Internet Engineering Task Force M. Goyal, Ed.
Internet-Draft University of Wisconsin
Intended status: Experimental Milwaukee
Expires: June 27, 2013 E. Baccelli
INRIA
A. Brandt
Sigma Designs
J. Martocci
Johnson Controls
December 24, 2012
A Mechanism to Measure the Routing Metrics along a Point-to-point Route
in a Low Power and Lossy Network
draft-ietf-roll-p2p-measurement-07
Abstract
This document specifies a mechanism that enables an RPL router to
measure the aggregated values of given routing metrics along an
existing route towards another RPL router in a low power and lossy
network, thereby allowing the router to decide if it wants to
initiate the discovery of a better route.
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
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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 June 27, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The Measurement Object (MO) . . . . . . . . . . . . . . . . . 5
3.1. Format of the base MO . . . . . . . . . . . . . . . . . . 6
3.2. Secure MO . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Originating a Measurement Request . . . . . . . . . . . . . . 10
4.1. When Measuring A Hop-by-hop Route with a Global
RPLInstanceID . . . . . . . . . . . . . . . . . . . . . . 11
4.2. When Measuring A Hop-by-hop Route with a Local
RPLInstanceID With Route Accumulation Off . . . . . . . . 12
4.3. When Measuring A Hop-by-hop Route with a Local
RPLInstanceID With Route Accumulation On . . . . . . . . . 13
4.4. When Measuring A Source Route . . . . . . . . . . . . . . 14
5. Processing a Measurement Request at an Intermediate Point . . 15
5.1. When Measuring A Hop-by-hop Route with a Global
RPLInstanceID . . . . . . . . . . . . . . . . . . . . . . 16
5.2. When Measuring A Hop-by-hop Route with a Local
RPLInstanceID With Route Accumulation Off . . . . . . . . 17
5.3. When Measuring A Hop-by-hop Route with a Local
RPLInstanceID With Route Accumulation On . . . . . . . . . 18
5.4. When Measuring A Source Route . . . . . . . . . . . . . . 19
5.5. Final Processing . . . . . . . . . . . . . . . . . . . . . 19
6. Processing a Measurement Request at the End Point . . . . . . 20
6.1. Generating the Measurement Reply . . . . . . . . . . . . . 20
7. Processing a Measurement Reply at the Start Point . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1. Normative References . . . . . . . . . . . . . . . . . . . 23
11.2. Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
Point to point (P2P) communication between arbitrary routers in a Low
power and Lossy Network (LLN) is a key requirement for many
applications [RFC5826][RFC5867]. The IPv6 Routing Protocol for LLNs
(RPL) [RFC6550] constrains the LLN topology to a Directed Acyclic
Graph (DAG) built to optimize the routing costs to reach the DAG's
root. The P2P routing functionality, available under RPL, has the
following key limitations:
o The P2P routes are restricted to use the DAG links only. Such P2P
routes may potentially be suboptimal and may lead to traffic
congestion near the DAG root.
o RPL is a proactive routing protocol and hence requires all P2P
routes to be established ahead of the time they are used. Many
LLN applications require the ability to establish P2P routes "on
demand".
To ameliorate situations, where the core RPL's P2P routing
functionality does not meet the application requirements,
[I-D.ietf-roll-p2p-rpl] describes P2P-RPL, an extension to core RPL.
P2P-RPL provides a reactive mechanism to discover P2P routes that
meet the specified routing constraints [RFC6551]. In some cases, the
application requirements or the LLN's topological features allow a
router to infer these routing constraints implicitly. For example,
the application may require the end-to-end loss rate and/or latency
along the route to be below certain thresholds or the LLN topology
may be such that a router can safely assume its destination to be
less than a certain number of hops away from itself.
When the existing routes are deemed unsatisfactory but the router
does not implicitly know the routing constraints to be used in P2P-
RPL route discovery, it may be necessary for the router to measure
the aggregated values of the routing metrics along the existing
route. This knowledge will allow the router to frame reasonable
routing constraints to discover a better route using P2P-RPL. For
example, if the router determines the aggregate ETX [RFC6551] along
an existing route to be "x", it can use "ETX < x*y", where y is a
certain fraction, as the routing constraint for use in P2P-RPL route
discovery. Note that it is important that the routing constraints
are not overly strict; otherwise the P2P-RPL route discovery may fail
even though a route, much better than the one currently being used,
exists.
This document specifies a mechanism that enables an RPL router to
measure the aggregated values of the routing metrics along an
existing route to another RPL router in an LLN, thereby allowing the
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router to decide if it wants to discover a better route using P2P-RPL
and determine the routing constraints to be used for this purpose.
Thus, the utility of this mechanism is dependent on the existence of
P2P-RPL, which is targeting publication as an Experimental RFC. It
makes sense, therefore, for this document also to target publication
as an Experimental RFC. As more operational experience is gained
using P2P-RPL, it is hoped that the mechanism described in this
document will also be used, and feedback will be provided to the ROLL
working group on the utility and benefits of this document.
