Supporting Asymmetric Links in Low Power Networks: AODV-RPL
draft-ietf-roll-aodv-rpl-13
| Document | Type | Active Internet-Draft (roll WG) | |
|---|---|---|---|
| Authors | Charles E. Perkins , S.V.R Anand , Satish Anamalamudi , Bing (Remy) Liu | ||
| Last updated | 2022-04-11 (Latest revision 2022-03-07) | ||
| Replaces | draft-satish-roll-aodv-rpl | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
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draft-ietf-roll-aodv-rpl-13
ROLL C.E. Perkins
Internet-Draft Lupin Lodge
Intended status: Standards Track S.V.R.Anand
Expires: 8 September 2022 Indian Institute of Science
S. Anamalamudi
SRM University-AP
B. Liu
Huawei Technologies
7 March 2022
Supporting Asymmetric Links in Low Power Networks: AODV-RPL
draft-ietf-roll-aodv-rpl-13
Abstract
Route discovery for symmetric and asymmetric Peer-to-Peer (P2P)
traffic flows is a desirable feature in Low power and Lossy Networks
(LLNs). For that purpose, this document specifies a reactive P2P
route discovery mechanism for both hop-by-hop routing and source
routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL
protocol (AODV-RPL). Paired Instances are used to construct
directional paths, for cases where there are asymmetric links between
source and target nodes.
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 https://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 8 September 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6
4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 7
4.1. AODV-RPL RREQ Option . . . . . . . . . . . . . . . . . . 7
4.2. AODV-RPL RREP Option . . . . . . . . . . . . . . . . . . 9
4.3. AODV-RPL Target Option . . . . . . . . . . . . . . . . . 10
5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 12
6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 14
6.1. Route Request Generation . . . . . . . . . . . . . . . . 14
6.2. Receiving and Forwarding RREQ messages . . . . . . . . . 14
6.2.1. Step 1: RREQ reception and evaluation . . . . . . . . 15
6.2.2. Step 2: TargNode and Intermediate Router
determination . . . . . . . . . . . . . . . . . . . . 15
6.2.3. Step 3: Intermediate Router RREQ processing . . . . . 16
6.2.4. Step 4: Symmetric Route Processing at an Intermediate
Router . . . . . . . . . . . . . . . . . . . . . . . 16
6.2.5. Step 5: RREQ propagation at an Intermediate Router . 17
6.2.6. Step 6: RREQ reception at TargNode . . . . . . . . . 17
6.3. Generating Route Reply (RREP) at TargNode . . . . . . . . 17
6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 18
6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 18
6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 18
6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 19
6.4.1. Step 1: Receiving and Evaluation . . . . . . . . . . 19
6.4.2. Step 2: OrigNode or Intermediate Router . . . . . . . 19
6.4.3. Step 3: Build Route to TargNode . . . . . . . . . . . 20
6.4.4. Step 4: RREP Propagation . . . . . . . . . . . . . . 20
7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 20
8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Normative References . . . . . . . . . . . . . . . . . . 23
12.2. Informative References . . . . . . . . . . . . . . . . . 24
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Appendix A. Example: Using ETX/RSSI Values to determine value of S
bit . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 27
B.1. Changes from version 12 to version 13 . . . . . . . . . . 27
B.2. Changes from version 11 to version 12 . . . . . . . . . . 28
B.3. Changes from version 10 to version 11 . . . . . . . . . . 28
B.4. Changes from version 09 to version 10 . . . . . . . . . . 29
B.5. Changes from version 08 to version 09 . . . . . . . . . . 30
B.6. Changes from version 07 to version 08 . . . . . . . . . . 30
B.7. Changes from version 06 to version 07 . . . . . . . . . . 31
B.8. Changes from version 05 to version 06 . . . . . . . . . . 31
B.9. Changes from version 04 to version 05 . . . . . . . . . . 31
B.10. Changes from version 03 to version 04 . . . . . . . . . . 32
B.11. Changes from version 02 to version 03 . . . . . . . . . . 32
Appendix C. Contributors . . . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
Routing Protocol for Low-Power and Lossy Networks (RPL) [RFC6550] is
an IPv6 distance vector routing protocol designed to support multiple
traffic flows through a root-based Destination-Oriented Directed
Acyclic Graph (DODAG). Typically, a router does not have routing
information for most other routers. Consequently, for traffic
between routers within the DODAG (i.e., Peer-to-Peer (P2P) traffic)
data packets either have to traverse the root in non-storing mode, or
traverse a common ancestor in storing mode. Such P2P traffic is
thereby likely to traverse longer routes and may suffer severe
congestion near the root (for more information see [RFC6997],
[RFC6998]). The network environment that is considered in this
document is assumed to be the same as described in Section 1 of
[RFC6550].
The route discovery process in AODV-RPL is modeled on the analogous
procedure specified in AODV [RFC3561]. The on-demand nature of AODV
route discovery is natural for the needs of peer-to-peer routing in
RPL-based LLNs. AODV terminology has been adapted for use with AODV-
RPL messages, namely RREQ for Route Request, and RREP for Route
Reply. AODV-RPL currently omits some features compared to AODV -- in
particular, flagging Route Errors, "blacklisting" unidirectional
links ([RFC3561]), multihoming, and handling unnumbered interfaces.
AODV-RPL reuses and extends the core RPL functionality to support
routes with bidirectional asymmetric links. It retains RPL's DODAG
formation, RPL Instance and the associated Objective Function
(defined in [RFC6551]), trickle timers, and support for storing and
non-storing modes. AODV-RPL adds basic messages RREQ and RREP as
part of RPL DODAG Information Object (DIO) control message, which go
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in separate (paired) RPL instances. AODV-RPL does not utilize the
Destination Advertisement Object (DAO) control message of RPL. AODV-
RPL uses the "P2P Route Discovery Mode of Operation" (MOP == 4) with
three new Options for the DIO message, dedicated to discover P2P
routes. These P2P routes may differ from routes discoverable by
native RPL. Since AODV-RPL uses newly defined Options, there is no
conflict with P2P-RPL [RFC6997], a previous document using the same
MOP. AODV-RPL can be operated whether or not P2P-RPL or native RPL
is running otherwise. For many networks AODV-RPL could be a
replacement for RPL, since it can find better routes at very moderate
extra cost. Consequently, it is unlikely that RPL would be needed in
a network that is running AODV-RPL, even though it would be possible
to run both protocols at the same time.
2. Terminology
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.
AODV-RPL reuses names for messages and data structures, including
Rank, DODAG and DODAGID, as defined in RPL [RFC6550].
AODV
Ad Hoc On-demand Distance Vector Routing [RFC3561].
Asymmetric Route
The route from the OrigNode to the TargNode can traverse different
nodes than the route from the TargNode to the OrigNode. An
asymmetric route may result from the asymmetry of links, such that
only one direction of the series of links satisfies the Objective
Function during route discovery.
Bi-directional Asymmetric Link
A link that can be used in both directions but with different link
characteristics.
