wdiff draft-ietf-roll-turnon-rfc8138-04.txt draft-ietf-roll-turnon-rfc8138-05.txt

ROLL P. Thubert, Ed.
Internet-Draft L. Zhao
Updates: 6550, 8138 (if approved) Cisco Systems
Intended status: Standards Track 24 January March 2020
Expires: 27 July 25 September 2020

Configuration option for RFC 8138
draft-ietf-roll-turnon-rfc8138-04
draft-ietf-roll-turnon-rfc8138-05

Abstract

This document complements RFC 8138 and dedicates a bit in the RPL
configuration option defined in RFC 6550 to indicate whether RFC 8138
compression is used within the RPL Instance.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BCP 14 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. References . . 2 . . . . . . . . . . . . . . . . . . . . . 3
2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 3 4
4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 3 4
5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 4 5
5.1. Inconsistent State While Migrating . . . . . . . . . . . 5 6
5.2. Single RPL Instance Scenario . . . . . . . . . . . . . . 5 6
5.3. Double RPL Instances Scenario . . . . . . . . . . . . . . 6 7
5.4. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 6 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 7 8
10. Informative References . . . . . . . . . . . . . . . . . . . 8 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 10

1. Introduction

The transition of a RPL [RFC6550] network to activate the compression
defined in [RFC8138] can only be done when all routers in the network
support it. A Otherwise, a non-capable node acting as a router would
drop the compressed packets and black-hole its subDAG. In a mixed
case with both RFC8138-capable and non-capable nodes, the compression
may be turned on only if all the non-capable nodes act as leaves Hosts and
their RPL parents handle the compression/decompression on their behalf. for them.

This document complements RFC 8138 [RFC8138] and dedicates a flag in the RPL
configuration option to indicate whether RFC 8138 [RFC8138] compression should
be used within the RPL Instance. The setting of this new flag is
controlled by the Root and propagates as is in the whole network.
When the bit is not set, source nodes that support RFC 8138 [RFC8138] should
refrain from using the compression unless the information is
superseded by configuration.

With RPL, a leaf is an IPv6 Host, which implies that leaves do not
forward packets. This specification provides scenarios that force a legacy node
non-capable RPL-Aware Node (RAN) to become a RPL-Aware-Leaf (RAL). In that case, the 6LR leaf. The parent router
must be aware know, e.g., by means out of scope that it configuration, or leveraging "RPL Capabilities"
[CAPABILITIES], when a leaf does not support the compression defined
in [RFC8138]. This is implicitly the case for a RPL-Unaware Leaf
(RUL) but is not known for a RPL-Aware Leaf (RAL). The parent router
must uncompress the packets before delivering them to a non-capable
leaf and it must compress the RAL. traffic from the leaf.

2. BCP 14 Terminology

2.1. References

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" Terminology used in this document are to be interpreted as is consistent with and
incorporates that described in BCP
14 [RFC2119][RFC8174] when, "Terms Used in Routing for Low-Power
and only when, they appear Lossy Networks (LLNs)" [RFC7102]. Other terms in all
capitals, as shown here.

3. Updating RFC 6550

This specification defines a new use in LLNs are
found in "Terminology for Constrained-Node Networks" [RFC7228].

"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 RPI is the abstract
information that RPL defines to be placed in data packets, e.g., as
the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header. By
extension the term "RPI" is often used to refer to the RPL Option
itself. The DODAG Information Solicitation (DIS), Destination
Advertisement Object (DAO) and DODAG Information Object (DIO)
messages are also specified in [RFC6550].

This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware
Leaf (RAL) consistently with "Using RPI Option Type, Routing Header
for Source Routes and IPv6-in-IPv6 encapsulation in the RPL Data
Plane" [USEofRPLinfo]. The term RPL-Aware Node (RAN) refers to a
node that is either a RAL or a RPL Router. A RAN manages the
reachability of its addresses and prefixes by injecting them in RPL
by itself. In contrast, a RUL leverages "Registration Extensions for
IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery" [RFC8505] to obtain reachability services from its parent
router(s) as specified in "Routing for RPL Leaves" [UNAWARE-LEAVES].

