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Network Working Group                                         A. Ebalard
Internet-Draft                                                      EADS
Intended status: Informational                                S. Decugis
Expires: April 3, 2011                                              NICT
                                                      September 30, 2010

   PF_KEY Extension as an Interface between Mobile IPv6 and IPsec/IKE


   This document describes the need for an interface between Mobile IPv6
   and IPsec/IKE and shows how the two protocols can interwork.  An
   extension of the PF_KEY framework is proposed which allows smooth and
   solid operation of IPsec/IKE in a Mobile IPv6 environment.

   This document is heavily based on a previous draft [MIGRATE] written
   by Shinta Sugimoto, Masahide Nakamura and Francis Dupont.  It simply
   reuses the MIGRATE mechanism defined in the expired document, removes
   a companion extension (SADB_X_EXT_PACKET) based on implementation
   feedback (complexity, limitations, ...) and fills the gap by very
   simple changes to MIGRATE mechanism.  This results in a more simple
   and consistent mechanism, which also proved to be easier to
   implement.  This document is expected to serve as a continuation of
   [MIGRATE] work.  For that reason, the name of the extension has been

   PF_KEY MIGRATE message serves as a carrier for updated information
   for both the in-kernel IPsec structures (Security Policy Database /
   Security Association Database) and those maintained by the key
   managers.  This includes in-kernel Security Policy / Security
   Association endpoints, key manager maintained equivalents, and
   addresses used by IKE_SA (current and to be negotiated).  The
   extension is helpful for assuring smooth interworking between Mobile
   IPv6 and IPsec/IKE for the bootstrapping of mobile nodes and their

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 3, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Needs for Interactions between Mobile IPv6 and IPsec/IKE . . .  5
   4.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  PF_KEY Extensions for Mobile IPv6: PF_KEY MIGRATE Message  . .  6
     5.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  7
       5.1.1.  System Overview  . . . . . . . . . . . . . . . . . . .  7
       5.1.2.  Bootstrapping  . . . . . . . . . . . . . . . . . . . .  8
       5.1.3.  Movement . . . . . . . . . . . . . . . . . . . . . . .  9
       5.1.4.  IKE_SA Update  . . . . . . . . . . . . . . . . . . . . 10
     5.2.  Issuing PF_KEY MIGRATE Message . . . . . . . . . . . . . . 11
     5.3.  Processing PF_KEY MIGRATE Message  . . . . . . . . . . . . 12
     5.4.  NAT Traversal  . . . . . . . . . . . . . . . . . . . . . . 13
     5.5.  Limitations of PF_KEY MIGRATE  . . . . . . . . . . . . . . 13
   6.  Necessary Modifications to Mobile IPv6 and IPsec/IKE . . . . . 14
   7.  Implementation . . . . . . . . . . . . . . . . . . . . . . . . 15
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   10. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     11.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Appendix A.  PF_KEY MIGRATE Message Format . . . . . . . . . . . . 17
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21

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1.  Introduction

   In Mobile IPv6 [RFC3775], the Mobile Node (MN) and the Home Agent
   (HA) use some IPsec Security Associations (SA):

   o  in transport mode to protect signaling traffic (Binding Update and
      Binding Ack).  Those SA reference the Home Address (HoA) of the
   o  in tunnel mode to protect some mobility signaling messages, mobile
      prefix discovery and optionally payload traffic.  Those SA
      reference both the Care-of Address (CoA) and the HoA of the MN.

   To negotiate initial transport mode SA, the IKE daemon needs to be
   directed to use current CoA as source of the IKE exchanges.  By
   default, the (currently unusable) HoA would be used.

   Later, since the MN may change its attachment point to the Internet,
   it is necessary for it to update the tunnel endpoint address of its
   IPsec SA.  This indicates that corresponding entries in IPsec
   databases (Security Policy (SPD) and Security Association (SAD)
   databases) should be updated when MN performs movements.

   In a Mobile IPv6 environment, the key manager (KM) also needs to be
   notified when the SPD and SAD are updated.  More generally, it needs
   to be provided with updated addresses for already negotiated and
   future IKE_SA.  Because of its role and unlike common applications, a
   key manager has to take part to the mobility process it secures: it
   needs to be aware of address changes.

