MANET Autoconfiguration (Autoconf)                     E. Baccelli (Ed.)
Internet-Draft                                                     INRIA
Expires: December 20, 2007                                       K. Mase
                                                      Niigata University
                                                              S. Ruffino
                                                          Telecom Italia
                                                                S. Singh
                                                           June 18, 2007

 Address Autoconfiguration for MANET: Terminology and Problem Statement

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   Copyright (C) The IETF Trust (2007).

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   Traditional dynamic IPv6 address assignment solutions are not adapted
   to mobile ad hoc networks.  This document elaborates on this problem,
   states the need for new solutions, and requirements to these

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Standalone MANET . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Connected MANET  . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Deployment Scenarios Selection . . . . . . . . . . . . . .  5
   4.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  MANET Autoconfiguration Goals  . . . . . . . . . . . . . .  6
     4.2.  Existing Solutions' Shortcomings . . . . . . . . . . . . .  6
       4.2.1.  Lack of Multi-hop Support  . . . . . . . . . . . . . .  7
       4.2.2.  Lack of Dynamic Topology Support . . . . . . . . . . .  7
       4.2.3.  Lack of Network Merging Support  . . . . . . . . . . .  7
       4.2.4.  Lack of Network Partitionning Support  . . . . . . . .  8
     4.3.  MANET Autoconfiguration Issues . . . . . . . . . . . . . .  8
       4.3.1.  Address and Prefix Generation  . . . . . . . . . . . .  9
       4.3.2.  Address Uniqueness Requirements  . . . . . . . . . . .  9
       4.3.3.  MANET Border Routers Related Issues  . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   7.  Informative References . . . . . . . . . . . . . . . . . . . . 13
   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
   Intellectual Property and Copyright Statements . . . . . . . . . . 16

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1.  Introduction

   A Mobile Ad hoc NETwork (also known as a MANET [2] [1]) consists of a
   loosely connected set of MANET routers.  Each MANET router embodies
   IP routing/forwarding functionality and may also incorporate host
   functionality.  These routers dynamically self-organize and maintain
   a routing structure among themselves, regardless of the availability
   of a connection to any infrastructure.  MANET routers may be mobile
   and may communicate over symmetric or assymetric wireless links.
   They may thus join and leave the MANET at any time.

   However, prior to participation in IP communication, each MANET
   interface that does not benefit from appropriate static configuration
   needs to automatically acquire at least one IP address, that may be
   required to be unique within a given scope.

   Standard automatic IPv6 address/prefix assignment solutions [5], [3]
   [4] do not work "as-is" on MANETs due to ad hoc networks' unique
   characteristics [2], and new mechanisms are therefore needed.  This
   document thus details and categorizes the issues that need to be

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2.  Terminology

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.  The key
   "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
   are to be interpreted as described in [RFC2119].

   In addition, this document uses the MANET architecture terminology
   defined in [2], as well as the following terms :

   Local address  - An IP address configured on an interface of a router
      in a MANET and valid for communication inside this MANET.  A local
      address MUST NOT be used for communication including routers
      outside the MANET.

   Global address  - An IP address configured on a MANET router and
      valid for communication with routers in the Internet, as well as
      internally within the MANET.

   Standalone MANET  - An independent ad hoc network, which does not
      contain a border router through which it is connected to the

   Network merger  - The process by which two or more previously
      disjoint ad hoc networks get connected.

   Network partitioning  - The process by which an ad hoc network splits
      into two or more disconnected ad hoc networks.

   Address generation  - The process of selecting a tentative address in
      view to configure an interface.

   Address assignment  - The process of configuring a generated address
      on an interface.

   Pre-service address uniqueness  - The property of an address which is
      assigned at most once at this given point in time, within a given

   In-service address uniqueness  - The property of an address which was
      assigned at most once within a given scope, and which remains
      unique over time, as the address is being used.

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3.  Deployment Scenarios

   Automatic configuration of IP addresses and/or prefixes on MANET
   interfaces is necessary in a number of deployment scenarios.  This
   section outlines the different categories of scenarios that are

3.1.  Standalone MANET

   Standalone MANETs are not connected to any external network: all
   traffic is generated by MANET nodes and destined to nodes in the same

   Routers joining a standalone MANET may either have (i) no previous
   configuration, or (ii) pre-configured local or global IP addresses
   (or prefixes).  Due to potential network partitions and mergers,
   standalone MANETs may be composed of routers of either either types.

   Typical instances of this scenario include private or temporary
   networks, set-up in areas where neither wireless coverage nor network
   infrastructure exist (e.g. emergency networks for disaster recovery,
   or conference-room networks).

