





Network Working Group                                           T. Ernst
Request for Comments: 4886                                         INRIA
Category: Informational                                        July 2007


            Network Mobility Support Goals and Requirements

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Network mobility arises when a router connecting a network to the
   Internet dynamically changes its point of attachment to the Internet
   thereby causing the reachability of the said network to be changed in
   relation to the fixed Internet topology.  Such a type of network is
   referred to as a mobile network.  With appropriate mechanisms,
   sessions established between nodes in the mobile network and the
   global Internet can be maintained after the mobile router changes its
   point of attachment.  This document outlines the goals expected from
   network mobility support and defines the requirements that must be
   met by the NEMO Basic Support solution.






















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Table of Contents

   1. Introduction ....................................................2
   2. NEMO Working Group Objectives and Methodology ...................3
   3. NEMO Support Design Goals .......................................5
      3.1. Migration Transparency .....................................5
      3.2. Performance Transparency and Seamless Mobility .............5
      3.3. Network Mobility Support Transparency ......................5
      3.4. Operational Transparency ...................................5
      3.5. Arbitrary Configurations ...................................5
      3.6. Local Mobility and Global Mobility .........................6
      3.7. Scalability ................................................7
      3.8. Backward Compatibility .....................................7
      3.9. Secure Signaling ...........................................7
      3.10. Location Privacy ..........................................8
      3.11. IPv4 and NAT Traversal ....................................8
      3.12. Minimal Impact on Internet Routing ........................8
   4. NEMO Basic Support One-Liner Requirements .......................8
   5. Security Considerations ........................................10
   6. Acknowledgments ................................................11
   7. References .....................................................11
      7.1. Normative References ......................................11
      7.2. Informative References ....................................11

1.  Introduction

   Network mobility support (see [1] for the related terminology) is
   concerned with managing the mobility of an entire network, viewed as
   a single unit that changes its point of attachment to the Internet
   and thus its reachability in the Internet topology.  Such a network
   is referred to as a mobile network and includes one or more mobile
   routers (MRs), which connect it to the global Internet.  Nodes behind
   the MR(s) (MNNs) are both fixed (LFNs) and mobile (VMNs or LMNs).  In
   most cases, the internal structure of the mobile network will be
   relatively stable (no dynamic change of the topology), but this is
   not always true.

   Cases of mobile networks include, for instance:

   o  Networks attached to people (Personal Area Networks or PANs): a
      cell phone with one cellular interface and one Bluetooth interface
      together with a Bluetooth-enabled PDA constitute a very simple
      instance of a mobile network.  The cell phone is the mobile router
      while the PDA is used for web browsing or runs a personal web
      server.






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   o  Networks of sensors and computers deployed in vehicles: vehicles
      are increasingly equipped with a number of processing units for
      safety and ease of driving reasons, as advocated by ITS
      (Intelligent Transportation Systems) applications ([4]).

   o  Access networks deployed in public transportation (buses, trains,
      taxis, aircrafts): they provide Internet access to IP devices
      carried by passengers (laptop, camera, mobile phone); host
      mobility within network mobility or PANs; network mobility within
      network mobility, i.e., nested mobility (see [1] for the
      definition of nested mobility).

   o  Ad-hoc networks connected to the Internet via an MR: for instance,
      students in a train who need to both set up an ad-hoc network
      among themselves and get Internet connectivity through the MR
      connecting the train to the Internet.

   Mobility of networks does not cause MNNs to change their own physical
   point of attachment; however, they do change their topological
   location with respect to the global Internet.  If network mobility is
   not explicitly supported by some mechanisms, the mobility of the MR
   results in MNNs losing Internet access and breaking ongoing sessions
   between arbitrary correspondent nodes (CNs) in the global Internet
   and those MNNs located within the mobile network.  In addition, the
   communication path between MNNs and correspondent nodes becomes sub-
   optimal, and multiple levels of mobility will cause extremely sub-
   optimal routing.