DIO
DODAG Information Object
DODAG RREQ-Instance (or simply RREQ-Instance)
RPL Instance built using the DIO with RREQ option; used for
transmission of control messages from OrigNode to TargNode, thus
enabling data transmission from TargNode to OrigNode.
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DODAG RREP-Instance (or simply RREP-Instance)
RPL Instance built using the DIO with RREP option; used for
transmission of control messages from TargNode to OrigNode thus
enabling data transmission from OrigNode to TargNode.
Downward Direction
The direction from the OrigNode to the TargNode.
Downward Route
A route in the downward direction.
hop-by-hop routing
Routing when each router stores routing information about the next
hop.
on-demand routing
Routing in which a route is established only when needed.
OrigNode
The IPv6 router (Originating Node) initiating the AODV-RPL route
discovery to obtain a route to TargNode.
Paired DODAGs
Two DODAGs for a single route discovery process between OrigNode
and TargNode.
P2P
Peer-to-Peer -- in other words, not constrained a priori to
traverse a common ancestor.
reactive routing
Same as "on-demand" routing.
RREQ-DIO message
A DIO message containing the RREQ option. The RPLInstanceID in
RREQ-DIO is assigned locally by the OrigNode. The RREQ-DIO
message has a secure variant as noted in [RFC6550].
RREQ-InstanceID
The RPLInstanceID for the RREQ-Instance. This term is used to
indicate the value of the RPLInstanceID as provided by OrigNode in
the RREQ message. The RPLInstanceID in the RREP message along
with the Delta value determines the associated RREQ-InstanceID.
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RREP-DIO message
A DIO message containing the RREP option. OrigNode pairs the
RPLInstanceID in RREP-DIO to the one in the associated RREQ-DIO
message (i.e., the RREQ-InstanceID) as described in Section 6.3.2.
The RREP-DIO message has a secure variant as noted in [RFC6550].
Source routing
A mechanism by which the source supplies the complete route
towards the target node along with each data packet [RFC6550].
Symmetric route
The upstream and downstream routes traverse the same routers and
over the same links.
TargNode
The IPv6 router (Target Node) for which OrigNode requires a route
and initiates Route Discovery within the LLN network.
Upward Direction
The direction from the TargNode to the OrigNode.
Upward Route
A route in the upward direction.
ART option
AODV-RPL Target option: a target option defined in this document.
3. Overview of AODV-RPL
With AODV-RPL, routes from OrigNode to TargNode within the LLN
network are established "on-demand". In other words, the route
discovery mechanism in AODV-RPL is invoked reactively when OrigNode
has data for delivery to the TargNode but existing routes do not
satisfy the application's requirements. AODV-RPL works without
requiring the use of RPL or any other routing protocol.
The routes discovered by AODV-RPL are not constrained to traverse a
common ancestor. AODV-RPL can enable asymmetric communication paths
in networks with bidirectional asymmetric links. For this purpose,
AODV-RPL enables discovery of two routes: namely, one from OrigNode
to TargNode, and another from TargNode to OrigNode. AODV-RPL also
enables discovery of symmetric routes along Paired DODAGs, when
symmetric routes are possible (see Section 5).
In AODV-RPL, routes are discovered by first forming a temporary DAG
rooted at the OrigNode. Paired DODAGs (Instances) are constructed
during route formation between the OrigNode and TargNode. The RREQ-
Instance is formed by route control messages from OrigNode to
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TargNode whereas the RREP-Instance is formed by route control
messages from TargNode to OrigNode. Intermediate routers join the
DODAGs based on the Rank [RFC6550] as calculated from the DIO
message. Henceforth in this document, "RREQ-DIO message" means the
DIO message from OrigNode toward TargNode, containing the RREQ option
as specified in Section 4.1. Similarly, "RREP-DIO message" means the
DIO message from TargNode toward OrigNode, containing the RREP option
as specified in Section 4.2. The route discovered in the RREQ-
Instance is used for transmitting data from TargNode to OrigNode, and
the route discovered in RREP-Instance is used for transmitting data
from OrigNode to TargNode.
4. AODV-RPL DIO Options
4.1. AODV-RPL RREQ Option
OrigNode selects one of its IPv6 addresses and sets it in the DODAGID
field of the RREQ-DIO message. Exactly one RREQ option MUST be
present in a RREQ-DIO message, otherwise the message MUST be dropped.
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 |S|H|X| Compr | L | RankLimit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Orig SeqNo | |
+-+-+-+-+-+-+-+-+ |
| |
| |
| Address Vector (Optional, Variable Length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format for AODV-RPL RREQ Option
OrigNode supplies the following information in the RREQ option:
Option Type
TBD2
Option Length
The length of the option in octets, excluding the Type and Length
fields. Variable due to the presence of the address vector and
the number of octets elided according to the Compr value.
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S
Symmetric bit indicating a symmetric route from the OrigNode to
the router transmitting this RREQ-DIO. See Section 5.
H
Set to one for a hop-by-hop route. Set to zero for a source
route. This flag controls both the downstream route and upstream
route.
X
Reserved; MUST be initialized to zero and ignored upon reception.
Compr
4-bit unsigned integer. When Compr is nonzero, exactly that
number of prefix octets MUST be elided from each address before
storing it in the Address Vector. The octets elided are shared
with the IPv6 address in the DODAGID. This field is only used in
source routing mode (H=0). In hop-by-hop mode (H=1), this field
MUST be set to zero and ignored upon reception.
L
2-bit unsigned integer determining the length of time that a node
is able to belong to the RREQ-Instance (a temporary DAG including
the OrigNode and the TargNode). Once the time is reached, a node
MUST leave the RREQ-Instance and stop sending or receiving any
more DIOs for the RREQ-Instance. This naturally depends on the
node's ability to keep track of time. Once a node leaves an RREQ-
Instance, it MUST NOT rejoin the same RREQ-Instance. L is
independent from the route lifetime, which is defined in the DODAG
configuration option.
* 0x00: No time limit imposed.
* 0x01: 16 seconds
* 0x02: 64 seconds
* 0x03: 256 seconds
RankLimit
This field indicates the upper limit on the integer portion of the
Rank (calculated using the DAGRank() macro defined in [RFC6550]).
A value of 0 in this field indicates the limit is infinity.
Orig SeqNo
Sequence Number of OrigNode. See Section 6.1.
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Address Vector
A vector of IPv6 addresses representing the route that the RREQ-
DIO has passed. It is only present when the H bit is set to 0.
The prefix of each address is elided according to the Compr field.
TargNode can join the RREQ instance at a Rank whose integer portion
is less than or equal to the RankLimit. Any other node MUST NOT join
a RREQ instance if its own Rank would be equal to or higher than
RankLimit. A router MUST discard a received RREQ if the integer part
of the advertised Rank equals or exceeds the RankLimit.
4.2. AODV-RPL RREP Option
TargNode sets one of its IPv6 addresses in the DODAGID field of the
RREP-DIO message. Exactly one RREP option MUST be present in a RREP-
DIO message, otherwise the message MUST be dropped. TargNode
supplies the following information in the RREP option:
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 |G|H|X| Compr | L | RankLimit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Delta |X X| |
+-+-+-+-+-+-+-+-+ |
| |
| |
| Address Vector (Optional, Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Format for AODV-RPL RREP option
Option Type
TBD3
Option Length
The length of the option in octets, excluding the Type and Length
fields. Variable due to the presence of the address vector and
the number of octets elided according to the Compr value.
