Internet Engineering Task Force M. Goyal, Ed.
Internet-Draft University of Wisconsin Milwaukee
Intended status: Informational E. Baccelli, Ed.
Expires: December 16, 2010 INRIA
P2P. Team
June 14, 2010
Reactive Discovery of Point-to-Point Routes in Low Power and Lossy
Networks
draft-dt-roll-p2p-rpl-01
Abstract
This document describes a mechanism to discover and establish "on
demand" one or more routes between two routers in a low power and
lossy network.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 16, 2010.
Copyright Notice
Copyright (c) 2010 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
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the Trust Legal Provisions and are provided without warranty as
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Targeted Use Cases . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Functional Overview . . . . . . . . . . . . . . . . . . . . . 5
5. Propagation of Discovery Messages . . . . . . . . . . . . . . 7
5.1. The Route Discovery Option . . . . . . . . . . . . . . . . 7
5.2. Setting a DIO Carrying a Route Discovery Option . . . . . 9
5.3. Processing of a DIO Carrying a Route Discovery Option
At An Intermediate Node . . . . . . . . . . . . . . . . . 10
5.4. Processing of a DIO Carrying a Route Discovery Option
At The Target Router . . . . . . . . . . . . . . . . . . . 12
6. Propagation of Discovery Reply Messages . . . . . . . . . . . 13
6.1. The Discovery Reply Object (DRO) . . . . . . . . . . . . . 13
6.1.1. The Source Route Option . . . . . . . . . . . . . . . 15
6.2. DRO as Acknowledgement for Backward Source Routes . . . . 16
6.3. DRO as Carrier of Forward/Bidirectional Source Routes . . 17
6.4. Establishing Hop-by-hop Routes Via DRO . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Authors and Contributors . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
RPL [I-D.ietf-roll-rpl] provides multipoint-to-point (MP2P) routes
from routers in a low power and lossy network (LLN) to a sink router
by organizing the routers along a Directed Acyclic Graph (DAG) rooted
at the sink. The DAG root initiates the DAG formation by originating
a DODAG Information Object (DIO) message. The DIO message is sent
via link-local multicast and carries information about the
originating router's position (the "rank") in the DAG. On receiving
DIO messages sent by its neighbors, a router determines its own
"rank" in the DAG and originates its own DIO message.
RPL enables point-to-multipoint (P2MP) routing from a router to its
descendants in the DAG by allowing a router to send a Destination
Advertisement Object (DAO) upwards along the DAG. The DAO carries
the aggregated information regarding the descendants (and other local
prefixes) reachable through the originating router.
RPL also provides mechanisms for point-to-point (P2P) routing between
any two routers in the DAG. If the destination is within the
source's "range", the source may directly send packets to the
destination. Otherwise, if the destination is a DAG descendant and
the source maintains "downwards" routing state about this descendant,
it can forward the packet along this route. Otherwise, the source
sends the packet to a DAG parent, which then applies the same set of
rules to forward the packet further. Thus, a packet travels up the
DAG until it reaches a router that knows of the downwards route to
the destination and then it travels down the DAG towards its
destination. A router may or may not maintain routing state about a
descendant depending on whether its immediate children send it such
information in their DAOs and whether the router can store this
information. Thus, in the best case scenario, the "upwards" segment
of the P2P route between a source and a destination ends at the first
common ancestor of the source and the destination. In the worst
case, the "upwards" segment would extend all the way to the DAG's
root. If the destination did not originate a DAO, the packet will
travel all the way to the DAG's root, where it will be dropped.
The P2P routing functionality available in RPL suffers from several
shortcomings [I-D.brandt-roll-rpl-applicability-home-building]:
o The need to maintain routes "proactively", i.e. every possible
destination in the DAG must originate a DAO.
o The constraint to route only along a DAG potentialy leading to
significantly suboptimal P2P routes and traffic congestion near
the DAG root.
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These shortcomings are not compatible with the home and commercial
building domain application requirements described in [RFC5826] and
[I-D.ietf-roll-building-routing-reqs]. Such applications require a
mechanism providing source-initiated discovery of P2P routes that are
not along a DAG. This document thus describes such a mechanism,
complementary to the basic RPL specification.
