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Versions: 00 01 02 03 04 05 06 07                                       
MANET Autoconfiguration (AUTOCONF)                           I. Chakeres
Internet-Draft                                                  Motorola
Intended status: Informational                                 J. Macker
Expires: December 21, 2007                     Naval Research Laboratory
                                                              T. Clausen
                                                LIX, Ecole Polytechnique
                                                           June 19, 2007

                   Mobile Ad hoc Network Architecture

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on December 21, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This document discusses Mobile Ad hoc NETworks (MANETs).  It
   introduces basic MANET terms, characteristics, and challenges.  This
   document also defines several MANET entities and architectural

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Borrowed Terminology . . . . . . . . . . . . . . . . . . .  3
     2.2.  MANET Terminology  . . . . . . . . . . . . . . . . . . . .  5
   3.  MANET Motivation Discussion  . . . . . . . . . . . . . . . . .  6
   4.  MANET Interface Characteristics  . . . . . . . . . . . . . . .  7
     4.1.  Qualities - Wireless, Mobile, Ad hoc . . . . . . . . . . .  7
     4.2.  Challenges . . . . . . . . . . . . . . . . . . . . . . . .  8
       4.2.1.  Semi-Broadcast Interface . . . . . . . . . . . . . . .  8
       4.2.2.  Fuzzy Relationships Between Nearby MANET Routers &
               MANET Routers Extended Neighborhood  . . . . . . . . .  9
       4.2.3.  MANET Membership . . . . . . . . . . . . . . . . . . .  9
   5.  Addressing & the MANET Prefix Model  . . . . . . . . . . . . . 10
     5.1.  General Address Architecture . . . . . . . . . . . . . . . 11
     5.2.  MANET Interface Configuration  . . . . . . . . . . . . . . 12
     5.3.  Routers and Hosts in a MANET . . . . . . . . . . . . . . . 13
   6.  MANETs' Place in the Network Stack . . . . . . . . . . . . . . 14
   7.  Cross Layering . . . . . . . . . . . . . . . . . . . . . . . . 15
   8.  Deployment Taxonomy  . . . . . . . . . . . . . . . . . . . . . 15
     8.1.  Service Availability . . . . . . . . . . . . . . . . . . . 15
     8.2.  Number of MANET Routers in a MANET . . . . . . . . . . . . 16
     8.3.  Example Deployments  . . . . . . . . . . . . . . . . . . . 17
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 17
   12. Informative References . . . . . . . . . . . . . . . . . . . . 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
   Intellectual Property and Copyright Statements . . . . . . . . . . 21

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1.  Introduction

   A Mobile Ad hoc NETwork (MANET) consists of a loosely connected set
   of MANET routers.  Each MANET router embodies routing/forwarding
   functionality and may also incorporate host functionality.  These
   routers organize and maintain a routing structure among themselves.
   These routers may communicate over wireless links with asymmetric
   reachability, may be mobile, and may join and leave the network at
   any time.  MANETs' characteristics create challenges in several
   areas, and may require protocol extensions or new MANET protocols

   This document is focused on IP networking, though many of MANETs'
   concepts and issues span the protocol stack.

   This document is meant to complement [RFC2501] in describing and
   defining MANET.

2.  Terminology

   Much of the terminology in this document was borrowed from existing
   documents, to list a few [RFC1812], [RFC2328], [RFC2453], [RFC2460],
   [RFC2461], [RFC3513], [RFC3753], [I-D.iab-multilink-subnet-issues],
   [I-D.templin-autoconf-dhcp], and [I-D.ietf-ipv6-2461bis].  Note that
   the original text for the terms is often modified, though we have
   attempted to maintain the same meaning.

2.1.  Borrowed Terminology

   This document employs the following definitions:

   Node (N)
      any device (router or host) that implements IP.

   Router (R)
      a node that forwards IP packets not explicitly addressed to

   Host (H)
      any node that is not a router, i.e. a host does not forward
      packets addressed to others.