G
Gratuitous route (see Section 7).
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H
The H bit in the RREP option MUST be set to be the same as the H
bit in RREQ option. It requests either source routing (H=0) or
hop-by-hop (H=1) for the downstream route.
X
Reserved; MUST be initialized to zero and ignored upon reception.
Compr
4-bit unsigned integer. Same definition as in RREQ option.
L
2-bit unsigned integer defined as in RREQ option. The lifetime of
the RREP-Instance MUST be shorter than the lifetime of the RREQ-
Instance to which it is paired.
RankLimit
Similarly to RankLimit in the RREQ message, this field indicates
the upper limit on the integer portion of the Rank. A value of 0
in this field indicates the limit is infinity.
Delta
6-bit unsigned integer. This field is used to recover the RREQ-
InstanceID (see Section 6.3.3); 0 indicates that the RREQ-
InstanceID has the same value as the RPLInstanceID of the RREP
message.
X X
Reserved; MUST be initialized to zero and ignored upon reception.
Address Vector
Only present when the H bit is set to 0. For an asymmetric route,
the Address Vector represents the IPv6 addresses of the path
through the network the RREP-DIO has passed. For a symmetric
route, it is the Address Vector when the RREQ-DIO arrives at the
TargNode, unchanged during the transmission to the OrigNode.
4.3. AODV-RPL Target Option
The AODV-RPL Target (ART) Option is based on the Target Option in
core RPL [RFC6550]. The Flags field is replaced by the Destination
Sequence Number of the TargNode and the Prefix Length field is
reduced to 7 bits so that the value is limited to be no greater than
127.
A RREQ-DIO message MUST carry at least one ART Option. A RREP-DIO
message MUST carry exactly one ART Option. Otherwise, the message
MUST be dropped.
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OrigNode can include multiple TargNode addresses via multiple AODV-
RPL Target Options in the RREQ-DIO, for routes that share the same
requirement on metrics. This reduces the cost to building only one
DODAG.
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 | Dest SeqNo |X|Prefix Length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ |
| Target Prefix / Address (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: ART Option format for AODV-RPL
Option Type
TBD4
Option Length
Length of the option in octets excluding the Type and Length
fields.
Dest SeqNo
In RREQ-DIO, if nonzero, it is the Sequence Number for the last
route that OrigNode stored to the TargNode for which a route is
desired. In RREP-DIO, it is the destination sequence number
associated to the route. Zero is used if there is no known
information about the sequence number of TargNode, and not used
otherwise.
X
A one-bit reserved field. This field MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Prefix Length
7-bit unsigned integer. Number of valid leading bits in the IPv6
Prefix. If Prefix Length is 0, then the value in the Target
Prefix / Address field represents an IPv6 address, not a prefix.
Target Prefix / Address
(variable-length field) An IPv6 destination address or prefix.
The Prefix Length field contains the number of valid leading bits
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in the prefix. The Target Prefix / Address field contains the
least number of octets that can represent all of the bits of the
Prefix, in other words Ceil(Prefix Length/8) octets. The initial
bits in the Target Prefix / Address field preceding the prefix
length (if any) MUST be set to zero on transmission and MUST be
ignored on receipt. If Prefix Length is zero, the Address field
is 128 bits for IPv6 addresses.
5. Symmetric and Asymmetric Routes
Links are considered symmetric until indication to the contrary is
received. In Figure 4 and Figure 5, BR is the Border Router, O is
the OrigNode, each R is an intermediate router, and T is the
TargNode. If the RREQ-DIO arrives over an interface that is known to
be symmetric, and the S bit is set to 1, then it remains as 1, as
illustrated in Figure 4. If an intermediate router sends out RREQ-
DIO with the S bit set to 1, then each link en route from the
OrigNode O to this router has met the requirements of route
discovery, and the route can be used symmetrically.
BR
/----+----\
/ | \
/ | \
R R R
_/ \ | / \
/ \ | / \
/ \ | / \
R -------- R --- R ----- R -------- R
/ \ <--S=1--> / \ <--S=1--> / \
<--S=1--> \ / \ / <--S=1-->
/ \ / \ / \
O ---------- R ------ R------ R ----- R ----------- T
/ \ / \ / \ / \
/ \ / \ / \ / \
/ \ / \ / \ / \
R ----- R ----------- R ----- R ----- R ----- R ---- R----- R
>---- RREQ-Instance (Control: O-->T; Data: T-->O) ------->
<---- RREP-Instance (Control: T-->O; Data: O-->T) -------<
Figure 4: AODV-RPL with Symmetric Instances
Upon receiving a RREQ-DIO with the S bit set to 1, a node determines
whether this link can be used symmetrically, i.e., both directions
meet the requirements of data transmission. If the RREQ-DIO arrives
over an interface that is not known to be symmetric, or is known to
be asymmetric, the S bit is set to 0. If the S bit arrives already
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set to be '0', it is set to be '0' when the RREQ-DIO is propagated
(Figure 5). For an asymmetric route, there is at least one hop which
doesn't satisfy the Objective Function. Based on the S bit received
in RREQ-DIO, TargNode T determines whether or not the route is
symmetric before transmitting the RREP-DIO message upstream towards
the OrigNode O.
It is beyond the scope of this document to specify the criteria used
when determining whether or not each link is symmetric. As an
example, intermediate routers can use local information (e.g., bit
rate, bandwidth, number of cells used in 6tisch [RFC9030]), a priori
knowledge (e.g., link quality according to previous communication) or
use averaging techniques as appropriate to the application. Other
link metric information can be acquired before AODV-RPL operation, by
executing evaluation procedures; for instance test traffic can be
generated between nodes of the deployed network. During AODV-RPL
operation, OAM techniques for evaluating link state (see [RFC7548],
[RFC7276], [co-ioam]) MAY be used (at regular intervals appropriate
for the LLN). The evaluation procedures are out of scope for AODV-
RPL.
Appendix A describes an example method using the upstream Expected
Number of Transmissions (ETX) and downstream Received Signal Strength
Indicator (RSSI) to estimate whether the link is symmetric in terms
of link quality using an averaging technique.
BR
/----+----\
/ | \
/ | \
R R R
/ \ | / \
/ \ | / \
/ \ | / \
R --------- R --- R ---- R --------- R
/ \ --S=1--> / \ --S=0--> / \
--S=1--> \ / \ / --S=0-->
/ \ / \ / \
O ---------- R ------ R------ R ----- R ----------- T
/ \ / \ / \ / \
/ <--S=0-- / \ / \ / <--S=0--
/ \ / \ / \ / \
R ----- R ----------- R ----- R ----- R ----- R ---- R----- R
<--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0--
>---- RREQ-Instance (Control: O-->T; Data: T-->O) ------->
<---- RREP-Instance (Control: T-->O; Data: O-->T) -------<
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Figure 5: AODV-RPL with Asymmetric Paired Instances
As illustrated in Figure 5, an intermediate router determines the S
bit value that the RREQ-DIO should carry using link asymmetry
detection methods as discussed earlier in this section. In many
cases the intermediate router has already made the link asymmetry
decision by the time RREQ-DIO arrives.
