


6MAN                                                              J. Hui
Internet-Draft                                               JP. Vasseur
Intended status: Standards Track                      Cisco Systems, Inc
Expires: June 18, 2012                                         D. Culler
                                                             UC Berkeley
                                                               V. Manral
                                                     Hewlett Packard Co.
                                                       December 16, 2011


           An IPv6 Routing Header for Source Routes with RPL
                 draft-ietf-6man-rpl-routing-header-07

Abstract

   In Low power and Lossy Networks (LLNs), memory constraints on routers
   may limit them to maintaining at most a few routes.  In some
   configurations, it is necessary to use these memory constrained
   routers to deliver datagrams to nodes within the LLN.  The Routing
   for Low Power and Lossy Networks (RPL) protocol can be used in some
   deployments to store most, if not all, routes on one (e.g. the
   Directed Acyclic Graph (DAG) root) or few routers and forward the
   IPv6 datagram using a source routing technique to avoid large routing
   tables on memory constrained routers.  This document specifies a new
   IPv6 Routing header type for delivering datagrams within a RPL
   Instance.

Status of this Memo

   This Internet-Draft is submitted 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 June 18, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Format of the RPL Routing Header . . . . . . . . . . . . . . .  7
   4.  RPL Router Behavior  . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Generating Source Routing Headers  . . . . . . . . . . . . 10
     4.2.  Processing Source Routing Headers  . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
     5.1.  Source Routing Attacks . . . . . . . . . . . . . . . . . . 14
     5.2.  ICMPv6 Attacks . . . . . . . . . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   8.  Changes  . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 19
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20





















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1.  Introduction

   Routing for Low Power and Lossy Networks (RPL) is a distance vector
   IPv6 routing protocol designed for Low Power and Lossy networks (LLN)
   [I-D.ietf-roll-rpl].  Such networks are typically constrained in
   resources (limited communication data rate, processing power, energy
   capacity, memory).  In particular, some LLN configurations may
   utilize LLN routers where memory constraints limit nodes to
   maintaining only a small number of default routes and no other
   destinations.  However, it may be necessary to utilize such memory-
   constrained routers to forward datagrams and maintain reachability to
   destinations within the LLN.

   To utilize paths that include memory-constrained routers, RPL relies
   on source routing.  In one deployment model of RPL, more capable
   routers collect routing information and form paths to arbitrary
   destinations within a RPL Instance.  However, a source routing
   mechanism supported by IPv6 is needed to deliver datagrams.

   This document specifies the Source Routing Header (SRH) for use
   strictly between RPL routers in the same RPL Instance.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].
























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2.  Overview

   The format of SRH draws from that of the Type 0 Routing header (RH0)
   [RFC2460].  However, SRH introduces mechanisms to compact the source
   route entries when all entries share the same prefix with the IPv6
   Destination Address of a packet carrying a SRH, a typical scenario in
   LLNs using source routing.  The compaction mechanism reduces
   consumption of scarce resources such as channel capacity.

   SRH also differs from RH0 in the processing rules to alleviate
   security concerns that led to the deprecation of RH0 [RFC5095].
   First, RPL routers implement a strict source route policy where each
   and every IPv6 hop between the source and destination of the source
   route is specified within the SRH.  Note that the source route may be
   a subset of the path between the actual source and destination and is
   discussed further below.  Second, a SRH is only used between RPL
   routers within a RPL Instance.  RPL Border Routers, responsible for
   connecting other RPL Instances and IP domains that use other routing
   protocols, do not allow datagrams already carrying a SRH header to
   enter or exit a RPL Instance.  Third, a RPL router drops datagrams
   that includes multiple addresses assigned to any interfaces on that
   router to avoid forwarding loops.

   There are two cases that determine how to include a SRH when a RPL
   router requires the use of a SRH to deliver a datagram to its
   destination.

   1.  If the SRH specifies the complete path from source to
       destination, the router places the SRH directly in the datagram
       itself.

   2.  If the SRH only specifies a subset of the path from source to
       destination, the router uses IPv6-in-IPv6 tunneling [RFC2473] and
       places the SRH in the outer IPv6 header.  Use of tunneling
       ensures that the datagram is delivered unmodified and that ICMP
       errors return to the source of the SRH rather than the source of
       the original datagram.

