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Versions: 00 01 02

Ad-Hoc Network Autoconfiguration                                 T. Boot
(Autoconf)                                             Infinity Networks
Internet-Draft                                                A. Holtzer
Intended status: Standards Track                                 TNO ICT
Expires: January 14, 2010                                  July 13, 2009


Border Router Discovery Protocol (BRDP) based Address Autoconfiguration
                    draft-boot-autoconf-brdp-02.txt

Status of this Memo

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Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   Mobile Ad hoc Networks (MANET) may be attached to a fixed
   infrastructure network, like the Internet.  This document specifies a
   mechanism for Border Router discovery and utilization in such a
   subordinate, possibly multi-homed, MANET.  It provides facilities for
   choosing preferred Border Router(s) and configuring IP address(es)
   needed for communication between MANET nodes and nodes on the
   Internet via the selected Border Router.  Autonomous MANETs do not
   have Border Routers; a self-sufficient Address Autoconfiguration
   mechanism for Autonomous MANETs is defined as well.


































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Protocol overview and functioning  . . . . . . . . . . . . . .  7
     3.1.  Border Router Discovery Protocol (BRDP)  . . . . . . . . .  7
     3.2.  BRDP-based Address Autoconfiguration . . . . . . . . . . .  7
     3.3.  Issues with Address Autoconfiguration in a MANET . . . . .  8
   4.  Border Router Discovery Protocol . . . . . . . . . . . . . . .  9
     4.1.  Border Router Information Option (BRIO)  . . . . . . . . .  9
       4.1.1.  BRIO Base option . . . . . . . . . . . . . . . . . . .  9
       4.1.2.  BRIO suboptions  . . . . . . . . . . . . . . . . . . . 12
     4.2.  BRDP processing  . . . . . . . . . . . . . . . . . . . . . 13
       4.2.1.  BRDP message generation and transmission . . . . . . . 13
       4.2.2.  BRDP message reception . . . . . . . . . . . . . . . . 15
       4.2.3.  BRIO-Cache maintenance . . . . . . . . . . . . . . . . 16
       4.2.4.  BRDP loop prevention . . . . . . . . . . . . . . . . . 17
     4.3.  Unified Path Metric (UPM)  . . . . . . . . . . . . . . . . 18
   5.  BRDP-based Address Autoconfiguration . . . . . . . . . . . . . 20
     5.1.  Border Router selection  . . . . . . . . . . . . . . . . . 20
       5.1.1.  Border Router Selection based on UPM . . . . . . . . . 20
       5.1.2.  Border Router Selection based on BRIO flags and
               options  . . . . . . . . . . . . . . . . . . . . . . . 21
     5.2.  MANET address generation and configuration . . . . . . . . 21
     5.3.  Support for Autonomous MANETs  . . . . . . . . . . . . . . 22
   6.  Support for IPv4 . . . . . . . . . . . . . . . . . . . . . . . 23
   7.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 23
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 24
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     10.1. Normative reference  . . . . . . . . . . . . . . . . . . . 24
     10.2. Informative Reference  . . . . . . . . . . . . . . . . . . 24
   Appendix A.  Change Log From Previous Versions . . . . . . . . . . 26
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26

















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1.  Introduction

   This document describes a complete solution for configuring globally
   routable and/or unique local IPv6 addresses for ad hoc network nodes.

   The new Border Router Discovery Protocol (BRDP) is defined for Border
   Router discovery.  Existing IETF mechanisms can be used for address
   generation, but may use BRDP provided information as an enhancement.
   BRDP provided information may also be used for other purposes, such
   as source address selection [RFC3484].

   The Address Autoconfiguration solution for subordinate MANETs uses
   two phases:

   o  Discovery of one or more Border Routers

   o  Selection of a Border Router and Address Autoconfiguration of
      globally routable IPv6 addresses to be used in conjunction with
      that Border Router

   In case of an Autonomous MANET no Border Routers have to be
   discovered.  In that case Unique Local Addresses [RFC4193] are
   generated by individual MANET routers.

   BRDP is a simple distance vector protocol that distributes Border
   Router information, where each MANET Router selects one or more
   Border Routers and forwards the Border Router information in the
   MANET.  It extends the IPv6 Neighbor Discovery Protocol (NDP)
   [RFC4861] to make it carry information, such as prefix information
   and metrics which help a MANET Router to select a Border Router and
   to help to configure globally unique addresses for communication with
   nodes on the Internet.

   Address uniqueness is assured by the IPv6 address generation
   mechanisms used.  Additional mechanisms may be used, such as
   Duplicate Address Detection.  However, in a MANET the overhead of
   performing Duplicate Address Detection can easily outweigh the
   benefits.  For such a case, [RFC4862] specifies that Duplicate
   Address Detection can be disabled.