The specified scheme is based on a reactive on-demand approach, which
enables a router to discover one or more "good-enough" routes in
either direction between itself and another router in the LLN without
any constraints regarding the existing DAG-membership of the links
that such routes may use. Such routes may be source-routes or hop-
by-hop ones. A complementary functionality, necessary to help decide
whether to initiate a route discovery, is a mechanism to measure the
end-to-end cost of an existing route. Such functionality will be
described in a separate document.
2. Targeted Use Cases
The mechanisms described in this document are intended to be employed
as complementary to RPL in specific scenarios that need point-to-
point (P2P) routes between arbitrary routers.
One target use case, common in a home environment, involves a remote
control (or a motion sensor) that suddenly needs to communicate with
a lamp module, whose network address it knows apriori. In this case,
the source of data (the remote control or the motion sensor) must be
able to discover a route to the destination (the lamp module) "on
demand".
Another target use case, common in a large commercial building
environment, involves a large LLN deployment where P2P communication
along a particular DAG among hundreds (or thousands) of routers
creates severe traffic congestion near that DAG's root, and thus
routes across this DAG are desirable.
Targeted use cases also include scenarios where energy or delay
constraints are not satisfied by the P2P routes along a DAG because
they involve traversing many more intermediate routers than necessary
to reach the destination.
3. 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
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[RFC2119].
Additionally, this document uses terminology from
[I-D.ietf-roll-terminology] and [I-D.ietf-roll-rpl], and introduces
the following terminology:
Origin Router: The router initiating the route discovery. The origin
router acts as one end point of the routes to be discovered.
Target Router: The other end point of the routes to be discovered.
Intermediate Router: A router that is neither the origin nor the
target.
Forward Route: A route from the origin router to the target router.
Backward Route: A route from the target router to the origin router.
Bidirectional Route: A route that can be used in both directions:
from the origin router to the target router and vice versa.
Source Route: A complete and ordered list of routers that can be used
by a packet to travel from a source to a destination. Such source
routes can be carried by a packet in a proposed Type 4 Routing Header
[I-D.hui-6man-rpl-routing-header].
Hop-by-hop Route: A route from a source to a destination where each
router in the route knows only the address of the next hop on the
route.
In this document, the term 'router' refers to any LLN device that can
forward packets generated at other devices.
4. Functional Overview
Router A originates a "Discovery" message listing router B as the
target. Node A also indicates in the message:
o The nature of the routing cost, the method for accumulating the
end-to-end cost and the criteria used to determine if a route is
"good enough";
o The direction (forward: router A to router B; backward: router B
to router A; or both) of the route being discovered;
o The desired number of routes;
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o Whether the route is a source-route or a hop-by-hop one; and
o A limit on the "distance" the Discovery message may travel.
The Discovery message propagates via link-local multicast with each
receiving router making the decision regarding whether to forward the
message further based on the "distance" (from router A) that this
particular copy of the message has already traveled. Note that this
document does not require a receiving router to use the "good enough"
criteria to make the forwarding decision. This is because the
evaluation of such criteria may be too complex for a constrained
intermediate router to perform for each received copy of the
Discovery message. The calculation of the "distance" that a copy of
the Discovery message has already travelled should be simple enough
for a constrained router to perform. A router may optionally decide
not to forward a copy of the Discovery message further because the
aggregated cost of the route so far fails the "good enough" criteria.
The underlying mechanism being used to propagate the Discovery
message may put further restrictions on its propagation. A router
should not propagate the Discovery message further if hop-by-hop
routes are desired and the router can not store state for this route.
As a copy of the Discovery message travels towards router B, it
accumulates the relevant forward/backward costs as well as the route
it takes. When router B receives a copy of the Discovery message, it
determines whether the route traveled by the message meets the "good
enough" criteria.
If router A had requested the discovery of backward source-routes,
router B caches one or more good enough source-routes it identifies.
Additionally, router B sends one or more "Discovery Reply" message to
router A to acknowledge the discovery of these routes. These
acknowledgements allow router A to judge the success of the route
discovery. The Discovery Reply messages can travel towards router A
in any manner chosen by router B. For example, router B may source-
route the messages or send them towards router A along a DAG.
