Routing for RPL Leaves
draft-ietf-roll-unaware-leaves-09
The information below is for an old version of the document.
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| Authors | Pascal Thubert , Michael Richardson | ||
| Last updated | 2020-01-27 (Latest revision 2019-12-16) | ||
| Replaces | draft-thubert-roll-unaware-leaves | ||
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draft-ietf-roll-unaware-leaves-09
ROLL P. Thubert, Ed.
Internet-Draft Cisco Systems
Updates: 6550, 8505 (if approved) M. Richardson
Intended status: Standards Track Sandelman
Expires: 30 July 2020 27 January 2020
Routing for RPL Leaves
draft-ietf-roll-unaware-leaves-09
Abstract
This specification extends RFC6550 and RFC8505 to provide unicast and
multicast routing services in a RPL domain to 6LNs that are plain
Hosts and do not participate to RPL, and enables the RPL Root to
proxy the EDAR/EDAC flow on behalf of the RULs and RANs in its DODAG.
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 30 July 2020.
Copyright Notice
Copyright (c) 2020 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 Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. References . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 5
3. 6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . . 7
3.1. RFC 6775 . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. RFC 8505 Extended ARO . . . . . . . . . . . . . . . . . . 7
3.2.1. R Flag . . . . . . . . . . . . . . . . . . . . . . . 8
3.2.2. TID, I Field and Opaque Fields . . . . . . . . . . . 8
3.2.3. ROVR . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. RFC 8505 Extended DAR/DAC . . . . . . . . . . . . . . . . 9
3.3.1. RFC 7400 Capability Indication Option . . . . . . . . 9
4. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 10
5. Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . . 11
6. Requirements on the RPL-Unware Leaf . . . . . . . . . . . . . 11
6.1. Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . . 11
6.2. External Routes and RPL Artifacts . . . . . . . . . . . . 12
6.2.1. Support of the HbH Header . . . . . . . . . . . . . . 13
6.2.2. Support of the Routing Header . . . . . . . . . . . . 13
6.2.3. Support of IPv6 Encapsulation . . . . . . . . . . . . 13
7. Updated RPL Status . . . . . . . . . . . . . . . . . . . . . 13
8. Updated RPL Target option . . . . . . . . . . . . . . . . . . 14
9. Protocol Operations for Unicast Addresses . . . . . . . . . . 15
9.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 15
9.1.1. In RPL Non-Storing-Mode . . . . . . . . . . . . . . . 16
9.1.2. In RPL Storing-Mode . . . . . . . . . . . . . . . . . 19
9.2. Detailed Operation . . . . . . . . . . . . . . . . . . . 19
9.2.1. By the 6LN . . . . . . . . . . . . . . . . . . . . . 20
9.2.2. By the 6LR . . . . . . . . . . . . . . . . . . . . . 21
9.2.3. By the RPL Root . . . . . . . . . . . . . . . . . . . 23
9.2.4. By the 6LBR . . . . . . . . . . . . . . . . . . . . . 24
10. Protocol Operations for Multicast Addresses . . . . . . . . . 24
11. Security Considerations . . . . . . . . . . . . . . . . . . . 26
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
12.1. New DODAG Configuration Option Flag . . . . . . . . . . 27
12.2. RPL Target Option Flags . . . . . . . . . . . . . . . . 27
12.3. New Subregistry for the RPL Non-Rejection Status
values . . . . . . . . . . . . . . . . . . . . . . . . . 27
12.4. New Subregistry for the RPL Rejection Status values . . 27
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
14. Normative References . . . . . . . . . . . . . . . . . . . . 28
15. Informative References . . . . . . . . . . . . . . . . . . . 30
Appendix A. Example Compression . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
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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 IETF produced the "Routing Protocol for Low Power and Lossy
Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services
within such constraints. RPL belongs to the class of Distance-Vector
protocol, which, compared to link-state protocols, limits the amount
of topological knowledge that needs to be installed and maintained in
each node.
In order to operate in constrained networks, RPL allows a routing
stretch (see [RFC6687]), whereby routing is only performed along an
acyclic graph optimized to reach a Root node, as opposed to straight
along a shortest path between 2 peers, whatever that would mean in a
given 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 a any-to-any shortest path protocol. Finally,
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.
In order to cope with lossy transmissions, RPL forms Direction-
Oriented Directed Acyclic Graphs (DODAGs) using DODAG Information
Solicitation (DIS) and DODAG Information Object (DIO) messages. For
most of the nodes, though not all, a DODAG provides multiple
forwarding solutions towards the Root of the topology via so-called
parents. RPL is designed to adapt to fuzzy connectivity, whereby the
physical topology cannot be expected to reach a stable state, with a
lazy control that creates routes proactively but only fixes them when
they are used by actual traffic.
The result is that RPL provides reachability for most of the LLN
nodes, most of the time, but may not really converge in the classical
sense. RPL provides unicast and multicast routing services back to
RPL-Aware nodes (RANs).
A RAN will inject routes to itself using Destination Advertisement
Object (DAO) messages sent to either parent-nodes in Storing Mode or
to the Root indicating their parent in Non-Storing Mode. This
process effectively forms a DODAG back to the device that is a subset
of the DODAG to the Root with all links reversed.
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RPL can be deployed as an extension to IPv6 Neighbor Discovery (ND)
[RFC4861][RFC4862] and 6LoWPAN ND [RFC6775][RFC8505] to maintain
reachability within a Non-Broadcast Multi-Access (NBMA) subnet. In
that mode, some nodes may act as Routers and participate to the
forwarding operations whereas others will only terminate packets,
acting as Hosts in the data-plane. In [RFC6550] terms, a Host that
is reachable over the RPL network is called a Leaf.
"When to use RFC 6553, 6554 and IPv6-in-IPv6" [USEofRPLinfo]
introduces the term RPL-Aware-Leaf (RAL) for a Leaf that injects
routes in RPL to manage the reachability of its own IPv6 addresses.
In contrast, a RPL-Unaware Leaf (RUL) designates a Leaf does not
participate to RPL at all. A RUL is a plain Host that needs an
interface to its RPL Router to obtain routing services over the LLN.
This specification enables a RUL that is a 6LoWPAN Node (6LN) to
announce itself as a Host to its 6LoWPAN Router (6LR) in the 6LoWPAN
ND Address Address Registration, and to request that the 6LR injects
the relevant routing information for the Registered Address in the
RPL domain on its behalf. The unicast packet forwarding operation by
the 6LR serving a 6LN that is a RPL Leaf is described in
[USEofRPLinfo].
