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Network Mobility                                             T. Kniveton
Internet-Draft                                                     Nokia
Expires: January 18, 2006                                     P. Thubert
                                                                   Cisco
                                                           July 17, 2005


                    Mobile Network Prefix Delegation
                draft-kniveton-nemo-prefix-delegation-01

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on January 18, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This paper extends the Nemo Basic Support [10] for a Mobile Router to
   synchronize its Mobile Network Prefixes with its Home Agents and
   obtain new ones dynamically.  The proposed prefix delegation
   mechanism is agnostic to the way the prefixes are managed and
   provisioned at the Home Agent; it might be used for bootstrapping,
   resynchronization at binding creation or after a loss of states (eg
   MR reboot), MNP Renumbering, and configuration checking for loop



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   avoidance.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Motivation for NEMO prefix delegation  . . . . . . . . . . . .  3
     2.1   Requirements . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2   Configuration Management . . . . . . . . . . . . . . . . .  4
     2.3   Provisioning . . . . . . . . . . . . . . . . . . . . . . .  4
     2.4   Renumbering  . . . . . . . . . . . . . . . . . . . . . . .  5
     2.5   The NEMO bootstrap problem . . . . . . . . . . . . . . . .  5
     2.6   Local Mobility Management  . . . . . . . . . . . . . . . .  5
   3.  Rationale  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1   Which capabilities?  . . . . . . . . . . . . . . . . . . .  6
       3.1.1   Prefix Request capability  . . . . . . . . . . . . . .  6
       3.1.2   Full prefix list capability for HA . . . . . . . . . .  6
       3.1.3   Full prefix list capability for MR . . . . . . . . . .  7
     3.2   Rationale for New Binding Options  . . . . . . . . . . . .  7
     3.3   Rationale for a new bit in the BU  . . . . . . . . . . . .  7
     3.4   Why not Alternate Standard-based Solutions?  . . . . . . .  7
   4.  Terminology and concepts . . . . . . . . . . . . . . . . . . .  9
   5.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.1   New Mobility Headers . . . . . . . . . . . . . . . . . . . 10
     5.2   New Prefix Status bit  . . . . . . . . . . . . . . . . . . 10
     5.3   Prefix Lease Duration  . . . . . . . . . . . . . . . . . . 10
     5.4   Protocol Flow  . . . . . . . . . . . . . . . . . . . . . . 11
     5.5   Renumbering  . . . . . . . . . . . . . . . . . . . . . . . 12
     5.6   Backward Compatibility . . . . . . . . . . . . . . . . . . 12
     5.7   Basic PD flow  . . . . . . . . . . . . . . . . . . . . . . 12
   6.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 13
     6.1   Binding Update . . . . . . . . . . . . . . . . . . . . . . 13
     6.2   Binding Acknowledgement  . . . . . . . . . . . . . . . . . 14
     6.3   Mobile Network Prefix option . . . . . . . . . . . . . . . 15
     6.4   Mobile Network Prefix Request option . . . . . . . . . . . 16
     6.5   Mobile Network Prefix Confirmation option  . . . . . . . . 18
   7.  Mobile Router Operation  . . . . . . . . . . . . . . . . . . . 21
   8.  Home Agent Operation . . . . . . . . . . . . . . . . . . . . . 22
   9.  Back End considerations  . . . . . . . . . . . . . . . . . . . 23
   10.   Security Considerations  . . . . . . . . . . . . . . . . . . 24
   11.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
   12.   References . . . . . . . . . . . . . . . . . . . . . . . . . 25
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 26
       Intellectual Property and Copyright Statements . . . . . . . . 27








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1.  Introduction

   The reader of that document is expected to be familiar with both the
   Mobile IPv6 [8] and NEMO Basic Support [10] documents.  As such, it
   is well understood that neither protocol provides the means for
   provisioning the Mobile Nodes and Routers with essential parameters
   such as Home Address and Home Network.

