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Versions: (draft-clausen-nemo-ro-problem-statement) 00 01 02 03 RFC 4888

NEMO Working Group                                                 C. Ng
Internet-Draft                                  Panasonic Singapore Labs
Expires: July 1, 2006                                         P. Thubert
                                                           Cisco Systems
                                                               M. Watari
                                                           KDDI R&D Labs
                                                                 F. Zhao
                                                                UC Davis
                                                       December 28, 2005


         Network Mobility Route Optimization Problem Statement
                draft-ietf-nemo-ro-problem-statement-02

Status of this Memo

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   This Internet-Draft will expire on July 1, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   With current Network Mobility (NEMO) Basic Support, all
   communications to and from Mobile Network Nodes must go through the
   bi-directional tunnel established between the Mobile Router and Home



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   Agent when the mobile network is away.  This sub-optimal routing
   results in various inefficiencies associated with packet delivery,
   such as increased delay and bottleneck links leading to traffic
   congestion, which can ultimately disrupt all communications to and
   from the Mobile Network Nodes.  Additionally, with nesting of Mobile
   Networks, these inefficiencies get compounded, and stalemate
   conditions may occur in specific dispositions.  This document
   investigates such problems, and provides for the motivation behind
   Route Optimization (RO) for NEMO.










































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  NEMO Route Optimization Problem Statement  . . . . . . . . . .  5
     2.1.  Sub-Optimality with NEMO Basic Support . . . . . . . . . .  5
     2.2.  Bottleneck in Home Network . . . . . . . . . . . . . . . .  7
     2.3.  Amplified Sub-Optimality in Nested Mobile Networks . . . .  7
     2.4.  Sub-Optimality with Combined Mobile IPv6 Route
           Optimization . . . . . . . . . . . . . . . . . . . . . . .  9
     2.5.  Security Policy Prohibiting Traffic From Visiting Nodes  . 10
     2.6.  Instability of Communications within a Nested Mobile
           Network  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     2.7.  Stalemate with a Home Agent Nested in a Mobile Network . . 11
   3.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Normative Reference  . . . . . . . . . . . . . . . . . . . 14
     7.2.  Informative Reference  . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 15
   Appendix B.  Various configurations involving Nested Mobile
                Networks  . . . . . . . . . . . . . . . . . . . . . . 16
     B.1.  CN located in the fixed infrastructure . . . . . . . . . . 16
       B.1.1.  Case A: LFN and standard IPv6 CN . . . . . . . . . . . 17
       B.1.2.  Case B: VMN and MIPv6 CN . . . . . . . . . . . . . . . 17
       B.1.3.  Case C: VMN and standard IPv6 CN . . . . . . . . . . . 17
     B.2.  CN located in distinct nested NEMOs  . . . . . . . . . . . 18
       B.2.1.  Case D: LFN and standard IPv6 CN . . . . . . . . . . . 19
       B.2.2.  Case E: VMN and MIPv6 CN . . . . . . . . . . . . . . . 19
       B.2.3.  Case F: VMN and standard IPv6 CN . . . . . . . . . . . 19
     B.3.  CN and MNN located in the same nested NEMO . . . . . . . . 20
       B.3.1.  Case G: LFN and standard IPv6 CN . . . . . . . . . . . 21
       B.3.2.  Case H: VMN and MIPv6 CN . . . . . . . . . . . . . . . 21
       B.3.3.  Case I: VMN and standard IPv6 CN . . . . . . . . . . . 22
     B.4.  CN located behind the same nested MR . . . . . . . . . . . 22
       B.4.1.  Case J: LFN and standard IPv6 CN . . . . . . . . . . . 23
       B.4.2.  Case K: VMN and MIPv6 CN . . . . . . . . . . . . . . . 23
       B.4.3.  Case L: VMN and standard IPv6 CN . . . . . . . . . . . 24
   Appendix C.  Example of How a Stalemate Situation can Occur  . . . 25
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
   Intellectual Property and Copyright Statements . . . . . . . . . . 29









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1.  Introduction

   With current Network Mobility (NEMO) Basic Support [1], all
   communications to and from nodes in a mobile network must go through
   the bi-directional tunnel established between the Mobile Router and
   its Home Agent (also known as the MRHA tunnel) when the mobile
   network is away.  Although such an arrangement allows Mobile Network
   Nodes to reach and be reached by any node on the Internet,
   limitations associated to the base protocol degrade overall
   performance of the network, and, ultimately, can prevent all
   communications to and from the Mobile Network Nodes.

   Some of these concerns already exist with Mobile IPv6 [4] and were
   addressed by the mechanism known as Route Optimization, which is part
   of the base protocol.  With Mobile IPv6, Route Optimization mostly
   improves the end to end path between Mobile Node and Correspondent
   Node, with an additional benefit of reducing the load of the Home
   Network, thus its name.

   NEMO Basic Support presents a number of additional issues, making the
   problem more complex, so it was decided to address Route Optimization
   separately.  In that case, the expected benefits are more dramatic,
   and a Route Optimization mechanism could enable connectivity that
   would be broken otherwise.  In that sense, Route Optimization is even
   more important to NEMO Basic Support than it is to Mobile IPv6.

   This document explores limitations inherent in NEMO Basic Support,
   and their effects on communications between a Mobile Network Node and
   its corresponding peer.  This is detailed in Section 2.  It is
   expected for readers to be familiar with general terminologies
   related to mobility in [4][2], NEMO related terms defined in [3], and
   NEMO goals and requirements [5].



















