IPv6 Neighbor Discovery Prefix Registration
draft-ietf-6lo-prefix-registration-02
| Document | Type | Active Internet-Draft (6lo WG) | |
|---|---|---|---|
| Author | Pascal Thubert | ||
| Last updated | 2024-02-13 | ||
| Replaces | draft-thubert-6lo-prefix-registration | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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| Additional resources | Mailing list discussion | ||
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draft-ietf-6lo-prefix-registration-02
6lo P. Thubert, Ed.
Internet-Draft 13 February 2024
Updates: 4861, 6550, 6553, 8505, 8928, 9010 (if
approved)
Intended status: Standards Track
Expires: 16 August 2024
IPv6 Neighbor Discovery Prefix Registration
draft-ietf-6lo-prefix-registration-02
Abstract
This document updates IPv6 Neighbor Discovery [RFC4861] and the
6LoWPAN extensions [RFC8505][RFC8928] to enable a node that owns or
is directly connected to a prefix to register that prefix to neighbor
routers. The registration indicates that the registered prefix can
be reached via the advertising node without a loop. The prefix
registration also provides a protocol-independent interface for the
node to request neighbor router(s) to redistribute the prefix to the
larger routing domain using their specific routing protocols. This
document extends RPL [RFC6550][RFC6553][RFC9010] to enable the 6LR to
inject the registered prefix in RPL.
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 August 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. References . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. New terms . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. LLN Mesh Network . . . . . . . . . . . . . . . . . . . . 7
3.2. Shared Link . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Hub Link . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Updating RFC 4861 . . . . . . . . . . . . . . . . . . . . . . 11
5. Extending RFC 7400 . . . . . . . . . . . . . . . . . . . . . 11
6. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 12
7. Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . . 13
7.1. New P field value . . . . . . . . . . . . . . . . . . . . 13
7.2. New EARO Prefix Length Field and F Flag . . . . . . . . . 13
7.3. New EDAR Prefix Length Field . . . . . . . . . . . . . . 15
7.4. Registering Extensions . . . . . . . . . . . . . . . . . 15
8. Updating RFC 9010 . . . . . . . . . . . . . . . . . . . . . . 18
9. Updating RFC 8928 . . . . . . . . . . . . . . . . . . . . . . 18
10. Security Considerations . . . . . . . . . . . . . . . . . . . 19
11. Backward Compatibility . . . . . . . . . . . . . . . . . . . 20
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12.1. Updated P-Field Registry . . . . . . . . . . . . . . . . 20
12.2. New 6LoWPAN Capability Bit . . . . . . . . . . . . . . . 20
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
14. Normative References . . . . . . . . . . . . . . . . . . . . 21
15. Informative References . . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
The design of Low Power and Lossy Networks (LLNs) is generally
focused on saving energy, which is the most constrained resource of
all. Other design constraints, such as a limited memory capacity,
duty cycling of the LLN devices and low-power lossy transmissions,
derive from that primary concern. The radio (both transmitting or
simply listening) is a major energy drain and the LLN protocols must
be adapted to allow the nodes to remain sleeping with the radio
turned off at most times.
The "Routing Protocol for Low Power and Lossy Networks" [RFC6550]
(RPL) provides IPv6 [RFC8200] routing services within such
constraints. To save signaling and routing state in constrained
networks, the RPL routing is only performed along a Destination-
Oriented Directed Acyclic Graph (DODAG) that is optimized to reach a
Root node, as opposed to along the shortest path between 2 peers,
whatever that would mean in each LLN.
This trades the quality of peer-to-peer (P2P) paths for a vastly
reduced amount of control traffic and routing state that would be
required to operate an any-to-any shortest path protocol.
Additionally, broken routes may be fixed lazily and on-demand, based
on dataplane inconsistency discovery, which avoids wasting energy in
the proactive repair of unused paths.
The "IPv6 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.
The "Architecture and Framework for IPv6 over Non-Broadcast Access"
(NBMA) [I-D.ietf-6man-ipv6-over-wireless] introduces an evolution of
IPv6 ND towards a proactive AR method also called Stateful Address
Autoconfiguration (SFAAC). Because the IPv6 model for NBMA depends
on a routing protocol to reach inside the Subnet, the IPv6 ND
extension for NBMA is refered to as Subnet Neighbor Discovery (SND).
SND is based on work done in the context of IoT, known as 6LoWPAN ND.
