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Versions: 00 01 02

Network Working Group                                         A. Ebalard
Internet-Draft                                                      EADS
Intended status: Informational                              May 21, 2009
Expires: November 22, 2009


               Mobile IPv6 IPsec Route Optimization (IRO)
                     draft-ebalard-mext-ipsec-ro-01

Status of this Memo

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

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   This Internet-Draft will expire on November 22, 2009.

Copyright Notice

   Copyright (c) 2009 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 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

   This memo specifies an improved alternate route optimization
   procedure for Mobile IPv6 designed specifically for environments
   where IPsec is used between peers (most probably with IKE).  The



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   replacement of the complex Return Routability procedure for a simple
   mechanism and the removal of HAO and RH2 extensions from exchanged
   packets result in performance and security improvements.


Table of Contents

   1.  Disclaimer and conventions . . . . . . . . . . . . . . . . . .  4
     1.1.  Disclaimer . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Conventions used in this document  . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Current situation  . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Characteristics of IRO . . . . . . . . . . . . . . . . . .  5
     2.3.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  7
     2.4.  Notes to the reader  . . . . . . . . . . . . . . . . . . .  8
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1.  The big picture  . . . . . . . . . . . . . . . . . . . . .  9
     3.2.  Pre-binding steps  . . . . . . . . . . . . . . . . . . . .  9
     3.3.  BU emission  . . . . . . . . . . . . . . . . . . . . . . . 11
     3.4.  Proof of CoA ownership . . . . . . . . . . . . . . . . . . 11
     3.5.  BA emission  . . . . . . . . . . . . . . . . . . . . . . . 12
     3.6.  Post-bindings steps  . . . . . . . . . . . . . . . . . . . 12
   4.  Proof of CoA ownership . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Position of the problem  . . . . . . . . . . . . . . . . . 13
     4.2.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . 13
     4.3.  Mobility Options . . . . . . . . . . . . . . . . . . . . . 14
       4.3.1.  Nonce option . . . . . . . . . . . . . . . . . . . . . 14
     4.4.  IRO Messages . . . . . . . . . . . . . . . . . . . . . . . 14
       4.4.1.  Address Ownership Test Offer (AOTO)  . . . . . . . . . 14
       4.4.2.  Address Ownership Test Challenge (AOTC)  . . . . . . . 15
       4.4.3.  Address Ownership Test Response (AOTR) . . . . . . . . 16
       4.4.4.  Address Ownership Test Status (AOTS) . . . . . . . . . 16
     4.5.  Concrete uses of AOT* Messages . . . . . . . . . . . . . . 17
       4.5.1.  Registration with a CN . . . . . . . . . . . . . . . . 17
       4.5.2.  Early test of CoA ownership  . . . . . . . . . . . . . 18
       4.5.3.  Test of HoA ownership  . . . . . . . . . . . . . . . . 19
   5.  Remapping rules  . . . . . . . . . . . . . . . . . . . . . . . 19
     5.1.  Requirements . . . . . . . . . . . . . . . . . . . . . . . 19
       5.1.1.  On-wire addresses access from userland . . . . . . . . 19
       5.1.2.  Non-MH traffic (data traffic)  . . . . . . . . . . . . 20
         5.1.2.1.  Compatibility with traffic using RH2 and HAO . . . 20
         5.1.2.2.  Incoming traffic . . . . . . . . . . . . . . . . . 20
         5.1.2.3.  Outgoing traffic . . . . . . . . . . . . . . . . . 20
         5.1.2.4.  Related traffic (ICMPv6 error traffic,
                   fragments) . . . . . . . . . . . . . . . . . . . . 21
       5.1.3.  MH traffic . . . . . . . . . . . . . . . . . . . . . . 21
         5.1.3.1.  Incoming traffic . . . . . . . . . . . . . . . . . 21
     5.2.  Rules syntax . . . . . . . . . . . . . . . . . . . . . . . 22