2.2. Glossary

This document often uses the following acronyms:

6LoWPAN: IPv6 over Low-Power Wireless Personal Area Network
6LoRH: 6LoWPAN Routing Header
DIO: DODAG Information Object (a RPL message)
DODAG: Destination-Oriented Directed Acyclic Graph
LLN: Low-Power and Lossy Network
RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks
OF: RPL Objective Function
OCP: RPL Objective Code Point
MOP: RPL Mode of Operation
RPI: RPL Packet Information
RAL: RPL-Aware Leaf
RAN: RPL-Aware Node
RUL: RPL-Unaware Leaf
SRH: Source Routing Header

2.3. 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.

3. Updating RFC 6550

This specification defines a new flag "Enable RFC8138 Compression"
(T). The "T" flag is set to turn on the use of the compression of
RPL artifacts with [RFC8138] within a RPL Instance. If a RPL
Instance has multiple Roots then they must be coordinated to use the
same setting.

RPL defines a Configuration Option that is registered to IANA in
section 20.14. of [RFC6550]. The "T" flag is encoded in one of the
reserved control bits in the RPL Configuration Option. The bit
position of the "T" flag is indicated in Section 6.

Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP)
in the DIO Base Object. The new "T" 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 "Enable
RFC8138 Compression" unless the specification of the MOP indicates to
do so.

4. Updating RFC 8138

A node that supports this specification MUST source packets in the
compressed form using [RFC8138] if and only if the "T" flag is set.
This behaviour can be overridden by a the configuration of the node in
order to cope with intermediate implementations of the root Root that
support [RFC8138] but not this specification and cannot set the "T"
flag.

The decision of using [RFC8138] is made by the originator of the
packet depending on its capabilities and its knowledge of the state
of the "T" flag. A router that encapsulates a packet is the
originator of the resulting packet and decides whether to compress
the outer headers as indicated above. An external target
[USEofRPLinfo] is not expected to support [RFC8138]. An intermediate
router MUST forward the packet in the form that the source used,
either compressed or uncompressed, unless it is either forwarding to an
external target or delivering to a leaf that is not known to support RFC 8138,
[RFC8138], in which cases it MUST uncompress the packet.

A RPL-Unaware Leaf (RUL) [UNAWARE-LEAVES] is both a leaf and an
external target. A RUL does not participate to RPL and depends on
the 6LR to ensure its connectivity. Packets from/to a RUL are
tunneled back and forth to the Root regardless of the MOP used in the
RPL Instance. A node that supports this specification but does not
support [RFC8138] SHOULD join as a RUL to ensure that the 6LR is
aware it needs to MUST uncompress the packets before delivering. packet.

5. Transition Scenarios

A node that supports [RFC8138] but not this specification can only be
used in a homogeneous network and an upgrade homogeneous network. Enabling the [RFC8138] compression
requires a "flag day"
where day"; all nodes are updated must be upgraded, and then the
network is can be rebooted with
implicitly RFC 8138 the [RFC8138] compression turned on with the "T" flag set on.

A node that supports this specification can work in a network with
RFC 8138
[RFC8138] compression turned on or off with the "T" flag set
accordingly and in a network in transition from off to on or on to
off (see Section 5.1).

A node that does not support [RFC8138] can interoperate with nodes
that do in a network with RFC 8138 [RFC8138] compression turned off. If the
compression is turned on, the node cannot forward compressed packets
and therefore it cannot act as a router. It may remain connected to
that network as a leaf, in which case it generates uncompressed
packets packets, and can
receive packets if they are delivered by the parent
6LR router in the
uncompressed form. Unless this is known by other means, the node
SHOULD join as a RUL as an indication that its parent router needs to
uncompress the packets before delivering.

[RFC6550] states that "Nodes other than the DODAG root Root MUST NOT
modify this information when propagating the DODAG Configuration
option". Therefore, even a legacy parent propagates the "T" flag as
set by the Root whether it supports this specification or not. So
when the "T" flag is set, it is transparently flooded to all the
nodes in the RPL Instance.

Sections 8.5 and 9.2 of [RFC6550] also suggests that a RPL-aware node RAN may only
attach to a DODAG as a leaf node when the node it does not support the Mode of
Operation of a RPL Instance, the Objective Function (OF) as indicated
by the Objective Code Point (OCP) or some other parameters in the
configuration option.