Examples of routing-agnostic 6LN may include lightly-powered sensors
such as window smash sensor (alarm system), and kinetically powered
light switches. Other application of this specification may include
a smart grid network that controls appliances - such as washing
machines or the heating system - in the home. Appliances may not
participate to the RPL protocol operated in the Smartgrid network but
can still receive control packet from the Smartgrid.
2. Terminology
2.1. BCP 14
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.
2.2. References
The Terminology used in this document is consistent with and
incorporates that described in Terms Used in Routing for Low-Power
and Lossy Networks (LLNs). [RFC7102].
A glossary of classical 6LoWPAN acronyms is given in Section 2.3.
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The term "byte" is used in its now customary sense as a synonym for
"octet".
"RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by
a RPLInstanceID)are defined in "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks" [RFC6550] . The DODAG Information
Solicitation (DIS), Destination Advertisement Object (DAO) and DODAG
Information Object (DIO) messages are also specified in [RFC6550].
The Destination Cleanup Object (DCO) message is defined in
[EFFICIENT-NPDAO].
This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware
Leaf (RAL) consistently with [USEofRPLinfo]. The term RPL-Aware Node
(RAN) is introduced to refer to a node that is either a RAL or a RPL
Router. As opposed to a RUL, a RAN manages the reachability of its
addresses and prefixes by injecting them in RPL by itself.
Other terms in use in LLNs are found in Terminology for
Constrained-Node Networks [RFC7228].
Readers are expected to be familiar with all the terms and concepts
that are discussed in
* "Neighbor Discovery for IP version 6" [RFC4861],
* "IPv6 Stateless Address Autoconfiguration" [RFC4862],
* "Problem Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606],
* "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals" [RFC4919],
* "Neighbor Discovery Optimization for Low-power and Lossy Networks"
[RFC6775], and
* "Registration Extensions for IPv6 over Low-Power Wireless Personal
Area Network (6LoWPAN) Neighbor Discovery" [RFC8505].
2.3. Glossary
This document often uses the following acronyms:
AR: Address Resolution (aka Address Lookup)
6CIO: 6LoWPAN Capability Indication Option
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6LN: 6LoWPAN Node (a Low Power Host or Router)
6LR: 6LoWPAN Router
(E)ARO: (Extended) Address Registration Option
(E)DAR: (Extended) Duplicate Address Request
(E)DAC: (Extended) Duplicate Address Confirmation
DAD: Duplicate Address Detection
DAO: Destination Advertisement Object (a RPL message)
DCO: Destination Cleanup Object (a RPL message)
DIS: DODAG Information Solicitation (a RPL message)
DIO: DODAG Information Object (a RPL message)
DODAG: Destination-Oriented Directed Acyclic Graph
LLN: Low-Power and Lossy Network
NA: Neighbor Advertisement
NCE: Neighbor Cache Entry
ND: Neighbor Discovery
NS: Neighbor Solicitation
RA: Router Advertisement
ROVR: Registration Ownership Verifier
RPI: RPL Packet Information (the abstract information RPL places in
data packets as the RPL Option within the IPv6 Hop-By-Hop Header,
and by extension the RPL Option itself)
RAL: RPL-Aware Leaf
RAN: RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf)
RUL: RPL-Unaware Leaf
TID: Transaction ID (a sequence counter in the EARO)
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3. 6LoWPAN Neighbor Discovery
3.1. RFC 6775
The "IPv6 Neighbor Discovery (IPv6 ND) Protocol" suite [RFC4861]
[RFC4862] was defined for transit media such a Ethernet, and relies
heavily on multicast operations for address discovery and duplicate
address detection (DAD). "Neighbor Discovery Optimizations for
6LoWPAN networks" [RFC6775] (6LoWPAN ND) adapts IPv6 ND for
operations over energy-constrained LLNs. In particular, 6LoWPAN ND
introduces a unicast Host Registration mechanism that contributes to
reducing the use of multicast messages that are present in the
classical IPv6 ND protocol.
6LoWPAN ND defines a new Address Registration Option (ARO) that is
carried in the unicast Neighbor Solicitation (NS) and Neighbor
Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the
6LoWPAN Router (6LR). 6LoWPAN ND also defines the Duplicate Address
Request (DAR) and Duplicate Address Confirmation (DAC) messages
between the 6LR and the 6LoWPAN Border Router (6LBR). In an LLN, the
6LBR is the central repository of all the Registered Addresses in its
domain.
The main functions of [RFC6775] are to proactively establish the
Neighbor Cache Entry in the 6LR and to avoid address duplication.
3.2. RFC 8505 Extended ARO
"Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
updates the behavior of RFC 6775 to enable a generic Address
Registration to services such as routing and ND proxy, and defines
the Extended Address Registration Option (EARO) as shown in Figure 1:
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 | Status | Opaque |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rsvd | I |R|T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
... Registration Ownership Verifier ...
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: EARO Option Format
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3.2.1. R Flag
[RFC8505] introduces the "R" flag in the EARO. The Registering Node
sets the "R" flag to indicate whether the 6LR should ensure
reachability for the Registered Address, e.g., by means of routing or
proxying ND. If the "R" flag is not set, then the Registering Node
is expected to be a RAN that handles the reachability of the
Registered Address by itself.
This document specifies how the "R" flag is used in the context of
RPL. A 6LN operates as a RUL for an IPv6 address iff it sets the "R"
flag in the EARO used to register the address. The RPL Router
generates a DAO message for the Registered Address upon an NS(EARO)
iff the "R" flag in the EARO is set. Conversely, this document
specifies the behavior of a RPL Router acting as 6LR that depends on
the setting of the "R" flag in the EARO.
3.2.2. TID, I Field and Opaque Fields
The EARO also includes a sequence counter called Transaction ID
(TID), which maps to the Path Sequence Field found in Transit Options
in RPL DAO messages. This is the reason why the support of [RFC8505]
by the RUL as opposed to only [RFC6775] is a prerequisite for this
specification (more in Section 6.1). The EARO also transports an
Opaque field and an "I" field that describes what the Opaque field
transports and how to use it. Section 9.2.1 specifies the use of the
"I" field and of the Opaque field by a RUL.
3.2.3. ROVR
Section 5.3. of [RFC8505] introduces the Registration Ownership
Verifier (ROVR) field of variable length from 64 to 256 bits. The
ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was
used to identify uniquely an Address Registration with the Link-Layer
address of the owner, but provided no protection against spoofing.