   This document describes the need for an interface between Mobile IPv6
   and IPsec/IKE and shows how the two protocols can interwork.  An
   extension to the PF_KEY framework [RFC2367] which allows smooth and
   solid operation of IKE in a Mobile IPv6 environment is defined.  The
   extension is called PF_KEY MIGRATE and serves as a carrier for the
   necessary information for both the in-kernel IPsec stack and the key

   For the IPsec stack, this allows migrating the endpoint addresses of
   the IPsec SA (and associated SP).  For the key managers, this allows
   the mirrored structures to be updated (SAD and SPD).  This also
   allows the addresses of already negotiated and associated IKE_SA to
   be migrated, and to make specific addresses available for
   negotiations of future IKE_SA.  This set of operations performed by
   the key manager on its internal structures is initiated by the MIPv6

   With the extension, the bootstrapping of the MN appears as a common
   operation for IKE, by having the right addresses needed for the

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   negotiation available prior to its beginning (i.e. at the reception
   of the PF_KEY ACQUIRE message by the IKE daemon).

   The extension is helpful for assuring smooth interworking between
   Mobile IPv6 and IPsec/IKE and achieving performance optimization:
   upon movement, both sides (MN and HA) locally notify the IPsec stack
   and the key manager of the new CoA, thus preventing the need to flush
   and renegotiate existing SA.

   As stated in the abstract, this document is heavily based on the
   content of a previous draft MIGRATE [MIGRATE].  This expired memo
   served as the basis for this work both from technical and editorial
   standpoints.  Numerous technical discussions with some of its authors
   took place while working on this memo and associated implementations.

2.  Terminology

   In this document, the term IKE implicitly stands for both IKEv1
   [RFC2409] and IKEv2 [RFC5996].  IKEv2 terminology is used
   preferentially when describing actions performed by the key manager
   but they also apply to the IKEv1 counterparts.  For instance, when
   actions occur on IKE_SA, they also apply to ISAKMP SA for IKEv1,
   except otherwise specified.  The terms "IKE daemon" and "Key Manager
   (KM)" are used interchangeably in the document.

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Needs for Interactions between Mobile IPv6 and IPsec/IKE

   Sections 4.4 of [RFC3776] and [RFC4877] specify the rules which apply
   to IKE for MN and HA.  The first requirement is to run IKE over the
   Care-of Address because the Home Address is usable only after the
   home registration but not yet in the bootstrapping phase, when
   Transport mode IPsec SA are commonly negotiated to protect BU/BA.

   A tunnel IPsec SA pair protects some signaling messages and
   optionally all the traffic between the MN and HA.  The initial SPD
   entry uses the HoA for the MN endpoint address and updates this
   address to the new CoA at each movement.  A tunnel SA pair is created
   on demand and is updated too.  RFC 3775 [RFC3775] assumes there is an
   API which performs the update in the SPD and SAD on both the MN and
   HA, and notify the IKE daemon.  This memo proposes such an API based
   on PF_KEY framework both to document the needs and ease
   interoperability between components which may be provided by

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   different vendors.

   Mobile IPv6 may need to make an access to the SPD not only for
   updating an endpoint address but also for deleting/inserting a
   specific SPD entry.  When the MN performs Foreign-to-Home movement,
   IPsec SA established between the MN and HA to protect data traffic
   should be deleted, and associated SPD entries should have no effect
   anymore.  On the other hand, when the MN performs Home-to-Foreign
   movement, those IPsec SP should be restored.  Hence security policy
   entries that are associated with tunnel mode SA may dynamically be
   added/removed (enabled/disabled) in along with MN's movements.  As a
   side note for such a scenario, Home Link detection mechanism becomes
   critical security-wise [hld-sec].

   It should be noted that NEMO Basic Support [RFC3963] has similar
   requirements for the Mobile Router (MR) and MR's HA (MRHA).  In NEMO,
   the MR works just like a MN registering its location information to
   the MRHA and establishes a tunnel (IP-in-IP or IPsec tunnel).  When
   an IPsec tunnel is established between MR and MRHA, the MR serves as
   a Security Gateway for the nodes connected to the mobile network.
   The MR is responsible for handling its tunnel endpoint properly.

4.  Requirements

   Despite the need for an interface between Mobile IPv6 and IPsec/IKE,
   it should be kept simple.  Following are the requirements for the
   interface from a software engineering point of view.

   o  Necessary modifications to the existing software, namely Mobile
      IPv6 and IPsec/IKE, in order to realize proposed mechanisms,
      should be kept minimum.
   o  Proposed mechanism should not be platform dependent.  The
      mechanism should be based on technology which is commonly
      available on various platforms.  This seems to be essential for
      achieving high portability of the implementation which supports
      proposed mechanisms.

5.  PF_KEY Extensions for Mobile IPv6: PF_KEY MIGRATE Message

   In order to fulfill the needs and requirements described in Section 3
   and Section 4 an extension of PF_KEY framework is proposed so that
   Mobile IPv6 and IPsec/IKE can interact with each other.  The new
   message dedicated to that function is called MIGRATE.  A new simple
   PF_KEY structure (struct sadb_x_kmaddress, see Appendix A) is also
   defined to be used by MIGRATE to serve the purpose of IKE_SA update.