   Additional mechanisms may be used for solving problems with ingress
   filtering, which occur when traffic is sent to the Internet via a
   border router that doesn't correspond with the source address of the
   packets.  In a multi-homed MANET, the probability of such a problem
   to occur is highly increased due to mobility.  This problem can be
   solved by using BRDP based routing [I-D.boot-brdp-based-routing] in
   which the routing mechanism assures traffic to the Internet is
   forwarded to the Border Router that corresponds with the source



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   address of the packets.


















































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2.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Readers are expected to be familiar with all the terms defined
   "Mobility Related Terminology" [RFC3753], "Mobile Ad hoc Network
   Architecture" [I-D.ietf-autoconf-manetarch] and "Address
   Autoconfiguration for MANET: Terminology and Problem Statement"
   [I-D.ietf-autoconf-statement].


   Border Router
      MANET Router that connects the MANET to the Internet

   BRDP
      Border Router Discovery Protocol

   BRIO
      Border Router Information Option

   BRIO-Cache
      Table, populated with information on discovered Border Routers,
      learned through received or initiated Border Router Information
      Options

   MANET
      A routing domain containing MANET routers
      [I-D.ietf-autoconf-manetarch]

   Subordinate MANET
      a MANET, connected to the Internet

   Autonomous MANET
      a MANET, not connected to the Internet

   MANET Generated Address
      Globally unique and topologically correct IPv6 address generated
      to enable connectivity between nodes in the MANET and
      Corresponding Nodes on the Internet via a Border Router

   UPM
      Uniform Path Metric







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3.  Protocol overview and functioning

   In this section, the subcomponents of BRDP-based Address
   Autoconfiguration are briefly introduced.

3.1.  Border Router Discovery Protocol (BRDP)

   BRDP is a simple distance vector protocol that distributes Border
   Router information, where each MANET Router selects one or more
   Border Routers and forwards the Border Router information in the
   MANET.  It extends the IPv6 Neighbor Discovery Protocol (NDP)
   [RFC4861] to make it carry information and metrics which help a MANET
   Router to generate and configure globally unique addresses for
   communication with nodes on the Internet.

   BRDP is a derivative of Tree Discovery [I-D.thubert-tree-discovery].
   It suits the Autoconf Working Group Charter and is particularly
   designed for Address Autoconfiguration in subordinate, possibly
   multi-homed, Mobile Ad hoc Networks.

   BRDP uses ICMP Router Advertisement (RA) messages in NDP to
   distribute Border Router information by extending it with the Border
   Router Information Option (BRIO).  BRDP allows MANET Routers to
   advertise Border Router reachability, including information for
   selecting a preferred Border Router.  A MANET Router selects at least
   one BRIO from its cache, for dissemination in the MANET.

   BRIOs are distributed hop by hop from a Border Router downwards in
   the MANET using a tree structure.  The presence of multiple Border
   Routers results in multiple, potentially overlapping logical trees,
   i.e. a Directed Acyclic Graph (DAG).

   The amount of flooding of BRDP messages MAY be reduced.  A MANET
   Router MAY filter BRIOs, based on the Unified Path Metric (UPM).  The
   UPM is the advertized bidirectional distance to the Internet Default
   Free Zone (DFZ), via that Border Router.

   BRDP MAY carry more detailed information of the Border Router, such
   as a provider name and AAA options.  AAA enables access network
   providers to control access to their network.  MANET Routers MAY
   select a Border Router based on preferences for a provider.

3.2.  BRDP-based Address Autoconfiguration

   BRDP provides prefix information to configure MANET Generated
   Addresses.  The prefix information is sent in the BRIO in the form of
   the Border Router address and the prefix length.  A MANET Generated
   Address is a globally unique and topologically correct IPv6 address



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   generated to enable connectivity between nodes in the MANET and
   Corresponding Nodes on the Internet via a Border Router.

   The nodes using BRDP-based Address Autoconfiguration MUST implement a
   mechanism to generate a unique 64-bit Interface Identifier.  An
   extremely high probability of uniqueness can be achieved by using
   Modified EUI-64 format-based Interface Identifiers [RFC4291] or by
   generating these identifiers randomly [RFC4941] or by means of a
   well-distributed hash function [RFC3972].

   The generated Interface Identifier is combined with a 64-bit prefix,
   which is provided by BRDP, thus forming a topologically correct
   address.