"Address Protected Neighbor Discovery for Low-power and Lossy
Networks" [AP-ND] leverages the ROVR field as a cryptographic proof
of ownership to prevent a rogue third party from misusing the
address. [AP-ND] adds a challenge/response exchange to the [RFC8505]
Address Registration and enables Source Address Validation by a 6LR
that will drop packets with a spoofed address.
This specification does not address how the protection by [AP-ND]
could be extended to RPL. On the other hand, it adds the ROVR to the
DAO to build the proxied EDAR at the Root, which means that nodes
that are aware of the Host route to the 6LN are now aware of the
associated ROVR as well.
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3.3. RFC 8505 Extended DAR/DAC
[RFC8505] updates the periodic DAR/DAC exchange that takes place
between the 6LR and the 6LBR using Extended DAR/DAC messages. The
Extended Duplicate Address messages can carry a ROVR field of
variable size. The periodic EDAR/EDAC exchange is triggered by a
NS(EARO) message and is intended to create and then refresh the
corresponding state in the 6LBR for a lifetime that is indicated by
the 6LN. Conversely, RPL [RFC6550] specifies a periodic DAO from the
6LN all the way to the Root that maintains the routing state in the
RPL network for a lifetime that is indicated by the source of the
DAO. This means that there are two periodic messages that traverse
the whole network to indicate that an address is still reachable, one
to the Root and one to the 6LBR.
This specification saves the support of RPL in a 6LN called a RUL and
avoids an extraneous periodic flow across the LLN. The RUL only
needs to perform a [RFC8505] Address Registration to the 6LR. The
6LR turns it into a DAO message to the Root on behalf of the RUL.
Upon the new DAO, the Root proxies the EDAR exchange to the 6LBR on
behalf of the 6LR. This is illustrated in Figure 6.
3.3.1. RFC 7400 Capability Indication Option
"6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the
6LoWPAN Capability Indication Option (6CIO) that enables a node to
expose its capabilities in Router Advertisement (RA) Messages.
[RFC8505] defines a number of bits in the 6CIO, in particular:
L: Node is a 6LR.
E: Node is an IPv6 ND Registrar -- i.e., it supports registrations
based on EARO.
P: Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that
also provides reachability services for the Registered Addres
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 |D|L|B|P|E|G|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: 6CIO flags
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A RUL can get reachability services from a 6LR if and only if the L,
P and E flags are set in a 6CIO originated by the 6LR. A 6LR that
can provide reachability services for a RUL node in a RPL network as
specified in this document sets the L, P and E flags.
4. Updating RFC 6550
This document specifies a new behavior whereby a 6LR injects DAO
messages for unicast addresses (see Section 9) and multicast
addresses (see Section 10) on behalf of leaves that are not aware of
RPL. The Targets are exposed as External addresses. An IP-in-IP
encapsulation that terminates at the border 6LR is used to remove RPL
artifacts and compression techniques that may not be processed
correctly outside of the RPL domain.
This document also synchronizes the liveness monitoring at the Root
and the 6LBR. A same value of lifetime is used for both, and a
single heartbeat message, the RPL DAO, traverses the RPL network. A
new behavior is introduced whereby the RPL Root proxies the EDAR
message to the 6LBR on behalf of the 6LR (more in Section 5), for any
6LN, RUL or RAN.
RPL defines a configuration option that is registered to IANA in
section 20.14. of [RFC6550]. This specification defines a new flag
"Root Proxies EDAR/EDAC" (P) that is encoded in one of the reserved
control bits in the option. The new flag is set to indicate that the
Root performs the proxy operation and that all nodes in the network
must refrain from renewing the 6LBR state directly. The bit position
of the "P" flag is indicated in Section 12.1.
Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP)
in the DIO Base Object. The new "P" flag is defined only for MOP
value between 0 to 6. For a MOP value of 7 or above, the flag MAY
indicate something different and MUST NOT be interpreted as "Root
Proxies EDAR/EDAC" unless the specification of the MOP indicates to
do so.
The RPL Status defined in section 6.5.1. of [RFC6550] for use in the
DAO-Ack message is extended to be used in the DCO messages
[EFFICIENT-NPDAO] as well. Furthermore, this specification enables
to use a RPL Status to transport the IPv6 ND Status defined for use
in the EARO, more in Section 7.
Section 6.7. of [RFC6550] introduces the RPL Control Message Options
such as the RPL Target Option that can be included in a RPL Control
Message such as the DAO. Section 8 updates the RPL Target Option to
optionally transport the ROVR used in the IPv6 Registration (see
Section 3.2.3) so the RPL Root can generate a full EDAR Message.
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5. Updating RFC 8505
This document updates [RFC8505] to introduce a keep-alive EDAR
message and a keep-alive NS(EARO) message. The keep-alive messages
are used for backward compatibility, when the DAO does not transport
a ROVR as specified in Section 8. The keep-alive messages have a
zero ROVR field and can only be used to refresh a pre-existing state
associated to the Registered Address. More specifically, a keep-
alive message can only increase the lifetime and/or increment the TID
of the existing state in a 6LBR.
Upon the renewal of a 6LoWPAN ND Address Registration, this
specification changes the behavior of a RPL Router acting as 6LR for
the Address Registration as follows. If the Root indicates the
capability to proxy the EDAR/EDAC exchange to the 6LBR then the 6LR
refrains from sending an EDAR message; if the Root is separated from
the 6LBR, the Root regenerates the EDAR message to the 6LBR upon a
DAO message that signals the liveliness of the Address.
6. Requirements on the RPL-Unware Leaf
This document provides RPL routing for a RUL, that is a 6LN acting as
an IPv6 Host and not aware of RPL. Still, a minimal RPL-independent
functionality is required from the RUL in order to obtain routing
services from the 6LR.
6.1. Support of 6LoWPAN ND
In order to obtain routing services from a 6LR, a RUL MUST implement
[RFC8505] and set the "R" flag in the EARO option. The RUL MAY
request routing services from a 6LR if and only if the L, R and E
flags are all set in the 6CIO [RFC7400] originated by the 6LR.
The RUL MUST register to all the 6LRs from which it requests routing
services. The Address Registrations SHOULD be performed in a rapid
sequence, using the exact same EARO for a same Address. Gaps between
the Address Registrations will invalidate some of the routes till the
Address Registration finally shows on those routes as well.