      A communications facility at a layer below IP, over which nodes
      exchange IP packets directly without decrementing IP TTL (Hop

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   Asymmetric Reachability
      A link where non-reflexive and/or non-transitive reachability is
      part of normal operation.  Non-reflexive reachability means that
      packets from X reach Y but packets from Y don't reach X. Non-
      transitive reachability means packets from X reach Y, and packets
      from Y reach Z, but packets from X don't reach Z. Many radio/
      wireless interfaces exhibit these properties.

      If node X can directly exchange IP packets with node Y, then node
      Y is node X's neighbor.

      A node's point of attachment to a communication link.

   Broadcast Interface
      An interface supporting many attached nodes, together with the
      capability to address a single link layer transmission to all of
      the attached nodes (broadcast).  The set of nodes receiving a
      given physical broadcast message are the neighbors of the node
      originating the message.

   Full-Broadcast Interface (FBI)
      A broadcast interface which does not exhibit asymmetric
      reachability.  All nodes on the interface can send and receive IP
      packets directly, all nodes are symmetric neighbors.  An Ethernet
      segment is an example of a FBI.

   Semi-Broadcast Interface (SBI)
      A broadcast interface that may exhibit asymmetric reachability.  A
      FBI is a special case of SBI.  Multiple access wireless radio
      interfaces are often SBI.

      a set of one or more links.

      The process of forwarding or distributing information to all
      devices with in a bounded region.

   Border Router (BR)
      a router that participates in multiple routing regions, and often
      multiple routing protocols.  A BR defines the border between its
      multiple routing regions.  A BR is responsible for presenting a
      consistent picture of the nodes reachable through itself to each
      routing region.  A BR determines the routing information to
      propagate between different routing regions.

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2.2.  MANET Terminology

   We define the following MANET entity:

   MANET Router (MNR)
      a MANET router embodies router functionality and may also
      incorporate an internally addressable host (IAH) logic, as
      illustrated in Figure 1.  A MANET router has one or more
      interfaces.  To simplify discussion we will classify the
      interfaces into two categories: classic IP interfaces & MANET
      interfaces.  MANET interfaces are defined as interfaces that
      demonstrate asymmetric reachability and/or neighboring nodes with
      addresses that are not known a priori.  A MANET router may also
      have zero or more classic IP interfaces to which other nodes may
      connect; i.e. the router may be responsible for several IP
      prefixes.  A MANET router may participate in routing on zero or
      more MANET interfaces.  A MANET router may participate in routing
      on zero or more classic IP interfaces.

         <~~~~~~+~~~~~~>            Routing-MANET
                |                   Interface(s)
      ' +-------|--------------+ '
      ' | Router Functionality |...................
      ' +-------+-+------------+ '  Routing-Classic
      '         :  :             '  IP Interface(s)
      ' MANET   :  +-----------+ '
      ' Router  :  | Internal  | '
      '         :  |Addressable| '
      '         :  |Host Logic | '
      '         :  |   (IAH)   | '
      '         :  +-----------+ '
                : Nodes that live behind the router
         +......+.........+           ============
         :                :           =    :     =
       +-+-+         +----+----+      =CLASSIC IP=
       | N |  * * *  | Node(s) |      =INTERFACES=
       +---+         +---------+      ============

                          Figure 1: MANET Router

   In MANETs there are several architectural scopes.  We define the
   following scopes:

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   MANET Neighbors
      a set of MANET routers that is reachable via one IP hop, reachable
      via link-local [RFC4007] messaging.

   MANET N-Neighborhood
      a set of MANET routers that is reachable via N-hops.  These
      routers usually have a large number of common neighboring MANET
      routers and may directly compete for the same shared wireless

      a routing region consisting of a set of MANET routers that is
      reachable via one or more MANET router hops.  If a MANET connects
      to other routing regions, its border is defined by Border Routers.

   If a link forms between two previously separated MANET routers or
   MANETs, the two MANETs will merge to form a single larger MANET.
   Similarly, if a critical link between two MANET routers is lost, then
   the MANET will be partitioned into two now separate MANETs.

