Internet DRAFT - draft-hushe-roll-dodag-metric
draft-hushe-roll-dodag-metric
ROLL H. She
Internet-Draft L. Zhao
Intended status: Standards Track P. Thubert
Expires: 21 June 2021 Cisco Systems
18 December 2020
A DODAG Metric Used for DODAG Selection in Low-Power and Lossy Networks
draft-hushe-roll-dodag-metric-00
Abstract
This document extends [RFC6551] by defining a new DODAG metric called
DODAG size, which can be used for DODAG selection in Low-Power and
Lossy Networks (LLNs). DODAG size is an important metric for nodes
to decide which DODAG to join, or which DODAG to migrate. This
document proposes methods to disseminate DODAG size from the Root to
all nodes in the DODAG, so that the DODAG size can be advertised to
new joining nodes.
Status of This Memo
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This Internet-Draft will expire on 21 June 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
2.1. References . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Disseminating DODAG size . . . . . . . . . . . . . . . . . . 4
3.1. DODAG Size Object . . . . . . . . . . . . . . . . . . . . 4
3.2. Disserminating DODAG size through DIO . . . . . . . . . . 5
3.3. Disserminating DODAG size through DAO-ACK . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
8. Informative References . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Low-power and Lossy Networks (LLNs) typically consist of large number
of nodes connected by lossy and unstable links. Such networks are
typically compised of nodes that are constrained in CPU power,
memory, and energy.
RPL, the "Routing Protocol for LLNs" [RFC6550], is an IPv6 routing
procotol with specific optimizations for such networks. RPL builds
routes proactively but maintains them on-demand based on their
utilization. Point-to-multipoint (P2MP) and multipoint-to-point
(MP2P) routes to and from the Root are optimized, but other point-to-
point (P2P) routes are stretched to minimize the control traffic and
the state in every node.
When used in conjunction with IEEE Std. 802.15.4 [IEEE802154], RPL
can be used to form a Personal Area Network (PAN) composed by a
6LoWPAN Border Router (6LBR) that is typically collocated with the
DODAG Root, and multiple 6LoWPAN Nodes (6LN), that can be RPL routers
of leaves.
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The PAN formation process starts from a DODAG Root. Before a node
joins a PAN, it has no information regarding available neighbors or
PANs. To discover available PANs, a joining node transmits PAN
Advertisement Solicits and listens for PAN Advertisements from either
the Root or other joined nodes.
The PAN Advertisements contain minimum information (such as network
name, DODAG size, etc.) for a node to select an appropriate PAN to
join or migrate. The DODAG size is the number of nodes in the DODAG
and communicating through the Root. The DODAG size thus is an
important metric for a node to decide which PAN to join. Therefore,
it is essential to ensure the value of DODAG size advertised is up-
to-date.
At this early stage, this document propose two methods to
disserminates the DODAG size to the PAN.
2. Terminology
2.1. 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].
"RPL", the "RPL Packet Information" (RPI), and "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 [RFC6551] 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].
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: Directed Acyclic Graph
DODAG: Destination-Oriented Directed Acyclic Graph
LLN: Low-Power and Lossy Network
PAN: Personal Area Network
RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks
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2.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Disseminating DODAG size
The value of DODAG size is collected by the Root, and disseminated to
all nodes in the PAN. To ensure timely delivering of DODAG size, it
has to be contained in periodic PAN-wide messages that can reach
every node in the PAN.
The DODAG size is defined by the DODAG Size Object and MAY be present
in the DODAG Metric Container option [RFC6551].
3.1. DODAG Size Object
[RFC6551] specifies a set of link and node routing metrics and
constraints suitable to LLNs. This document extends [RFC6551] by
defining a new DODAG metric called DODAG size.
The DODAG size object MAY be present in the DODAG Metric Container.
There MUST NOT be more than one DODAG size object as a metric per
DODAG Metric Container.
The DODAG size object is made of DODAG size fields and MUST at least
comprise one DODAG size field. Each DODAG size field has a fixed
length of 16 bits.
The DODAG size object does not contain any additional TLVs.
The DODAG size object Type has been assigned value TBD by IANA.
The format of the ETX object body is as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (field) ..... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: DODAG Size Object Body Format
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DODAG Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: DODAG Size field Format
DODAG Size: 16 bits. It is encoded using 16 bits in unsigned integer
format.
3.2. Disserminating DODAG size through DIO
According to [RFC6550], the DIO message is periodically sent to the
PAN, and it MAY carry an option called DODAG Metric Container. The
DODAG size object can be present in this option. Through the DIO
message, the DODAG size is gradually disseminated to nodes in the PAN
3.3. Disserminating DODAG size through DAO-ACK
The DAO-ACK message [RFC6550] is sent as unicast packet by the DODAG
Root in response to a unicast DAO message.
It MAY carry the DODAG Metric Container option [RFC6550]. The DODAG
size MAY be present in the DODAG Metric Container option.
The nodes in a PAN might be able to get the DODAG size timely through
the DAO-ACK messsage.. Compared with the DIO message, the DAO-ACK
message is tyipcally sent more frequently. Moreover, nodes deep in
the DODAG can get the DODAG size more quickly since the DAO-ACK is
directly sent by the Root in unicast.
4. IANA Considerations
This specification updates the "Routing Metric/Constraint Type"
subregistry of the "Routing Protocol for Low Power and Lossy Networks
(RPL) Routing Metric/Constraint" Registry that was created for
[RFC6551].
IANA is thereby requested to allocate one new value as follows:
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+---------------+-------------+---------------+
| Value | Description | Reference |
+---------------+-------------+---------------+
| 9 (suggested) | DODAG size | This document |
+---------------+-------------+---------------+
Table 1: New DODAG Metric Object Type
5. Security Considerations
It is worth noting that in RPL [RFC6550], every node in the LLN that
is RPL-aware and has access to the RPL domain can inject any RPL-
based attack in the network, more in [RFC7416]. This document
applies typically to an existing deployment and does not change its
security requirements and operations. It is assumed that the
security mechanisms as defined for RPL are followed.
6. Acknowledgments
The authors wish to thank TBD.
7. 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>.
[RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
and D. Barthel, "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks", RFC 6551,
DOI 10.17487/RFC6551, March 2012,
<https://www.rfc-editor.org/info/rfc6551>.
[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>.
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8. Informative References
[IEEE802154]
IEEE standard for Information Technology, "IEEE Std.
802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low-Rate
Wireless Personal Area Networks".
[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>.
Authors' Addresses
Huimin She
Cisco Systems, Inc
Xinsi Building
No. 926 Yishan Road, Xuhui District
SHANGHAI
200233
China
Email: hushe@cisco.com
Li Zhao
Cisco Systems, Inc
Xinsi Building
No. 926 Yishan Road, Xuhui District
SHANGHAI
200233
China
Email: liz3@cisco.com
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Pascal Thubert
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
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