   Mobility-related terms used in this document are defined in [2],
   whereas terms specifically pertaining to network mobility are defined
   in [1].  This document is structured as follows: in Section 2, we
   define the rough objectives and methodology of the NEMO working group
   to handle network mobility issues and we emphasize the stepwise
   approach the working group has decided to follow.  A number of
   desirable design goals are listed in Section 3.  Those design goals
   then serve as guidelines to define the requirements listed in Section
   4 for basic network mobility support [3].

2.  NEMO Working Group Objectives and Methodology

   The mechanisms required for handling network mobility issues were
   lacking within the IETF standards when the NEMO working group (WG)
   was set up at the IETF in 2002.  At that time, work conducted on
   mobility support (particularly in the Mobile IP working group) was to
   provide continuous Internet connectivity and optimal routing to
   mobile hosts only (host mobility support).  Such mechanisms specified





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   in Mobile IPv6 [5] are unable to support network mobility.  The NEMO
   working group has therefore been set up to deal with issues specific
   to network mobility.

   The primary objective of the NEMO work is to specify a solution that
   allows mobile network nodes (MNNs) to remain connected to the
   Internet and continuously reachable while the mobile router serving
   the mobile network changes its point of attachment.  The secondary
   goal of the work is to investigate the effects of network mobility on
   various aspects of Internet communication such as routing protocol
   changes, implications of real-time traffic and fast handovers, and
   optimizations.  This should support the primary goal of reachability
   for mobile network nodes.  Security is an important consideration
   too, and efforts should be made to use existing security solutions if
   they are appropriate.  Although a well-designed solution may include
   security inherent in other protocols, mobile networks also introduce
   new challenges.

   To complete these tasks, the NEMO working group has decided to take a
   stepwise approach.  The steps in this approach include standardizing
   a basic solution to preserve session continuity (NEMO Basic Support,
   see [3]) and studying the possible approaches and issues with
   providing more optimal routing with potentially nested mobile
   networks (NEMO Extended Support, see [6] and [7] for a discussion on
   routing optimization issues and [8] for a discussion on multihoming
   issues).  However, the working group is not chartered to actually
   standardize a solution for Extended Support at this point in time.
   If deemed necessary, the working group will be rechartered based on
   the conclusions of the discussions.

   For NEMO Basic Support, the working group assumes that none of the
   nodes behind the MR is aware of the network's mobility; thus, the
   network's movement needs to be completely transparent to the nodes
   inside the mobile network.  This assumption accommodates nodes inside
   the network that are not generally aware of mobility.

   The efforts of the Mobile IP working group have resulted in the
   Mobile IPv4 and Mobile IPv6 protocols, which have already solved the
   issue of host mobility support.  Since challenges to enabling mobile
   networks are vastly reduced by this work, basic network mobility
   support has adopted the methods for host mobility support used in
   Mobile IP and has extended them in the simplest way possible to
   achieve its goals.  The Basic Support solution, now defined in [3]
   following the requirements stated in Section 4 of the present
   document, is for each MR to have a Home Agent (HA), and use bi-
   directional tunneling between the MR and HA to preserve session
   continuity while the MR moves.  The MR acquires a Care-of Address
   (CoA) at its attachment point much like what is done for mobile hosts



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   (MHs), using Mobile IP.  This approach allows nested mobile networks,
   since each MR will appear to its attachment point as a single node.

3.  NEMO Support Design Goals

   This section details the fundamental design goals the solutions will
   intend to achieve.  Those design goals serve to define the issues and
   to impose a list of requirements for forthcoming solutions.  Actual
   requirements for NEMO Basic Support are in Section 4; NEMO Extended
   Support is not yet considered at the time of this writing.

3.1.  Migration Transparency

   Permanent connectivity to the Internet has to be provided to all
   MNNs, since continuous sessions are expected to be maintained as the
   mobile router changes its point of attachment.  For maintaining those
   sessions, MNNs are expected to be reachable via their permanent IP
   addresses.

3.2.  Performance Transparency and Seamless Mobility

   NEMO support is expected to be provided with limited signaling
   overhead and to minimize the impact of handovers on applications, in
   terms of packet loss or delay.  However, although variable delays of
   transmission and losses between MNNs and their respective CNs could
   be perceived as the network is displaced, it would not be considered
   a lack of performance transparency.