1.1. 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
[RFC2119].
This document uses terminology from [RFC6550] and
[I-D.ietf-roll-p2p-rpl]. Additionally, this document defines the
following terms.
Start Point: The Start Point refers to the RPL router that initiates
the measurement process defined in this document and is the start
point of the P2P route being measured.
End Point: The End Point refers to the RPL router at the end point of
the P2P route being measured.
Intermediate Point: An RPL router, other than the Start Point and the
End Point, on the P2P route being measured.
The following terms, already defined in [I-D.ietf-roll-p2p-rpl], have
been redefined in this document in the following manner.
Forward direction: The direction from the Start Point to the End
Point.
Backward direction: The direction from the End Point to the Start
Point.
2. Overview
The mechanism described in this document can be used by a Start Point
in an LLN to measure the aggregated values of selected routing
metrics along a P2P route to an End Point within the LLN. The route
is measured in the Forward direction. Such a route could be a Source
Route [I-D.ietf-roll-p2p-rpl] or a Hop-by-hop Route
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[I-D.ietf-roll-p2p-rpl] established using RPL [RFC6550] or P2P-RPL
[I-D.ietf-roll-p2p-rpl]. Such a route could also be a "mixed" route
with the initial part consisting of hop-by-hop ascent to the root of
a non-storing DAG [RFC6550] and the final part consisting of a
source-routed descent to the End Point. The Start Point decides what
metrics to measure and sends a Measurement Request message, carrying
the desired routing metric objects, along the route. On receiving a
Measurement Request, an Intermediate Point updates the routing metric
values inside the message and forwards it to the next hop on the
route. Thus, the Measurement Request accumulates the values of the
routing metrics for the complete route as it travels towards the End
Point. The Measurement Request may also accumulate a Source Route
that the End Point may use to reach the Start Point. Upon receiving
the Measurement Request, the End Point unicasts a Measurement Reply
message, carrying the accumulated values of the routing metrics, back
to the Start Point. Optionally, the Start Point may allow an
Intermediate Point to generate the Measurement Reply if the
Intermediate Point already knows the relevant routing metric values
along rest of the route.
3. The Measurement Object (MO)
This document defines two new RPL Control Message types, the
Measurement Object (MO), with code TBD1, and the Secure MO, with code
TBD2. An MO serves as both Measurement Request and Measurement
Reply.
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3.1. Format of the base MO
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 | Compr |T|H|A|R|B|I| SequenceNo| Num | Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Start Point Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| End Point Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Address[1..Num] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Metric Container Option(s) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of the base Measurement Object (MO)
The format of a base MO is shown in Figure 1. A base MO consists of
the following fields:
o RPLInstanceID: This field specifies the RPLInstanceID of the Hop-
by-hop Route along which the Measurement Request travels (or
traveled initially until it switched over to a Source Route).
o Compr: In many LLN deployments, IPv6 addresses share a well known,
common prefix. In such cases, the common prefix can be elided
when specifying IPv6 addresses in the Start Point/End Point
Address fields and the Address vector. The "Compr" field, a 4-bit
unsigned integer, is set by the Start Point to specify the number
of prefix octets that are elided from the IPv6 addresses in Start
Point/End Point Address fields and the Address vector. The Start
Point will set the Compr value to zero if full IPv6 addresses are
to be carried in the Start Point Address/End Point Address fields
and the Address vector.
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o Type (T): This flag is set to one if the MO represents a
Measurement Request. The flag is set to zero if the MO is a
Measurement Reply.
o Hop-by-hop (H): The Start Point MUST set this flag to one if (at
least the initial part of) the route being measured is hop-by-hop.
In that case, the Hop-by-hop Route is identified by the
RPLInstanceID, the End Point Address and, if the RPLInstanceID is
a local value, the Start Point Address (required to be same as the
DODAGID of the route being measured) fields inside the Measurement
Request. The Start Point MUST set this flag to zero if the route
being measured is a Source Route specified in the Address vector.
An Intermediate Point MUST set the H flag in an outgoing
Measurement Request to the same value that it had in the
corresponding incoming Measurement Request unless it is the root
of the non-storing global DAG, identified by the RPLInstanceID,
along which the Measurement Request had been traveling so far and
the Intermediate Point intends to insert a Source Route inside the
Address vector to direct it towards the End Point. In that case,
the Intermediate Point MUST set the H flag to zero.
o Accumulate Route (A): A value 1 in this flag indicates that the
Measurement Request is accumulating a Source Route for use by the
End Point to send the Measurement Reply back to the Start Point.