If router A had requested the discovery of "n" forward source-routes,
router B sends the "n" good enough source-routes it identifies to
router A in one or more Discovery Reply messages. Again, these
Discovery Reply messages can travel towards router A in any manner
chosen by router B.
If router A had requested the discovery of "n" bidirectional source-
routes, router B caches the "n" good enough source-routes it
identifies and also sends these routes to router A in one or more
Discovery Reply messages. These Discovery Reply messages can travel
towards router A in any manner chosen by router B.
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If router A had requested the discovery of "n" forward/backward/
bidirectional hop-by-hop routes, router B sends out a Discovery Reply
message to router A for each one of the "n" good enough routes it
identifies. The Discovery Reply message travels towards router A
using the source-route accumulated by the Discovery message. As this
message travels towards router A, it establishes appropriate forward/
backward routing state in the en-route routers. This "non DAG"
routing state should be specially marked to associate it with the
routing metrics used to discover the route and to distinguish such
state from other DAG-specific routing state the router may have.
5. Propagation of Discovery Messages
RPL uses DIO message propagation to build a DAG. The DIO message
travels via link-local multicast. Each router joining the DAG
determines a rank for itself and ignores the subsequent DIO messages
received from lower (higher in numerical value) ranked neighbors.
Thus, the DIO messages propagate outwards rather than return inwards
towards the DAG root. The DIO message generation at a router is
further controlled by a trickle timer that allows a router to avoid
generating unnecessary messages. The link-local multicast based
propagation, trickle-controlled generation and the rank-based
poisoning of messages traveling in the wrong direction (towards the
DAG root) provide powerful incentives to use the DIO message as the
Discovery message and propagate the DIO/Discovery message by creating
a "temporary" DAG.
5.1. The Route Discovery 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 9 | Option Length | D |S| N | L |O| Max Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Target Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OCP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of the Route Discovery Option
In order to be used as a Discovery message, a DIO MUST carry a "Route
Discovery" option illustrated in Figure 1. A DIO MUST NOT carry more
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than one Route Discovery options. A Route Discovery option consists
of the following fields:
o Option Type = 0x09 (to be confirmed by IANA).
o Option Length = 20 or 22 octets depending on whether the OCP field
is included or not.
o D: A 2-bit field that indicates the direction of the desired
routes:
* D = 0x00: Forward;
* D = 0x01: Backward;
* D = 0x02: Bidirectional.
o S: A flag that indicates whether source routes are desired. The
flag is set if the source routes are desired. The flag is clear
if hop-by-hop routes are desired.
o N: A 3-bit unsigned integer indicating the number of routes
desired.
o L: A 2-bit field indicating the minimum "Life Time" of the
temporary DAG, i.e., the minimum duration a router joining the
temporary DAG must maintain its membership in the DAG:
* L = 0x00: Minimum life time is 5 seconds;
* L = 0x01: Minimum life time is 10 seconds;
* L = 0x02: Minimum life time is 1 minute;
* L = 0x03: Minimum life time is 10 minutes.
o O: A flag that indicates whether the same OCP is used for route
discovery as well as temporary DAG formation. If this flag is
clear, the OCP contained in the DODAG Configuration option in the
DIO is used for route discovery as well. Otherwise, the OCP
specified in the Route Discovery option is used for route
selection and the metrics/constraints used for route selection are
carried in a Metrics Container option immediately following the
Route Discovery option.
o Max Rank: A 7-bit unsigned integer that indicates the maximum rank
allowed in the temporary DAG advertised by the DIO message. This
upper limit on the DAG rank serves as the "distance" referred to
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in Section 4 and provides a control over how far the Route
Discovery option contained in the DODAG Configuration option in
the DIO message may travel. A router MUST not join the temporary
DAG if its rank in the DAG will exceed this limit. Later versions
of this draft will map the 128 value space available in this field
to 16-bit long limits on the DAG rank.
o Target Address: The IPv6 address of the target router.
o OCP: 16 bit unsigned integer. An optional field, present only if
the O flag is set, that indicates the objective code point (OCP)
to be used for route selection.