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5.1.  Overview

5.1.1.  System Overview

   The MIGRATE message is used for providing updated information to its
   two targets, the kernel IPsec stack and the key manager (when used).
   The figure below illustrates how Mobile IPv6 and IPsec/IKE components
   interact with each other using PF_KEY MIGRATE message in a dynamic
   keying scenario.  On left top is a Mobile IPv6 entity (it may be
   possible that Mobile IPv6 component is completely implemented inside
   the kernel).  In any case, Mobile IPv6 should be the one issuing the
   MIGRATE message.  On right top is an IKE daemon which is responsible
   for establishing SA required for Mobile IPv6 operation.  In a manual
   keying scenario, the difference is mainly that there is no IKE daemon
   running on the system.

                  +-------------+           +------------+
                  |             |           |            |
                  | Mobile IPv6 |           | IKE Daemon |
                  |             |           |            |
                  +-------------+           +------------+
                         | 1. PF_KEY               A 4. Update SPD & SAD
                         |    MIGRATE              | 5. Update IKE_SA
                         +-----------+ +-----------+
                                     | |
      Userland                       V |
     ==========================[PF_KEY Socket]========================
      Kernel                         | |
                          +----------+ +----------+
                          | 2. Update             | 3. Update
                          V    SPD                V    SAD
                    +-----------+           +------------+
                    |           |           |            |
                    |    SPD    |           |    SAD     |
                    |           |           |            |
                    +-----------+           +------------+

   In the kernel, the primary role of PF_KEY MIGRATE message is to
   change the endpoint addresses of SA, i.e. requesting IPsec to update
   its databases (SPD and SAD).  Even if tunnel mode is the primary
   target for MIPv6, MIGRATE is not limited to that mode.  Then, after
   proper processing by the kernel, the MIGRATE message is sent to all
   open PF_KEY socket.  A listening key manager processes it , which
   results in a possible update of its internal structures.  The
   specific actions are introduced on the following figure.

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      MIPv6 ---------------- kernel -------------------> IKE
                       1) update of SP        1) Update of SA and SP
                         endpoints and           endpoints (in image)
                         associated SA.       2) Update of source and
                                                 destination addresses
                                                 in SPD image for
                                                 future SA negotiation
                                              3) Update of IKE_SA
                                                 source and destination
                                                 addresses associated
                                                 with provided SA

   In more details, the processing of a MIGRATE message can be divided
   in following steps:

   o  Mobile IPv6 issues a PF_KEY MIGRATE message to the PF_KEY socket.
   o  The operating system (kernel IPsec stack) validates the message
      and checks if corresponding security policy entry exists in SPD.
   o  When the message is confirmed to be valid, the SPD entry is
      updated according to the MIGRATE message.  If there is any target
      SA found that is also target of the update, it is also updated.
      This is detailed in Section 5.3.
   o  After the MIGRATE has been successfully processed inside the
      kernel, it is sent to all open PF_KEY sockets.
   o  The IKE daemon receives the MIGRATE message from its PF_KEY socket
      and validates it.
   o  The key manager starts by updating the SP entries described in the
      message with the updated endpoint information.  It also updates in
      its SPD image the local and remote addresses to be used for future
      negotiation of SA associated with those SP (addresses used by
      future IKE_SA).  Then, it updates the SA related information: the
      endpoints of already negotiated SA and the local and remote values
      of associated IKE_SA.

   Note that the way IKE maintains its local copy of SPD (the SPD image)
   is an implementation specific issue since there is no standard
   interface to access SPD.  Some IKE implementations may continuously
   monitor the SPD inside the kernel.  Some IKE implementation may
   expect notifications from the kernel when the SPD is modified.  In
   either way, the proposed mechanism gives a chance for IKE to keep its
   SPD image up-to-date which is significant in Mobile IPv6 operation.

5.1.2.  Bootstrapping

   In the bootstrapping stage of Mobile IPv6, the MN and the HA need to
   establish IPsec SA to protect signaling messages of Mobile IPv6 such
   as BU and BA.  When IKE is used to establish and maintain the SA

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   pairs, the IKE negotiation is the very first transaction made between
   the MN and the HA.