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The original 6LoWPAN ND, "Neighbor Discovery Optimizations for
6LoWPAN networks" [RFC6775], was introduced to avoid the excessive
use of multicast messages and enable IPv6 ND for operations over
energy-constrained nodes. [RFC6775] changes the classical IPv6 ND
model to proactively establish the Neighbor Cache Entry (NCE)
associated to the unicast address of a 6LoWPAN Node (6LN) in the a
6LoWPAN Router(s) (6LR) that serves it. To that effect, [RFC6775]
defines a new Address Registration Option (ARO) that is placed in
unicast Neighbor Solicitation (NS) and Neighbor Advertisement (NA)
messages between the 6LN and the 6LR.
"Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
updates [RFC6775] into a generic Address Registration mechanism that
can be used to access services such as routing and ND proxy and
introduces the Extended Address Registration Option (EARO) for that
purpose. This provides a routing-agnostic interface for a host to
request that the router injects a unicast IPv6 address in the local
routing protocol and provide return reachability for that address.
"IPv6 Neighbor Discovery Multicast Address Listener Subscription"
[I-D.ietf-6lo-multicast-registration] updates [RFC8505] to enable a
listener to subscribe an IPv6 anycast or multicast address; the draft
also extends [RFC9010] to enable the 6LR to inject the anycast and
multicast addresses in RPL. Similarly, this specification extends
[RFC8505] and [RFC9010] to add the capability for the 6LN to register
prefixes as opposed to addresses, and to signal in a protocol-
independant fashion to the 6LR that it is expected to redistribute
the prefixes in their specific routing protocols.
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.
In addition, the terms "Extends" and "Amends" are used as per
[I-D.kuehlewind-update-tag] section 3.
2.2. References
This document uses terms and concepts that are discussed in:
* "Neighbor Discovery for IP version 6" [RFC4861] and "IPv6
Stateless address Autoconfiguration" [RFC4862],
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* Neighbor Discovery Optimization for Low-Power and Lossy Networks
[RFC6775], as well as
* "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
and
* "Using RPI Option Type, Routing Header for Source Routes, and
IPv6-in-IPv6 Encapsulation in the RPL Data Plane" [RFC9008].
2.3. Acronyms
This document uses the following abbreviations:
6BBR: Backbone Router
6LN: (6LoWPAN) Node
6LR: (6LoWPAN) Router
ARO: address Registration Option
DAC: Duplicate address Confirmation (message)
DAD: Duplicate address Detection
DAR: Duplicate address Request (message)
EDAC: Extended Duplicate address Confirmation
EDAR: Extended Duplicate address Request
LLN: Low-Power and Lossy Network
LLA: link-local address
LoWPAN: Low-Power WPAN
MAC: Medium Access Control
MLSN: Multi-link Subnet
MLD: multicast Listener Discovery
NA: Neighbor Advertisement (message)
NBMA: Non-Broadcast Multi-Access (full mesh)
NCE: Neighbor Cache Entry
ND: Neighbor Discovery (protocol)
NDP: Neighbor Discovery Protocol
NS: Neighbor Solicitation (message)
P2P: Point-to-Point
P2MP: Point-to-Multipoint (partial mesh)
RPL: IPv6 Routing Protocol for LLNs
RA: Router Advertisement (message)
RS: Router Solicitation (message)
SGP: Subnet Gateway Protocol
SPL: Subnet Prefix Length
ULP: Upper-Layer Protocol
VLAN: Virtual LAN
VxLAN: Virtual Extensible LAN
VPN: Virtual Private Network
WAN: Wide Area Network
SND: Subnet Neighbor Discovery (protocol)
WLAN: Wireless Local Area Network
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WPAN: Wireless Personal Area Network
2.4. New terms
This document introduces the following terms:
Origin The node that issued the prefix advertisement, either in the
form of a NS(EARO) or as a DAO(TIO, RTO)
Merge/merging The action of receiving multiple anycast or multicast
advertisements, either internally from self, in the form of a
NS(EARO), or as a DAO(TIO, RTO), and generating a single
DAO(TIO, RTO). The 6RPL router maintains a state per origin
for each advertised address, and merges the advertisements for
all subsriptions for the same address in a single
advertisement. A RPL router that merges becomes the origin of
the merged advertisement and uses its own values for the Path
Sequence and ROVR fields.
3. Overview
This specification inherits from [RFC6550], [RFC8505], and [RFC9010]
to register prefixes as opposed to addresses. Unless specified
otherwise therein, the behavior of the 6LBR that acts as RPL Root, of
the intermediate routers down the RPL graph, of the 6LR that act as
access routers and of the 6LNs that are the RPL-unaware destinations,
is the same as for unicast addresses. In particular, forwarding a
packet happens as specified in section 11 of [RFC6550], including
loop avoidance and detection, though in the case of multicast
multiple copies might be generated.