5.2. Setting a DIO Carrying a Route Discovery Option
A DIO message that carries a Route Discovery option MUST set the Base
Object, described in [I-D.ietf-roll-rpl], in the following manner:
o RPLInstanceID: RPLInstanceID MUST be a local value as described in
Section 4.1 of [I-D.ietf-roll-rpl].
o Grounded (G) Flag: MUST be clear since the objective of DAG
formation is the propagation of Route Discovery option. This DAG
is temporary in nature and is not used for routing purpose.
o Destination Advertisement Supported (A) Flag: MUST be clear for
same reasons as described above.
o Destination Advertisement Trigger (T) Flag: MUST be clear.
o Mode of Operation (MOP): Since the temporary DAG is not to be used
for routing purposes, the value of this field is immaterial. To
allow constrained routers to join the DAG, the MOP field SHOULD be
set to 00 (non-storing).
o DODAGPreference (Prf): TBD
o Destination Advertisement Trigger Sequence Number (DTSN): TBD
o DODAGID: IPv6 address of the router initiating the route
discovery.
The other fields in the Base Object are set as per the rules
described in [I-D.ietf-roll-rpl].
The DODAG Configuration option, carried in the DIO message, specifies
the parameters for the trickle timer operation that governs the
generation of DIO messages by the routers joining the temporary DAG.
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The other fields defined in the DODAG Configuration option are set as
follows:
o The MaxRankIncrease field MUST be set to 0 to disable local repair
of the temporary DAG.
o This document RECOMMENDS a value 1 for the MinHopRankInc field.
o Objective Code Point (OCP): The OCP to be used for temporary DAG
formation. This document RECOMMENDS RPL Objective Function 0, as
defined in [I-D.ietf-roll-of0], for use as the objective function
for the formation of the temporary DAG.
A DIO, that contains a Route Discovery option with O flag set, MUST
also contain a Metric Container option immediately following the
Route Discovery option. This Metric Container option carries the
values for the routing metrics as well as the constraints
(constituting the "good enough" criteria) used for route selection.
Note that if O flag in the Route Discovery option is clear, the OCP
and Metric Container used for temporary DAG formation are used for
route selection as well.
A DIO, carrying a Route Discovery option, MUST not carry any Route
Information or Prefix Information options described in
[I-D.ietf-roll-rpl].
5.3. Processing of a DIO Carrying a Route Discovery Option At An
Intermediate Node
The rules for DIO processing and transmission, described in Section 7
of RPL [I-D.ietf-roll-rpl], apply to DIOs carrying a Route Discovery
option as well except as modified in this document.
When an intermediate router joins a temporary DAG advertized by a DIO
carrying the Route Discovery option, it MUST maintain its membership
in the DAG for the Minimum Life Time duration listed in the Route
Discovery option. Maintaining membership in the DAG implies
remembering:
o The RPLInstanceID, the DODAGID and the DODAGVersionNumber for the
temporary DAG;
o The router's rank in the temporary DAG;
o The best Metric Container, along with the associated source route
from the initiator of route discovery till this router (carried in
a Record Route IPv6 Extension Header proposed in
[I-D.thubert-6man-reverse-routing-header]), for the Route
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Discovery option being propagated by the temporary DAG. If the
router can not compare Metric Containers, it MUST remember the
latest Metric Container it has received, along with the associated
source route.
A router belonging to a temporary DAG need not remember the identity
of its DAG parents since the temporary DAG is not used for routing.
The main purpose of a temporary DAG's existence is to facilitate the
propagation of the Route Discovery option.
The router does not process a Route Discovery option, contained in
the received DIO, any further if any of the following conditions are
true:
o The router does not support the objective function being used for
route discovery
o The router does not have sufficient information to calculate the
relevant routing metrics/constraints in the right direction (as
specified by the D field).
o The S field is clear, i.e. hop-by-hop routes are desired, but the
router can not participate in a hop-by-hop route.
o The router is an intermediate router and the router's rank in the
temporary DAG, calculated on the basis of the rank and objective
function carried in the Base Object in the DIO, exceeds the Max
Rank value specified in the Route Discovery option.
A router MUST discard the DIO if the Route Discovery option contained
in the message does not need further processing. Otherwise, the
Route Discovery option is processed as follows.