   As mentioned in [RFC3776], some care is needed for the address
   management during IKE negotiations in Mobile IPv6 environments.  In
   particular, IKE negotiation to be made to establish a transport mode
   IPsec SA pair is tricky because the local IKE_SA address and the SA
   endpoint on the MN side (the Home Address) are different.  This is
   because the Home Address cannot be used prior to the initial home
   registration.  SADB_X_EXT_KMADDRESS extension defined in this memo
   enables the MIPv6 module to notify the IKE module about the IKE

   A simple solution to make the key manager aware that a different
   address must be used for the negotiation of SA is to have it record
   this address within its mirrored SPD entries as soon as it becomes
   available.  With that information, the key manager is able to inflect
   its usual processing where it selects by default the source address
   of the SA for the negotiation (i.e. as local address of the IKE_SA).
   By having the MIGRATE message emitted by the Mobile IPv6 process
   before the emission of the BU, the address is already available to
   the key manager when the ACQUIRE message is received.

   Even if the bootstrapping process initially appears differently than
   the usual process, having the internal structure of the key manager
   explicitly record the address (to be used for the negotiation of the
   SA for a specific SP) allows to keep things simple.  The only
   requirement is that the MIGRATE message be emitted by the Mobile IPv6
   process before it sends its Binding Update.

5.1.3.  Movement

   Next, we will see how migration takes place along with home
   registration.  The figure below shows a sequence of mobility
   signaling and PF_KEY MIGRATE messages while the MN roams around
   links.  It is assumed that in the initial state the tunnel endpoint
   address for a given MN is set as its home address.  In the initial
   home registration, the MN and HA migrate the tunnel endpoint address
   from the HoA to CoA1.  It should be noted that no migration takes
   place when the MN performs re-registration since the care-of address
   remains the same.  Accordingly, the MN performs movement and changes
   its primary care-of address from CoA1 to CoA2.  A PF_KEY MIGRATE
   message is issued both on MN and HA for each direction.  When the MN
   returns home, migration takes place updating the endpoint address
   with the MN's home address.

   With regard to the timing of issuing the MIGRATE message on the MN
   during a handover, it must occur immediately before the emission of

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   the binding update performing the home registration (as for
   bootstrapping).  It is possible that ESP-protected (IPsec tunneled)
   user traffic be sent from the new CoA which is not known to the HA
   yet.  As the HA processes the packets protected under IPsec, and as
   far as it finds a valid SA, then those packets will be authenticated
   regardless of their source IP address.  In the end, there is no
   security issue in updating the IPsec SA endpoint while sending the BU
   and no reason not to do it.  Furthermore, this may help the MN to
   minimize the packet loss of its outbound traffic during the handover.

               MN                                        HA
               |                                          |
               ~                                          ~
     MIGRATE ->|      BU (Initial home registration)      |
               |                   BA                     |<- MIGRATE
               |<-----------------------------------------| (HoA->CoA1)
               |                                          |
               ~         BU (Home re-registration)        ~
               |                   BA                     |
               |                                          |
               ~                                          ~
               |                                          |
     Movement->|           BU (Home registration)         |
     MIGRATE ->|                   BA                     |
               |                                          |<- MIGRATE
               |<-----------------------------------------| (CoA1->CoA2)
               |                                          |
               ~                                          ~
     Movement->|         BU (Home de-registration)        |
     MIGRATE ->|                   BA                     |
               |                                          |<- MIGRATE
               |<-----------------------------------------| (CoA2->HoA)
               |                                          |

5.1.4.  IKE_SA Update

   The bootstrapping process described in Section 5.1.2 allows the
   creation of the SA by having the right source address available to
   the key manager before the beginning of the negotiation.  When the SA
   has been negotiated, some further exchanges are expected to happen
   during the lifetime of the SA, including rekeying related exchanges.
   After the first movement (and obviously further ones), the address

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   used during the bootstrapping process becomes invalid.  Even if the
   SPD and SAD entries are updated (as described in Section 5.1.1),
   there is also a need for the key manager to update the addresses used
   by the IKE_SA.

   When the key manager processes the MIGRATE message, it uses the local
   and remote address information provided by the sadb_x_kmaddress
   structure to update:
   o  local copy of the SP entry maintained by the IKE daemon which is
      specified in the MIGRATE message (as described in Section 5.1.2).
   o  the existing IKE_SA associated with the SP entry which is
      specified by the MIGRATE message.

5.2.  Issuing PF_KEY MIGRATE Message

   The Mobile IPv6 entity (MN or HA) code triggers the migration by
   sending a PF_KEY MIGRATE message to its PF_KEY socket.  Conceptually,
   the PF_KEY MIGRATE message should contain following information:

    o  Key manager address information                 \
       *  source address                                |  For IKE only
       *  destination address                          /
    o  Selector information:                           \
       *  source address/port                           |
       *  destination address/port                      |
       *  upper layer protocol (i.e., Mobility Header)  |
       *  direction (inbound/outbound)                  |
    o  Old SA information:                              |
       *  old source endpoint address                   |  For IKE and
       *  old destination endpoint address              |  IPsec stack
       *  IPsec protocol (ESP/AH)                       |
       *  mode (Tunnel/Transport)                       |
    o  New SA information:                              |
       *  new source endpoint address                   |
       *  new destination endpoint address              |
       *  IPsec protocol (ESP/AH)                       |
       *  mode (Tunnel/Transport)                      /

   Key manager address information content (source and destination
   address) is recorded in the associated entry of the SPD image.  Those
   SHOULD be used from now on by the key manager for SA negotiation
   associated with that SP.  The information SHOUD also be used by the
   key manager to update the local and remote addresses of the IKE_SA
   (used by already negotiated SA associated with the SP).