6. AODV-RPL Operation
6.1. Route Request Generation
The route discovery process is initiated when an application at the
OrigNode has data to be transmitted to the TargNode, but does not
have a route that satisfies the Objective Function for the target of
the application's data. In this case, the OrigNode builds a local
RPLInstance and a DODAG rooted at itself. Then it transmits a DIO
message containing exactly one RREQ option (see Section 4.1) to
multicast group all-RPL-nodes. The DIO MUST contain at least one ART
Option (see Section 4.3), which indicates the TargNode. The S bit in
RREQ-DIO sent out by the OrigNode is set to 1.
Each node maintains a sequence number; the operation is specified in
section 7.2 of [RFC6550]. When the OrigNode initiates a route
discovery process, it MUST increase its own sequence number to avoid
conflicts with previously established routes. The sequence number is
carried in the Orig SeqNo field of the RREQ option.
The address in the ART Option can be a unicast IPv6 address or a
prefix. The OrigNode can initiate the route discovery process for
multiple targets simultaneously by including multiple ART Options.
Within a RREQ-DIO the Objective Function for the routes to different
TargNodes MUST be the same.
OrigNode can maintain different RPLInstances to discover routes with
different requirements to the same targets. Using the RPLInstanceID
pairing mechanism (see Section 6.3.3), route replies (RREP-DIOs) for
different RPLInstances can be generated.
The transmission of RREQ-DIO obeys the Trickle timer [RFC6206]. If
the length of time specified by the L field has elapsed, the OrigNode
MUST leave the DODAG and stop sending RREQ-DIOs in the related
RPLInstance.
6.2. Receiving and Forwarding RREQ messages
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6.2.1. Step 1: RREQ reception and evaluation
When a router X receives a RREQ message over a link from a neighbor
Y, X first determines whether or not the RREQ is valid. If so, X
then determines whether or not it has sufficient resources available
to maintain the state needed to process an eventual RREP if the RREP
were to be received. If not, then X MUST drop the packet and
discontinue processing of the RREQ. Otherwise, X next determines
whether the RREQ advertises a usable route to OrigNode, by checking
whether the link to Y can be used to tramsmit packets to OrigNode.
When H=0 in the incoming RREQ, the router MUST drop the RREQ-DIO if
one of its addresses is present in the Address Vector. When H=1 in
the incoming RREQ, the router MUST drop the RREQ message if Orig
SeqNo field of the RREQ is older than the SeqNo value that X has
stored for a route to OrigNode. Otherwise, the router determines
whether to propagate the RREQ-DIO. It does this by determining
whether or not a route to OrigNode using the upstream direction of
the incoming link satisfies the Objective Function (OF). In order to
evaluate the OF, the router first determines the maximum useful rank
(MaxUsefulRank). If the router has previously joined the RREQ-
Instance associated with the RREQ-DIO, then MaxUsefulRank is set to
be the Rank value that was stored when the router processed the best
previous RREQ for the DODAG with the given RREQ-Instance. Otherwise,
MaxUsefulRank is set to be RankLimit. If OF cannot be satisfied
(i.e., the Rank evaluates to a value greater than MaxUsefulRank) the
RREQ-DIO MUST be dropped, and the following steps are not processed.
Otherwise, the router MUST join the RREQ-Instance and prepare to
propagate the RREQ-DIO, as follows. The upstream neighbor router
that transmitted the received RREQ-DIO is selected as the preferred
parent.
6.2.2. Step 2: TargNode and Intermediate Router determination
After determining that a received RREQ provides a usable route to
OrigNode, a router determines whether it is a TargNode, or a possible
intermediate router between OrigNode and a TargNode, or both. The
router is a TargNode if it finds one of its own addresses in a Target
Option in the RREQ. After possibly propagating the RREQ according to
the procedures in Steps 3, 4, and 5, the TargNode generates a RREP as
specified in Section 6.3.
If the OrigNode tries to reach multiple TargNodes in a single RREQ-
Instance, one of the TargNodes can be an intermediate router to other
TargNodes. In this case, before transmitting the RREQ-DIO to
multicast group all-RPL-nodes, a TargNode MUST delete the Target
Option encapsulating its own address, so that downstream routers with
higher Rank values do not try to create a route to this TargNode.
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An intermediate router could receive several RREQ-DIOs from routers
with lower Rank values in the same RREQ-Instance with different lists
of Target Options. For the purposes of determining the intersection
with previous incoming RREQ-DIOs, the intermediate router maintains a
record of the targets that have been requested for a given RREQ-
Instance. An incoming RREQ-DIO message having multiple ART Options
coming from a router with higher Rank than the Rank of the stored
targets is ignored. When transmitting the RREQ-DIO, the intersection
of all received lists MUST be included if it is nonempty after
TargNode has deleted the Target Option encapsulating its own address.
If the intersection is empty, it means that all the targets have been
reached, and the router MUST NOT transmit any RREQ-DIO. Otherwise it
proceeds to Section 6.2.3.
For example, suppose two RREQ-DIOs are received with the same
RPLInstance and OrigNode. Suppose further that the first RREQ has
(T1, T2) as the targets, and the second one has (T2, T4) as targets.
Then only T2 needs to be included in the generated RREQ-DIO.
6.2.3. Step 3: Intermediate Router RREQ processing
The intermediate router establishes itself as a viable node for a
route to OrigNode as follows. If the H bit is set to 1, for hop-by-
hop routing, then the router MUST build or update its upward route
entry towards OrigNode, which includes at least the following items:
Source Address, RPLInstanceID, Destination Address, Next Hop,
Lifetime, and Sequence Number. The Destination Address and the
RPLInstanceID respectively can be learned from the DODAGID and the
RPLInstanceID of the RREQ-DIO. The Source Address is the address
used by the router to send data to the Next Hop, i.e., the preferred
parent. The lifetime is set according to DODAG configuration (not
the L field) and can be extended when the route is actually used.
The sequence number represents the freshness of the route entry; it
is copied from the Orig SeqNo field of the RREQ option. A route
entry with the same source and destination address, same
RPLInstanceID, but stale sequence number, MUST be deleted.
6.2.4. Step 4: Symmetric Route Processing at an Intermediate Router
If the S bit of the incoming RREQ-DIO is 0, then the route cannot be
symmetric, and the S bit of the RREQ-DIO to be transmitted is set to
0. Otherwise, the router MUST determine whether the downward (i.e.,
towards the TargNode) direction of the incoming link satisfies the
OF. If so, the S bit of the RREQ-DIO to be transmitted is set to 1.
Otherwise the S bit of the RREQ-DIO to be transmitted is set to 0.
