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Internet Engineering Task Force (IETF) M. Goyal, Ed.
Request for Comments: 6998 Univ. of Wisconsin Milwaukee
Category: Experimental E. Baccelli
ISSN: 2070-1721 INRIA
A. Brandt
Sigma Designs
J. Martocci
Johnson Controls
August 2013
A Mechanism to Measure the Routing Metrics along a Point-to-Point Route
in a Low-Power and Lossy Network
Abstract
This document specifies a mechanism that enables a Routing Protocol
for Low-power and Lossy Networks (RPL) router to measure the
aggregated values of given routing metrics along an existing route
towards another RPL router, thereby allowing the router to decide if
it wants to initiate the discovery of a better route.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). It represents the consensus of the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are a candidate for any level of
Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6998.
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RFC 6998 Measurement of Routing Metrics in LLNs August 2013
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Goyal, et al. Experimental [Page 2]
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Table of Contents
1. Introduction ....................................................4
1.1. Terminology ................................................5
2. Overview ........................................................6
3. The Measurement Object (MO) .....................................7
3.1. Format of the Base MO ......................................8
3.2. Secure MO .................................................12
4. Originating a Measurement Request ..............................13
4.1. When Measuring a Hop-by-Hop Route with a Global
RPLInstanceID .............................................14
4.2. When Measuring a Hop-by-Hop Route with a Local
RPLInstanceID with Route Accumulation Off .................15
4.3. When Measuring a Hop-by-Hop Route with a Local
RPLInstanceID with Route Accumulation On ..................16
4.4. When Measuring a Source Route .............................17
5. Processing a Measurement Request at an Intermediate Point ......19
5.1. When Measuring a Hop-by-Hop Route with a Global
RPLInstanceID .............................................19
5.2. When Measuring a Hop-by-Hop Route with a Local
RPLInstanceID with Route Accumulation Off .................21
5.3. When Measuring a Hop-by-Hop Route with a Local
RPLInstanceID with Route Accumulation On ..................21
5.4. When Measuring a Source Route .............................22
5.5. Final Processing ..........................................23
6. Processing a Measurement Request at the End Point ..............23
6.1. Generating the Measurement Reply ..........................24
7. Processing a Measurement Reply at the Start Point ..............25
8. Security Considerations ........................................25
9. IANA Considerations ............................................27
10. Acknowledgements ..............................................27
11. References ....................................................28
11.1. Normative References .....................................28
11.2. Informative References ...................................28
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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 home
and commercial building automation 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 that all
P2P routes 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 an application's requirements, [RFC6997]
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's
requirements or the LLN's topological features allow a router to
infer these routing constraints implicitly. For example, the
application may require that the end-to-end loss rate and/or latency
along the route be below certain thresholds, or the LLN topology may
be such that a router can safely assume that its destination is 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
(expected transmission count) [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 not be overly strict;
otherwise, the P2P-RPL route discovery may fail even though a route
exists that is much better than the one currently being used.
Goyal, et al. Experimental [Page 4]
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This document specifies a mechanism that enables a 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
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 [RFC6997]. The hope is that experiments with P2P-RPL and the
mechanism defined in this document will result in feedback on the
utility and benefits of this document, so that a Standards Track
version of this document can then be developed.
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].
Additionally, this document uses terminology from [RFC6550],
[RFC6554], and [RFC6997]. Further terminology may be found in
[ROLL-TERMS]. This document defines the following terms:
Start Point: The RPL router that initiates the measurement process
defined in this document and that is the start point of the P2P
route being measured.
End Point: The RPL router at the end point of the P2P route being
measured.
Intermediate Point: A RPL router, other than the Start Point and the
End Point, on the P2P route being measured.
The following terms, as already defined in [RFC6997], are redefined
in this document in the following manner:
Forward direction: The direction from the Start Point to the
End Point.
Reverse direction: The direction from the End Point to the
Start Point.
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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 or a Hop-by-hop Route established using RPL [RFC6550] or
P2P-RPL [RFC6997]. 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. If a Source
Route is being measured, the Measurement Request carries the route
inside an Address vector. If a Hop-by-hop Route is being measured,
the Measurement Request identifies the route by its RPLInstanceID
[RFC6550] (and, if the RPLInstanceID is a local value, the
Start Point's IPv6 address associated with 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. 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 the rest of the route.
