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Versions: 00 01 02 03 04 05 06 07                                       
Network Working Group                                         P. Thubert
Internet-Draft                                                M. Molteni
Expires: April 1, 2007                                     Cisco Systems
                                                      September 28, 2006


   IPv6 Reverse Routing Header and its application to Mobile Networks
              draft-thubert-nemo-reverse-routing-header-06

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

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   This Internet-Draft will expire on April 1, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   NEMO basic support enables Mobile Networks by extending Mobile IP to
   Mobile Routers.  In the case of nested Mobile Networks, this involves
   the overhead of nested tunnels between the Mobile Routers and their
   Home Agents, and causes a number of security issues.

   This proposal alleviates those problems as well as other minor ones,
   by using a source routing within the mobile nested structure,
   introducing a new routing header, called the reverse routing header.



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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1  Recursive complexity . . . . . . . . . . . . . . . . . . .   3
   2.   Terminology and Assumptions  . . . . . . . . . . . . . . . .   5
     2.1  Terminology  . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2  Assumptions  . . . . . . . . . . . . . . . . . . . . . . .   6
   3.   An Example . . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.   New Routing Headers  . . . . . . . . . . . . . . . . . . . .  11
     4.1  Routing Header Type 2 (MIPv6 RH with extended semantics) .  11
     4.2  Routing Header Type 4 (The Reverse Routing Header) . . . .  13
     4.3  Extension Header order . . . . . . . . . . . . . . . . . .  16
   5.   Optimum number of slots in RRH . . . . . . . . . . . . . . .  18
   6.   Modifications to IPv6 Neighbor Discovery . . . . . . . . . .  20
     6.1  Modified Router Advertisement Message Format . . . . . . .  20
   7.   MIPv6 flows  . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.1  DHAAD  . . . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.2  Binding Updates  . . . . . . . . . . . . . . . . . . . . .  21
   8.   Home Agent Operation . . . . . . . . . . . . . . . . . . . .  22
   9.   Mobile Router Operation  . . . . . . . . . . . . . . . . . .  24
     9.1  Processing of ICMP "RRH too small" . . . . . . . . . . . .  24
     9.2  Processing of ICMP error . . . . . . . . . . . . . . . . .  25
     9.3  Processing of RHH for Outbound Packets . . . . . . . . . .  25
     9.4  Processing of the extended Routing Header Type 2 . . . . .  26
     9.5  Decapsulation  . . . . . . . . . . . . . . . . . . . . . .  28
   10.  Mobile Host Operation  . . . . . . . . . . . . . . . . . . .  28
   11.  Security Considerations  . . . . . . . . . . . . . . . . . .  29
     11.1   IPsec Processing . . . . . . . . . . . . . . . . . . . .  29
       11.1.1   Routing Header type 2  . . . . . . . . . . . . . . .  29
       11.1.2   Routing Header type 4  . . . . . . . . . . . . . . .  29
     11.2   New Threats  . . . . . . . . . . . . . . . . . . . . . .  31
   12.  IANA considerations  . . . . . . . . . . . . . . . . . . . .  32
   13.  Protocol Constants . . . . . . . . . . . . . . . . . . . . .  32
   14.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  32
   15.  References . . . . . . . . . . . . . . . . . . . . . . . . .  33
     15.1   informative reference  . . . . . . . . . . . . . . . . .  33
     15.2   normative reference  . . . . . . . . . . . . . . . . . .  33
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  34
   A.   Optimizations  . . . . . . . . . . . . . . . . . . . . . . .  35
     A.1  Path Optimization with RRH . . . . . . . . . . . . . . . .  35
     A.2  Packet Size Optimization . . . . . . . . . . . . . . . . .  36
       A.2.1  Routing Header Type 3 (Home Address option
              replacement) . . . . . . . . . . . . . . . . . . . . .  37
   B.   Multi Homing . . . . . . . . . . . . . . . . . . . . . . . .  39
     B.1  Multi-Homed Mobile Network . . . . . . . . . . . . . . . .  39
     B.2  Multihomed Mobile Router . . . . . . . . . . . . . . . . .  41
   C.   Changes from Previous Version of the Draft . . . . . . . . .  42
        Intellectual Property and Copyright Statements . . . . . . .  44



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1.  Introduction

   This document assumes that the reader is familiar with the Mobile
   Networks terminology defined in [17] and [4], with Mobile IPv6
   defined in [18], and with the NEMO basic support defined in [19].

   Generally a Mobile Network may be either solid (a network with one
   mobile router) or nested, single or multi-homed.  This proposal
   starts from the assumption that nested Mobile Networks will be the
   norm, and so presents a solution that avoids the tunnel within tunnel
   overhead of already existing proposals.

   The solution is based on a single, telescopic tunnel between the
   first Mobile Router (MR) to forward a packet and its Home Agent (HA).
   By using IPsec ESP on that tunnel, home equivalent privacy is
   obtained without further encapsulation.

   The solution introduces a new Routing Header (RH), called the Reverse
   Routing Header (RRH), to perform source routing within the mobile
   structure.  RRH is a variant of IPv4 Loose Source and Record Route
   (LSRR) [9] adapted for IPv6.  RRH records the route out of the nested
   Mobile Network and can be trivially converted into a routing header
   for packets destined to the Mobile Network.

   This version focuses on single-homed Mobile Networks.  Hints for
   further optimizations and multi-homing are given in the appendixes.

   Local Fixed Node (LFN) and Correspondent Node (CN) operations are
   left unchanged from Mobile IPv6 [18].  Specifically the CN can also
   be a LFN.

   Section 3 proposes an example to illustrate the operation of the
   proposed solution, leaving detailed specifications to the remaining
   chapters.  The reader may refer to Section 2.1 for the specific
   terminology.

1.1  Recursive complexity

   A number of drafts and publications suggest -or can be extended to- a
   model where the Home Agent and any arbitrary Correspondent would
   actually get individual binding from the chain of nested Mobile
   Routers, and form a routing header appropriately.

   An intermediate MR would keep track of all the pending communications
   between hosts in its subtree of Mobile Networks and their CNs, and a
   binding message to each CN each time it changes its point of
   attachment.




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   If this was done, then each CN, by receiving all the binding messages
   and processing them recursively, could infer a partial topology of
   the nested Mobile Network, sufficient to build a multi-hop routing
   header for packets sent to nodes inside the nested Mobile Network.

   However, this extension has a cost:

   1.  Binding Update storm

       when one MR changes its point of attachment, it needs to send a
       BU to all the CNs of each node behind him.  When the Mobile
       Network is nested, the number of nodes and relative CNs can be
       huge, leading to congestions and drops.

   2.  Protocol Hacks

       Also, in order to send the BUs, the MR has to keep track of all
       the traffic it forwards to maintain his list of CNs.  In case of
       IPSec tunneled traffic, that CN information may not be available.

   3.  CN operation

       The computation burden of the CN becomes heavy, because it has to
       analyze each BU in a recursive fashion in order to infer nested
       Mobile Network topology required to build a multi hop routing
       header.