The router updates the Metrics Container associated with the received
Route Discovery option as per the specified objective function. The
router may optionally check the Metric Container to determine if the
aggregated values for the routing metrics meet all the constraints
listed in the Metric Container. If not, the Route Discovery option
is discarded without further processing. Otherwise, the router
updates its in-memory copy of the latest/best Metric Container for
this Route Discovery option along with the associated source route
updated in the correct direction (based on the D field of the Route
Discovery option). Any change in the in-memory copy also requires
resetting the trickle timer and generating a new DIO carrying the
Route Discovery option, the updated latest/best Metric Container and
the associated source route (in a Record Route IPv6 extension header
proposed in [I-D.thubert-6man-reverse-routing-header]) when the timer
fires. Note that the Metric Container MUST immediately follow the
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Route Discovery option if the O flag in the Route Discovery option is
set.
5.4. Processing of a DIO Carrying a Route Discovery Option At The
Target Router
When the target router joins the temporary DAG advertized by a DIO
carrying the Route Discovery option, it MUST maintain its membership
in the DAG for the Minimum Life Time duration listed in the Route
Discovery option. Maintaining membership in the DAG implies
remembering:
o The RPLInstanceID, the DODAGID and the DODAGVersionNumber for the
temporary DAG;
o The router's rank in the temporary DAG;
The target router does not process a Route Discovery option,
contained in the received DIO, any further if any of the following
conditions are true:
o The router does not support the objective function used for route
discovery
o The router does not have sufficient information to calculate the
relevant routing metrics/constraints in the right direction (as
specified by the D field).
The target router MUST discard the DIO if the Route Discovery option
contained in the message does not need further processing.
Otherwise, the Route Discovery option is processed as follows.
The target router updates the Metrics Container associated with the
received Route Discovery option as per the specified objective
function. The target router then checks the Metric Container to
determine if the aggregated values for the routing metrics meet all
the constraints listed in the Metric Container. If not, the Route
Discovery option is discarded without further processing. Otherwise,
the router MAY select the source route accumulated by the received
DIO as one of the discovered routes. The target router MUST send one
or more RPL Control Messages carrying a Discovery Reply Object
(defined in the next section) back to the origin router (identified
by the DODAGID field in the DIO Base Object) as discussed in the
following sections.
The target router MUST NOT forward a DIO carrying a Route Discovery
option that lists one of its own addresses as the Target Address.
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6. Propagation of Discovery Reply Messages
6.1. The Discovery Reply Object (DRO)
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 | D |S| N | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DODAGID |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Target Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
Figure 2: Format of the Discovery Reply Object (DRO)
This document defines a new RPL Control Message type, the Discovery
Reply Object (DRO) with code 0x04 (to be confirmed by IANA), that
serves the following functions:
o An acknowledgement from the target router to the origin router
regarding the successful discovery of backward source routes;
o Carries one or more forward/bidirectional source routes from the
target to the origin router;
o Establishes a hop-by-hop forward/backward/bidirectional route as
it travels from the target to the origin router.
The format for a Discovery Reply Object (DRO) is shown in Figure 2.
A DRO consists of the following fields:
o RPLInstanceID: The RPLInstanceID of the temporary DAG used for
route discovery.
o Version: The Version of the temporary DAG used for route
discovery.
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o DODAGID: The DODAGID of the temporary DAG used for route
discovery. The DODAGID also identifies the origin router. The
RPLInstanceID, the Version and the DODAGID together uniquely
identify the temporary DAG used for route discovery and can be
copied from the Base Object of the DIO advertizing the temporary
DAG.
o D: A 2-bit field that indicates the direction of the discovered
routes:
* D = 0x00: Forward;
* D = 0x01: Backward;
* D = 0x02: Bidirectional.
This field has the same value as the corresponding field in the
Route Discovery option.
o S: A flag that is clear if the Discovery Reply Object is
establishing an hop-by-hop route. The flag is set if the
Discovery Reply Object carries (or is an acknowledgement for the
discovery of) one or more source routes.
o N: A 3-bit field that indicates the number of source routes
carried or acknowledged in the Discovery Reply Object.
o Target Address: The IPv6 address of the target router originating
the Discovery Reply Object.
o Reserved: These bits are reserved for future use. These bits MUST
be set to zero on transmission and MUST be ignored on reception.
o Options: The Discovery Reply Object MAY carry up to 7 Source Route
options (defined in the next section) with each such option
carrying a complete forward/bidirectional source route and
optionally followed by a Metric Container option that lists the
aggregated values for the routing metrics for the source route.