[RFC8505] introduces error Status values in the NA(EARO) which can be
received synchronously upon an NS(EARO) or asynchronously. The RUL
MUST support both cases and refrain from using the Registered Address
as specified by [RFC8505] depending on the Status value.
A RUL SHOULD support [AP-ND] to protect the ownership of its
addresses.
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6.2. External Routes and RPL Artifacts
Section 4.1. of [USEofRPLinfo] provides a set of rules that MUST be
followed when forwarding packets over an external route:
RPL data packets are often encapsulated using IP-in-IP and in Non-
Storing Mode, packets going down will carry an SRH as well. RPL data
packets also typically carry a Hop-by-Hop Header to transport a RPL
Packet Information (RPI) [RFC6550]. These additional headers are
called RPL artifacts.
When IP-in-IP is used and the outer headers terminate at a 6LR down
the path (see Figure 10 for the compressed format in Storing Mode),
then the 6LR decapsulates the IP-in-IP and the packet that is
forwarded to the external destination is free of RPL artifacts - but
possibly an RPI if packet was generated by a RAN in the same RPL
domain as the destination RUL.
Non-Storing Mode DAO messages are used to signal external routes to
the Root, even if the DODAG is operated in Storing Mode. This
enables to advertise the 6LR that injects the route for use as tunnel
endpoint in the data path.
For all external routes, the Root should use an IP-in-IP tunnel to
that 6LR, with the RPL artifacts in the outer header to be stripped
by the 6LR. The IP-in-IP encapsulation may be avoided in Storing
Mode if the path to the external destination beyond the 6LR is known
to handle or ignore the RPL artifacts properly [RFC8200].
A RUL is an example of a destination that is reachable via an
external (Host) route for which IP-in-IP tunneling may be avoided as
it ignores the RPI and the consumed SRH artifacts. The use of non-
Storing Mode signaling in Storing Mode and the associated IP-in-IP
encapsulation are transparent to intermediate Routers that only see
packets back and forth between the Root and the 6LR and do not need a
special support for external routes.
The RUL may not support IP-in-IP tunneling [RFC8504], so if IP-in-IP
is used, and unless the Root as a better knowledge, the tunnel should
terminate at the 6LR that injected the external route to the RUL.
Additionally, the RUL is not expected to support the compression
method defined in [RFC8138]. The 6LR that injected the route MUST
uncompress the packet before forwarding over an external route, even
when delivering to a RUL, even when it is not the destination in the
outer header of the incoming packet, unless configured to do
otherwise.
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6.2.1. Support of the HbH Header
A RUL is expected to process an unknown Option Type in a Hop-by-Hop
Header as prescribed by section 4.2 of [RFC8200]. This means in
particular that an RPI with an Option Type of 0x23 [USEofRPLinfo] is
ignored when not understood.
6.2.2. Support of the Routing Header
A RUL is expected to process an unknown Routing Header Type as
prescribed by section 4.4 of [RFC8200]. This means in particular
that Routing Header with a Routing Type of 3 [RFC6553] is ignored
when the Segments Left is zero, and dropped otherwise.
6.2.3. Support of IPv6 Encapsulation
Section 2.1 of [USEofRPLinfo] sets the rules for forwarding IP-in-IP
either to the final 6LN or to a parent 6LR. In order to enable IP-
in-IP to the 6LN in Non-Storing Mode, the 6LN must be able to
decapsulate the tunneled packet and either drop the inner packet if
it is not the final destination, or pass it to the upper layer for
further processing. Unless it is aware that the RUL can handle IP-
in-IP properly, the Root that encapsulates a packet to a RUL
terminates the IP-in-IP tunnel at the parent 6LR . For that reason,
it is beneficial but not necessary for a RUL to support IP-in-IP.
7. Updated RPL Status
The RPL Status is defined in section 6.5.1. of [RFC6550] for use in
the DAO-Ack message and values are assigned as follows:
+---------+--------------------------------+
| Range | Meaning |
+=========+================================+
| 0 | Success/Unqualified acceptance |
+---------+--------------------------------+
| 1-127 | Not an outright rejection |
+---------+--------------------------------+
| 128-255 | Rejection |
+---------+--------------------------------+
Table 1: RPL Status per RFC 6550
This specification extends the scope of the RPL Status to be used in
RPL DCO messages. Furthermore, this specification enables to carry
the IPv6 ND Status values defined for use in the EARO and initially
listed in table 1 of [RFC8505] in a RPL Status. Only EARO Status
values in the range 0-63 can be transported.
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The resulting RPL Status is as follows:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|E|A| Value |
+-+-+-+-+-+-+-+-+
Figure 3: RPL Status Format
RPL Status subfields:
E: 1-bit flag. Set to indicate a rejection. When not set, a value
of 0 indicates Success/Unqualified acceptance and other values
indicate "not an outright rejection" as per RFC 6550.
A: 1-bit flag. Indicates the type of the Status value.
Status Value: 6-bit unsigned integer. If the 'A' flag is set this
field transports a Status value defined for IPv6 ND EARO. When
the 'A' flag is not set, the Status value is defined in a RPL
extension.
When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a DAC
message, the RPL Root MUST copy the ARO Status unchanged in a RPL
Status with the 'A' bit set. Conversely the 6LR MUST copy the value
of the RPL Status unchanged in the EARO of an NA message that is
built upon a RPL Status with the 'A' bit set in a DCO or a DAO-ACK
message.
8. Updated RPL Target option
This specification updates the RPL Target option to transport the
ROVR as illustrated in Figure 4. This enables the RPL Root to
generate a full EDAR Message as opposed to a keep-alive EDAR that has
restricted properties.
The Target Prefix MUST be aligned to the next 4-byte boundary after
the size indicated by the Prefix Length. if necessary it is padded
with zeros. The size of the ROVR is indicated in a new ROVR Type
field that is encoded to map the CodePfx in the EDAR message (see
section 4.2 of [RFC8505]).
With this specification the ROVR is the remainder of the RPL Target
Option. The format is backward compatible with the Target Option in
[RFC6550] and SHOULD be used as a replacement.
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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 = 0x05 | Option Length |ROVRsz | Flags | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Target Prefix (Variable Length) |
. Aligned to 4-byte boundary .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
... Registration Ownership Verifier (ROVR) ...
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Updated Target Option
New fields:
ROVRsz: Indicates the Size of the ROVR. It MAY be 1, 2, 3, or 4,
denoting a ROVR size of 64, 128, 192, or 256 bits, respectively.
