MANET Autoconfiguration (Autoconf)                     E. Baccelli (Ed.)
Internet-Draft                                                     INRIA
Expires: February 2, May 22, 2008                                            K. Mase
                                                      Niigata University
                                                              S. Ruffino
                                                          Telecom Italia
                                                                S. Singh
                                                       November 19, 2007

 Address Autoconfiguration for MANET: Terminology and Problem Statement

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Copyright Notice

   Copyright (C) The IETF Trust (2007).


   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  6
     3.1.  Standalone  Connected MANET  . . . . . . . . . . . . . . . . . . . . .  5  6
     3.2.  Connected  Standalone MANET . . . . . . . . . . . . . . . . . . . . .  5  6
     3.3.  Deployment Scenarios Selection . . . . . . . . . . . . . .  5  6
   4.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  7
     4.1.  MANET Autoconfiguration Goals  . . . . . . . . . . . . . .  7
     4.2.  Existing Protocols' Shortcomings . . . . . . . . .
       4.1.1.  Multi-hop Support  . . . .  7
       4.2.1.  Lack of Multi-hop Support . . . . . . . . . . . . . .  7
       4.2.2.  Lack of
       4.1.2.  Dynamic Topology Support . . . . . . . . . . . . . . .  8
       4.2.3.  Lack of
       4.1.3.  Network Merging Support  . . . . . . . . . . . . . . .  8
       4.2.4.  Lack of
       4.1.4.  Network Partitioning Support . . . . . . . . . . . . .  9
     4.2.  MANET Autoconfiguration Issues . . . . . . . . . . . . . .  9
       4.2.1.  Address and Prefix Generation  . . . . . . . . . . . .  9
       4.3.2. 10
       4.2.2.  Prefix and Address Uniqueness Requirements . . . . . . 10
       4.3.3.  MANET Border Routers
       4.2.3.  Internet Configuration Provider Related Issues . . . . . . . . . 10 11
   5.  Solutions Considerations . . . . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   8.  Informative References . . . . . . . . . . . . . . . . . . . . 15
   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 18
   Intellectual Property and Copyright Statements . . . . . . . . . . 18 19

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 [2].  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. time, at a rate that can be substantially higher than in usual

   However, prior to participation in IP communication, each MANET
   router that does not benefit from appropriate static configuration
   needs to automatically acquire at least one IP address, that and may also
   need to be delegated an IP prefix.  This address or this prefix may
   be required to be unique within a given scope, or to be topologically

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

2.  Terminology

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

   MANET Local address Prefix (MLP)  - An IP prefix delegated to a MANET router,
      consisting in chunks of IP addresses valid for communications
      inside the MANET.

   MANET Local Address (MLA)  - An IP address configured on an interface
      of a router in a MANET
      interface, and valid for communication communications inside this the MANET.

   Global prefix  - An IP prefix delegated to a MANET router, consisting
      in chunks of IP addresses valid for communications reaching
      outside the MANET (as well as communications within the MANET).

   Global address  - An IP address configured on a MANET router an interface and valid
      for communication with routers in communications reaching outside the Internet, as MANET (as well as
      communications within the MANET. MANET).

   Internet Configuration Provider (ICP)  - A router that can provide
      other routers requesting configuration with addresses or prefixes
      derived from a global prefix.

   Connected MANET  - A mobile ad hoc network, which contains at least
      one ICP.

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

   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
      with the purpose of configuring an interface.

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

   Pre-service address uniqueness interface with a
      given address.

   Prefix delegation  - The property process of an address which is
      assigned at most providing a router with a set of
      contiguous addresses it may manage for the purpose of configuring
      interfaces or other routers.

   Pre-service address uniqueness  - The property of an address which is
      assigned at most once within a given scope, and which is unique,
      before it is being used.

   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, after the address has started being used.

3.  Deployment Scenarios

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

3.1.  Standalone MANET

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

   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 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 (leaf networks, or other are mobile ad hoc networks that
   provide Internet connectivity) by means of which contain at least
   one or more MANET border ICP, i.e. a router [2].  MANET routers may generate traffic destined to remote
   hosts across these external networks, as well as to destination
   inside the MANET.

