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Versions: (draft-goyal-roll-p2p-measurement) 00 01 02 03 04 05 06 07 08 10 RFC 6998

Internet Engineering Task Force                            M. Goyal, Ed.
Internet-Draft                                   University of Wisconsin
Intended status: Experimental                                  Milwaukee
Expires: September 5, 2012                                   E. Baccelli
                                                                   INRIA
                                                               A. Brandt
                                                           Sigma Designs
                                                             J. Martocci
                                                        Johnson Controls
                                                           March 4, 2012


 A Mechanism to Measure the Quality of a Point-to-point Route in a Low
                        Power and Lossy Network
                   draft-ietf-roll-p2p-measurement-03

Abstract

   This document specifies a mechanism that enables an RPL router to
   measure the quality of an existing route towards another RPL router
   in a low power and lossy network, thereby allowing the router to
   decide if it wants to initiate the discovery of a better route.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 5, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  The Measurement Object (MO)  . . . . . . . . . . . . . . . . .  4
     3.1.  Format of the base MO  . . . . . . . . . . . . . . . . . .  5
     3.2.  Secure MO  . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Originating a Measurement Request  . . . . . . . . . . . . . .  9
     4.1.  To Measure A Hop-by-hop Route with a Global
           RPLInstanceID  . . . . . . . . . . . . . . . . . . . . . . 10
     4.2.  To Measure A Hop-by-hop Route with a Local
           RPLInstanceID  . . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  To Measure A Source Route  . . . . . . . . . . . . . . . . 11
   5.  Processing a Measurement Request at an Intermediate Router . . 12
     5.1.  Determining Next Hop For An MO Measuring A Source Route  . 13
     5.2.  Determining Next Hop For An MO Measuring A Hop-by-hop
           Route  . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   6.  Processing a Measurement Request at the Target . . . . . . . . 14
   7.  Processing a Measurement Reply at the Origin . . . . . . . . . 15
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     11.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
















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1.  Introduction

   Point to point (P2P) communication between arbitrary routers in a Low
   power and Lossy Network (LLN) is a key requirement for many
   applications [RFC5826][RFC5867].  RPL [I-D.ietf-roll-rpl], the IPv6
   Routing Protocol for LLNs, constrains the LLN topology to a Directed
   Acyclic Graph (DAG) built to optimize the routing costs to reach the
   DAG's root.  The P2P routing functionality, available under RPL, has
   the following key limitations:

   o  The P2P routes are restricted to use the DAG links only.  Such P2P
      routes may potentially be suboptimal and may lead to traffic
      congestion near the DAG root.

   o  RPL is a proactive routing protocol and hence requires all P2P
      routes to be established ahead of the time they are used.  Many
      LLN applications require the ability to establish P2P routes "on
      demand".

   To ameliorate situations, where the core RPL's P2P routing
   functionality does not meet the application requirements,
   [I-D.ietf-roll-p2p-rpl] describes P2P-RPL, an extension to core RPL.
   P2P-RPL provides a reactive mechanism to discover P2P routes that
   meet the specified routing constraints
   [I-D.ietf-roll-routing-metrics].  In some cases, the application
   requirements or the LLN's topological features allow a router to
   infer these routing constraints implicitly.  For example, the
   application may require the end-to-end loss rate and/or latency along
   the route to be below certain thresholds or the LLN topology may be
   such that a router can safely assume its destination to be less than
   a certain number of hops away from itself.

   When the existing routes are deemed unsatisfactory but the router
   does not implicitly know the routing constraints to be used in P2P-
   RPL route discovery, it may be necessary for the router to measure
   the aggregated values of the routing metrics along the existing
   route.  This knowledge will allow the router to frame reasonable
   routing constraints to discover a better route using P2P-RPL.  For
   example, if the router determines the aggregate ETX
   [I-D.ietf-roll-routing-metrics] along an existing route to be "x", it
   can use "ETX < x*y", where y is a certain fraction, as the routing
   constraint for use in P2P-RPL route discovery.  Note that it is
   important that the routing constraints are not overly strict;
   otherwise the P2P-RPL route discovery may fail even though a route,
   much better than the one currently being used, exists.