Route accumulation is allowed (i.e., this flag MAY be set to one)
inside a Measurement Request only if it travels along a Hop-by-hop
Route represented by a local RPLInstanceID (i.e., H = 1,
RPLInstanceID has a local value). In this case, an Intermediate
Point adds its unicast IPv6 address (after eliding Compr number of
prefix octets) to the Address vector in the manner specified in
Section 5.3. In other cases, this flag MUST be set to zero on
transmission and ignored on reception. Route accumulation is not
allowed when the Measurement Request travels along a Hop-by-hop
Route with a global RPLInstanceID, i.e., along a global DAG,
because:
* The DAG's root may need the Address vector to insert a Source
Route to the End Point; and
* The End Point can presumably reach the Start Point along this
global DAG (identified by the RPLInstanceID field).
o Reverse (R): A value 1 in this flag inside a Measurement Request
indicates that the Address vector contains a complete Source Route
from the Start Point to the End Point, which can be used, after
reversal, by the End Point to send the Measurement Reply back to
the Start Point. This flag MAY be set to one inside a Measurement
Request only if a Source Route, from the Start Point to the End
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Point, is being measured. Otherwise, this flag MUST be set to
zero on transmission and ignored on reception.
o Back Request (B): A value 1 in this flag serves as a request to
the End Point to send a Measurement Request towards the Start
Point. On receiving a Measurement Request with the B flag set to
one, the End Point SHOULD generate a Measurement Request to
measure the cost of its current (or the most preferred) route to
the Start Point. Receipt of this Measurement Request would allow
the Start Point to know the cost of the back route from the End
Point to itself and thus determine the round-trip cost of reaching
the End Point.
o Intermediate Reply (I): A value 1 in this flag serves as a
permission to an Intermediate Point to generate a Measurement
Reply if it knows the aggregated values of the routing metrics
being measured for the rest of the route. Setting this flag to
one may be useful in scenarios where the Hop Count [RFC6551] is
the routing metric of interest and an Intermediate Point (e.g. the
root of a non-storing global DAG or a common ancestor of the Start
Point and the End Point in a storing global DAG) may know the Hop
Count of the remainder of the route to the End Point. This flag
MAY be set to one only if a Hop-by-hop Route with a global
RPLInstanceID is being measured (i.e., H = 1, RPLInstanceID has a
global value). Otherwise, this flag MUST be set to zero on
transmission and ignored on reception.
o SequenceNo: A 6-bit sequence number, assigned by the Start Point,
that allows the Start Point to uniquely identify a Measurement
Request and the corresponding Measurement Reply.
o Num: This field indicates the number of elements, each (16 -
Compr) octets in size, inside the Address vector. If the value of
this field is zero, the Address vector is not present in the MO.
o Index: If the Measurement Request is traveling along a Source
Route contained in the Address vector (i.e., H = 0), this field
indicates the index in the Address vector of the next hop on the
route. If the Measurement Request is traveling along a Hop-by-hop
Route with a local RPLInstanceID and the Route Accumulation is on
(i.e., H = 1, RPLInstanceID has a local value, A = 1), this field
indicates the index in the Address vector where an Intermediate
Point receiving the Measurement Request must store its IPv6
address. Otherwise, this field MUST be set to zero on
transmission and ignored on reception.
o Start Point Address: A unicast IPv6 address of the Start Point
after eliding Compr number of prefix octets. If the Measurement
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Request is traveling along a Hop-by-hop Route and the
RPLInstanceID field indicates a local value, the Start Point
Address field MUST specify the DODAGID value that, along with the
RPLInstanceID and the End Point Address, uniquely identifies the
Hop-by-hop Route being measured.
o End Point Address: A unicast IPv6 address of the End Point after
eliding Compr number of prefix octets.
o Address[0..Num-1]: A vector of unicast IPv6 addresses (with Compr
number of prefix octets elided) representing a Source Route:
* Each element in the vector has size (16 - Compr) octets.
* The total number of elements inside the Address vector is given
by the Num field.
* When the Measurement Request is traveling along a Hop-by-hop
Route with local RPLInstanceID and has the A flag set to one
(i.e., H = 1, RPLInstanceID has a local value, A = 1), the
Address vector is used to accumulate a Source Route that can be
used by the End Point, after reversal, to send the Measurement
Reply back to the Start Point. The route MUST be accumulated
in the Forward direction but the IPv6 addresses in the
accumulated route MUST be reachable in the Backward direction.
An Intermediate Point adding its address to the Address vector
MUST ensure that a routing loop involving this router does not
exist in the accumulated route.
* When the Measurement Request is traveling along a Source Route
(i.e., H = 0), the Address vector MUST contain a complete route
to the End Point and the IPv6 addresses in the Address vector
MUST be reachable in the Forward direction. A router (the
Start Point or an Intermediate Point) inserting an Address
vector inside a Measurement Request MUST ensure that no address
appears more than once inside the vector. Each router on the
way MUST ensure that a routing loop involving this router does
not exist within the Source Route. The Start Point MAY set the
R flag in the Measurement Request if the route in the Address
vector represents a complete route from the Start Point to the
End Point and this route can be used by the End Point, after
reversal, to send the Measurement Reply message back to the
Start Point (i.e., the IPv6 addresses in the Address vector are
reachable in the Backward direction).
* The Start Point and End Point addresses MUST NOT be included in
the Address vector.