Registration Ownership Verifier (ROVR): This is the same field as in
the EARO, see [RFC8505]
9. Protocol Operations for Unicast Addresses
The description below assumes that the Root sets the "P" flag in the
DODAG Configuration Option and performs the EDAR proxy operation.
9.1. General Flow
This specification enables to save the exchange of Extended Duplicate
Address messages, EDAR and EDAC, from a 6LN all the way to the 6LBR
across a RPL mesh, for the sole purpose of refreshing an existing
state in the 6LBR. Instead, the EDAR/EDAC exchange is proxied by the
RPL Root upon a DAO message that refreshes the RPL routing state.
To achieve this, the lifetimes and sequence counters in 6LoWPAN ND
and RPL are aligned. In other words, the Path Sequence and the Path
Lifetime in the DAO message are taken from the Transaction ID and the
Address Registration lifetime in the NS(EARO) message from the 6LN.
In that flow, the RPL Root acts as a proxy to refresh the state in
the 6LBR. The proxy operation applies to both RUL and RAN. This
means that in a RPL network where the function is enabled, refreshing
the state in the 6LBR is the responsibility of the Root.
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Consequently, only addresses that are injected in RPL will be kept
alive by the RPL Root.
In a same fashion, if an additional routing protocol is deployed on a
same network, that additional routing protocol may need to handle the
keep alive procedure for the addresses that it serves.
On the first Address Registration, illustrated in Figure 5 and
Figure 7 for RPL Non-Storing and Storing Mode respectively, the
Extended Duplicate Address exchange takes place as prescribed by
[RFC8505]. Any of the functions 6LR, Root and 6LBR might be
collapsed in a single node.
When successful, the flow creates a Neighbor Cache Entry (NCE) in the
6LR, and the 6LR injects the Registered Address in RPL using DAO/DAO-
ACK exchanges all the way to the RPL DODAG Root. The protocol does
not carry a specific information that the Extended Duplicate Address
messages were already exchanged, so the Root proxies them anyway.
9.1.1. In RPL Non-Storing-Mode
In Non-Storing Mode, the DAO message flow can be nested within the
Address Registration flow as illustrated in Figure 5 and it is
possible to carry information such as an updated lifetime from the
6LBR all the way back to the 6LN.
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6LN 6LR Root 6LBR
| | | |
| NS(EARO) | | |
|--------------->| |
| | Extended DAR |
| |--------------------------------->|
| | |
| | Extended DAC |
| |<---------------------------------|
| | DAO | |
| |------------->| |
| | | (keep-alive) EDAR |
| | |------------------>|
| | | EDAC |
| | |<------------------|
| | DAO-ACK | |
| |<-------------| |
| NA(EARO) | | |
|<---------------| | |
| | | |
(in case if an Error not reported in DAO-ACK)
| | | |
| | DCO | |
| |<-------------| |
| NA(EARO) | | |
|<---------------| | |
| | | |
Figure 5: First Registration Flow in Non-Storing Mode
An Address re-Registration is performed by the 6LN to maintain the
NCE in the 6LR alive before lifetime expires. Upon an Address re-
Registration, as illustrated in Figure 6, the 6LR redistributes the
Registered Address NS(EARO) in RPL.
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6LN 6LR Root 6LBR
| | | |
| NS(EARO) | | |
|--------------->| |
| | DAO | |
| |------------->| |
| | | (keep-alive) EDAR |
| | |------------------>|
| | | EDAC |
| | |<------------------|
| | DAO-ACK | |
| |<-------------| |
| NA(EARO) | | |
|<---------------| | |
Figure 6: Next Registration Flow in Non-Storing Mode
This causes the RPL DODAG Root to refresh the state in the 6LBR with
an EDAC message or a keep-alive EDAC if the ROVR is not indicated in
the Target Option. In any case, the EDAC message sent in response by
the 6LBR contains the actual value of the ROVR field for that Address
Registration. In case of an error on the proxied EDAR flow, the
error SHOULD be returned in the DAO-ACK - if one was requested -
using a RPL Status with the 'A' flag set that imbeds a 6LoWPAN Status
value as discussed in Section 7.
If the Root could not return the negative Status in the DAO-ACK then
it sends an asynchronous Destination Cleanup Object (DCO) message
[EFFICIENT-NPDAO] to the 6LR placing the negative Status in the RPL
Status with the 'A' flag set. Note that if both are used in a short
interval of time, the DAO-ACK and DCO messages are not guaranteed to
arrive in the same order at the 6LR.
The 6LR may still receive a requested DAO-ACK even after it received
a DCO, but the negative Status in the DCO supercedes a positive
Status in the DAO-ACK regardless of the order in which they are
received. Upon the DAO-ACK - or the DCO if it arrives first - the
6LR responds to the RUL with a NA(EARO). If the RPL Status has the
'A' flag set, then the ND Status is extracted and passed in the EARO;
else, if the 'E' flag is set, indicating a rejection, then the status
4 "Removed" is used; else, the ND Status of 0 indicating "Success" is
used.
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9.1.2. In RPL Storing-Mode
In RPL Storing Mode, the DAO-ACK is optional. When it is used, it is
generated by the RPL parent, which does not need to wait for the
grand-parent to send the acknowledgement. A successful DAO-ACK is
not a guarantee that the DAO has yet reached the Root or that the
keep-alive EDAR has succeeded.
6LN 6LR 6LR Root 6LBR
| | | | |
| NS(EARO) | | | |
|-------------->| | | |
| NA(EARO) | | | |
|<--------------| | | |
| | | | |
| | DAO | | |
| |-------------->| | |
| | DAO-ACK | | |
| |<--------------| | |
| | | | |
| | | DAO | |
| | |-------------->| |
| | | DAO-ACK | |
| | |<--------------| |
| | | | |
| | | | keep-alive EDAR |
| | | |---------------->|
| | | | EDAC(ROVR) |
| | | |<----------------|
| | | | |
(in case if an Error)
| | | | |
| | DCO | |
| |<------------------------------| |
| NA(EARO) | | | |
|<--------------| | | |
| | | | |
Figure 7: Next Registration Flow in Storing Mode
If the keep alive fails, the path is cleaned up asynchronously using
a DCO message [EFFICIENT-NPDAO] as illustrated in Figure 7 and
described in further details in Section 9.2.3.
9.2. Detailed Operation
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9.2.1. By the 6LN
This specification does not alter the operation of a 6LoWPAN ND-
compliant 6LN, and a RUL is expected to operate as follows:
* The 6LN obtains an IPv6 global address, for instance using
autoconfiguration [RFC4862] based on a Prefix Information Option
(PIO) [RFC4861] found in a Router Advertisement message or by some
other means such as DHCPv6 [RFC3315].