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2.  NEMO Route Optimization Problem Statement

   Given the NEMO Basic Support protocol, all data packets to and from
   Mobile Network Nodes must go through the Home Agent, even though a
   shorter path may exist between the Mobile Network Node and its
   Correspondent Node.  In addition, with the nesting of Mobile Routers,
   these data packets must go through multiple Home Agents and several
   levels of encapsulation, which may be avoided.  This results in
   various inefficiencies and problems with packet delivery which can
   ultimately disrupt all communications to and from the Mobile Network
   Nodes.

   In the following sub-sections, we will describe the effects of a
   pinball route with NEMO Basic Support, how it may cause a bottleneck
   to be formed in the home network, and how these get amplified with
   nesting of mobile networks.  Closely related to nesting, we will also
   look into the sub-optimality even when Mobile IPv6 Route Optimization
   is used over NEMO Basic Support.  This is followed by a description
   of security policy in home network that may forbid transit traffic
   from Visiting Mobile Nodes in mobile networks.  In addition, we will
   explore the impact of MRHA tunnel on communications between two
   Mobile Network Nodes on different links of the same mobile network.
   We will also provide additional motivations for Route Optimization by
   considering the potential stalemate situation when a Home Agent is
   part of a mobile network.


2.1.  Sub-Optimality with NEMO Basic Support

   With NEMO Basic Support, all packets sent between a Mobile Network
   Node and its Correspondent Node are forwarded through the MRHA
   tunnel, resulting in a pinball route between the two nodes.  This has
   the following sub-optimal effects:

   o  Longer route leading to increased delay and additional
      infrastructure load

      Because a packet must transit from a mobile network to the Home
      Agent then to the Correspondent Node, the transit time of the
      packet is usually longer than if the packet were to go straight
      from the mobile network to the Correspondent Node.  When the
      Correspondent Node (or the mobile network) resides near the Home
      Agent, the increase in packet delay can be very small.  However
      when the mobile network and the Correspondent Node are relatively
      near to one another but far away from the Home Agent on the
      Internet, the increase in delay is very large.  Applications such
      as real-time multimedia streaming may not be able to tolerate such
      increase in packet delay.  In general, the increase in delay may



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      also impact the performance of transport protocols such as TCP,
      since the sending rate of TCP is partly determined by the round-
      trip-time (RTT) perceived by the communication peers.

      Moreover, by using a longer route, the total resource utilization
      for the traffic would be much higher than if the packets were to
      follow a direct path between the Mobile Network Node and
      Correspondent Node.  This would result in additional load in the
      infrastructure.

   o  Increased packet overhead

      The encapsulation of packets in the MRHA tunnel results in
      increased packet size due to addition of an outer header.  This
      reduces the bandwidth efficiency, as IPv6 header can be quite
      substantial relative to the payload for applications such as voice
      samples.  For instance, given a voice application using a 8kbps
      algorithm (e.g.  G.729) and taking a voice sample every 20ms (as
      in RFC 1889), the packet transmission rate will be 50 packets per
      second.  Each additional IPv6 header is an extra 320 bits per
      packet (i.e. 16kbps), which is twice the actual payload!

   o  Increased processing delay

      The encapsulation of packets in the MRHA tunnel also results in
      increased processing delay at the points of encapsulation and
      decapsulation.  Such increased processing may include encryption/
      decryption, topological correctness verifications, MTU
      computation, fragmentation and reassembly.

   o  Increased chances of packet fragmentation

      The augmentation in packet size due to packet encapsulation may
      increase the chances of the packet being fragmented along the MRHA
      tunnel.  This can occur if there is no prior path MTU discovery
      conducted, or if the MTU discovery mechanism did not take into
      account the encapsulation of packets.  Packets fragmentation will
      result in a further increase in packet delays, and further
      reduction of bandwidth efficiency.

   o  Increased susceptibility to link failure

      Under the assumption that each link has the same probability of
      link failure, a longer routing path would be more susceptibility
      to link failure.  Thus, packets routed through the MRHA tunnel may
      be subjected to a higher probability of being lost or delayed due
      to link failure, compared to packets that traverse directly
      between the Mobile Network Node and its Correspondent Node.



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2.2.  Bottleneck in Home Network

   Apart from the increase in packet delay and infrastructure load,
   forwarding packets through the Home Agent may also lead to either the
   Home Agent or the Home Link becoming a bottleneck for the aggregated
   traffic from/to all the Mobile Network Nodes.  A congestion at home
   would lead to additional packet delay, or even packet loss.  In
   addition, Home Agent operations such as security check, packet
   interception and tunneling might not be as optimized in the Home
   Agent software as plain packet forwarding.  This could further limit
   the Home Agent capacity for data traffic.  Furthermore, with all
   traffic having to pass through the Home Link, the Home Link becomes a
   single point of failure for the mobile network.

   Data packets that are delayed or discarded due to congestion at the
   home network would cause additional performance degradation to
   applications.  Signaling packets, such as Binding Update messages,
   that are delayed or discarded due to congestion at the home network,
   may affect the establishment or update of bi-directional tunnels,
   causing disruption of all traffic flow through these tunnels.

   A NEMO Route Optimization mechanism that allows the Mobile Network
   Nodes to communicate with their Correspondent Nodes via a path that
   is different from the MRHA tunneling and thereby avoiding the Home
   Agent, may alleviate or even prevent the congestion at the Home Agent
   or Home Link.