The Measurement Request may include an Address vector that serves one
of the following functions:
o To accumulate a Source Route for the End Point's use: If a Hop-by-
hop Route with a local RPLInstanceID is being measured, the
Start Point may require that each Intermediate Point add its
global or unique-local IPv6 address to an Address vector inside
the Measurement Request. The Source Route, thus accumulated, can
be used by the End Point to reach the Start Point. In particular,
the End Point may use the accumulated Source Route to send the
Measurement Reply back to the Start Point. In this case, the
Start Point includes a suitably sized Address vector in the
Measurement Request. The size of the Address vector puts a hard
limit on the length of the accumulated route. An Intermediate
Point is not allowed to modify the size of the Address vector and
must discard a received Measurement Request if the Address vector
is not large enough to contain the complete route.
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o To carry the Source Route being measured: The Start Point may
insert an Address vector inside the Measurement Request to carry
the Source Route being measured. Also, the root of a global
non-storing DAG may insert an Address vector, carrying a Source
Route from itself to the End Point, inside a Measurement Request
message if this message had been traveling along this DAG so far.
This Source Route must consist of global or unique-local IPv6
addresses. An Intermediate Point is not allowed to modify an
existing Address vector before forwarding the Measurement Request
further. In other words, an Intermediate Point must not modify
the Source Route along which the Measurement Request is currently
traveling.
3. The Measurement Object (MO)
This document defines two new RPL control message types: the
Measurement Object (MO), with code 0x06; and the Secure MO, with
code 0x86. 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| SeqNo | Num | Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Start Point Address .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. End Point Address .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Address[0..Num-1] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. 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 fields inside the
Measurement Request. Here, the Start Point Address field is
required to be the same as the DODAGID (the identifier of the
Destination-Oriented DAG (DODAG) root) [RFC6550] of the route
being measured. The Start Point MUST set the H 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, except under the
following circumstance: If the Intermediate Point is the root of
the non-storing global DAG along which the Measurement Request had
been traveling so far and it intends to insert a Source Route
inside the Address vector to direct the Measurement Request
towards the End Point, then it MUST set the H flag to zero.
o Accumulate Route (A): A value of 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 MUST NOT be used (i.e., this flag MUST NOT be
set to one) inside a Measurement Request, unless it travels along
a Hop-by-hop Route represented by a local RPLInstanceID (i.e., H =
1 and RPLInstanceID has a local value). Route accumulation MAY be
used (i.e., this flag MAY be set to one) if the Measurement
Request is traveling along a Hop-by-hop Route with a local
RPLInstanceID. In this case, if the route accumulation is on, an
Intermediate Point adds its unicast global/unique-local 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).
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o Reverse (R): A value of 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 Point, is being measured. Otherwise, this flag MUST be
set to zero on transmission and ignored on reception.
o Back Request (B): A value of 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 of 1 in this flag serves as
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 and
RPLInstanceID has a global value). Otherwise, this flag MUST be
set to zero on transmission and ignored on reception.
o SeqNo: This is 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, and A = 1), this
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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: This is a unicast global or unique-local IPv6
address of the Start Point after eliding Compr number of prefix
octets. If the Measurement 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: This is a unicast global or unique-local IPv6
address of the End Point after eliding Compr number of prefix
octets.
o Address[0..Num-1]: This field is a vector of unicast global or
unique-local 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.
* The Start Point and End Point addresses MUST NOT be included in
the Address vector.
* The Address vector MUST NOT contain any multicast addresses.
* If the Start Point wants to measure a Hop-by-hop Route with a
local RPLInstanceID and accumulate a Source Route for the
End Point's use (i.e., the Measurement Request has the H flag
set to one, RPLInstanceID set to a local value, and the A flag
set to one), it MUST include a suitably sized Address vector in
the Measurement Request. As the Measurement Request travels
over the route being measured, the Address vector accumulates a
Source Route that can be used by the End Point, after reversal,
to reach (and, in particular, 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 Reverse direction. An
Intermediate Point MUST add only a global or unique-local IPv6
address to the Address vector and MUST NOT modify the size of
the Address vector.