3.2.  Connected MANET

   Connected MANETs have, contrary to standalone MANETs, connectivity to
   one or more external networks, typically the Internet, by means of
   one or more MBR (Manet Border Router, see [2]).  MANET routers may
   generate traffic destined to remote hosts accross these external
   networks, as well as to destination inside the MANET.

   Again, routers joining a connected MANET may either (i) have no
   previous configuration, or (i) already own pre-configured local or
   global IP addresses (or prefixes).

   Typical instances of this scenario include public wireless networks
   of scattered fixed WLAN Access Points participating in a MANET of
   mobile users, and acting as MBRs.  Another example of such a scenario
   is coverage extension of a fixed wide-area wireless network, where
   one or more mobile routers in the MANET are connected to the Internet
   through technologies such as UMTS or WiMAX.

3.3.  Deployment Scenarios Selection

   Both "Standalone MANET" scenario and "Connected MANET" scenarii are
   to be addressed by solutions for MANET autoconfiguration.

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4.  Problem Statement

   This section details the goals of MANET autoconfiguration, and
   highlights the shortcomings of existing autoconfiguration solutions.
   A taxonomy of autoconfiguration issues on MANETs is then elaborated.

4.1.  MANET Autoconfiguration Goals

   A MANET router needs to configure an IPv6 prefix(es) on its host
   interface and/or an IPv6 address on its loopback interface.  Besides,
   it needs to configure a /128 and/or a link local address on its MANET
   interface.  A MANET router may also configure a prefix shorter than
   /128 on its MANET interface provided prefix uniqueness is guaranteed

   The primary goal of MANET autoconfiguration is thus to provide
   mechanisms for IPv6 prefix allocation and address assignment, that
   are suited for mobile ad hoc environments.  Note that this task is
   namely distinct from that of just vehiculing knowledge about address
   or prefix location such as a routing protocol does (see for example
   [8], [9]), or such as described in [7].

   The mechanisms employed by solutions to be designed must address the
   distributed, multi-hop nature of MANETs [2], and be able to follow
   topology and connectivity changes by (re)configuring addresses and/or
   prefixes accordingly.

   Solutions must achieve their task with (i) low overhead, due to
   scarse bandwidth, and (ii) low delay, due to the dynamicity of the
   topology.  Solutions are designed to work at the network layer and
   thus applies to all link types.  However, in situations where link-
   layer multicast is needed it is possible that on some link types
   (e.g.  NBMA links), alternative mechanisms or protocols specifying
   operation over a particular link type would be required.

   Besides the possible use of the well-known IPv6 multicast addresses
   defined for neighbor discovery in [3] (e.g. for Duplicate Address
   Detection), solutions may also use some addresses defined in [10] for
   auto-configuration purposes.

4.2.  Existing Solutions' Shortcomings

   Traditional dynamic IP address assignment solutions, such as [5], [3]
   or [4], do not work as-is on MANETs due to these networks' unique
   properties.  This section overviews the shortcomings of these
   solutions in mobile ad hoc environments.

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4.2.1.  Lack of Multi-hop Support

   Traditional solutions assume that a broadcast directly reaches every
   router or host on the subnetwork, whereas this generally is not the
   case in MANETs (see [2]).  Some routers in the MANET will typically
   assume multihop broadcast, and expect to receive through several
   intermediate relayings by peer MANET routers.  For example, in Fig.
   1, the MANET router MR3 cannot communicate directly with a DHCP
   server [4] that would be available through an MBR, since the server
   and the MANET router are not located on the same logical link.  While
   some DHCP extensions (such as the relay-agent [11]) overcome this
   issue in a static network, it is not the case in a dynamic topology,
   as explained below.

                                                       ----- MR1...MR3
                                                      /      .
              +-------------+         +------------+ /       .
              |             |   p2p   |  MANET     |/        .
              |  ISP Edge   |   Link  |  Border    |         .
              |   Router    +---------+  Router    |\        .
              |             |         |  (MBR)     | \       .
              +-------------+         +------------+  \----- MR2

                       Fig. 1. Connected MANET router topology.

4.2.2.  Lack of Dynamic Topology Support

   A significant proportion of the routers in the MANET may be mobile
   with wireless interface(s), leading to ever changing neighbor sets
   for most MANET routers (see [1]).  Therefore, network topology may
   change rather dynamically compared to traditional networks, which
   invalidates traditional delegation solutions that were developed for
   infrastructure-based networks, such as [11], which assume the
   existence of a permanent hierarchy among devices and the permanent
   reachability of a configuration server.  For instance, in Fig. 1,
   even if MR1 would be able to delegate prefixes to MR3 with DHCP [4],
   it cannot be assumed that MR1 and MR3 will not move and become unable
   to communicate directly.