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       5.2.1.  Remapping rules content  . . . . . . . . . . . . . . . 22
       5.2.2.  Remapping rules simple syntax  . . . . . . . . . . . . 23
   6.  Tracking SPI changes . . . . . . . . . . . . . . . . . . . . . 23
     6.1.  Initial collect ?  . . . . . . . . . . . . . . . . . . . . 24
     6.2.  SADB related PF_KEY events . . . . . . . . . . . . . . . . 25
       6.2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . 25
       6.2.2.  Reception of a PF_KEY SADB_GETSPI message  . . . . . . 25
       6.2.3.  Reception of a PF_KEY SADB_UPDATE message  . . . . . . 26
       6.2.4.  Reception of a PF_KEY SADB_ADD message . . . . . . . . 26
       6.2.5.  Reception of a PF_KEY SADB_DELETE message  . . . . . . 26
       6.2.6.  Reception of a PF_KEY SADB_EXPIRE message  . . . . . . 26
     6.3.  Rekeying . . . . . . . . . . . . . . . . . . . . . . . . . 26
       6.3.1.  Phase 2  . . . . . . . . . . . . . . . . . . . . . . . 26
   7.  Extending advantages of IRO to the HA  . . . . . . . . . . . . 27
     7.1.  Rationale and expected advantages  . . . . . . . . . . . . 27
     7.2.  Changes to HA processing . . . . . . . . . . . . . . . . . 27
     7.3.  Changes to MN processing . . . . . . . . . . . . . . . . . 28
   8.  Implementation Notes . . . . . . . . . . . . . . . . . . . . . 28
     8.1.  Nested SA  . . . . . . . . . . . . . . . . . . . . . . . . 28
     8.2.  Having IKE traffic flow via the IPsec tunnel to the HA . . 29
     8.3.  Remapping rules and old IPsec architecture . . . . . . . . 31
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 31
     9.1.  Proof of address ownership . . . . . . . . . . . . . . . . 31
       9.1.1.  Position of the problem  . . . . . . . . . . . . . . . 31
       9.1.2.  Home Address ownership . . . . . . . . . . . . . . . . 32
       9.1.3.  Care-of Address ownership  . . . . . . . . . . . . . . 32
     9.2.  Remapping (comparison with explicit HAO/RH2 inclusion) . . 33
     9.3.  Anonymity  . . . . . . . . . . . . . . . . . . . . . . . . 33
     9.4.  Limiting attack surface  . . . . . . . . . . . . . . . . . 33
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 33
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 33
     12.2. Informative References . . . . . . . . . . . . . . . . . . 34
   Appendix A.  Ability to send does not prove CoA ownership  . . . . 35
   Appendix B.  IKE exchanges use the HoA and the tunnel to the HA  . 36
   Appendix C.  Arguments for no regular check of HoA ownership . . . 37
   Appendix D.  Lack of encryption between MN and HA  . . . . . . . . 38
   Appendix E.  What if I don't need protection?  . . . . . . . . . . 39
   Appendix F.  MTU Gains . . . . . . . . . . . . . . . . . . . . . . 40
   Appendix G.  Compatibility with static keying  . . . . . . . . . . 41
   Appendix H.  Compatibility with the use of CoA in SP/SA  . . . . . 42
   Appendix I.  Rationale for not specifying a new BU . . . . . . . . 42
   Appendix J.  Anonymity . . . . . . . . . . . . . . . . . . . . . . 44
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 45






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1.  Disclaimer and conventions

1.1.  Disclaimer

   This memo covers MIPv6 Route Optimization in IPsec/IKE environments.
   For that reasons it is expected that the reader be familiar with the
   main reference documents associated with those topics.

   This includes the main MIPv6 reference documents ([RFC3775],
   [RFC3776], [RFC4877], ...) and main IPsec/IKE reference documents
   ([RFC4301], [RFC4303], [RFC4306] and their previous versions).

   For the discussions regarding the security of route optimization
   (proof of address ownership, mainly) [RFC4225] is a must read and
   [RFC4651] provides a good summary of the issues and previous work on
   possible solutions.

   The Security Considerations section (section 6) of [RFC4866] also
   provides a good security-oriented introduction to the address
   ownership problem.

1.2.  Conventions used in this document

   In this document, except otherwise specified:

   o  "IKE" is used as a placeholder for both IKEv1 [RFC2409] and IKEv2
      [RFC4306].
   o  "Peer" is used as a placeholder for a MIPv6 end entity, i.e. a CN
      or a MN.
   o  "HAO" is used as a placeholder for Destination Options Header
      carrying a Home Address Option.  When the address in a HAO is
      considered, it denotes the address found in the Home Address field
      of the Home Address option carried in the Destination Options
      Header.
   o  When "tunnel" is used to designate the IPv6-in-IPv6 path between
      the MN and its HA, IPsec in tunnel mode is assumed to be in place.
   o  When "MN-CN" is used it also obviously includes the MN-MN case
      where the second MN acts as a CN for the first MN.
   o  When "IPsec flow" applies to a MN-MN or MN-CN communication, the
      address of the MN considered for the associated SP is the HoA.

   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].







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2.  Introduction

2.1.  Current situation

   Mobile IPv6 specification [RFC3775] mandates the use of IPsec for
   protection of communications (control and optionally data) between a
   Mobile Node and its Home Agent.  Support for static keying is made
   mandatory, and dynamic keying optional.  The protection is made
   possible by the trust relationship that preexists between the HA and
   the MN: they belong to a common trust domain (the same network, a
   PKI).  Interactions between MIPv6 and IPsec/IKE for MN and HA
   exchanges are partly covered in [RFC3776] and [RFC4877].

   For implementation reasons outside the scope of previous reference
   documents, some additional changes to IPsec/IKE are required to
   support Mobile IPv6.  [MIGRATE] specifies a way to implement those
   changes by extending PF_KEY framework.