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* The Address vector MUST NOT contain any multicast addresses.
o Metric Container Options: A Measurement Request MUST contain one
or more Metric Container options [RFC6550] to accumulate the
values of the selected routing metrics in the manner described in
[RFC6551] for the route being measured.
Section 4 describes how does a Start Point set various fields inside
a Measurement Request in different cases. Section 5 describes how
does an Intermediate Point process a received Measurement Request
before forwarding it further. Section 6 describes how does the End
Point process a received Measurement Request and generate a
Measurement Reply. Finally, Section 7 describes how does the Start
Point process a received Measurement Reply.
3.2. Secure MO
A Secure MO follows the format in Figure 7 of [RFC6550], where the
base format is the base MO shown in Figure 1.
4. Originating a Measurement Request
A Start Point sets various fields inside the Measurement Request it
generates in the manner described below. The Start Point MUST also
include the routing metric objects [RFC6551] of interest inside one
or more Metric Container options inside the Measurement Request. The
Start Point then determines the next hop on the route being measured.
If a Hop-by-hop route is being measured (i.e., H = 1), the next hop
is determined using the RPLInstanceID, the End Point Address and, if
RPLInstanceID is a local value, the Start Point Address fields in the
Measurement Request. If a Source Route is being measured (i.e., H =
0), the Address[0] element inside the Measurement Request contains
the next hop address. The Start Point MUST discard the Measurement
Request if:
o the next hop address is not a unicast address; or
o the next hop is not on-link; or
o the next hop is not in the same RPL routing domain as the Start
Point.
Otherwise, depending on the routing metrics, the Start Point must
initiate the routing metric objects inside the Metric Container
options by including the routing metric values for the first hop on
the route being measured. Finally, the Start Point MUST unicast the
Measurement Request to the next hop on the route being measured.
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4.1. When Measuring A Hop-by-hop Route with a Global RPLInstanceID
If a Hop-by-hop Route with a global RPLInstanceID is being measured
(i.e., H = 1, RPLInstanceID has a global value), the MO MUST NOT
contain an Address vector and various MO fields MUST be set in the
following manner:
o RPLInstanceID: MUST be set to the RPLInstanceID of the route being
measured.
o Compr: MUST be set to specify the number of prefix octets that are
elided from the IPv6 addresses in Start Point/End Point Address
fields.
o Type (T): MUST be set to one since the MO represents a Measurement
Request.
o Hop-by-hop (H): MUST be set to one.
o Accumulate Route (A): This flag MUST be set to zero.
o Reverse (R): This flag MUST be set to zero.
o Back Request (B): This flag MAY be set to one to request the End
Point to send a Measurement Request to the Start Point.
o Intermediate Reply (I): This flag MAY be set to one if the Start
Point expects an Intermediate Point to know the values of the
routing metrics being measured for the remainder of the route.
o SequenceNo: Assigned by the Start Point so that it can uniquely
identify the Measurement Request and the corresponding Measurement
Reply.
o Num: This field MUST be set to zero.
o Index: This field MUST be set to zero.
o Start Point Address: MUST be set to a unicast IPv6 address of the
Start Point after eliding Compr number of prefix octets.
o End Point Address: MUST be set to a unicast IPv6 address of the
End Point after eliding Compr number of prefix octets.
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4.2. When Measuring A Hop-by-hop Route with a Local RPLInstanceID With
Route Accumulation Off
If a Hop-by-hop Route with a local RPLInstanceID is being measured
and the Start Point does not want the MO to accumulate a Source Route
for the End Point's use, the MO MUST NOT contain the Address vector
and various MO fields MUST be set in the following manner:
o RPLInstanceID: MUST be set to the RPLInstanceID of the route being
measured.
o Compr: MUST be set to specify the number of prefix octets that are
elided from the IPv6 addresses in Start Point/End Point Address
fields.
o Type (T): MUST be set to one since the MO represents a Measurement
Request.
o Hop-by-hop (H): MUST be set to one.
o Accumulate Route (A): This flag MUST be set to zero.
o Reverse (R): This flag MUST be set to zero.
o Back Request (B): This flag MAY be set to one to request the End
Point to send a Measurement Request to the Start Point.
o Intermediate Reply (I): This flag MUST be set to zero.
o SequenceNo: Assigned by the Start Point so that it can uniquely
identify the Measurement Request and the corresponding Measurement
Reply.
o Num: This field MUST be set to zero.
o Index: This field MUST be set to zero.
o Start Point Address: This field MUST contain the DODAGID value
(after eliding Compr number of prefix octets) associated with the
route being measured.
o End Point Address: MUST be set to a unicast IPv6 address of the
End Point after eliding Compr number of prefix octets.
