wdiff draft-thubert-roll-eliding-dio-information-00.txt draft-thubert-roll-eliding-dio-information-01.txt

ROLL P. Thubert, Ed.
Internet-Draft Cisco Systems
Updates: 6550 (if approved) D. Barthel
Intended status: Standards Track Orange Labs
Expires: 17 19 April 2020 R.A. Jadhav
Huawei Tech
15
17 October 2019

Eliding and Querying RPL Information
draft-thubert-roll-eliding-dio-information-00
draft-thubert-roll-eliding-dio-information-01

Abstract

This document presents a method to safely elide a group of global RPL
options by synchonizing the state associated with each of these
options between parent and child using a new sequence counter in DIO
messages. A child that missed a DIO message with an update of any of
those protected options detects it by the change of sequence counter
and queries the update with a DIS Message.

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
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This Internet-Draft will expire on 17 19 April 2020.

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Please review these documents carefully, as they describe your rights
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4
2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 3 4
2.2. References . . . . . . . . . . . . . . . . . . . . . . . 3 4
2.3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 4 5
4. New RPL Configuration State Sequence Message Formats . . . . . . . . . . . . . . 4
5. Protected Options . . . . . . . . . 5
4.1. Updated DIO Base Object . . . . . . . . . . . . . . . . . 5
6. Child
4.2. Updated DIS Base Object . . . . . . . . . . . . . . . . . 6
4.3. New Abbreviated Option Option . . . . . . . . . . . . . . 7
5. RCSS Operation . . . . . . . . . . . . . . . . . . . . . . . 6
7. Pulling Options 8
5.1. Updating the RCSS . . . . . . . . . . . . . . . . . . . . 8
5.2. RCSS Freshness and Parent selection . . . . . . 7
8. . . . . . 9
5.3. RCSS of an Option . . . . . . . . . . . . . . . . . . . . 10
6. Synchronizing Options . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations 11
8.1. New DODAG Information Object Flags . . . . . . . . . . . 11
8.2. New RPL Control Message Option . . . . . . . . 7
11. . . . . . 12
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
12. 12
10. Normative References . . . . . . . . . . . . . . . . . . . . 7
13. 12
11. Informative References . . . . . . . . . . . . . . . . . . . 8 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 13

1. Introduction

Classical Link State protocol synchronize their Link State Database
(LSDB) by sequencing every change. Each interested node maintains
the last sequence of the LSDB it is synchronizing with. If a the last
known sequence number is older than the current, the node needs to
learn one by one all the state changes between the last known and the
current state.

[RPL] does not operate that way. With RPL, the routing information
is repeated over and over in DODAG Information Object (DIO) and
Destination Advertisement Object (DAO) messages. There is no concept
of synchronization. The most recent information overrides a previous
one and a stale state eventually times out.

The RPL way was designed to enable routing from most nodes to most
nodes most of the time in a Low-Power Lossy Network (LLN) where the
quality of the links and the cost of communications does not permit
to maintain a permanent synchronization.

This principle was applied to both the routing information and non-routing state
information such as configuration settings, prefix information, and
node capabilities.

This non-routing state is carried in RPL Messages as options. Some
of the DIO options may be needed to decide whether a node can join a
network as a leaf or as a router, and may affect the parent selection
or the address selection. It is thus critical that each node
maintains its state to the freshest and selects parents that are also
synchronized to the freshest.

[RPL] allows a parent to elide that information options in the DIO messages that it
sends repeatedly, but if to conserve battery and save bandwidth. When it
does so, a newcomer child may have that missed the early DIOs that contained the
configuration option and
live with only may operate on default or partial information.
If it is pessimistic, it may query all possible the information even
when it is not needed. Conversely, a node that slept may have missed
a DIO message with a change in some critical information and may not be even
aware of it, so it may fail to query for the update and operate on
deprecated parameters.

This document uses a new sequence counter called RCSS to synchronize
the state in a child node with that of its parent, and recursively
with that of the network. whole network, to the latest setting from the Root.

The protected options are:

1. The Route Information Option (RIO) defined in section 6.7.5 of
[RPL]

2. The DODAG Configuration Option (DCO) defined in section 6.7.6 of
[RPL]

3. The Prefix Information Option (PIO) defined in section 6.7.10 of
[RPL]

4. The Extended MOP Option (MOPex) defined in [MOPEX-CAP]

5. The Global Capabilities Option (GCO) defined in [MOPEX-CAP]

Any change in those options causes an increment of the RCSS and
enables a network-wide synchronization to the new state. If the
change impacts the routing substantially, the Root should decide to
increment the Version Number at the same time to fully rebuild the
DODAG with the new settings of the options. It must be noted that
the operation of the Version Number in itself provides no guarantee
that the non-routing state is fully resynchronized everywhere unless
all the options are present in all the DIO messages.