   The process by which a router obtains a prefix dynamically is called
   prefix delegation.  In the NEMO context, the prefix assignment is
   managed by an authority in the Home Network and divides it into
   subnets for MNPs, which are then assigned to the MRs.  An MNP can be
   preassigned to the associated MR (e.g. manually or automatically with
   a provisionning system), or assigned dynamically by a server such as
   a DHCP Prefix Delegation server.

   As prescribed by [10], the HA checks whether a MR is authorized for
   the MNPs it claims as part of the NEMO Binding Update with the
   explicit prefix option.  Also, MNPs have to belong to an aggregation
   that is permanently advertised be the HA to the routing
   infrastruture.  Consequently, there is a strong relationship between
   the HA that the MR registers to and the prefixes it claims with the
   registration, and it makes sense for the HA to participate actively
   to the delegation process as well.

   [10] standardizes an interface between a Mobile Router and its Home
   Agent, as well as an interface between Home Agents.  The protocol is
   agnostic as to how the back-end is implemented in terms of AAA,
   provisioning, or routing between the HAs and their IGP, and enables
   various forms of deployment, as described in [11].

   In the same fashion, the document extends [10] for a Mobile Router to
   obtain its Mobile Network Prefix dynamically from its Home Agent,
   with no assumption about the specific back-end implementation for
   prefix management and service authorization.

2.  Motivation for NEMO prefix delegation

   A number of reasons motivate adding this capability to NEMO Basic
   Support [10].

   Mainly, there is an unanswered question as to how a MR could be
   dynamically assigned its prefix.  In a situation where a site has
   many MRs, it may be impractical to assign the prefixes statically in
   the non-volatile memory of the MR.  Consequently, we would like a
   mechanism for the HA to assign the prefix, similar to how a MN can
   bootstrap its Home Address.




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2.1  Requirements

   There is thus a need for a Mobile Router to obtain dynamically one or
   more MNPs, linked to the HA that the MR binds with.

   Since the process might be used as part of a mobility scenario, there
   is also a need to optimize the delegation flow by limiting the number
   of protocol exchanges that take place for delegation and
   registration.

   Since the initial configuration may be erroneous or may need to
   evolve overtime, there is a need to manage the MNPs on a Mobile
   Router.  This includes initial setting up, and synchronizing
   overtime.

2.2  Configuration Management

   The Implicit Mode of NEMO 'externalizes' the configuration of the
   MNPs in a MR and its HA.  In the example of a static configuration,
   both side are initially provisioned with the association between the
   MRs and their MNPs, and maintain matching states between them.

   The failure to configure and maintain these matching states, over
   time, ends up in routing loops and unreachable prefixes.  Tools for
   synchronizing MNPs in the runtime environment would be a valuable
   addition to [10].

2.3  Provisioning

   In practice, provisioning both sides manually is error-prone and
   should be avoided.  It can not be taken for granted, either, that in
   all cases, a provisioning system can be deployed with the capability
   to configure both the Mobile Router and the back-end in a
   transactional manner.

   Consequently, it appears necessary to provide a way to configure one
   side only, and have the other side learn from it in a trusted fashion
   and with no additional manual intervention.

   The Explicit Prefix mode enables a flow where the configuration of
   that association is not centralized at the HA but distributed to all
   the MRs.  In fact, the HA is required to validate that the MR has
   been authorized for the MNPs it claims and then again, some level of
   information duplication might occur.

   In the general case, it may be easier to manage the prefix
   attribution in a centralized manner and have the MRs learn their
   prefixes dynamically.



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2.4  Renumbering

   The concept of lifetime is one core idea with IPv6.  Nothing is
   eternal.  Overtime, it might be desirable to modify the configuration
   of the MNPs.  This task, called renumbering, is especially difficult
   for Mobile Routers when they are geographically distributed and not
   be readily available to the administrators.

   It is thus desirable to extend [10] with a renumbering mechanism.  In
   particular, it makes sense to provide that extension within the
   prefix delegation mechanism, since the operations that take place are
   vastly similar.

