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Network Working Group                                           T. ErnstRequest for Comments: 4886                                         INRIACategory: Informational                                        July 2007Network Mobility Support Goals and RequirementsStatus 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.Ernst                        Informational                      [Page 1]

RFC 4886                       NEMO Goals                      July 2007Table of Contents1. Introduction ....................................................22. NEMO Working Group Objectives and Methodology ...................33. NEMO Support Design Goals .......................................53.1. Migration Transparency .....................................53.2. Performance Transparency and Seamless Mobility .............53.3. Network Mobility Support Transparency ......................53.4. Operational Transparency ...................................53.5. Arbitrary Configurations ...................................53.6. Local Mobility and Global Mobility .........................63.7. Scalability ................................................73.8. Backward Compatibility .....................................73.9. Secure Signaling ...........................................73.10. Location Privacy ..........................................83.11. IPv4 and NAT Traversal ....................................83.12. Minimal Impact on Internet Routing ........................84. NEMO Basic Support One-Liner Requirements .......................85. Security Considerations ........................................106. Acknowledgments ................................................117. References .....................................................117.1. Normative References ......................................117.2. Informative References ....................................111.  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.Ernst                        Informational                      [Page 2]

RFC 4886                       NEMO Goals                      July 2007   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: inSection 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 inSection 3.  Those design goals   then serve as guidelines to define the requirements listed inSection4 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 specifiedErnst                        Informational                      [Page 3]

RFC 4886                       NEMO Goals                      July 2007   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 inSection 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 hostsErnst                        Informational                      [Page 4]

RFC 4886                       NEMO Goals                      July 2007   (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 inSection 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 mobileErnst                        Informational                      [Page 5]

RFC 4886                       NEMO Goals                      July 2007   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.Ernst                        Informational                      [Page 6]

RFC 4886                       NEMO Goals                      July 20073.7.  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.Ernst                        Informational                      [Page 7]

RFC 4886                       NEMO Goals                      July 2007   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 IPErnst                        Informational                      [Page 8]

RFC 4886                       NEMO Goals                      July 2007   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]).Ernst                        Informational                      [Page 9]

RFC 4886                       NEMO Goals                      July 2007   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.Ernst                        Informational                     [Page 10]

RFC 4886                       NEMO Goals                      July 20076.  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.  References7.1.  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",RFC3753, 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.Ernst                        Informational                     [Page 11]

RFC 4886                       NEMO Goals                      July 2007   [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/imaraErnst                        Informational                     [Page 12]

RFC 4886                       NEMO Goals                      July 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Ernst                        Informational                     [Page 13]