   When discussing MANETs' connectivity to other networks, such as the
   Internet, a MANET is bounded by border routers (BR).  That is, a
   MANETs' BR form a border between a MANET and other routing regions.

3.  MANET Motivation Discussion

   The Internet Protocol (IP) core design tenets -- connectionless
   networking and packet-based forwarding -- are ideally suited for use
   in highly dynamic contexts, such as MANETs.  Yet, some additional
   functionality is required to meet the unique challenges and
   opportunities present in MANETs.

   The initial motivation for MANETs was called Packet Radio (PR)
   networking [FL01].  In PR, each router is equipped with a single SBI.
   This configuration is the simplest MANET router configuration.  Each
   router may be mobile, and the routers may be or may become spatially
   distributed such that all routers cannot communicate directly.  That
   is, two routers might require one or more intermediate routers to
   forward (route) packets on their behalf.  In the example shown in
   Figure 2: for R1 to send packets to R3, the intermediary R2 must
   relay the packets.  This implies that R2 must receive the packet from
   R1 on its interface and determine that it must retransmit the packet
   over the same interface as the one where the packet was received, in
   order for the packet to reach R3.  This example also illustrates how
   SBIs differ from FBIs: from the point of view of R2, both R1 and R3
   are neighboring routers, whereas R1 and R3 are not themselves
   neighboring routers of one another.

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         <~~~~~~+~~~~~~>   <~~~~~~+~~~~~~>
   Single       | <~~~~~~+~~~~~~> |
   SBI        +-|-+    +-|-+    +-|-+
              | R1|    | R2|    | R3|
              +---+    +---+    +---+

                       Figure 2: Basic MANET Network

   In addition to nodes' asymmetric reachability other challenges exist.
   In PR networks, shared wireless resources result in interdependence
   between nearby nodes, and these nodes often communicate directly or
   indirectly.  The dynamic wireless interface characteristics and node
   mobility often manifest as frequent network topology changes.

   PR networks also lead to several other architecture related
   challenges.  One challenge was to attach these PR networks to other
   networks, especially fixed networks like the ARPANET.  Another
   related challenge was how to deal with the large disparity between
   different node and interface characteristics.

   These PR network challenges helped stimulate the Internet Protocol;
   an architecture based on connectionless networking and packet-based
   forwarding that enables interconnection of heterogeneous devices over
   heterogeneous interfaces.

4.  MANET Interface Characteristics

   Inheriting from Packet Radio as described above, chief
   particularities of MANETs are the characteristics and qualities of
   MANET interfaces, and the challenges these entail for protocol design
   and development.

4.1.  Qualities - Wireless, Mobile, Ad hoc

   In MANET several qualities impact protocol design.  The most
   fundamental qualities are wireless interface characteristics,
   mobility, and ad hoc interaction.

   Wireless interfaces exhibit challenging characteristics when compared
   to wired interfaces.  Many protocols (e.g.  IPv6 neighbor discovery
   [RFC2461]) do not operate in wireless networks with asymmetric
   reachability.  Wireless interfaces also exhibit time varying
   performance that can significantly impact local communication.

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   Mobility can also exacerbates wireless networking issues, making it
   more challenging to attain, establish, and maintain network
   relationships between nodes.

   Ad hoc networking further compounds problems by allowing nodes to
   join and leave the network, or even form new networks, at will.

4.2.  Challenges

   MANETs characteristics result in many challenges.  These challenges
   reveal themselves in many forms, and MANET specific protocols must
   often be developed.

4.2.1.  Semi-Broadcast Interface

   Given a wireless SBI (with non-transitive and non-reflexive
   properties) and spatially distributed nodes, each node may have a
   different unique partial view of the MANET.  That is, each node may
   have a different set of adjacent nodes.