   [RFC3775] also specifies a Route Optimization procedure which allows
   direct communications to occur between a Mobile Node (MN) and a
   Correspondent Node (CN), without suffering the delay associated with
   the routing through the MN's Home Agent.  The setup of this optimized
   routing is based on a mechanism called Return Routability Procedure
   (RRP).

   One of the main hypothesis behind the design of Return Routability
   Procedure is the lack of trust relationship between the MN and its
   CN.  This results in a complete lack of security in terms of privacy
   and authentication of data: the procedure mainly provides a limited
   proof of MN's HoA and CoA addresses ownership to the CN.

   In trust domains (networks with an underlying PKI infrastructure)
   where Mobile IPv6 gets deployed using dynamic keying (IKE or IKEv2)
   for negotiating Security Associations, Mobile Nodes are already
   provisioned with credentials (X.509 certificates).  In those
   environments, the initial hypothesis that led to the design of RRP
   and its associated limited security abilities does not hold anymore.

   At the moment, [CNIPsec] only describes how IPsec can be used to
   protect signaling traffic between the Mobile Node and the
   Correspondent Node but only provides a limited coverage of the
   problem.

2.2.  Characteristics of IRO

   This document defines an extension of Mobile IPv6 protocol that aims
   at replacing common RRP and RO procedures by a mechanism called IPsec
   Route Optimization (IRO) in environments where IPsec and IKE are



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   used.

   It allows MN to mount and maintain direct IPsec-protected
   communications with CN and other MN with which they share some trust
   relationship, in a completely transparent fashion for upper layer
   protocols.

   IRO is not a detailed set of requirements for IPsec to work between
   MN and CN but a new mechanism resulting from the tight integration
   and joint efforts of MIPv6, IKE and IPsec to provide a secure and
   scalable mobility service.

   The main functional and security advantages that best describe IRO
   are:

   o  Protected MN-CN binding using IKE-negotiated IPsec SAs.
   o  Complete transparency for IKE (negotiation, rekeying, movement,
      ...) and other upper layers, including layer 14 (the user).
   o  Compatibility with both tunnel and transport mode IPsec protection
      between peers.
   o  Compatibility with static keying (See Appendix G).
   o  In MN-CN case, non-disclosure of MN's HoA on its foreign link.
   o  No additional changes to IPsec or IKE protocols and limited
      changes to MIPv6 via four simple messages and an option resulting
      in simple and generic integration within IPsec and Mobile IPv6
      stacks.
   o  Improved and more generic proof of address ownership mechanism.
   o  Safe by default behavior avoiding direct unprotected traffic
      flows.
   o  Complete removal of RH2 and HAO, resulting in simplified packet
      handling on both sides and possibly better compatibility with
      filtering implemented in the network.
   o  Per packet MTU gains between 24 and 48 bytes in comparison with
      equivalent uses of IPsec in standard RO context.  Details are
      provided in Appendix F.

   The main prerequisites of IRO are:

   o  Existence of a trust relationship between peers (i.e. shared
      secret or ability to use IKE).
   o  Required protection of peers' exchanges (i.e.  IPsec is used
      between peers).  IRO does not apply to direct unprotected
      communications between peers.  More precisely, IRO prevents them.
   o  To fully benefit from IRO improvements, data traffic between the
      MN and its HA must be exchanged through an IKE-negotiated movement
      resistant IPsec tunnel.  If this hypothesis is not fulfilled, IRO
      will still be usable but some security features listed previously
      will be lost (Appendix D).



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2.3.  Motivation

   The motivation behind this work is the direct need for both efficient
   and secure communications in Mobile IPv6 environments already
   benefiting from an underlying trust domain.

   The first intended target of the mechanism described in this memo is
   the growing number of corporate networks where PKI are now
   widespread.  This is generally due to the increasing number of
   services (802.1X, SSL/IPsec VPN, TLS Web portal, S/MIME, ...) that
   use them on a daily basis as the root of their security and to
   provide logical segregation.  It is also suitable for other kinds of
   communities.

   In environments where data confidentiality and privacy do matter
   (IPsec is used for the protection of data between the MN and its HA),
   current RRP and RO between peers of the trust domain are usually
   deactivated:

   o  to prevent direct unprotected communications between peers that
      would bypass protected tunneling through the Home Network.
   o  because their implementation and setup with IPsec/IKE does not
      work out of the box and is not trivial even if [CNIPsec] helps for
      signaling.

   This results in heavy constraints on the HA (which handles all the
   traffic to/from its MN) and the de-facto inability to get direct end-
   to-end IPsec-protected MN-CN and MN-MN communications.

   The ability to reduce the number of communications performed by the
   Mobile Node that get tunneled through the HA is both an improvement
   in term of upload bandwidth consumption on the link to the HA,
   cryptographic processing requirements on the HA and also in term of
   latency for applications that directly benefit from end-to-end
   connections, like Chat, VoIP, Videoconferencing or direct file
   exchanges.