   In this document, it is assumed the MANET is connected to the
   Internet and globally unique addresses are used.  Border Routers MUST
   have a globally unique and reachable 64-bit prefix.  The mechanisms
   described in this document are compatible with private networks and
   usage of Unique Local Addresses [RFC4193].  An implementation MAY
   provide configuration options for Border Router selection based on
   offered global prefixes or unique local prefixes, in cases where both
   types are used in the same MANET.

3.3.  Issues with Address Autoconfiguration in a MANET

   After Address Autoconfiguration, additional mechanism(s) would be
   needed to enable usage of the correct Border Router and to enable
   session continuity.  This document does not prescribe any solutions
   for this purpose.  Usage of the correct Border Router is provided by
   BRDP Based Routing [I-D.boot-brdp-based-routing] and session
   continuity can be arranged with Mobility Support in IPv6 [RFC3775],
   NEMO basic support [RFC3963] or Shim6 [RFC5533].



















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4.  Border Router Discovery Protocol

   This section explains the details of the BRDP protocol.  Topics are
   the Border Router Information Option (BRIO), the generation,
   transmission, forwarding and reception of BRIOs and BRIO cache
   maintenance.

4.1.  Border Router Information Option (BRIO)

   The Border Router Information Option carries information that allows
   a MANET Router to select and utilize a Border Router.

4.1.1.  BRIO Base option

   The BRIO is a container option, which MAY contain a number of
   suboptions.  The BRIO base option groups the minimum information set
   that is mandatory in all cases.


      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     | Prefix Length |A|F|E|L|S|D| r |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Sequence Number        |   Hopcount    |   reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Uniform Path Metric                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            reserved                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                    Border Router Address                      +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   sub-option(s)...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+


                        Figure 1: BRIO base option

   Fields:






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   Type:

      8-bit identifier of the Border Router Information Option type.
      The value of this option identifier is to be determined.

   Length:

      8-bit unsigned integer.  The length of the option (including the
      type and length fields) in units of 8 octets.  A BRIO without
      suboptions has a length value of 4.

   Prefix Length:

      8-bit unsigned integer.  The number of leading bits in the Border
      Router Address, that indicates the assigned prefix for that Border
      Router.  The Prefix Length is used for BRDP Based Routing
      [I-D.boot-brdp-based-routing].

   AAA(A):

      Flag indicating whether the Border Router requires authentication,
      authorization and accounting.  When set, a Service Selection
      suboption immediately follows the BRIO base option.  This document
      only describes BRIO forwarding rules considering the A-flag and
      Service Selection suboption.  Details on performing AAA are out-
      of-scope for this document.

   Floating(F):

      When the F-flag is set, the Border Router has lost contact with
      the Internet.  MANET Routers SHOULD stop using MANET generated
      source addresses based on the prefix of a Border Router that
      indicates that it is floating.

   Emergency Response Services(E):

      When the E-flag is set, the Border Router provides support for
      emergency response services.  Details on applications for
      emergency response services are out-of-scope for this document.
      The E-flag contributes to the distribution of BRIOs in the MANET
      in the BRIO selection mechanism.  Access to emergency response
      services SHOULD be enabled for all MANET nodes.

   Loop-prone(L):







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      When the L-flag is set, an upstream MANET Router cannot guarantee
      a loop-free path to the Border Router advertized in this BRIO.

   Solicitation Response(S):

      When the S-flag is set, the Border Router requests forwarding of
      the BRIO downstream the BRIO forwarding tree as a response to a
      special Router Solicitation.  This provides a mechanism to speed
      up convergence, requested by a downstream MANET Router.

   DHCP (D):

      When the D-flag is set, the Border Router is acting as a DHCP
      server or DHCP relay agent [RFC3315].

   r, reserved:

      Reserved bits.  Currently unused, set to 0.

   Sequence Number:

      16-bit unsigned integer.  It is set by the Border Router and
      incremented with each new BRIO it sends on a link.  The sequence
      number is propagated without change down the tree.

   Hopcount:

      8-bit field registering the number of hops from the advertizing
      MANET Router to the Border Router.  Border Routers send an
      original BRIO with its Hopcount set to zero.  MANET Routers
      increment the Hopcount by one when forwarding a BRIO.

   Uniform Path Metric (UPM):

      A measure for the quality of the bi-directional path between the
      MANET Router and the Default Free Zone of the Internet.  Uniform
      Path Metric is set to some initial value by the Border Router and
      is incremented by each MANET Router forwarding the BRIO.

   Border Router Address:

      128-bit address of the Border Router.  The Border Router is
      expected to add its own address as a /128 prefix in the MANET
      routing system.






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4.1.2.  BRIO suboptions

   In addition to the BRIO Base option, a number of suboptions are
   defined.  Suboptions MAY have alignment requirements.