   Selector information is required to specify the target SPD entry to
   be updated.  Basically the information should contain necessary
   elements which characterize traffic selector as specified in the

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   IPsec architecture ([RFC2401], [RFC4301]).  With regard to the upper
   layer protocol, when the Mobile IPv6 stack is not fully aware of
   IPsec configuration, a wildcard value can be given.  In such case, an
   upper layer protocol information SHOULD NOT be taken into account for
   searching SPD entry.  Plus, the direction of the security policy
   (inbound/outbound) SHOULD be provided.

   The old SA information, along with old locator information is used to
   specify target SA to be updated.  For tunnel mode, the endpoint
   addresses refer to the source and destination IP addresses that
   appear in the IP header, and those should be provided by the MIGRATE
   message.  For transport mode, we require it to be present to keep a
   fixed message format.  For all modes, the address information
   represents the locators of the SA.  For transport mode, it must match
   the addresses provided in the selector.  For tunnel mode, it is
   obviously not required.

   The source and destination addresses (locators) of the target entry
   should be overwritten.  New locator values should also be used to
   update SP.  Note that the IPsec protocol and mode fields SHOULD NOT
   be updated by a PF_KEY MIGRATE message.

   A PF_KEY MIGRATE message should be formed, based on security policy
   configuration and binding record.  The selector information and some
   parts of the SA information (IPsec protocol and mode) should be taken
   from the policy configuration.  The rest of the information should be
   taken from the sequential binding information.  For example, in the
   case where the MN updates its inbound security policy and
   corresponding tunnel mode SA pair, the old source address should be
   set as its previous CoA, and the new source address should be set as
   its current CoA.  Hence, the MN should sequentially keep track of its
   CoA record.  Such information shall be stored in binding update list
   entry.  For the same reason, the HA should keep track of previous
   CoAs of MNs.  Such information shall be stored in binding cache
   entry.  In previous scenario, the source and destination entries of
   the address information for the key manager should respectively be
   set to the CoA and the address of the HA.

   A detailed format of MIGRATE message is provided in Appendix A.

5.3.  Processing PF_KEY MIGRATE Message

   Since a PF_KEY MIGRATE message is applied to a single SPD entry, the
   kernel should first check validity of the message.  During this
   process, the content of sadb_x_kmaddress structure is skipped,
   because its content is intended for the key manager and is simply
   relayed by the kernel.

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   If the message is invalid, an EINVAL error MUST be returned as a
   return value for the write() operation made to the PF_KEY socket.
   After the validation, the kernel checks if the target SPD entry
   really exists.  If no entry is found, an ENOENT error MUST be
   returned.  If a SPD entry is found and successfully updated, a
   success (0) MUST be returned regardless of subsequent result of SAD
   lookup/update.  Note that there may be cases where a corresponding
   SAD entry does not exist even if a SPD entry is successfully updated.
   In any error case, a PF_KEY MIGRATE message MUST NOT have any effect
   on the SPD and SAD.

   With respect to the behavior of a normal process (including the IKE
   daemon) which receives a PF_KEY MIGRATE message from a PF_KEY socket,
   it SHOULD first check if the message does not include erroneous
   information.  When there is any error indicated, the process MUST
   silently discard the PF_KEY MIGRATE message.  Otherwise, the
   processing of the message may continue.  This implies that the kernel
   is the only entity responsible for returning a status regarding
   message validation.

5.4.  NAT Traversal

   Dual Stack Mobile IPv6 [DSMIPv6] supports a scenario where a MN is
   connected to an IPv4 network behind a Network Address Translator
   (NAT).  In such case, the MN assigns an IPv4 private address to its
   network interface but it is still capable of registering its care-of
   address to the HA, using the NAT Traversal technique [RFC3948].  The
   MN and HA may set up an IPsec tunnel to protect data and return
   routability traffic.

   The PF_KEY MIGRATE mechanism described in this document does not
   support [DSMIPv6] operations.  Even if it may be possible to extend
   it to support DSMIPv6, it is left for future work.  The main reasons
   for that decision are:

   o  the current complexity of IPsec and IKE NAT-T implementations,
      including system specific differences.
   o  the current lack of feedback and available complete implementation
      of DSMIPv6 on which to implement and test extensions of MIGRATE to
      support DSMIPv6.