3.3.  Network Mobility Support Transparency

   MNNs behind the MR(s) do not change their own physical point of
   attachment as a result of the mobile network's displacement in the
   Internet topology.  Consequently, NEMO support is expected to be
   performed only by the MR(s).  Specific support functions on any node
   other than the MR(s) would better be avoided.

3.4.  Operational Transparency

   NEMO support is to be implemented at the level of IP layer.  It is
   expected to be transparent to upper layers so that any upper-layer
   protocol can run unchanged on top of an IP layer extended with NEMO
   support.

3.5.  Arbitrary Configurations

   The formation of a mobile network can occur in various levels of
   complexity.  In the simplest case, a mobile network contains just a
   mobile router and a host.  In the most complicated case, a mobile



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   network is multihomed and is itself a multi-level aggregation of
   mobile networks with collectively thousands of mobile routers and
   hosts.  While the list of potential configurations of mobile networks
   cannot be limited, at least the following ones are desirable:

   o  Mobile networks of any size, ranging from a sole subnet with a few
      IP devices to a collection of subnets with a large number of IP
      devices.

   o  Nodes that change their point of attachment within the mobile
      network.

   o  Foreign mobile nodes that attach to the mobile network.

   o  Multihomed mobile network: either when a single MR has multiple
      attachments to the internet, or when the mobile network is
      attached to the Internet by means of multiple MRs (see definition
      in [1] and the analysis in [8]).

   o  Nested mobile networks (mobile networks attaching to other mobile
      networks (see definition in [1]).  Although the complexity
      requirements of these nested networks are not clear, it is
      desirable to support arbitrary levels of recursive networks.  The
      solution should only impose restrictions on nesting (e.g., path
      MTU) when this is impractical and protocol concerns preclude such
      support.

   o  Distinct mobility frequencies (see mobility factor in [2]).

   o  Distinct access media.

   In order to keep complexity minimal, transit networks are excluded
   from this list.  A transit network is one in which data would be
   forwarded between two endpoints outside of the network, so that the
   network itself simply serves as a transitional conduit for packet
   forwarding.  A stub network (leaf network), on the other hand, does
   not serve as a data forwarding path.  Data on a stub network is
   either sent by or addressed to a node located within that network.

3.6.  Local Mobility and Global Mobility

   Mobile networks and mobile nodes owned by different administrative
   entities are expected to be displaced within a domain boundary or
   between domain boundaries.  Multihoming, vertical and horizontal
   handoffs, and access control mechanisms are desirable to achieve this
   goal.  Such mobility is not expected to be limited for any
   consideration other than administrative and security policies.




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3.7.  Scalability

   NEMO support signaling and processing is expected to scale to a
   potentially large number of mobile networks irrespective of their
   configuration, mobility frequency, size, and number of CNs.

3.8.  Backward Compatibility

   NEMO support will have to co-exist with established IPv6 standards
   and not interfere with them.  Standards defined in other IETF working
   groups have to be reused as much as possible and extended only if
   deemed necessary.  For instance, the following mechanisms defined by
   other working groups are expected to function without modification:

   o  Address allocation and configuration mechanisms.

   o  Host mobility support: mobile nodes and correspondent nodes,
      either located within or outside the mobile network, are expected
      to continue operating protocols defined by the Mobile IP working
      group.  This includes mechanisms for host mobility support (Mobile
      IPv6) and seamless mobility (FMIPv6).

   o  Multicast support intended for MNNs is expected to be maintained
      while the mobile router changes its point of attachment.

   o  Access control protocols and mechanisms used by visiting mobile
      hosts and routers to be authenticated and authorized, gaining
      access to the Internet via the mobile network infrastructure
      (MRs).

   o  Security protocols and mechanisms.

   o  Mechanisms performed by routers deployed in both visited networks
      and mobile networks (routing protocols, Neighbor Discovery, ICMP,
      Router Renumbering).