4.2.3.  Lack of Network Merging Support

   Network merging is a potential event that was not considered in the
   design of traditional solutions, and that may greatly disrupt the
   autoconfiguration mechanisms in use (see [2]).  Examples of network
   merging related issues include cases where a MANET A may feature

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   routers and hosts that use IP addresses that are locally unique
   within MANET A, but this uniqueness is not guaranteed anymore if
   MANET A merges with another MANET B. If address uniqueness is
   required within the MANET (see Section 4.3.2), issues arise that were
   not accounted for in traditional networks and solutions.

4.2.4.  Lack of Network Partitionning Support

   Network partinionning is a potential event that was not considered in
   the design of traditional solutions, and that may invalidate usual
   autoconfiguration mechanisms (see [2]).  Examples of related issues
   include cases such as a standalone MANET, whereby connection to the
   infrastructure is not available, possibly due to network
   partitnionning and loss of connectivity to an MBR.  The MANET must
   thus function without traditional server availability.  While
   stateless protocols such as [5] and [3] could provide IP address
   configuration (for MANET interfaces, loopback interfaces), these
   solutions do not provide any mechanism for allocating "unique
   prefix(es)" to routers in order to enable the configuration of host
   interfaces.  Moreover, [5] and [3] test address uniqueness via
   messages that are sent to neighbors only, and as such cannot detect
   the presence of duplicate addresses configured within the network but
   located several hops away.  However, since MANETs are generally
   multi-hop, detection of duplicate addresses over several hops is a
   feature that is required in most cases of MANET interface address
   assignment (see Section 4.3.2).

                          ----- MR1...MR3...MR5
                         /      .
                        /       .
                       /        .
                    MR4         .
                       \        .
                        \       .
                         \----- MR2

                       Fig. 2. Standalone MANET router topology.

4.3.  MANET Autoconfiguration Issues

   Taking into account the shortcomings of traditional solutions, this
   section categorizes general issues with regards to MANET

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4.3.1.  Address and Prefix Generation

   The distributed nature of MANETs brings the need for address
   generation algorithms that are not always based on traditional
   "client-server" schemes and hierarchies to provide MANET routers with
   addresses and prefixes.  In addition, the multi-hop aspect of mobile
   ad hoc networking makes it difficult to totally avoid address and
   prefix duplication a priori over all the MANET.

4.3.2.  Address Uniqueness Requirements

   If address uniqueness is required within a specific scope, and if the
   address/prefix generation mechanism in use does not totally avoid
   address/prefix duplication, then additional issues arise.  This
   section overviews these problems.

   Pre-service Issues -- One category of problems due to address
   uniqueness requirements are called pre-service issues.  Conceptually,
   they relate to the fact that before a generated address is assigned
   and used, it should be verified that it will not create an address
   conflict within the specified scope.  This is essential in the
   context of routing, where it is desireable to reduce the risks of
   loops due to routing table pollution with duplicate addresses.

   In-Service Issues -- Another category of problems due to address
   uniqueness are called in-service issues.  They come from the fact
   that even if an assigned address is currently unique within the
   specified scope, it cannot be ensured that it will indeed remain
   unique over time.

   Phenomena such as MANET merging and MANET partitionning can bring the
   need for checking the uniqueness (within the specified scope) of
   addresses that are already assigned and used, if in-service address
   uniqueness is required.

   The need for checking uniqueness of addresses that are to be assigned
   or already assigned and used may depend on (i) the probability of
   address conflicts, (ii) the amount of the overhead for checking
   uniqueness of addresses, and (iii) address uniqueness requirements
   from applications.

   For instance, if (i) is extremely low and (ii) significant, checking
   uniqueness of addresses may not be used.  If on the other hand (i) is
   not extremely low, checking uniqueness of addresses should be used.
   In any case, if the application has a hard requirement for address
   uniqueness assurance, checking uniqueness of addresses should always
   be used, no matter how unlikely is the event of address conflict.

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4.3.3.  MANET Border Routers Related Issues

   Another category of problems concern MBR management.

   MBR Mobility -- Some addresses may be configured by servers available
   through MBRs that may themselves be mobile and that may therefore
   leave the MANET.  In this case, global addresses used by routers in
   the MANET may no longer be valid.