   In a sense, there is a kind of vicious circle regarding the use of
   IPsec/IKE with various protocols, including MIPv6: because dynamic
   keying and IPsec are not considered the common case, they are not
   fully covered in specifications (static keying for simple modes).
   The net effect is that their implementation and deployment is then
   complicated, which results in limited use.  In a sense, IRO tries to
   break that circle.  Simply put, this specification considers IKE-
   enabled environments as the first target and then covers static
   keying cases.





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2.4.  Notes to the reader

   The mechanism described in this memo is very simple from a design
   perspective.  To keep this apparent simplicity and the reading of the
   document pleasant, all design decisions and main justifications are
   provided in the numerous appendices (around 10 pages).  This allows
   to focus on the details of the mechanism in the body of the document
   (around 20 pages).

   For previous reason, the reading of the document can be performed
   linearly.  The not so curious reader can skip over the appendices
   which are only a must read for developers and security people to
   acquire a deep understanding of the mechanism and how security has
   been taken into account in its design.

   Unlike many other IETF documents, this memo voluntarily provides a
   practical implementation feedback geared towards developers.  Even if
   the associated section does not mandate an implementation design, it
   might be of interest anyway.


3.  Overview

   The whole document is geared towards improved security between MIPv6
   nodes and also improved usability of IPsec/IKE with MIPv6.  This
   section provides to the reader a quick non-normative overview of how
   IRO works, before entering the details of the mechanism in next
   sections.  The reader is expected to be familiar with the vocabulary
   used in [RFC3775].  We do not consider in this section the
   relationship between the MN and its HA, only the relationship between
   a MN and its CNs.  In the whole document, IKE is considered as the
   default mechanism used for SA setup.

   This section provides a quick and non-normative overview of IRO and
   introduces next sections that contain normative details.  The first
   subsection provides a rough outline of IRO.  It is followed by 5
   small subsections that cover the steps of IRO processing, in the
   order they occur:

   o  Pre-binding steps: installation of remapping rules, which IRO uses
      to prevent the use of RH2 and HAO in incoming and outgoing
      signaling packets (MH traffic).
   o  BU emission: description of the steps that apply to the emission
      of the BU by the MN in the context of IRO.
   o  Proof of CoA ownership: description of the steps that occur when a
      proof of CoA ownership is requested by the peer.





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   o  BA emission: description of the steps that apply to the emission
      of the BA to the MN in the context of IRO.
   o  Post-binding steps: installation of additional remapping rules,
      which IRO uses to prevent the use of RH2 and HAO in incoming and
      outgoing data packets.

3.1.  The big picture

   This section simply lists the key ideas and design concepts behind
   IRO.

   When IPsec is used between two peers, every packet de facto contains
   a simple piece of information (the SPI) that gives access to many
   parameters.  Among those parameters synchronized between the two
   IPsec stacks are address information for both peers.  Unlike IPsec,
   MIPv6 uses specific extensions (RH2 and HAO) to explicitly carry
   address information.  When both protocols are used together and the
   IPsec SA/SP make use of HoA (i.e. not CoA), the RH2 and HAO
   extensions in packets carry the HoA.  It could easily be deduced from
   the SPI.  Based on this observation, IRO removes RH2 and HAO
   extensions from packets and replace them by simple additional steps
   on the sender and the receiver: remapping rules for address based on
   the SPI.

   Previous removal of HAO and RH2 extensions from traffic between peers
   is also perfectly applicable to the traffic between a MN and its HA.
   This specification extend the remapping rules to the traffic between
   a MN and its HA.  When IRO is used, RH2 and HAO extensions are simply
   not seen on the wire.

   As stated previously, the hypothesis on which common RO and RRP are
   based simply do not hold when peers are able to use IPsec/IKE between
   them.  For that reason, even if some proof of address ownership is
   still required, a more suitable (read simple) mechanism is defined
   for that purpose.

   To sum it up (simplistic vision):

   o  IRO simplifies packets format by removing HAO and RH2 extensions.
   o  IRO fully replaces RRP by a more suitable and simple mechanism
      taking into account the use of IPsec/IKE between peers.
   o  IRO defines how this can be extended to MN-HA exchanges.

3.2.  Pre-binding steps

   Before any direct communication can take place between a MN and a CN,
   the CN must accept a binding between the CoA and the HoA of the MN.
   For that to happen, the CN must have acquired the proof of both HoA



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   and CoA addresses ownership by the MN.

   In RRP, the MN proves to the CN its ability to both send and receive
   traffic from and at those addresses by a four messages exchange
   combining both direct and HA-tunneled packets.

   In the context of IRO, the binding registration between peers is
   IPsec protected.  It is expected that IKE be used for negotiating an
   initial pair of ESP transport mode IPsec SAs between the HoA of the
   MN and the address of the CN for protecting this registration (static
   keying is covered later in the document).  IKE negotiation occurs
   using the tunnel between the MN and its HA, i.e. the MN uses the HoA
   for that purpose.  This provides the CN the initial proof of HoA
   ownership by the MN.