   In a RPL network, Case 1 occurs when both source and destinations are
   within a RPL Instance and a single SRH is used to specify the entire
   path from source to destination, as shown in the following figure:


                           +--------------------+
                           |                    |
                           |  (S) -------> (D)  |
                           |                    |
                           +--------------------+



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                                RPL Instance


   In the above scenario, datagrams traveling from source, S, to
   destination, D, have the following packet structure:


                   +--------+---------+-------------//-+
                   | IPv6   | Source  | IPv6           |
                   | Header | Routing | Payload        |
                   |        | Header  |                |
                   +--------+---------+-------------//-+


   S's address is carried in the IPv6 Header's Source Address field.
   D's address is carried in the last entry of SRH for all but the last
   hop, when D's address is carried in the IPv6 Header's Destination
   Address field of the packet carrying the SRH.

   In a RPL network, Case 2 occurs for all datagrams that have source
   and/or destination outside the RPL Instance, as shown in the
   following diagram:


                            +-----------------+
                            |                 |
                            |  (S) --------> (R) --------> (D)
                            |                 |
                            +-----------------+
                               RPL Instance

                            +-----------------+
                            |                 |
             (S) --------> (R) --------> (D)  |
                            |                 |
                            +-----------------+
                               RPL Instance

                            +-----------------+
                            |                 |
             (S) --------> (R) ------------> (R) --------> (D)
                            |                 |
                            +-----------------+
                               RPL Instance


   In the scenarios above, R may indicate a RPL Border Router (when
   connecting to other routing domains) or a RPL Router (when connecting



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   to hosts).  The datagrams have the following structure when traveling
   within the RPL Instance:


              +--------+---------+--------+-------------//-+
              | Outer  | Source  | Inner  | IPv6           |
              | IPv6   | Routing | IPv6   | Payload        |
              | Header | Header  | Header |                |
              +--------+---------+--------+-------------//-+
                                  <--- Original Packet --->
               <---           Tunneled Packet            --->


   Note that the outer header (including the SRH) is added and removed
   by the RPL router.

   Case 2 also occurs whenever a RPL router needs to insert a source
   route when forwarding datagram.  One such use case with RPL is to
   have all RPL traffic flow through a Border Router and have the Border
   Router use source routes to deliver datagrams to their final
   destination.  When including the SRH using tunneled mode, the Border
   Router would encapsulate the received datagram unmodified using IPv6-
   in-IPv6 and include a SRH in the outer IPv6 header.


                           +-----------------+
                           |                 |
                           |  (S) -------\   |
                           |              \  |
                           |               (LBR)
                           |              /  |
                           |  (D) <------/   |
                           |                 |
                           +-----------------+
                              RPL Instance


   In the above scenario, datagrams travel from S to D through LBR.
   Between S and LBR, the datagrams are routed using the DAG built by
   RPL and do not contain a SRH.  LBR encapsulates received datagrams
   unmodified using IPv6-in-IPv6 and the SRH is included in the outer
   IPv6 header.









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3.  Format of the RPL Routing Header

   The Source Routing Header has the following format:


      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Next Header  |  Hdr Ext Len  | Routing Type  | Segments Left |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | CmprI | CmprE |  Pad  |       Reserved        | RPLInstanceID |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                        Addresses[1..n]                        .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Next Header         8-bit selector.  Identifies the type of header
                       immediately following the Routing header.  Uses
                       the same values as the IPv6 Next Header field
                       [RFC2460].

   Hdr Ext Len         8-bit unsigned integer.  Length of the Routing
                       header in 8-octet units, not including the first
                       8 octets.  Note that when Addresses[1..n] are
                       compressed (i.e. value of CmprI or CmprE is not
                       0), Hdr Ext Len does not equal twice the number
                       of Addresses.

   Routing Type        8-bit selector.  Identifies the particular
                       Routing header variant.  A SRH should set the
                       Routing Type to TBD by IANA.

   Segments Left       8-bit unsigned integer.  Number of route segments
                       remaining, i.e., number of explicitly listed
                       intermediate nodes still to be visited before
                       reaching the final destination.  The originator
                       of a SRH sets this field to n, the number of
                       addresses contained in Addresses[1..n].

   CmprI               4-bit unsigned integer.  Number of prefix octets
                       from each segment, except than the last segment,
                       (i.e. segments 1 through n-1) that are elided.
                       For example, a SRH carrying full IPv6 addresses
                       in Addresses[1..n-1] sets CmprI to 0.