* Once it has formed an address, the 6LN (re)registers its address
periodically, within the Lifetime of the previous Address
Registration, as prescribed by [RFC6775] and [RFC8505].
* A 6LN acting as a RUL sets the "R" flag in the EARO whereas a 6LN
acting as a RAN does not set the "R" flag as prescribed by
[RFC8505] section 5.1.
* Upon each consecutive Address Registration, the 6LN increases the
TID field in the EARO, as prescribed by [RFC8505] section 5.2.
* The 6LN can register to more than one 6LR at the same time. In
that case, it MUST use the same value of TID for all of the
parallel Address Registrations.
* The 6LN may use any of the 6LRs to which it register to forward
its packets. Using a 6LR to which the 6LN is not registered may
result in packets dropped at the 6LR by a Source Address
Validation function (SAVI).
Even without support for RPL, a RUL may be aware of opaque values to
be provided to the routing protocol. If the RUL has a knowledge of
the RPL Instance the packet should be injected into, then it SHOULD
set the Opaque field in the EARO to the RPLInstanceID, else it MUST
leave the Opaque field to zero.
Regardless of the setting of the Opaque field, the 6LN MUST set the
"I" field to zero to signal "topological information to be passed to
a routing process" as specified in section 5.1 of [RFC8505].
A RUL is not expected to produce RPL artifacts in the data packets,
but it MAY do so. for instance, if the RUL has a minimal awareness of
the RPL Instance and can build an RPI. A RUL that places an RPI in a
data packet MUST indicate the RPLInstanceID that corresponds to the
RPL Instance the packet should be injected into. All the flags and
the Rank field are set to zero as specified by section 11.2 of
[RFC6550].
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9.2.2. By the 6LR
Also as prescribed by [RFC8505], the 6LR generates a DAR message upon
reception of a valid NS(EARO) message for the Address Registration of
a new IPv6 Address by a 6LN. If the Duplicate Address exchange
succeeds, then the 6LR installs an NCE. If the "R" flag was set in
the EARO of the NS message, and this 6LR can manage the reachability
of Registered Address, then the 6LR sets the "R" flag in the EARO of
the NA message that is sent in response.
From then on, the 6LN periodically sends a new NS(EARO) to refresh
the NCE state before the lifetime indicated in the EARO expires, with
TID that is incremented each time till it wraps in a lollipop fashion
(see section 5.2.1 of [RFC8505] which is fully compatible with
section 7.2 of [RFC6550]). As long as the R flag is set and this
Router can still manage the reachability of Registered Address, the
6LR keeps setting the "R" flag in the EARO of the response NA
message, but the exchange of Extended Duplicate Address messages is
skipped.
The Opaque field in the EARO hints the 6LR on the RPL Instance that
should be used for the DAO advertisements, and for the forwarding of
packets sourced at the registered address when there is no RPI in the
packet, in which case the 6LR MUST enacapsulate the packet to the
Root adding an RPI in the outer header. if the "I" field is not
zero, then the 6LR MUST consider that the Opaque field is zero. If
the Opaque field is not set to zero, then it should carry a
RPLInstanceID for the Instance suggested by the 6LN. If the 6LR does
not participate to the associated Instance, then the 6LR MUST
consider that the Opaque field is zero. If the Opaque field is zero,
the 6LR is free to use the default RPL Instance (zero) for the
registered address or to select an Instance of its choice; else, that
is if the 6LR participates to the suggested Instance, then the 6LR
SHOULD use that Instance for the registered address.
The DAO message advertising the Registered Address MUST be
constructed as follows:
* The Registered Address is placed in a RPL Target Option in the DAO
message as the Target Prefix, and the Prefix Length is set to 128;
* RPL Non-Storing Mode is used, and the 6LR indicates one of its
global IPv6 unicast addresses as the Parent Address in the RPL
Transit Information Option (TIO) associated to the Target Option.
* the External 'E' flag in the TIO is set to indicate that the 6LR
redistributes an external target into the RPL network.
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* the Path Lifetime in the TIO is computed from the Lifetime in the
EARO Option to adapt it to the Lifetime Units used in the RPL
operation. Note that if the lifetime is 0, then the 6LR generates
a No-Path DAO message that cleans up the routes down to the
Address of the 6LN;
* the Path Sequence in the TIO is set to the TID value found in the
EARO option;
Upon a successful NS/NA(EARO) exchange: if the "R" flag was set in
the EARO of the NS message, then the 6LR SHOULD inject the Registered
Address in RPL by sending a DAO message on behalf of the 6LN; else
the 6LR MUST NOT inject the Registered Address into RPL.
If a DAO-ACK is not requested, or has a Status that is not a
rejection, indicating the DAO was accepted respectively by a parent
in Storing Mode or by the Root in non-Storing Mode, the 6LR replies
with a NA(EARO) to the RUL with a Status of 0 (Success).
In case of a DAO-ACK or a DCO indicating a rejection and transporting
an EARO Status Value of 5 (Validation Requested) the 6LR challenges
the 6LN for ownership of the address, as described in section 6.1 of
[RFC8505]. If the challenge succeeds then the operations continue as
normal. In particular a DAO message is generated upon the NS(EARO)
that proves the ownership of the address. If the challenge failed
the 6LR MUST refrain from injecting the address in RPL and may take
actions to protect itself against DoS attacks by a rogue 6LN, see
Section 11
The other rejection codes indicate that the 6LR failed to inject the
address into the RPL network. If an EARO Status is transported, the
6LR MUST send a NA(EARO) to the RUL with that Status value. If for
any other reason the 6LR fails to inject the address into the RPL
network, the 6LR SHOULD send a NA(EARO) to the RUL with a Status of 2
(Out of Storage) which indicates a possibility to retry later.
Similarly, upon a DCO message indicating that the address of a RUL
should be removed from the routing table, the 6LR issues an
asynchronous NA(EARO) to the RUL with the embedded ND Status value.
If a 6LR receives a valid NS(EARO) message with the "R" flag reset
and the 6LR was redistributing the Registered Address due to previous
NS(EARO) messages with the flag set, then it MUST stop injecting the
address. It is up to the Registering Node to maintain the
corresponding route from then on, either keeping it active by sending
further DAO messages, or destroying it using a No-Path DAO.