   On both entities, the specific IPsec ESP transport mode SAs
   (protecting MH traffic) created between the peers are taken into
   account by IRO code in Mobile IPv6 stack.  This triggers the setup of
   specific "remapping rules" on both entities, that will be applied to
   incoming and outgoing IPsec packets whose SPI matches the one of
   tracked SAs:

   1.  On the MN, the outgoing IPsec traffic matching the SPI of the
       associated SA to the CN has its source address remapped to the
       address stored (by MIPv6 process) in the ancillary data of the
       packet (the CoA).
   2.  On the CN, the incoming IPsec traffic matching the SPI of the
       associated SA with the MN has its source address remapped to the
       specific source address in the SA (the HoA of the MN).  The
       remapped address is kept as an ancillary data in the local packet
       structure for further processing.  The packet is then naturally
       handled by the IPsec stack.
   3.  On the CN, the outgoing IPsec traffic matching the SPI of the
       associated SA to the MN has its destination address remapped to
       the address stored in the ancillary data of the packet, if not
       null.
   4.  On the MN, the incoming IPsec traffic matching the SPI of the
       associated SA to the CN has its destination address compared with
       the CoA the MN is asking a binding for to the CN.  On match, the
       destination address of the IPsec packet is remapped to the
       destination address in the SA (the HoA of the MN).  The packet is
       then naturally handled by the IPsec stack.

   Simply stated, rules 1 and 3 will end up performing a remapping of
   HoA used in outgoing IPsec packets in their CoA counterparts and
   rules 2 and 4 will do the opposite on the other side for incoming
   IPsec packets.




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   Note that these rules apply only to IPsec packets associated with SA
   that protect MH traffic.  They are used before any data packet is
   received or sent by the entities using a direct path.

3.3.  BU emission

   The MIPv6 stack on the MN emits a Binding Update packet containing a
   Mobility Header AltCoA option which carries the CoA it is proposing a
   binding for to the CN.  This packet is sent from the HoA of the MN to
   the address of the peer.  The CoA is put as an ancillary data in the
   local packet structure for further processing.  As it matches the
   IPsec SA put in place between the MN and the peer, it gets handled by
   the IPsec stack to be ESP protected.  Before leaving the MN, it
   passes the set of MIPv6 rules for the MN; a match is found against
   rule 1, so that the source address of the packet is remapped to the
   address available as an ancillary data in the packet, the CoA of the
   MN.

   When the IPsec protected BU hits the MN, it passes the set of MIPv6
   rules for the CN.  It matches rule 2 so that its source address is
   remapped to the source address of the SA (the HoA of the MN).  The
   source address found in the packet is stored as ancillary data.  The
   packet is handled by the IPsec module, matches the SA, is decrypted
   and passed to the upper layer, the MIPv6 process.

   During parsing, the CN compares the content of the AltCoA option with
   the address previously stored as ancillary data.

3.4.  Proof of CoA ownership

   At that point, before accepting the binding and replying with a BA,
   the CN must have the proof of CoA ownership from the MN.  If one is
   already available, it simply goes on and sends a BA, as described in
   3.4.  Otherwise, it first performs following steps.

   It sends a newly defined MH message (AOTC, Address Ownership Test
   Challenge) to the MN, providing the CoA as ancillary data, so that
   the remapping rules will make the packet use the CoA for the address
   found in the IPv6 header destination field.  This packets carries a
   freshly generated nonce.

   On the MN, the packet follows the reverse remapping process, the CoA
   being remapped to the HoA and passed as ancillary data.  The MIPv6
   stack replies with an IPsec protected MH message to the CN (AOTR,
   Address Ownership Test Request), using the HoA as local source but
   providing the CoA as ancillary data.  The remapping rule makes the
   CoA the on-wire address of the packet.  This packets carries the
   nonce sent by the CN.



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   The CN receives the packet and after having checked the source
   address and the nonce against the one previously sent, the MIPv6
   stack records the address ownership of the CoA for that MN, and
   continues with the steps described in Section 3.5

3.5.  BA emission

   The CN constructs a Binding Acknowledgement packet to be sent to the
   HoA of the MN.  The CoA of the MN is put as an ancillary data in the
   local packet structure for further processing.  Now, as the BA
   matches the SA, it is ESP-protected and passes the set of MIPv6 rules
   for the CN.  It matches rule 3 and the HoA is replaced with the
   address available in the ancillary data of the packet (MN's CoA).
   The packet is then sent.  At that moment, if the status code in the
   BA is 0 (Binding Update Accepted), the binding is effective on the
   CN.

