Configuration option for RFC 8138
draft-ietf-roll-turnon-rfc8138-04
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (roll WG) | |
|---|---|---|---|
| Authors | Pascal Thubert , Li Zhao | ||
| Last updated | 2020-01-24 | ||
| Replaces | draft-thubert-roll-turnon-rfc8138 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-roll-turnon-rfc8138-04
ROLL P. Thubert, Ed.
Internet-Draft L. Zhao
Updates: 6550, 8138 (if approved) Cisco Systems
Intended status: Standards Track 24 January 2020
Expires: 27 July 2020
Configuration option for RFC 8138
draft-ietf-roll-turnon-rfc8138-04
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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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 27 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 3
4. Updating RFC 8138 . . . . . . . . . . . . . . . . . . . . . . 3
5. Transition Scenarios . . . . . . . . . . . . . . . . . . . . 4
5.1. Inconsistent State While Migrating . . . . . . . . . . . 5
5.2. Single RPL Instance Scenario . . . . . . . . . . . . . . 5
5.3. Double RPL Instances Scenario . . . . . . . . . . . . . . 6
5.4. Rolling Back . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . 7
10. Informative References . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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 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 and their
RPL parents handle the compression/decompression on their behalf.
This document complements RFC 8138 and dedicates a flag in the RPL
configuration option to indicate whether RFC 8138 compression should
be used within the RPL Instance. The setting of 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 should
refrain from using the compression unless the information is
superseded by configuration.
This specification provides scenarios that force a legacy node to
become a RPL-Aware-Leaf (RAL). In that case, the 6LR must be aware
by means out of scope that it must uncompress the packets before
delivering to the RAL.
2. 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.
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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 configuration of the node in
order to cope with intermediate implementations of the 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, 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 uncompress the packets before delivering.
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5. Transition Scenarios
A node that supports [RFC8138] but not this specification can only be
used in a homogeneous network and an upgrade requires a "flag day"
where all nodes are updated and then the network is rebooted with
implicitly RFC 8138 compression turned on with the "T" flag set on.
A node that supports this specification can work in a network with
RFC 8138 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 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 and can receive packets if they are delivered by the parent
6LR in the uncompressed form.
[RFC6550] states that "Nodes other than the DODAG 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
may only attach to a DODAG as a leaf node when the node 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 that is configured to operate in
a RPL Instance but does not support a value for a known parameter
that is mandatory for routing MUST NOT operate as a router but MAY
still join as a leaf. Note that a legacy node 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).
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5.1. Inconsistent State While Migrating
When the "T" flag is turned on in the configuration option by the
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 will start using RFC 8138 with a SRH-6LoRH that routes all
the way to the last router or possibly to the leaf, if the leaf
supports RFC 8138.
This is why it is required that all the routers in the RPL Instance
support [RFC8138] at the time of the switch, and 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 are
configured with a new OCP, that may use the same OF operation or a
variation of it. The root sets the "T" flag at the time it migrates
to the new OCP. As a result, nodes that do not support RFC 8138 join
as leaves and do not forward packets anymore. The leaves generate
packets without compression. The parents - which supports RFC 8138 -
may encapsulate the packets using RFC 8138 if needed. The other way
around, the root encapsulates packets to the leaves all the way to
the parent, which decapsulates and distribute the uncompressed inner
packet to the leaf.
This scenario presents a number of caveats:
* The method consumes an extra OCP. It also requires a means to
signal the capabilities of the leaf, e.g., using "RPL Mode of
Operation extension" [MOP-EXT].
* If an implementation does not move 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, 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.
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* 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 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 participate to both Instances but favor
the new RPL Instance for the traffic that they source. On the other
hand, 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:
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+------------+---------------------------------+-----------+
| Bit Number | Capability Description | Reference |
+============+=================================+===========+
| 2 | Turn on RFC8138 Compression (T) | THIS RFC |
+------------+---------------------------------+-----------+
Table 1: New DODAG Configuration Option Flag
7. Security Considerations
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 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 Rahul Jadhav for his in-depth review 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>.
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[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>.
[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, <https://tools.ietf.org/html/
draft-ietf-roll-unaware-leaves-08>.
10. Informative References
[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] Jadhav, R., Thubert, P., and M. Richardson, "Mode of
Operation extension and 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>.
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
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Email: liz3@cisco.com
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