Internet DRAFT - draft-guo-roll-loop-free-dodag-repair
draft-guo-roll-loop-free-dodag-repair
ROLL J. Guo
Internet-Draft P. Orlik
Intended status: Standards Track G. Bhatti
Expires: October 5, 2013 Mitsubishi Electric Research Laboratories
April 3, 2013
Loop Free DODAG Local Repair
draft-guo-roll-loop-free-dodag-repair-01
Abstract
IETF has been developing IPv6 based standards for Low-power and Lossy
Networks (LLNs) to meet requirements of constrained applications,
such as field monitoring, inventory control and so on. IPv6 Routing
Protocol for LLNs (RPL) has been published in [RFC6550]. Based on
routing metrics and constraints [RFC6551], RPL builds Directed
Acyclic Graph (DAG) topology to establish bidirectional routes for
LLNs for traffic types of multipoint-to-point, point-to-multipoint,
and point-to-point. RPL routes are optimized for traffic to or from
one or more roots that act as sinks. As a result, a DAG is
partitioned into one or more Destination Oriented DAGs (DODAGs), one
DODAG per sink. RPL is widely considered as a feasible routing
protocol for LLNs. However, DODAG loops caused by local DODAG repair
mechanism is an issues to be addressed. This draft introduces a loop
free local DODAG repair mechanism. This draft also introduces a
piggybacked data option for transferring delay sensitive data during
route repair process. The piggybacked data can be included in DODAG
Repair Request (DRQ) message or DODAG Information Solicitation (DIS)
message.
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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 http://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 April 4, 2013.
Copyright Notice
Copyright (c) 2012 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
(http://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 . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. ICMPv6 RPL Control Message Extension . . . . . . . . . . . . . . 6
3.1. DODAG Repair Request (DRQ) . . . . . . . . . . . . . . . . 6
3.1.1. Format of the DRQ Base Object . . . . . . . . . . . 6
3.1.2. Secure DRQ . . . . . . . . . . . . . . . . . . . . . 7
3.1.3. DRQ Options . . . . . . . . . . . . . . . . . . . . 8
3.2. DODAG Repair Reply (DRP). . . . . . . . . . . . . . . . . . 8
3.2.1. Format of the DRP Base Object . . . . . . . . . . . 8
3.2.2. Secure DRP . . . . . . . . . . . . . . . . . . . . . 9
3.2.3. DRP Options . . . . . . . . . . . . . . . . . . . . 9
3.3. Format of the Path Option . . . . . . . . . . . . . . . . . 9
4. DODAG Local Repair . . . . . . . . . . . . . . . . . . . . . . 10
4.1. DODAG Local Repair in Storing Mode . . . . . . . . . . . . 11
4.1.1. DRQ Message Processing . . . . . . . . . . . . . . 11
4.1.2. DRP Message Processing . . . . . . . . . . . . . . 12
4.2. DODAG Local Repair in Non-Storing Mode . . . . . . . . . . 13
4.2.1. DRQ Message Processing . . . . . . . . . . . . . . . 14
4.2.2. DRP Message Processing . . . . . . . . . . . . . . . 14
5. DIS Message with Piggybacked Data . . . . . . . . . . . . . . . 15
5.1. Format of the Modified DIS Base Object . . . . . . . . . . 17
5.2. Modified DIS Options . . . . . . . . . . . . . . . . . . . 17
5.3. Process of the Modified DIS message . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
Low-power and Lossy Networks (LLNs) are a class of networks in which
nodes and their communication links are constrained. LLN nodes
typically operate with constrains on processing power, physical size,
memory, power consumption, lifetime, and rate of activity. Their
communication links are characterized by high loss rate, low data
rate, instability, low transmission power, and short transmission
range. There can be from a few dozen up to thousands of nodes within
a LLN. Routing in LLNs is different from routing in mobile ad-hoc
networks. IETF has developed an IPv6 Routing Protocol for LLNs (RPL)
in [RFC6550]. RPL supports multipoint-to-point traffic and point-to-
multipoint traffic. The support for point-to-point traffic is also
available.