2.5  The NEMO bootstrap problem

   Nemo basic support expects a Mobile router to be provisioned with
   some information in order to start up - Home Network or Home Agent
   address, Home Address, Mobile Network Prefixes, security tokens,
   etc...

   In some situations, it may be impractical to actually provision all
   this information into the router at deployment time, and some of it
   has to be obtained dynamically when a system boots up, possibly
   through manually keying by the final user.

   It is absolutely required to reduce such manual keying of information
   to the bare minimum, like a user ID and password.  And while NEMO can
   benefit from the MIP6 effort on the bootstrap problem (as described
   in the MIP6 bootstrap problem statement document [9]) for most
   parameters, the dynamic provisionning of Mobile Network Prefix(es) is
   not considered by MIPv6.

2.6  Local Mobility Management

   In turn, the bootstrap problem is linked to the Local Mobility
   Management problem; some LMM solutions such as HMIP deploy regional
   Home Agents from which bootstrap information has to be obtained when
   moving into their area of coverage; as opposed to the initial
   bootstrap problem which occurs at the first startup of a device and
   may not happen again for an extensive period of time, LMM is tied to
   movement, and could be quite frequent.

3.  Rationale

   This section details the rationale behind some of the design
   decisions that lead to this solution.





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3.1  Which capabilities?

3.1.1  Prefix Request capability

   The minimum capability that could be envisionned for a NEMO Prefix
   Delegation mechanism is for a MR to request a new prefix in a Binding
   Update and for the HA to provide the prefix as part of the Binding
   Acknowledgement.  Then the Mobile Router installs the newly obtained
   prefix on the interface that needs it, and moves forward in implicit
   or explicit mode.

3.1.2  Full prefix list capability for HA

   The capability to request a new prefix is sufficient in a basic
   delegation flow where a MR that is already bound and -hopefully-
   synchronized with its HA in terms of prefix ownership; it is also
   required in some bootstrapping and renumbering flows; but it is
   hardly sufficient in order to synchronize the MR and the HA states
   regarding MNPs:

   Bootstrapping: At bootstrapping time, the MR needs the list of all
      the prefixes that are attributed in order to populate its
      interfaces.  Asking them one by one and having to make a
      distinction between already allocated prefixes versus dynamic
      allocation would make the flow much more complex.

   Expired prefixes: That list is also needed for a MR in order to
      synchronize its current configuration  with that of the HA.  In
      particular, it is used for a MR to discover when the HA does not
      have the associated states in place for one of its MNPs.  This may
      happen for some configuration error or because the prefix has
      expired, and the only way to know is if the prefix is missing in a
      full list of all prefixes by the HA.

   Newly allocated prefixes: Finally, the list is needed for a MR to
      learn new prefixes that would be attributed in runtime, and to
      install those prefixes on its interfaces.  Once the new prefixes
      are installed, it is required that the MR confirms its use of the
      prefixes so that the HA can set up routing in a loopfree fashion.

   So, the capability for a HA to list all the prefixes for a MR is
   needed for the MR to realize that the HA is missing some state and
   eventually to try to get the missing prefixes in explicit mode.  This
   may happen on demand by the MR (e.g. at bootstrap time or binding
   creation time), or whenever the HA needs to communicate a change,
   such as a shortened or expired MNP lifetime.





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3.1.3  Full prefix list capability for MR

   So the capability for a HA to list all the prefixes is not
   sufficient, as the HA is not the repository of that knowledge.  It
   might be simpler for the MR to dump its own list of prefixes and have
   the HA check the list, even for implicit prefixes.

3.2  Rationale for New Binding Options

   Associated with the capability to request a new prefix, it seems
   relevant to specify whether the prefix is for implicit or explicit
   mode, or if its lifetime is limited to that of the binding cache or
   not.  Other fields such as the prefix length are needed as well.  In
   order to convey that information, an optional field is needed in the
   BU.