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4.3. When Measuring A Hop-by-hop Route with a Local RPLInstanceID With
Route Accumulation On
If a Hop-by-hop Route with a local RPLInstanceID is being measured
and the Start Point desires the MO to accumulate a Source Route for
the End Point to send the Measurement Reply message back, the MO MUST
contain an Address vector and various MO fields MUST be set in the
following manner:
o RPLInstanceID: MUST be set to the RPLInstanceID of the route being
measured.
o Compr: MUST be set to specify the number of prefix octets that are
elided from the IPv6 addresses in Start Point/End Point Address
fields and the Address vector.
o Type (T): MUST be set to one since the MO represents a Measurement
Request.
o Hop-by-hop (H): MUST be set to one.
o Accumulate Route (A): This flag MUST be set to one.
o Reverse (R): This flag MUST be set to zero.
o Back Request (B): This flag MAY be set to one to request the End
Point to send a Measurement Request to the Start Point.
o Intermediate Reply (I): This flag MUST be set to zero.
o SequenceNo: Assigned by the Start Point so that it can uniquely
identify the Measurement Request and the corresponding Measurement
Reply.
o Num: This field MUST specify the number of address elements, each
(16 - Compr) octets in size, that can fit inside the Address
vector.
o Index: This field MUST be set to zero to indicate the position in
the Address vector where the next hop must store its IPv6 address.
o Start Point Address: This field MUST contain the DODAGID value
(after eliding Compr number of prefix octets) associated with the
route being measured.
o End Point Address: MUST be set to a unicast IPv6 address of the
End Point after eliding Compr number of prefix octets.
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o Address vector: The Address vector must be large enough to
accomodate a complete Source Route from the End Point to the Start
Point. All the bits in the Address vector field MUST be set to
zero.
4.4. When Measuring A Source Route
If a Source Route is being measured, the Start Point MUST set various
MO fields in the following manner:
o RPLInstanceID: MUST be set to the binary value 10000000.
o Compr: MUST be set to specify the number of prefix octets that are
elided from the IPv6 addresses in Start Point/End Point Address
fields and the Address vector.
o Type (T): MUST be set to one since the MO represents a Measurement
Request.
o Hop-by-hop (H): MUST be set to zero.
o Accumulate Route (A): This flag MUST be set to zero.
o Reverse (R): This flag SHOULD be set to one if the Source Route in
the Address vector can be reversed and used by the End Point to
send the Measurement Reply message back to the Start Point.
Otherwise, this flag MUST be set to zero.
o Back Request (B): This flag MAY be set to one to request the End
Point to send a Measurement Request to the Start Point.
o Intermediate Reply (I): This flag MUST be set to zero.
o SequenceNo: Assigned by the Start Point so that it can uniquely
identify the Measurement Request and the corresponding Measurement
Reply.
o Num: This field MUST specify the number of address elements, each
(16 - Compr) octets in size, inside the Address vector.
o Index: This field MUST be set to zero to indicate the position in
the Address vector of the next hop on the route.
o Start Point Address: MUST be set to a unicast IPv6 address of the
Start Point after eliding Compr number of prefix octets.
o End Point Address: MUST be set to a unicast IPv6 address of the
End Point after eliding Compr number of prefix octets.
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o Address vector:
* The Address vector MUST contain a complete Source Route from
the Start Point to the End Point (excluding the Start Point and
the End Point).
* The IPv6 addresses (with Compr prefix octets elided) in the
Address vector MUST be reachable in the Forward direction.
* If the R flag is set to one, the IPv6 addresses (with Compr
prefix octets elided) in the Address vector MUST also be
reachable in the Backward direction.
* To avoid loops in the Source Route, the Start Point MUST ensure
compliance to the following rules:
+ Any IPv6 address MUST NOT appear more than once in the
Address vector.
+ If the Address vector includes multiple IPv6 addresses
assigned to the Start Point's interfaces, such addresses
MUST appear back to back inside the Address vector.
* Each address appearing in the Address vector MUST be a unicast
address.
5. Processing a Measurement Request at an Intermediate Point
A router (an Intermediate Point or the End Point) MAY discard a
received MO with no processing to meet any policy-related goal. Such
policy goals may include the need to reduce the router's CPU load or
to enhance its battery life or to prevent misuse of this mechanism by
unauthorized nodes.
A router MUST discard a received MO with no further processing if the
value in the Compr field inside the received message is more than
what the router considers the length of the common prefix used in
IPv6 addresses in the LLN to be.
On receiving an MO, if a router chooses to process the packet
further, it MUST check if one of its IPv6 addresses is listed as
either the Start Point or the End Point Address. If neither, the
router considers itself an Intermediate Point and MUST process the
received MO in the following manner.
An Intermediate Point MUST discard the packet with no further
processing if the received MO is not a Measurement Request (i.e., T =
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0).
Next, the Intermediate Point determines the type of the route being
measured (by checking the values of the H flag and the RPLInstanceID
field) and processes the received MO accordingly in the manner
specified next.
5.1. When Measuring A Hop-by-hop Route with a Global RPLInstanceID
If a Hop-by-hop Route with a global RPLInstanceID is being measured
(i.e. H = 1 and RPLInstanceID has a global value), the Intermediate
Point MUST process the received Measurement Request in the following
manner.
