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Versions: (draft-hui-6man-rpl-routing-header) 00 01 02 03 04 05 06 07 RFC 6554

6MAN                                                              J. Hui
Internet-Draft                                     Arch Rock Corporation
Intended status: Standards Track                             JP. Vasseur
Expires: January 27, 2011                             Cisco Systems, Inc
                                                               D. Culler
                                                             UC Berkeley
                                                           July 26, 2010


           An IPv6 Routing Header for Source Routes with RPL
                 draft-ietf-6man-rpl-routing-header-00

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
   domain.

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 January 27, 2011.

Copyright Notice

   Copyright (c) 2010 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  . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Generating Type 4 Routing Headers  . . . . . . . . . . . .  9
     4.2.  Processing Type 4 Routing Headers  . . . . . . . . . . . .  9
   5.  RPL Border Router Behavior . . . . . . . . . . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
     6.1.  Source Routing Attacks . . . . . . . . . . . . . . . . . . 12
     6.2.  ICMPv6 Attacks . . . . . . . . . . . . . . . . . . . . . . 12
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   8.  Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 14
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17




















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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, necessary
   mechanisms are used to collect routing information at more capable
   routers and form paths from those routers to arbitrary destinations
   within the RPL domain.  However, a source routing mechanism supported
   by IPv6 is needed to deliver datagrams.

   This document specifies the Type 4 Routing header (RH4) (to be
   confirmed by IANA) for use strictly within a RPL domain.

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 basic format of RH4 draws from that of the Type 0 Routing header
   (RH0) [RFC2460].  However, RH4 introduces mechanisms to compact the
   source route entries when all entries share the same prefix with the
   IPv6 Destination Address of the encapsulating header, a typical
   scenario in LLNs using source routing.  The compaction mechanism
   reduces consumption of scarce resources such as bandwidth.

   RH4 also differs from RH0 in the processing rules to alleviate
   security concerns that lead to the deprecation of RH0 [RFC5095].
   First, routers processing RH4 MUST implement a strict source route
   policy where each and every IPv6 hop is specified within the datagram
   itself.  Second, a RH4 header MUST only be used within a RPL domain.
   RPL Border Routers, responsible for connecting RPL domains and IP
   domains that use other routing protocols, MUST NOT allow datagrams
   already carrying a RH4 header to enter or exit the RPL domain.
   Third, to avoid some attacks that lead to the deprecation of RH0,
   routers along the way MUST verify that loops do not exist with in the
   source route.

   To deliver a datagram, a router MAY specify a source route to reach
   the destination using a RH4.  There are two cases that determine how
   to include an RH4 with a datagram.

   1.  If the RH4 specifies the complete path from source to
       destination, the RH4 should be included directly within the
       datagram itself.

   2.  If the RH4 only specifies a subset of the path from source to
       destination, IPv6-in-IPv6 tunneling MUST be used as specified in
       [RFC2473].  The router MUST prepend a new IPv6 header and RH4 to
       the original datagram.  Use of tunneling ensures that the
       datagram is delivered unmodified and that ICMP errors return to
       the source of the RH4 rather than the source of the original
       datagram.

   In a RPL network, Case 1 occurs when both source and destinations are
   within a RPL domain and a single RH4 header is used to specify the
   entire path from source to destination, as shown in the following
   figure:


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



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                                  RPL Domain


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


                     +------+------+------+--------//-+
                     | IPv6 | IPv6 | IPv6 | Packet    |
                     | Src  | Dst  | RH4  | Payload   |
                     +------+------+------+--------//-+


   S's address is carried in the IPv6 Source Address field.  D's address
   is carried in the last entry of RH4 for all but the last hop, when
   D's address is carried in the IPv6 Destination Address field.

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


                     +-----------------+
                     |                 |
                     |  (S) -------> (BR1) -------> (D)
                     |                 |
                     +-----------------+
                          RPL Domain

                     +-----------------+
                     |                 |
                     |  (D) <------- (BR1) <------- (S)
                     |                 |
                     +-----------------+
                          RPL Domain


   In the above scenario, datagrams traveling within the RPL domain have
   the following packet structure:


              +------+------+------+------+------+--------//-+
              | IPv6 | IPv6 | IPv6 | IPv6 | IPv6 | Packet    |
              | Src  | Dst  | RH4  | Src  | Dst  | Payload   |
              +------+------+------+------+------+--------//-+
                                    <--- Original Packet --->
               <---           Tunneled Packet            --->




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   Note that the outer header (including the RH4) is added and removed
   by the RPL Border 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.  The Border Router in this case would encapsulate the
   received datagram unmodified using IPv6-in-IPv6 and include a RH4 in
   the outer IPv6 header.