   It is not desirable to extend the existing NEMO MNP option, which
   carries a prefix that is not needed.  As a result, we propose a new
   option type, the MNP Request Option.

   Associated with the capability for a HA to list all the prefixes for
   a MR, one critical piece of information is needed that would not fit
   in the NEMO MNP option.  Again, we propose a new option for the
   Binding Acknowledgement, the MNP Confirmation Option.

3.3  Rationale for a new bit in the BU

   A single bit in the BU is enough for a MR to request a full list of
   prefixes from the HA, if we do not need a filter of any sort?

   It is important that the HA set that bit in its full list of prefixes
   in order to differentiate between an empty list (there is no prefix
   for that MR) and no list (HA is not providing a list in that BA).

3.4  Why not Alternate Standard-based Solutions?

   Proposing a new, specific solution might seem irrelevant when a
   standard, generic mechanism already exists: in this case, the DHCPv6
   Prefix Delegation.  In fact, it is  possible for the Home Agent to
   act as a  DHCPv6PD Delegating Router.  This solution presents the
   advantage of reusing existing standard flows from RFC3633 [6].

   Yet, in a deployment where the MNPs are preassigned to the MR, a AAA
   server, interfacing with the HA, and eventually coupled with a
   provisioning system in its back-end, can provide the required service
   for assigning and authorizing the prefixes to the MRs; in such a
   case, the value of implementing a DHCPv6PD server is highly arguable.
   It is more generic to let the HA handle the backend interfaces on



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   behalf of the MR and expose a consistent NEMO interface for all
   deployments.

   In more detail, a DHCPv6PD based solution presents a number of
   inconveniences:

   Delegating Router: A collocated Delegating Router function may  not
      be available for all implementation of NEMO Home Agent.  In
      particular, some implementations are server based.

   Operational overhead: Depending on the mechanism that is used to
      attribute the MNPs to the MRs, the Delegating  function, even if
      available, might be a costly overhead.  Rather, an embedded, back-
      end agnostic flow might be a desirable option.

   Movement overhead: Some flows, for instance local mobility
      management, might require a prefix delegation as part of the
      handling of the movement.  Segregating the delegation from the
      binding adds a round trip delay to the recovery from the movement.

   Binding Lifetime: It might be useful to associate implicitly the
      lifetime of a delegated prefix with that of the binding.  This
      pleads for a design that places the Home Agent function in the
      flow by construction.

   Authentication Mechanism: While NEMO basic Support protects its own
      flows, there is no mandate to secure the tunneled packets.

   Back-end interaction: If a prefix is attributed to a MR for a
      duration that exceeds that of its binding, this information needs
      to be shared with all HAs, at least for authorization purposes.
      This requires a specific backend integration that does not exist
      in the Prefix Delegation Function, for instance via a AAA server.


















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4.  Terminology and concepts

   The key words 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 [1].

   Most of the mobility related terms used in this document are defined
   in the Mobility Related Terminology document [7] and in the Mobile
   IPv6 specification [8].

   Additionally, some terms were created or extended for NEMO.  These
   specific terms are defined in the Mobile Network Terminology document
   [12]

   This draft introduces the following definitions:

   Mobile Network Prefix Request (MNPReq) Option: A new optional field
      in the MIPv6 Mobility Header for use with the Binding Update
      message, as described further in this document.  This field is set
      by a MR to request the delegation of a new prefix as a Mobile
      Network Prefix.

   Mobile Network Prefix Confirmation (MNPConf) Option: A new optional
      field in the MIP6 Mobility Header for use with the Binding
      Acknowledgement message, as described further in this document.

   transient prefix: A prefix that is attributed to a Mobile Router in
      association with a binding cache entry.  If the BCE is removed,
      the prefix is freed.

   Persistent prefix: A prefix that is attributed to a Mobile Router for
      a period of time that does not depend on the existence of a
      binding cache entry.


