         <~~~~~~+~~~~~~>   <~~~~~~+~~~~~~>
   Single       | <~~~~~~+~~~~~~> |
   SBI        +-|-+    +-|-+    +-|-+
              | R1|    | R2|    | R3|
              +---+    +---+    +---+

                R1       R2       R3
   Neighboring  R2       R1       R2
   Routers               R3

       Figure 3: Semi-Broadcast Interface (SBI) Neighboring Routers

   The possibly unique set of adjacent nodes in each node often requires
   nodes to forward packets out the same wireless interface as the one
   over which they were received.  Topologically, this act of forwarding
   out the same interface causes a packet to reach a possibly different
   set of nodes by traversing the wireless communication medium in a new
   location.  An example is provided in Figure 3, where each router is
   capable of reaching a different set of routers.

   The act of forwarding packets out of the same interface as the one
   over which they were received often results in duplicate IP packets
   being received at routers with more than one neighboring router,

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   while also reaching a new subset of nodes.

4.2.2.  Fuzzy Relationships Between Nearby MANET Routers & MANET Routers
        Extended Neighborhood

   Defining the process of determining neighboring MANET routers'
   existence, continued existence, and loss of existence is a
   fundamental challenge in MANETs.  Relationships with neighboring
   MANET routers are hard to define due to the expected interface
   characteristics: non-transitive, non-reflexive, time varying, and
   other wireless properties.

   Historically, two nodes are either neighbors or not neighbors and
   several simple mechanisms have been used to determine a neighbor
   relationship: single packet reception, acceptable loss rates, and
   simple handshakes.  In wireless networks the types of neighbor
   relationships expand, as do the mechanisms to detect and maintain the
   state of such relationships.

   In wireless networks, nodes may often have non-reflexive (also often
   seen called unidirectional) communication links.  Wireless networks
   also experience significant time varying packet delivery, so simple
   loss rates may not be sufficient to define a neighbor relationship.
   Similarly, as nodes move relatively to each other, past loss rates
   may not reflect future communication capabilities.

   In wireless systems, nodes within the same small geographic region
   are often densely connected with other nearby nodes.  These nodes
   form a set of extended neighbor relationships that is referred to as
   a neighborhood.  A neighborhood is typically composed of several
   nodes, with each node being densely connected to other nodes.

   These more dynamic neighbor relationships do not sit well with
   certain Internet Protocols designed assuming an fixed Ethernet like
   model to communication links (reflexive, transitive, and stable).
   Given the fuzzy neighbor relationships between MANET routers, the
   addressing model often associated with a Ethernet link is not valid.
   For example, in an Ethernet network routers are often told that a
   particular range of addresses are directly reachable.  In MANETs' a
   node often cannot make assumptions that a particular set of
   addressable nodes is always reachable.  Instead, nodes must detect
   and determine neighboring devices, and handle changes to this set
   over time.

4.2.3.  MANET Membership

   Given MANETs' characteristics (mobile, wireless, ad hoc), determining
   a MANETs' membership is difficult, if not impossible in certain

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      /----------------------\        /----------------------\
      |        MANET         |        |        MANET         |
      | +----+ +----+ +----+ |        | +----+ +----+ +----+ |
      | |MNR1+-+MNR2+-+MNR3| |        | |MNR1+-+MNR2+-+MNR3| |
      | +-+--+ +----+ +----+ |        | +----+ +----+ +-+--+ |
      |   |                  |        |                 |    |
      | +-+--+               | Change |               +-+--+ |
      | |MNR4|               |   in   |               |MNR7| |
      | +----+               |  Time  |               +----+ |
      |       \              |        \----------------------/
      |        +----+        |
      |        |MNR5|        |
      |        +----+        |        /----------------------\
      |       /      \       |        |        MANET         |
      | +----+        +----+ |        | +----+ +----+ +----+ |
      | |MNR6|        |MNR7| |        | |MNR6+-+MNR4+-+MNR5| |
      | +----+        +----+ |        | +----+ +----+ +----+ |
      \----------------------/        \----------------------/

                            Figure 4: MANET(s)

   At one moment a MANET might consist of a certain set of nodes, and
   the next the MANET could partition into several MANETs.  Later it
   might re-merge or merge with a new set of nodes and form a larger

   Certain routers in a MANET might connect to other routing regions.
   These routers are called Border Routers (BR), and they often run
   multiple routing protocol instances.  The BR are responsible for
   choosing the routing information to share between the various
   attached routing regions.  The BR should also present a consistent
   picture of the nodes reachable through them.