2.3.  Amplified Sub-Optimality in Nested Mobile Networks

   By allowing other mobile nodes to join a mobile network, and in
   particular mobile routers, it is possible to form arbitrary levels of
   nesting of mobile networks.  With such nesting, the use of NEMO Basic
   Support further amplifies the sub-optimality of routing.  We call
   this the amplification effect of nesting, where the undesirable
   effects of a pinball route with NEMO Basic Support are amplified with
   each level of nesting of mobile networks.  This is best illustrated
   by an example shown in Figure 1.













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               +--------+  +--------+  +--------+  +--------+
               | MR2_HA |  | MR3_HA |  | MR4_HA |  | MR5_HA |
               +------+-+  +---+----+  +---+----+  +-+------+
                       \       |           |        /
        +--------+    +------------------------------+
        | MR1_HA |----|         Internet             |-----CN1
        +--------+    +------------------------------+
                                    |
                                +---+---+
                      root-MR   |  MR1  |
                                +-------+
                                 |     |
                          +-------+   +-------+
                 sub-MR   |  MR2  |   |  MR4  |
                          +---+---+   +---+---+
                              |           |
                          +---+---+   +---+---+
                 sub-MR   |  MR3  |   |  MR5  |
                          +---+---+   +---+---+
                              |           |
                          ----+----   ----+----
                             MNN         CN2

   Figure 1: An example of nested Mobile Network


   Using NEMO Basic Support, the flow of packets between a Mobile
   Network Node, MNN, and a Correspondent Node, CN1, would need to go
   through three separate tunnels, illustrated in Figure 2 below.


                                ----------.
                      ---------/         /----------.
              -------/        |         |          /-------
    MNN -----( -  - | -  -  - | -  -  - | -  -  - |  -  - (------ CN1
           MR3-------\        |         |          \-------MR3_HA
                    MR2--------\         \----------MR2_HA
                              MR1---------MR1_HA

   Figure 2: Nesting of Bi-Directional Tunnels











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   This leads to the following problems:

   o  Pinball Route

      Both inbound and outbound packets will flow via the Home Agents of
      all the Mobile Routers on their paths within the mobile network,
      with increased latency, less resilience and more bandwidth usage.
      Appendix B illustrates in detail the packets routes under
      different nesting configurations of the Mobile Network Nodes.

   o  Increased Packet Size

      An extra IPv6 header is added per level of nesting to all the
      packets.  The header compression suggested in [6] cannot be
      applied because both the source and destination (the intermediate
      Mobile Router and its Home Agent), are different hop to hop.

   Nesting also amplifies the probability of congestion at the home
   networks of the upstream Mobile Routers.  In addition, the Home Link
   of each upstream Mobile Router will also be a single point of failure
   for the nested Mobile Router.


2.4.  Sub-Optimality with Combined Mobile IPv6 Route Optimization

   When a Mobile IPv6 host joins a mobile network, it becomes a Visiting
   Mobile Node of the mobile network.  Packets sent to and from the
   Visiting Mobile Node will have to be routed not only via the Home
   Agent of the Visiting Mobile Node, but also via the Home Agent of the
   Mobile Router in the mobile network.  This suffers the same
   amplification effect of nested mobile network mentioned in
   Section 2.3.

   In addition, although Mobile IPv6 [4] allows a mobile host to perform
   Route Optimization with its Correspondent Node in order to avoid
   tunneling with its Home Agent, the "optimized" route is no longer
   optimized when the mobile host is attached to a mobile network.  This
   is because the route between the mobile host and its Correspondent
   Node is subjected to the sub-optimality introduced by the MRHA
   tunnel.  Interested readers may refer to Appendix B for examples of
   how the routes will appear with nesting of Mobile IPv6 hosts in
   mobile networks.

   The readers should also note that the same sub-optimality would apply
   when the mobile host is outside the mobile network and its
   Correspondent Node is in the mobile network.





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2.5.  Security Policy Prohibiting Traffic From Visiting Nodes

   NEMO Basic Support requires all traffic from visitors to be tunneled
   to the Mobile Router's Home Agent.  This might represent a breach in
   the security of the home network (some specific attacks against the
   Mobile Router's binding by rogue visitors have been documented in
   [7][8]).  Administrators might thus fear that malicious packets will
   be routed into the Home Network via the bi-directional tunnel.  As a
   consequence, it can be expected that in many deployment scenarios,
   policies will be put in place to prevent unauthorized Visiting Mobile
   Nodes from attaching to the Mobile Router.

   However, there are deployment scenarios where allowing unauthorized
   Visiting Mobile Nodes is actually desirable.  For instance, when
   Mobile Routers attach to other Mobile Routers and form a nested NEMO,
   they depend on each other to reach the Internet.  When Mobile Routers
   have no prior knowledge of one another (no security association, AAA,
   PKI etc...), it could still be acceptable to forward packets,
   provided that the packets are not tunneled back to the Home Networks.

   A Route Optimization mechanism that allows traffic from Mobile
   Network Nodes to by-pass the bi-directional tunnel between a Mobile
   Router and its Home Agent would be a necessary first step towards a
   Tit for Tat model, where MRs would benefit from a reciprocal
   altruism, based on anonymity and innocuousness, to extend the
   Internet infrastructure dynamically.