                           +-----------------+
                           |                 |
                           |  (S) -------\   |
                           |              \  |
                           |               (BR1)
                           |              /  |
                           |  (D) <------/   |
                           |                 |
                           +-----------------+
                                RPL Domain


   In the above scenario, datagrams travel from S to D through BR1.
   Between S and BR1, the datagrams are routed using the DAG built by
   RPL and do not contain a RH4.  BR1 encapsulates received datagrams
   unmodified using IPv6-in-IPv6 and the RH4 is included in the outer
   IPv6 header.

   To help avoid IP-layer fragmentation, the RH4 header has a maximum
   size of RH4_MAX_SIZE octets and links within a RPL domain SHOULD have
   a MTU of at least 1280 + 40 (outer IP header) + RH4_MAX_SIZE (+
   additional extension headers or options needed within RPL domain)
   octets.
















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3.  Format of the RPL Routing Header

   The Type 4 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=4| Segments Left |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Compr |  Pad  |                   Reserved                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                        Addresses[1..n]                        .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Next Header         8-bit selector.  Identifies the type of header
                       immediately following the Routing header.  Uses
                       the same values as the IPv4 Protocol field
                       [RFC3232].

   Hdr Ext Len         8-bit unsigned integer.  Length of the Routing
                       header in 8-octet units, not including the first
                       8 octets.  Hdr Ext Len MUST NOT exceed
                       RH4_MAX_SIZE / 8.  Note that when Addresses[1..n]
                       are compressed (i.e. value of Compr is not 0),
                       Hdr Ext Len does not equal twice the number of
                       Addresses.

   Routing Type        8-bit selector.  Set to 4 (to be confirmed 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.  Value MUST be
                       between 0 and Segments, inclusive.

   Compr               4-bit unsigned integer.  Number of prefix octets
                       from each segment that is elided.  For example, a
                       Type 4 Routing header carrying full IPv6
                       addresses sets Compr to 0.





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   Pad                 4-bit unsigned integer.  Number of octets that
                       are used to for padding after Address[n] and the
                       end of the Type 4 Routing header.

   Address[1..n]       Vector of addresses, numbered 1 to n.  Each
                       vector element has size (16 - Compr).

   The Type 4 Routing header shares the same basic format as the Type 0
   Routing header [RFC2460].  When carrying full IPv6 addresses, the
   Compr and Pad fields are set to 0 and the only difference between the
   Type 4 and Type 0 encodings is the value of the Routing Type field.

   A common network configuration for a RPL domain is that all nodes
   within a LLN share a common prefix.  Type 4 Routing header introduces
   the Compr 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 encapsulating datagram.  The Compr field
   indicates the number of prefix octets that are shared with the IPv6
   Destination Address of the encapsulating header.  The shared prefix
   octets are not carried within the Routing header and each entry in
   Address[1..n] has size (16 - Compr) octets.  When Compr is non-zero,
   there may exists 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
   Compr is 0, Pad MUST be null and carry a value of 0.

   The Type 4 Routing header MUST NOT specify a path that visits a node
   more than once.  When generating a Type 4 Routing header, 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 the Type 4 Routing header.

   Multicast addresses MUST NOT appear in a Type 4 Routing header, or in
   the IPv6 Destination Address field of a datagram carrying a Type 4
   Routing header.















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4.  RPL Router Behavior

4.1.  Generating Type 4 Routing Headers

   To deliver an IPv6 datagram to its destination, a router may need to
   generate a new Type 4 Routing header and specify a strict source
   route.  Routers MUST use IPv6-in-IPv6 tunneling, as specified in
   [RFC2473] to include a new Type 4 Routing header in datagrams that
   are sourced by other nodes.  This ensures that the delivered datagram
   remains unmodified and that ICMPv6 errors generated by a Type 4
   Routing header are sent back to the router that generated the routing
   header.

   Performing IP-in-IP encapsulation may grow the datagram to a size
   larger than the IPv6 min MTU of 1280 octets.  To help avoid IP-layer
   fragmentation caused by IP-in-IP encapsulation, links within a RPL
   domain SHOULD be configured with a MTU of at least 1280 + 40 (outer
   IP header) + RH4_MAX_SIZE (+ additional extension headers or options
   needed within RPL domain) octets.