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5.  Overview

5.1  New Mobility Headers

   This paper introduces a new option to the MIP6 Mobility Header, for
   use with the Binding Update message, the Mobile Network Prefix
   Request Option.  A MR may include one or more MNPReq option(s) in a
   Binding Update message at any time, in order to obtain additional
   prefixes.

   This paper introduces another new option to the MIP6 Mobility Header,
   for use with the Binding Acknowledgement message, the Mobile Network
   Prefix Confirmation Option.  An HA will include one or more MNPConf
   option(s) in a Binding Acknowledgement message, either in response to
   a Mobile Network Prefix Request Option, or for its own purposes, for
   instance in order inform a MR about a change in the lifetime of an
   MNP.

5.2  New Prefix Status bit

   Finally, this paper introduces a new bit to both the MIP6 Binding
   Update and Binding Acknowledgement, the Prefix Status bit.  A MR may
   include the Prefix Status bit in a Binding Update message at any
   time, either in order to get its initial configuration, or to check
   whether its current configuration matches that of the Home Agent -
   which might be particularily useful in implicit mode.  When the
   Prefix Status bit is set in the BU, the Acknowledge bit MUST be set
   as well.

   The HA MAY set the Prefix Status bit in the Binding Acknowledgement
   even if it was not set by the MR in the Binding Update; the other way
   around, if the Prefix Status bit was set in the BU, then the HA MUST
   echo it in the BA.  When setting the Prefix Status bit, the HA also
   lists all the prefixes associated to that Mobile Router using Mobile
   Network Prefix Confirmation options.

5.3  Prefix Lease Duration

   A prefix may be obtained for the duration of the binding; in this
   case, the prefix is called 'transient'.  On the other hand, a prefix
   can be assigned to a MR for a duration that is independent of a BCE
   lifecycle, and that is controlled externally by the HA administrator;
   in that case, the prefix is called 'persistent'.

   A flag in the MNPReq option indicates the expectation of the MR in
   terms of persistence for the requested prefix.  If the HA can not
   fulfill that expectation, it must reject the binding with a negative
   status.



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   The lease of a transient prefix expires with the MR Binding Cache
   Entry; as a result, transient prefixes can be managed internally by a
   HA, for instance using a local pool that forms an aggregation owned
   by the HA.

   On the other hand, some of the information about a persistent prefix
   has to be shared between the HAs in a Home Network and the back-end
   systems that enable the authorization.  This is required to allow a
   Mobile Router to rebind, with the same persistent prefixes, to a
   different Home Agent, after a period of inactivity.

   It is possible to assign a persistent prefix dynamically at the time
   of the delegation; but the persistent mode also enables the
   preassignment of an MNP to an MR, for instance by provisionning a AAA
   server with the necessary information for each Mobile Router.

5.4  Protocol Flow

   The operation of prefix delegation has a slightly different semantic
   than home address delegation under Mobile IPv6.  If the HA or another
   router allowed the routing for an address to be changed, the worst
   possible effect would be unauthorized access, and possibly stealing a
   message flow from one node.  So we protect against this using reverse
   routability.

   On the other hand, if the routing for an entire prefix were changed
   in a malevolent manner, traffic for a large portion of a site could
   be lost or redirected.  Therefore, it is important to focus more
   closely on exactly how the authorization works for delegating that
   prefix.

   There is a 4-step flow for dynamic prefix delegation that must be
   followed:

   1. Provisioning -- The administrative entity managing the address
      space for a site must allocate, either manually or automatically,
      a prefix to be used by the MR.  This could be done when the MR's
      account with HoA and security association is established, or it
      could be done at the time of the delegation request.

      This provisioning must be stored in some permanent location
      accessible by the HA, since it is necessary to verify autorization
      for an MR to use a MNP.

   2. Request -- The MR must signal that it would like a prefix to be
      delegated by the HA.





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   3. Authorization -- The HA must check that the MR is allowed to use a
      certain prefix.  At this point, the HA does a lookup operation, or
      if this is a dynamic prefix that has not yet been allocated, the
      HA does step (1) and provisions a prefix for a certain time
      period.