4.1.2.1.  Pad suboption

   The Pad suboption format is as follows:


                             0
                             0 1 2 3 4 5 6 7
                             +-+-+-+-+-+-+-+-+
                             |   Type = 0    |
                             +-+-+-+-+-+-+-+-+


                          Figure 2: Pad suboption

   Fields:


   Type = 0

      8-bit identifier of the Pad suboption type.  The option identifier
      is determined as 0.

   The format of the Pad suboption has neither an suboption length nor
   suboption data fields.  The Pad suboption is used to insert one octet
   of padding in the BRIO to enable alignment, either between suboptions
   or for the whole suboption container.

4.1.2.2.  Service Selection suboption

   Each BRIO MAY have a single Service Selection suboption, identifying
   the Service Provider and/or the provided service offered by the
   Border Router.  The Service Selection suboption MUST be the first
   BRIO suboption.

   The Service Selection suboption is equivalent to the Service
   Selection Mobility Option defined in "Service Selection for Mobile
   IPv6" [RFC5149].









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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Type = 1     |   Length      | Identifier...                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 3: Service Selection suboption

   Fields:


   Type = 1

      8-bit identifier of the Service Selection suboption type.  The
      suboption identifier is determined as 1.

   Length:

      8-bit unsigned integer.  The length represents the length of the
      Service Selection Identifier in octets, excluding the suboption
      type and length fields.  Usage of the Length field is equivalent
      to [RFC5149].

   Identifier:

      A variable length UTF-8 encoded Service Selection Identifier
      string used to identify the Border Router service provider and
      optionally the type of service.  Valid examples are 'ims', 'voip'
      and 'voip.companyxyz.example.com'.

   A Border Router MAY offer multiple services using multiple BRIOs.
   However, each of those BRIOs MUST use a unique Border Router address.

4.2.  BRDP processing

   The main BRDP processing functions of a MANET Router are BRDP message
   generation, transmission and reception and the maintenance of a BRIO-
   Cache.  MANET Routers forward BRDP messages using ICMP ND Router
   Advertisements.

4.2.1.  BRDP message generation and transmission

   A BRDP message is part of a Router Advertisement and includes a set
   of BRIOs.  It provides the current state of paths to the Border
   Routers listed in the set of BRIOs.  BRIOs originate from a Border



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   Router, and contain initially metric information on connectivity to
   the Internet.  BRIOs are forwarded downwards in the MANET.

   When a MANET Router sends a ICMP ND Router Advertisement, it SHOULD
   include a set of BRIOs by appending them to the message.  The maximum
   number of BRIOs in a single BRDP message is a MANET Router
   configuration parameter.  BRIO selection for advertisement is done
   based on the information stored in the BRIO-Cache.  As a minimum, the
   following rules apply to a MANET Router selecting BRIOs for
   advertisement:

   o  BRIOs with the L-flag set SHOULD NOT be selected.

   o  BRIOs that do not pass the loop prevention check described in
      Section 4.2.4 SHOULD NOT be selected.

   o  At minimum, one BRIO with the E-flag set MUST be selected, when
      such an entry exists in the BRIO-Cache.

   o  BRIO selection SHOULD select a number of BRIOs with distinct
      Service Selection Identifiers.  The BRIO selection mechanism MAY
      use a preference scheme selecting and filtering Service Selection
      Identifiers.

   The UPM and Hopcount fields of the advertised BRIOs are updated.  An
   UPM-increment, based on uniformized bi-directional link metrics, is
   added to the UPM and the Hopcount is incremented by 1.  UPM-increment
   MAY be governed by a hysteresis and dampening mechanism.  Also
   forecasted information MAY be used.

   Each BRIO originating from a Border Router has an increased Sequence
   Number.  This BRIO is forwarded in the MANET and refreshes entries in
   BRIO-Caches of downstream MANET Routers.

   Router Advertisements are sent in response to Router Solicitation
   messages or unsolicited with a uniformly-distributed random interval
   between MinRtrAdvInterval and MaxRtrAdvInterval [RFC4861].  The
   MaxRtrAdvInterval falls between a minimum of 30 milliseconds,
   specified in [RFC3775] and a maximum of 1800 seconds, specified in
   [RFC4861].  In addition, the MANET Router MAY send a Router
   Advertisement when an important change in a to be sent BRIO would
   occur.

   When a MANET Router sends Router Advertisements more frequently than
   an upstream MANET Router, this MANET Router MAY repeatedly send BRIOs
   with a constant Sequence Number but with an updated UPM or Hopcount.