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   CmprE               4-bit unsigned integer.  Number of prefix octets
                       from the last segment (i.e. segment n) that are
                       elided.  For example, a SRH carrying a full IPv6
                       address in Addresses[n] sets CmprE to 0.

   Pad                 4-bit unsigned integer.  Number of octets that
                       are used for padding after Address[n] at the end
                       of the SRH.

   Reserved            This field is unused.  It MUST be initialized to
                       zero by the sender and MUST be ignored by the
                       receiver.

   RPLInstanceID       8-bit unsigned integer.  Indicates the RPL
                       Instance along which the packet is sent.

   Address[1..n]       Vector of addresses, numbered 1 to n.  Each
                       vector element in [1..n-1] has size (16 - CmprI)
                       and element [n] has size (16-CmprE).  The
                       originator of a SRH places the next-hop's IPv6
                       address as the first address in Address[1..n]
                       (i.e.  Address[1]).

   The SRH shares the same basic format as the Type 0 Routing header
   [RFC2460].  When carrying full IPv6 addresses, the CmprI, CmprE, and
   Pad fields are set to 0 and the only difference between the SRH and
   Type 0 encodings is the value of the Routing Type field.

   A common network configuration for a RPL Instance is that all routers
   within a RPL Instance share a common prefix.  The SRH introduces the
   CmprI, CmprE, and Pad fields to allow compaction of the Address[1..n]
   vector when all entries share the same prefix as the IPv6 Destination
   Address field of the packet carrying the SRH.  The CmprI and CmprE
   field indicates the number of prefix octets that are shared with the
   IPv6 Destination Address of the packet carrying the SRH.  The shared
   prefix octets are not carried within the Routing header and each
   entry in Address[1..n-1] has size (16 - CmprI) octets and Address[n]
   has size (16 - CmprE) octets.  When CmprI or CmprE is non-zero, there
   may exist unused octets between the last entry, Address[n], and the
   end of the Routing header.  The Pad field indicates the number of
   unused octets that are used for padding.  Note that when CmprI and
   CmprE are both 0, Pad MUST carry a value of 0.

   The SRH MUST NOT specify a path that visits a node more than once.
   When generating a SRH, the source may not know the mapping between
   IPv6 addresses and nodes.  Minimally, the source MUST ensure that
   IPv6 Addresses do not appear more than once and the IPv6 Source and
   Destination addresses of the encapsulating datagram do not appear in



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   the SRH.

   Multicast addresses MUST NOT appear in a SRH, or in the IPv6
   Destination Address field of a datagram carrying a SRH.















































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4.  RPL Router Behavior

4.1.  Generating Source Routing Headers

   To deliver an IPv6 datagram to its destination, a router may need to
   generate a new SRH and specify a strict source route.  When the
   router is the source of the original packet and the destination is
   known to be within the same RPL Instance, the router SHOULD include
   the SRH directly within the original packet.  Otherwise, the router
   MUST use IPv6-in-IPv6 tunneling [RFC2473] and place the SRH in the
   tunnel header.  Using IPv6-in-IPv6 tunneling ensures that the
   delivered datagram remains unmodified and that ICMPv6 errors
   generated by a SRH are sent back to the router that generated the
   SRH.

   In order to respect the IPv6 Hop Limit value of the original
   datagram, a RPL router generating an SRH MUST set the Segments Left
   to no greater than the original datagram's IPv6 Hop Limit value upon
   forwarding.  In the case that the source route is longer than the
   original datagram's IPv6 Hop Limit, only the initial hops (determined
   by the original datagram's IPv6 Hop Limit) should be included in the
   SRH.  If the RPL router is not the source of the original datagram,
   the original datagram's IPv6 Hop Limit field is decremented before
   generating the SRH.  After generating the SRH, the RPL router
   decrements the original datagram's IPv6 Hop Limit value by the SRH
   Segments Left value.  Processing the SRH Segments Left and original
   datagram's IPv6 Hop Limit fields in this way ensures that ICMPv6 Time
   Exceeded errors occur as would be expected on more traditional IPv6
   networks that forward datagrams without tunneling.