5.5.  Limitations of PF_KEY MIGRATE

   A Security Parameter Index (SPI) is not included in the old SA
   information to specify target SAD entry.  This helps to lessen
   operational burden of Mobile IPv6.  However, this simplification can
   produce ambiguity in searching for the target security association
   entry.  When the unique SPD level is available, it should be used

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   because it avoids this problem both by marking the SA to update and
   by limiting SA sharing.

   It should be noted that delivery of PF_KEY MIGRATE messages cannot be
   guaranteed, which is common to other PF_KEY messages.  It may be
   possible (even if highly unlikely) that a MIGRATE message be lost.
   In such case, there will be inconsistency between the binding record
   managed by Mobile IPv6 and IPsec database inside the kernel or the
   IKE daemon.  Once a PF_KEY MIGRATE message is lost, it would not be
   possible for the receiver to process some subsequent MIGRATE messages
   properly.  Reinitialization of the Mobile IPv6 stack and IPsec
   databases may be needed for recovery.

6.  Necessary Modifications to Mobile IPv6 and IPsec/IKE

   In order to realize the proposed mechanism, there are some necessary
   modifications to Mobile IPv6 and IPsec/IKE.  They are listed below
   for implementors of Mobile IPv6 and/or IPsec/IKE.

   o  Modifications to Mobile IPv6:
      *  The Mobile IPv6 code needs to make an access to PF_KEY socket.
         In particular, the Mobile IPv6 code should have privilege to
         write messages into a PF_KEY socket.
      *  Issuing PF_KEY MIGRATE messages: in order to send MIGRATE
         messages, it is required that the Mobile IPv6 code has some
         knowledge of its IPsec configuration and precise binding
         record.  The Mobile IPv6 code may be aware of exact IPsec
         configuration in form of security policy.  It would also be
         possible that the Mobile IPv6 code is only aware of minimum
         IPsec configuration whether IPsec is used or not.
      *  With regard to the emission of the MIGRATE message during the
         home registration, the Mobile IPv6 code need to emit it before
         issuing the Binding Update.
   o  Modifications to IPsec stack:
      *  Processing PF_KEY MIGRATE messages: the kernel should be able
         to process PF_KEY MIGRATE messages sent by the Mobile IPv6
         code.  Unless the message is invalid, it should be sent to all
         open PF_KEY sockets.
   o  Modifications to IKE (associated with processing of MIGRATE):
      *  the IKE code needs to update its local copy of IPsec databases
         (SPD and SAD) in accordance with received PF_KEY MIGRATE
      *  the IKE code needs to update its associated IKE_SA with new
         local and remote addresses specifically provided in PF_KEY
         MIGRATE messages (in sadb_x_kmaddress structure).  It also
         needs to maintain in its SPD the addresses to be used for
         future negotiation of IKE_SA.

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7.  Implementation

   The mechanism described in this memo has been implemented for Linux:

   o  Linux kernel IPsec stack: the mechanism is fully implemented since
      version 2.6.28 (released in December 2008) both for PF_KEY (as
      described in this memo) and Linux native interface (Netlink, see
      [RFC3549]) with in-kernel XFRM transformation framework (basis of
      the IPsec stack).
   o  UMIP (Linux Mobile IPv6 Daemon): the mechanism is fully supported
      for years.  Details and documentation are available at
      http://umip.org.  Linux native interface (Netlink) is used by UMIP
      to pass MIGRATE message to the kernel which passes it after
      processing to registered (PF_KEY and Netlink/XFRM) key managers.
   o  Racoon IKEv1 daemon: the mechanism is fully supported and
      available upstream since 2008.  Racoon relies on PF_KEY for
      communications with the kernel IPsec stack.
   o  StrongSwan IKEv2 daemon for Linux: the mechanism is fully
      supported upstream since version 4.2.9, released in November 2008.
      Support has been developed by StrongSwan's main developers (Martin
      Willi and Andreas Steffen) based on this specification.
      StrongSwan IKEv2 daemon uses Netlink for communications with the

8.  Security Considerations

   There is no specific security considerations for the mechanisms
   introduced by the document but as it makes deployment of dynamic
   keying in Mobile IPv6 environments easier it should improve the
   security of such environments.  Note that dynamic keying is known to
   be more secure (it provides anti-replay for instance) and far more

9.  IANA Considerations

   This document has no actions for IANA.