   The ICMP ND Router Advertisement SHOULD include the Advertisement



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   Interval Option [RFC3775].  This option contains the interval at
   which the sending router sends unsolicited multicast Router
   Advertisements.

   The Border Router MAY request that the sent BRIO SHOULD be forwarded
   instantly downstream in the MANET, by setting the S-flag.

   A MANET Router SHOULD inform downstream MANET Routers in case the
   path to a previous advertized Border Router is lost, by at least 3
   times retransmitting the previously sent BRIO with a UPM value of
   4294967295.  When an alternative BRIO for the same Service Selection
   Identifier is available, this BRIO SHOULD be advertised, for
   continued connectivity to this Service.

   In case a Border Router loses its connection to the infrastructure it
   will lose its Border Router functionality and become a normal MANET
   Router.  In that case it performs the same procedure as a MANET
   Router that has lost the path to a previous advertised Border Router.
   In addition, it sets the F-flag.

   For each Border Router listed in the BRIO-Cache, the UPM-loop-
   prevention-threshold and the Hopcount-loop-prevention-threshold
   variables are maintained.  These variables are used by the loop
   prevention mechanism described in Section 4.2.4.  The thresholds are
   set or updated when sending BRDP messages.  When sending a BRIO with
   a higher Sequence Number than the previously sent BRIO for that
   Border Router, the threshold variables are set to the UPM and
   Hopcount values in BRIO to be sent.  When sending a BRIO with the
   same Sequence Number as the previously sent BRIO, the loop-
   prevention-thresholds are independently updated if either the UPM or
   Hopcount of the outgoing BRIO is lower than their thresholds.

   A MANET Router that detects an attractive candidate BRIO but is
   prohibited from using it because of the loop prevention check, MAY
   send a special Router Solicitation message to the Border Router.  The
   Border Router responds to such a Router Solicitation message with a
   BRIO with the S-flag set.  Sending Router Solicitations MUST be rate
   limited.  A next version of this document would include a
   specification for the special Router Solicitation message.

4.2.2.  BRDP message reception

   When a BRDP message is received, the Sequence Number fields of the
   contained BRIOs are checked; the Sequence Number of a received BRIO
   MUST be equal to or higher than the Sequence Number in the cache for
   an existing entry in the cache, with wrap-around checking.
   Otherwise, the BRIO will be discarded.




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   BRIO messages do not need to be forwarded at fixed time intervals,
   because the RA intervals on different MANET Routers are not
   synchronized.  Therefore, large gaps in Sequence Numbers may occur.
   Increment values between 0 and 65000 are accepted.  Increment values
   between 65001 and 65535 are rejected.

   Information in received BRIOs is stored in a BRIO-Cache table.  Other
   information is stored as well, such as the BRIO sender, a timestamp
   indicating when the most recent message was received and the measured
   or signaled RA interval.

4.2.3.  BRIO-Cache maintenance

   Each MANET Router maintains a BRIO-Cache that stores all information
   on Border Routers.  Unique cache entries are maintained on (Border
   Router Address, address of the neighbor router that forwarded the
   BRIO) tuples.  This information is obtained by receiving BRIOs or, in
   case of a Border Router, by getting information from the interface
   that connects to the Internet.  The BRIO-Cache also maintains context
   information for the BRIO such as the BRIO sender, link metrics and
   UPM-increment for this sender, history, statistics and status
   information.  History information includes a timestamp indicating
   when the most recent message was received and a measured or signaled
   RA interval.  Status information includes the BRIO selection outcome
   for BRIO forwarding as explained in Section 4.2.1 and the Border
   Router selected for address generation as explained in Section 5.1.

   BRIO entries in the BRIO-Cache stay valid for a certain period of
   time.  During this period, they can be used for Border Router
   selection by the MANET Router, for forwarding BRIOs and for address
   generation.  BRIO-Cache information could also be useful for source
   address selection [RFC3484].  The lifetime of a BRIO is determined by
   using the timing information sent along with the RA ([RFC3775],
   section 7.3) or statistics of received BRIOs.

   Some values in the BRIO-Cache can be updated independent of incoming
   BRDP messages.  A MANET Router MAY update the UPM-increment based on
   link quality measurements performed in an environment with changing
   link metrics.  A MANET Router SHOULD indicate in its BRIO-Cache which
   BRIO entries are currently selected for forwarding and for address
   generation.  Border Router Selection MAY take place after the UPM of
   a BRIO entry has been updated.

   In case the link to the MANET Router from which a BRIO has been
   received is broken, the UPM and the Hopcount of the BRIO entry in the
   cache are set to the maximum value, i.e. 4294967295 and 255.