The Intermediate Point MUST discard the received Measurement Request
with no further processing if the Num field is not set to zero or if
the Address vector is present in the received message.
If the Intermediate Reply (I) flag is set to one in the received
Measurement Request and the Intermediate Point knows the values of
the routing metrics, specified in the Metric Container options, for
the remainder of the route, it MAY generate a Measurement Reply on
the End Point's behalf in the manner specified in Section 6.1 (after
including in the Measurement Reply the relevant routing metric values
for the complete route being measured). Otherwise, the Intermediate
Point MUST process the received message in the following manner.
The Intermediate Point MUST then determine the next hop on the route
being measured using the RPLInstanceID and the End Point Address. If
the Intermediate Point is the root of the non-storing global DAG
along which the received Measurement Request had been traveling so
far, it MUST process the received Measurement Request in the
following manner:
o The router MUST discard the Measurement Request with no further
processing and MAY send an ICMPv6 Destination Unreachable (with
Code 0 - No Route To Destination) error message to the Start Point
if it does not know how to reach the End Point.
o Otherwise, unless the router determines the End Point itself to be
the next hop, the router MUST make the following changes in the
received Measurement Request:
* Set the H, A, R and I flags to zero (the A and R flags should
already be zero in the received message).
* Leave remaining fields unchanged (the Num field would be
modified in next steps). Note that the RPLInstanceID field
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identifies the non-storing global DAG along which the
Measurement Request traveled so far. This information MUST be
preserved so that the End Point may use this DAG to send the
Measurement Reply back to the Start Point.
* Insert a new Address vector inside the Measurement Request and
specify a Source Route to the End Point inside the Address
vector as per the following rules:
+ The Address vector MUST contain a complete route from the
router to the End Point (excluding the router and the End
Point);
+ The IPv6 addresses (with Compr prefix octets elided) in the
Address vector MUST be reachable in the Forward direction;
+ To avoid loops in the Source Route, the router MUST ensure
that
- Any IPv6 address MUST NOT appear more than once in the
Address vector;
- If the Address vector includes multiple IPv6 addresses
assigned to the router's interfaces, such addresses MUST
appear back to back inside the Address vector.
+ Each address appearing in the Address vector MUST be a
unicast address.
* Specify in the Num field the number of address elements in the
Address vector.
* Set the Index field to zero to indicate the position in the
Address vector of the next hop on the route. Thus, Address[0]
element contains the address of the next hop on the route.
The Intermediate Point MUST then complete the processing of the
received Measurement Request as specified in Section 5.5.
5.2. When Measuring A Hop-by-hop Route with a Local RPLInstanceID With
Route Accumulation Off
If a Hop-by-hop Route with a local RPLInstanceID is being measured
and the route accumulation is off (i.e., H = 1, RPLInstanceID has a
local value, A = 0), the Intermediate Point MUST process the received
Measurement Request in the following manner.
The Intermediate Point MUST discard the received Measurement Request
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with no further processing if the Num field is not zero or if the
Address vector is present in the received message.
The Intermediate Point MUST then determine the next hop on the route
being measured using the RPLInstanceID, the End Point Address and the
Start Point Address (which represents the DODAGID of the route being
measured). The Intermediate Point MUST discard the Measurement
Request with no further processing and MAY send an ICMPv6 Destination
Unreachable (with Code 0 - No Route To Destination) error message to
the Start Point if it can not determine the next hop. Otherwise, the
Intermediate Point MUST complete the processing of the received
Measurement Request as specified in Section 5.5.
5.3. When Measuring A Hop-by-hop Route with a Local RPLInstanceID With
Route Accumulation On
If a Hop-by-hop Route with a local RPLInstanceID is being measured
and the route accumulation in on (i.e., H = 1, RPLInstanceID has a
local value, A = 1), the Intermediate Point MUST process the received
Measurement Request in the following manner.
The Intermediate Point MUST discard the received Measurement Request
with no further processing if the Num field is set to zero or if the
Address vector is not present in the received message.
The Intermediate Point MUST then determine the next hop on the route
being measured using the RPLInstanceID, the End Point Address and the
Start Point Address (which represents the DODAGID of the route being
measured). The Intermediate Point MUST discard the Measurement
Request with no further processing and MAY send an ICMPv6 Destination
Unreachable (with Code 0 - No Route To Destination) error message to
the Start Point if it can not determine the next hop. The
Intermediate Point MUST drop the received Measurement Request with no
further processing if the index field has value Num - 1 and the next
hop is not same as the End Point. In this case, the next hop would
have no space left in the Address vector to store its address.
Otherwise, the Intermediate Point MUST check if adding one of its
IPv6 addresses to the the Address vector would create a routing loop
in the accumulated route. If yes, the router MUST discard the packet
with no further processing. Otherwise, the router MUST store one of
its unicast IPv6 addresses (after eliding Compr prefix octets) at
location Address[Index] and then increment the Index field. The IPv6
address added to the Address vector MUST be reachable in the Backward
direction.