   4.  Missing BU

       If a CN doesn't receive the full set of PSBU sent by the MR, it
       will not be able to infer the full path to a node inside the
       nested Mobile Network.  The RH will be incomplete and the packet
       may or may not be delivered.

   5.  Obsolete BU

       If the Binding messages are sent asynchronously by each MR, then,
       when the relative position of MRs and/or the TLMR point of
       attachment change rapidly, the image of Mobile Network that the
       CN maintains is highly unstable.  If only one BU in the chain is
       obsolete due to the movement of an intermediate MR, the
       connectivity may be lost.

   A conclusion is that the path information must be somehow aggregated
   to provide the CN with consistent snapshots of the full path across
   the Mobile Network.  This can be achieved by an IPv6 form of loose
   source / record route header, that we introduce here as a Reverse
   Routing Header



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2.  Terminology and Assumptions

2.1  Terminology

   This document assumes that the reader is familiar with Mobile IPv6 as
   defined in [18] and with the concept of Mobile Router defined in the
   NEMO terminology document [4].  In particular, the "Nested Mobility
   Terms" introduced in the NEMO terminology are repeatedly used in this
   document.

   Solid Mobile Network:

      One or more IP subnets attached to a MR and mobile as a unit, with
      respect to the rest of the Internet.  A Solid Mobile Network can
      be either singly or multi-homed.  A Solid Mobile Network may be
      composed of more then one link and may interconnect several
      routers, but all routers in the Solid Mobile Network are fixed
      with respect to each other.

      We like to represent a simple single-homed Mobile Network as an
      hanger, because it has only one uplink hook and a bar to which
      multiple hooks can be attached.  Graphically we use the question
      mark "?" to show the uplink hook (interface) connected to the MR,
      and the "=" sign to represent the bar:

                                   ?
                                  MR1
                                   |
                            ===============

   IPv6 Mobile Host:

      A IPv6 Host, with support for MIPv6 MN, and the additional NEMO
      capability described in this draft.

   Home prefix

      Network prefix, which identifies the home link within the Internet
      topology.

   Mobile Network prefix

      Network prefix, common to all IP addresses in the Mobile Network
      when the MR is attached to the home link.  It may or may not be a
      subset of the Home subnet prefix.






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   Inbound direction:

      direction from outside the Mobile Network to inside

   Outbound direction:

      direction from inside the Mobile Network to outside

   RRH:

      Reverse Routing Header, defined in this specification

   NULL RRH:

      A NULL RRH is an RRH with a null "Segments Used" field


2.2  Assumptions

   We make the following assumptions:

   1.  A MR has one Home Agent and one Home Address -> one primary CoA.

   2.  A MR attaches to a single Attachment Router as default router.

   3.  A MR may have more than one uplink interface.

   4.  An interface can be either wired or wireless.  The text assumes
       that interfaces are wireless for generality.

   5.  Each Solid Mobile Network may have more that one L2 Access Point,
       all of them controlled by the same Attachment Router, which we
       assume to be the Mobile Router.

   Since an MR has only one primary CoA, only one uplink interface can
   be used at a given point of time.  Since the MR attaches to a single
   attachment router, if due care is applied to avoid loops, then the
   resulting topology is a tree.













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3.  An Example

   The nested Mobile Network in the following figure has a tree
   topology, according to the assumptions in Section 2.2.  In the tree
   each node is a Solid Mobile Network, represented by its MR.

                          +---------------------+
                          |     Internet        |---CN
                          +---------------|-----+
                           /         Access Router
                      MR3_HA              |
                                 ======?======
                                      MR1
                                       |
                         ====?=============?==============?===
                            MR5           MR2            MR6
                             |             |              |
                       ===========   ===?=========   =============
                                       MR3
                                        |
                                  ==|=========?==   <-- Mobile Network3
                                   LFN1      MR4
                                              |
                                          =========

                       An example nested Mobile Network

   This example focuses on a Mobile Network node at depth 3 (Mobile
   Network3) inside the tree, represented by its mobile router MR3.  The
   path to the Top Level Mobile Router (TLMR) MR1 and then the Internet
   is

                       MR3 -> MR2 -> MR1 -> Internet

   Consider the case where a LFN belonging to Mobile Network3 sends a
   packet to a CN in the Internet, and the CN replies back.  With the
   tunnel within tunnel approach described by [19], we would have three
   bi-directional nested tunnels:


                                 -----------.
                       --------/          /-----------.
              -------/        |          |           /--------
    CN ------( -  - | -  -  - |  -  -  - | -  -  -  |  -  -  (----- LFN
       MR3_HA -------\        |          |           \-------- MR3
                MR2_HA --------\          \----------- MR2
                          MR1_HA ----------- MR1




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   Depending on the relative location of MR1_HA, MR2_HA and MR3_HA, this
   may lead to a very inefficient "pinball" routing in the
   Infrastructure.

   On the other hand, with the RRH approach we would have only one bi-
   directional tunnel:


              --------------------------- MR1 ---- MR2 ---- MR3
    CN ------(  -  -  -  -  -  -  -  -  -  -  -  -  -  -  (------- LFN
       MR3_HA --------------------------- MR1 ---- MR2 ---- MR3



   The first mobile router on the path, MR3, in addition to tunneling
   the packet to its HA, adds a reverse routing header with N = 3 pre-
   allocated slots.  Choosing the right value for N is discussed in
   Section 5.  The bottom slot is equivalent to the MIPv6 Home Address
   option.  MR3 inserts its home address MR3_HoA into slot 0.

   The outer packet has source MR3's Care of Address, MR3_CoA, and
   destination MR3's Home Agent, MR3_HA:


   <-------------- outer IPv6 header -------------------->
   +-------+-------++ -- ++----+-------+-------+---------+ +-------
   |oSRC   |oDST   |:    :|oRRH| slot2 | slot1 | slot0   | |
   |MR3_CoA|MR3_HA |:oEXT:|type|       |       |MR3_HoA  | |iPACKET
   |       |       |:    :| 4  |       |       |         | |
   +-------+-------++ -- ++----+-------+-------+---------+ +-------


   The second router on the path, MR2, notices that the packet already
   contains an RRH, and so it overwrites the source address of the
   packet with its own address, MR2_CoA, putting the old source address,
   MR3_CoA, in the first free slot of the RRH.