2.6.  Instability of Communications within a Nested Mobile Network

   Within a nested mobile network, two Mobile Network Nodes may
   communicate with each other.  Let us consider the previous example
   illustrated in Figure 1 where MNN and CN2 are sharing a communication
   session.  With NEMO Basic Support, a packet sent from MNN to CN2 will
   need to be forwarded to the Home Agent of each Mobile Router before
   reaching CN2.  Whereas, a packet following the direct path between
   them need not even leave the mobile network.  Readers are referred to
   Appendix B.3 for detailed illustration of the resulting routing
   paths.

   Apart from the consequences of increased packet delay and packet size
   which are discussed in previous sub-sections, there are two
   additional effects that are undesirable:

   o  when the nested mobile network is disconnected from the Internet
      (e.g.  MR1 loses its egress connectivity), MNN and CN2 can no
      longer communicate with each other, even though the direct path
      from MNN to CN2 is unaffected;



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   o  the egress link(s) of the root Mobile Router (i.e.  MR1) becomes a
      bottleneck for all the traffic that is coming in and out of the
      nested mobile network.

   A Route Optimization mechanism could allow traffic between two Mobile
   Network Nodes nested within the same mobile network to follow a
   direct path between them, without being routed out of the mobile
   network.  This may also off-load the processing burden of the
   upstream Mobile Routers when the direct path between the two Mobile
   Network Nodes does not traverse these Mobile Routers.


2.7.  Stalemate with a Home Agent Nested in a Mobile Network

   Several configurations for the Home Network are described in [9].  In
   particular, there is a mobile home scenario where a (parent) Mobile
   Router is also a Home Agent for its mobile network.  In other words,
   the mobile network is itself an aggregation of Mobile Network
   Prefixes assigned to (children) Mobile Routers.

   A stalemate situation exists in the case where the parent Mobile
   Router visits one of its children.  The child Mobile Router cannot
   find its Home Agent in the Internet and thus cannot establish its
   MRHA tunnel and forward the visitors traffic.  The traffic from the
   parent is thus blocked from reaching the Internet and it will never
   bind to its own (grand parent) Home Agent.  Appendix C gives a
   detailed illustration of how such a situation can occur.

   Then again, a Route Optimization mechanism that bypasses the nested
   tunnel might enable the parent traffic to reach the Internet and let
   it bind.  At that point, the child Mobile Router would be able to
   reach its parent and bind in turn.  Additional nested Route
   Optimization solutions might also enable the child to locate its Home
   Agent in the nested structure and bind regardless of whether the
   Internet is reachable or not.
















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3.  Conclusion

   With current NEMO Basic Support, all communications to and from
   Mobile Network Nodes must go through the MRHA tunnel when the mobile
   network is away.  This results in various inefficiencies associated
   with packet delivery.  This document investigates such
   inefficiencies, and provides for the motivation behind Route
   Optimization for NEMO.

   We have described the sub-optimal effects of pinball routes with NEMO
   Basic Support, how they may cause a bottleneck to be formed in the
   home network, and how they get amplified with nesting of mobile
   networks.  These effects will also be seen even when Mobile IPv6
   Route Optimization is used over NEMO Basic Support.  In addition,
   other issues concerning the nesting of mobile networks that might
   provide additional motivation for a NEMO Route Optimization mechanism
   were also explored, such as the prohibition of forwarding traffic
   from a Visiting Mobile Node through a MRHA tunnel due to security
   concerns, the impact of MRHA tunnel on communications between two
   Mobile Network Nodes on different links of the same mobile network,
   and the possibility of a stalemate situation when Home Agents are
   nested within a mobile network.


4.  IANA Considerations

   This is an informational document and does not require any IANA
   action.


5.  Security Considerations

   This document highlights some limitations of the NEMO Basic Support.
   In particular, some security concerns could prevent interesting
   applications of the protocol, as detailed in Section 2.5.

   Route Optimization for RFC 3963 [1] might introduce new threats, just
   as it might alleviate existing ones.  This aspect will certainly be a
   key criterion in the evaluation of the proposed solutions.












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6.  Acknowledgments

   The authors wish to thank the co-authors of previous drafts from
   which this draft is derived: Marco Molteni, Paik Eun-Kyoung, Hiroyuki
   Ohnishi, Thierry Ernst, Felix Wu, and Souhwan Jung.  Early work by
   Masafumi Watari on the extracted appendix was written while still at
   Keio University.  In addition, sincere appreciation is also extended
   to Jari Arkko, Carlos Bernardos, Greg Daley, T.J. Kniveton, Henrik
   Levkowetz, Erik Nordmark, Alexandru Petrescu, Hesham Soliman, Ryuji
   Wakikawa and Patrick Wetterwald for their various contributions.









































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7.  References

7.1.  Normative Reference

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

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

   [3]  Ernst, T. and H. Lach, "Network Mobility Support Terminology",
        draft-ietf-nemo-terminology-04 (work in progress), October 2005.

7.2.  Informative Reference

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

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

   [6]   Deering, S. and B. Zill, "Redundant Address Deletion when
         Encapsulating IPv6 in IPv6",
         draft-deering-ipv6-encap-addr-deletion-00 (work in progress),
         November 2001.

   [7]   Petrescu, A., Olivereau, A., Janneteau, C., and H-Y. Lach,
         "Threats for Basic Network Mobility Support (NEMO threats)",
         draft-petrescu-nemo-threats-01 (work in progress),
         January 2004.

   [8]   Jung, S., Zhao, F., Wu, S., Kim, H-G., and S-W. Sohn, "Threat
         Analysis on NEMO Basic Operations",
         draft-jung-nemo-threat-analysis-02 (work in progress),
         February 2004.