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When a router joins the RREQ-Instance, it also associates within its
data structure for the RREQ-Instance the information about whether or
not the RREQ-DIO to be transmitted has the S-bit set to 1. This
information associated to RREQ-Instance is known as the S-bit of the
RREQ-Instance. It will be used later during the RREP-DIO message
processing Section 6.3.2.
Suppose a router has joined the RREQ-Instance, and H=0, and the S-bit
of the RREQ-Instance is set to 1. In this case, the router MAY
optionally associate to the RREQ-Instance, the Address Vector of the
symmetric route back to OrigNode. This is useful if the router later
receives an RREP-DIO that is paired with the RREQ.
6.2.5. Step 5: RREQ propagation at an Intermediate Router
If the router is an intermediate router, then it transmits the RREQ-
DIO to the multicast group all-RPL-nodes; if the H bit is set to 0,
the intermediate router MUST append the address of its interface
receiving the RREQ-DIO into the address vector.
6.2.6. Step 6: RREQ reception at TargNode
If the router is a TargNode and was already associated with the RREQ-
Instance, it takes no further action and does not send an RREP-DIO.
If TargNode is not already associated with the RREQ-Instance, it
prepares and transmits a RREP-DIO, possibly after waiting for
RREP_WAIT_TIME, as detailed in (Section 6.3).
6.3. Generating Route Reply (RREP) at TargNode
When a TargNode receives a RREQ message over a link from a neighbor
Y, TargNode first follows the procedures in Section 6.2. If the link
to Y can be used to tramsmit packets to OrigNode, TargNode generates
a RREP according to the steps below. Otherwise TargNode drops the
RREQ and does not generate a RREP.
If the L field is not 0, the TargNode MAY delay transmitting the
RREP-DIO for duration RREP_WAIT_TIME to await a route with a lower
Rank. The value of RREP_WAIT_TIME is set by default to 1/4 of the
duration determined by the L field. For L == 0, RREP_WAIT_TIME is
set by default to 0. Depending upon the application, RREP_WAIT_TIME
may be set to other values. Smaller values enable quicker formation
for the P2P route. Larger values enable formation of P2P routes with
better Rank values.
The address of the OrigNode MUST be encapsulated in the ART Option
and included in this RREP-DIO message along with the SeqNo of
TargNode.
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6.3.1. RREP-DIO for Symmetric route
If the RREQ-Instance corresponding to the RREQ-DIO that arrived at
TargNode has the S bit set to 1, there is a symmetric route both of
whose directions satisfy the Objective Function. Other RREQ-DIOs
might later provide better upward routes. The method of selection
between a qualified symmetric route and an asymmetric route that
might have better performance is implementation-specific and out of
scope.
For a symmetric route, the RREP-DIO message is unicast to the next
hop according to the Address Vector (H=0) or the route entry (H=1);
the DODAG in RREP-Instance does not need to be built. The
RPLInstanceID in the RREP-Instance is paired as defined in
Section 6.3.3. In case the H bit is set to 0, the address vector
from the RREQ-DIO MUST be included in the RREP-DIO.
6.3.2. RREP-DIO for Asymmetric Route
When a RREQ-DIO arrives at a TargNode with the S bit set to 0, the
TargNode MUST build a DODAG in the RREP-Instance corresponding to the
RREQ-DIO rooted at itself, in order to provide OrigNode with a
downstream route to the TargNode. The RREP-DIO message is
transmitted to multicast group all-RPL-nodes.
6.3.3. RPLInstanceID Pairing
Since the RPLInstanceID is assigned locally (i.e., there is no
coordination between routers in the assignment of RPLInstanceID), the
tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely
identify a discovered route. It is possible that multiple route
discoveries with dissimilar Objective Functions are initiated
simultaneously. Thus between the same pair of OrigNode and TargNode,
there can be multiple AODV-RPL route discovery instances. So that
OrigNode and Targnode can avoid any mismatch, they MUST pair the
RREQ-Instance and the RREP-Instance in the same route discovery by
using the RPLInstanceID.
When preparing the RREP-DIO, a TargNode could find the RPLInstanceID
candidate for the RREP-Instance is already occupied by another RPL
Instance from an earlier route discovery operation which is still
active. This unlikely case might happen if two distinct OrigNodes
need routes to the same TargNode, and they happen to use the same
RPLInstanceID for RREQ-Instance. In such cases, the RPLInstanceID of
an already active RREP-Instance MUST NOT be used again for assigning
RPLInstanceID for the later RREP-Instance. Reusing the same
RPLInstanceID for two distinct DODAGs originated with the same
DODAGID (TargNode address) would prevent intermediate routers from
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distinguishing between these DODAGs (and their associated Objective
Functions). Instead, the RPLInstanceID MUST be replaced by another
value so that the two RREP-instances can be distinguished. In the
RREP-DIO option, the Delta field of the RREP-DIO message (Figure 2)
indicates the increment to be applied to the pre-existing
RPLInstanceID to obtain the value of the RPLInstanceID that is used
in the RREP-DIO message. When the new RPLInstanceID after
incrementation exceeds 255, it rolls over starting at 0. For
example, if the RREQ-InstanceID is 252, and incremented by 6, the new
RPLInstanceID will be 2. Related operations can be found in
Section 6.4. RPLInstanceID collisions do not occur across RREQ-DIOs;
the DODAGID equals the OrigNode address and is sufficient to
disambiguate between DODAGs.
6.4. Receiving and Forwarding Route Reply
Upon receiving a RREP-DIO, a router which already belongs to the
RREP-Instance SHOULD drop the DIO. Otherwise the router performs the
steps in the following subsections.
6.4.1. Step 1: Receiving and Evaluation
If the Objective Function is not satisfied, the router MUST NOT join
the DODAG; the router MUST discard the RREP-DIO, and does not execute
the remaining steps in this section. An Intermediate Router MUST
discard a RREP if one of its addresses is present in the Address
Vector, and does not execute the remaining steps in this section.
If the S bit of the associated RREQ-Instance is set to 1, the router
MUST proceed to Section 6.2.2.
If the S-bit of the RREQ-Instance is set to 0, the router MUST
determine whether the downward direction of the link (towards the
TargNode) over which the RREP-DIO is received satisfies the Objective
Function, and the router's Rank would not exceed the RankLimit. If
so, the router joins the DODAG of the RREP-Instance. The router that
transmitted the received RREP-DIO is selected as the preferred
parent. Afterwards, other RREP-DIO messages can be received.
6.4.2. Step 2: OrigNode or Intermediate Router
The router updates its stored value of the TargNode's sequence number
according to the value provided in the ART option. The router next
checks if one of its addresses is included in the ART Option. If so,
this router is the OrigNode of the route discovery. Otherwise, it is
an intermediate router.