   The outer packet now has source MR2_CoA and destination MR3_HA; the
   RRH from top to bottom is MR3_CoA | MR3_HoA:


   <-------------- outer IPv6 header -------------------->
   +-------+-------++ -- ++----+-------+-------+---------+ +-------
   |oSRC   |oDST   |:    :|oRRH| slot2 | slot1 | slot0   | |
   |MR2_CoA|MR3_HA |:oEXT:|type|       |MR3_CoA|MR3_HoA  | |iPACKET
   |       |       |:    :| 4  |       |       |         | |
   +-------+-------++ -- ++----+-------+-------+---------+ +-------




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   In general the process followed by the second router is repeated by
   all the routers on the path, including the TLMR (in this example
   MR1).  When the packet leaves MR1 the source address is MR1_CoA and
   the RRH is MR2_CoA | MR3_CoA | MR3_HoA:


   <-------------- outer IPv6 header -------------------->
   +-------+-------++ -- ++----+-------+-------+---------+ +-------
   |oSRC   |oDST   |:    :|oRRH| slot2 | slot1 | slot0   | |
   |MR1_CoA|MR3_HA |:oEXT:|type|MR2_CoA|MR3_CoA|MR3_HoA  | |iPACKET
   |       |       |:    :| 4  |       |       |         | |
   +-------+-------++ -- ++----+-------+-------+---------+ +-------


   In a colloquial way we may say that while the packet travels from MR3
   to MR3_HA, the Mobile Network tunnel end point "telescopes" from MR3
   to MR2 to MR1.

   When the home agent MR3_HA receives the packet it notices that it
   contains a RRH and it looks at the bottom entry, MR3_HoA.  This entry
   is used as if it were a MIPv6 Home Address destination option, i.e.
   as an index into the Binding Cache.  When decapsulating the inner
   packet the home agent performs the checks described in Section 8, and
   if successful it forwards the inner packet to CN.

   MR3_HA stores two items in the Bind Cache Entry associated with MR3:
   the address entries from RRH, to be used to build the RH, and the
   packet source address MR1_CoA, to be used as the first hop.

   Further packets from the CN to the LFN are plain IPv6 packets.
   Destination is LFN, and so the packet reaches MR3's home network.

   MR3_HA intercepts it, does a Bind Cache prefix lookup and obtains as
   match the MR3 entry, containing the first hop and the information
   required to build the RH.  It then puts the packet in the tunnel
   MR3_HA -- MR3 as follows: source address MR3_HA and destination
   address the first hop, MR1_CoA.  The RH is trivially built out of the
   previous RRH: MR2_CoA | MR3_CoA | MR3_HoA:


   <-------------- outer IPv6 header -------------------->
   +-------+-------++ -- ++----+-------+-------+---------+ +-------
   |oSRC   |oDST   |:    :|oRH |       |       |         | |
   |MR3_HA |MR1_CoA|:oEXT:|type|MR2_CoA|MR3_CoA|MR3_HoA  | |iPACKET
   |       |       |:    :| 2  |       |       |         | |
   +-------+-------++ -- ++----+-------+-------+---------+ +-------





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   The packet is routed with plain IP routing up to the first
   destination MR1_CoA.

   The RH of the outer packet is type 2 as in MIPv6 [18], but has
   additional semantics inherited from type 0: it contains the path
   information to traverse the nested Mobile Network from the TLMR to
   the tunnel endpoint MR3.  Each intermediate destination forwards the
   packet to the following destination in the routing header.  The
   security aspects of this are treated in Section 11.2.

   MR1, which is the initial destination in the IP header, looks at the
   RH and processes it according to Section 9, updating the RH and the
   destination and sending it to MR2_CoA.  MR2 does the same and so on
   until the packet reaches the tunnel endpoint, MR3.

   When the packet reaches MR3, the source address in the IP header is
   MR3_HA, the destination is MR3_CoA and in the RH there is one segment
   left, MR3_HoA.  As a consequence the packet belongs to the MR3_HA --
   MR3 tunnel.  MR3 decapsulates the inner packet, applying the rules
   described in Section 9 and sends it to LFN.  The packet that reaches
   LFN is the plain IPv6 packet that was sent by CN.






























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4.  New Routing Headers

   This draft modifies the MIPv6 Routing Header type 2 and introduces
   two new Routing Headers, type 3 and 4.  Type 3, which is an
   optimization of type 4 will be discussed in Appendix A.2.1.  The
   draft presents their operation in the context of Mobile Routers
   although the formats are not tied to Mobile IP and could be used in
   other situations.

4.1  Routing Header Type 2 (MIPv6 RH with extended semantics)

   Mobile IPv6 uses a Routing header to carry the Home Address for
   packets sent from a Correspondent Node to a Mobile Node.  In [18],
   this Routing header (Type 2) is restricted to carry only one IPv6
   address.  The format proposed here extends the Routing Header type 2
   to be multi-hop.

   The processing of the multi-hop RH type 2 inherits from the RH type 0
   described in IPv6 [13].  Specifically: the restriction on multicast
   addresses is the same; a RH type 2 is not examined or processed until
   it reaches the node identified in the Destination Address field of
   the IPv6 header; in that node, the RH type 0 algorithm applies, with
   added security checks.

   The construction of the multi-hop RH type 2 by the HA is described in
   Section 8; the processing by the MRs is described in Section 9.4; and
   the security aspects are treated in Section 11.2.

   The destination node of a packet containing a RH type 2 can be a MR
   or some other kind of node.  If it is a MR it will perform the
   algorithm described in Section 9.4, otherwise it will operate as
   prescribed by IPv6 [13] when the routing type is unrecognized.



















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   The multi-hop Routing Header type 2, as extended by this draft, 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=2| Segments Left |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            Reserved                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                           Address[1]                          +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                           Address[2]                          +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                               .                               .
    .                               .                               .
    .                               .                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                           Address[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 [16].







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   Hdr Ext Len

      8-bit unsigned integer.  Length of the Routing header in 8-octet
      units, not including the first 8 octets.  For the Type 2 Routing
      header, Hdr Ext Len is equal to two times the number of addresses
      in the header.

   Routing Type

      8-bit unsigned integer.  Set to 2.

   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.

   Reserved

      32-bit reserved field.  Initialized to zero for transmission;
      ignored on reception.

   Address[1..n]

      Vector of 128-bit addresses, numbered 1 to n.


4.2  Routing Header Type 4 (The Reverse Routing Header)

   The Routing Header type 4, or Reverse Routing Header (RRH), is a
   variant of IPv4 loose source and record route (LSRR) [9] adapted for
   IPv6.

   Addresses are added from bottom to top (0 to n-1 in the picture).
   The RRH is designed to help the destination build an RH for the
   return path.

   When a RRH is present in a packet, the rule for upper-layer checksum
   computing is that the source address used in the pseudo-header is
   that of the original source, located in the slot 0 of the RRH, unless
   the RRH slot 0 is empty, in which case the source in the IP header of
   the packet is used.

   As the 'segment left' field of the generic RH is reassigned to the
   number of segments used, an IPv6 node that does not support RRH will
   discard the packet, unless the RRH is empty.

   The RRH contains n pre-allocated address slots, to be filled by each



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   MR in the path.  It is possible to optimize the number of slots using
   the Tree Information Option described in Section 5.

















































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   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 Used |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Sequence Number                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                          Slot[n-1]                            +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                               .                               .
    .                               .                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                     Slot[1] (1st MR CoA)                      +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                   Slot[0] (Home address)                      +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Next Header

      8-bit selector.  Identifies the type of header immediately
      following the Routing header.  Uses the same values as the IPv4
      Protocol field [16].