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* If the Start Point wants to measure a Source Route, it MUST
include an Address vector, containing the route being measured,
inside the Measurement Request. Similarly, if the Measurement
Request had been traveling along a global non-storing DAG so
far, the root of this DAG may insert an Address vector,
containing a Source Route from itself to the End Point, inside
the Measurement Request. In both cases, the Source Route
inside the Address vector MUST consist only of global or
unique-local IPv6 addresses that are reachable in the Forward
direction. Further, in both cases, an Intermediate Point MUST
NOT modify the contents of the existing Address vector before
forwarding the Measurement Request further. In other words, an
Intermediate Point MUST NOT modify the Source Route along which
the Measurement Request is currently traveling. The
Start Point MAY set the R flag in the Measurement Request to
one if the Source Route inside the Address vector can be used
by the End Point, after reversal, to reach (and, in particular,
to send the Measurement Reply back to) the Start Point. In
other words, the Start Point MAY set the R flag to one only if
all the IPv6 addresses in the Address vector are reachable in
the Reverse direction.
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 a Start Point sets various fields inside a
Measurement Request in different cases. Section 5 describes how an
Intermediate Point processes a received Measurement Request before
forwarding it further. Section 6 describes how the End Point
processes a received Measurement Request and generates a Measurement
Reply. Finally, Section 7 describes how the Start Point processes a
received Measurement Reply. In the following discussion, any
reference to discarding a received Measurement Request/Reply with "no
further processing" does not preclude updating the appropriate error
counters or any similar actions.
3.2. Secure MO
A Secure MO follows the format shown in Figure 7 of [RFC6550], where
the base format is the base MO shown in Figure 1. Sections 6.1, 10,
and 19 of [RFC6550] describe the RPL security framework. These
sections are applicable to the use of Secure MO messages as well,
except as constrained in this section. An LLN deployment MUST
support the use of Secure MO messages so that it has the ability to
invoke RPL-provided security mechanisms and prevent misuse of the
measurement mechanism by unauthorized routers.
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The Start Point determines whether Secure MO messages are to be used
in a particular route measurement and, if yes, the Security
Configuration (see definition in [RFC6997]) to be used for that
purpose. The Start Point MUST NOT set the "Key Identifier Mode"
field to a value of 1 inside this Security Configuration, since this
setting indicates the use of a per-pair key, which is not suitable
for securing the Measurement Request messages that travel over
multiple hops. A router (an Intermediate Point or the End Point)
participating in a particular route measurement
o MUST generate a Secure MO message (a Measurement Request or a
Measurement Reply) if the received Measurement Request is a Secure
MO. The Security Configuration used in generating a Secure MO
message MUST be the same as the one used in the received message.
o MUST NOT generate a Secure MO message if the received Measurement
Request is not a Secure MO.
A router MUST discard a received Measurement Request if it cannot
follow the above-mentioned rules. If the Start Point sends a
Measurement Request in a Secure MO message using a particular
Security Configuration, it MUST discard the corresponding Measurement
Reply it receives with no further processing, unless the Measurement
Reply is received in a Secure MO message generated with the same
Security Configuration as the one used in the Measurement Request.
In the following discussion, any reference to an MO message is also
applicable to a Secure MO message, unless noted otherwise.
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 ensure that
o the next-hop address is a unicast address, and
o the next hop is on-link, and
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o the next hop is in the same RPL routing domain [RFC6554] as the
Start Point,
failing which the Start Point MUST discard the Measurement Request
without sending. 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.
The Start Point MUST maintain state for a just-transmitted
Measurement Request, for a lifetime duration that is large enough to
allow the corresponding Measurement Reply to return. This state
consists of the RPLInstanceID, the SeqNo, and the End Point Address
fields of the Measurement Request. The lifetime duration for this
state is locally determined by the Start Point and may be deployment
specific. This state expires when the corresponding Measurement
Reply is received or when the lifetime is over, whichever occurs
first. Failure to receive the corresponding Measurement Reply before
the expiry of a state may occur due to a number of reasons, including
the unwillingness on the part of an Intermediate Point or the
End Point to process the Measurement Request. The Start Point should
take such possibilities into account when deciding whether to
generate another Measurement Request for this route. The Start Point
MUST discard a received Measurement Reply with no further processing
if the state for the corresponding Measurement Request has already
expired.