RPL builds Directed Acyclic Graph (DAG) topology, which is
partitioned into one or more Destination Oriented DAGs (DODAGs).
DODAG is basic logical structure in RPL. RPL nodes construct and
maintain DODAG through the DODAG Information Object (DIO) message
which is transmitted via link-local multicasting by using the Trickle
timer [RFC6206]. The sink in a DODAG is called the DODAG root. RPL
defines rules to transmit the DIO messages within a DODAG. The DODAG
root configures the DODAG parameters including RPLInstanceID,
DODAGVersionNumber, DODAGID, Rank, etc. and advertises the DODAG
parameters in the DIO messages. To join a DODAG, a node selects a set
of DODAG parents, on the routes towards the DODAG root, and a
preferred DODAG parent as the preferred next hop node for upward
traffic. Once a node joins a DODAG, it transmits DIO messages to
advertise the DODAG parameters.
The traffic inside a LLN flows along the edges of the DODAG, either
upward or downward. In RPL, upward routes, having the DODAG root as
destination, are provided by the DODAG construction mechanism using
DIO messages. Downward routes, from the DODAG root to any other
destination, are provided by these destinations transmitting the
Destination Advertisement Object (DAO) messages.
Three different modes of operation (MOP) for downward routes are
specified in [RFC6550]:
1) No downward routes maintained by RPL.
2) Storing mode of operation in which each router stores downward
routing tables for its sub-DODAG. In Storing mode, the DAO message
is sent to DAO parents. A node unicasts the DAO messages to the
selected parent(s). Transmission of the DAO messages propagates
from the nodes towards the DODAG root, where each intermediate
router adds its downward routing stack to the DAO messages. In
Storing mode, downward traffic is sent by using the downward
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routing tables.
3) Non-Storing mode of operation in which only the DODAG root
stores routes to all nodes in the network. In Non-Storing mode,
the DAO message is sent to the DODAG root. A node unicasts the DAO
messages to the DODAG root, which then calculates routes to all
destinations by piecing together the information collected from
the DAO messages. In Non-Storing mode, downward traffic is sent by
way of source routing.
An RPL node may act as a leaf node or as a router. RPL defines
operation rules for both leaf node and router in [RFC6550]. For
example, a leaf node does not extend DODAG connectivity. An RPL
router needs to implement Trickle [RFC6206]. An RPL router
implementation needs to support the MOP in use by the DODAG, that is,
support for upward routes only or support for upward routes and
downward routes in Storing mode or support for upward routes and
downward routes in Non-Storing mode.
RPL has been implemented and tested. It has been shown that DODAG
loops occur quite often [83rd IETF Meeting Presentation]. The cause
of DODAG loops comes from rank increase by DODAG local repair
mechanism. This draft introduces a method for repairing DODAG locally
without causing any DODAG loops. The DODAG local repair method
applies to both Storing and Non-Storing modes of operation in RPL.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Additionally, this draft employs terminologies defined in [RFC6550],
and extends following terminologies:
DIO: DODAG Information Object in which the rank is represented by two
integers.
Up: Up refers to the direction from leaf node or router node towards
the DODAG root.
Down: Down refers to the direction from the DODAG root towards leaf
node or router node.
This draft introduces the following new terminologies:
DRQ: DODAG Repair Request
DRP: DODAG Repair Reply
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Rank_DRQ: The rank of the node generating the DRQ message.
Rank_DRP: The rank of the node transmitting the DRP message.
DRQID: IPv6 address of the node generating DRQ message.
DRSN: Sequence number of the DRQ message of the node generating DRQ
message.
3. ICMPv6 RPL Control Message Extension
This draft uses RPL control messages defined in in Figure 6 and
Figure 7 of [RFC6550]. In addition, to repair DODAG locally,
two new RPL control messages, DODAG Repair Request (DRQ)
message and DODAG Repair Reply (DRP) message, are introduced.
The code field for the DRQ and DRP messages needs to be
assigned by IANA. The message base for DRQ and DRP are defined
as follows.