   [9]   Thubert, P., Wakikawa, R., and V. Devarapalli, "NEMO Home
         Network models", draft-ietf-nemo-home-network-models-05 (work
         in progress), October 2005.

   [10]  Draves, R., "Default Address Selection for Internet Protocol
         version 6 (IPv6)", RFC 3484, February 2003.







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Appendix A.  Change Log

   o  draft-ietf-nemo-ro-problem-statement-02:

      *  Added Appendix C to illustrate the formation of stalemate
         situation in Section 2.7

      *  Editorial changes to the Abstract to better reflect the
         document contents

      *  Minor editorial changes throughout Section 2

   o  draft-ietf-nemo-ro-problem-statement-01:

      *  Added text on effect on TCP contributed by Carlos in Sect 2.1 -
         "Sub-Optimality with NEMO Basic Support"

      *  Added text on VMN using CoA as source address in Appendix B.4.3

      *  Re-written Section 2.5 - "Security Policy Prohibiting Traffic
         From Visiting Nodes"

      *  Replaced "deadlock" with "stalemate" in Section 2.7.

      *  Minor typographical corrections

   o  draft-ietf-nemo-ro-problem-statement-00:

      *  Initial version adapted from Section 1 & 2 of
         'draft-thubert-nemo-ro-taxonomy-04.txt'

      *  Added Section 2.2: Bottleneck in the Home Network

      *  Added Section 2.5: Security Policy Prohibiting Traffic From
         Visiting Nodes

      *  Added Section 2.7: Deadlock with a Home Agent Nested in a
         Mobile Network

      *  Appendix B extracted from 'draft-watari-nemo-nested-cn-01.txt'











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Appendix B.  Various configurations involving Nested Mobile Networks

   In the following sections, we try to describe different communication
   models which involve a nested mobile network, and to clarify the
   issues for each case.  We illustrate the path followed by packets if
   we assume nodes only use Mobile IPv6 and NEMO Basic Support
   mechanisms.  Different cases are considered where a Correspondent
   Node is located in the fixed infrastructure, in a distinct nested
   mobile network as the Mobile Network Node, or in the same nested
   mobile network as the Mobile Network Node.  Additionally, cases where
   Correspondent Nodes and Mobile Network Nodes are either standard IPv6
   nodes or Mobile IPv6 nodes are considered.  As defined in [3],
   standard IPv6 nodes are nodes with no mobility functions whatsoever,
   i.e. they are not Mobile IPv6 nor NEMO enabled.  This mean that not
   only can they not move around keeping open connections, but also they
   cannot process Binding Updates sent by peers.

B.1.  CN located in the fixed infrastructure

   The most typical configuration is the case where a Mobile Network
   Node communicates with a Correspondent Node attached in the fixed
   infrastructure.  Figure 3 below shows an example of such topology.

                    +--------+  +--------+  +--------+
                    | MR1_HA |  | MR2_HA |  | MR3_HA |
                    +---+----+  +---+----+  +---+----+
                        |           |           |
                       +-------------------------+
                       |        Internet         |----+ CN
                       +-------------------------+
                               |               |
                           +---+---+        +--+-----+
                 root-MR   |  MR1  |        | VMN_HA |
                           +---+---+        +--------+
                               |
                           +---+---+
                  sub-MR   |  MR2  |
                           +---+---+
                               |
                           +---+---+
                  sub-MR   |  MR3  |
                           +---+---+
                               |
                           ----+----
                              MNN

   Figure 3: CN located at the infrastructure




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B.1.1.  Case A: LFN and standard IPv6 CN

   The simplest case is where both MNN and CN are fixed nodes with no
   mobility functions.  That is, MNN is a Local Fixed Node, and CN is a
   standard IPv6 node.  Packets are encapsulated between each Mobile
   Router and its respective Home Agent.  As shown in Figure 4, in such
   case, the path between the two nodes would go through:


        1       2       3       4          3          2          1
   MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA --- CN
   LFN                                                         IPv6 Node

             The digits represent the number of IPv6 headers.


   Figure 4: MNN and CN are standard IPv6 nodes

B.1.2.  Case B: VMN and MIPv6 CN

   In this second case, both end nodes are Mobile IPv6 enabled mobile
   nodes, that is, MNN is a Visiting Mobile Node.  Mobile IPv6 route
   optimization may thus be initiated between the two and packets would
   not go through the Home Agent of the Visiting Mobile Node nor the
   Home Agent of the Correspondent Node (not shown in the figure).
   However, packets will still be tunneled between each Mobile Router
   and its respective Home Agent, in both directions.  As shown in
   Figure 5, the path between MNN and CN would go through:


        1       2       3       4          3          2          1
   MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA --- CN
   VMN                                                             MIPv6


   Figure 5: MNN and CN are MIPv6 mobile nodes

B.1.3.  Case C: VMN and standard IPv6 CN

   When the communication involves a Mobile IPv6 node either as a
   Visiting Mobile Node or as a Correspondent Node, Mobile IPv6 route
   optimization cannot be performed because the standard IPv6
   Correspondent Node cannot process Mobile IPv6 signaling.  Therefore,
   MNN would establish a bi-directional tunnel with its HA, which causes
   the flow to go out the nested NEMO.  Packets between MNN and CN would
   thus go through MNN's own Home Agent (VMN_HA).  The path would
   therefore be as shown on Figure 6:




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               2       3       4       5          4
          MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA
          VMN                                           |
                                                        | 3
                                       1          2     |
                                   CN --- VMN_HA --- MR3_HA
                                IPv6 Node


   Figure 6: MNN is a MIPv6 mobile node and CN is a standard IPv6 node

   Providing Route Optimization involving a Mobile IPv6 node may require
   optimization among the Mobile Routers and the Mobile IPv6 node.