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6.1.1. The Source Route 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 10 | Option Length | Compr | Pad | Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Addresses[1..n] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Format of the Source Route Option
The Source Route option, illustrated in Figure 3, carries a complete
forward/bidirectional source route from the target router to the
origin router. A Source Route option can only be a part of the
Discovery Reply Object and MAY be immediately followed by a Metric
Container option that contains the aggregated values of the routing
metrics for this source route.
A Route Discovery option consists of the following fields:
o Option Type = 0x0A (to be confirmed by IANA).
o Option Length = Variable, depending on the size of the Addresses
vector.
o Compr: 4-bit unsigned interger indicating the number of prefix
octets that are elided from each address. For example, Compr
value will be 0 if full IPv6 addresses are carried in the
Addresses vector.
o Pad: 4-bit unsigned integer. Number of octets that are used for
padding between Address[n] and the end of the Source Route option.
o Address[1..n]: Vector of addresses, numbered 1 to n. Each vector
element has size (16 - Compr) octets.
A common network configuration for an RPL domain is that all routers
within an LLN share a common prefix. The Source Route option uses
the Compr field to allow compaction of the Addresses[1..n] vector
when all entries share the same prefix as the DODAGID or the Target
Address of the encapsulating Discovery Reply Object. The shared
prefix octets are not carried within the Source Route option and each
entry in Address[1..n] has size (16 - Compr) octets. When Compr is
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non-zero, there may exist unused octets between the last entry,
Address[n], and the end of the Source Route option. The Pad field
indicates the number of unused octets that are used for padding.
Note that when Compr is 0, Pad MUST be null and carry a value 0.
The Source Route option MUST NOT specify a path that visits a router
more than once. When generating a Source Route option, the target
router may not know the mapping between IPv6 addresses and routers.
Minimally, the target router MUST ensure that:
o The IPv6 Addresses do not appear more than once;
o The IPv6 addresses of the origin and the target routers do not
appear in the Address vector;
o The Address vector represents a source route in forward direction
with Address[1] being the next hop for the origin router.
Multicast addresses MUST NOT appear in a Source Route option.
6.2. DRO as Acknowledgement for Backward Source Routes
When a target router discovers a backward source route, it sends a
DRO message to the origin router as an acknowlegement for the
discovered route. Optionally, a target router MAY send a DRO
acknowledgement to the origin router after discovering multiple
backward source routes. A DRO, serving as an acknowledgement for
backward source route discovery, has its D field set to 0x01
(indicating backward) while the S flag is set to 1 (indicating source
route). The N field is set to indicate the number of discovered
backward source routes being acknowledged. Such a DRO message MUST
NOT contain any option.
This document does not require a particular method for sending such a
DRO message to the origin router. The target router MAY send the DRO
message to the origin router in any fashion, including:
o Using a source route carried in a Type 4 Routing header
[I-D.hui-6man-rpl-routing-header];
o Along any DAG connecting the target and the origin routers;
o Along the temporary DAG created for route discovery, provided that
the target router is reasonably sure that the DAG's life time is
sufficiently long and the routers in the DAG do remember one or
more of their parents in the DAG.
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6.3. DRO as Carrier of Forward/Bidirectional Source Routes
When a target router discovers a forward source route, it sends a DRO
message to the origin router carrying the discovered source route
inside a Source Route option. Similarly, when a target router
discovers a bidirectional source route, it caches the route for its
own use and then sends a DRO message to the origin router carrying
the discovered route inside a Source Route option. Rather than
immediately sending a discovered route back to the origin router, a
target router MAY optionally send one DRO message after discovering
multiple forward/bidirectional source routes with the sent DRO
carrying the discovered source routes (in multiple Source Route
options).