   To avoid fragmentation, it is desirable to employ MTU sizes that
   allow for the header expansion (i.e. at least 1280 + 40 (outer IP
   header) + SRH_MAX_SIZE), where SRH_MAX_SIZE is the maximum path
   length for a given RPL network.  To take advantage of this, however,
   the communicating endpoints need to be aware of the MTU along the
   path (i.e. through Path MTU Discovery).  Unfortunately, the larger
   MTU size may not be available on all links (e.g. 1280 octets on
   6LoWPAN links).  However, it is expected that much of the traffic on
   these types of networks consists of much smaller messages than the
   MTU, so performance degradation through fragmentation would be
   limited.

4.2.  Processing Source Routing Headers

   As specified in [RFC2460], a routing header is not examined or
   processed until it reaches the node identified in the Destination
   Address field of the IPv6 header.  In that node, dispatching on the
   Next Header field of the immediately preceding header causes the



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   Routing header module to be invoked.

   The function of SRH is intended to be very similar to the Type 0
   Routing Header defined in [RFC2460].  After the routing header has
   been processed and the IPv6 datagram resubmitted to the IPv6 module
   for processing, the IPv6 Destination Address contains the next hop's
   address.  When forwarding an IPv6 datagram that contains a SRH with a
   non-zero Segments Left value, if the IPv6 Destination Address is not
   on-link, a router MUST drop the datagram and SHOULD send an ICMP
   Destination Unreachable (ICMPv6 Type 1) message with ICMPv6 Code set
   to (TBD by IANA) to the packet's Source Address.  This ICMPv6 Code
   indicates that the IPv6 Destination Address is not on-link and the
   router cannot satisfy the strict source route requirement.  When
   generating ICMPv6 error messages, the rules in Section 2.4 of
   [RFC4443] must be observed.

   To detect loops in the SRH, a router MUST determine if the SRH
   includes multiple addresses assigned to any interface on that router.
   If such addresses appear more than once and are separated by at least
   one address not assigned to that router, the router MUST drop the
   packet and SHOULD send an ICMP Parameter Problem, Code 0, to the
   Source Address.  While this loop check does add significant per-
   packet processing overhead, it is required to mitigate bandwidth
   exhaustion attacks that led to the deprecation of RH0 [RFC5095].

   The following describes the algorithm performed when processing a
   SRH:
























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    if Segments Left = 0 {
       proceed to process the next header in the packet, whose type is
       identified by the Next Header field in the Routing header
    }
    else {
       compute n, the number of addresses in the Routing header, by
       n = (((Hdr Ext Len * 8) - Pad - (16 - CmprE)) / (16 - CmprI)) + 1

       if Segments Left is greater than n {
          send an ICMP Parameter Problem, Code 0, message to the Source
          Address, pointing to the Segments Left field, and discard the
          packet
       }
       else {
          decrement Segments Left by 1

          compute i, the index of the next address to be visited in
          the address vector, by subtracting Segments Left from n

          if Address[i] or the IPv6 Destination Address is multicast {
             discard the packet
          }
          else if 2 or more entries in Address[1..n] are assigned to
                  local interface and are separated by at least one
                  address not assigned to local interface {
             send an ICMP Parameter Problem (Code 0) and discard the
             packet
          }
          else {
             swap the IPv6 Destination Address and Address[i]

             if the IPv6 Hop Limit is less than or equal to 1 {
                send an ICMP Time Exceeded -- Hop Limit Exceeded in
                Transit message to the Source Address and discard the
                packet
             }
             else {
                decrement the Hop Limit by 1

                resubmit the packet to the IPv6 module for transmission
                to the new destination
             }
          }
       }
    }


   RPL routers are responsible for ensuring that a SRH is only used



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   between RPL routers:

   1.  For datagrams destined to a RPL router, the router processes the
       packet in the usual way.  For instance, if the SRH was included
       using tunneled mode and the RPL router serves as the tunnel
       endpoint, the router removes the outer IPv6 header, at the same
       time removing the SRH as well.

   2.  Datagrams destined elsewhere within the same RPL Instance are
       forwarded to the correct interface.

   3.  Datagrams destined to nodes outside the RPL Instance are dropped
       if the outer-most IPv6 header contains a SRH not generated by the
       RPL router forwarding the datagram.





































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5.  Security Considerations

5.1.  Source Routing Attacks

   The RPL message security mechanisms defined in [I-D.ietf-roll-rpl] do
   not apply to the RPL Source Route Header.  This specification does
   not provide any confidentiality, integrity, or authenticity
   mechanisms to protect the SRH.