[RFC8505] is a pre-requisite to this specification. A node that
implements this MUST also implement [RFC8505]. This specification
does not introduce a new option; it modifies existing options and
updates the associated behaviors to enable the Registration for
Multicast Addresses as an extension to [RFC8505].
This specification updates the P field introduced in
[I-D.ietf-6lo-multicast-registration] for use in EARO, DAR, and RTO,
with the new value of 3 to indicate the registration of a prefix, as
detailed in Section 7.2. With this extension the 6LNs can now
attract the traffic for a full prefix, using the P field value of 3
in the EARO to signal that the registration is for a prefix.
Multiple 6LN may register the same prefix to the same 6LR or to
different 6LRs.
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If the R flag is set in the registration of one or more 6LNs for the
same prefix, the 6LR is requested to redistributes the prefix in
other routing protocol (e.g., RPL), based on the longest registration
lifetime across the active registrations for the prefix.
This specification extends 6LoWPAN work, and it is certainly possible
to leverage it between the 6LN and the 6LR where the 6LR is a RPL
router, as discussed in Section 3.1. But as for [RFC8505] in
general, this specification applies, beyond IoT use cases, to
networks that are not necessarily LLNs, and/or where the routing
protocol between the 6LR and above is not necessarily RPL. Examples
of shared links and hub links are provided in Section 3.2 and
Section 3.3, respectively.
3.1. LLN Mesh Network
This specification also extends [RFC6550] and [RFC9010] in the case
of a route-over multilink subnet based on the RPL routing protocol,
to add multicast ingress replication in Non-Storing Mode and anycast
support in both Storing and Non-Storing modes. A 6LR that implements
the RPL extensions specified therein MUST also implement [RFC9010].
Figure 1 illustrates the classical situation of an LLN as a single
IPv6 Subnet, with a 6LoWPAN Border Router (6LBR) that acts as Root
for RPL operations and maintains a registry of the active
registrations as an abstract data structure called an Address
Registrar for 6LoWPAN ND.
The LLN may be a hub-and-spoke access link such as (Low-Power) Wi-Fi
[IEEE80211] and Bluetooth (Low Energy) [IEEE802151], or a Route-Over
LLN such as the Wi-SUN and 6TiSCH meshes
[I-D.heile-lpwan-wisun-overview] that leverages 6LoWPAN
[RFC4919][RFC6282] and RPL [RFC6550] over [IEEE802154].
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|
----+-------+------------
| Wire side
+------+
| 6LBR |
|(Root)|
+------+
o o o Wireless side
o o o o o o
o o o o o o o
o o o LLN o +---+
o o o o o |6LR|
o o o o o +---+
o o o o o o z
o o oo o o +---+
o |6LN|
+---+
Figure 1: Wireless Mesh
A leaf acting as a 6LN registers its unicast, multicast, and anycast
addresses a RPL router acting as a 6LR, using a layer-2 unicast NS
message with an EARO as specified in [RFC8505] and
[I-D.ietf-6lo-multicast-registration]. The registration state is
periodically renewed by the Registering Node, before the lifetime
indicated in the EARO expires. As for unicast IPv6 addresses, the
6LR uses an EDAR/EDAC exchange with the 6LBR to notify the 6LBR of
the presence of the listeners. With this specification, a router
that own a prefix of provides reachability to an external prefix but
is not a RPL router may also register those prefixes with the R flag
set, to enable reachability via the RPL domain. As usual
3.2. Shared Link
A shared link is a situation where more than one Prefix is deployed
over a L2 link (say a switched Ethernet + Wi-Fi ESS), and not
necessarily all nodes are aware of all prefixes. Figure 2 depicts
such a situation, with 2 routers 6LR1 and 6LR2 that own respective
prefixes P1:: and P2::, and expose those in their RA messages over
the same link.
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+-----+ +-----+ +-----+ +-----+ +-----+
|P1::c| |P2::d| |P2::e| |P1::f| |P1::g|
+--+--+ +--+--+ +--+--+ +--+--+ +--+--+
| | | | |
----+--+------+---------+--+------+---------+---+--
| | |
+---+---+ +---+---+
| P1::a | | P2::b |
| 6LR1 | | 6LR2 |
+----+--+ +-------+
|
....
. . ..
...