   Again, that can provide other routers requesting
   configuration with addresses or prefixes derived from a global
   prefix.  Routers joining a connected MANET may either (i) have no
   previous configuration, or (ii) 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 MANET border routers.  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.

3.2.  Standalone MANET

   Standalone MANETs are mobile ad hoc networks which do not contain any
   ICP, i.e. which do not contain any router able to provide other
   routers requesting configuration with addresses or prefixes derived
   from a global prefix.  Again, 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 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).

3.3.  Deployment Scenarios Selection

   Both "Standalone MANET" and "Connected MANET" scenarios are to be
   addressed by solutions for MANET autoconfiguration.  Note that
   solutions should also aim at addressing cases where a MANET transits
   from one scenario to an other.

4.  Problem Statement

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

4.1.  MANET Autoconfiguration Goals

   A MANET router needs to configure IP addresses and/or and prefixes as usual,
   on its non-MANET interfaces. interfaces as well as its attached hosts and
   routers, if any.  In addition, it a MANET router needs to configure at
   least one IP address on its MANET interface, this being a link local
   address, a /128 and/or an MLA on its MANET interface. or a global address.  A MANET router may also configure require
   a IP prefix shorter than /128 on its MANET
   interface, delegated MLP, provided prefix uniqueness is guaranteed [2].

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

4.2.  Existing Protocols' Shortcomings

   Traditional dynamic IP address assignment protocols, such as [5], [3]
   or [4], do not work as-is efficiently (if at all) on MANETs MANETs, due to these
   networks' unique properties.  This section  The following thus overviews the shortcomings of these
   solutions in what must
   be specifically supported for efficient operation on mobile ad hoc environments.

4.2.1.  Lack of

4.1.1.  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 a MANET border router,
   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]) can to some extent 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    |\        .
              |             |         |            | \       .
              +-------------+         +------------+  \----- MR2

                       Fig. 1. Connected MANET router topology.

4.2.2.  Lack of

4.1.2.  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 do not assume
   intermittent reachability of configuration server(s), and a
   potentially ever changing hierarchy among devices.  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 MR1 and MR3 will not move and
   become unable to communicate directly.  Moreover, possible frequent
   reconfiguration due to intermittent reachability cause [5] to be less
   efficient than expected, due to large amounts of control signalling.

   In particular, supporting multihop dynamic topologies means that even
   if some address configuration servers are present somewhere, it
   cannot be assumed that they are reachable most of the time, contrary
   to communicate directly.

4.2.3.  Lack usual scenarios.  Therefore, reusing "as-is" existing solutions
   (for instance [4]) using servers on a MANET would basically imply
   that "everyone is a server" in order to ensure server reachability.
   This implication is the specificity of MANETs that brings the
   requirement for new levels of service distribution, since the
   "everyone is a server" approach is essentially not functional.

4.1.3.  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
   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), 4.2.2), issues arise that were
   not accounted for in traditional networks and solutions.  For
   instance, [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 may be
   required for MANET interface address assignment (see Section 4.3.2).

4.2.4.  Lack of 4.2.2).

4.1.4.  Network Partitioning Support

   Network partitioning 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 partitioning
   and loss of connectivity to a MANET border router.  The MANET must
   thus function without traditional address allocation 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.

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

                       Fig. 2. Standalone MANET router topology.


4.2.  MANET Autoconfiguration Issues

   Taking into account the shortcomings of traditional solutions, solutions in the
   mobile ad hoc context, this section categorizes general issues with
   regards to MANET autoconfiguration.


4.2.1.  Address and Prefix Generation

   The distributed nature of MANETs brings the need for address
   generation algorithms that are not always based on traditional can complement existing solutions by
   supporting operation outside "client-server" schemes and without
   fixed hierarchies to provide MANET routers with appropriate addresses and
   prefixes.  In addition, the multi-hop aspect of mobile
   ad hoc networking makes it difficult to totally avoid MANETs brings
   specific needs as far as address and prefix duplication a priori over all the MANET.