   4. Delegation  -- The HA signals to the MR that it is authorized to
      use a certain prefix for a certain period of time.  For
      simplicity, it should be assumed that this lifetime is the length
      of the MR's binding, since it is not useful for the MR to continue
      to have a binding if its MNP has expired.  It is possible the
      lifetime is longer (i.e. infinity if it is a (statically
      provisioned) persistent prefix).


5.5  Renumbering

   It is possible to redeploy the persistent prefix space, for instance
   if Home is being renumbered, or if a dynamically attributed prefix
   has not been bound for a long period of time.  In that case, the HA
   rejects a new binding as the routing states can not be set up, and
   the MR has to request one or more new persistent prefix(es).

5.6  Backward Compatibility

   An HA that does not support this extension will ignore the
   unrecognized option.  If the HA supports this extension, a binding
   update with the MNPReq option can be accepted per the NEMO basic
   support checks: after the packet is checked according to the NEMO
   spec, the HA processes the option(s).

5.7  Basic PD flow

   When a MR needs an additional prefix to populate an interface, it
   adds an MNPreq option to its Binding update message.

   If the HA can obtain the required prefix for that MR, it operates
   following the NEMO basic support, in either Implicit Mode or Explicit
   Mode, using the prefixes as if they were received with the BU.  This
   includes setting up the routing states and responding with a positive
   or a negative status.

   If the routing states are established correctly and the HA responds
   with a positive status, then the HA adds the prefix list to the
   binding ack message.

   From that point on, both the MR and the HA operate as prescribed by
   the NEMO basic standard, either in implicit or explicit mode.



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6.  Message Formats

6.1  Binding Update

   A new flag (S) is included in the Binding Update to indicate to the
   Home Agent that the MR wishes to get the full list of all prefixes
   that are already assigned to it.  The rest of the Binding Update
   format remains the same as defined in [10].

   When the (S) bit is set, the (R) and and (A) bits MUST be set as
   well.


                     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
                                          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                          |          Sequence #           |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |A|H|L|K|M|R|S|    Reserved     |           Lifetime            |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                                                               |
          .                                                               .
          .                        Mobility options                       .
          .                                                               .
          |                                                               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Prefix Status (S) The Prefix Status (S) bit is set by a MR to request
      the full list of all prefixes that are already assigned to it





















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6.2  Binding Acknowledgement

   A new flag (S) is included in the Binding Acknowledgement to indicate
   to the Mobile Router that the Home Agent is providing the complete
   list of prefixes that are already assigned to the MR.  The rest of
   the Binding Acknowledgement format remains the same as defined in
   [10].

   When the (S) bit is set, the (R) bit MUST be set as well.


           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
                                          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                          |   Status      |K|R|S|Reserved |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |         Sequence #            |           Lifetime            |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                                                               |
          .                                                               .
          .                        Mobility options                       .
          .                                                               .
          |                                                               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   Prefix Status (S) The Prefix Status (S) bit is set by a HA to
      indicate that it provides the full list of all prefixes that are
      already assigned to the MR.





















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6.3  Mobile Network Prefix option

   New flags are included in the Mobile Network Prefix option defined in
   [10].  This allows the option to cover all the prefixes owned by the
   MR, including those that are managed using the implicit prefix mode.




           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      |P|I|D|Reserved1| Prefix Length |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                                                               |
          +                                                               +
          |                                                               |
          +                   Mobile Network Prefix                       +
          |                                                               |
          +                                                               +
          |                                                               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





   The new flags introduced by this specification are:

   Persistent (P) The (P) bit is set if the prefix is expected to be
      persistently assigned to the MR beyond the lifetime of the
      associated binding.

   Implicit (I) The (I) bit is set if the prefix is expected to be
      assigned to and routed via the MR even if the prefix is not listed
      in an explicit mode BU.