Figure 2: Shared Link
Say that 6LR1 is the router providing access to the outside, and 6LR2
is aware of 6LR1 as its default gateway. With this specification,
6LR2 registers P2:: to 6LR1 and 6LR1 installs a route to P2:: via
6LR2. This way, addresses that derive from P2:: can still be reached
via 6LR1 and then 6LR2. 6LR2 may then leverage ICMP Redirect
messages [RFC4861] to shorten the path between 6LR1 and the nodes
that own those addresses.
If P2 was delegated by 6LR1, then the expectation is that 6LR1
aggregates P1:: and P2:: in its advertisements to the outside, and
the is no need to set the R flag. But unless 6LR2 knows about such a
situation, e.g., through configuration, it is probably safer for 6LR2
to set the R flag requesting 6LR1 to advertise P2:: to the outside.
3.3. Hub Link
A hub link is a situation where stub links are deployed around a hub
like and interconnected by routers. Figure 3 depicts such a
situation, with one router 6LR1 serving the hub link and at least one
router like 6LR3 and 6LR3 providing connectivity from the stub links
to the hub link. In this example, say that the there is one prefix
on each link, P1:: on the hub link and P2::, P3::, etc. on the stub
links.
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+-----+ +-----+ +-----+ +-----+ +-----+
|P2::s| |P2::d| |P2::e| |P2::f| |P2::g|
+--+--+ +--+--+ +--+--+ +--+--+ +--+--+
| | | | |
----+----+----+---------+----STUB-+-LINK----+-----
|
+---+---+ +-------+ .
| P2::r | | | .. . .
| 6LR2 | | 6LR1 +--- . . ..
| P1::b | | P1::a | . ...
+---+---+ +---+---+ . ...
| |
-------+-+---------+--HUB-LINK--+-----+--
| | |
+---+---+ +--+--+ +--+--+
| P1::c | |P1::n| |P1::q|
| 6LR3 | +-----+ +-----+
| P3::m |
+---+---+
|
----+--+------+---------+----STUB-+-LINK----+-----
| | | | |
+--+--+ +--+--+ +--+--+ +--+--+ +--+--+
|P3::h| |P3::i| |P3::j| |P3::k| |P3::a|
+-----+ +-----+ +-----+ +-----+ +-----+
Figure 3: Hub and Stubs
As before, say that 6LR1 is the router providing access to the
outside, and 6LR2 is aware of 6LR1 as its default gateway. With this
specification, 6LR2 registers P2:: to 6LR1 and 6LR1 installs a route
to P2:: via 6LR2. This way, nodes on the stub link behind 6LR2 that
derive their addresses from P2:: can still be reached via 6LR1 and
then 6LR2. The same goes for 6LR3 and all other routers serving stub
links.
If P2 was delegated by 6LR1, then the expectation is that 6LR1
aggregates P1:: and P2:: in its advertisements to the outside, and
the is no need to set the R flag. But unless 6LR2 knows about such a
situation, e.g., through configuration, it is probably safer for 6LR2
to set the R flag requesting 6LR1 to advertise P2:: to the outside.
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4. Updating RFC 4861
[RFC4861] expects that the NS/NA exchange is for a unicast address,
which is indicated in the Target Address field of the ND message.
This specification Amends [RFC4861] by allowing to advertise a prefix
in the Target Address field when the NS or NA message is used for a
registration, per section 5.5 of [RFC8505]; in that case, the prefix
length is indicated in the EARO of the NS message, overloading the
field that is used in the NA response for the Status.
5. Extending RFC 7400
This specification Extends "6LoWPAN-GHC: Generic Header Compression
for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)"
[RFC7400] by defining a new capability bit for use in the 6CIO.
[RFC7400] was already extended by [RFC8505] for use in IPv6 ND
messages.
The new "Registration for prefixes Supported" (F) flag indicates to
the 6LN that the 6LR accepts IPv6 prefix registrations as specified
in this document and will ensure that packets for the addresses that
match this prefix will be routed to the 6LNs that registered the
prefix, and the route to the prefix will be redistributed if the R
flag is set to 1.
Figure 4 illustrates the X flag in its suggested position (7,
counting 0 to 15 in network order in the 16-bit array), to be
confirmed by IANA.
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 |F|X|A|D|L|B|P|E|G|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: New Capability Bit in the 6CIO
New Option Field:
X 1-bit flag: "Registration for prefixes Supported"
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6. Updating RFC 6550
[RFC6550] uses the Path Sequence in the Transit Information Option
(TIO) to retain only the freshest unicast route and remove stale
ones, e.g., in the case of mobility. [RFC9010] copies the TID from
the EARO into the Path Sequence, and the ROVR field into the
associated RPL Target Option (RTO). This way, it is possible to
identify both the registering node and the order of registration in
RPL for each individual advertisement, so the most recent path and
lifetime values are used.