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 and 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: This field MUST be set to the RPLInstanceID of the
route being measured.
o Compr: This field 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): This flag MUST be set to one, since the MO represents a
Measurement Request.
o Hop-by-hop (H): This flag MUST be set to one.
o Accumulate Route (A): This flag MUST be set to zero.
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o Reverse (R): This flag MUST be set to zero.
o Back Request (B): This flag MAY be set to one to request that the
End Point 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 SeqNo: This is 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 be set to a unicast
global/unique-local IPv6 address of the Start Point after eliding
Compr number of prefix octets.
o End Point Address: This field MUST be set to a unicast
global/unique-local IPv6 address of the End Point after eliding
Compr number of prefix octets.
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: This field MUST be set to the RPLInstanceID of the
route being measured.
o Compr: This field 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): This flag MUST be set to one, since the MO represents a
Measurement Request.
o Hop-by-hop (H): This flag 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.
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RFC 6998 Measurement of Routing Metrics in LLNs August 2013
o Back Request (B): This flag MAY be set to one to request that the
End Point send a Measurement Request to the Start Point.
o Intermediate Reply (I): This flag MUST be set to zero.
o SeqNo: This is 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. This DODAGID MUST also be a global or
unique-local IPv6 address of the Start Point.
o End Point Address: This field MUST be set to a unicast global or
unique-local IPv6 address of the End Point after eliding Compr
number of prefix octets.
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 a suitably sized Address vector, and various MO fields MUST
be set in the following manner:
o RPLInstanceID: This field MUST be set to the RPLInstanceID of the
route being measured.
o Compr: This field 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): This flag MUST be set to one, since the MO represents a
Measurement Request.
o Hop-by-hop (H): This flag 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.
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o Back Request (B): This flag MAY be set to one to request that the
End Point send a Measurement Request to the Start Point.
o Intermediate Reply (I): This flag MUST be set to zero.
o SeqNo: This is 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. This DODAGID MUST also be a global or
unique-local IPv6 address of the Start Point.
o End Point Address: This field MUST be set to a unicast global or
unique-local IPv6 address of the End Point after eliding Compr
number of prefix octets.
o Address vector: The Address vector must be large enough to
accommodate 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: This field does not have any significance when a
Source Route is being measured and hence can be set to any value.
o Compr: This field 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): This flag MUST be set to one, since the MO represents a
Measurement Request.
o Hop-by-hop (H): This flag MUST be set to zero.
o Accumulate Route (A): This flag MUST be set to zero.
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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 that the
End Point send a Measurement Request to the Start Point.
o Intermediate Reply (I): This flag MUST be set to zero.
o SeqNo: This is 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: This field MUST be set to a unicast global or
unique-local IPv6 address of the Start Point after eliding Compr
number of prefix octets.
o End Point Address: This field MUST be set to a unicast global or
unique-local IPv6 address of the End Point after eliding Compr
number of prefix octets.
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).
* Each address appearing in the Address vector MUST be a unicast
global or unique-local IPv6 address. Further, each address
MUST have the same prefix as the Start Point Address and the
End Point Address. This prefix, whose length in octets is
specified in the Compr field, MUST be elided from each address.
* The IPv6 addresses in the Address vector MUST be reachable in
the Forward direction.
* If the R flag is set to one, the IPv6 addresses in the Address
vector MUST also be reachable in the Reverse direction.
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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, in order to meet any policy-related
goals. Such policy goals may include the need to reduce the router's
CPU load, or to enhance its battery life, or to prevent the 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 to be the length of the common prefix used
in IPv6 addresses in the LLN.
On receiving an MO, if a router chooses to process the packet
further, it MUST determine whether or not one of its IPv6 addresses
is listed as either the Start Point or the End Point Address. If
not, 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 = 0). This is because the End Point unicasts a Measurement Reply
directly to the Start Point. So, the Intermediate Point treats a
transiting Measurement Reply as a data packet and not a RPL control
message.
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.