   This document specifies a mechanism that enables an RPL router to
   measure the aggregated values of the routing metrics along an



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   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.

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
   [I-D.ietf-roll-terminology], [I-D.ietf-roll-rpl] and
   [I-D.ietf-roll-p2p-rpl].  The following terms, originally defined in
   [I-D.ietf-roll-p2p-rpl], are redefined in the following manner.

   Origin: The origin refers to the RPL router that initiates the
   measurement process defined in this document and is the start point
   of the P2P route being measured.

   Target: The target refers to the RPL router at the end point of the
   P2P route being measured.

   Intermediate Router: An RPL router, other than the origin and the
   target, on the P2P route being measured.


2.  Overview

   The mechanism described in this document can be used by an origin in
   an LLN to measure the aggregated values of the routing metrics along
   a P2P route to a target within the LLN.  Such a route could be a
   source route or a hop-by-hop route established using RPL
   [I-D.ietf-roll-rpl] or P2P-RPL [I-D.ietf-roll-p2p-rpl].  The origin
   sends a Measurement Request message along the route.  The Measurement
   Request accumulates the values of the routing metrics as it travels
   towards the target.  Upon receiving the Measurement Request, the
   target unicasts a Measurement Reply message, carrying the accumulated
   values of the routing metrics, back to the origin.  Optionally, the
   origin may allow an intermediate router to generate the Measurement
   Reply if it already knows the relevant routing metric values along
   rest of the route.


3.  The Measurement Object (MO)

   This document defines two new RPL Control Message types, the
   Measurement Object (MO), with code 0x06 (to be confirmed by IANA),



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   and the Secure MO, with code 0x86 (to be confirmed by IANA).  An MO
   serves as both Measurement Request and Measurement Reply.

3.1.  Format of the base MO

       0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | RPLInstanceID | Compr |T|H|A|R|B|I| SequenceNo|  Num  | Index |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                       Origin Address                          |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                       Target Address                          |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                       Address[1..Num]                         .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                   Metric Container Option(s)                  .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


           Figure 1: Format of the base Measurement Object (MO)

   The format of a base MO is shown in Figure 1.  A base MO consists of
   the following fields:

   o  RPLInstanceID: The origin sets this field to indicate the
      RPLInstanceID of the route being measured.  An intermediate router
      MUST discard the received MO message if it is not aware of the RPL
      Instance specified by the RPLInstanceID value.  If the
      RPLInstanceID is a local value, the RPL Instance is identified by
      both the RPLInstanceID and the Origin Address fields.  An
      intermediate router MUST set the RPLInstanceID field in the
      outgoing MO packet to the same value that it had in the
      corresponding incoming MO packet.





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   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 Origin/Target Address fields
      and the Address vector.  The "Compr" field, a 4-bit unsigned
      integer, is set by the origin to specify the number of prefix
      octets that are elided from the IPv6 addresses in Origin/Target
      Address fields and the Address vector.  An intermediate router
      MUST set the Compr field in the outgoing MO packet to the same
      value that it had in the corresponding incoming MO packet.  The
      Compr value will be 0 if full IPv6 addresses are carried in the
      Origin/Target Address fields and the Address vector.

   o  Type (T): This flag is set to 1 if the MO represents a Measurement
      Request.  The flag is cleared to 0 if the MO is a Measurement
      Reply.

   o  Hop-by-hop (H): The origin sets this flag to 1 if the route being
      measured is a hop-by-hop route.  In that case, the hop-by-hop
      route is identified by the RPLInstanceID and, if the RPLInstanceID
      is a local value, the Origin Address serving as the DODAGID.  The
      origin resets this flag to 0 if the route being measured is a
      source route specified in the Address vector.  An intermediate
      router MUST set the H flag in an outgoing MO packet to the same
      value that it had in the corresponding incoming MO packet unless
      the router is the root of the non-storing global DAG, identified
      by the RPLInstanceID, along which the MO packet had been traveling
      so far.  In that case, the DAG root MUST reset the H flag to 0 in
      the outgoing MO packet if it intends to insert a source route in
      the Address vector to direct the MO packet towards the target.