3.1. DODAG Repair Request (DRQ)
The DRQ message is used by a node to repair a DODAG locally if
a parent becomes unreachable. A node may also use the DRQ
message to discover additional parents if it is necessary.
3.1.1. Format of the DRQ Base Object
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 | RankQ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DRSN | HC | MH |P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DRQID +
| |
+ +
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| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
Figure 1: The DRQ Base Object
RPLInstanceID: 8-bit unsigned field as described in [RFC6550] to
indicate which RPL Instance the DODAG is a part.
Version Number: 8-bit unsigned integer as described in [RFC6550] to
indicate the DODAGVersionNumber.
RankQ: 16-bit unsigned integer indicating rank of the node generating
the DRQ message.
DRSN: 8-bit field indicating sequence number of the DRQ message at
the node generating the DRQ message.
HC: 4-bit field to indicate the number of hops traveled by a DRQ
message.
MH: 4-bit field to indicate the maximum number of hops a DRQ message
can travel. If a DRQ message reaches the maximum number of
hops, it must be ignored.
P: 1-bit flag to indicate if the sender has included the piggybacked
data. If P = 1, piggybacked data is present and a receiver MAY
consider to forward piggybacked data towards the DODAG root. If
P = 0, piggybacked is not present. A node sets P flag to 1 only
if its parent set is empty and it has a delay sensitive packet
to transmit. For example, if a building monitoring sensor
detects fire, it must send a notification as soon as possible.
Reserved: 15 bits of the DRQ Base are reserved. They must be set to
zero on transmission and must be ignored on reception.
DODAGID: 128-bit field as defined in [RFC6550]. A DODAGID is the
identifier of a DODAG root. The DODAGID is unique within the
scope of a RPL Instance in the LLN. The DODAGID must be a
routable IPv6 address belonging to the DODAG root.
DRQID: 128-bit IPv6 address of the node generating the DRQ message.
3.1.2. Secure DRQ
A Secure DRQ message follows the format in Figure 7 of [RFC6550],
where the base format is the DRQ message shown in Figure 1.
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3.1.3. DRQ Options
The DRQ message may carry valid options.
This draft allows for the DRQ message to carry the following options:
0x00 Pad1
0x01 PadN
Path: This option field is present only if MOP is Non-Storing. The
Path field contains IPv6 addresses of traversed nodes by the DRQ
message along the path.
PiggyData: This option field is present only if flag P = 1.
PiggyData field contains data to be forward to the root..
3.2. DODAG Repair Reply (DRP)
Upon receiving a DRQ message, a router with lower rank and non-
empty DODAG parent set may generate a DRP message in responding to
a received DRQ message.
3.2.1. Format of the DRP Base Object
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 | RankQ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RankP | DRSN | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DRPID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
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Figure 2: The DRP Base Object
RPLInstanceID: 8-bit unsigned field as described in [RFC6550] to
indicate which RPL Instance the DODAG is a part.
Version Number: 8-bit unsigned integer as described in [RFC6550] to
indicate the DODAGVersionNumber.
RankQ: 16-bit unsigned integer indicating rank of the node generating
the DRQ message.
RankP: 16-bit unsigned integer indicating rank of the node
transmitting the DRP message.
DRSN: 8-bit field indicating the sequence number of DRQ message at
the node generating the DRQ message.
Reserved: 8 bits of the DRP Base are reserved. They must be set to
zero on transmission and must be ignored on reception.
DODAGID: 128-bit field as defined in [RFC6550]. A DODAGID is the
identifier of a DODAG root. The DODAGID is unique within the
scope of a RPL Instance in the LLN. The DODAGID MUST be a
routable IPv6 address belonging to the DODAG root.
DRPID: 128-bit IPv6 address of the node that is destination of the
DRP message.
3.2.2. Secure DRP
A Secure DRP message follows the format in Figure 7 of [RFC6550],
where the base format is the DRP message shown in Figure 2.
3.2.3. DRP Options
The DRP message may carry valid options.
This draft allows for the DRP message to carry the following options:
0x00 Pad1
0x01 PadN
Path: This option is present only if MOP is Non-Storing. The Path
field contains IPv6 addresses of traversed nodes by the DRQ
message along the path.