[I-D.ietf-6lo-multicast-registration] requires the use of the ROVR
field as the indication of the origin of a Target advertisement in
the RPL DAO messages, as specified in section 6.1 of [RFC9010]. For
anycast and multicast advertisements (in NS or DAO messages),
multiple origins may subscribe to the same address, in which case the
multiple advertisements from the different or unknown origins are
merged by the common parent; in that case, the common parent becomes
the origin of the merged advertisements and uses its own ROVR value.
On the other hand, a parent that propagates an advertisement from a
single origin uses the original ROVR in the propagated RTO, as it
does for unicast address advertisements, so the origin is recognized
across multiple hops.
This specification Extends [RFC6550] to require that, for prefix
routes, the Path Sequence is used between and only between
advertisements for the same Target and from the same origin (i.e,
with the same ROVR value); in that case, only the freshest
advertisement is retained. But the freshness comparison cannot apply
if the origin is not determined (i.e., the origin did not support
this specification).
[RFC6550] uses the Path Lifetime in the TIO to indicate the remaining
time for which the advertisement is valid for unicast route
determination, and a Path Lifetime value of 0 invalidates that route.
[RFC9010] maps the Address Registration lifetime in the EARO and the
Path Lifetime in the TIO so they are comparable when both forms of
advertisements are received.
The RPL router that merges multiple advertisement for the same prefix
must use and advertise the longest remaining lifetime across all the
origins of the advertisements for that prefix. When the lifetime
expires, the router sends a no-path DAO (i.e. the lifetime is 0)
using the same value for ROVR value as for the previous
advertisements, that is either self or the single descendant that
advertised the Target.
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Note that the Registration Lifetime, TID and ROVR fields are also
placed in the EDAR message so the state created by EDAR is also
comparable with that created upon an NS(EARO) or a DAO message. For
simplicity the text below mentions only NS(EARO) but applies also to
EDAR.
7. Updating RFC 8505
7.1. New P field value
[I-D.ietf-6lo-multicast-registration] defines a P-field of 2 bits and
defines the values 0 to 2, leaving the value of 3 reserved. This
specification adds a new value to the P field to signal that the
Registered Address is a prefix. The receiver should install a route
to the prefix via the sender's address used as source address in the
NS(EARO) registration message.
This specification assigns the value of 3, resulting in the complete
tabel as follows:
+-------+--------------------------------------+
| Value | Meaning |
+-------+--------------------------------------+
| 0 | Registration for a Unicast Address |
+-------+--------------------------------------+
| 1 | Registration for a Multicast Address |
+-------+--------------------------------------+
| 2 | Registration for an Anycast Address |
+-------+--------------------------------------+
| 3 | Registration for a prefix |
+-------+--------------------------------------+
Table 1: P-field Values
7.2. New EARO Prefix Length Field and F Flag
Section 4.1 of [RFC8505] defines the EARO as an extension to the ARO
option defined in [RFC6775].
The Status Field that is used only when the EARO is placed in an NA
message. This specification repurposes that field to carry the
prefix length (plen) when the EARO is placed in an NS message as
illustrated in Figure 5. The plen is expressed as 7 bits and the
most significant bit of the field is reserved. A 7-bit value of 0 is
understood as a truncated 128, meaning that this registration is for
an address as opposed to a prefix. This approach is backward
compatible with [RFC8505] and spans both addresses and prefixes.
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This specification adds a new F flag to signal that the Registered
Prefix is topologically correct through the Registering Node. This
means that the Registering Node can relay packets that are sourced in
the Registered Prefix to the outside, and the packets will be not be
filtered by the application of [BCP38]. The receiver should forward
packets to the Registering Node address when the source address of
the packets derives from the Registered Prefix. Note that to avoid
loops, the receiver must be in the inside so packets sent by the
sender towards the outside may never reach the receiver. The notion
of inside and outside are administratively defined, e.g., inside is a
particular Layer-2 network such as an Ethernet fabric.
When the F flag is not set, the Registering Node owns the prefix and
will deliver packets to the destination if the destination address
derives from the prefix. Conversely, if the F flag is set, the
Registering Node will forward traffic which source address derives
from the Registered Prefix into a network location (e.g., to an ISP
Provider Edge) where this source address is topologically correct
(e.g., derives from a prefix assigned by that ISP). The F flag is
encoded in the most significant bit of the EARO status field when the
status field is used to transport a Prefix Length as shown in
Figure 5.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | P | I |R|T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
... Registration Ownership Verifier ...