   o  Accumulate Route (A): This flag is relevant only if the MO
      represents a Measurement Request that travels along a hop-by-hop
      route represented by a local RPLInstanceID.  In other words, this
      flag MAY be set to 1 only if T = 1, H = 1 and the RPLInstanceID
      field has a local value.  Otherwise, this flag MUST be cleared to
      0.  A value 1 in this flag indicates that the Measurement Request
      MUST accumulate a source route for use by the target to send the
      Measurement Reply back to the origin.  In this case, an
      intermediate router MUST add its unicast IPv6 address (after
      eliding Compr number of prefix octets) to the Address vector in
      the manner specified later.  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 target; and





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      *  The target can presumably reach the origin along this global
         DAG.

   o  Reverse (R): This flag is relevant only if the MO represents a
      Measurement Request that travels along a source route, specified
      in the Address vector, to the target.  In other words, this flag
      MAY be set to 1 only if T = 1 and H = 0.  Otherwise, this flag
      MUST be cleared to 0.  A value 1 in the flag indicates that the
      Address vector contains a complete source route from the origin to
      the target, which can be used, after reversal, by the target to
      source route the Measurement Reply message back to the origin.

   o  Back Request (B): This flag serves as a request to the target to
      send a Measurement Request towards the origin.  The origin MAY set
      this flag to 1 if it wants to make such a request to the target.
      An intermediate router MUST set the B flag in an outgoing MO
      packet to the same value that it had in the corresponding incoming
      MO packet.  On receiving a Measurement Request with the B flag set
      to 1, the target SHOULD generate a Measurement Request to measure
      the cost of its current (or the most preferred) route to the
      origin.  Receipt of this Measurement Request would allow the
      origin to know the cost of the back route from the target to
      itself and thus determine the round-trip cost of reaching the
      target.

   o  Intermediate Reply (I): Relevant only if a hop-by-hop route is
      being measured, this flag serves as a permission to an
      intermediate router to generate a Measurement Reply if it knows
      the cost of the rest of the route being measured.  The origin MAY
      set this flag to 1 if a hop-by-hop route is being measured (i.e.,
      H = 1) and the origin wants to allow an intermediate router to
      generate the Measurement Reply in response to this Measurement
      Request.  Setting this flag may be useful in scenarios where the
      Hop Count [I-D.ietf-roll-routing-metrics] is the routing metric of
      interest and the origin expects an intermediate router (e.g. the
      root of a non-storing DAG or a common ancestor of the origin and
      the target in a storing DAG) to know the Hop Count of the
      remainder of the route to the target.  This flag MUST be cleared
      to 0 if the route being measured is a source route (i.e., H = 0).

   o  SequenceNo: A 6-bit sequence number, assigned by the origin, that
      allows the origin to uniquely identify a Measurement Request and
      the corresponding Measurement Reply.  An intermediate router MUST
      set this field in the outgoing MO packet to the same value that it
      had in the corresponding incoming MO packet.  The target MUST set
      this field in a Measurement Reply message to the same value that
      it had in the corresponding Measurement Request message.




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   o  Num: The origin sets this field to indicate the number of fields
      in 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 (T=1,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 A flag is set
      (T=1,H=1,A=1 and RPLInstanceID field has a local value), this
      field indicates the index in the Address vector where an
      intermediate router receiving the MO message must store its IPv6
      address.  Otherwise, this field MUST be set to zero on
      transmission and ignored on reception.

   o  Origin Address: A unicast IPv6 address of the origin after eliding
      Compr number of prefix octets.  If the MO is traveling along a
      hop-by-hop route and the RPLInstanceID field indicates a local
      value, the Origin Address field MUST specify the DODAGID value
      that, along with the RPLInstanceID, uniquely identifies the hop-
      by-hop route being measured.

   o  Target Address: A unicast IPv6 address of the target after eliding
      Compr number of prefix octets.

   o  Address[1..Num]: A vector of unicast IPv6 addresses (with Compr
      number of prefix octets elided) representing a source route to the
      target:

      *  Each element in the vector has size (16 - Compr) octets.

      *  The total number of elements inside the Address vector is given
         by the Num field.