3.3. RPL Control Message Options
The formats of option Pad1 and PadN are described in Figure 20 and
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Figure 21 of [RFC6550], respectively.
The format of the Path option is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
| Option Type | Option Length | Path Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 3: Format of the Path Option
Option Type: 8-bit identifier of the type of option. The Option Type
value needs to be assigned by IANA.
Option Length: 8-bit unsigned integer, representing the length in
octets of the option Path Data field, not including the Option
Type and Option Length fields.
Path Data: A variable length field that contains a list of IPv6
addresses.
The format of the PiggyData option is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | RPLInstanceID |Version Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ SourceID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload
+-+-+-+-+-+-+-+-+
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Figure 4: Format of the PiggyData Option
Option Type: 8-bit identifier of the type of option. The Option Type
value needs to be assigned by IANA.
Option Length: 8-bit unsigned integer, representing the length in
octets of the option PiggyData field, not including the Option
Type and Option Length fields.
RPLInstanceID, Version Number and DODAGID are described in RFC 6550.
SourceID is same as DRQID.
PiggyData: A variable length field that contains payload of
piggybacked data.
4. Loop Free DODAG Local Repair
In RPL, the rank plays very important role in the DODAG construction
and maintenance. The rank of a node defines a position of the node
relative to other nodes with respect to the DODAG root. Each node
maintains its own rank. The DODAG root has the lowest rank. Nodes
maintain their ranks based on parent-child relationship such that a
child must have a rank strictly greater than ranks of all its DODAG
parents. The DODAG root has no parent. The acyclic structure of the
DODAG is guaranteed as long as the rank of any node is strictly
greater than ranks of its DODAG parents. It is safe for a node to
decrease its rank, as long as its rank remains greater than the ranks
of its DODAG parents. However, rank increase can cause DODAG loops.
The DODAG local repair methods provided in this draft does not
increase the rank, and therefore, is loop free.
When a DODAG parent becomes unreachable, a node may switch to another
DODAG parent for upward traffic. DODAG may be locally repaired by the
node transmitting a DRQ message. The DRQ message is transmitted by
the DRQ message generator via link-local multicasting to all-RPL-
nodes.
Upon receiving a DRQ message, a link-local neighboring router which
is not the DODAG root discards the DRQ message if it does not have
any DODAG parent. If the link-local neighboring router is the DODAG
root, it accepts the DRQ message and generates a DRP message. If the
link-local neighboring router is not the DODAG root and has a non-
empty DODAG parent set and its rank is lower than RankQ, it accepts
the DRQ message and generates a DRP message. If the link-local
neighboring router is not the DODAG root and has a non-empty DODAG
parent set and its rank is greater than or equal to RankQ, it
forwards the DRQ message to its preferred DODAG parent. This
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forwarding process continues until the DRQ message is discarded by a
router that has an empty DODAG parent set or the DRQ message reaches
a node which is either the DODAG root or a router that has a non-
empty DODAG parent set and a rank lower than RankQ, a DRP message is
then generated.
The DRP message is unicasted. In Storing mode, the DRP message
generator transmits the DRP message to the DRQ message generator by
using a downward routing table. In Non-Storing mode, the DRP message
generator transmits the DRP message to the DRQ message generator by
way of source routing via the Path option.
4.1. DODAG Local Repair in Storing Mode
In Storing mode, if a DODAG parent becomes unreachable, a node
removes that DODAG parent from its DODAG parent set.
If the updated DODAG parent set becomes empty, the node shall
transmit a DRQ message to discover new DODAG parents.
If the updated DODAG parent set is not empty, the node checks if the
removed DODAG parent is its preferred DODAG parent. If yes, the node
shall select a new preferred DODAG parent. Whether or not the removed
DODAG parent is the preferred DODAG parent, the node may transmit a
DRQ message to discover additional parents. The node may also
schedule a No-Path DAO message transmission if the removed DODAG
parent is its DAO parent.