B.2.  CN located in distinct nested NEMOs

   The Correspondent Node may be located in another nested mobile
   network, different from the one MNN is attached to, as shown in
   Figure 7.  We define such configuration as "distinct nested mobile
   networks".

              +--------+  +--------+  +--------+  +--------+
              | MR2_HA |  | MR3_HA |  | MR4_HA |  | MR5_HA |
              +------+-+  +---+----+  +---+----+  +-+------+
                      \       |           |        /
         +--------+    +-------------------------+    +--------+
         | MR1_HA |----|        Internet         |----| VMN_HA |
         +--------+    +-------------------------+    +--------+
                          |                   |
                      +---+---+           +---+---+
            root-MR   |  MR1  |           |  MR4  |
                      +---+---+           +---+---+
                          |                   |
                      +---+---+           +---+---+
             sub-MR   |  MR2  |           |  MR5  |
                      +---+---+           +---+---+
                          |                   |
                      +---+---+           ----+----
             sub-MR   |  MR3  |              CN
                      +---+---+
                          |
                      ----+----
                         MNN

   Figure 7: MNN and CN located in distinct nested NEMOs






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B.2.1.  Case D: LFN and standard IPv6 CN

   Similar with Case A, we start off with the case where both end nodes
   do not have any mobility functions.  Packets are encapsulated at
   every mobile router on the way out the nested mobile network,
   decapsulated by the Home Agents and then encapsulated again on its
   way down the nested mobile network.


            1       2       3       4          3          2
       MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
       LFN                                                      |
                                                                | 1
                               1       2       3          2     |
                           CN --- MR5 --- MR4 --- MR4_HA --- MR5_HA
                        IPv6 Node


   Figure 8: MNN and CN are standard IPv6 nodes

B.2.2.  Case E: VMN and MIPv6 CN

   Similar with Case B, when both end nodes are Mobile IPv6 nodes, the
   two nodes may initiate Mobile IPv6 route optimization.  Again,
   packets will not go through the Home Agent of the MNN nor the Home
   Agent of the Mobile IPv6 Correspondent Node (not shown in the
   figure).  However, packets will still be tunneled for each Mobile
   Router to its Home Agent and vise versa.  Therefore, the path between
   MNN and CN would go through:


            1       2       3       4          3          2
       MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
       VMN                                                      |
                                                                | 1
                               1       2       3          2     |
                           CN --- MR5 --- MR4 --- MR4_HA --- MR5_HA
                       MIPv6 Node


   Figure 9: MNN and CN are MIPv6 mobile nodes

B.2.3.  Case F: VMN and standard IPv6 CN

   Similar to Case C, when the communication involves a Mobile IPv6 node
   either as a Visiting Mobile Node or as a Correspondent Node, MIPv6
   route optimization can not be performed because the standard IPv6
   Correspondent Node cannot process Mobile IPv6 signaling.  MNN would



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   therefore establish a bi-directional tunnel with its Home Agent.
   Packets between MNN and CN would thus go through MNN's own Home Agent
   as shown on figure Figure 10:



            2       3       4       5          4          3
       MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
       VMN                                                      |
                                                                | 2
                   1       2       3           2          1     |
               CN --- MR5 --- MR4 --- MR4_HA  --- MR5_HA --- VMN_HA
            IPv6 Node


   Figure 10: MNN is a MIPv6 mobile node and CN is a standard IPv6 node

B.3.  CN and MNN located in the same nested NEMO

   Figure 11 below shows the case where the two communicating nodes are
   connected behind different Mobile Routers that are connected in the
   same nested mobile network, and thus behind the same root Mobile
   Router.  Route optimization can avoid packets being tunneled outside
   the nested mobile network.

              +--------+  +--------+  +--------+  +--------+
              | MR2_HA |  | MR3_HA |  | MR4_HA |  | MR5_HA |
              +------+-+  +---+----+  +---+----+  +-+------+
                      \       |           |        /
         +--------+    +-------------------------+    +--------+
         | MR1_HA |----|        Internet         |----| VMN_HA |
         +--------+    +-------------------------+    +--------+
                                    |
                                +---+---+
                      root-MR   |  MR1  |
                                +-------+
                                 |     |
                          +-------+   +-------+
                 sub-MR   |  MR2  |   |  MR4  |
                          +---+---+   +---+---+
                              |           |
                          +---+---+   +---+---+
                 sub-MR   |  MR3  |   |  MR5  |
                          +---+---+   +---+---+
                              |           |
                          ----+----   ----+----
                             MNN          CN




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   Figure 11: CN and MNN located in the same nested NEMO

B.3.1.  Case G: LFN and standard IPv6 CN

   Again, we start off with the case where both end nodes do not have
   any mobility functions.  Packets are encapsulated at every Mobile
   Router on the way out the nested mobile network via the root Mobile
   Router, decapsulated and encapsulated by the Home Agents and then
   make their way back to the nested mobile network through the same
   root Mobile Router.  Therefore, the path between MNN and CN would go
   through:


            1       2       3       4          3          2
       MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
       LFN                                                      |
                                                                | 1
            1       2       3       4          3          2     |
        CN --- MR5 --- MR4 --- MR1 --- MR1_HA --- MR4_HA --- MR5_HA
     IPv6 Node


   Figure 12: MNN and CN are standard IPv6 nodes

B.3.2.  Case H: VMN and MIPv6 CN

   Similar with Case B and E, when both end nodes are Mobile IPv6 nodes,
   the two nodes may initiate Mobile IPv6 route optimization which will
   avoid the packets to go through the Home Agent of MNN nor the Home
   Agent of the Mobile IPv6 CN (not shown in the figure).  However,
   packets will still be tunneled between each Mobile Router and its
   respective Home Agent in both directions.  Therefore, the path would
   be the same with Case G and go through:


             1       2       3       4          3          2
        MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
        LFN                                                      |
                                                                 | 1
             1       2       3       4          3          2     |
         CN --- MR5 --- MR4 --- MR1 --- MR1_HA --- MR4_HA --- MR5_HA
     MIPv6 Node


   Figure 13: MNN and CN are MIPv6 mobile nodes






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B.3.3.  Case I: VMN and standard IPv6 CN

   As for Case C and Case F, when the communication involves a Mobile
   IPv6 node either as a Visiting Mobile Node or as a Correspondent
   Node, Mobile IPv6 Route Optimization can not be performed.
   Therefore, MNN will establish a bi-directional tunnel with its Home
   Agent.  Packets between MNN and CN would thus go through MNN's own
   Home Agent.  The path would therefore be as shown on Figure 14:


            2       3       4       5          4          3
       MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
       VMN                                                      |
                                                                | 2
                                                                |
                                                             VMN_HA
                                                                |
                                                                | 1
             1       2       3       4          3          2    |
         CN --- MR5 --- MR4 --- MR1 --- MR1_HA --- MR4_HA --- MR5_HA
      IPv6 Node


   Figure 14: MNN is a MIPv6 mobile node and CN is a standard IPv6 node

B.4.  CN located behind the same nested MR

   Figure 15 below shows the case where the two communicating nodes are
   connected behind the same nested Mobile Router.  The optimization is
   required when the communication involves MIPv6-enabled nodes.





















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              +--------+  +--------+  +--------+  +--------+
              | MR2_HA |  | MR3_HA |  | MR4_HA |  | MR5_HA |
              +------+-+  +---+----+  +---+----+  +-+------+
                      \       |           |        /
         +--------+    +-------------------------+    +--------+
         | MR1_HA |----|        Internet         |----| VMN_HA |
         +--------+    +-------------------------+    +--------+
                                    |
                                +---+---+
                      root-MR   |  MR1  |
                                +---+---+
                                    |
                                +-------+
                       sub-MR   |  MR2  |
                                +---+---+
                                    |
                                +---+---+
                       sub-MR   |  MR3  |
                                +---+---+
                                    |
                                -+--+--+-
                                MNN    CN

   Figure 15: MNN and CN located behind the same nested MR

B.4.1.  Case J: LFN and standard IPv6 CN

   If both end nodes are Local Fixed Nodes, no special function is
   necessary for optimization of their communications.  The path between
   the two nodes would go through:


                                  1
                             MNN --- CN
                             LFN   IPv6 Node


   Figure 16: MNN and CN are standard IPv6 nodes

B.4.2.  Case K: VMN and MIPv6 CN

   Similar with Case H, when both end nodes are Mobile IPv6 nodes, the
   two nodes may initiate Mobile IPv6 route optimization.  Although few
   packets would go out the nested mobile network for the Return
   Routability initialization, however, unlike Case B and Case E,
   packets will not get tunneled outside the nested mobile network.
   Therefore, packets between MNN and CN would eventually go through:




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                                  1
                             MNN --- CN
                             VMN   MIPv6 Node


   Figure 17: MNN and CN are MIPv6 mobile nodes

   If the root Mobile Router is disconnected while the nodes exchange
   keys for the Return Routability procedure, they may not communicate
   even though they are connected on the same link.

B.4.3.  Case L: VMN and standard IPv6 CN

   When the communication involves a Mobile IPv6 node either as a
   Visiting Mobile Network Node or as a Correspondent Node, Mobile IPv6
   Route Optimization cannot be performed.  Therefore, even though the
   two nodes are on the same link, MNN will establish a bi-directional
   tunnel with it's Home Agent, which causes the flow to go out the
   nested mobile network.  Path between MNN and CN would require another
   Home Agent (VMN_HA) to go through for this Mobile IPv6 node:


            2       3       4       5          4          3
       MNN --- MR3 --- MR2 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
       VMN                                                      |
                                                                | 2
                                                                |
                                                             VMN_HA
                                                                |
                                                                | 1
             1       2       3       4          3          2    |
         CN --- MR5 --- MR4 --- MR1 --- MR1_HA --- MR2_HA --- MR3_HA
      IPv6 Node


   Figure 18: MNN is a MIPv6 mobile node and CN is a standard IPv6 node

   However, MNN may also decide to use its care-of address as the source
   address of the packets, thus avoiding the tunneling with the MNN's
   Home Agent.  This is particularly useful for a short-term
   communications that may easily be retried if it fails.  Default
   Address Selection [10] provides some mechanisms for controlling the
   choice of the source address.








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Appendix C.  Example of How a Stalemate Situation can Occur

   Section 2.7 describes the occurence of a stalemate situation where a
   Home Agent of a Mobile Router is nested behind the Mobile Router.
   Here, we illustrate a simple example where such a situation can
   occur.