   On the MN, the IPsec protected BA is received, it passes through the
   set of MIPv6 rules for the MN and matches rule 4.  The destination
   address is changed to the destination address of the SA (HoA of the
   MN).  It is then handled by the IPsec module, and then to the MIPv6
   process.  If the status code in the BA is 0, the binding is effective
   on the MN.

   For the rest of this section, we consider the binding is effective on
   both sides.  Other scenarios are covered in details in Section 3.

3.6.  Post-bindings steps

   In [RFC3775], when the RRP has completed successfully, routing of
   traffic between the MN and the CN is automatically modified to follow
   a direct path.  With IRO, on the contrary, a successful binding
   between a MN and a CN does not trigger any change in routing of
   _regular_ traffic between the MN and the CN.  It still flows using
   the IPsec tunnel through the MN's HA.  Only IPsec traffic is
   optimized.

   This design decision provides a "safe by default" behavior and avoid
   a successful binding to lead to unprotected direct communications.

   Furthermore, only IPsec flows will be able to take advantage of the
   direct path between the MN and the CN.  Arguments for this design are
   provided in Appendix E.

   So, if existing IPsec SAs protecting non-signaling traffic (data) are
   already available on both sides, that have the HoA and the address of
   the MN as address selectors, remapping rules are put in place to
   perform the same kind of address changes presented in four previous



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   rules.  Those rules are static ones (they do not use any ancillary
   data) that remap CoA to HoA and HoA to CoA (after some checks),
   respectively before and after IPsec processing.

   They simply replace the HAO and RH2 headers inclusion and parsing on
   both sides by using the SPI information as an opaque multiplexing/
   demultiplexing value available on both ends.


4.  Proof of CoA ownership

4.1.  Position of the problem

   A CN accepting a binding for the CoA of a peer is not something
   harmless.  In the context of IRO, this decision is based on:

   o  a proof of HoA ownership by the MN at the time the SA is
      negotiated.
   o  a proof of CoA ownership by the MN.

   The existence of a strong trust relationship between the two (pairs
   of SA) and an easy proof of emission capability from the CoA are
   unfortunately insufficient proofs of CoA ownership.  As covered in
   Appendix A, a proof of the ability for the MN to receive traffic at
   its asserted CoA is required to workaround the lack of ingress-
   filtering at the scale of Internet: it avoids the CN to involuntarily
   take part in a DoS against the provided CoA.

4.2.  Overview

   As the proof of HoA ownership is only required to occur once in the
   context of IRO, the mechanism focuses on the proof of CoA ownership.
   Instead of reusing the complicated RRP, IRO directly benefits from
   the available IPsec protection between the MN and its CN to simplify
   things.

   Furthermore, in the context of IRO, the lifetime of the provided
   proof is no longer limited and generally de-correlated from
   registration steps.  This already reduces the amount of transferred
   data and leaves room for further optimizations (nodes with multiple
   simultaneous connections, nodes with limited numbers of foreign
   networks, ...)

   As CoTI and CoT messages have some associated requirements, options
   and semantic, and also lacks some expressiveness, they are not reused
   for IRO proof of address ownership.  It is based on four new
   extremely simple messages:




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   o  AOTO: Sent by a MN to a CN to offer to prove address ownership.
   o  AOTC: Sent by a CN to the MN at the address to be tested, with a
      Nonce option that will be returned in an AOTR message.
   o  AOTR: Sent by the MN as a response to an AOTC, with the received
      Nonce option.
   o  AOTS: Sent by the CN to the MN to provide a status on ongoing
      address ownership test.

4.3.  Mobility Options

4.3.1.  Nonce option

   The Nonce option has type XX and an alignment requirement of 8n+6.
   Its format is as follows:

    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 = XX   |  Length = 8   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                             Nonce                             +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The content of the Nonce field MUST always be filled with a freshly
   generated 64-bit random value.

   XXX For testing purposes, the Nonce option has type value 88.

4.4.  IRO Messages

   All the normative information associated with the four new messages
   specified by IRO are provided in this subsection.  This includes
   their format, associated constants, security related information and
   processing requirements.

   Note that the messages defined below are used for proof of ownership
   of the CoA.  They are not used to prove ownership of the HoA: this is
   either not done (static keying) or the result of the ability to
   negotiate SA using IKE.

4.4.1.  Address Ownership Test Offer (AOTO)

   This message is sent by a MN to a CN to offer to prove its ownership
   of the CoA the packet was sent from.  An AOTO message MUST NOT be
   sent by a MN if it is not already registered with the CN.  If that
   happens, the CN simply drops the message without further processing.



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   Reception of this message can trigger the emission of either:

   o  an AOTC containing a Nonce option, sent back to the source address
      of the AOTO.
   o  an AOTS with status 0, indicating that the peer does not allow the
      peer to pre-register CoA ownership information.
   o  an AOTS with status 1, indicating to the peer that the proof of
      Address ownership is still valid.
   o  nothing if it is invalid or sent by an unregistered MN.

