.¶
It results that the 6LBR is capable of providing the LLA mapping for any address that was proactively registered with an SLLAO. This draft defines the protocol elements and the operations to try a unicast lookup with the 6LBR. This may save a reactive IPv6 ND Neighbor Solicitation (NS) message, which is based on multicast and may be problematic in extensive wireless domains (see [I-D.ietf-mboned-ieee802-mcast-problems]) as well as in large switched fabrics.¶
The registration and lookup services that the 6LBR provides do not have to be limited to 6BBRs and are available to any node that supports [RFC8505] and [RFC8929] to register an address, and / or this specification to resolve a mapping. The services are available on-link using an IPv6 NDP NS and off-link using a new variation of the Extended Duplicate Address messages called Address Mapping Messages. The policy and security settings that allow the access to the 6LBR are out of scope.¶
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.¶
This document uses terms and concepts that are discussed in:¶
This document introduces the following terminology:¶
This document uses terminology defined in [RFC8505], in particular:¶
This document uses the following acronyms:¶
Figure 1 illustrates a Backbone Link that federates a collection of LLNs as a single IPv6 Subnet, with a number of 6BBRs providing proxy-ND services to their attached LLNs.¶
A collection of IPv6 Nodes are present on the Backbone and use IPv6 ND [RFC4861][RFC4862] procedures for DAD and Lookup.¶
The LLN may be a hub-and-spoke access link such as (Low-Power) IEEE STD. 802.11 (Wi-Fi) [IEEEstd80211] and IEEE STD. 802.15.1 (Bluetooth) [IEEEstd802151], or a Mesh-Under or a Route-Over network [RFC8505].¶
|
+-----+ +-----+ +-----+
(default) | | 6LBR | | | | IPv6
Router | | | | | | Node
+-----+ +-----+ +-----+
| Backbone side | |
----+-------+-----------------+---+-------------+----+-----
| | |
+------+ +------+ +------+
| 6BBR | | 6BBR | | 6BBR |
| | | | | |
+------+ +------+ +------+
o Wireless side o o o o o
o o o o o o o o o o o o o o
o o o o o o o o o o o o o o o
o o o o o o o o o o
o o o o o o o
LLN LLN LLN
A 6LBR provides registration services for the purpose of proactive IPv6 ND and maintains a registry of the active registrations as an abstract data structure called an Address Registrar. An entry in the Address Registrar is called an "Address Registration".¶
The Address Registration retains:¶
Examples where more than one address may be available include the case of an anycast address and the case of an LLN address that is proxied by more than one 6BBR.¶
Unless otherwise configured, a 6LBR does the following:¶
The Address Mapping messages can be exchanged using global unicast addresses as source and destination addresses, so they can be used for both on-link and off-link queries. NS and NA messages may also be used, but in that case the unicast source and destination addresses are link-local addresses and the 6LBR must be on-link.¶
The 6LBR proactive operations may coexist on the Backbone with reactive IPv6 ND [RFC4861][RFC4862] that rely on multicast for Duplicate Address Detection (DAD) and Address Lookup. Nodes that support this specification operate with the 6LBR before attempting the reactive operation, which may be avoided if the 6LBR is conclusive, either detecting a duplication or returning a mapping.¶
This specification leverages the capability to insert IPv6 ND options in the EDAR and EDAC messages that was introduced in [RFC8929].¶
It extends DAR and DAR ICMP messages for address lookup in Section 4.1.2 that use the same ICMP types as EDAR and EDAC but a different Code Prefix.¶
It also adds a new Status "Not Found" in Section 4.1.3) that indicates that the address being searched is not present in the Address Registrar.¶
A 6LBR signals itself by setting the "B" bit in the 6CIO of the RA messages that it generates [RFC8505]. This specification adds a new "A" bit in the 6CIO to indicate support of address mapping (see Section 4.1.1).¶
This specification does not introduce new options; it modifies existing options and updates the associated behaviors.¶
This specification defines a new capability bit for use in the 6CIO, as defined by [RFC7400] and extended in[RFC8505] for use in IPv6 ND messages.¶
The new "A" bit indicates that the 6LBR provides address mapping services per this specification.¶
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 = 1 | Reserved |A|D|L|B|P|E|G|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Fields:¶
The Extended Duplicate Address messages share a common base format defined in section 4.2 of [RFC8505], with the ICMP type respectively set to 157 and 158 that is inherited from the DAR and DAC messages defined in section 4.4 of [RFC6775]. The ICMP Code is split in two 4-bit fields, the Code Prefix and the Code Suffix, and the only Code Prefix defined in [RFC8505] is 0, signaling a DAD.¶