      *  When the Measurement Request is traveling along a hop-by-hop
         route with local RPLInstanceID and has the A flag set, the
         Address vector is used to accumulate a source route to be used
         by the target to send the Measurement Reply back to the origin.
         In this case, the route MUST be accumulated in the forward
         direction, i.e., from the origin to the target.  The target
         router would reverse this route to obtain a source route from
         itself to the origin.  The IPv6 addresses in the accumulated
         route MUST be accessible in the backward direction, i.e., from
         the target to the origin.  An intermediate router adding its
         address to the Address vector MUST ensure that its address does
         not already exist in the vector.





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      *  When the Measurement Request is traveling along a source route,
         the Address vector MUST contain a complete route to the target
         and the IPv6 addresses in the Address vector MUST be accessible
         in the forward direction, i.e., from the origin to the target.
         A router (origin or an intermediate router) inserting an
         Address vector inside an MO MUST ensure that no address appears
         more than once inside the vector.  Each router on the way MUST
         ensure that the loops do not exist within the source route.
         The origin MAY set the R flag in the MO if the route in the
         Address vector represents a complete route from the origin to
         the target and this route can be used after reversal by the
         target to send the Measurement Reply message back to the
         origin.

      *  The origin and target addresses MUST NOT be included in the
         Address vector.

      *  The Address vector MUST NOT contain any multicast addresses.

   o  Metric Container Options: An MO MUST contain one or more Metric
      Container options to accumulate the routing metric values for the
      route being measured.

3.2.  Secure MO

   A Secure MO message follows the format in Figure 7 of
   [I-D.ietf-roll-rpl], where the base format is the base MO shown in
   Figure 1.


4.  Originating a Measurement Request

   If an origin needs to measure the routing metric values along a P2P
   route towards a target, it generates an MO message and sets its
   fields as described in Section 3.1.  The setting of MO fields in
   specific cases is described below.  In all cases, the origin MUST set
   the T flag to 1 to indicate that the MO represents a Measurement
   Request.  The origin MUST also include one or more Metric Container
   options inside the MO to carry the routing metric objects of
   interest.  Depending on the metrics being measured, the origin must
   also initiate these routing metric objects by including the values of
   the routing metrics for the first hop on the P2P route being
   measured.

   After setting the MO fields appropriately, the origin MUST unicast
   the MO message to the next hop on the P2P route.





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4.1.  To Measure A Hop-by-hop Route with a Global RPLInstanceID

   If a hop-by-hop route with a global RPLInstanceID is being measured,
   the MO message MUST NOT contain the Address vector and the following
   MO fields MUST be set in the manner specified below:

   o  Hop-by-hop (H): This flag MUST be set to 1.

   o  Accumulate Route (A): This flag MUST be cleared to 0.

   o  Reverse (R): This flag MUST be cleared to 0.

   o  Num: This field MUST be cleared to 0.

   o  Index: This field MUST be cleared to 0.

4.2.  To Measure A Hop-by-hop Route with a Local RPLInstanceID

   If a hop-by-hop route with a local RPLInstanceID is being measured
   and the MO is not accumulating a source route for the target's use,
   the MO message MUST NOT contain the Address vector and the following
   MO fields MUST be set in the manner specified below:

   o  Hop-by-hop (H): This flag MUST be set to 1.

   o  Accumulate Route (A): This flag MUST be cleared to 0.

   o  Reverse (R): This flag MUST be cleared to 0.

   o  Num: This field MUST be cleared to 0.

   o  Index: This field MUST be cleared to 0.

   o  Origin Address: This field MUST contain the DODAGID value (after
      eliding Compr number of prefix octets) associated with the route
      being measured.

   If a hop-by-hop route with a local RPLInstanceID is being measured
   and the origin desires the MO to accumulate a source route for the
   target to send the Measurement Reply message back, it MUST set the
   following MO fields in the manner specified below:

   o  Hop-by-hop (H): This flag MUST be set to 1.

   o  Accumulate Route (A): This flag MUST be set to 1.

   o  Reverse (R): This flag MUST be cleared to 0.




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   o  Intermediate Reply (I): This flag MUST be cleared to 0.

   o  Address vector: The Address vector must be large enough to
      accomodate a complete source route from the origin to the target.
      All the bits in the Address vector field MUST be cleared to 0.

   o  Num: This field MUST specify the number of address elements that
      can fit inside the Address vector.

   o  Index: This field MUST be set to 1.

   o  Origin Address: This field MUST contain the DODAGID value (after
      eliding Compr number of prefix octets) associated with the route
      being measured.