   As MANET membership changes, so does the connectivity of BR within
   the MANET.  Therefore, a BR may be challenged to present a consistent
   set of reachable nodes.  It may even choose not to share routing
   information about the MANET topology to other routing regions.

5.  Addressing & the MANET Prefix Model

   This section presents an architectural model for MANETs which
   preserves the integrity of the IP addressing architecture while
   allowing for the particularities of MANETs.

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5.1.  General Address Architecture

   This architectural model considers MANET routers as simply routers
   with nodes attached, as illustrated in Figure 5.  The attached nodes
   may be "external" (i.e. attached to the router via other network
   interfaces) or an internal addressable host logic (IAH) - however the
   important observation to make is, that the links between these
   entities and the router are classic IP links.  This fact implies
   that, from the point of view of these entities and the applications
   running on them, connectivity is via a classic IP link.  Therefore
   applications are not exposed to the specific characteristics of
   interfaces with asymmetric reachability or unknown address
   membership.  Hosts are connected to the MANET via a MANET router,
   which has one or more interfaces participating in MANET routing.

         <~~~~~~+~~~~~~>       MANET        <~~~~~~+~~~~~~>
                |            Interfaces            |
      ''''''''''|''''''''''              ''''''''''|''''''''''
      'MANET  +-|-+       '              '       +-|-+ MANET '
      'Router | R ................................ R | Router'
      '       +-+-+       '              '       +-+-+       '
      '         :  :      '              '         :  :      '
      '         :  +---+  '              '         :  +---+  '
      '         :  |IAH|  ' ============ '         :  |IAH|  '
      '         :  +---+  ' =    :     = '         :  +---+  '
      '''''''''':'''''''''' =Classic IP= '''''''''':''''''''''
         +......+......+    =Interfaces=    +......+......+
         :             :    ============    :             :
       +-+-+         +-+-+                +-+-+         +-+-+
       | N |  * * *  | N |                | N |  * * *  | N |
       +---+         +---+                +---+         +---+'

                     Figure 5: MANET Addressing Model

   A MANET router can be delegated zero or more prefixes.  If a MANET
   router is delegated a prefix p::, then prefixes derived from this
   prefix (p:1::, p:2::, ...) may be assigned to the MANET routers
   interfaces towards classic IP link(s), and nodes on these classic IP
   links may be assigned addresses from within this prefix, and
   configured with this prefix according to the address
   autoconfiguration mechanisms governing these links [RFC2461] and
   [RFC2462].  This concept is illustrated in Figure 6.

   Interface(s) with asymmetric reachability or unknown/indeterministic
   membership attached to the router are specifically *NOT* configured
   with this prefix.  The configuration of these MANET interfaces are

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   detailed in Section 5.2.

   If a MANET router via one of its interfaces is connected to a classic
   IP link, on which an existing prefix and address allocation entity is
   present, then this interface towards that classic IP link may be
   configured with addresses and prefixes from that classic IP link.
   This information may be in addition to or instead of configuring the
   MANET routers interface towards that classic IP link with a prefix
   derived from the prefix delegated to the MANET router.  A MANET
   routing protocol running on the MANET routers' MANET interface(s) may
   or may not include addresses and prefixes acquired on that MANET
   routers' interfaces towards classic IP links in its routing messages.
   The routing protocol configuration is administratively determined
   when deploying a MANET.