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6.4.3. Step 3: Build Route to TargNode
If the H bit is set to 1, then the router (OrigNode or intermediate)
MUST build a downward route entry towards TargNode which includes at
least the following items: OrigNode Address, RPLInstanceID, TargNode
Address as destination, Next Hop, Lifetime and Sequence Number. For
a symmetric route, the Next Hop in the route entry is the router from
which the RREP-DIO is received. For an asymmetric route, the Next
Hop is the preferred parent in the DODAG of RREP-Instance. The
RPLInstanceID in the route entry MUST be the RREQ-InstanceID (i.e.,
after subtracting the Delta field value from the value of the
RPLInstanceID). The source address is learned from the ART Option,
and the destination address is learned from the DODAGID. The
lifetime is set according to DODAG configuration (i.e., not the L
field) and can be extended when the route is actually used. The
sequence number represents the freshness of the route entry, and is
copied from the Dest SeqNo field of the ART option of the RREP-DIO.
A route entry with same source and destination address, same
RPLInstanceID, but stale sequence number (i.e., incoming sequence
number is less than the currently stored sequence number of the route
entry), MUST be deleted.
6.4.4. Step 4: RREP Propagation
If the receiver is the OrigNode, it can start transmitting the
application data to TargNode along the path as provided in RREP-
Instance, and processing for the RREP-DIO is complete. Otherwise,
the RREP will be propagated towards OrigNode. If H=0, the
intermediate router MUST include the address of the interface
receiving the RREP-DIO into the address vector. If H=1, according to
the last step the intermediate router has set up a route entry for
TargNode. If the intermediate router has a route to OrigNode, it
uses that route to unicast the RREP-DIO to OrigNode. Otherwise, in
case of a symmetric route, the RREP-DIO message is unicast to the
Next Hop according to the address vector in the RREP-DIO (H=0) or the
local route entry (H=1). Otherwise, in case of an asymmetric route,
the intermediate router transmits the RREP-DIO to multicast group
all-RPL-nodes. The RPLInstanceID in the transmitted RREP-DIO is the
same as the value in the received RREP-DIO.
7. Gratuitous RREP
In some cases, an Intermediate router that receives a RREQ-DIO
message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode
instead of continuing to multicast the RREQ-DIO towards TargNode.
The intermediate router effectively builds the RREP-Instance on
behalf of the actual TargNode. The G bit of the RREP option is
provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the
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Intermediate router from the RREP-DIO sent by TargNode (G=0).
The gratuitous RREP-DIO MAY be sent out when an intermediate router
receives a RREQ-DIO for a TargNode, and the router has a pair of
downward and upward routes to the TargNode which also satisfy the
Objective Function and for which the destination sequence number is
at least as large as the sequence number in the RREQ-DIO message.
In case of source routing, the intermediate router MUST unicast the
received RREQ-DIO to TargNode including the address vector between
the OrigNode and the router. Thus the TargNode can have a complete
upward route address vector from itself to the OrigNode. Then the
router MUST include the address vector from the TargNode to the
router itself in the gratuitous RREP-DIO to be transmitted.
In case of hop-by-hop routing, the intermediate router MUST unicast
the received RREQ-DIO to the Next Hop on the route. The Next Hop
router along the route MUST build new route entries with the related
RPLInstanceID and DODAGID in the downward direction. The above
process will happen recursively until the RREQ-DIO arrives at the
TargNode. Then the TargNode MUST unicast recursively the RREP-DIO
hop-by-hop to the intermediate router, and the routers along the
route SHOULD build new route entries in the upward direction. Upon
receiving the unicast RREP-DIO, the intermediate router sends the
gratuitous RREP-DIO to the OrigNode as defined in Section 6.3.
8. Operation of Trickle Timer
RREQ-Instance/RREP-Instance multicast uses trickle timer operations
[RFC6206] to control RREQ-DIO and RREP-DIO transmissions. The
Trickle control of these DIO transmissions follows the procedures
described in the Section 8.3 of [RFC6550] entitled "DIO
Transmission". If the route is symmetric, the RREP DIO does not need
the Trickle timer mechanism.
9. IANA Considerations
Note to RFC editor:
The sentence "The parenthesized numbers are only suggestions." is to
be removed prior publication.
A Subregistry in this section refers to a named sub-registry of the
"Routing Protocol for Low Power and Lossy Networks (RPL)" registry.
AODV-RPL uses the "P2P Route Discovery Mode of Operation" (MOP == 4)
with new Options as specified in this document. Please cite AODV-RPL
and this document as one of the protocols using MOP 4.
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IANA is asked to assign three new AODV-RPL options "RREQ", "RREP" and
"ART", as described in Figure 6 from the "RPL Control Message
Options" Subregistry. The parenthesized numbers are only
suggestions.
+-------------+------------------------+---------------+
| Value | Meaning | Reference |
+-------------+------------------------+---------------+
| TBD2 (0x0B) | RREQ Option | This document |
+-------------+------------------------+---------------+
| TBD3 (0x0C) | RREP Option | This document |
+-------------+------------------------+---------------+
| TBD4 (0x0D) | ART Option | This document |
+-------------+------------------------+---------------+
Figure 6: AODV-RPL Options
10. Security Considerations
The security considerations for the operation of AODV-RPL are similar
to those for the operation of RPL (as described in Section 19 of the
RPL specification [RFC6550]). Sections 6.1 and 10 of [RFC6550]
describe RPL's optional security framework, which AODV-RPL relies on
to provide data confidentiality, authentication, replay protection,
and delay protection services. Additional analysis for the security
threats to RPL can be found in [RFC7416].
A router can join a temporary DAG created for a secure AODV-RPL route
discovery only if it can support the security configuration in use
(see Section 6.1 of [RFC6550]), which also specifies the key in use.
It does not matter whether the key is preinstalled or dynamically
acquired. The router must have the key in use before it can join the
DAG being created for secure route discovery.
If a rogue router knows the key for the security configuration in
use, it can join the secure AODV-RPL route discovery and cause
various types of damage. Such a rogue router could advertise false
information in its DIOs in order to include itself in the discovered
route(s). It could generate bogus RREQ-DIO, and RREP-DIO messages
carrying bad routes or maliciously modify genuine RREP-DIO messages
it receives. A rogue router acting as the OrigNode could launch
denial-of-service attacks against the LLN deployment by initiating
fake AODV-RPL route discoveries. When rogue routers might be
present, RPL's preinstalled mode of operation, where the key to use
for route discovery is preinstalled, SHOULD be used.
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When a RREQ-DIO message uses the source routing option by setting the
H bit to 0, a rogue router may populate the Address Vector field with
a set of addresses that may result in the RREP-DIO traveling in a
routing loop.
If a rogue router is able to forge a gratuitous RREP, it could mount
denial-of-service attacks.
11. Acknowledgements
The authors thank Pascal Thubert, Rahul Jadhav, and Lijo Thomas for
their support and valuable inputs. The authors specially thank
Lavanya H.M for implementing AODV-RPl in Contiki and conducting
extensive simulation studies.
The authors would like to acknowledge the review, feedback and
comments from the following people, in alphabetical order: Roman
Danyliw, Lars Eggert, Benjamin Kaduk, Tero Kivinen, Erik Kline,
Murray Kucherawy, Warren Kumari, Francesca Palombini, Alvaro Retana,
Ines Robles, John Scudder, Meral Shirazipour, Peter Van der Stok,
Eric Vyncke, and Robert Wilton.