   Hdr Ext Len

      8-bit unsigned integer.  Length of the Routing header in 8-octet
      units, not including the first 8 octets.  For the Type 4 Routing
      header, Hdr Ext Len is equal to two times the number of addresses



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      in the header.

   Routing Type

      8-bit unsigned integer.  Set to 4.

   Segments Used

      8-bit unsigned integer.  Number of slots used.  Initially set to 1
      by the MR when only the Home Address is there.  Incremented by the
      MRs on the way as they add the packets source addresses to the
      RRH.

   Sequence Number

      32-bit unsigned integer.  The Sequence Number starts at 0, and is
      incremented by the source upon each individual packet.  Using the
      Radia Perlman's lollipop algorithm, values between 0 and 255 are
      'negative', left to indicate a reboot or the loss of HA
      connectivity, and are skipped when wrapping and upon positive
      Binding Ack. The sequence number is used to check the freshness of
      the RRH; anti-replay protection is left to IPsec AH.

   Slot[n-1..0]

      Vector of 128-bit addresses, numbered n-1 to 0.

   When applied to the NEMO problem, the RRH can be used to update the
   HA on the actual location of the MR.  Only MRs forwarding packets on
   an egress interface while not at home update it on the fly.

   A RRH is inserted by the first MR on the Mobile Network outbound
   path, as part of the reverse tunnel encapsulation; it is removed by
   the associated HA when the tunneled packet is decapsulated.

4.3  Extension Header order

   The RH type 2 is to be placed as any RH as described in [13] section
   4.1.  If a RH type 0 is present in the packet, then the RH type 2 is
   placed immediately after the RH type 0, and the RH type 0 MUST be
   consumed before the RH type 2.

   RH type 3 and 4 are mutually exclusive.  They are to be placed right
   after the Hop-by-Hop Options header if any, or else right after the
   IPv6 header.






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   As a result, the order prescribed in section 4.1 of RFC 2460 becomes:

      IPv6 header

      Hop-by-Hop Options header

      Routing header type 3 or 4

      Destination Options header (note 1)

      Routing header type 0

      Routing header type 2

      Fragment header

      Authentication header (note 2)

      Encapsulating Security Payload header (note 2)

      Destination Options header (note 3)

      upper-layer header




























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5.  Optimum number of slots in RRH

   If its current Attachment Router conforms to Tree Discovery as
   specified in [7], a MR knows its current tree depth from the Tree
   Information Option (RA-TIO).  The maximum number of slots needed in
   the RRH is the same value as the MR's own tree depth (that is the
   TreeDepth as received from the AR incremented by one).

   When sending a Binding Update, a MR always reinitializes the number
   of slots in the RRH to the maximum of DEF_RRH_SLOTS and its tree
   depth, if the latter is known from a reliable hint such as RA-TIO.
   The message may have a number of unused (NULL) slots, when it is
   received by the Home Agent.  The HA crops out the extra entries in
   order to send a RH of type 2 back with its response.  The RH type 2
   in the resulting Binding Ack contains the number of required slots
   that the MR now uses until it gets a hint that the topology changes
   or until the next Binding update.

   In the case of a NULL RRH, the HA does not include a RH 2 at all.
   This may happen in the process of a DHAAD message (see Section 7.1)

   The number of slots in the RRH MUST NOT be larger than MAX_RRH_SLOTS.
   If a MR is deeper in a tree then MAX_RRH_SLOTS, the packets will be
   reencapsulated by a MR up high in the tree, or dropped, depending on
   that MR security policy.

   In runtime, it may happen that the RRH has fewer slots than required
   for the number of MRs in the path because either the nested Mobile
   Network topology is changing too quickly, or the MR that inserted the
   RRH had a wrong representation of the topology.

   To solve this problem a new ICMP message is introduced, "RRH
   Warning", type 64.  A MR on the tree egress path that gets a packet
   without a free slot in the RRH MAY send that ICMP "RRH warning" back
   to the MR that inserted the RRH in the first place.

   This message allows a MR on the path to propose a larger number of
   slots to the MR that creates the RRH.  The Proposed Size MUST NOT be
   larger than MAX_RRH_SLOTS.  The originating MR must rate-limit the
   ICMP messages to avoid excessive ICMP traffic in the case of the
   source failing to operate as requested.

   The originating MR must insert an RH type 2 based on the RRH in the
   associated IP header, in order to route the ICMP message back to the
   source of the reverse tunnel.  A MR that receives this ICMP message
   is the actual destination and it MUST NOT forward it to the (LFN)
   source of the tunneled packet.




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   The type 64 ICMP 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Type = 64   |    Code = 0   |           Checksum            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Current Size  | Proposed Size |          Reserved             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    As much of invoking packet                 |
    +               as will fit without the ICMPv6 packet           +
    |               exceeding the minimum IPv6 MTU                  |
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      64 [To Be Assigned]

   Code 0: RRH too small

      The originating MR requires the source to set the RRH size to a
      larger value.  The packet that triggered the ICMP will still be
      forwarded by the MR, but the path cannot be totally optimized (see
      Section 9.3).

   Checksum

      The ICMP checksum [15].

   Current Size

      RRH size of the invoking packet, as a reference.

   Proposed Size

      The new value, expressed as a number of IPv6 addresses that can
      fit in the RRH.

   Reserved

      16-bit reserved field.  Initialized to zero for transmission;
      ignored on reception.







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6.  Modifications to IPv6 Neighbor Discovery

6.1  Modified Router Advertisement Message Format

   Mobile IPv6 [18] modifies the format of the Router Advertisement
   message [14] by the addition of a single flag bit (H) to indicate
   that the router sending the Advertisement message is serving as a
   home agent on this link.

   This draft adds another single flag bit (N) to indicate that the
   router sending the advertisement message is a MR.  This means that
   the link on which the message is sent is a Mobile Network, which may
   or may not be at home.

   The Router Advertisement message 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Type      |     Code      |          Checksum             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Cur Hop Limit |M|O|H|N|Reservd|       Router Lifetime         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Reachable Time                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Retrans Timer                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Options ...
    +-+-+-+-+-+-+-+-+-+-+-+-

   This format represents the following changes over that originally
   specified for Neighbor Discovery [14]:

   Home Agent (H)

      The Home Agent (H) bit is set in a Router Advertisement to
      indicate that the router sending this Router Advertisement is also
      functioning as a Mobile IP home agent on this link.

   NEMO Capable (N)

      The NEMO Capable (N) bit is set in a Router Advertisement to
      indicate that the router sending this Router Advertisement is also
      functioning as a Mobile Router on this link, so that the link is a
      Mobile Network, possibly away from home.






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7.  MIPv6 flows

7.1  DHAAD

   Conforming MIPv6 [18], a MR normally does not identify itself in its
   DHAAD messages, using a Home Address option.  For the same reason, a
   RRH with a Home address in slot 0 is not required here, either.  Yet,
   this specification allows a MR to send its DHAAD messages with a NULL
   RRH, as opposed to no RRH at all.