Per the above, changing the OCP in a DODAG can be used to force nodes
that do not support a particular feature to join as leaf only.

This specification reiterates that a node RAN that is configured to
operate in a RPL Instance but does not support a value for a known
parameter that is mandatory for routing routing, such as the OCP, MUST NOT
operate as a router but MAY still join as a leaf. Note that a legacy node
RAN will not recognize when a reserved field is now used and will not
turn to a leaf when the "T" flag is set.

The intent for this specification is to perform a migration once and
for all without the need for a flag day. In particular it is not the
intention to undo the setting of the "T" flag, and though it is
possible to roll back (see Section 5.4), adding nodes that do not
support [RFC8138] after a roll back may be problematic if the roll
back is not fully complete (see caveats in Section 5.2).

5.1. Inconsistent State While Migrating

When the "T" flag is turned on in the configuration option by the
root,
Root, the information slowly percolates through the DODAG as the DIO
gets propagated.

Some nodes will see the flag and start sourcing packets in the
compressed form while other nodes in the same RPL Instance are still
not aware of it. Conversely, in non-storing mode, the root Root will
start using RFC 8138 [RFC8138] with a SRH-6LoRH Source Routing Header 6LoRH (SRH-6LoRH)
that routes all the way to the last parent router or possibly to the leaf, if the leaf
supports RFC 8138.

This leaf.

To ensure that a packet is why forwarded across the RPL Instance in the
form in which it was generated, it is required that all the routers in the RPL Instance
support [RFC8138] at the time of the switch, and that all nodes that
do not support [RFC8138] only operate as leaves.

Setting the "T" flag is ultimately the responsibility of the network
administrator. In a case of upgrading a network to turn the
compression on, the network SHOULD be operated with the "T" flag
reset until all targeted nodes are upgraded to support this
specification. Section 5.2 and Section 5.3 provide possible
transition scenarios where this can be enforced.

5.2. Single RPL Instance Scenario

In a Single RPL Instance Scenario, nodes that support RFC 8138 [RFC8138] are
configured with a new OCP, that may use the same OF operation or a
variation of it. it, while nodes that do not support [RFC8138] are not,
but are configured to join an unknown OCP.

The root sets the "T" flag at the time it Root migrates to the new OCP. As a result, OCP before it sets the "T" flag, so that
nodes that do not support RFC 8138 join [RFC8138] are all attached as leaves and do not forward packets anymore. The leaves generate
packets without compression. when
the "T" flag is eventually set.

The parents parent router - which supports RFC 8138 [RFC8138] -
may encapsulate compresses the packets using RFC 8138
originated from the leaf and uncompresses the packets going to the
leaf. This may be done on the fly by the parent of a non-capable
RAL, or as part of the tunneling operation between the parent and the
Root, if needed. The other way
around, the root encapsulates packets leaf behaves as a RUL. This is described in section 7,
8, and 9 of [USEofRPLinfo].

Note that though tunneling from the Root to the leaves all parent is the way to generic
case for RULs, on paper it is possible for the parent, which decapsulates and distribute Root to avoid it for
the uncompressed inner
packet traffic that it originates. The Root SHOULD always use tunneling
to the leaf. parent of a RUL, even for its own packets, unless it knows
that the leaf supports [RFC8138].

This scenario presents a number of caveats:

* The method consumes an extra OCP. It also requires forces nodes that do
not support [RFC8138] to operate as RULs, unless there is a means method
to
signal let the capabilities of parent router know that it must uncompress the leaf, e.g., using "RPL Mode of
Operation extension" [MOP-EXT]. packet
for this RAL.

* If an the RPL implementation of a node does not move turn it to a leaf mode
when the OCP is changed to an unknown one, then the node may be
stalled.

* If the only possible parents of a node are nodes that do not
support RFC 8138, [RFC8138], then that node will loose all its parent at the
time of the migration and it will be stalled until a parent is
deployed with the new capability.

* Nodes that only support RFC8138 for forwarding may not parse the
RPI in native form. If such nodes are present, the parent needs
to encapsulate with RFC8138.

5.3. Double RPL Instances Scenario

An alternate alternative to the Single RPL Instance Scenario is to deploy an
additional RPL Instance for the nodes that support [RFC8138].