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: EARO Option Format in NS messages
New and updated Option Fields:
PrefixLength 8-bit field: 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. 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.
F: 1-bit flag; set to 1 to indicate that the sender expects other
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routers to forward packets to self when the packets are sourced
with the registered prefix.
7.3. New EDAR Prefix Length Field
This specification adds the new value of 3 to the P field to signal
that the Registered Address is a prefix. When that is the case, the
prefix length is assumed to be less than 112 bits and the last 8 bits
are dedicated to the prefix length.
Figure 6 illustrates the EDAR message when the value of the P field
is 3.
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 |CodePfx|CodeSfx| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P=3| Reserved | TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
... Registration Ownership Verifier (ROVR) ...
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Prefix +
| |
+ (up to 112 bits, padded with 0s) +
| |
+ +-+-+-+-+-+-+-+-+
| | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: EDAR Message Format with P == 3
New and updated Option Fields:
Reserved 6-bit field: reserved, MUST be set to 0 and ignored by the
receiver
Prefix 15 bytes: up to 112 bits of prefix, padded with 0s
Prefix Length 1-bit flag: length of the prefix, in bits
7.4. Registering Extensions
With [RFC8505]:
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* A router that expects to reboot may send a final RA message, upon
which nodes should register elsewhere or redo the registration to
the same router upon reboot. In all other cases, a node reboot is
silent. When the node comes back to life, existing registration
state might be lost if it was not persisted, e.g., in persistent
memory.
* Only unicast addresses can be registered.
* The 6LN must register all its ULA and GUA with a NS(EARO).
* The 6LN may set the R flag in the EARO to obtain return
reachability services by the 6LR, e.g., through ND proxy
operations, or by injecting the route in a route-over subnet.
* the 6LR maintains a registration state per Registered Address,
including an NCE with the Link Layer Address (LLA) of the
Registered Node (the 6LN here).
This specification adds the following behavior, similar to that
introduced by [I-D.ietf-6lo-multicast-registration] for multicast
addresses:
* The operation for registering prefixes is similar as for addresses
from the perspective of the 6LN, but show important differences on
the router side, which maintains a separate state for each origin
and merges them in its own advertisements.
* The ARO Status indicating a "Registration Refresh Request" applies
to prefixes as well.
This status is used in asynchronous NA(EARO) messages to indicate
to peer 6LNs that they are requested to reregister all addresses
and prefixes that were previously registered to the originating
node. The NA message may be sent to a unicast or a multicast
link-scope address and should be contained within the L2 range
where nodes may effectively have registered/subscribed to this
router, e.g., a radio broadcast domain.
A device that wishes to refresh its state, e.g., upon reboot if it
may have lost some registration state, SHOULD send an asynchronous
NA(EARO) with this new status value. That asynchronous NA(ARO)
SHOULD be sent to the all-nodes link scope multicast address
(FF02::1) and Target MUST be set to the link local address that
was exposed previously by this node to accept registrations, and
the TID MUST be set to 0.
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In an unreliable environment, the multicast NA(EARO) message may
be resent in a fast sequence, in which case the TID must be
incremented each time. A 6LN that has recently processed the
NA(ARO) ignores the NA(EARO) with a newer TID received within the
duration of the fast sequence. That duration depends on the
environent and has to be configured. By default, it is of 10
seconds.
* Registration for prefixes is now supported. The value of 3 in the
P field of the EARO and the EDAR message signals when the
registration is for a prefix as opposed to an address. DAD for
prefixes and addresses becomes a prefix overlap match. Whether
overlapping addresses and prefixes may be registered is a network
policy decision and out of scope. The same prefix may be injected
twice (multiple routes) as long as they use the same value of the
ROVR.
Overlaps may be desirable. It may happen for instance that a
proxy registers a prefix while a host using an address from that
prefix also registers. It might also occur that an aggregated
prefix is owned as a catch all, and subdivised into subnets that
are allocated to and then registered by other nodes.
In case of an overlapping registration, the longest match wins,
meaning that if the network policy allows for overlapping
registrations, then the registration the routes are installed
towards the node that registered with the longest match, all the
way to /128.
* If the 6LR acts as a router to prefixes or owns the prefixes
entirely, it SHOULD register all those prefixes on all interface
from which it might be needed to relay traffic to that prefix, and
it MUST set the P field in the EARO to 3 for those prefixes.
* The 6LN MAY set the R flag in the EARO to request the 6LR to
redistribute the prefix on other links using a routing protocol.