4.3.  To Measure A Source Route

   If a source route is being measured, the origin MUST set the
   following MO fields in the manner specified below:

   o  Hop-by-hop (H): This flag MUST be cleared to 0.

   o  Accumulate Route (A): This flag MUST be cleared to 0.

   o  Reverse (R): This flag SHOULD be set to 1 if the source route in
      the Address vector can be reversed and used by the target to
      source route the Measurement Reply message back to the origin.
      Otherwise, this flag MUST be cleared to 0.

   o  Intermediate Reply (I): This flag MUST be cleared to 0.

   o  Address vector:

      *  The Address vector MUST contain a complete route from the
         origin to the target (excluding the origin and the target).

      *  The IPv6 addresses (with Compr prefix octets elided) in the
         Address vector MUST be accessible in the forward direction,
         i.e., from the origin to the target.

      *  To prevent loops in the source route, the origin MUST ensure
         compliance to the following rules:

         +  Any IPv6 address MUST NOT appear more than once in the
            Address vector.

         +  If the Address vector includes multiple IPv6 addresses
            assigned to the origin's interfaces, such addresses MUST



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            appear back to back inside the Address vector.

      *  Each address appearing in the Address vector MUST be a unicast
         address.

   o  Num: This field MUST be set to indicate the number of elements in
      the Address vector.

   o  Index: This field MUST be set to 1.

   The origin MUST NOT send the packet further if the next hop address
   on the source route is not on-link.


5.  Processing a Measurement Request at an Intermediate Router

   A router (an intermediate router or the target) MAY discard a
   received MO with no further processing to meet any policy-related
   goal.  Such policy goals may include the need to reduce the router's
   CPU load or to enhance its battery life.

   A router MUST discard a received MO with no further processing:

   o  If the router is not aware of the RPL Instance identified by the
      RPLInstanceID (and the Origin Address, if RPLInstanceID is a local
      value) field in the message.

   o  If the Compr field is not same as what the router considers as 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 check if one of its IPv6 addresses is listed as
   either the Origin or the Target Address.  If neither, the router
   considers itself an Intermediate Router and MUST process the received
   MO in the following manner.

   An intermediate router MUST discard the packet with no further
   processing if the received MO is not a Measurement Request.

   If the I flag is set to 1 in the received MO and the intermediate
   router knows the values of the routing metrics, specified in the
   Metric Container, for the remainder of the route, it MAY generate a
   Measurement Reply on the target's behalf in the manner specified in
   Section 6 (after including in the Measurement Reply the relevant
   routing metric values for the complete route being measured).
   Otherwise, the intermediate router MUST process the received MO in
   the following manner.




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   The router MUST determine the next hop on the P2P route being
   measured in the manner described below.  The router MUST drop the MO
   with no further processing and MAY send an ICMPv6 Destination
   Unreachable (with Code 0 - No Route To Destination) error message to
   the source of the message if it can not determine the next hop for
   the message.

   After determining the next hop, the router MUST update the routing
   metric objects, contained in the Metric Container options inside the
   MO, either by updating the aggregated value for the routing metric or
   by attaching the local values for the metric inside the object.
   After updating the routing metrics, the router MUST unicast the MO to
   the next hop.

5.1.  Determining Next Hop For An MO Measuring A Source Route

   In case the received MO is measuring a source route (H=0),

   o  The router MUST verify that the Address[Index] element lists one
      of its unicast IPv6 addresses, failing which the router MUST
      discard the MO packet with no further processing;

   o  The router MUST then increment the Index field and use the
      Address[Index] element as the next hop.  If Index is greater than
      Num, the router MUST use the Target Address as the next hop.

   An intermediate router MUST discard the MO packet with no further
   processing if the next hop address is not on-link or is not a unicast
   address.  To prevent loops, an intermediate router MUST check if the
   Address vector includes multiple IPv6 addresses assigned to the
   router's interfaces and if such addresses do not appear back to back
   inside the Address vector.  In this case, the router MUST discard the
   MO packet with no further processing.