       MANET        <~~~~~~+~~~~~~>        Example
     Interface             |               Assigned
                 ''''''''''|''''''''''     Prefix
                 ' MANET +-|-+       '    =========
                 ' Router| R |       ' <=== P::   =
                 '       +-+-+       '    =========
                 '         :  :      '
                 '         :  +---+  '    =========
    ============ '         :  |IAH|  ' <=== P:1:: =
    =    :     = '         :  +---+  '    =========
    =Classic IP= '''''''''':''''''''''
    =Interfaces=           :
    ============           :              =========
                    +......+......+    <=== P:2:: =
                    :             :       =========
                  +-+-+         +-+-+
                  | N |  * * *  | N |
                  +---+         +---+
                  P:2::1       P:2::N

                    Figure 6: MANET Router and Prefixes

5.2.  MANET Interface Configuration

   MANET specific behaviors are exclusively exposed to the MANET
   interface(s) of the routers.  This behaviors may include asymmetric
   reachability, semi-broadcast interfaces, fuzzy MANET router neighbor
   relationships, unknown/indeterministic MANET membership, rapid
   topology dynamics, etc.

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   The following characteristics deserve particular mention, since they
   distinguish these MANET interface(s) and the MANET link model from
   the classic IP link model:

   Unique Prefixes
      MANET interfaces must be configured with unique prefixes.  The
      reason for this requirements is so that no two MANET interfaces
      are configured to appear within the same IP prefix, since node
      membership cannot be ensured.  Some common ways to achieve this

      *  unnumbered interfaces (IPv4) [RFC1812];

      *  link-local addresses (IPv6);

      *  /128 (IPv6) or /32 (IPv4) prefixes.

      It is worth noting that prefix lengths shorter than /128 (IPv6) or
      /32 (IPv4) are possible on the MANET interfaces, as long as the
      prefixes are unique to a single MANET interface.  Note that the
      above statement is not an exception, but simply a clarification
      that MANET are no different from other networks in this respect.

   Link-local Multicast/Broadcast Scope
      On a MANET interface, a packet sent to a link-local multicast or
      broadcast addresses reaches the interfaces of neighboring MANET
      routers, regardless of their configured addresses.  Link-local
      packets are never forwarded and since a MANET may span several
      hops, nodes cannot assume that a packet sent to a link-local
      address will reach all MANET routers within a MANET.

5.3.  Routers and Hosts in a MANET

   The MANET addressing model presented in this section makes a clear
   separation between the role of router and host in a MANET,
   recognizing that:

   o  MANET interfaces are seen only by the MANET aware router, assumed
      to be MANET aware, and running appropriate protocols;

   o  nodes and subnets on non-MANET interface(s) assume a classic IP
      link model;

   o  applications on hosts and protocols assuming classic IP interfaces
      run unmodified.

   MANET protocols are protocols which are developed to work on MANET
   interfaces and to be MANET-aware.  The MANET WG is chartered to

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   develop routing protocols for MANET interfaces.  The Autoconf WG is
   chartered to develop autoconfiguration protocols for MANET interfaces
   and MANET routers.

   Note that this addressing framework is similar to how routing in the
   existing Internet is structured.  Routers run their routing protocol
   over router interconnects with various characteristics to which only
   the routing protocols are privy.  On the other hand, hosts connect to
   the routers over classic IP interfaces with well-known

6.  MANETs' Place in the Network Stack

   While the MANET WG is focused on network (L3) routing, that does not
   imply that MANETs and their protocols are limited to L3.  Several
   previous and existing efforts are applying MANET protocols at various
   layers.  The challenges discussed above, exist independent of at
   which layer MANET protocols are deployed.  Of course, the protocols
   themselves may need to be retooled slightly to accommodate the
   information available to the deployed layer.

   MANET MAC layer (L2) routing, more often called bridging, may work in
   homogeneous wireless networks for delivering frames over multiple
   hops.  One example of L2 MANET is being developed in the IEEE 802.11s

   L2 routing/bridging hides the multiple L2 hops from L3.  This
   behavior can be advantageous as this network can transparently mimic
   an Ethernet, to some extent.  The ability to mimic Ethernet allows
   the L2 MANET to utilize existing L3 network protocols.  On the other
   hand, this transparency may lead to performance problems.  For
   example, if the L3 protocols make heavy use of broadcast messaging or
   if devices assume that high-speed wired bandwidth resources are

   L2 MANET does not enable heterogeneity.  That is, L2 MANET is not
   capable of bridging across heterogeneous interfaces.  For example, L2
   bridging cannot directly bridge two L2 technologies with different
   addressing schemes.  It can also be difficult if the frame sizes of
   two L2 vary, as this could require breaking a single frame into
   multiple frames of a different format.