If the Num field inside the received Measurement Request is not set
to zero, thereby implying that an Address vector is present, the
Intermediate Point MUST discard the received message with no further
processing.
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 (as 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
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(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 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 If the router does not know how to reach the End Point, it 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 [RFC4443] to the Start 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 the remaining fields unchanged (the Num field would be
modified in the next steps). Note that the RPLInstanceID field
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).
+ Each address appearing in the Address vector MUST be a
unicast global or unique-local IPv6 address. Further, each
address MUST have the same prefix as the Start Point Address
and the End Point Address. This prefix, whose length in
octets is specified in the Compr field, MUST be elided from
each address.
+ The IPv6 addresses in the Address vector MUST be reachable
in the Forward direction.
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If the router cannot insert an Address vector satisfying the
rules mentioned above, it 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 [RFC4443] to the Start Point.
* 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, the
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, and A = 0), the Intermediate Point MUST process the
received Measurement Request in the following manner.
If the Num field inside the received Measurement Request is not set
to zero, thereby implying that an Address vector is present, the
Intermediate Point MUST discard the received message with no further
processing.
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). If the Intermediate Point cannot determine the next
hop, it 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 [RFC4443] to the
Start Point. 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 is on (i.e., H = 1, RPLInstanceID has a
local value, and A = 1), the Intermediate Point MUST process the
received Measurement Request in the following manner.
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If the Num field inside the received Measurement Request is set to
zero, thereby implying that an Address vector is not present, the
Intermediate Point MUST discard the received message with no further
processing.
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). If the Intermediate Point cannot determine the next
hop, it 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 [RFC4443] to the
Start Point. If the index field has value Num - 1 and the next hop
is not the same as the End Point, the Intermediate Point MUST drop
the received Measurement Request with no further processing. In this
case, the next hop would have no space left in the Address vector to
store its address. Otherwise, the router MUST store one of its IPv6
addresses at location Address[Index] and then increment the Index
field. The IPv6 address added to the Address vector MUST have the
following properties:
o This address MUST be a unicast global or unique-local address.
o This address MUST have the same prefix as the Start Point Address
and the End Point Address. This prefix, whose length in octets is
specified in the Compr field, MUST be elided before the address is
added to the Address vector.
o This address MUST be reachable in the Reverse direction.
If the router does not have an IPv6 address that satisfies the
properties mentioned above, it MUST discard the Measurement Request
with no further processing.
The Intermediate Point MUST then complete the processing of the
received Measurement Request as specified in Section 5.5.
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.
If the Num field inside the received Measurement Request is set to
zero, thereby implying that an Address vector is not present, the
Intermediate Point MUST discard the received message with no further
processing.
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The Intermediate Point MUST verify that the Address[Index] element
lists one of its unicast global or unique-local IPv6 addresses (minus
the prefix whose length in octets is specified in the Compr field),
failing which it MUST discard the Measurement Request with no further
processing. The Intermediate Point MUST then increment the Index
field and use the Address[Index] element as the next hop (unless the
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 objects 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.
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 global or unique-local IPv6
addresses (minus the prefix whose length in octets is specified in
the Compr field) 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).
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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, which the
End Point MAY use, after reversal, to reach the Start Point. Note
that the Source Route in the Address vector does not include the
Start Point and the End Point addresses, and that the individual
addresses do not include the common prefix whose length in octets is
specified in the Compr field.
If the received Measurement Request traveled on a Source Route and
the Reverse flag is set to one (i.e., H = 0 and 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, which
the End Point MAY use, after reversal, to reach the Start Point.
Again, the Source Route in the Address vector does not include the
Start Point and the End Point addresses, and the individual addresses
do not include the common prefix whose length in octets is specified
in the Compr field.
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 the 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
corresponding Measurement Request: RPLInstanceID, Compr, SeqNo,
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 can, therefore, trivially be converted
into a Measurement Reply by setting the Type (T) flag to zero.
Goyal, et al. Experimental [Page 24]
RFC 6998 Measurement of Routing Metrics in LLNs August 2013
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 the MO to see 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.
If the Start Point discovers that the received MO is not a
Measurement Reply, or if it no longer maintains state for the
corresponding Measurement Request, it MUST discard the received
message with no further processing.