To transmit a DRQ message in Storing mode, the node generates a DRQ
message. It sets RPLInstanceID, DODAGVersionNumber and DODAGID by
using the maintained DODAG parameters. It sets RankQ to its rank. The
node increases its DRSN by 1 and sets HC = 0, and MH to an
appropriate value. There is no Path option field in Storing mode.
4.1.1. DRQ Message Processing
When a router receives a DRQ message, it discards the DRQ message if
its DODAG parent set is empty. Otherwise, the router performs the
following filtering process and discards the DRQ message if any of
following conditions is true:
i) RPLInstanceID or DODAGVersionNumber or DODAGID in the DRQ
message is not equal to the respective value maintained by the
router.
ii) The DRQ message was received already by comparing DRQID and
DRSN.
iii) HC is equal to MH.
iv) The DRQ message is transmitted by router's DODAG parent.
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v) The DRQ message is generated by router itself or by its DODAG
parent.
If the DRQ message passes filtering process, the receiving router
processes the DRQ message further.
If the receiving router is the DODAG root, it accepts the DRQ message
and generates a DRP message. To generate a DRP message, the DODAG
root copies RPLInstanceID, DODAGVersionNumber, DRSN, and DODAGID from
the DRQ message. It sets DRPID to DRQID, RankQ to the RankQ in DRQ
message, and RankP to its rank. The DODAG root forwards the DRP
message to the node from which it received the DRQ message.
If the receiving router is not the DODAG root and its rank is lower
than RankQ, the router accepts the DRQ message and generates a DRP
message as the root does. The router forwards the DRP message to the
node from which it received the DRQ message.
If the receiving router is not the DODAG root and its rank is greater
than or equal to RankQ, it adds a route entry to node DRQID into its
downward routing table, increases value of HC field by 1 and forwards
the DRQ message to its preferred DODAG parent.
If P = 1 and the receiver is the DODAG root, the root processes
piggybacked data. The root MAY also mark downward routes to sender as
invalid and waits for new DAO messages to reestablish downward
routes.
If P = 1 and the receiver is not the DODAG root, besides generating
DRP message, the receiver MAY forward the piggybacked data to its
parent.
4.1.2. DRP Message Processing
When a node receives a DRP message, it first performs filtering
process and discards the DRP message if any of following conditions
is true:
i) RPLInstanceID or DODAGVersionNumber or DODAGID in the DRP
message is not equal to the respective value maintained by the
receiving node.
ii) The DRP message was received already by comparing DRPID and
DRSN.
iii) The receiving node is leaf node and is not the DRQ message
generator.
If DRP message passes filtering process, the receiving node processes
the DRP message further.
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The receiving node can be a leaf node or a router.
If the receiving node is the DRQ message generator and the DRP
message sender is not in its DODAG parent set, it may add the DRP
message sender into its DODAG parent set and select a new preferred
DODAG parent. The receiving node may schedule a DAO message
transmission if the DRP message sender is added into its DAO parent
set.
If the receiving node is not the DRQ message generator, it must be a
router. If the receiving router has no route entry to node DRPID in
its downward routing table, it discards the DRP message.
If the receiving router has a downward route entry to node DRPID and
its rank is greater than or equal to RankQ, it checks if it can
decrease its rank such that RankQ > its rank > RankP. If not, the
receiving router discards the DRP message. If yes, the receiving
router decreases its rank to an appropriate value and may add the DRP
message sender into its DODAG parent set if the sender is not in its
DODAG parent set. The receiving router updates its DODAG parent set
caused by its rank decrease, that is, removing DODAG parents whose
ranks are greater than or equal to its new rank. If its preferred
DODAG parent is removed, it selects a new preferred DODAG parent. The
receiving router then updates the RankP of the DRP message to its
rank, and forwards the DRP message to next hop node on the downward
route. It may schedule a No-Path DAO message transmission if any of
its DAO parents is removed due to its rank decrease or the DRP sender
was added into its DAO parent set.
If the receiving router has a downward route entry to node DRPID and
its rank is lower than RankQ, it updates the RankP field of the DRP
message to its rank, and forwards the DRP message to next hop node on
the downward route.