   L3 MANET enables heterogeneous networking, as IP was built with this
   feature in mind.  Forming a MANET at L3 implies that the L3 protocols
   must handle the challenges presented in this document.

   MANET like protocols can also be used at higher layers.  One example

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   is peer-to-peer (P2P) networks.  These networks have some of the same
   challenges as MANET, e.g. variable neighbor relationships and
   changing membership.

7.  Cross Layering

   In wireless networks, and especially in MANET, extended interfacing
   among the network layers (physical, MAC, link, network, etc.) can be
   extremely useful.  Arguably, for MANET deployments to be successful,
   some degree of cross layering should be considered.  For example,
   link layer feedback that a packet/frame was not able to be sent or
   that it was not received could be used by the network layer to
   indicate that a neighboring MANET router is no longer reachable.
   This information and other extended interfacing could reduce, or
   eliminate, some upper layer messaging.  Further, it could
   significantly reduce the latency in decision making.  Note that
   though a certain lower layer information is valuable, it likely needs
   to be extrapolated or filtered before accurate assumptions about the
   network state can be made.  For example, failure to deliver a single
   frame by itself may not be a good indicator that a node is or is not

   In networks with several different layers of MANET mechanism, the
   sharing of information across different layers can be even more vital
   to creating and maintaining the network.  For example, if a P2P
   network is run on top of a L3 MANET, the two networks can share
   information to use a similar optimized topology, and neighboring
   MANET router state changes to reduce the messaging or the latency in
   making decisions.

8.  Deployment Taxonomy

   The present and future proliferation of inexpensive wireless
   interfaces continues to stimulate technical interest and developments
   in the area of MANET for a wide variety of deployment scenarios.  In
   this section, we present several characteristics for describing
   expected MANET deployments.

8.1.  Service Availability

   Nodes often expect certain services/servers to be available.  When
   describing a deployment scenario, it is important to specify the
   expected services available and the distance between the
   participating devices.  In MANET, nodes might assume a service is
   available locally (within one IP hop) or within a particular scope
   (one or more IP hops - MANET, site, global).  Nodes might assume in

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   certain deployments that no special servers/services are available.
   Finally, nodes might assume that servers are sometimes available, but
   their availability is not guaranteed or ensured.

   Different frameworks for autoconfiguration, network management, and
   intra-AS routing can be developed based upon the expected constraints
   and operating conditions.

8.2.  Number of MANET Routers in a MANET

   The number of peer MANET routers in a MANET is an important
   consideration.  This number is not the complete number of nodes in a
   MANET (since MANET routers may support an arbitrary number of
   connected nodes) but a measure of the number of MANET routers
   participating as a cohesive flat routing region.  That is, the number
   of MANET routers within a single routing region.

   While the number of peer MANET routers does not define scalability of
   a MANET protocol, it is often useful to discuss the number of peer
   MANET router to get a feel for maturity of typical deployment
   solutions.  For simplicity we define the following network sizes to
   aid in discussion:

      2-30 peer MANET routers

      30-100 peer MANET routers

      100-1000 peer MANET routers

   Very large
      Larger than 1000 peer MANET routers

   At the time of writing, small and moderate size peer MANET routing
   scenarios have matured and have reasonable testing and deployment
   experience.  These sizes can perform reasonably well in many cases
   without hierarchy.  MANET architectures can, of course, support
   routing hierarchies to improve scaling.  Large and very large MANET
   routing regions that are flat are still a topic of active research
   and are not considered here.  One can apply hierarchy to achieve
   scaling, but again that is not being discussed here.  Existing MANET
   routing developments, such as SMF [I-D.ietf-manet-smf], have shown
   significant performance improvements and capabilities even in small
   peer router size deployments and experiments using classical routing

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8.3.  Example Deployments

   Here we provide a short list of example deployment scenarios:

   Home, office, campus, and community mesh networks

   Disaster relief and first responder networks

   Sensor networks

   Range extension

   Military communications

   Automotive networks

9.  Security Considerations


10.  IANA Considerations

   This is an informational document.  IANA requirements for MANET
   related protocols will be developed within the protocol
   specifications for MANET protocols.