   This is generally useful if the attachment router is not bound yet,
   for whatever reason, and more specifically in the case of the Mobile
   Home Network as described in [3].  In the latter case, an HA is
   mobile and may happen to be located under one of its MRs (within its
   subtree), which is a dead lock for the NEMO basic support..

   Since MRs may forward packets with an RRH even if themselves are not
   bound yet, the packets from nested MRs can be forwarded and the
   responses are source routed back, allowing the nested MRs to bind.
   In particular, if a nested MR is also a mobile Home Agent, it becomes
   reachable from its own MRs, which breaks the deadlock.

   Also, this alleviates the need for the attachment router to forward
   DHAAD messages across its own MRHA tunnel.

   HAs MUST respond by reversing the RRH into a RH2 if a RRH is present
   and not NULL.  A NULL RRH is ignored.

7.2  Binding Updates

   A MIPv6 or NEMO Binding Update provides more information than just
   the path in the nested cloud so they are still used as described in
   MIPv6 [18] for Home Registration and de-registration.  The only
   difference when using a RRH is that the Home Address Destination
   Option and the alternate CareOf MIP option MUST be omitted.

   The Binding Update flow is also used to update the optimum size of
   the RRH, as described in  Section 5.

   The HA MUST save the RRH in its binding cache, either in the original
   form or in the form of an RH type 2, ready to be added to the tunnel
   header of the MRHA packets.  The RRH format is very close to that of
   the RH type 2, designed to minimize the process of the transmutation.








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8.  Home Agent Operation

   This section inherits from chapter 10 of MIPv6 [18], which is kept
   unmodified except for parts 10.5 and 10.6 which are extended.  This
   draft mostly adds the opportunity for a MN to update the Binding
   Cache of its Home Agent using RRH, though it does not change the fact
   that MNs still need to select a home agent, register and deregister
   to it, using the MIP Bind Update.

   This draft extends [18] section 10.6 as follows:

   o  The entry point of the tunnel is now checked against the TLMR as
      opposed to the primary CoA.

   o  The Binding Cache can be updated based on RRH with proper AH
      authentication.

   As further explained in Section 7.2, this specification modifies MIP
   so that the HA can rely on the RH type 4 (RRH) to update its Bind
   Cache Entry (BCE), when the Mobile Node moves.  The conceptual
   content of the BCE is extended to contain a sequence counter, and the
   sequence of hops within the --potentially nested-- Mobile Network to
   a given Mobile Node.  The sequence counter is initially set to 0.

   When the HA receives a packet destined to itself, it checks for the
   presence of a Routing Header of type 3 or 4.  Both contain as least
   the entry for the home address of the MN in slot 0; this replaces the
   MIP Home Address Option and allows the HA to determine the actual
   source of the packet, to access the corresponding security
   association.

   As explained in Section 11.2, the HA MUST verify the authenticity of
   the packet using IPSEC AH and drop packets that were not issued by
   the proper Mobile Node.  An RRH is considered only if the packet is
   authenticated and if its sequence number is higher than the one saved
   in the BCE.

   Also, an RRH is considered only if an initial Bind Update exchange
   has been successfully completed between the Mobile Node and its Home
   Agent for Home Registration.  If the RRH is valid, then the Bind
   Cache Entry is revalidated for a lifetime as configured from the
   initial Bind Update.









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   The BCE abstract data is updated as follows:

      The first hop for the return path is the last hop on the path of
      the incoming packet, that is between the HA and the Top Level
      Mobile Router (TLMR) of the Mobile Network.  The HA saves the IP
      address of the TLMR from the source field in the IP header.

      The rest of the path to the MN is found in the RRH.

      The sequence counter semantics is changed as described in
      Section 4.2


   This draft extends [18] section 10.5 as follows:

      A Home Agent advertises the prefixes of its registered Mobile
      Routers, during the registration period, on the local Interior
      Gateway Protocol (IGP).

      The Routing Header type 2 is extended to be multi-hop.

   The Home Agent is extended to support routes to prefixes that are
   owned by Mobile Routers.  This can be configured statically, or can
   be exchanged using a routing protocol as in [19], which is out of the
   scope of this document.  As a consequence of this process, the Home
   Agent which is selected by a Mobile Router advertises reachability of
   the MR prefixes for the duration of the registration over the local
   IGP.

   When a HA gets a packet for which the destination is a node behind a
   Mobile Router, it places the packet in the tunnel to the associated
   MR.  This ends up with a packet which destination address in the IP
   Header is the TLMR, and with a Routing Header of type 2 for the rest
   of the way to the Mobile Router, which may be multi-hop.

   To build the RH type 2 from the RRH, the HA sets the type to 2, and
   clears the bits 32-63 (byte 4 to 7).














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9.  Mobile Router Operation

   This section inherits from chapter 11 of [18], which is extended to
   support Mobile Networks and Mobile Routers as a specific case of
   Mobile Node.

   This draft extends section 11.2.1 of MIPv6 [18] as follows:

   o  When not at home, an MR uses a reverse tunnel with its HA for all
      the traffic that is sourced in its mobile network(s); traffic
      originated further down a nested network is not tunneled twice but
      for exception cases.

   o  The full path to and within the Mobile Network is piggy-backed
      with the traffic on a per-packet basis to cope with rapid
      movement.  This makes the packet construction different from
      MIPv6.

   The MR when not at home sets up a bi-directional tunnel with its HA.
   The reverse direction MR -> HA is needed to assure transparent
   topological correctness to LFNs, as in [19].  But, as opposed to the
   NEMO Basic Support, nested tunnels are generally avoided.

9.1  Processing of ICMP "RRH too small"

   The New ICMP message "RRH too Small" is presented in Section 5.  This
   message is addressed to the MR which performs the tunnel
   encapsulation and generates the RRH.

   Hence, a MR that receives the ICMP "RRH too small" MUST NOT propagate
   it to the originating LFN or inner tunnel source, but MUST process it
   for itself.

   If the Current Size in the ICMP messages matches the actual current
   number of slots in RRH, and if the ICMP passes some safety checks as
   described in Section 5, then the MR MAY adapt the number of slots to
   the Proposed Size.














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9.2  Processing of ICMP error


   ICMP back {

      if RRH is present {
         compute RH type 2 based on RRH
         get packet source from IP header
         send ICMP error to source including RH type 2.
      }
      else {
         get packet source from IP header
         send ICMP error to source with no RH.
      }
   }


   When the MR receives an ICMP error message, it checks whether it is
   the final destination of the packet by looking at the included
   packet.  If the included packet has an RRH, then the MR will use the
   RRH to forward the ICMP to the original source of the packet.

9.3  Processing of RHH for Outbound Packets

   The forwarding of a packet with a non saturated RRH consists in fact
   in passing the hot potato to the attachment router, which does not
   require the MRHA tunnel to be up.