The 6LR MUST NOT reregister that prefix to yet another router as
it may create a loop.
* The 6LR and the 6LBR are extended to accept more than one
registration for the same prefix, since multiple 6LNs may register
it. The Registration Ownership Verifier (ROVR) in the EARO
identifies uniquely a registration within the namespace of the
Registered Prefix.
* The 6LR MUST maintain a registration state per tuple (IPv6 prefix/
length, ROVR) for all registered prefix. It SHOULD notify the
6LBR with an EDAR message, unless it determined that the 6LBR is
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legacy and does not support this specification. In turn, the 6LBR
MUST maintain a registration state per tuple (IPv6 prefix, ROVR)
for all prefixes.
8. Updating RFC 9010
With [RFC9010]:
* The 6LR injects only unicast routes in RPL
* Upon a registration with the R flag set to 1 in the EARO, the 6LR
injects the address in the RPL unicast support.
* Upon receiving a packet directed to a unicast address for which it
has an active registration, the 6LR delivers the packet as a
unicast layer-2 frame to the LLA the nodes that registered the
unicast address.
This specification adds the following behavior:
* Upon a registration with the R flag set to 1 and the P field set
to 3 in the EARO, the 6LR injects the prefix in RPL using a prefix
RTO. The P field in the RTP MUST be set to 3.
* Upon receiving a packet directed to an address that derives from a
prefix for which it has at least one registration, the 6LR
delivers a copy of the packet as a unicast layer-2 frame to the
LLA of exactly one of the nodes that registered to that prefix,
using the longest match derivation to find the best 6LN.
9. Updating RFC 8928
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].
With [RFC8928], it is possible for a node to autoconfigure a pair of
public and private keys and use them to sign the registration of
addresses that are either autoconfigured or obtained through other
methods.
The first hop router (the 6LR) may then validate a registration and
perform source address validation on packets coming from the sender
node (the 6LN).
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Prefixes are not always owned by one node. Multiple nodes may
register the same prefix. In that context, the method specified in
[RFC8928] cannot be used with node-local autoconfigured keypairs
which protect a single ownership only.
For a prefix, as for an anycast or a multicast address, it is still
possible to leverage [RFC8928] to enforce the right to register. If
[RFC8928] is used, a keypair MUST be created and associated with the
prefix before the prefix is deployed, and a ROVR MUST be generated
from that keypair as specified in [RFC8928]. The prefix and the ROVR
MUST then be installed in the 6LBR at the first registration, or by
an external mechanism such as IPAM or DHCPv6 snooping prior to the
first registration. This way, the 6LBR can recognize the prefix on
the future registrations and validate the right to register based on
the ROVR.
The keypair MUST then be provisioned in each node that needs to
register the prefix or a prefix within, so the node can follow the
steps in [RFC8928] to register the prefix.
Upon a NA Message with the status set to 5 "Validation Requested",
the node that registered addresses or prefixes with use the longest
matching address or prefix and perform the proof of ownership based
on that longest match.
10. Security Considerations
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.
Section 9 leverages [RFC8928] to prevent an rogue node to register a
unicast address that it does not own. The mechanism could be
extended to anycast and multicast addresses if the values of the ROVR
they use is known in advance, but how this is done is not in scope
for this specification. One way would be to authorize in a advance
the ROVR of the valid users. A less preferred way could be to
synchronize the ROVR and TID values across the valid registering
nodes as a preshared key material.
In the latter case, it could be possible to update the keys
associated to a prefix in all the 6LNs, but the flow is not clearly
documented and may not complete in due time for all nodes in LLN use
cases. It may be simpler to install a all-new address with new keys
over a period of time, and switch the traffic to that address when
the migration is complete.
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11. Backward Compatibility
A legacy 6LN will not register prefixess and the service will be the
same when the network is upgraded. A legacy 6LR will not set the F
flag in the 6CIO and an upgraded 6LN will not register prefixes.
Upon an EDAR message, a legacy 6LBR may not realize that the address
being registered is anycast or multicast, and return that it is
duplicate in the EDAC status. The 6LR MUST ignore a duplicate status
in the EDAR for anycast and multicast addresses.
12. IANA Considerations
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. Also, the I Field is defined in [RFC9010] but
is missing from the registry, so the bit positions must be added for
completeness.