The rank of receiving router is less than RankQ if the receiving
router is on multiple DODAG repair downward routes. When the
receiving router receives a DRP message, it may decrease its rank.
Therefore, subsequent DRP messages may carry a RankQ greater than or
equal to the rank of receiving router. If the receiving router is
only on a single DODAG repair downward route, its rank must be
greater than or equal to RankQ based on the DRQ message process
procedure.
4.2. DODAG Local Repair in Non-Storing Mode
The handling of unreachable parent in Non-Storing mode is similar to
that in Storing mode. However, there are two differences. The first
difference is that after removing a DAO parent from its DAO parent
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set, if its DODAG parent set is not empty, a node may schedule a DAO
message transmission instead of the No-Path DAO message transmission.
The second difference is that to generate a DRQ message in Non-
Storing mode, a node adds a Path option field by inserting its IPv6
address into the Path option field.
4.2.1. DRQ Message Processing
When a router receives a DRQ message, it performs same filtering
process as that in Storing mode. If the DRQ message passes filtering
process, the receiving router processes the DRQ message further.
If the receiving router is the DODAG root, it accepts the DRQ message
and generates a DRP message similarly as in Storing mode. In
addition, the DODAG root adds a Path option in DRP message and copies
Path option field from DRQ message to Path option field of DRP
message. The DODAG root transmits the DRP message to destination node
DRPID along the route specified by the Path option, and on the
downward route, intermediate routers obtain route information from
the Path option field of DRP message.
If the receiving router is not the DODAG root and its rank is lower
than Rank_DRQ, it accepts the DRQ message and generates a DRP message
as the DODAG root does. It then transmits the DRP message to
destination node DRPID along the route specified by the Path option.
If the receiving router is not the DODAG root and its rank is greater
than or equal to RankQ, it updates the DRQ message by inserting its
own IPv6 address into the Path option field, increasing the value of
HC field by 1 and forwards the DRQ message to its preferred DODAG
parent.
If P = 1 and the receiver is the DODAG root, the DODAG root processes
piggybacked data. The DODAG root MAY also mark downward routes to
node REQID as invalid and waits for new DAO messages to reestablish
downward routes.
If P = 1 and the receiver is not the DODAG root, besides generating
the DRP message, the receiver MAY forward the piggybacked data to its
parent.
4.2.2. DRP Message Processing
When a node receives a DRP message, it performs the same filtering
process as in Storing mode. If the DRP message passes filtering
process, the receiving node processes the DRP message further.
The receiving node can be a leaf node or a router.
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If the receiving node is the DRQ message generator and the DRP
message sender is not in its DODAG parent set, it may add the DRP
message sender into its DODAG parent set. The receiving node may
select a new preferred DODAG parent. It may also schedule a DAO
message transmission if the DRP message sender is added into its DAO
parent set.
If the receiving node is not DRQ message generator, it must be a
router. If the receiving router is not on the route specified by Path
option, it discards the DRP message.
If the receiving router is on the route specified by Path option and
its rank is greater than or equal to RankQ, the receiving router
checks if it can decrease its rank such that RankQ > its rank >
RankP. If no, the receiving node discards the DRP message. If yes,
the receiving node decreases its rank to an appropriate value and may
add the DRP message sender into its DODAG parent set if the sender is
not in its DODAG parent set. The receiving router updates its DODAG
parent set by removing any DODAG parent whose rank is greater than or
equal to its new rank. If its preferred DODAG parent is removed, it
selects a new preferred DODAG parent. The receiving router updates
the RankP of DRP message to its new rank, and forwards the DRP
message to the destination node DRPID by obtaining next hop node via
the Path option field. Furthermore, the receiving router may schedule
a DAO message transmission if any of its DAO parents was removed due
to its rank decrease or the DRP sender was added into its DAO parent
set.
If the receiving router is on the route specified by Path option and
its rank is lower than RankQ, the receiving router updates the RankP
to its rank, and forwards the DRP message to destination node DRPID
by obtaining next hop node via Path option.
The rank of receiving router is less than RankQ if the receiving
router is on multiple DODAG repair downward routes. When the
receiving router receives a DRP message, it may decrease its rank.