   So, it happens as soon as a MR has selected its attachment router and
   before the binding flow has actually taken place.  Also, this process
   is much safer since the packet is not forwarded home.




















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   if no RRH in outer header          /* First Mobile Router specific */
      or RRH present but saturated {  /* Need a nested encapsulation  */

      if RRH is saturated {
         do ICMP back (RRH too small)
      }

      /* put packet in sliding reverse tunnel if bound */
      if reverse tunnel is established {
         insert new IP header plus RRH
         set source address to the MR Home Address
         set destination address to the MR Home Agent Address
         add an RRH with all slots zeroed out
         compute IPsec AH on the resulting packet
       } else return
   }

   /* All MRs including first, even if not bound home */
   if packet size <= MTU {
      select first free slot in RRH bottom up
      set it to source address from IP header
      overwrite source address in IP header with MR CareOf
      transmit packet
   } else {
      do ICMP back (Packet too Big)
   }

   If the packet already contains an RRH in the outer header, and has a
   spare slot, the MR adds the source address from the packet IP header
   to the RRH and overwrites the source address in the IP header with
   its CoA.  As a result, the packets are always topologically correct.

   Else, if the RRH is present but is saturated, and therefore the
   source IP can not be added, the MR sends a ICMP 'RRH too small' to
   the tunnel endpoint which originated the outer packet, using the RRH
   info to route it back.  The ICMP message is a warning, and the packet
   is not discarded.  Rather, the MR does a nested encapsulation of the
   packet in its own reverse tunnel home with an additional RRH.

   Else, if the packet does not have an RRH, the MR puts it in its
   reverse tunnel, sourced at the CoA, with an RRH indicating in slot 0
   the Home Address of the MR, and with proper IPsec AH as described
   further in Section 11.1.

9.4  Processing of the extended Routing Header Type 2

   if Segments Left = 0 {




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      /* new check: packet must be looped back internally */
      if packet doesn't come from a loopback interface {
          discard the packet
          return
      }

      proceed to process the next header in the packet, whose type is
      identified by the Next Header field in the Routing header
   }
   else if Hdr Ext Len is odd {
         send an ICMP Parameter Problem, Code 0, message to the Source
         Address, pointing to the Hdr Ext Len field, and discard the
         packet
   }
   else {
      compute n, the number of addresses in the Routing header, by
      dividing Hdr Ext Len by 2

      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 {
            /* new security check */
            if Address [i] doesn't belong to one of the MNP {
                discard the packet
                return
            }

            /* new check: keep MIPv6 behavior prevent packets from being
             * forwarded outside the node.
             */
            if Segments Left is 0 and Address[i] isn't the node's own
            home address {
                discard the packet
                return
            }
            swap the IPv6 Destination Address and Address[i]



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            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;
            }
         }
      }
   }



9.5  Decapsulation

   A MR when decapsulating a packet from its HA must perform the
   following checks

   1.  Destination address

       The destination address of the inner packet must belong to one of
       the Mobile Network prefixes.


10.  Mobile Host Operation

   When it is at Home, a Mobile Host issues packets with source set to
   its home address and with destination set to its CN, in a plain IPv6
   format.

   When a MH is not at home but is attached to a foreign link in the
   Fixed Infrastructure, it SHOULD use MIPv6 as opposed to this draft to
   manage its mobility.

   When a MH is visiting a foreign Mobile Network, it forwards its
   outbound packets over the reverse tunnel (including RRH) to its HA.
   One can view that operation as a first MR process applied on a plain
   IPv6 packet issued by a LFN.

   As a result, the encapsulating header include:

      with source set to the MH COA and destination set to the MH HA

      with slot 0 set to the MH Home Address




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   The inner packet is the plain IPv6 packet from the MH Home Address to
   the CN.

11.  Security Considerations

   This section is not complete; further work is needed to analyze and
   solve the security problems of record and source route.

   Compared to MIPv6, the main security problem seems to be the fact
   that the RRH can be modified in transit by an attacker on the path.
   It has to be noted that such an attacker (for example any MR in the
   Mobile Network) can perform more effective attacks than modifying the
   RRH.

11.1  IPsec Processing

   The IPsec [10] AH [11] and ESP [12] can be used in tunnel mode to
   provide different security services to the tunnel between a MR and
   its HA.  ESP tunnel mode SHOULD be used to provide confidentiality
   and authentication to the inner packet.  AH tunnel mode MUST be used
   to provide authentication of the outer IP header fields, especially
   the Routing Headers.

11.1.1  Routing Header type 2

   Due to the possible usage of Doors [8] to enable IPv4 traversal, the
   Routing Header type 2 cannot be treated as type 0 for the purpose of
   IPsec processing (i.e. it cannot be included in its intirety in the
   Integrity Check Value (ICV) computation, because NAT/PAT may mangle
   one of the MR care-of-addresses along the HA-MR path.

   The sender (the HA) will put the slot 0 entry (the MR Home Address)
   of the RH as destination of the outer packet, will zero out
   completely the Routing Header and will perform the ICV computation.

   The receiver (the MR) will put the slot 0 entry as destination of the
   outer packet, will zero out the Routing Header and will perform the
   ICV validation.

11.1.2  Routing Header type 4

   The Routing Header type 4 is "partially mutable", and as such can be
   included in the Authentication Data calculation.  Given the way type
   4 is processed, the sender cannot order the field so that it appears
   as it will at the receiver; this means the receiver will have to
   shuffle the fields.

   The sender (the MR) will zero out all the slots and the Segment Used



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   field of the RRH, and will put as source address of the outer packet
   its Home Address, and then will perform the ICV computation.

   The receiver (the HA) will put the entry in slot 0 (the MR Home
   Address) in the source address and will zero out all the slots and
   the Segment Used field of the RRH, and then will perform the ICV
   verification.












































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11.2  New Threats

   The RH type 4 is used to construct a MIPv6 RH type 2 with additional
   semantics, as described in Section 4.1.  Since RH type 2 becomes a
   multi hop option like RH type 0, care must be applied to avoid the
   spoofing attack that can be performed with the IPv4 source route
   option.  This is why IPv6 [13] takes special care in responding to
   packets carrying Routing Headers.

   AH authenticates the MR Home Address identity and the RRH sequence
   number.  The RRH sequence number is to be used to check the freshness
   of the RRH; anti-replay protection can be obtained if the receiver
   enables the anti-replay service of AH [11].

   In particular, if IPSec is being used, the content is protected and
   can not be read or modified, so there is no point in redirecting the
   traffic just to screen it.

   Say a MR in a nested structure modifies the RRH in order to bomb a
   target outside of the tree.  If that MR forwards the packet with
   itself as source address, the MR above it will make sure that the
   response packets come back to the attacker first, since that source
   is prepended to the RRH.  If it forges the source address, then the
   ingress filtering at the MR above it should detect the irregularity
   and drop the packet.  Same if the attacker is actually TLMR.  The
   conclusion is that ingress filtering is recommended at MR and AR.