12. References
12.1. 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>.
[RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
"The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206,
March 2011, <https://www.rfc-editor.org/info/rfc6206>.
[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>.
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[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>.
12.2. Informative References
[co-ioam] Ballamajalu, Rashmi., S.V.R., Anand., and Malati Hegde,
"Co-iOAM: In-situ Telemetry Metadata Transport for
Resource Constrained Networks within IETF Standards
Framework", 2018 10th International Conference on
Communication Systems & Networks (COMSNETS) pp.573-576,
January 2018.
[contiki] Contiki contributors, "The Contiki Open Source OS for the
Internet of Things (Contiki Version 2.7)", November 2013,
<https://github.com/contiki-os/contiki>.
[Contiki-ng]
Contiki-NG contributors, "Contiki-NG: The OS for Next
Generation IoT Devices (Contiki-NG Version 4.6)", December
2020, <https://github.com/contiki-ng/contiki-ng>.
[cooja] Contiki/Cooja contributors, "Cooja Simulator for Wireless
Sensor Networks (Contiki/Cooja Version 2.7)", November
2013, <https://github.com/contiki-
os/contiki/tree/master/tools/cooja>.
[RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
Demand Distance Vector (AODV) Routing", RFC 3561,
DOI 10.17487/RFC3561, July 2003,
<https://www.rfc-editor.org/info/rfc3561>.
[RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and
J. Martocci, "Reactive Discovery of Point-to-Point Routes
in Low-Power and Lossy Networks", RFC 6997,
DOI 10.17487/RFC6997, August 2013,
<https://www.rfc-editor.org/info/rfc6997>.
[RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci,
"A Mechanism to Measure the Routing Metrics along a Point-
to-Point Route in a Low-Power and Lossy Network",
RFC 6998, DOI 10.17487/RFC6998, August 2013,
<https://www.rfc-editor.org/info/rfc6998>.
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[RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
Weingarten, "An Overview of Operations, Administration,
and Maintenance (OAM) Tools", RFC 7276,
DOI 10.17487/RFC7276, June 2014,
<https://www.rfc-editor.org/info/rfc7276>.
[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>.
[RFC7548] Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A.
Sehgal, "Management of Networks with Constrained Devices:
Use Cases", RFC 7548, DOI 10.17487/RFC7548, May 2015,
<https://www.rfc-editor.org/info/rfc7548>.
[RFC9030] Thubert, P., Ed., "An Architecture for IPv6 over the Time-
Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)",
RFC 9030, DOI 10.17487/RFC9030, May 2021,
<https://www.rfc-editor.org/info/rfc9030>.
Appendix A. Example: Using ETX/RSSI Values to determine value of S bit
The combination of Received Signal Strength Indication(downstream)
(RSSI) and Expected Number of Transmissions(upstream) (ETX) has been
tested to determine whether a link is symmetric or asymmetric at
intermediate routers. We present two methods to obtain an ETX value
from RSSI measurement.
Method 1: In the first method, we constructed a table measuring RSSI
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vs ETX using the Cooja simulation [cooja] setup in the Contiki OS
environment[contiki]. We used Contiki-2.7 running 6LoWPAN/RPL
protocol stack for the simulations. For approximating the number
of packet drops based on the RSSI values, we implemented simple
logic that drops transmitted packets with certain pre-defined
ratios before handing over the packets to the receiver. The
packet drop ratio is implemented as a table lookup of RSSI ranges
mapping to different packet drop ratios with lower RSSI ranges
resulting in higher values. While this table has been defined for
the purpose of capturing the overall link behavior, it is highly
recommended to conduct physical radio measurement experiments, in
general. By keeping the receiving node at different distances, we
let the packets experience different packet drops as per the
described method. The ETX value computation is done by another
module which is part of RPL Objective Function implementation.
Since ETX value is reflective of the extent of packet drops, it
allowed us to prepare a useful ETX vs RSSI table. ETX versus RSSI
values obtained in this way may be used as explained below:
Source---------->NodeA---------->NodeB------->Destination
Figure 7: Communication link from Source to Destination
+=========================+========================================+
| RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA |
+=========================+========================================+
| > -60 | 150 |
+-------------------------+----------------------------------------+
| -70 to -60 | 192 |
+-------------------------+----------------------------------------+
| -80 to -70 | 226 |
+-------------------------+----------------------------------------+
| -90 to -80 | 662 |
+-------------------------+----------------------------------------+
| -100 to -90 | 3840 |
+-------------------------+----------------------------------------+
Table 1: Selection of S bit based on Expected ETX value
Method 2: One could also make use of the function
guess_etx_from_rssi() defined in the 6LoWPAN/RPL protocol stack of
Contiki-ng OS [Contiki-ng] to obtain RSSI-ETX mapping. This
function outputs ETX value ranging between 128 and 3840 for -60 <=
rssi <= -89. The function description is beyond the scope of this
document.
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We tested the operations in this specification by making the
following experiment, using the above parameters. In our experiment,
a communication link is considered as symmetric if the ETX value of
NodeA->NodeB and NodeB->NodeA (see Figure 7) are within, say, a 1:3
ratio. This ratio should be understood as determining the link's
symmetric/asymmetric nature. NodeA can typically know the ETX value
in the direction of NodeA -> NodeB but it has no direct way of
knowing the value of ETX from NodeB->NodeA. Using physical testbed
experiments and realistic wireless channel propagation models, one
can determine a relationship between RSSI and ETX representable as an
expression or a mapping table. Such a relationship in turn can be
used to estimate ETX value at nodeA for link NodeB--->NodeA from the
received RSSI from NodeB. Whenever nodeA determines that the link
towards the nodeB is bi-directional asymmetric then the S bit is set
to 0. Afterwards, the link from NodeA to Destination remains
designated as asymmetric and the S bit remains set to 0.
Determination of asymmetry versus bidirectionality remains a topic of
lively discussion in the IETF.
Appendix B. Changelog
Note to the RFC Editor: please remove this section before
publication.
B.1. Changes from version 12 to version 13
* Changed name of "Shift" field to be the "Delta" field.
* Specified that if a node does not have resources, it MUST drop the
RREQ.
* Changed name of MaxUseRank to MaxUsefulRank.
* Revised a sentence that was not clear about when a TargNode can
delay transmission of the RREP in response to a RREQ.
* Provided advice about running AODV-RPL at same time as P2P-RPL or
native RPL.
* Small reorganization and enlargement of the description of Trickle
time operation in Section 8.
* Added definition for "RREQ-InstanceID" to Terminology section.
* Specified that once a node leaves an RREQ-Instance, it MUST NOT
rejoin the same RREQ-Instance.
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B.2. Changes from version 11 to version 12
* Defined RREP_WAIT_TIME for asymmetric as well as symmetric
handling of RREP-DIO.
* Clarifed link-local multicast transmission to use link-local
multicast group all-RPL nodes.
* Identified some security threats more explicitly.
* Specified that the pairing between RREQ-DIO and RREP-DIO happens
at OrigNode and TargNode. Intermediate routers do not necessarily
maintain the pairing.