The Intermediate Point MUST then complete the processing of the
received Measurement Request as specified in Section 5.5.
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5.4. When Measuring A Source Route
If a Source Route is being measured (i.e., H = 0), the Intermediate
Point MUST process the received Measurement Request in the following
manner.
The Intermediate Point MUST discard the received Measurement Request
with no further processing if the Num field is set to zero or if the
Address vector is not present in the received message.
The Intermediate Point MUST then determine the next hop on the route
being measured in the manner described below. The Intermediate Point
MUST verify that the Address[Index] element lists one of its unicast
IPv6 addresses, failing which it MUST discard the Measurement Request
with no further processing. To prevent loops, the Intermediate Point
MUST discard the Measurement Request with no further processing if
the Address vector includes multiple IPv6 addresses assigned to its
interfaces and if such addresses do not appear back to back inside
the Address vector. The Intermediate Point MUST then increment the
Index field and use the Address[Index] element as the next hop
(unless Index value is now Num). If the Index value is now Num, the
Intermediate Point MUST use the End Point Address as the next hop.
The Intermediate Point MUST then complete the processing of the
received Measurement Request as specified in Section 5.5.
5.5. Final Processing
The Intermediate Point MUST drop the received Measurement Request
with no further processing:
o If the next hop address is not a unicast address; or
o If the next hop is not on-link; or
o If the next hop is not in the same RPL routing domain as the
Intermediate Point.
Next, the Intermediate Point MUST update the routing metric objects,
inside the Metric Container option(s) inside the Measurement Request,
either by updating the aggregated value for the routing metric or by
attaching the local values for the metric inside the object. An
Intermediate Point can only update the existing metric objects and
MUST NOT add any new routing metric object to the Metric Container.
An Intermediate Point MUST drop the Measurement Request with no
further processing if it cannot update a routing metric object
specified inside the Metric Container.
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Finally, the Intermediate Point MUST unicast the Measurement Request
to the next hop.
6. Processing a Measurement Request at the End Point
On receiving an MO, if a router chooses to process the message
further and finds one of its unicast IPv6 addresses listed as the End
Point Address, the router considers itself the End Point and MUST
process the received MO in the following manner.
The End Point MUST discard the received message with no further
processing if it is not a Measurement Request (i.e., T = 0).
If the received Measurement Request traveled on a Hop-by-hop Route
with a local RPLInstanceID with route accumulation on (i.e., H = 1,
RPLInstanceID has a local value and A = 1), elements Address[0]
through Address[Index - 1] in the Address vector contain a complete
Source Route from the Start Point to the End Point (excluding the
Start Point and the End Point), which the End Point MAY use, after
reversal, to reach the Start Point.
If the received Measurement Request traveled on a Source Route and
the Reverse flag is set to one (i.e., H = 0, R = 1), elements
Address[0] through Address[Num - 1] in the Address vector contain a
complete Source Route from the Start Point to the End Point
(excluding the Start Point and the End Point), which the End Point
MAY use, after reversal, to reach the Start Point.
The End Point MUST update the routing metric objects in the Metric
Container options if required and MAY note the measured values for
the complete route (especially, if the received Measurement Request
is likely a response to an earlier Measurement Request that the End
Point had sent to the Start Point with B flag set to one).
The End Point MUST generate a Measurement Reply message as specified
in Section 6.1. If the B flag is set to one in the received
Measurement Request, the End Point SHOULD generate a new Measurement
Request to measure the cost of its current (or the most preferred)
route to the Start Point. The routing metrics used in the new
Measurement Request MUST include the routing metrics specified in the
received Measurement Request.
6.1. Generating the Measurement Reply
A Measurement Reply MUST have the Type (T) flag set to zero and need
not contain the Address vector. The following fields inside a
Measurement Reply MUST have the same values as they had inside the
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corresponding Measurement Request: RPLInstanceID, Compr, SequenceNo,
Start Point Address, End Point Address and Metric Container
Option(s). The remaining fields inside a Measurement Reply may have
any value and MUST be ignored on reception at the Start Point. The
received Measurement Request MAY trivially be converted into a
Measurement Reply by setting the Type (T) flag to zero.
A Measurement Reply MUST be unicast back to the Start Point:
o If the Measurement Request traveled along a global DAG, identified
by the RPLInstanceID field, the Measurement Reply MAY be unicast
back to the Start Point along the same DAG.
o If the Measurement Request traveled along a Hop-by-hop Route with
a local RPLInstanceID and accumulated a Source Route from the
Start Point to the End Point, this Source Route MAY be used after
reversal to send the Measurement Reply back to the Start Point.
o If the Measurement Request traveled along a Source Route and the R
flag inside the received message is set to one, the End Point MAY
reverse the Source Route contained in the Address vector and use
it to send the Measurement Reply back to the Start Point.
7. Processing a Measurement Reply at the Start Point
When a router receives an MO, it examines if one of its unicast IPv6
addresses is listed as the Start Point Address. If yes, the router
is the Start Point and MUST process the received message in the
following manner.