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9.2.3. By the RPL Root
In RPL Storing Mode of Operation (MOP), the DAO message is propagated
from child to parent all the way to the Root along the DODAG,
populating routing state as it goes. In Non-Storing Mode, The DAO
message is sent directly to the RPL Root. Upon reception of a DAO
message, for each RPL Target option that creates or updates an
existing RPL state:
* the Root notifies the 6LBR using an internal API if they are co-
located, or performs an EDAR/EDAC exchange on behalf of the 6LR if
they are separated. If the Target option transports a ROVR, then
the Root MUST use it to build a full EDAR message as the 6LR
would. Else, a keep-alive EDAR is used with the ROVR field set to
zero.
An EDAR message MUST be constructed as follows:
* The Target IPv6 address from in the RPL Target Option is placed in
the Registered Address field of the EDAR message and in the Target
field of the NS message, respectively;
* the Registration Lifetime is adapted from the Path Lifetime in the
TIO by converting the Lifetime Units used in RPL into units of 60
seconds used in the 6LoWPAN ND messages;
* the RPL Root indicates its own MAC Address as Source Link Layer
Address (SLLA) in the NS(EARO);
* the TID value is set to the Path Sequence in the TIO and indicated
with an ICMP code of 1 in the EDAR message;
* when present in the RPL Target option, the ROVR field is used as
is in the EDAR and the ICMP Code Suffix is set to the appropriate
value as shown in Table 4 of [RFC8505] depending on the length of
the ROVR field. If it is not present the ROVR field in the EDAR
is set to zero indicating that this is a keep-alive EDAR.
Upon a Status value in an EDAC message that is not "Success", the
Root SHOULD destroy the formed paths using either a DAO-ACK (in Non-
Storing Mode) or a DCO downwards as specified in [EFFICIENT-NPDAO].
Failure to destroy the former path would result in Stale routing
state and local black holes if the address belongs to another party
elsewhere in the network. The RPL Status value that maps the 6LowpAN
ND Status value MUST be placed in the DCO.
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9.2.4. By the 6LBR
Upon reception of an EDAR message with the ROVR field is set to zero
indicating a keep-alive EDAR, the 6LBR checks whether an entry exists
for the and computes whether the TID in the DAR message is fresher
than that in the entry as prescribed in section 4.2.1. of [RFC8505].
If the entry does not exist, the 6LBR does not create the entry, and
answers with a Status "Removed" in the EDAC message.
If the entry exists but is not fresher, the 6LBR does not update the
entry, and answers with a Status "Success" in the EDAC message.
If the entry exists and the TID in the DAR message is fresher, the
6LBR updates the TID in the entry, and if the lifetime of the entry
is extended by the Registration Lifetime in the DAR message, it also
updates the lifetime of the entry. In that case, the 6LBR replies
with a Status "Success" in the DAC message.
The EDAC that is constructed is the same as if the keep-alive EDAR
was a full EDAR, and includes the ROVR that is associated to the
Address Registration.
10. Protocol Operations for Multicast Addresses
Section 12 of [RFC6550] details the RPL support for multicast flows.
This support is not source-specific and only operates as an extension
to the Storing Mode of Operation for unicast packets. Note that it
is the RPL model that the multicast packet is passed as a Layer-2
unicast to each if the interested children. This remains true when
forwarding between the 6LR and the listener 6LN.
"Multicast Listener Discovery (MLD) for IPv6" [RFC2710] and its
updated version "Multicast Listener Discovery Version 2 (MLDv2) for
IPv6" [RFC3810] provide an interface for a listener to register to
multicast flows. MLDv2 is backwards compatible with MLD, and adds in
particular the capability to filter the sources via black lists and
white lists. In the MLD model, the Router is a "querier" and the
Host is a multicast listener that registers to the querier to obtain
copies of the particular flows it is interested in.
On the first Address Registration, as illustrated in Figure 8, the
6LN, as an MLD listener, sends an unsolicited Report to the 6LR in
order to start receiving the flow immediately. Since multicast
Layer-2 messages are avoided, it is important that the asynchronous
messages for unsolicited Report and Done are sent reliably, for
instance using an Layer-2 acknoledgement, or attempted multiple
times.
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The 6LR acts as a generic MLD querier and generates a DAO for the
multicast target. The lifetime of the DAO is set to be in the order
of the Query Interval, yet larger to account for variable propagation
delays.
The Root proxies the MLD echange as listener with the 6LBR acting as
the querier, so as to get packets from a source external to the RPL
domain. Upon a DAO with a multicast target, the RPL Root checks if
it is already registered as a listener for that address, and if not,
it performs its own unsolicited Report for the multicast target.
6LN 6LR Root 6LBR
| | | |
| unsolicited Report | | |
|------------------->| | |
| <L2 ack> | | |
| | DAO | |
| |-------------->| |
| | DAO-ACK | |
| |<--------------| |
| | | <if not listening> |
| | | unsolicited Report |
| | |------------------->|
| | | |
| | | |
Figure 8: First Multicast Registration Flow
An Address re-Registration is pulled by 6LR acting as querier. Note
that the message may be sent unicast to all the known individual
listeners. Upon a time out of the Query Interval, the 6LR sends a
Query to each of its listeners, and gets a Report back that is mapped
into a DAO, as illustrated in Figure 9:
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6LN 6LR Root 6LBR
| | | |
| Query | | |
|<-------------------| | |
| Report | | |
|------------------->| | |
| | DAO | |
| |-------------->| |
| | DAO-ACK | |
| |<--------------| |
| | | |
| | | Query |
| | |<-------------------|
| | | Report |
| | |------------------->|
| | | |
| | | |
Figure 9: Next Registration Flow
Note that any of the functions 6LR, Root and 6LBR might be collapsed
in a single node, in which case the flow above happens internally,
and possibly through internal API calls as opposed to messaging.
11. Security Considerations
The LLN nodes depend on the 6LBR and the RPL participants for their
operation. A trust model must be put in place to ensure that the
right devices are acting in these roles, so as to avoid threats such
as black-holing, (see [RFC7416] section 7) or bombing attack whereby
an impersonated 6LBR would destroy state in the network by using the
"Removed" Status code. This trust model could be at a minimum based
on a Layer-2 access control, or could provide role validation as
well. This is a generic 6LoWPAN requirement, see Req5.1 in
Appendix of [RFC8505].
The keep-alive EDAR message does not carry a valid Registration
Unique ID [RFC8505] and it cannot be used to create a binding state
in the 6LBR. The 6LBR MUST NOT create an entry based on a keep-alive
EDAR that does not match an existing entry. All it can do is refresh
the lifetime and the TID of an existing entry.