3.9.  Secure Signaling

   NEMO support will have to comply with the usual IETF security
   policies and recommendations and is expected to have its specific
   security issues fully addressed.  In practice, all NEMO support
   control messages transmitted in the network will have to be protected
   with an acceptable level of security to prevent intruders from
   usurping identities and forge data.  Specifically, the following
   issues have to be considered:

   o  Authentication of the sender to prevent identity usurpation.




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   o  Authorization, to make sure the sender is granted permission to
      perform the operation as indicated in the control message.

   o  Confidentiality of the data contained in the control message.

3.10.  Location Privacy

   Location privacy means hiding the actual location of MNN to third
   parties other than the HA are desired.  It is not clear to which
   extend this has to be enforced, since it is always possible to
   determine the topological location by analyzing IPv6 headers.  It
   would thus require some kind of encryption of the IPv6 header to
   prevent third parties from monitoring IPv6 addresses between the MR
   and the HA.  On the other hand, it is at the very least desirable to
   provide a means for MNNs to hide their real topological location to
   their CNs.

3.11.  IPv4 and NAT Traversal

   IPv4 clouds and NAT are likely to co-exist with IPv6 for a long time,
   so it is desirable to ensure that mechanisms developed for NEMO will
   be able to traverse such clouds.

3.12.  Minimal Impact on Internet Routing

   Any NEMO solution needs have minimal negative effect on the global
   Internet routing system.  The solution must therefore limit both the
   amount of information that must be injected into Internet routing, as
   well as the dynamic changes in the information that is injected into
   the global routing system.

   As one example of why this is necessary, consider the approach of
   advertising each mobile network's connectivity into BGP and, for
   every movement, withdrawing old routes and injecting new routes.  If
   there were tens of thousands of mobile networks each advertising and
   withdrawing routes, for example, at the speed that an airplane can
   move from one ground station to another, the potential effect on BGP
   could be very unfortunate.  In this example, the total amount of
   routing information advertised into BGP may be acceptable, but the
   dynamic instability of the information (i.e., the number of changes
   over time) would be unacceptable.

4.  NEMO Basic Support One-Liner Requirements

   For basic network mobility support, the NEMO WG is to specify a
   unified and unique "Network Mobility (NEMO) Basic Support" solution,
   hereafter referred to as "the solution".  This solution is to allow
   all nodes in the mobile network to be reachable via permanent IP



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   addresses, as well as maintain ongoing sessions as the MR changes its
   point of attachment to the Internet topology.  This is to be done by
   maintaining a bi-directional tunnel between an MR and its Home Agent.

   The NEMO Working Group, after some investigation of alternatives, has
   decided to reuse and extend the existing Mobile IPv6 [5] mechanisms
   for tunnel management.

   The list of requirements below has been imposed on the NEMO Basic
   Support solution.  The requirements have mostly been met by the
   resulting specification, which can now be found in [3].  Associated
   deployment issues are discussed in [9].

   R01: The solution must be implemented at the IP layer level.

   R02: The solution must set up a bi-directional tunnel between a
        mobile router and its Home Agent (MRHA tunnel).

   R03: All traffic exchanged between an MNN and a CN in the global
        Internet must transit through the bi-directional MRHA tunnel.

   R04: MNNs must be reachable at a permanent IP address and name.

   R05: The solution must maintain continuous sessions (both unicast and
        multicast) between MNNs and arbitrary CNs after IP handover of
        (one of) the MRs.

   R06: The solution must not require modifications to any node other
        than MRs and HAs.

   R07: The solution must support fixed nodes, mobile hosts, and mobile
        routers in the mobile network.

   R08: The solution must allow MIPv6-enabled MNNs to use a mobile
        network link as either a home link or a foreign link.

   R09: The solution must ensure backward compatibility with other
        standards defined by the IETF.  In particular, this includes the
        following:

        R09.1: The solution must not prevent the proper operation of
               Mobile IPv6 (i.e., the solution must allow MIPv6-enabled
               MNNs to operate either the CN, HA, or MN operations
               defined in [5]).







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   R10: The solution must be agnostic to the internal configuration.
        This means the solution will behave the same way if NEMO is
        nested, comprises one or several subnets, or comprises MNNs that
        are LFNs, VMNs, LFNs or a mixture of them.