   Say that an attacker in the infrastructure and on the path of the
   MRHA tunnel modifies the RRH in order to redirect the response
   packets and bomb a target.  Considering the position of the attacker
   - a compromised access or core router - there's a lot more it could
   do to send perturbations to the traffic, like changing source and
   destinations of packets on the fly or eventually pollute the routing
   protocols.

   Say a MR in a nested structure modifies the RH 2 in order to attack a
   target outside of the tree.  The RH type 2 forwarding rules make sure
   that the packet can only go down a tree.  So unless the attacker is
   TLMR, the packet will not be forwarded.  In any case, the attacker
   will be bombed first.

   Say that an attacker on the path of the MRHA tunnel modifies the RRH
   in order to black out the MR.  The result could actually be
   accomplished by changing any bit in the packet since the IPSec
   signature would fail, or scrambling the radio waves in the case of
   wireless.

   Selecting the tree to attach to is a security critical operation



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   outside of the scope of this draft.  Note that the MR should not
   select a path based on trust but rather on measured service.  If a
   better bandwidth is obtained via an untrusted access using IPSec,
   isn't it better than a good willing low bandwidth trusted access?

12.  IANA considerations

   This document requires IANA to define 2 new IPv6 Routing Header
   types.

13.  Protocol Constants

      DEF_RRH_SLOTS:           7

      MAX_RRH_SLOTS:           10


14.  Acknowledgements

   The authors wish to thank David Auerbach, Fred Baker, Dana Blair,
   Steve Deering, Dave Forster, Thomas Fossati, Francois Le Faucheur,
   Kent Leung, Massimo Lucchina, Vincent Ribiere, Dan Shell and Patrick
   Wetterwald -last but not least :)-.




























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15.  References

15.1  informative reference

   [1]  Devarapalli, V., "Local HA to HA protocol",
        draft-devarapalli-mip6-nemo-local-haha-01 (work in progress),
        March 2006.

   [2]  Giaretta, G. and A. Patel, "Problem Statement for bootstrapping
        Mobile IPv6", draft-ietf-mip6-bootstrap-ps-05 (work in
        progress), May 2006.

   [3]  Thubert, P., "NEMO Home Network models",
        draft-ietf-nemo-home-network-models-06 (work in progress),
        February 2006.

   [4]  Ernst, T. and H. Lach, "Network Mobility Support Terminology",
        draft-ietf-nemo-terminology-05 (work in progress), March 2006.

   [5]  Ernst, T., "Network Mobility Support Goals and Requirements",
        draft-ietf-nemo-requirements-05 (work in progress),
        October 2005.

   [6]  Ng, C., "Analysis of Multihoming in Network Mobility Support",
        draft-ietf-nemo-multihoming-issues-06 (work in progress),
        June 2006.

   [7]  Thubert, P., "Nested Nemo Tree Discovery",
        draft-thubert-tree-discovery-03 (work in progress), April 2006.

   [8]  Thubert, P., Molteni, M., and P. Wetterwald, "IPv4 traversal for
        MIPv6 based Mobile Routers",
        draft-thubert-nemo-ipv4-traversal-01 (work in progress),
        May 2003.

15.2  normative reference

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

   [10]  Kent, S. and R. Atkinson, "Security Architecture for the
         Internet Protocol", RFC 2401, November 1998.

   [11]  Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
         November 1998.

   [12]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
         (ESP)", RFC 2406, November 1998.



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

   [14]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
         for IP Version 6 (IPv6)", RFC 2461, December 1998.

   [15]  Conta, A. and S. Deering, "Internet Control Message Protocol
         (ICMPv6) for the Internet Protocol Version 6 (IPv6)
         Specification", RFC 2463, December 1998.

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

   [17]  Manner, J. and M. Kojo, "Mobility Related Terminology",
         RFC 3753, June 2004.

   [18]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
         IPv6", RFC 3775, June 2004.

   [19]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
         "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
         January 2005.


Authors' Addresses

   Pascal Thubert
   Cisco Systems Technology Center
   Village d'Entreprises Green Side
   400, Avenue Roumanille
   Biot - Sophia Antipolis  06410
   FRANCE

   Email: pthubert@cisco.com


   Marco Molteni
   Cisco Systems Technology Center
   Village d'Entreprises Green Side
   400, Avenue Roumanille
   Biot - Sophia Antipolis  06410
   FRANCE

   Email: mmolteni@cisco.com







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Appendix A.  Optimizations

A.1  Path Optimization with RRH

   The body of the draft presents RRH as a header that circulates in the
   reverse tunnel exclusively.  The RRH format by itself has no such
   limitation.  This section illustrates a potential optimization for
   end-to-end traffic between a Mobile Network Node and its
   Correspondent Node.

   The MNN determines that it is part of a Mobile Network by screening
   the Tree Information option in the RA messages from its Attachment
   Router.  In particular, the MNN knows the TreeDepth as advertised by
   the AR.  An initial test phase could be derived from MIPv6 to decide
   whether optimization with a given CN is possible.

   When an MNN performs end-to-end optimization with a CN, the MNN
   inserts an empty RRH inside its packets, as opposed to tunneling them
   home, which is the default behavior of a Mobile Host as described in
   Section 10.

   The number of slots in the RRH is initially the AR treeDepth plus 1,
   but all slots are clear as opposed to the MR process as described in
   Section 9.  The source address in the header is the MNN address, and
   the destination is the CN.

   The AR of the MNN is by definition an MR.  Since an RRH is already
   present in the packet, the MR does not put the packets from the MNN
   on its reverse tunnel, but acts as an intermediate MR; it adds the
   source address of the packet (the MNN's address) in the RRH (in slot
   0) and stamps its careOf instead in the IP header source address
   field.  Recursively, all the MRs on a nested network trace in path in
   the RRH and take over the source IP.

   The support required on the CN side extends MIPv6 in a way similar to
   the extension that this draft proposes for the HA side.  The CN is
   required to parse the RRH when it is valid, refresh its BCE
   accordingly, and include an RH type 2 with the full path to its
   packets to the MNN.

   Note that there is no Bind Update between the MNN and the CN.  The
   RRH must be secured based on tokens exchanged in the test phase.  For
   the sake of security, it may be necessary to add fields to the RRH or
   to add a separate option in the Mobility Header.







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A.2  Packet Size Optimization

   RRH allows to update the Correspondent BCE on a per packet basis,
   which is the highest resolution that we can achieve.  While this may
   cope with highly mobile and nested configurations, it can also be an
   overkill in some situations.

   The RRH comes at a cost: it requires processing in all intermediate
   Mobile Routers and in the Correspondent Node.  Also, a RRH increases
   the packet size by more than the size of an IP address per hop in the
   Mobile Network.