5.2.  Determining Next Hop For An MO Measuring A Hop-by-hop Route

   If the received MO is measuring a hop-by-hop route (H=1), the router
   MUST use the RPLInstanceID, the Target Address and, if RPLInstanceID
   is a local value, the Origin Address to determine the next hop for
   the MO.  Moreover,

   o  If the RPLInstanceID of the hop-by-hop route is a local value and
      the A flag is set, the router MUST check if the Address vector
      already contains one of its IPv6 addresses.  If yes, the router
      MUST discard the packet with no further processing.  Otherwise,
      the router MUST store one of its IPv6 addresses (after eliding
      Compr prefix octets) at location Address[Index] and then increment
      the Index field.



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   o  If the router is the root of the non-storing DAG along which the
      received MO message has been traveling so far, the router MUST do
      the following:

      *  Reset the H, A and R flags.

      *  Remove any existing Address vector inside the MO.

      *  Insert a new Address vector inside the MO and specify a source
         route to the target inside the Address vector as per the
         following rules:

         +  The Address vector MUST contain a complete route from the
            router to the target (excluding the router and the target);

         +  The IPv6 addresses (with Compr prefix octets elided) in the
            Address vector MUST be accessible in the forward direction,
            i.e., towards the target;

         +  To prevent loops in the source route, the router MUST ensure
            that

            -  Any IPv6 address MUST NOT appear more than once in the
               Address vector;

            -  If the Address vector includes multiple IPv6 addresses
               assigned to the router's interfaces, such addresses MUST
               appear back to back inside the Address vector.

         +  Each address appearing in the Address vector MUST be a
            unicast address.

      *  Specify in the Num field the number of address elements in the
         Address vector.

      *  Set the Index field to 1.


6.  Processing a Measurement Request at the Target

   On receiving an MO, if a router chooses to process the packet further
   and finds one of its unicast IPv6 addresses listed as the Target
   Address, the router considers itself the target and MUST process the
   received MO in the following manner.

   The target MUST discard the packet with no further processing if the
   received MO is not a Measurement Request.




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   The target 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
   target had sent to the origin with B flag set to 1).

   The target MUST generate a Measurement Reply message.  The
   Measurement Reply message MUST have the same SequenceNo field as the
   received Measurement Request message.  The received Measurement
   Request message can be trivially converted into the Measurement Reply
   by reseting the T flag to zero.  The target MAY remove the Address
   vector from the Measurement Reply if desired.  The target MUST then
   unicast the Measurement Reply back to the origin:

   o  If the Measurement Request traveled along a DAG with a global
      RPLInstanceID, the Measurement Reply MAY be unicast back to the
      origin along the same DAG.

   o  If the Measurement Request traveled along a hop-by-hop route with
      a local RPLInstanceID and the A flag inside the received message
      is set to 1, the target MAY reverse the source route contained in
      the Address vector and use it to send the Measurement Reply back
      to the origin.

   o  If the Measurement Request traveled along a source route and the R
      flag inside the received message is set to 1, the target MAY
      reverse the source route contained in the Address vector and use
      it to send the Measurement Reply back to the origin.

   If the B flag in the received Measurement Request is set to 1, the
   target MAY generate a new Measurement Request to measure the cost of
   its current (or the most preferred) route to the origin.  The routing
   metrics used in the new Measurement Request MUST include the routing
   metrics specified in the received Measurement Request.


7.  Processing a Measurement Reply at the Origin

   When a router receives an MO, it examines if one of its unicast IPv6
   addresses is listed as the Origin Address.  If yes, the router is the
   origin and MUST process the received message in the following manner.

   The origin MUST discard the packet with no further processing if the
   received MO is not a Measurement Reply or if the origin has no
   recollection of sending a Measurement Request with the sequence
   number listed in the received MO.

   The origin MUST examine the routing metric objects inside the Metric



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   Container options to evaluate the quality of the measured P2P route.
   If a routing metric object contains local metric values recorded by
   routers on the route, the origin MUST aggregate these local values
   into an end-to-end value as per the aggregation rules for the metric.