   R11: The solution must support at least 2 levels of nested mobile
        networks, while, in principle, arbitrary levels of recursive
        mobile networks should be supported.

   R12: The solution must function for multihomed MRs and multihomed
        mobile networks as defined in [1].

   R13: NEMO support signaling over the bi-directional must be
        minimized.

   R14: Signaling messages between the HA and the MR must be secured:

        R14.1: The receiver must be able to authenticate the sender.

        R14.2: The function performed by the sender must be authorized
               for the content carried.

        R14.3: Anti-replay must be provided.

        R14.4: The signaling messages may be encrypted.

   R15: The solution must ensure transparent continuation of routing and
        management operations over the bi-directional tunnel (this
        includes, e.g., unicast and multicast routing protocols, router
        renumbering, Dynamic Host Configuration Protocol (DHCPv6)).

   R16: When one egress interface fails, the solution may preserve
        sessions established through another egress interface.

   R17: The solution should have a minimal impact on the global Internet
        routing system.

5.  Security Considerations

   Security considerations of the NEMO Basic Support solution are
   addressed in [RFC3963].

   Section 3.9 of this document discusses the security goals for all
   forms of existing and forthcoming NEMO solutions.







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6.  Acknowledgments

   The material presented in this document takes most of its text from
   discussions and previous documents submitted to the NEMO working
   group.  This includes initial contributions from Motorola, INRIA,
   Ericsson, and Nokia.  We are particularly grateful to Hesham Soliman
   (Ericsson) and the IETF Area Directors (ADs) at the time (Erik
   Nordmark and Thomas Narten), who greatly helped to set up the NEMO
   working group.  We are also grateful to all the following people
   whose comments greatly contributed to the present document: T.J.
   Kniveton (Nokia), Alexandru Petrescu (Motorola), Christophe Janneteau
   (Motorola), Pascal Thubert (Cisco), Hong-Yon Lach (Motorola), Mattias
   Petterson (Ericsson), and all the others who have expressed their
   opinions on the NEMO mailing lists (formerly known as MONET).
   Thierry Ernst wishes to personally acknowledge INRIA Rhone-Alpes and
   Motorola Labs Paris for their support and direction in bringing up
   this topic to the IETF in 2001--particularly Claude Castelluccia
   (INRIA) and Hong-Yon Lach (Motorola)--and his past employer, Keio
   University, Japan, which supported most of the costs associated with
   the IETF during the timelife of previous versions of this document.

7.  References

7.1.  Normative References

   [1]  Ernst, T. and H. Lach, "Network Mobility Support Terminology",
        RFC 4885, July 2007.

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

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

7.2.  Informative References

   [4]  "CALM - Medium and Long Range, High Speed, Air Interfaces
        parameters and protocols for broadcast, point to point, vehicle
        to vehicle, and vehicle to point communication in the ITS sector
        - Networking Protocol - Complementary Element", ISO Draft ISO/WD
        21210, February 2005.

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

   [6]  Ng, C., Thubert, P., Watari, M., and F. Zhao, "Network Mobility
        Route Optimization Problem Statement", RFC 4888, July 2007.



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   [7]  Ng, C., Zhao, F., Watari, M., and P. Thubert, "Network Mobility
        Route Optimization Solution Space Analysis", RFC 4889, July
        2007.

   [8]  Ng, C., Ernst, T., Paik, E., and M. Bagnulo, "Analysis of
        Multihoming in Network Mobility Support", Work in Progress),
        February 2007.

   [9]  Thubert, P., Wakikawa, R., and V. Devarapalli, "Network Mobility
        (NEMO) Home Network Models", RFC 4887, July 2007.

Author's Address

   Thierry Ernst
   INRIA
   INRIA Rocquencourt
   Domaine de Voluceau B.P. 105
   78 153 Le Chesnay Cedex
   France

   Phone: +33 1 39 63 59 30
   Fax:   +33 1 39 63 54 91
   EMail: thierry.ernst@inria.fr
   URI:   http://www-rocq.inria.fr/imara



























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