   Delegated (D) The (D) bit is set if the prefix was obtained using the
      Delegation Mechanism as described in this specification.  It is
      used to acknowledge that a previously delegated prefix is actually
      installed and routable via the Mobile Router.

   Alignment: Must be 8n + 4.








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6.4  Mobile Network Prefix Request option

   This new option is included in the Binding Update to indicate to the
   Home Agent that the MR wishes to get a new prefix assigned to it for
   use as a MNP.

   When this option is present, the (S) MAY be set as well in the BU in
   order to get the full list of all prefixes.



           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 |P|I| Reserved1 |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |     CorID                     |   Reserved2   | Prefix type   |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   Type: TBA

   Length: 8-bit unsigned integer indicating the length in octets of the
      option excluding the type and length fields.  Set to 6.

   Prefix Length: 8-bit unsigned integer indicating the prefix length of
      the IPv6  prefix contained in the option (valid range isno
      1..128).

   Persistent (P): The (P) bit is set if the prefix that is requested to
      be persistently assigned to the MR.

   Implicit (I): The (I) bit is set if the prefix that is requested to
      be assigned to, and routed via the MR, even if the prefix was not
      listed in an explicit mode BU.

   CorId: A Correlator that is set by the MR in order to associate a MNP
      request with the prefix given in the confirmation.  There can be
      at most one active prefix associated with each Correlator.  This
      mechanism ensures the uniqueness of the allocation of a prefix,
      should either the BU or the BA be lost in transit.

   Prefix Type: Indicates the type of prefix that is requested:







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      0: None Specified

      1: Private

      2: Unique Local

      3: Global












































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6.5  Mobile Network Prefix Confirmation option

   This new option is included in the Binding Acknowledgment to indicate
   to the Mobile Router whether a new prefix was assigned, and what it
   is.

   When this option is present, the (S) MAY be set as well in the BU in
   order to indicate that the complete list of prefixes is attached.



          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 |P|I|D|Reserved1|
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |     CorID                     |    Status     | Prefix type   |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                         Valid Lifetime                        |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                                                               |
          +                                                               +
          |                                                               |
          +                   Mobile Network Prefix                       +
          |                                                               |
          +                                                               +
          |                                                               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




   Type TBA

   Length: 8-bit unsigned integer indicating the length in octets of the
      option excluding the type and length fields.  Set to 26.

   Prefix Length: 8-bit unsigned integer indicating the length of the
      IPv6 prefix contained in the option (valid range is 1..128).

   Persistent (P): The (P) bit is set if the prefix is persistently
      assigned to the MR.

   Implicit (I): The (I) bit is set if the prefix is assigned to and
      routed via the MR even if the prefix is not listed in explicit
      mode BU.





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   Delegated (D): The (D) bit is set if the prefix was obtained using a
      the Delegation Mechanism described in this specification.

   CorId: If the (D) bit is set, this option contains the prefix being
      delegated in response to the MNPReq containing the same Correlator
      If the (D) bit is not set, the Correlator value is unused.

   Status: Indicates what happened in response to the corresponding
      request:

      0: OK (Route successfully created for designated prefix)

      1: Prefix is not currently registered

      2: Mobile Network Option sent from non-MR

      3: Invalid prefix (not part of valid address space)

      4: Prefix not owned by this domain/link (HA can not delegate)

      5: Prefix not owned by MR which sent this MNO

      6: Could not create route / insufficient resources

      7: Policy does not allow allocation of PrefixLen.  Prefix
         allocated as shown, with longer prefixlen.

      8: Persistent prefixes are not supported.

      9: Transient prefixes are not supported.

      10: NEMO Implicit mode is not supported.

   Prefix Type: Indicates the type of prefix enclosed:

      0: None Specified

      1: Private

      2: Unique Local

      3: Global

   Valid Lifetime: 32-bit unsigned integer.  The length of time in
      seconds (relative to the time the packet is sent) that the prefix
      is valid for being installed on an MR ingress interface.  A value
      of all one bits  (0xffffffff) represents infinity.  The Valid
      Lifetime is also used by RFC2461 [3] and RFC2462 [4], and must be



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      used in the RAs sent over the MR ingress interface for that
      prefix.