   [RFC5095] deprecates the Type 0 Routing header due to a number of
   significant attacks that are referenced in that document.  Such
   attacks include bypassing filtering devices, reaching otherwise
   unreachable Internet systems, network topology discovery, bandwidth
   exhaustion, and defeating anycast.

   Because this document specifies that SRH is only for use within a RPL
   Instance, such attacks cannot be mounted from outside a RPL Instance.
   As specified in this document, RPL routers MUST drop datagrams
   entering or exiting a RPL Instance that contain a SRH in the IPv6
   Extension headers.

   Such attacks, however, can be mounted from within a RPL Instance.  To
   mitigate bandwidth exhaustion attacks, this specification requires
   RPL routers to check for loops in the SRH and drop datagrams that
   contain such loops.  Attacks that include bypassing filtering devices
   and reaching otherwise unreachable Internet systems are not as
   relevant in mesh networks since the topologies are, by their very
   nature, highly dynamic.  The RPL routing protocol is designed to
   provide reachability to all devices within a RPL Instance and may
   utilize routes that traverse any number of devices in any order.
   Even so, these attacks and others (e.g. defeating anycast and routing
   topology discovery) can occur within a RPL Instance when using this
   specification.

5.2.  ICMPv6 Attacks

   The generation of ICMPv6 error messages may be used to attempt
   denial-of-service attacks by sending error-causing SRH in back-to-
   back datagrams.  An implementation that correctly follows Section 2.4
   of [RFC4443] would be protected by the ICMPv6 rate limiting
   mechanism.










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6.  IANA Considerations

   This document defines a new IPv6 Routing Type, the "RPL Source Route
   Header", and has been assigned assigned number TBD by IANA.

   This document defines a new ICMPv6 Destination Unreachable Code, the
   "strict source route failed" error, and has been assigned number TBD
   by IANA.











































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7.  Acknowledgements

   The authors thank Jari Arkko, Ralph Droms, Adrian Farrel, Stephen
   Farrell, Richard Kelsey, Suresh Krishnan, Erik Nordmark, Pascal
   Thubert, Sean Turner, and Tim Winter for their comments and
   suggestions that helped shape this document.













































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8.  Changes

   (This section to be removed by the RFC editor.)

   Draft 06:

      - Address IESG comments.

   Draft 05:

      - Address LC comments.

   Draft 04:

      - Updated text on recommendations for avoiding fragmentation.

      - Clarify definition of CmprE where it is first mentioned.

      - Change use of IPv6-in-IPv6 tunneling from SHOULD to MUST.

      - Update packet processing pseudocode to match the text on sending
      back a parameter problem error.

      - Recommend that non-RPL devices drop packets with SRH by default.

      - Clarify packet structure figures.

      - State that checking for cycles represents significant per-packet
      processing.

   Draft 03:

      - Removed any presumed values that are TBD by IANA.

   Draft 02:

      - Updated to send ICMP Destination Unreachable error only after
      the SRH has been processed.

      - Updated pseudocode to reflect encoding changes in draft-01.

      - Allow multiple addresses assigned to same node as long as they
      are not separated by other addresses.

   Draft 01:






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      - Allow Addresses[1..n-1] and Addresses[n] to have a different
      number of bytes elided.

















































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9.  References

9.1.  Normative References

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [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.

   [RFC5095]  Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
              of Type 0 Routing Headers in IPv6", RFC 5095,
              December 2007.

9.2.  Informative References

   [I-D.ietf-roll-rpl]
              Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., and J.
              Vasseur, "RPL: IPv6 Routing Protocol for Low power and
              Lossy Networks", draft-ietf-roll-rpl-19 (work in
              progress), March 2011.






















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Authors' Addresses

   Jonathan W. Hui
   Cisco Systems, Inc
   170 West Tasman Drive
   San Jose, California  95134
   USA

   Phone: +408 424 1547
   Email: jonhui@cisco.com


   JP Vasseur
   Cisco Systems, Inc
   11, Rue Camille Desmoulins
   Issy Les Moulineaux,   92782
   France

   Email: jpv@cisco.com


   David E. Culler
   UC Berkeley
   465 Soda Hall
   Berkeley, California  94720
   USA

   Phone: +510 643 7572
   Email: culler@cs.berkeley.edu


   Vishwas Manral
   Hewlett Packard Co.
   19111 Pruneridge Ave.
   Cupertino, California  95014
   USA

   Email: vishwas.manral@hp.com













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