The two RPL Instances operate independently as specified in
[RFC6550]. The preexisting RPL Instance that does not use [RFC8138],
whereas the new RPL Instance does. This is signaled by the "T" flag
which is only set in the configuration option in DIO messages in the
new RPL Instance.

Nodes that support RFC 8138 [RFC8138] participate to in both Instances but favor
the new RPL Instance for the traffic that they source. On the other
hand, By contrast,
nodes that only support the uncompressed format would either not be
configured for the new RPL Instance, or would be configured to join
it as leaves only.

This method eliminates the risks of nodes being stalled that are
described in Section 5.2 but requires implementations to support at
least two RPL Instances and demands management capabilities to
introduce new RPL Instances and deprecate old ones.

5.4. Rolling Back

After downgrading a network to turn the [RFC8138] compression off,
the administrator SHOULD make sure that all nodes have converged to
the "T" flag reset before allowing nodes that do not support the
compression in the network (see caveats in Section 5.2).

It is RECOMMENDED to only deploy nodes that support [RFC8138] in a
network where the compression is turned on. A node that does not
support [RFC8138] MUST only be used as a leaf.

6. IANA Considerations

This specification updates the Registry for the "DODAG Configuration
Option Flags" that was created for [RFC6550] as follows:

+------------+---------------------------------+-----------+
| Bit Number | Capability Description | Reference |
+============+=================================+===========+
| 2 | Turn on RFC8138 Compression (T) | THIS RFC |
+------------+---------------------------------+-----------+

Table 1: New DODAG Configuration Option Flag

7. Security Considerations

First of all, it is worth noting that with [RFC6550], every node in
the LLN that is RPL-aware can inject any RPL-based attack in the
network. A trust model MUST be put in place so that rogue nodes are
excluded from participating to the RPL and the 6LowpAN signaling, and
from the data packet exchange. This trust model could be at a
minimum based on a Layer-2 Secure joining and the Link-Layer
security. This is a generic RPL and 6LoWPAN requirement, see Req5.1
in Appendix of [RFC8505].

Setting the "T" flag before some routers are upgraded may cause a
loss of packets. The new bit is protected as the rest of the
configuration so this is just one of the many attacks that can happen
if an attacker manages to inject a corrupted configuration.

Setting and resetting the "T" flag may create inconsistencies in the
network but as long as all nodes are upgraded to RFC 8138 [RFC8138] support
they will be able to forward both forms. The draft insists that the source is responsible
for selecting whether the packet is compressed or not, and all
routers must use the format that the source selected. So the result
of an inconsistency is merely that both forms will be present in the
network, at an additional cost of bandwidth for packets in the
uncompressed form.

8. Acknowledgments

The authors wish to thank Dominique Barthel and Rahul Jadhav for his
their in-depth review reviews and constructive suggestions.

9. 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>.

[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>.

[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>.

[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>.

[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>.

[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 draft-ietf-roll-useofrplinfo-38,
23 March 2020, <https://tools.ietf.org/html/draft-ietf-
roll-useofrplinfo-34>.
roll-useofrplinfo-38>.

[UNAWARE-LEAVES]
Thubert, P. and M. Richardson, "Routing for RPL Leaves",
Work in Progress, Internet-Draft, draft-ietf-roll-unaware-
leaves-08, 16 December 2019,
leaves-13, 17 March 2020, <https://tools.ietf.org/html/
draft-ietf-roll-unaware-leaves-08>.
draft-ietf-roll-unaware-leaves-13>.

10. Informative References

[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>.

[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>.

[MOP-EXT]

[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>.

[CAPABILITIES]
Jadhav, R., Thubert, P., and M. Richardson, "Mode of
Operation extension M., and R. Sahoo,
"RPL Capabilities", Work in Progress, Internet-Draft, draft-ietf-roll-mopex-cap-01, 2 November
2019, <https://tools.ietf.org/html/draft-ietf-roll-mopex-
cap-01>.
draft-ietf-roll-capabilities-02, 11 March 2020,
<https://tools.ietf.org/html/draft-ietf-roll-capabilities-
02>.

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

Li Zhao
Cisco Systems, Inc
Xinsi Building
No. 926 Yi Shan Rd
SHANGHAI
200233
China

Email: liz3@cisco.com