10.  Conclusion

   o  There is a need for Mobile IPv6 and IPsec/IKE to interact with
      each other to provide full support of IPsec security functions.
   o  An extension to the PF_KEY framework (PF_KEY MIGRATE message) is
      proposed, which makes it possible:

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      *  for the IPsec/IKE to migrate endpoint addresses IPsec SA from
         one to another.
      *  to make the source address to be used by the key manager for SA
         negotiation available before it is needed.
      *  to update addresses of IKE_SA after movement.
   o  An additional requirement associated with the solution for IKE is
      the addition in SPD image of additional per-SP hints to be used as
      addresses for negotiation of SA.
   o  Currently, large portion of the proposed mechanism is
      implementation dependent due to lack of standard interface to
      access the SPD (PF_POLICY?).

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key Words for Use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [RFC2367]  McDonald, D., Metz, C., and B. Phan, "PF_KEY Key
              Management API, Version 2", RFC 2367, July 1998.

   [RFC2401]  Kent, S. and R. Atkinson, "Security Architecture for the
              Internet Protocol", RFC 2401, November 1998.

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, November 1998.

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

   [RFC3776]  Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
              Protect Mobile IPv6 Signaling Between Mobile Nodes and
              Home Agents", RFC 3776, June 2004.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4877]  Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
              IKEv2 and the Revised IPsec Architecture", RFC 4877,
              April 2007.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol version 2 (IKEv2)",
              RFC 5996, September 2010.

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11.2.  Informative References

   [DSMIPv6]  Soliman, H., "Mobile IPv6 support for dual stack Hosts and
              Routers", RFC 5555, June 2009.

   [MIGRATE]  Sugimoto, S., Nakamura, M., and F. Dupont, "PF_KEY
              Extension as an Interface between Mobile IPv6 and IPsec/
              IKE", draft-sugimoto-mip6-pfkey-migrate-04 (work in
              progress), December 2007.

   [RFC3549]  Salim, J., Khosravi, H., Kleen, A., and A. Kuznetsov,
              "Linux Netlink as an IP Services Protocol", RFC 3549,
              July 2003.

   [RFC3948]  Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets",
              RFC 3948, January 2005.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, January 2005.

   [hld-sec]  Ebalard, A., "Mobile IPv6 Home Link Detection Mechanism
              Security considerations",
              draft-ebalard-mext-hld-security-00 (work in progress),
              April 2009.

Appendix A.  PF_KEY MIGRATE Message Format

   The figure below shows the message format of PF_KEY MIGRATE.  The
   message consists of 7 parts (boundary of each part is marked with
   ">").  The message starts with PF_KEY base message header directly
   followed by a sadb_x_kmaddress{} structure.  The extension holds the
   two IKE_SA local and remote addresses as opaque data for the key
   manager (two 64-bit aligned sockaddr).  It is then followed by two
   address extensions: those respectively hold source and destination
   addresses of the selector.  The rest of the message is specific to
   IPsec implementations on BSD and Linux. sadb_x_policy{} structure
   holds additional information of security policy.  The last part of
   the message is a pair of sadb_x_ipsecrequest{} structures that hold
   old and new SA information.

      0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
     |  ...version   | sadb_msg_type | sadb_msg_errno| ...msg_satype |
     |          sadb_msg_len         |       sadb_msg_reserved       |

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     |                         sadb_msg_seq                          |
     |                         sadb_msg_pid                          |
     |     sadb_x_kmaddress_len      |   sadb_x_kmaddress_exttype    |
     |                    sadb_x_kmaddress_reserved                  |
     ~         IKE_SA local address            (64-bit aligned ...   ~
     ~         IKE_SA remote address           ... pair of sockaddr) ~
     |       sadb_address_len        |     sadb_address_exttype      |
     | _address_proto| ..._prefixlen |     sadb_address_reserved     |
     ~         selector source address (64-bit aligned sockaddr)     ~
     |       sadb_address_len        |     sadb_address_exttype      |
     | _address_proto| ..._prefixlen |     sadb_address_reserved     |
     ~     selector destination address (64-bit aligned sockaddr)    ~
     |       sadb_x_policy_len       |     sadb_x_policy_exttype     |
     |       sadb_x_policy_type      |     ..._dir   |  ..._reserved |
     |                        sadb_x_policy_id                       |
     |                     sadb_x_policy_priority                    |
     |    sadb_x_ipsecrequest_len    |    sadb_x_ipsecrequest_proto  |
     |    ..._mode   |   ..._level   | sadb_x_ipsecrequest_reserved1 |
     |                   sadb_x_ipsecrequest_reqid                   |
     |                 sadb_x_ipsecrequest_reserved2                 |
     ~     old source endpoint address         (64-bit aligned ...   ~
     ~  old destination endpoint address       ... pair of sockaddr) ~
     |    sadb_x_ipsecrequest_len    |    sadb_x_ipsecrequest_proto  |
     |    ..._mode   |   ..._level   | sadb_x_ipsecrequest_reserved1 |