The Start Point MUST discard the packet with no further processing if
the received MO is not a Measurement Reply or if the Start Point has
no recollection of sending the corresponding Measurement Request.
The Start Point can use the routing metric objects inside the Metric
Container to evaluate the metrics for the measured P2P route. If a
routing metric object contains local metric values recorded by
routers on the route, the Start Point can make use of these local
values by aggregating them into an end-to-end metric according to the
aggregation rules for the specific metric. A Start Point is then
free to interpret the metrics for the route according to its local
policy.
8. Security Considerations
The mechanism defined in this document can potentially be used by a
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compromised router to send bogus Measurement Requests to arbitrary
End Points. Such Measurement Requests may cause CPU overload in the
routers in the network, drain their batteries and cause traffic
congestion in the network. Note that some of these problems would
occur even if the compromised router were to generate bogus data
traffic to arbitrary destinations.
Since a Measurement Request can travel along a Source Route specified
in the Address vector, some of the security concerns that led to the
deprecation of Type 0 routing header [RFC5095] may be valid here. To
address such concerns, the mechanism described in this document
includes several remedies:
o This document requires that a route inserted inside the Address
vector must be a strict Source Route and must not include any
multicast addresses.
o This document requires that an MO message must not cross the
boundaries of the RPL routing domain where it originated. A
router must not forward a received MO message further if the next
hop belongs to a different RPL routing domain. Hence, any
security problems associated with the mechanism would be limited
to one RPL routing domain.
o This document requires that a router must drop a received MO
message if the next hop address is not on-link or if it is not a
unicast address.
o This document requires that a router must check the Source Route
inside the Address vector of each received MO message to ensure
that it does not contain a loop involving the router. The router
must drop the received packet if the Source Route does contain
such a loop. This and the previous two rules protect the network
against some of the security concerns even if a compromised node
inserts a malformed Address vector inside the MO message.
The measurement mechanism described in this document may potentially
be used by a rogue node to find out key information about the LLN,
e.g., the topological features of the LLN (such as the identity of
the key nodes in the topology) or the remaining energy levels
[RFC6551] in the LLN routers. This information can potentially be
used to attack the LLN. To protect against such misuse, this
document allows RPL routers implementing this mechanism to not
process MO messages (or process such messages selectively) based on a
local policy. Further, an LLN deployment may use Secure MO
Section 3.2 messages to invoke RPL-provided security mechanisms and
prevent misuse of the measurement mechanism by unauthorized nodes.
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9. IANA Considerations
This document defines two new RPL messages:
o "Measurement Object" (see Section 3.1), assigned a value TBD1 from
the "RPL Control Codes" space [to be removed upon publication:
http://www.iana.org/assignments/rpl/rpl.xml#control-codes]
[RFC6550]. IANA is requested to allocate TBD1 from the range
0x00-0x7F to indicate a message without security enabled. The
string TBD1 in this document should be replaced by the allocated
value. These last two sentences should be removed before
publication.
o "Secure Measurement Object" (see Section 3.2), assigned a value
TBD2 from the "RPL Control Codes" space [to be removed upon
publication:
http://www.iana.org/assignments/rpl/rpl.xml#control-codes]
[RFC6550]. IANA is requested to allocate TBD2 from the range
0x80-0xFF to indicate a message with security enabled. The string
TBD2 in this document should be replaced by the allocated value.
These last two sentences should be removed before publication.
+------+---------------------------+---------------+
| Code | Description | Reference |
+------+---------------------------+---------------+
| TBD1 | Measurement Object | This document |
| TBD2 | Secure Measurement Object | This document |
+------+---------------------------+---------------+
RPL Control Codes
10. Acknowledgements
Authors gratefully acknowledge the contributions of Matthias Philipp,
Pascal Thubert, Richard Kelsey and Zach Shelby in the development of
this document.
11. References
11.1. Normative References
[I-D.ietf-roll-p2p-rpl]
Goyal, M., Baccelli, E., Philipp, M., Brandt, A., and J.
Martocci, "Reactive Discovery of Point-to-Point Routes in
Low Power and Lossy Networks", draft-ietf-roll-p2p-rpl-15
(work in progress), December 2012.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
11.2. Informative References
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
December 2007.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, April 2010.
[RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, June 2010.
[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
Lossy Networks", RFC 6550, March 2012.
[RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D.
Barthel, "Routing Metrics Used for Path Calculation in
Low-Power and Lossy Networks", RFC 6551, March 2012.
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
INRIA
Phone: +33-169-335-511
Email: Emmanuel.Baccelli@inria.fr
URI: http://www.emmanuelbaccelli.org/
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Anders Brandt
Sigma Designs
Emdrupvej 26A, 1.
Copenhagen, Dk-2100
Denmark
Phone: +45 29609501
Email: abr@sdesigns.dk
Jerald Martocci
Johnson Controls
507 E Michigan Street
Milwaukee 53202
USA
Phone: +1 414 524 4010
Email: jerald.p.martocci@jci.com
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