Therefore, subsequent DRP messages may carry a RankQ greater than or
equal to the rank of receiving router. If the receiving router is
only on a single DODAG repair downward route, its rank must be
greater than or equal to RankQ based on the DRQ message process
procedure.
5. DIS Message with Piggybacked Data
For some delay sensitive applications, data must be sent to data sink
as soon as possible. For example, if a building monitoring sensor
detects fire, it must send the alert message to system controller
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without delay since in this case, any delay could be costly.
If a node has a delay sensitive dada and an empty parent set, it MAY
piggyback data into the DIS message. To accomplish this, a modified
DIS message is proposed.
5.1 Format of the Modified DIS Base Object
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
|P| Flags | Reserved | Option(s) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - -
Figure 5: Modified Format of the DIS Base Object
P: 1-bit flag to indicate if sender has included a piggybacked data
option. If P = 1, piggybacked data is present, and the receiver
MAY consider to forward piggybacked data towards the DODAG
root. If P = 0, piggybacked is not present. A sender sets P
flag to 1 only if its parent set is empty and it has a delay
sensitive data to transmit.
Flags: 7-bit unused filed reserved for flags. The filed MUST be
initialized to zero by the sender and MUST be ignored by the
receiver.
8-bit Reserved filed and Option(s) field are same as described in RFC
6550.
5.2 Modified DIS Options
Besides options specified in RFC 6550, the DIS message MAY carry
PiggyData option as shown in Figure 4. However, this option is
present only if flag P = 1.
5.3 Process of the Modified DIS Message
If flag P = 0, the process of the DIS message is same as specified in
RFC 6550. If flag P = 1, the receiver MAY perform extra process. If
receiver is the DODAG root, the root processes piggybacked data. The
root MAY also mark downward routes to node REQID as invalid and waits
for new DAO messages to reestablish downward routes. If the receiver
is not the DODAG root and sender is not its parent, it MAY forward
the piggybacked data to its parent.
6. Security Considerations
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This draft introduces an alternative rank computation method and a
DODAG local repair mechanism. In general, the security considerations
for the DODAG construction and maintenance are similar to the ones
for the operation of RPL as described in Section 19 of [RFC6550].
Section 10 of RPL specification [RFC6550] describes a variety of
security mechanisms that provide data confidentiality,
authentication, replay protection and delay protection services. Each
RPL control message has a secure version that allows the
specification of the level of security and the algorithms used to
secure the message. New RPL control messages (DRQ and DRP) defined in
this draft have secure versions as well.
7. IANA Considerations
This draft defines two new RPL Control Messages types and a new RPL
Control Message Option.
Code field for the DODAG Repair Request (DRQ) message needs to be
assigned by IANA.
Code field for the DODAG Repair Reply (DRP) message needs to be
assigned by IANA.
Option Type field for Path option field needs to be assigned by IANA.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC6550] Winter, T., Thubert, P., 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, March 2012.
[RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., Ko, J., "The
Trickle Algorithm", RFC 6206, March 2011.
[RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D.
Barthel, "Routing Metrics Used for Path Calculation in
Low-Power and Lossy Networks", RFC 6551, March 2012.
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8.2. Informative References
[83rd IETF Meeting Presentation] Clausen, T., Yi, J., Colin de
Verdiere, A., Herberg, U., "Experiences with RPL: IPv6
Routing Protocol for Low power and Lossy Networks", Paris,
France, March 2012.
Authors' Addresses
Jianlin Guo
Mitsubishi Electric Research Laboratories
201 Broadway
Cambridge, Massachusetts 02139
USA
Phone: +1 617 621 7541
Email: guo@merl.com
Philip Orlik
Mitsubishi Electric Research Laboratories
201 Broadway
Cambridge, Massachusetts 02139
USA
Phone: +1 617 621 7570
Email: porlik@merl.com
Ghulam Bhatti
Mitsubishi Electric Research Laboratories
201 Broadway
Cambridge, Massachusetts 02139
USA
Phone: +1 617 621 7513
Email: gbhatti@merl.com
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