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     |                   sadb_x_ipsecrequest_reqid                   |
     |                 sadb_x_ipsecrequest_reserved2                 |
     ~     new source endpoint address         (64-bit aligned ...   ~
     ~  new destination endpoint address       ... pair of sockaddr) ~

   Following is a structure of PF_KEY base message header specified in
   [RFC2367].  A new message type for PF_KEY MIGRATE (i.e.,
   SADB_X_MIGRATE) should be specified in member sadb_msg_type.

              struct sadb_msg {
                      uint8_t         sadb_msg_version;
                      uint8_t         sadb_msg_type;
                      uint8_t         sadb_msg_errno;
                      uint8_t         sadb_msg_satype;
                      uint16_t        sadb_msg_len;
                      uint16_t        sadb_msg_reserved;
                      uint32_t        sadb_msg_seq;
                      uint32_t        sadb_msg_pid;

   Following is the structure of key manager address extension header.
   SADB_X_EXT_KMADDRESS should be specified in sadb_x_kmaddress_exttype
   field.  It is followed by a pair of sockaddr structures holding
   respectively up-to-date local and remote address to be used by
   IKE_SA.  The pair is globally 64-bit aligned.

              struct sadb_x_kmaddress {
                      uint16_t        sadb_x_kmaddress_len;
                      uint16_t        sadb_x_kmaddress_exttype;
                      uint32_t        sadb_x_kmaddress_reserved;
              /* sizeof(struct sadb_x_kmaddress) == 8 */
              /* Followed by two sockaddr (local and remote) */

   Following is a structure of address extension header specified in
   [RFC2367].  Upper layer protocol should be specified in member

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           struct sadb_address {
                   uint16_t        sadb_address_len;
                   uint16_t        sadb_address_exttype;
                   uint8_t         sadb_address_proto;
                   uint8_t         sadb_address_prefixlen;
                   uint16_t        sadb_address_reserved;

   Following is a structure for holding attributes that are relevant to
   security policy, which is available on BSD and Linux IPsec
   implementations.  Direction of the target security policy should be
   specified in member sadb_x_policy_dir.

           struct sadb_x_policy {
                   uint16_t        sadb_x_policy_len;
                   uint16_t        sadb_x_policy_exttype;
                   uint16_t        sadb_x_policy_type;
                   uint8_t         sadb_x_policy_dir;
                   uint8_t         sadb_x_policy_reserved;
                   uint32_t        sadb_x_policy_id;
                   uint32_t        sadb_x_policy_priority;

   Following is a structure for holding attributes that are relevant to
   security association, which is available on BSD and Linux IPsec
   implementation.  IPsec protocol (ESP or AH) and mode of the target
   security association should be provided in member
   sadb_x_ipsecrequest_proto and sadb_x_ipsecrequest_mode, respectively.

           struct sadb_x_ipsecrequest {
                   uint16_t        sadb_x_ipsecrequest_len;
                   uint16_t        sadb_x_ipsecrequest_proto;
                   uint8_t         sadb_x_ipsecrequest_mode;
                   uint8_t         sadb_x_ipsecrequest_level;
                   uint16_t        sadb_x_ipsecrequest_reserved1;
                   uint32_t        sadb_x_ipsecrequest_reqid;
                   uint32_t        sadb_x_ipsecrequest_reserved2;

Appendix B.  Acknowledgements

   Various people had contributed and were acknowledged in previous
   version of [MIGRATE] draft.  Because most of the text from previous
   draft has been kept in this document, those acknowledgements are
   still valid: Mitsuru Kanda, Kazunori Miyazawa, Tsuyoshi Momose
   Shoichi Sakane, Keiichi Shima, Noriaki Takamiya, and Hideaki

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   We would also like to acknowledge here the positive technical
   feedback from Shinta Sugimoto while extending his MIGRATE mechanism
   and also the work provided by people of USAGI (Masahide Nakamura,
   Shinta Sugimoto, Hideaki Yoshifuji, ...) on Linux kernel's Mobile
   IPv6 and IPsec stack.  Additionally, Romain Kuntz and Jean-Michel
   Combes provided thorough reviews of the document during the
   publication process.

   This document was generated by xml2rfc.

Authors' Addresses

   Arnaud Ebalard
   EADS Innovation Works
   12, rue Pasteur - BP76
   Suresnes  92152

   Email: arno@natisbad.org

   Sebastien Decugis
   National Institute of Information and Communications Technology
   4-2-1, Nukui-Kitamachi,
   Koganei, Tokyo  184-8795

   Email: sdecugis@nict.go.jp

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