At the time of this writing RPL does not have a zerotrust model
whereby the it is possible to validate the origin of an address that
is injected in a DAO. This specification makes a first step in that
direction by allowing the Root to challenge the RUL by the 6LR that
serves it.
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12. IANA Considerations
12.1. New DODAG Configuration Option Flag
This specification updates the Registry for the "DODAG Configuration
Option Flags" that was created for [RFC6550] as follows:
+------------+----------------------------+-----------+
| Bit Number | Capability Description | Reference |
+============+============================+===========+
| 1 | Root Proxies EDAR/EDAC (P) | THIS RFC |
+------------+----------------------------+-----------+
Table 2: New DODAG Configuration Option Flag
12.2. RPL Target Option Flags
Section 20.15 of [RFC6550] creates a registry for the 8-bit RPL
Target Option Flags field. This specification reduces the field to 4
bits. The IANA is requested to reduce the size of the registry
accordingly.
12.3. New Subregistry for the RPL Non-Rejection Status values
This specification creates a new Subregistry for the RPL Non-
Rejection Status values for use in RPL DAO-ACK and RCO Messages,
under the ICMPv6 parameters registry.
* Possible values are 6-bit unsigned integers (0..63).
* Registration procedure is "Standards Action" [RFC8126].
* Initial allocation is as indicated in Table 3:
+-------+------------------------+-----------+
| Value | Meaning | Reference |
+=======+========================+===========+
| 0 | Unqualified acceptance | RFC 6550 |
+-------+------------------------+-----------+
Table 3: Acceptance values of the RPL Status
12.4. New Subregistry for the RPL Rejection Status values
This specification creates a new Subregistry for the RPL Rejection
Status values for use in RPL DAO-ACK and RCO Messages, under the
ICMPv6 parameters registry.
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* Possible values are 6-bit unsigned integers (0..63).
* Registration procedure is "Standards Action" [RFC8126].
* Initial allocation is as indicated in Table 4:
+-------+-----------------------+---------------+
| Value | Meaning | Reference |
+=======+=======================+===============+
| 0 | Unqualified rejection | This document |
+-------+-----------------------+---------------+
Table 4: Rejection values of the RPL Status
13. Acknowledgments
The authors wish to thank Georgios Papadopoulos for their early
reviews of and contributions to this document
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>.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
DOI 10.17487/RFC2710, October 1999,
<https://www.rfc-editor.org/info/rfc2710>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[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>.
[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>.
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[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>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<https://www.rfc-editor.org/info/rfc6553>.
[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>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
"IPv6 over Low-Power Wireless Personal Area Network
(6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
April 2017, <https://www.rfc-editor.org/info/rfc8138>.
[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>.
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[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>.
[AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
"Address Protected Neighbor Discovery for Low-power and
Lossy Networks", Work in Progress, Internet-Draft, draft-
ietf-6lo-ap-nd-13, 6 January 2020,
<https://tools.ietf.org/html/draft-ietf-6lo-ap-nd-13>.
[USEofRPLinfo]
Robles, 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", Work in
Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-34,
20 January 2020, <https://tools.ietf.org/html/draft-ietf-
roll-useofrplinfo-34>.
[EFFICIENT-NPDAO]
Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient
Route Invalidation", Work in Progress, Internet-Draft,
draft-ietf-roll-efficient-npdao-17, 30 October 2019,
<https://tools.ietf.org/html/draft-ietf-roll-efficient-
npdao-17>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
15. Informative References
[RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing",
RFC 6606, DOI 10.17487/RFC6606, May 2012,
<https://www.rfc-editor.org/info/rfc6606>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <https://www.rfc-editor.org/info/rfc3315>.
[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>.
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[RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur,
Ed., "Performance Evaluation of the Routing Protocol for
Low-Power and Lossy Networks (RPL)", RFC 6687,
DOI 10.17487/RFC6687, October 2012,
<https://www.rfc-editor.org/info/rfc6687>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
[RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A.,
and M. Richardson, Ed., "A Security Threat Analysis for
the Routing Protocol for Low-Power and Lossy Networks
(RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015,
<https://www.rfc-editor.org/info/rfc7416>.
[RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
RFC 8025, DOI 10.17487/RFC8025, November 2016,
<https://www.rfc-editor.org/info/rfc8025>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>.
Appendix A. Example Compression
Figure 10 illustrates the case in Storing Mode where the packet is
received from the Internet, then the Root encapsulates the packet to
insert the RPI and deliver to the 6LR that is the parent and last hop
to the final destination, which is not known to support [RFC8138].
The difference with the format presented in Figure 19 of [RFC8138] is
the addition of a SRH-6LoRH before the RPI-6LoRH to transport the
destination address of the outer IPv6 header.
+-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-...
|11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP
|Page 1 |Type1 S=0| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld
+-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-...
<-4bytes-> <- RFC 6282 ->
No RPL artifact
Figure 10: Encapsulation to Parent 6LR in Storing Mode
In Figure 10, the source of the IP-in-IP encapsulation is the Root,
so it is elided in the IP-in-IP 6LoRH. The destination is the parent
6LR of the destination of the inner packet so it cannot be elided.
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In Storing Mode, it is placed as the single entry in an SRH-6LoRH as
the first 6LoRH. Since there is a single entry so the SRH-6LoRH Size
is 0. In this particular example, the 6LR address can be compressed
to 2 bytes so a Type of 1 is used. It results that the total length
of the SRH-6LoRH is 4 bytes.
In Non-Storing Mode, the encapsulation from the Root would be similar
to that represented in Figure 10 with possibly more hops in the SRH-
6LoRH and possibly multiple SRH-6LoRHs if the various addresses in
the routing header are not compressed to the same format. Note that
on the last hop to the parent 6LR, the RH3 is consumed and removed
from the compressed form, so the use of Non-Storing Mode vs. Storing
Mode is indistinguishable from the packet format.
Follows the RPI-6LoRH and then the IP-in-IP 6LoRH. When the IP-in-IP
6LoRH is removed, all the Router headers that precede it are also
removed.
The Paging Dispatch [RFC8025] may also be removed if there was no
previous Page change to a Page other than 0 or 1, since the
LOWPAN_IPHC is encoded in the same fashion in the default Page 0 and
in Page 1. The resulting packet to the destination is the inner
packet compressed with [RFC6282].
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 Mougins - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Michael C. Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
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