   The format of the message is as follows:

    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
                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  |            Reserved           |
                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reserved field is not used yet but might be for future need.  It
   currently serves padding requirements.  It should be set to null on
   emission and ignored on reception by peers complying with this
   specification.

   AOTO messages do not carry options.  MH Type field in Mobility Header
   takes value XX when carrying an AOTO message.

   XXX For test purposes, MH Type field should use value 30

4.4.2.  Address Ownership Test Challenge (AOTC)

   The purpose of this message is to provide a nonce to an MN at the
   address the MN wants to provide proof of ownership for.  The ability
   for the MN to return the nonce to the CN (in an AOTR) provides a live
   proof of its ability to receive traffic at that address.  This
   message is possibly sent by a CN to a MN in two situations:

   o  After receiving a Binding Update message that the CN is willing to
      accept but for which it does not already has a proof of address
      ownership for the originating CoA the packet was sent from
      (correlated with the content of the AltCoA option).
   o  After receiving an AOTO from a MN that wants to perform a proof of
      address ownership for the source address of the packet.

   The format of the message is as follows:







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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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                                                               .
   .                        Mobility Options                       .
   .                                                               .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Mobility Options field must always contain a Nonce option.  The
   nonce must be stored locally by the CN for that MN, along with the
   address being tested.  The nonce will be compared with the content of
   the nonce option found in the AOTR messages.

   MH Type field in Mobility Header takes value XX when carrying an AOTC
   message.

   XXX For test purposes, MH Type field should be set to 31

4.4.3.  Address Ownership Test Response (AOTR)

   This message is sent by the MN as a result of receiving an AOTC
   (resulting from an initial action, BU or AOTO).  It contains the same
   nonce, in a Nonce option, the peer had included in its AOTC.  The
   AOTR message is sent from the address to be tested (the on-wire
   destination address of the AOTC).

   When received by the CN, on-wire source address is used to access the
   stored nonce previously sent in an AOTC message and compare it with
   the one in the Nonce option found in the message.  On match, the
   address ownership by the peer is considered proved.

   The format of the message is the same as the AOTC message except for
   MH Type field in Mobility Header which takes value XX when carrying
   an AOTR message.

   XXX For test purposes, MH Type field should be set to 32

4.4.4.  Address Ownership Test Status (AOTS)

   This message is sent by the CN with a status regarding a proof of
   address ownership.  The status can be generic (not associated to an
   address whose ownership is being proved), for instance if this CN
   does not allow MN initiated Address Ownership Tests to occur.  It can
   also be specific to an ongoing or already performed Test of Address



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   Ownership, for instance to explicitly acknowledge the result of the
   test.

   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
                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  |      Code     |    Reserved   |
                                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   MH Type field in Mobility Header takes value XX when carrying an AOTS
   message.  Code field provides the status code the message carries.
   The list of status codes is provided below:

   AOTS status codes:

   o  0 AOTO not allowed
   o  1 Proof of Address Ownership is valid

   XXX For test purposes, MH Type field should be set to value 33

4.5.  Concrete uses of AOT* Messages

4.5.1.  Registration with a CN

   The registration process between a MN and its HA is simple and
   efficient, being made of a simple BU [/BA] exchange.  This is because
   the proof of CoA ownership is not required by the HA from the MN.

   Like with other route optimization procedures, with IRO, the CN is
   required to have a proof of CoA ownership available for the MN before
   accepting a binding and replying with a Binding Ack. More precisely,
   the proof is needed only before sending traffic to the CoA of the MN
   but does not impact the reception of traffic from the CoA.  This is
   of particular importance in the rest of the discussion.

   Unlike in other more common environments where the proof has to be
   made at every binding, or "renewed", IRO uses proofs with unlimited
   lifetimes.  This does not mean that once the ownership has been
   proved to a CN the CoA will indefinitely belong to a MN.  The
   decision is always left to the CN, with the expectation that some
   sufficient temporary storage will make it capable to keep the binding
   for a while.

   This means that if a proof of CoA ownership for a MN is available
   locally on its CN, no live proof is required and a simple BU [/BA]
   exchange is sufficient for the registration to occur.  This also
   means that inside small or medium communities, where MN move between
   few locations, the number of potential CoA remains quite low and



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   stable, and can be kept locally on nodes acting as CN.

   For instance, without limiting the possible uses, a typical scenario
   for a daily use includes an address at home (wifi, ...), another on a
   mobile network (3G, ...) and another at work (wifi, Ethernet, ...).

   With IRO, when a MN sends a BU to a CN for registration or
   reregistration purposes, it starts directing its traffic instantly
   after the emission of the BU to the address of the CN.  Then, the CN
   will either ask for proof of CoA ownership if it has none available
   from that MN for that CoA or send a BA to the peer.  In all cases, it
   puts in place the remapping rules for accepting traffic from the CoA
   (and not the one for emission).  That way, there is no disruption of
   traffic from the MN to the CN.