   A cache cleanup routine SHOULD run at regular intervals to get rid of



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   stale entries.  Stale entries are removed when the entry is not
   updated for 5400 seconds or all of the following conditions are met:

   o  The stale entry is not used by the MANET Router itself for address
      generation.

   o  The stale entry was not selected for forwarding in the last three
      Router Advertisement.

   o  The stale entry was not recently updated by a received BRIO.  In
      this context, recently is defined as the maximum of a) three times
      its own unsolicited multicast Router Advertisements interval and
      b) three times the senders unsolicited multicast Router
      Advertisements interval.

   Cache entries MAY also be removed, under the condition that the BRIO-
   Cache has reached a configured maximum number of entries and a new,
   to be stored BRIO is received.  A removal candidate is selected based
   on:

   o  The candidate entry is not used by the MANET Router itself.

   o  The candidate entry was not selected for forwarding in the last
      Router Advertisement.

   o  The candidate entry is redundant; other information for the same
      Border Router is stored in the cache with a better UPM and / or
      was received more recently.

   o  The candidate entry is redundant; other information for the same
      Service Selection Identifier is stored in the cache with a better
      UPM and / or was received more recently.

   o  The candidate entry is less attractive; other Border Routers are
      stored in the cache with better UPM and / or were received more
      recently.

4.2.4.  BRDP loop prevention

   A BRDP loop check mechanism prevents that a MANET Router forwards an
   earlier advertized BRIO.

   BRDP loop-free operation is guaranteed as long as at least one of the
   following conditions is true:

   o  The to be sent BRIO has a higher Sequence Number than a BRIO for
      this Border Router that was sent before.  The loop check mechanism
      uses wrap-around logic.  Increments up to 32768 are acceptable



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      (wrap-around logic needs checking).

   o  The to be sent BRIO is generated from the same BRIO-Cache entry as
      the BRIO that was sent most recently.

   o  The to be sent BRIO has the same Sequence Number as the BRIO for
      this Border Router that was sent before but the BRIO-Cache entry
      UPM is equal to or lower than the UPM-loop-prevention-threshold
      for this Border Router.

   o  The to be sent BRIO has the same Sequence Number as the BRIO for
      this Border Router that was sent before but the BRIO-Cache entry
      Hopcount is equal to or lower than the Hopcount-loop-prevention-
      threshold for this Border Router.

   In some circumstances, a MANET Router MAY select a BRIO for
   forwarding that fails the loop prevention check or with the L-flag
   set.  For example, the link to the upstream neighbor is lost and an
   alternative path is available, with a higher UPM and a higher
   Hopcount or with a lower Sequence Number.  The MANET Router cannot
   assure this candidate BRIO is not reflecting its own advertized
   message, but it could be better sending this BRIO than sending
   nothing or repeatedly sending a BRIO with a maximum UPM and Hopcount
   value.  When a MANET Router forwards a BRIO that failed the loop
   prevention check, the L-flag MUST be set.  A looped BRIO results in a
   Hopcount counting to infinity.

4.3.  Unified Path Metric (UPM)

   Unified Path Metric (UPM) is a measure for the quality of the path
   between the MANET Router and the Internet Default Free Zone.  It is a
   united metric for both inbound and outbound paths.  On each hop, the
   UPM is incremented with an UPM-increment, which is derived from the
   routing protocol and / or is obtained from lower layers.

   It is on forehand not known what is more important; Border Router
   selection based on path metric to the Border Router or the path
   metric for the reverse path.  In BRDP, UPM is used for optimizing
   Border Router selection for both the inbound and the outbound
   traffic.  Note that actual traffic will use the path provided by the
   routing protocols, not by BRDP.

   Since the UPM uses 32 bits, its maximum value is 4294967295.  On each
   hop, an UPM-increment is calculated for each MANET Router from which
   a BRIO has been received.  UPM-increments have a value between 1 and
   16777215.

   Further discussion on metrics and how the UPM-increment value is



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   determined is outside the scope of this document.


















































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5.  BRDP-based Address Autoconfiguration

5.1.  Border Router selection

   When a MANET Router needs to communicate to nodes on the Internet, it
   MUST select a set of Border Routers for address generation.  A MANET
   Router MAY generate multiple addresses for smooth handover
   implementing make-before-break or distributing traffic over multiple
   Border Routers.  A description how Border Routers can be used
   concurrently is out-of-scope for this document.

   Information concerning available Border Routers is kept in the BRIO-
   Cache.

   The Border Router selection mechanism MAY be triggered by received
   BRDP messages, changes in metrics on links to neighbors advertising
   BRDP messages, changes in MANET metrics to Border Routers used or on
   a time-driven basis.