IANA is requested to make changes under the "Internet Control Message
Protocol version 6 (ICMPv6) Parameters" [IANA.ICMP] and the "Routing
Protocol for Low Power and Lossy Networks (RPL)" [IANA.RPL] registry
groupings, as follows:
12.1. Updated P-Field Registry
This specification updates the P field introduced in
[I-D.ietf-6lo-multicast-registration] to assign the value of 3, which
is the only remaining unasssigned value for the 2-bits field. To
that effect, IANA is requested to update the "P-field values"
registry under the heading "Internet Control Message Protocol version
6 (ICMPv6) Parameters" as indicated in Table 2:
+-------+---------------------------+-----------+
| Value | Meaning | Reference |
+-------+---------------------------+-----------+
| 3 | Registration for a prefix | This RFC |
+-------+---------------------------+-----------+
Table 2: New P-field value
12.2. New 6LoWPAN Capability Bit
IANA is requested to make an addition to the "6LoWPAN Capability
Bits" [IANA.ICMP.6CIO] registry under the heading "Internet Control
Message Protocol version 6 (ICMPv6) Parameters" as indicated in
Table 3:
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+----------------+--------------------------+-----------+
| Capability Bit | Meaning | Reference |
+----------------+--------------------------+-----------+
| 7 (suggested) | F flag: Registration for | This RFC |
| | prefixes Supported (F) | |
+----------------+--------------------------+-----------+
Table 3: New 6LoWPAN Capability Bit
13. Acknowledgments
14. 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>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[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>.
[RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
2014, <https://www.rfc-editor.org/info/rfc7400>.
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[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>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[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>.
[RFC9010] Thubert, P., Ed. and M. Richardson, "Routing for RPL
(Routing Protocol for Low-Power and Lossy Networks)
Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021,
<https://www.rfc-editor.org/info/rfc9010>.
[IANA.ICMP]
IANA, "IANA Registry for ICMPv6", IANA,
https://www.iana.org/assignments/icmpv6-parameters/
icmpv6-parameters.xhtml.
[IANA.ICMP.6CIO]
IANA, "IANA Registry for the 6LoWPAN Capability Bits",
IANA, https://www.iana.org/assignments/icmpv6-parameters/
icmpv6-parameters.xhtml#sixlowpan-capability-bits.
[IANA.RPL] IANA, "IANA Registry for the RPL",
IANA, https://www.iana.org/assignments/rpl/rpl.xhtml.
15. Informative References
[BCP38] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <https://www.rfc-editor.org/info/rfc2827>.
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[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
<https://www.rfc-editor.org/info/rfc4919>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC9008] Robles, M.I., Richardson, M., and P. Thubert, "Using RPI
Option Type, Routing Header for Source Routes, and IPv6-
in-IPv6 Encapsulation in the RPL Data Plane", RFC 9008,
DOI 10.17487/RFC9008, April 2021,
<https://www.rfc-editor.org/info/rfc9008>.
[I-D.kuehlewind-update-tag]
Kühlewind, M. and S. Krishnan, "Definition of new tags for
relations between RFCs", Work in Progress, Internet-Draft,
draft-kuehlewind-update-tag-04, 12 July 2021,
<https://datatracker.ietf.org/doc/html/draft-kuehlewind-
update-tag-04>.
[I-D.heile-lpwan-wisun-overview]
Robert, H., Liu, B. R., Zhang, M., and C. E. Perkins, "Wi-
SUN FAN Overview", Work in Progress, Internet-Draft,
draft-heile-lpwan-wisun-overview-00, 3 July 2017,
<https://datatracker.ietf.org/doc/html/draft-heile-lpwan-
wisun-overview-00>.
[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-05, 20
November 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-6man-ipv6-over-wireless-05>.
[I-D.ietf-6lo-multicast-registration]
Thubert, P., "IPv6 Neighbor Discovery Multicast and
Anycast Address Listener Subscription", Work in Progress,
Internet-Draft, draft-ietf-6lo-multicast-registration-16,
10 November 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-6lo-multicast-registration-16>.
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[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".
[IEEE80211]
IEEE standard for Information Technology, "IEEE Standard
802.11 - IEEE Standard for Information Technology -
Telecommunications and information exchange between
systems Local and metropolitan area networks - Specific
requirements - Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) Specifications.",
<https://ieeexplore.ieee.org/document/9363693>.
[IEEE802151]
IEEE standard for Information Technology, "IEEE Standard
for Information Technology - Telecommunications and
Information Exchange Between Systems - Local and
Metropolitan Area Networks - Specific Requirements. - Part
15.1: Wireless Medium Access Control (MAC) and Physical
Layer (PHY) Specifications for Wireless Personal Area
Networks (WPANs)".
Author's Address
Pascal Thubert (editor)
06330 Roquefort-les-Pins
France
Email: pascal.thubert@gmail.com
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