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
In general, the security considerations for the route measurement
mechanism described in this document are similar to those for RPL (as
described in Section 19 of the RPL specification [RFC6550]).
Sections 6.1 and 10 of [RFC6550] describe RPL's security framework,
which provides data confidentiality, authentication, replay
protection, and delay protection services. This security framework
is applicable to the route measurement mechanism described here as
well, after taking into account the constraints specified in
Section 3.2.
Goyal, et al. Experimental [Page 25]
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This document requires that all routers participating in a secure
invocation of the route measurement process use the Security
Configuration chosen by the Start Point. The intention is to avoid
compromising the overall security of the route measurement due to
some routers using a weaker Security Configuration. A router is
allowed to participate in a "secure" route measurement only if it can
support the Security Configuration in use, which also specifies the
key in use. It does not matter whether the key is preinstalled or
dynamically acquired after proper authentication. The router must
have the key in use before it can process or generate Secure MO
messages. Hence, from the perspective of the route measurement
mechanism, there is no distinction between the "preinstalled" and
"authenticated" security modes described in the RPL specification
[RFC6550]. Of course, if a compromised router has the key being
used, it could cause the route measurement to fail, or worse, insert
wrong information in Secure MO messages.
A rogue router acting as the Start Point could use the route
measurement mechanism defined in this document to measure routes from
itself to other routers and thus find out key information about the
LLN, e.g., the topological features of the LLN (such as the identity
of the key routers in the topology) or the remaining energy levels
[RFC6551] in the routers. This information can potentially be used
to attack the LLN. A rogue router could also use this mechanism to
send bogus Measurement Requests to arbitrary End Points. If
sufficient Measurement Requests are sent, then it 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.
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. For example, an
LLN deployment might require the use of Secure MO messages generated
using a key that could be obtained only after proper authentication.
Note that this document requires that an LLN deployment support
Secure MO messages so that such policies can be enforced where
considered essential.
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 headers [RFC5095] may be valid here.
To address such concerns, the mechanism described in this document
includes several remedies, in the form of the following requirements:
o A route inserted inside the Address vector must be a strict Source
Route and must not include any multicast addresses.
Goyal, et al. Experimental [Page 26]
RFC 6998 Measurement of Routing Metrics in LLNs August 2013
o 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 A router must drop a received Measurement Request if the next-hop
address is not on-link or if it is not a unicast address.
9. IANA Considerations
This document defines two new RPL messages:
o "Measurement Object" (see Section 3.1), assigned a value of 0x06
from the "RPL Control Codes" space [RFC6550].
o "Secure Measurement Object" (see Section 3.2), assigned a value of
0x86 from the "RPL Control Codes" space [RFC6550].
+------+---------------------------+---------------+
| Code | Description | Reference |
+------+---------------------------+---------------+
| 0x06 | Measurement Object | This document |
| 0x86 | Secure Measurement Object | This document |
+------+---------------------------+---------------+
RPL Control Codes
10. Acknowledgements
The authors gratefully acknowledge the contributions of Ralph Droms,
Adrian Farrel, Joel Halpern, Matthias Philipp, Pascal Thubert,
Richard Kelsey, and Zach Shelby in the development of this document.
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11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
Lossy Networks", RFC 6550, March 2012.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
March 2012.
[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, August 2013.
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.
[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.
[ROLL-TERMS]
Vasseur, JP., "Terminology in Low power And Lossy
Networks", Work in Progress, March 2013.
Goyal, et al. Experimental [Page 28]
RFC 6998 Measurement of Routing Metrics in LLNs August 2013
Authors' Addresses
Mukul Goyal (editor)
University of Wisconsin Milwaukee
3200 N. Cramer St.
Milwaukee, WI 53201
USA
Phone: +1-414-229-5001
EMail: mukul@uwm.edu
Emmanuel Baccelli
INRIA
Phone: +33-169-335-511
EMail: Emmanuel.Baccelli@inria.fr
URI: http://www.emmanuelbaccelli.org/
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, WI 53202
USA
Phone: +1-414-524-4010
EMail: jerald.p.martocci@jci.com
Goyal, et al. Experimental [Page 29]