A DRO message carrying one or more Source Route options MUST have its
D field set to 0x00 (for forward routes) or 0x02 (for bidirectional
routes). The S flag MUST be set to 1 and the N field MUST indicate
the number of Source Route options in the message. A Source Route
option MAY immediately be followed by a Metric Container option that
carries the aggregated values of the routing metrics for this source
route. The target router may send this DRO message to the origin
router in any fashion it desires including the options listed in
Section 6.2.
6.4. Establishing Hop-by-hop Routes Via DRO
In order to establish a hop-by-hop route, the target router sends a
DRO message along the reverse of the discovered route (via a Type 4
Routing Header specified in [I-D.hui-6man-rpl-routing-header]). The
D field of the message is set to convey the route's direction
(forward/backward/bidirectional) and the S flag MUST be clear
(indicating hop-by-hop). The N field MUST be set to 1. Such a DRO
MUST NOT contain any option.
A router receiving such a DRO message SHOULD establish hop-by-hop
state in the right direction corresponding to the route carried in
the Type 4 Routing Header of the DRO message. If a router does not
establish such state, it MUST drop the DRO message. Otherwise, it
MUST forward the DRO message along the source route contained in Type
4 Routing Header of the received message.
A router SHOULD associate the hop-by-hop routing state, thus
established, with the objective function and metrics used for route
discovery.
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7. Security Considerations
TBA
8. IANA Considerations
TBA
9. Authors and Contributors
In addition to the editor, the authors of this document include the
following individuals (listed in alphabetical order).
Anders Brandt, Sigma Designs, Emdrupvej 26A, 1., Copenhagen, Dk-2100,
Denmark. Phone: +45 29609501; Email: abr@sdesigns.dk
Robert Cragie, Gridmerge Ltd, 89 Greenfield Crescent, Wakefieldm WF4
4WA, UK. Phone: +44 1924910888; Email: robert.cragie@gridmerge.com
Jerald Martocci, Johnson Controls, Milwaukee, WI 53202, USA. Phone:
+1 414 524 4010; Email:jerald.p.martocci@jci.com
Charles Perkins, Tellabs Inc., USA. Email:charliep@computer.org
Authors gratefully acknowledge the contributions of Richard Kelsey
and Zach Shelby in the development of this document.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[I-D.brandt-roll-rpl-applicability-home-building]
Brandt, A., Baccelli, E., and R. Cragie, "Applicability
Statement: The use of RPL in Building and Home
Environments",
draft-brandt-roll-rpl-applicability-home-building-00 (work
in progress), April 2010.
[]
Hui, J., Vasseur, J., and D. Culler, "A Source Routing
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Header for RPL", draft-hui-6man-rpl-routing-header-00
(work in progress), May 2010.
[I-D.ietf-roll-building-routing-reqs]
Martocci, J., Riou, N., Mil, P., and W. Vermeylen,
"Building Automation Routing Requirements in Low Power and
Lossy Networks", draft-ietf-roll-building-routing-reqs-09
(work in progress), January 2010.
[I-D.ietf-roll-of0]
Thubert, P., "RPL Objective Function 0",
draft-ietf-roll-of0-02 (work in progress), June 2010.
[I-D.ietf-roll-routing-metrics]
Vasseur, J., Kim, M., Networks, D., and H. Chong, "Routing
Metrics used for Path Calculation in Low Power and Lossy
Networks", draft-ietf-roll-routing-metrics-07 (work in
progress), June 2010.
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., and R. Team, "RPL: IPv6 Routing
Protocol for Low power and Lossy Networks",
draft-ietf-roll-rpl-09 (work in progress), June 2010.
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-03 (work in
progress), March 2010.
[]
Thubert, P., "Reverse Routing Header",
draft-thubert-6man-reverse-routing-header-00 (work in
progress), June 2010.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, April 2010.
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Authors' Addresses
Mukul Goyal (editor)
University of Wisconsin Milwaukee
3200 N Cramer St
Milwaukee, WI 53211
USA
Phone: +1 414 2295001
Email: mukul@uwm.edu
Emmanuel Baccelli (editor)
INRIA
Phone: +33-169-335-511
Email: Emmanuel.Baccelli@inria.fr
URI: http://www.emmanuelbaccelli.org/
P2P Team
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