* When RREQ-DIO is received with H=0 and S=1, specified that
intermediate routers MAY store symmetric Address Vector
information for possible use when a matchine RREP-DIO is received.
* Specified that AODV-RPL uses the "P2P Route Discovery Mode of
Operation" (MOP == 4), instead of requesting the allocation of a
new MOP. Clarified that there is no conflict with [RFC6997].
* Fixed several important typos and improved language in numerous
places.
* Reorganized the steps in the specification for handling RREQ and
RREP at an intermediate router, to more closely follow the order
of processing actions to be taken by the router.
B.3. Changes from version 10 to version 11
* Numerous editorial improvements.
* Replace Floor((7+(Prefix Length))/8) by Ceil(Prefix Length/8) for
simplicity and ease of understanding.
* Use "L field" instead of "L bit" since L is a two-bit field.
* Improved the procedures in section 6.2.1.
* Define the S bit of the data structure a router uses to represent
whether or not the RREQ instance is for a symmetric or an
asymmetric route. This replaces text in the document that was a
holdover from earlier versions in which the RREP had an S bit for
that purpose.
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* Quote terminology from AODV that has been identified as possibly
originating in language reflecting various kinds of bias against
certain cultures.
* Clarified the relationship of AODV-RPL to RPL.
* Eliminated the "Point-to-Point" terminology to avoid suggesting
only a single link.
* Modified certain passages to better reflect the possibility that a
router might have multiple IP addresses.
* "Rsv" replaced by "X X" for reserved field.
* Added mandates for reserved fields, and replaces some ambiguous
language phraseology by mandates.
* Replaced "retransmit" terminology by more correct "propagate"
terminology.
* Added text about determining link symmetry near Figure 5.
* Mandated checking the Address Vector to avoid routing loops.
* Improved specification for use of the Delta value in
Section 6.3.3.
* Corrected the wrong use of RREQ-Instance to be RREP-Instance.
* Referred to Subregistry values instead of Registry values in
Section 9.
* Sharpened language in Section 10, eliminated misleading use of
capitalization in the words "Security Configuration".
* Added acknowledgements and contributors.
B.4. Changes from version 09 to version 10
* Changed the title for brevity and to remove acronyms.
* Added "Note to the RFC Editor" in Section 9.
* Expanded DAO and P2MP in Section 1.
* Reclassified [RFC6998] and [RFC7416] as Informational.
* SHOULD changed to MUST in Section 4.1 and Section 4.2.
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* Several editorial improvements and clarifications.
B.5. Changes from version 08 to version 09
* Removed section "Link State Determination" and put some of the
relevant material into Section 5.
* Cited security section of [RFC6550] as part of the RREP-DIO
message description in Section 2.
* SHOULD has been changed to MUST in Section 4.2.
* Expanded the terms ETX and RSSI in Section 5.
* Section 6.4 has been expanded to provide a more precise
explanation of the handling of route reply.
* Added [RFC7416] in the Security Considerations (Section 10) for
RPL security threats. Cited [RFC6550] for authenticated mode of
operation.
* Appendix A has been mostly re-written to describe methods to
determine whether or not the S bit should be set to 1.
* For consistency, adjusted several mandates from SHOULD to MUST and
from SHOULD NOT to MUST NOT.
* Numerous editorial improvements and clarifications.
B.6. Changes from version 07 to version 08
* Instead of describing the need for routes to "fulfill the
requirements", specify that routes need to "satisfy the Objective
Function".
* Removed all normative dependencies on [RFC6997]
* Rewrote Section 10 to avoid duplication of language in cited
specifications.
* Added a new section "Link State Determination" with text and
citations to more fully describe how implementations determine
whether links are symmetric.
* Modified text comparing AODV-RPL to other protocols to emphasize
the need for AODV-RPL instead of the problems with the other
protocols.
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* Clarified that AODV-RPL uses some of the base RPL specification
but does not require an instance of RPL to run.
* Improved capitalization, quotation, and spelling variations.
* Specified behavior upon reception of a RREQ-DIO or RREP-DIO
message for an already existing DODAGID (e.g, Section 6.4).
* Fixed numerous language issues in IANA Considerations Section 9.
* For consistency, adjusted several mandates from SHOULD to MUST and
from SHOULD NOT to MUST NOT.
* Numerous editorial improvements and clarifications.
B.7. Changes from version 06 to version 07
* Added definitions for all fields of the ART option (see
Section 4.3). Modified definition of Prefix Length to prohibit
Prefix Length values greater than 127.
* Modified the language from [RFC6550] Target Option definition so
that the trailing zero bits of the Prefix Length are no longer
described as "reserved".
* Reclassified [RFC3561] and [RFC6998] as Informative.
* Added citation for [RFC8174] to Terminology section.
B.8. Changes from version 05 to version 06
* Added Security Considerations based on the security mechanisms
defined in [RFC6550].
* Clarified the nature of improvements due to P2P route discovery
versus bidirectional asymmetric route discovery.
* Editorial improvements and corrections.
B.9. Changes from version 04 to version 05
* Add description for sequence number operations.
* Extend the residence duration L in section 4.1.
* Change AODV-RPL Target option to ART option.
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B.10. Changes from version 03 to version 04
* Updated RREP option format. Remove the T bit in RREP option.
* Using the same RPLInstanceID for RREQ and RREP, no need to update
[RFC6550].
* Explanation of Delta field in RREP.
* Multiple target options handling during transmission.
B.11. Changes from version 02 to version 03
* Include the support for source routing.
* Import some features from [RFC6997], e.g., choice between hop-by-
hop and source routing, the L field which determines the duration
of residence in the DAG, RankLimit, etc.
* Define new target option for AODV-RPL, including the Destination
Sequence Number in it. Move the TargNode address in RREQ option
and the OrigNode address in RREP option into ADOV-RPL Target
Option.
* Support route discovery for multiple targets in one RREQ-DIO.
* New RPLInstanceID pairing mechanism.
Appendix C. Contributors
Abdur Rashid Sangi
Huaiyin Institute of Technology
No.89 North Beijing Road, Qinghe District
Huaian 223001
P.R. China
Email: sangi_bahrian@yahoo.com
Malati Hegde
Indian Institute of Science
Bangalore 560012
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India
Email: malati@iisc.ac.in
Mingui Zhang
Huawei Technologies
No. 156 Beiqing Rd. Haidian District
Beijing 100095
P.R. China
Email: zhangmingui@huawei.com
Authors' Addresses
Charles E. Perkins
Lupin Lodge
Los Gatos, 95033
United States
Email: charliep@lupinlodge.com
S.V.R Anand
Indian Institute of Science
Bangalore 560012
India
Email: anandsvr@iisc.ac.in
Satish Anamalamudi
SRM University-AP
Amaravati Campus
Amaravati, Andhra Pradesh 522 502
India
Email: satishnaidu80@gmail.com
Bing Liu
Huawei Technologies
No. 156 Beiqing Rd. Haidian District
Beijing
100095
China
Email: remy.liubing@huawei.com
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