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].

Other terms in use in LLNs are found in Terminology for
Constrained-Node Networks [RFC7228].

A glossary of classical RPL acronyms is given in Section 2.3.

The term "byte" is used in its now customary sense as a synonym for
"octet".

"RPL", "RPL Packet Information" (RPI) and "RPL Instance", DIO, DAO
and DIS messages are defined in the "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks" [RPL] specification.

This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware
Leaf (RAL) consistently with [USE_OF_RPL_INFO].

The term RPL-Unaware Leaf (RUL) is used to refer to a node that uses
a RPL router (without necessarily knowing it) as 6LR and depends on
that router to obtain reachability for its addresses inside the RPL
domain. On the contrary, the term RPL-Aware Node (RAN) is used to
refer to a RAL or a RPL router that participates to RPL and
advertises its addresses of prefixes by itself.

2.3. Glossary

This document often uses the following acronyms:

DODAG Destination-Oriented Directed Acyclic Graph
LLN Low-Power and Lossy Network

RPI RPL Packet Information (an Option in the Hop-By_Hop Header)

RAL RPL-Aware Leaf

RAN RPL-Aware Node, a RPL router or a RPL-Aware Leaf

RS Router Solicitation

RCSS RPL Configuration State Sequence

RPL IPv6 Routing Protocol for LLNs (pronounced ripple)

RUL RPL-Unaware Leaf

3. Updating RFC 6550

This document adds a sequence counter new field called RPL Configuration State
Sequence (RCSS) RCSS to the DIO message. The
RCSS is a sequence counter set by the root Root and operated as specified
in Section 7 of [RPL], more in Section 4. 5.

This document also introduces a new RPL Control Message Options Option called
the Abbreviated Option Option (AOO). The AOO is an empty the compressed
replacement of
an existing a protected option that indicates the RCSS of the last
change of that
option. option, but elides its content, more in Section 4.3.

This document modifies the Solicited Information Option to DIS Base Objectto enable the individual
query of the protected options by a node that missed a change, more
in Section 7. 4.2.

4. New RPL Configuration State Sequence Message Formats

4.1. Updated DIO Base Object

The format of the DIO Base Object is defined in section 6.3.1 of
[RPL]. This specification uses a 8th octet that was previously reserved in
[RPL] to transport the RCSS.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |Version Number | Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G|0| MOP | Prf | DTSN | Flags | RCSS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+

Figure 1: MOdified Updated DIO Base Object

Updated fields:

RCSS
One Byte, the RPL Configuration State Sequence

4.2. Updated DIS Base Object

The RCSS protects network-wide options that are set DIS Base Object is use by the root and
that are propagated without a change down the DODAG. The RCSS MUST
be incremented when the root sends child to query from a DIO where at least one of parent the most
recent changes in protected options. This specification adds flags
to indicate which options is modified. It MUST propagated down without a
change together with the options that it protects.

During the straight part of the lollipop, a second reboot of the root
might not be recognized are requested and a same value of the freshest RCSS may appear with
new values in to
which the protected options. For querying node was synchronized.

0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|D|P[M|O| Flg | LastSync RCSS | Option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Updated DIS Base Object

Updated fields:

R
One Bit, indicates that reason the protected
options MUST be present in the DIOs during the straight part of RIO is requested

D
One Bit, indicates that the
lollipop and DCO is requested

P
One Bit, indicates that the root SHOULD move rapidly away from PIO(s) is(are) requested

M
One Bit, indicates that the straight part
once MOPex is requested

O
One Bit, indicates that the network has settled by resetting GCO is requested

Last Synchronized RCSS
One Byte, indicates the freshest RCSS to 0, which places
the RCSS in the circular region of the lollipop.

5. Protected Options

The protected options are:

1. The Route Information Option (RIO) defined in section 6.7.5 of
[RPL]

2. The DODAG Configuration Option (DCO) defined in section 6.7.6 of
[RPL]

3. The Prefix Information Option (PIO) defined in section 6.7.10 of
[RPL]

4. The Extended MOP querier was
synchronized

4.3. New Abbreviated Option (MOPex) defined in [MOPEX-CAP]

5. The Global Capabilities Option (GCO) defined in [MOPEX-CAP]

When a protected option is unchanged from the previous DIOs, the root Root
MAY replace it with its abbreviated version. The abbreviated version
of an option is transported in a 4-bytes long Abbreviated Option
Option (AOO). The AOO indicates the RCSS at which the protected
option was last changed.