The Address Mapping messages use the same values for the ICMP Type as the corresponding Extended Duplicate Address messages. This specification adds the Code Prefix of 1 to signal Address Mapping. ICMP messages with the ICMP type set to 157 or 158, and a Code Prefix of 1 are thus respectively an Address Mapping Request (AMR) and an Address Mapping Confirm (AMC).¶
The Extended Address Registration Option (EARO) is defined in section 4.1 of [RFC8505]. It contains a Status field that is common with with the EDAR and EDAC messages defined in section 4.2 of [RFC8505]. This specification defines a new Status "Not Found" as indicated in Table 1¶
| Value | Description |
| 0..10 | As defined in [RFC6775] and [RFC8505] |
| 11 | Not Found: The address is not present in the Address Registrar (value to be confirmed by IANA) |
The Status of "Not Found" can be used in an NA(EARO) and in an AMC messages as a response to an address lookup operation.¶
A 6LBR signals that support by setting the "B" bit in the 6CIO of the RA messages that it generates. A 6LBR that supports this specification MUST also set the "A" bit, indicating support of the Address Mapping messages for address lookup.¶
In the Address Mapping flow, the querier IPv6 Node uses an AMR message, which is characterized by an ICMPv6 Type of 157 and a Code Prefix of 1. When used on-link, the AMR message SHOULD carry a SLLAO indicating the LLA of the querier. The Code Suffix MUST be set to 0 indicating a ROVR Length of 64 bits. The ROVR, TID and Lifetime fields MUST be set to 0 and ignored by the receiver.¶
The 6LBR MUST respond with an AMC message, which is characterized by an ICMPv6 Type of 158 and a Code Prefix of 1.¶
The AMC is sent unicast the 6LBR to the querier.¶
A 6LBR that is deployed on-link SHOULD provide NS/NA-based services. It signals that support by setting the "L" bit in the 6CIO of the RA messages that it generates, indicating that it is a 6LR [RFC8505].¶
A 6LBR thus typically sets the "A", the "B", and the "L" bits when attached to a Backbone Link that it serves, as illustrated in Figure 1. In that case, the IPv6 Nodes and 6BBRs can use an NS/NA exchange with the 6LBR for both duplicate detection and lookup services.¶
The NS(Lookup) is sent unicast from link-local address of the querier to the link-local address of the 6LBR. It carries a SLLAO [RFC4861] and it MUST NOT carry an EARO option to avoid the confusion with a registration.¶
The 6LBR MUST respond with an NA message that contains an EARO.¶
The NA is sent unicast from link-local address of the 6LBR to the link-local address of the querier.¶
This specification extends [RFC8505], and the security section of that document also applies to this document. In particular, the link layer SHOULD be sufficiently protected to prevent rogue access.¶
Note to RFC Editor, to be removed: please replace "This RFC" throughout this document by the RFC number for this specification once it is allocated.¶
IANA is requested to make a number of changes under the "Internet Control Message Protocol version 6 (ICMPv6) Parameters" registry, as follows.¶
IANA is requested to create 2 new subregistries of the ICMPv6 "Code" Fields registry, which itself is a subregistry of the Internet Control Message Protocol version 6 (ICMPv6) Parameters for the ICMP codes.¶
The new subregistries relate to the ICMP type 157, Duplicate Address Request (shown in Table 2), and 158, Duplicate Address Confirmation (shown in Table 3), respectively. For those two ICMP types, the ICMP Code field is split into 2 subfields, the "Code Prefix" and the "Code Prefix". The new subregistries relate to the "Code Prefix" portion of the ICMP Code. The range of "Code Prefix" is 0..15 in all cases. The policy is "IETF Review" or "IESG Approval" [RFC8126] for both subregistries.¶
The new subregistries are to be initialized as follows:¶
| Code Prefix | Meaning | Reference |
| 0 | Duplicate Address Detection | Duplicate Address Detection |
| 1 | Address Mapping | This RFC |
| 2...15 | Duplicate Address Detection |
| Code Prefix | Meaning | Reference |
| 0 | Duplicate Address Detection | Duplicate Address Detection |
| 1 | Address Mapping | This RFC |
| 2...15 | Duplicate Address Detection |
IANA is requested to make additions to the Address Registration Option Status Values Registry as follows:¶
| ARO Status | Meaning | Reference |
| 11 (suggested) | Not Found | This RFC |
IANA is requested to make additions to the Subregistry for "6LoWPAN Capability Bits" as follows:¶
| Capability Bit | Meaning | Reference |
| 9 (suggested) | AM Support (A bit) | This RFC |