4.3.2. uniqueness is concerned,
   as detailed below.

4.2.2.  Prefix and Address Uniqueness Requirements

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

   Pre-service Issues -- One category of problems due to address Address or prefix uniqueness requirements problems in this
   category are called pre-service issues.  Conceptually, they relate to
   the fact that before a generated address or prefix 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 and Address or prefix uniqueness problems in this
   category are called in-service issues.  They come from the fact that
   even if an assigned address or prefix 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 partitioning may bring the
   need for checking the uniqueness (within the specified scope) of
   addresses or prefixes that are already assigned and used.  This need
   may depend on (i) the probability of address conflicts, (ii) the
   amount of the overhead for checking uniqueness of addresses, and
   (iii) address/prefix uniqueness requirements from applications.

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

4.3.3.  MANET Border Routers

4.2.3.  Internet Configuration Provider Related Issues

   Another category of problems concern MANET border router(s)
   management. the management of Internet
   configuration providers (ICPs).

   In the case where multiple MANET border routers ICPs 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 result in invalid routes towards MANET
   routers, over the Internet.  On the other hand, the use of multiple
   network prefixes guarantees traffic is unambiguously routed from the
   hosts/routers in the Internet towards the MANET border router responsible
   for one particular prefix.  However, asymmetry in the routers' choice
   of ingress/egress MANET border router can lead to non-optimal paths
   followed by inbound/outbound data traffic, or to broken connectivity,
   if egress filtering is being done.

   When a device router changes its MANET border router attachment, ICP affiliation, some routes may be broken,
   affecting MANET packet forwarding performance and applications.  In a
   multiple border router / multiple-prefixes MANET, frequent
   reconfiguration could cause a large amount of control signalling (for
   instance if [5] is used "as-is"). used).

5.  Solutions Considerations

   Solutions must achieve their task with (i) low overhead, due to
   scarse bandwidth, and (ii) low delay/convergence time, due to the
   dynamicity of the topology.  The evaluation of such criteria may
   depend on the targeted network properties, which include (but are not
   limited to) node cardinality, node mobility characteristics, etc.

   Solutions are to be designed to work at the network layer and thus to
   apply 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.

   Solutions must interact with existing protocols in a way that
   leverages as much as possible appropriate mechanisms that are
   deployed.  For instance, 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 as well use some
   addresses defined in [10] for auto-configuration purposes.  However,
   it must be ensured that no modification of existing protocols is to
   be required outside of MANET scope.

   Solutions must also take into account the security and trust issues
   that are specific to ad hoc networking (see Section 6).

6.  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 may be suitable a priori for most ad hoc
   networks.  However, the other two models may be applicable in some
   cases, for example when a trust relationship exists between an
   operator and some MANET routers, or between military devices that are
   in the same unit.  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.

7.  IANA Considerations

   This document does currently not specify IANA considerations.

8.  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, W., and H. Soliman,
         "Neighbor Discovery for IPv6", RFC 2461, December 1998. 4861, September 2007.

   [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. T., Thomson, S., and T. Jinmei, "IPv6 Stateless Address
         Autoconfiguration", RFC 2462, December 1998. 4862, September 2007.

   [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,

   [12]  Narten, T. and R. Draves, "Privacy Extensions for Stateless
         Address Autoconfiguration in IPv6", RFC 3041, 2001.

   [13]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
         Neighbor Discovery (SEND)", RFC 3971, 2005.

   [14]  Aura, T., "Cryptographically Generated Addresses (CGA)",
         RFC 3972, 2005.

   [15]  Moore, N., "Optimistic Duplicate Address Detection (DAD) for
         IPv6", RFC 4429, 2006.

   [16]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
         Addresses", RFC 4193, 2005.

   [17]  Thubert, P. and TJ. Kniveton, "Mobile Network Prefix
         Delegation", ID draft-ietf-nemo-prefix-delegation, August 2007.

   [18]  Troan, O. and R. Droms, "IPv6 Prefix Options for DHCPv6",
         RFC 3633, 2003.


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

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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