   Consider a mobility configuration depicted in Figure 19 below.  MR1
   is served by HA1/BR and MR2 is served by HA2.  The 'BR' designation
   indicates that HA1 is a border router.  Both MR1 and MR2 are at home
   in the initial step.  HA2 is placed inside the first mobile network,
   thus representing a "mobile" Home Agent.

                                                     /-----CN
                                         +----------+
        home link 1         +--------+   |          |
      ----+-----------------| HA1/BR |---| Internet |
          |                 +--------+   |          |
          |                              +----------+
       +--+--+  +-----+
       | MR1 |  | HA2 |
       +--+--+  +--+--+
          |        |
         -+--------+-- mobile net 1 / home link 2
          |
       +--+--+  +--+--+
       | MR2 |  | LFN |
       +--+--+  +--+--+
           |        |
          -+--------+- mobile net 2

   Figure 19: Initial Deployment

   In Figure 19 above, communications between CN and LFN follows a
   direct path as long as both MR1 and MR2 are positioned at home.  No
   encapsulation intervenes.

   In the next step, consider that the MR2's mobile network leaves home
   and visits a foreign network, under Access Router (AR) like in
   Figure 20 below.











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                                               /-----CN
                                   +----------+
        home link 1   +--------+   |          |
        --+-----------| HA1/BR |---| Internet |
          |           +--------+   |          |
       +--+--+  +-----+            +----------+
       | MR1 |  | HA2 |                        \
       +--+--+  +--+--+                        +-----+
          |        |                           | AR  |
         -+--------+- mobile net 1             +--+--+
                      home link 2                 |
                                               +--+--+  +-----+
                                               | MR2 |  | LFN |
                                               +--+--+  +--+--+
                                                  |        |
                                    mobile net 2 -+--------+-

   Figure 20: Mobile Network 2 Leaves Home

   Once MR2 acquires a Care-of Address under AR, the tunnel setup
   procedure occurs between MR2 and HA2.  MR2 sends Binding Update to
   HA2 and HA2 replies Binding Acknowledgement to MR2.  The bi-
   directional tunnel has MR2 and HA2 as tunnel endpoints.  After the
   tunnel MR2HA2 has been set up, the path taken by a packet from CN
   towards LFN can be summarized as:

       CN->BR->MR1->HA2=>MR1=>BR=>AR=>MR2->LFN.

   Non-encapsulated packets are marked "->" while encapsulated packets
   are marked "=>".

   Consider next the attachment of the first mobile network under the
   second mobile network, like in Figure 21 below.

   After this movement, MR1 acquires a Care-of Address valid in the
   second mobile network.  Subsequently, it sends a Binding Update
   message addressed to HA1.  This Binding Update is encapsulated by MR2
   and sent towards HA2, which is expected to be placed in mobile net 1
   and expected to be at home.  Once HA1/BR receives this encapsulated
   BU, it tries to deliver to MR1.  Since MR1 is not at home, and a
   tunnel has not yet been set up between MR1 and HA1, HA1 is not able
   to route this packet and drops it.  Thus, the tunnel establishment
   procedure between MR1 and HA1 is not possible, due to the fact that
   the tunnel between MR2 and HA2 has been previously torn down (when
   the mobile net 1 has moved from home).  The communications between CN
   and LFN stops, even though both mobile networks are connected to the
   Internet.




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                                      /-----CN
                          +----------+
             +--------+   |          |
             | HA1/BR |---| Internet |
             +--------+   |          |
                          +----------+
                                      \
                                      +-----+
                                      | AR  |
                                      +--+--+
                                         |
                                      +--+--+  +-----+
                                      | MR2 |  | LFN |
                                      +--+--+  +--+--+
                                         |        |
                           mobile net 2 -+--------+-
                                         |
                                      +--+--+  +-----+
                                      | MR1 |  | HA2 |
                                      +--+--+  +--+--+
                                         |        |
                           mobile net 1 -+--------+-

   Figure 21: Stalemate Situation Occurs

   If both tunnels between MR1 and HA1, and between MR2 and HA2 were up
   simultaneously, they would have "crossed over" each other.  If the
   tunnels MR1-HA1 and MR2-HA2 were drawn in Figure 21, it could be
   noticed that the path of the tunnel MR1-HA1 includes only one
   endpoint of the tunnel MR2-HA2 (the MR2 endpoint).  Two MR-HA tunnels
   are crossing over each other if the IP path between two endpoints of
   one tunnel includes one and only one endpoint of the other tunnel
   (assuming that both tunnels are up).  When both endpoints of one
   tunnel are included in the path of the other tunnel, then tunnels are
   simply encapsulating each other.
















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Authors' Addresses

   Chan-Wah Ng
   Panasonic Singapore Laboratories Pte Ltd
   Blk 1022 Tai Seng Ave #06-3530
   Tai Seng Industrial Estate
   Singapore  534415
   SG

   Phone: +65 65505420
   Email: chanwah.ng@sg.panasonic.com


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

   Email: pthubert@cisco.com


   Masafumi Watari
   KDDI R&D Laboratories Inc.
   2-1-15 Ohara
   Fujimino, Saitama  356-8502
   JAPAN

   Email: watari@kddilabs.jp


   Fan Zhao
   University of California Davis
   One Shields Avenue
   Davis, CA  95616
   US

   Phone: +1 530 752 3128
   Email: fanzhao@ucdavis.edu











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