   This is why an additional Routing Header is proposed (type 3).  The
   semantics of type 3 are very close to type 4 but:

   o  Type 3 has only one slot, for the Home Address of the source.

   o  When it can not add the source to the RH type 3 of an outbound
      packet, an intermediate MR:

      *  MR MUST NOT send ICMP (RRH too small)

      *  MUST NOT put the packet in a reverse tunnel

      Rather, it simply overwrites the source and forwards the packet up
      the tree as if the RRH had been properly updated.

   o  Since the path information is not available, the correspondent
      MUST NOT update its BCE based on the RH type 3.  The CN (or HA)
      identifies the source from the entry in slot 0 and may reconstruct
      the initial packet using the CareOf in slot 1 as source for AH
      purposes.



















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   /* MR processing on outbound packet with RH type 3 support */
   {

      if no RH type 3 or 4 in outer header    /* Case of first MR     */
         or RH type 4 present but saturated { /* Causing nested encap */

         if RRH is saturated {
            do ICMP back (RRH too small)
         }

         /* put packet in sliding reverse tunnel */
         insert new IP header plus RRH
         set source address to the MR Home Address
         set destination address to the MR Home Agent Address
         add an RRH with all slots zeroed out
         compute IPsec AH on the resulting packet
      }

      /* All MRs including first */
      if packet size > MTU {
         do ICMP back (Packet too Big)
      } else if RRH {
         select first free slot in RRH bottom up
         set it to source address from IP header
         overwrite source address in IP header with MR CareOf
         transmit packet
      } else if RH type 3 {
         if slot 0 is still free {
            /* this is end-to-end optimization */
            set it to source address from IP header
         }
         overwrite source address in IP header with MR CareOf
         transmit packet
      }
   }


A.2.1  Routing Header Type 3 (Home Address option replacement)

   This is an RH-based alternative to the Home Address destination
   option.  Its usage is described in Appendix A.2.

   The decision to send RH type 3 or type 4 is up to the source of the
   RRH.  Several algorithms may apply, one out of N being the simplest.

   IPsec HA processing is done as described in Section 11.1 for Type 4.





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   The Type 3 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=3| Segments Used |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            Reserved                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                                                               +
    |                                                               |
    +                        Home Address                           +
    |                                                               |
    +                                                               +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Next Header

      8-bit selector.  Identifies the type of header immediately
      following the Routing header.  Uses the same values as the IPv4
      Protocol field [16].

   Hdr Ext Len

      8-bit unsigned integer.  Length of the Routing header in 8-octet
      units, not including the first 8 octets.  For the Type 3 Routing
      header, Hdr Ext Len is always 2.

   Routing Type

      8-bit unsigned integer.  Set to 3.

   Segment Used

      8-bit unsigned integer.  Number of slots used.  Either 0 or 1.
      When the field is zero, then there is no MR on the path and it is
      valid for a CN that does not support RRH to ignore this header.

   Reserved

      32-bit reserved field.  Initialized to zero for transmission;
      ignored on reception.







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   Home Address

      128-bit home address of the source of the packet.


Appendix B.  Multi Homing

B.1  Multi-Homed Mobile Network

   Consider difference between situation A and B in this diagram:



                ===?==          ==?===
                  MR1            MR2
                   |              |
              ==?=====?==   ==?======   situation A
               MR3   MR4     MR5
                |     |       |
               ===   ===     ===



                ===?==          ==?===
                  MR1            MR2
                   |              |
              ==?=====?=======?======   situation B
               MR3   MR4     MR5
                |     |       |
               ===   ===     ===




   Going from A to B, MR5 may now choose between MR1 and MR2 for its
   Attachment (default) Router.  In terms of Tree Information, MR5, as
   well as MR3 and MR4, now sees the MR1's tree and MR2's tree.  Once
   MR5 selects its AR, MR2, say, MR5 belongs to the associated tree and
   whether MR1 can be reached or not makes no difference.

   As long as each MR has a single default router for all its outbound
   traffic, 2 different logical trees can be mapped over the physical
   configurations in both situations, and once the trees are
   established, both cases are equivalent for the processing of RRH.

   Note that MR5 MUST use a CareOf based on a prefix owned by its AR as
   source of the reverse tunnel, even if other prefixes are present on
   the Mobile Network, to ensure that a RH type 2 can be securely routed



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   back.


















































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B.2  Multihomed Mobile Router

   Consider the difference between situation B and C in this diagram:



                ===?==          ==?===
                  MR1            MR2
                   |              |
              ==?=====?=======?======   situation B
               MR3   MR4     MR5
                |     |       |
               ===   ===     ===


                ==? ?==
                  MR1
                   |
              ==?=====?=======?======   situation C
               MR3   MR4     MR5
                |     |       |
               ===   ===     ===



   In situation C, MR2's egress interface and its properties are
   migrated to MR1.  MR1 has now 2 different Home Addresses, 2 Home
   Agents, and 2 active interfaces.

   If MR1 uses both CareOf addresses at a given point of time, and if
   they belong to different prefixes to be used via different attachment
   routers, then MR1 actually belongs to 2 trees.  It must perform some
   routing logic to decide whether to forward packets on either egress
   interface.  Also, it MUST advertise both tree information sets in its
   RA messages.

   The difference between situations C and B is that when an attached
   router (MR5, say) selects a tree and forwards egress packets via MR1,
   it can not be sure that MR1 will actually forward the packets over
   that tree.  If MR5 has selected a given tree for a specific reason,
   then a new source route header is needed to enforce that path on MR1.

   The other way around, MR5 may leave the decision up to MR1.  If MR1
   uses the same attachment router for a given flow or at least a given
   destination, then the destination receives consistent RRHs.
   Otherwise, the BCE cache will flap, but as both paths are valid, the
   traffic still makes it through.




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Appendix C.  Changes from Previous Version of the Draft

   From -04 to -05

      Tree Information option: now a reference to a separate draft.

      Removed RRH heartbeat.

      Added a DHAAD section

      Clarified how RRH solves the mobile home deadlock.

      new section "Optimum number of slots in RRH" from ICMP section

   From -03 to -04

      TI option: renamed the F (fixed) flag bit to G (grounded).

      Binding Update: Made clear that the BU flow conforms MIPv6 and
      NEMO but that RRH replaces both Home address Option and Alternate
      CareOf option.

   From -02 to -03

      Reworded the security part to remove an ambiguity that let the
      reader think that RRH is unsafe.

   From -01 to -02

      Made optional the usage of ICMP warning "RRH too small"
      (Section 5).

      Changed the IPsec processing for Routing Header type 2
      (Section 11.1).

   From -00 to -01

      Added new Tree Information Option fields:

         A 8 bits Bandwidth indication that provides an idea of the
         egress bandwidth.

         A CRC-32 that changes with the egress path out of the tree.

         a 32 bits unsigned integer, built by each MR out of a high
         order configured preference and 24 bits random constant.  This
         can help as a tie break in Attachment Router selection.




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      Reduced the 'negative' part of the lollipop space to 0..255

      Fixed acknowledgements (sorry Patrick :)

      Changed the type of Tree Information Option from 7 to 10.














































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