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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Abbrev. opt. | Last Mod RCSS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: 3: Abbreviated Option Option Format

Option fields:

Option Type
One byte indicating "Abbreviated Option", see Table 1 2 in
Section 8.2

Option Length
MUST be set to 2 indicating Option data of 2 bytes

Abbreviated Option
The Option Type of the option being abreviated abbreviated

Last Modification RCSS
The RCSS at which the option was last modified

6. Child

5. RCSS Operation

When

Settings and updates to network-wide parameters are initiated by the
Root and propagated down the DODAG in RPL Control Message Options in
DIO messages. The DIO messages arrive asynchronously via different
parents and may confuse a field child. The RCSS allows the child to keep
synchronized to the latest settings network-wide parameters that are
propagated in protected options.

The RCSS is modified a sequence number that is operated as specified in
section 7.2 of [RPL]. The scope of an RCSS is one DODAG within one
RPL Instance. The RCSS applies to a DIO Message and a same value of
the RCSS can be used in DIO messages that are sent consecutively with
no change in the protected options.

The Root of the DODAG is autoritative to set and update the RCSS and
the options that it protects. The RCSS and the protected options are
propagated together down the DODAG without a change, more in
Section 5.1.

The RCSS allows a fashion
that may affect child node to recognize the routing fresher DIO Message(s)
as received from one or forwarding decision inside more advertising parents and to use only
parents with a consistent state of network-wide parameters, more in
Section 5.2.

By extension, the RCSS is also defined for each protected option. A
child associates an option with the DODAG, values of the root MUST RCSS indicated in
DIO Messages in which the option is advertised and uses it to assess
the relative freshness of different versions of an option, more in
Section 5.3.

Unchanged options may be sent in full, elided, or in the abbreviated
form specified in Section 4.3. Eliding an option is NOT RECOMMENDED
as it may cause multiple children to resynchronize the option even if
it was not changed.

If the link MTU does not permit to send a single DIO message with all
the options packaged then the protected options. Unchanged options may be abreviated as discussed spread over multiple
consecutive DIO messages with the same RCSS that are sent in Section 5. a rapid
sequence.

5.1. Updating the RCSS

The freshness RCSS is incremented by the Root using a lollipop technique as
specified in section 7.2 of [RPL]. RCSS values are comparable if
they are within a window of comparison of SEQUENCE_WINDOW increments
or one indicates a reboot.

A reboot of the Root is detected when the RCSS moves from the
circular to the straight part of the lollipop. In order to maximize
the chances of detection, the straight part should be kept very short
with a RECOMMENDED initialization at 252 or above.

During the straight part of the lollipop, a second reboot of the Root
might not be recognized and a same value of the RCSS may reappear
with different settings in the protected options. For that reason
the protected options is asserted based MUST be provided in full with each increment on
the RCSS. RCSS during the straight part of the lollipop.

When a field is modified in one of the protected options, the Root
MUST send a DIO with an incremented RCSS and the modified protected
option(s) in full. The Root MAY also update the Version Number to
form a new DODAG altogether.

The Root SHOULD jump rapidly away from the straight part once the
network has sufficiently settled by resetting the RCSS to 0, which
places the RCSS in the circular region of the lollipop, where the
protected options MAY be elided or abbreviated.

5.2. RCSS Freshness and Parent selection

A child node maintains the freshest RCSS received from its parents in
each of the RPL Instances that it participates to, and uses that RCSS
for its own DIO messages.

A child and a candidate parent are out-of-sync when the RCSS values
that they maintain for a RPL Instance are compared as described not comparable. A child
MUST NOT use a parent that is out-of-sync unless no other parent is
available, in section 7.2 of [RPL]. which case it MAY align its RCSS and resynchronize to
that parent.

When a child receives from a candidate parent exposes a new RCSS, DIO with an RCSS that
is fresher than the one it is using, the child MUST synchronize the
state relative to the protected options with that parent. The child
node SHOULD MUST refrain from using that parent and the new state including
the RCSS, until it has resynchronized synchronized all of the protected fields options to
the latest.
that RCSS. When it is resynchronized, fully synchronized, the child may then use
that parent and the new RCSS.

Using a back-level parent may cause packets to be dropped,
misunderstood or misrouted. The child SHOULD refrain from using other parents a
parent that expose exposes an older RCSS. RCSS if the change causes an
incompatibility issue.

5.3. RCSS of an Option

By extension, the RCSS of an option is maintained by a child as the
freshest RCSS indicated by a DIO message from a candidate parent in
which the option was present in the abbreviated form or in full. A
child MUST store maintains a state for the content freshest RCSS received for each of all
the protected options and keep
track of synchronizes its state for each option to
the freshest RCSS of the that option.