   The Border Router selection algorithm SHOULD be based on Service
   Selection Identifiers (if available) and UPM.  UPM is used for
   selecting the Border Router with the best connectivity to the
   Internet.  However, such a Border Router MAY require authorization.
   The A-flag and the Service Selection Identifier provide the prime
   information for selecting a preferred provider or preferred service.
   The Border Router selection algorithm MAY be extended with any other
   information.  Future defined BRIO suboptions could provide additional
   information.  Border Router selection MAY be based on the type of the
   Border Router Address, e.g. a globally unique address or a unique
   local address.

   Border Router selection does not select a routing path to the Border
   Router.

5.1.1.  Border Router Selection based on UPM

   Assuming authentication requirements (if any) are satisfied, the
   MANET Router uses the UPM for Border Router selection preferring the
   best bi-directional path between the MANET Router and the Internet.
   Note that the BRIO UPM includes the initial metric set by the Border
   Router and is not solely a metric between the MANET Router and the
   Border Router.  The initial metric set by Border Routers can be used
   for Border Router preference and for load balancing.

   In order to use an up-to-date UPM in the selection procedure the UPM-
   increment is calculated by the MANET Router before selecting a Border
   Router.  UPM is discussed in Section 4.3.




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5.1.2.  Border Router Selection based on BRIO flags and options

   Some BRIO flags MUST and some flags MAY assist in Border Router
   selection.

   o  The A-flag and the Service Selection Identifier provide the prime
      information for selecting a preferred provider or preferred
      service.  Details on authentication and authorization to the
      Border Router are out-of-scope of this document.

   o  A (previous) Border Router could indicate that it is not connected
      to the Internet anymore, signaled with the F-flag.  Usage of this
      Border Router SHOULD be avoided.

   o  For emergency response applications, a Border Router providing
      such services, indicated by the E-flag, SHOULD be selected.

   o  The guarantee for a loop-free path to a Border Router can
      temporary be withdrawn, indicated by the L-flag set.  Usage of
      this Border Router SHOULD be avoided.

   The Border Router selection algorithm could be extended with using
   future defined BRIO suboptions or other information.

5.2.  MANET address generation and configuration

   The MANET Router MUST use a topologically correct address when
   communicating with corresponding nodes on the Internet.
   Topologically correct addresses SHOULD be generated for each Border
   Router used.

   A MANET Generated Address has a /128 prefix.  It is constructed from
   a 64-bit Interface Identifier and a 64-bit prefix from the Border
   Router Address.  A 64-bit prefix length from the Border Router is
   used since for a 64-bit Interface Identifier the use of a 64-bit
   prefix for Stateless Address Autoconfiguration (SLAAC) is prescribed
   in [RFC2464].  The generated 128-bit address SHOULD be advertised in
   the MANET routing system.  The MANET Generated Address MAY also be
   used for other traffic, either inside the MANET or towards the
   Internet.

   For the Interface Identifier used, the BRDP-based MANET Address
   Generation MUST implement a mechanism for generating a unique
   Interface Identifier.  Known mechanisms are:

   o  Modified EUI-64 format-based Interface Identifier, [RFC4291],
      based on IEEE 802 48-bit MAC address or IEEE EUI-64 identifier.
      However, this method does not guarantee identifiers are unique as



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      duplicate MAC addresses can occur.

   o  Generation of randomized Interface Identifiers, [RFC4941].

   o  Well-distributed hash function, [RFC3972].

   After MANET Address Generation, RFC4429 Optimistic Duplicate Address
   Detection [RFC4429] MAY be used, if one thinks the benefit outweigh
   the overhead.  A passive Duplicate Address Detection could be used as
   an alternative.  Still, uniqueness is not fully guaranteed.  Main
   reasons for non-uniqueness are merging of MANET segments, node
   movement, node misbehavior or address spoofing attacks.  Details on
   handling a duplicate address condition are out-of-scope for this
   document.

   Address generation for globally unique addresses and unique local
   addresses [RFC4193] is similar.  Nodes SHOULD NOT use unique local
   addresses to communicate with a Border Router with a globally unique
   address.  Nodes SHOULD NOT use globally unique addresses to
   communicate with a Border Router with a unique local address.

   A MANET Generated Addresses clean-up routine SHOULD run at regular
   intervals to get rid of stale addresses.

   When a node has selected a Border Router for which the D-flag is set,
   it MAY use DHCP [RFC3315] for configuration parameters or prefix
   delegation [RFC3633].  DHCP processing makes use of co-located DHCP
   Client and DHCP Relay functions and is unicast only.  DHCP is not
   used for address configuration, since it could introduce a lot of
   overhead in a MANET.