   Mobile Network Prefix: A 16 byte field containing the Mobile Network
      Prefix.














































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7.  Mobile Router Operation

   When the Mobile Router has determined the Home Address it is going to
   use and the Home Agent it is going to register with, it constructs a
   Binding Update with the R bit set.  At this time, the Mobile Router
   will add either a MNP Option, or a MNPReq Option, or both, to the BU.

   If the Mobile Router already has one or more persistent MNPs and does
   not need more, it simply adds a MNP Option.  If the MR is not pre-
   configured with a persistent prefix, it may request either a
   persistent or transient prefix.

   If more than one prefix is needed, than more than one can be
   requested by simply appending multiple MNPReq Options to the BU.

   When the Binding Acknowledgment is received back from the HA, the MR
   will process it as normal, and when the MNPC Option(s) are
   encountered, it should verify that it sent a request using the
   included CorID, and then react according to the status field, as
   follows:

   0: Begin forwarding this prefix and using it in Router Advertisements
      as described in NEMO.  If the P bit is set and the MR supports
      persisten prefixes, add it to the list of prefixes.

   1: (unknown)

   2: Contact system administrator.

   3: MR may try again with a different prefix.

   4: MR may try dynamic home agent discovery to contact correct HA.

   5: MR should retry, with P bit turned off, to obtain a transient
      prefix.

   6: MR should try another HA, or wait and try again later.

   7: Same response as for status 0.












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8.  Home Agent Operation

   The Home Agent receives a Binding Update from the Mobile Router, it
   processes the BU as described in the Mobile IPv6 protocol [8] and
   NEMO basic support [10].  When it arrives at a MNPO (assuming the
   Binding Update is valid as already processed), it takes steps as
   follows:

   Step 1. Verify that the MR is allowed to be allocated a prefix of the
      requested type and allocate one.

   Step 2. If the request is for a persistent prefix, save the
      allocation in the back-end permanent store.

   Step 3. Set up routing for this prefix.  If the BU was of lifetime 0,
      do not set up routing for this prefix, but simply allocate it.

   Step 4. For each MNPR option, respond with a MNPC option in the BAck.
      If the MNPR was received in a BU from a non-MR, send status 2 and
      0s for prefix information.  Otherwise, send a response with result
      code 0, and filling in the appropriate prefix information.

   If the Binding Update contains an S bit, the Home Agent includes a
   Mobile Network Prefix Option for each prefix the Home Agent believes
   is assigned to the Mobile Router.

   After these steps are followed, the Home Agent continues its
   operation as normal, until another MNPO or MNPR is received.























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9.  Back End considerations


















































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10.  Security Considerations

11.  Acknowledgements

   The authors wish to thank:

   Pekka Paakkonen and Juhani Latvakoski from VTT Electronics for their
   initial work on the matter.











































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12.  References

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

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

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

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

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

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

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

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

   [9]   Patel, A., "Problem Statement for bootstrapping Mobile IPv6",
         draft-ietf-mip6-bootstrap-ps-00 (work in progress), July 2004.

   [10]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
         "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
         January 2005.

   [11]  Thubert, P., Wakikawa, R., and V. Devarapalli, "NEMO Home
         Network models", draft-ietf-nemo-home-network-models-00 (work
         in progress), April 2004.

   [12]  Ernst, T. and H. Lach, "Network Mobility Support Terminology",
         draft-ietf-nemo-terminology-01 (work in progress),
         February 2004.










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Authors' Addresses

   T.J. Kniveton
   Nokia, Inc.
   313 Fairchild Dr.
   Building B-223
   Mountain View  94043
   USA

   Phone: +1 650 625 2025
   Email: tj@kniveton.com


   Pascal Thubert
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410
   FRANCE

   Phone: +33 4 97 23 26 34
   Email: pthubert@cisco.com




























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