   MBR Multiplicity -- In the case where multiple MBRs are available in
   the MANET, providing access to multiple address configuration
   servers, specific problems arise.  One problem is the way in which
   global prefixes are managed within the MANET.  If one prefix is used
   for the whole MANET, partitioning of the MANET may invalid routes in
   the Internet towards MANET routers.  On the other hand, use of
   multiple network prefixes guarantees traffic is unambiguously routed
   towards the MBR responsible for one particular prefix, but asymmetry
   in the routers' choice of ingress/egress MBR can lead to non-optimal
   paths followed by inbound/outbound data traffic.  When a device
   changes its MBR attachment, some routes may be broken, affecting
   MANET packet forwarding performance and applications.

   IPv6 Specifications -- Additional problems come from issues with
   current IPv6 specifications.  For example, the strict application of
   [5] may lead to check every IPv6 unicast address for uniqueness: in a
   multiple-MBR / multiple-prefixes MANET, this could bring to a large
   amount of control signalling, due to frequent reconfiguration.
   Moreover, IPv6 does not currently specify an address scope that is
   appropriate to fit the scope of a MANET, which could lead to
   undesireable behavior such as MBRs leaking MANET local traffic
   outside the MANET.

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5.  Security Considerations

   Address configuration in MANET could be prone to security attacks, as
   in other types of IPv6 networks.  Security threats to IPv6 neighbor
   discovery were discussed in SEND WG and described in [6]: three
   different trust models are specified, with varying levels of trust
   among network nodes and routers.  Among them, the model by which no
   trust exists among nodes is considered most suitable for ad hoc
   networks, although the other two models may also be applicable in
   some cases, for example when a trust relationship exists between an
   operator and some MANET routers.  Although [6] does not explicitly
   address MANETs, the trust models it provides for ad hoc networks can
   be valid also in the context of MANET autoconfiguration.

   It is worth noting that analysis of [6] is strictly related to
   Neighbor Discovery, Neighbor Unreachability Detection and Duplicate
   Address Detection procedures, as defined in [3] and [5].  As
   explained in the present document, current standard procedures cannot
   be used as-is in MANET context to achieve autoconfiguration of MANET
   routers and, therefore, design of new mechanisms can be foreseen.

   In this case, although security threats and attacks defined in [6]
   could also apply in presence of new solutions, additional threats and
   attacks could be possible (e.g., non-cooperation in message
   forwarding in multi-hop communications).  Therefore, the security
   analysis has to be further extended to include threats, specific to
   multi-hop networks and related to the particular address
   configuration solution.

   General security issues of ad hoc routing protocols' operations are
   not in the scope of MANET autoconfiguration.

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6.  IANA Considerations

   This document does currently not specify IANA considerations.

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7.  Informative References

   [1]   Macker, J. and S. Corson, "MANET Routing Protocol Performance
         Issues and Evaluation Considerations", RFC 2501, January 1999.

   [2]   Macker, J., Chakeres, I., and T. Clausen, "Mobile Ad hoc
         Network Architecture", ID draft-ietf-autoconf-manetarch,
         February 2007.

   [3]   Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
         for IPv6", RFC 2461, December 1998.

   [4]   Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
         Carney, "Dynamic Host Configuration Protocol for IPv6",
         RFC 3315, July 2003.

   [5]   Narten, T. and S. Thomson, "IPv6 Stateless Address
         Autoconfiguration", RFC 2462, December 1998.

   [6]   Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
         Discovery (ND) Trust Models and Threats", RFC 3756, May 2004.

   [7]   Draves, R. and D. Thaler, "Default Router Preferences and More-
         Specific Routes", RFC 4191, 2005.

   [8]   Moy, J., "OSPF version 2", RFC 2328, 1998.

   [9]   Moy, J., Coltun, R., and D. Ferguson, "OSPF for IPv6",
         RFC 2740, 1999.

   [10]  Chakeres, I., "Internet Assigned Numbers Authority (IANA)
         Allocations for the  Mobile Ad hoc Networks (MANET) Working
         Group", ID draft-ietf-manet-iana, May 2007.

   [11]  Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,

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   This document is the result of joint efforts, including those of the
   following contributers, listed in alphabetical order: C. Adjih, T.
   Boot, T. Clausen, C. Dearlove, C. Perkins, A. Petrescu, P. Ruiz, P.
   Stupar, F. Templin, D. Thaler, K. Weniger.

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Authors' Addresses

   Emmanuel Baccelli

   Phone: +33 1 69 33 55 11

   Kenichi Mase
   Niigata University

   Phone: +81 25 262 7446

   Simone Ruffino
   Telecom Italia

   Phone: +39 011 228 7566

   Shubhranshu Singh

   Phone: +82 31 280 9569

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Full Copyright Statement

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