5.3.  Support for Autonomous MANETs

   Autonomous MANETs do not have Border Routers, and MANET Routers will
   have empty BRIO-Caches.  No 64-bit prefixes from the Border Router
   Addresses are available, and globally unique IPv6 addresses cannot be
   generated.  For communication within the MANET, a MANET Router MAY
   generate an address using a self-generated unique local addresses
   [RFC4193] /64 prefix.  Alternatively some mechanism could provide
   already in-use /64 unique local prefix(es) in the MANET, these
   prefixes MAY be used as well.










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6.  Support for IPv4

   BRDP-based Address Autoconfiguration is currently designed for IP
   version 6.  The used mechanism for address generation extends the
   functionality specified in "IPv6 Stateless Address Autoconfiguration"
   [RFC4862].  Because of certain scenarios where IPv4 and IPv6 coexist
   in a network, BRDP support for IPv4 is currently under consideration.


7.  IANA considerations

   The IANA is requested to define a new IPv6 Neighbor Discovery option
   for the Border Router Information Option, defined in this document.


          +------+----------------------------------+-----------+
          | Type | Description                      | Reference |
          +------+----------------------------------+-----------+
          | TBA  | Border Router Information Option | [RFCXXXX] |
          +------+----------------------------------+-----------+


                      Figure 4: IANA BRIO assignment

   The registry for these options can be found at:
   http://www.iana.org/assignments/icmpv6-parameters

   The IANA is requested to create a new registration for BRIO
   suboptions.


8.  Security Considerations

   BRDP-based Address Autoconfiguration inherits security considerations
   from MANET technology.  Since it is a new mechanism based on ND it
   inherits security considerations from ND.

   Traffic anonymity and traffic flow confidentiality are important
   issues in MANET communications.  Considerations related to traffic
   flows should be discussed in context with the mechanisms that are
   chosen to perform path setup, routing and session continuity and are
   therefore not covered by this document.

   A more detailed description on Address Autoconfiguration security
   considerations is to be included in a next version of this document.






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9.  Acknowledgments

   The authors want to thank anyone involved in IETF on MANET and NEMO
   technology for their efforts on mobile network infrastructures.
   Special thanks to Pascal Thubert, Thomas Clausen and Ryuji Wakikawa
   for their efforts in defining MANEMO technology, which inspired the
   authors to compose this document.  Also special thanks to Ronald in
   't Velt for reviewing.


10.  References

10.1.  Normative reference

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

10.2.  Informative Reference

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

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

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",



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              RFC 3963, January 2005.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
              for IPv6", RFC 4429, April 2006.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, September 2007.

   [RFC5149]  Korhonen, J., Nilsson, U., and V. Devarapalli, "Service
              Selection for Mobile IPv6", RFC 5149, February 2008.

   [RFC5533]  Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
              Shim Protocol for IPv6", RFC 5533, June 2009.

   [I-D.ietf-autoconf-statement]
              Baccelli, E., Mase, K., Ruffino, S., and S. Singh,
              "Address Autoconfiguration for MANET: Terminology and
              Problem Statement", draft-ietf-autoconf-statement-04 (work
              in progress), February 2008.

   [I-D.ietf-autoconf-manetarch]
              Chakeres, I., Macker, J., and T. Clausen, "Mobile Ad hoc
              Network Architecture", draft-ietf-autoconf-manetarch-07
              (work in progress), November 2007.

   [I-D.boot-brdp-based-routing]
              Boot, T., "Border Router Discovery Protocol (BRDP) Based
              Routing", draft-boot-brdp-based-routing-00 (work in
              progress), November 2008.

   [I-D.thubert-tree-discovery]
              Thubert, P., "Nested Nemo Tree Discovery",
              draft-thubert-tree-discovery-08 (work in progress),
              June 2009.







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Appendix A.  Change Log From Previous Versions


   00:
      Initial Document.

   Changes from -00 to -01:
      Added fields in BRIO: D-flag, Prefix Length
      Added section on DHCP for obtaining configuration parameters
      Added section on autonomous MANETs
      Removed section about path setup, routing and session continuity

   Changes from -01 to -02:
      Made several changes to the text throughout the document, mainly
      for clarification.


Authors' Addresses

   Teco Boot
   Infinity Networks B.V.
   Elperstraat 4
   Schoonloo  9443TL
   The Netherlands

   Email: teco@inf-net.nl


   Arjen Holtzer
   TNO Information and Communication Technology
   Brassersplein 2
   Delft  2612CT
   The Netherlands

   Email: arjen.holtzer@tno.nl
















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