





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.












Goyal, et al.                 Experimental                      [Page 1]

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]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


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

















Goyal, et al.                 Experimental                      [Page 3]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


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]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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.











Goyal, et al.                 Experimental                      [Page 5]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


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.





Goyal, et al.                 Experimental                      [Page 6]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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.
































Goyal, et al.                 Experimental                      [Page 7]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


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.




Goyal, et al.                 Experimental                      [Page 8]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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).





Goyal, et al.                 Experimental                      [Page 9]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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



Goyal, et al.                 Experimental                     [Page 10]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


      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.





Goyal, et al.                 Experimental                     [Page 11]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


      *  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.



Goyal, et al.                 Experimental                     [Page 12]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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





Goyal, et al.                 Experimental                     [Page 13]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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.



Goyal, et al.                 Experimental                     [Page 14]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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.



Goyal, et al.                 Experimental                     [Page 15]

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.





Goyal, et al.                 Experimental                     [Page 16]

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 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.



Goyal, et al.                 Experimental                     [Page 17]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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.






Goyal, et al.                 Experimental                     [Page 18]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


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



Goyal, et al.                 Experimental                     [Page 19]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   (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.



Goyal, et al.                 Experimental                     [Page 20]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


         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.



Goyal, et al.                 Experimental                     [Page 21]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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.




Goyal, et al.                 Experimental                     [Page 22]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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).



Goyal, et al.                 Experimental                     [Page 23]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


   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.


















Goyal, et al.                 Experimental                     [Page 27]

RFC 6998         Measurement of Routing Metrics in LLNs      August 2013


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]