8.  Security Considerations

   The mechanism defined in this document can potentially be used by a
   compromised router to generate bogus Measurement Requests to
   arbitrary target routers.  Such Measurement Requests may cause
   processing overload in the routers in the network, drain their
   batteries and cause traffic congestion in the network.  Note that
   some of these problems would occur even if the compromised router
   were to generate bogus data traffic to arbitrary destinations.

   Since a Measurement Request can travel along a source route specified
   in the Address vector, some of the security concerns that led to the
   deprecation of Type 0 routing header [RFC5095] may be valid here.  To
   address such concerns, the mechanism described in this document
   includes several remedies:

   o  This document requires that a route inserted inside the Address
      vector must be a strict source route and must not include any
      multicast addresses.

   o  This document requires that an MO message must not cross the
      boundaries of the RPL Instance where it originated.  A router must
      drop a received MO message if it is not aware of the RPL Instance
      referred to in the message.  Hence, any security problems
      associated with the mechanism would be limited to one RPL
      Instance.

   o  This document requires that a router must drop a received MO
      message if the next hop address is not on-link or if it is not a
      unicast address.

   o  This document requires that a router must check the source route
      inside the Address vector of each received MO message to ensure
      that it does not contain a loop involving the router.  The router
      must drop the received packet if the source route does contain
      such a loop.  This and the previous two rules protect the network
      against some of the security concerns even if a compromised node
      inserts a malformed Address vector inside the MO message.







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9.  IANA Considerations

   IANA is requested to allocate new code points in the "RPL Control
   Codes" registry for the "Measurement Object" and "Secure Measurement
   Object" described in this document.

           +------+---------------------------+---------------+
           | Code |        Description        |   Reference   |
           +------+---------------------------+---------------+
           | 0x06 |     Measurement Object    | This document |
           | 0x86 | Secure Measurement Object | This document |
           +------+---------------------------+---------------+

                             RPL Control Codes


10.  Acknowledgements

   Authors gratefully acknowledge the contributions of Matthias Philipp,
   Pascal Thubert, Richard Kelsey and Zach Shelby in the development of
   this document.


11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

11.2.  Informative References

   [I-D.ietf-roll-p2p-rpl]
              Goyal, M., Baccelli, E., Philipp, M., Brandt, A., and J.
              Martocci, "Reactive Discovery of Point-to-Point Routes in
              Low Power and Lossy Networks", draft-ietf-roll-p2p-rpl-08
              (work in progress), March 2012.

   [I-D.ietf-roll-routing-metrics]
              Barthel, D., Vasseur, J., Pister, K., Kim, M., and N.
              Dejean, "Routing Metrics used for Path Calculation in Low
              Power and Lossy Networks",
              draft-ietf-roll-routing-metrics-19 (work in progress),
              March 2011.

   [I-D.ietf-roll-rpl]
              Brandt, A., Vasseur, J., Hui, J., Pister, K., Thubert, P.,
              Levis, P., Struik, R., Kelsey, R., Clausen, T., and T.



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              Winter, "RPL: IPv6 Routing Protocol for Low power and
              Lossy Networks", draft-ietf-roll-rpl-19 (work in
              progress), March 2011.

   [I-D.ietf-roll-terminology]
              Vasseur, J., "Terminology in Low power And Lossy
              Networks", draft-ietf-roll-terminology-06 (work in
              progress), September 2011.

   [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.


Authors' Addresses

   Mukul Goyal (editor)
   University of Wisconsin Milwaukee
   3200 N Cramer St
   Milwaukee, WI  53211
   USA

   Phone: +1 414 2295001
   Email: mukul@uwm.edu


   Emmanuel Baccelli
   INRIA

   Phone: +33-169-335-511
   Email: Emmanuel.Baccelli@inria.fr
   URI:   http://www.emmanuelbaccelli.org/











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   Anders Brandt
   Sigma Designs
   Emdrupvej 26A, 1.
   Copenhagen, Dk-2100
   Denmark

   Phone: +45 29609501
   Email: abr@sdesigns.dk


   Jerald Martocci
   Johnson Controls
   507 E Michigan Street
   Milwaukee  53202
   USA

   Phone: +1 414 524 4010
   Email: jerald.p.martocci@jci.com

































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