4.2.  Processing Type 4 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
   Routing header module to be invoked.

   The function of Type 4 Routing header is intended to be very similar
   to IPv4's Strict Source and Record Route option [RFC0791].  When
   processing the Type 4 Routing header, a router MUST drop the packet
   if the next entry is not on-link and SHOULD send an ICMP Destination
   Unreachable (ICMPv6 Type 1) message with ICMPv6 Code set to 7 (to be
   confirmed by IANA) to the packet's Source Address.  An ICMPv6 Code of
   7 indicates that the next Address entry is not on-link and the router
   cannot satisfy the strict source route.  When generating ICMPv6 error
   messages, the rules in Section 2.4 of [RFC4443] must be observed.

   To detect loops in the Type 4 Routing headers, a router MUST
   determine if the Type 4 Routing header includes more than one address
   assigned any interface on that router.  If such addresses appear more
   than once, the router MUST drop the packet and SHOULD send an ICMP
   Parameter Problem, Code 0, to the Source Address.

   The following describes the algorithm performed when processing a
   Type 4 Routing header:





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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 - Comp)

       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 entries in Address[1..n] are assigned to local
                  interface and are separated by an address not assigned
                  to local interface {
             discard the packet
          }
          else if i < n and Address[i] is not on-link {
             send an ICMP Destination Unreachable, Code 7, message to
             the Source Address 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
             }
          }
       }
    }




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5.  RPL Border Router Behavior

   RPL Border Routers (referred to as LBRs in
   [I-D.ietf-roll-terminology]) are responsible for ensuring that a Type
   4 Routing header is only used within the RPL domain it was created.

   For datagrams entering the RPL domain, RPL Border Routers MUST drop
   received datagrams that contain a Type 4 Routing header in the IPv6
   Extension headers.

   For datagrams exiting the RPL domain, RPL Border Routers MUST check
   for a Type 4 Routing header.  If Segments Left is 0, the router MUST
   remove the RH4 header from the datagram and update the IPv6 Payload
   Length field accordingly.  If Segments Left is non-zero, the router
   MUST drop the datagram.




































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6.  Security Considerations

6.1.  Source Routing Attacks

   [RFC5095] deprecates the Type 0 Routing header due to a number of
   significant attacks that are referenced in that document.  Such
   attacks include network discovery, bypassing filtering devices,
   denial-of-service, and defeating anycast.

   Because this document specifies that Type 4 Routing headers are only
   for use within a RPL domain, such attacks cannot be mounted from
   outside the RPL domain.  As described in Section 5, RPL Border
   Routers MUST drop datagrams entering or exiting the RPL domain that
   contain a Type 4 Routing header in the IPv6 Extension headers.

6.2.  ICMPv6 Attacks

   The generation of ICMPv6 error messages may be used to attempt
   denial-of-service attacks by sending error-causing Type 4 Routing
   headers 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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7.  IANA Considerations

   This document defines a new IPv6 Routing Type of 4 (to be confirmed).

   This document defines a new ICMPv6 Destination Unreachable Code of 7
   to indicate that the router does not have the next Address element as
   a neighbor and could not satisfy the strict source route.












































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8.  Protocol Constants

   RH4_MAX_SIZE        136

   With a base header size of 8 octets, 136 octets will allow for up to
   8 16-octet address entries in the Type 4 Routing header.  More
   entries are possible within 136 octets when compression is used.












































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9.  Acknowledgements

   The authors thank Vishwas Manral and Erik Nordmark for their comments
   and suggestions that helped shape this document.















































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10.  References

10.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

   [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.

10.2.  Informative References

   [I-D.ietf-roll-rpl]
              Winter, T., Thubert, P., and R. Team, "RPL: IPv6 Routing
              Protocol for Low power and Lossy Networks",
              draft-ietf-roll-rpl-10 (work in progress), June 2010.

   [I-D.ietf-roll-terminology]
              Vasseur, J., "Terminology in Low power And Lossy
              Networks", draft-ietf-roll-terminology-03 (work in
              progress), March 2010.

   [RFC3232]  Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by
              an On-line Database", RFC 3232, January 2002.













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Authors' Addresses

   Jonathan W. Hui
   Arch Rock Corporation
   501 2nd St. Ste. 410
   San Francisco, California  94107
   USA

   Phone: +415 692 0828
   Email: jhui@archrock.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






















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