11.  Acknowledgments

   Discussions and developments concepts and architectural issues have
   evolved over many years of discussion of related work within the
   MANET WG.  There are obviously many people that have contributed to
   past discussions and related draft documents within the WG that have
   influenced the development of these concepts that deserve
   acknowledgment.  The authors would like to thank all contributors to
   the MANET and AUTOCONF WG efforts and those that have helped in the
   review and content process.

      While not entirely complete the authors would like to in
      particular thank the following individuals for there discussions
      and contributions:

      Jari Akko

      Emmanuel Baccelli

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      Alan Cullen

      Justin Dean

      Christopher Dearlove

      Tom Henderson

      Bob Hinden

      Thomas Narten

      Charles Perkins

      Subhranshu Singh

      Fred Templin

      Dave Thaler

      Seung Yi

12.  Informative References

   [DWN03]    Macker, J. and S. Corson, "Mobile Ad hoc Networking:
              Routing Technology for Dynamic, Wireless Networks", IEEE
              Press,  Mobile Ad hoc Networking, Chapter 9, 2003.

   [FL01]     Freebersyser, J. and B. Leiner, "A DoD perspective on
              mobile ad hoc networks", Addison Wesley C. E. Perkin, Ed.,
              2001, pp. 29--51, July 2001.

              Thaler, D., "Multilink Subnet Issues",
              draft-iab-multilink-subnet-issues-03 (work in progress),
              January 2007.

              Narten, T., "Neighbor Discovery for IP version 6 (IPv6)",
              draft-ietf-ipv6-2461bis-11 (work in progress), March 2007.

              Macker, J., "Simplified Multicast Forwarding for MANET",
              draft-ietf-manet-smf-04 (work in progress), March 2007.

              Templin, F., "MANET Autoconfiguration",

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              draft-templin-autoconf-dhcp-07 (work in progress),
              March 2007.

   [RFC1812]  Baker, F., "Requirements for IP Version 4 Routers",
              RFC 1812, June 1995.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC2453]  Malkin, G., "RIP Version 2", STD 56, RFC 2453,
              November 1998.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461,
              December 1998.

   [RFC2462]  Thomson, S. and T. Narten, "IPv6 Stateless Address
              Autoconfiguration", RFC 2462, December 1998.

   [RFC2501]  Corson, M. and J. Macker, "Mobile Ad hoc Networking
              (MANET): Routing Protocol Performance Issues and
              Evaluation Considerations", RFC 2501, January 1999.

   [RFC3513]  Hinden, R. and S. Deering, "Internet Protocol Version 6
              (IPv6) Addressing Architecture", RFC 3513, April 2003.

   [RFC3753]  Manner, J. and M. Kojo, "Mobility Related Terminology",
              RFC 3753, June 2004.

   [RFC4007]  Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
              B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
              March 2005.

Authors' Addresses

   Ian D Chakeres
   Bagmane Tech Park
   66/1, Plot 5, CV Raman Nagar
   Bangalore, Karnataka  560093

   Email: ian.chakeres@gmail.com
   URI:   http://www.ianchak.com/

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   Joe Macker
   Naval Research Laboratory
   Washington, DC  20375

   Email: macker@itd.nrl.navy.mil

   Thomas Heide Clausen
   LIX, Ecole Polytechnique
   91128 Palaiseau CEDEX

   Email: T.Clausen@computer.org
   URI:   http://www.thomasclausen.org/

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