When a child receives a DIO where each of these option was last seen
in from a non-abbreviated version. candidate parent, for each option:

If that the Option is advertised in the abbreviated form then the RCSS
that the DIO advertises for the option is fresher than the Last Modification
RCSS of the AOO, else

If the Option is advertised in full then the abbreviated version of RCSS that the DIO
advertises for the option is the RCSS of the DIO, else

If the Option is elided then the
child RCSS is up-to-date unspecified but it is at
most as fresh as the RCSS of the DIO, and the RCSS of the DIO is
assumed for the comparison

This means that option. If a protected option elided if an Option is advertised in both the abbreviated
form and in full in a same DIO and not abbreviated, and message then the child RCSS in the AOO has
precedence.

To keep the RCSS comparable for each option, the RCSS of an option
must lazily progress along with the global RCSS even if there was no
change in the options. Each parent including the Root MUST advertise
a stored new RCSS value for
that each of the protected options at least once within a
sliding window of SEQUENCE_WINDOW increments.

When an option was not changed for a new RCSS, one parent may
advertise it in the abbreviated form while another sends the option
in full only, e.g., in response to a DIS message. A fresher RCSS
indicates that the option is lower either the same or carries a more recent
update than the one with an older RCSS.

The RCSS of an option may be obtained from a DIO message that carries
the option in full even if the DIO, RCSS of the DIO is not the freshest
across parents, as long as the RCSS of the DIO is fresher than the
current one for that option.

If current value of the maintained RCSS for an given option is not as
fresh or fresher than that advertised in a DIO message, then the
child MUST query update its state for that option from as specified in
Section 6.

6. Synchronizing Options

A child can resynchronize any of the protected options to the latest
RCSS by sending a DIS Message to a candidate parent that advertises
that RCSS in DIO messages. The child MUST set the desired
combination of 'R', 'D', 'P', 'M' and 'O' flags to ensure indicate the
option(s) that it needs updated. The child MUST signal in the Last
Synchronized RCSS field of the DIS the freshest value of RCSS for
which it was fully synchronized, or a conventional value of OUT-OF-
SYNC-RCSS of 129 if it was never synchronized or is out-of-sync with
the parent.

The DIO message that is has sent in response MUST contain in full all the
options that are requested and that were updated since the
latest. Last
Synchronized RCSS in the DIS Message. This means all of the
protected options of the child was never synchronized or is done out-of-
sync with a DIS the parent. The other options MUST be added in the
abbreviated form. The options MAY be spread over more than one DIO
message as indicated sent in Section 7. a quick sequence and the child SHOULD wait a
reasonable technology-dependent time before it retries the request.

7. Pulling Options

8. Security Considerations

TBD

8. IANA Considerations

8.1. New DODAG Information Object Flags

5 new bits are allocated in the Registry for the DODAG Information
Object (DIO) Flags defined for [RPL].

+------------+----------------------------+--------------+
| Bit Number | Capability description | Defining RFC |
+============+============================+==============+
| 0 | 'R' bit "RIO requested" | THIS RFC |
+------------+----------------------------+--------------+
| 1 | 'D' bit "DCO requested" | THIS RFC |
+------------+----------------------------+--------------+
| 2 | 'P' bit "PIO(s) requested" | THIS RFC |
+------------+----------------------------+--------------+
| 3 | 'M' bit "MOPex requested" | THIS RFC |
+------------+----------------------------+--------------+
| 4 | 'O' bit "GCO irequested" | THIS RFC |
+------------+----------------------------+--------------+

Table 1: New DIO Flags

8.2. New RPL Control Message Option

A new entries entry is required for the new option of type "Abbreviated
Option", from the "RPL Control Message Options" space defined for
[RPL].

+----------+--------------------+-----------+

Table 1: 2: New Option Type

10. Security Considerations

TBD

11.

9. Acknowledgments

12.

10. Normative References

[MOPEX-CAP]
Jadhav, R. and P. Thubert, "Mode of Operation extension
and Capabilities", Work in Progress, Internet-Draft, draft-ietf-roll-mopex-
cap-00,
draft-ietf-roll-mopex-cap-00, 9 August 2019, <https://tools.ietf.org/html/draft-
ietf-roll-mopex-cap-00>.
<https://tools.ietf.org/html/draft-ietf-roll-mopex-cap-
00>.

[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>.

[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>.

[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>.

[RPL] 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>.

[USE_OF_RPL_INFO]
Robles, I., Richardson, M., and P. Thubert, "Using RPL
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-31,
7 August 2019,
<https://tools.ietf.org/html/draft-ietf-roll-useofrplinfo-
31>.

13. <https://tools.ietf.org/html/draft-ietf-
roll-useofrplinfo-31>.

11. Informative References

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

Dominique Barthel
Orange Labs
28 chemin du Vieux Chêne
38243 Meylan
France

Email: dominique.barthel@orange.com

Rahul Arvind Jadhav
Huawei Tech
Kundalahalli Village, Whitefield,
Bangalore 560037
Karnataka
India

Phone: +91-080-49160700
Email: rahul.ietf@gmail.com