   If the CN replies with an AOTC message sent to the CoA of the MN, the
   MN replies with an AOTR, proving its complete ownership.  The CN then
   replies with the expected BA and puts in place the required remapping
   rules for the traffic to flow to the MN at its CoA.

   Regarding re-emission, if the MN has no reply from the CN (i.e. no BA
   or AOTC), common re-emission rules apply.  Then, if the CN has sent
   an AOTC, but receives no reply, it can keep things that way or
   garbage collect the remapping rule (i.e. remove it after some time).
   If the MN receives no BA from the CN, it performs re-emission of the
   AOTR (This implies that the Nonce must be kept locally on the CN even
   after the emission of the BA).

4.5.2.  Early test of CoA ownership

   There are cases where a MN will be willing to perform early proof of
   address ownership, allowing it to avoid the delay during movement.
   In that case, the MN sends an AOTO message to the CN, and receives
   either and AOTC or an AOTS.  If the received message is an AOTS, the
   exchange is over.  If the message is an AOTC, it replies with an AOTR
   and waits for an AOTS.

   A possible use of that early test of CoA ownership is by multi-homed
   nodes that already have a list of possible CoAs they will switch to
   if they lose their primary connectivity mean.  Note that:

   o  this is only a possible optimization allowed by the AOT* framework
      introduced in this document, not a requirement.
   o  it still requires the MN to be registered with the CN.
   o  it requires the MN to exchange AOT* messages using the address
      whose ownership is to be proved.





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4.5.3.  Test of HoA ownership

   IRO does not mandate regular proofs of HoA ownership, for the reasons
   covered in Appendix C.  For those who have the need, and can afford
   to lose the associated bits on a regular basis, the AOT* messages can
   be used for that purpose.

   If a CN wants to get a live proof of HoA ownership from a MN, it
   simply emits an AOTC message (with a fresh Nonce option) to the HoA
   of the MN for which it has already accepted a registration.  The MN
   MUST reply with an AOTR message containing the received Nonce option.
   The exchange occurs using respectively the HoA as on-wire destination
   and source address.  This implies that the packets are tunneled
   through MN's HA.  In the MN-MN case, this mainly results in packets
   never following a direct path.

   Note that this specification does not define the action taken by a CN
   if it does not receive AOTR messages as response to its AOTC messages
   sent to the HoA.


5.  Remapping rules

   This section covers the heart of IRO processing, the remapping rules
   that are applied to incoming and outgoing IPsec protected traffic.

5.1.  Requirements

5.1.1.  On-wire addresses access from userland

   With IRO, there is a need for the MIPv6 processing engine to both
   pass and get on-wire source and destination addresses of received and
   emitted IPsec protected MH packets.  This need is mainly associated
   with the proof of address ownership and binding exchanges.  The need
   is simply the same as the one associated with the ability to set and
   get HAO/RH2 for a common MIPv6 process.  Instead of having explicit
   information in the packet, an ancillary path is required.

   This requirement is limited only to MH traffic in general and some
   specific MH types in particular.

   For incoming IPsec protected MH packets, this means that during the
   handling by remapping rules, the remapped on-wire address must be
   kept in the local packet structure as an ancillary data that the
   MIPv6 process will be able to access.

   For outgoing MH packets, this means that the addresses MUST be made
   available as ancillary data in the local packet structures by the



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   MIPv6 process and then be used, if available, by the remapping rules.

   For all incoming IPsec packets associated with a coarse or fine
   grained SA for MH traffic, if a remapping rule is applied to the
   traffic, the on-wire source and destination addresses MUST be made
   available as ancillary data to the userland process that will process
   the packet (i.e. at socket level).  In all cases (remapping rule
   being applied or not), if an on-wire source or destination address is
   not changed, the associated ancillary data MUST contain the
   unspecified address (::).

5.1.2.  Non-MH traffic (data traffic)

   Data traffic exchanged between MN and CN using IRO has simple
   requirements in term of remapping.  We consider here only IPsec
   packets that are not associated with a transport mode IPsec SA
   protecting MH traffic.

5.1.2.1.  Compatibility with traffic using RH2 and HAO

   This specification is compatible with RH2 and HAO extensions even if
   some care is obviously required in the order in which they are
   handled.  This is generally an implementation dependent issue outside
   the scope of this specification.

   In practice, it is expected (except otherwise specified) that IRO
   module handles incoming traffic after RH* or HAO processing and
   outgoing traffic just before emission, i.e. with expected-on wire
   address w.r.t. to RH* and HAO.

5.1.2.2.  Incoming traffic

   When an incoming IPsec packet is handled by IRO, as the last step
   before being processed by the IPsec module, the SPI is used as the
   main key to find existing source and destination addresses remapping
   rules for that traffic (at most one for each).

   Each rule has an expected on-wire address.  The expected address is
   checked against the on-wire one found in the packet.  If it matches,
   the remapping occurs.  Note that the remapping rules for source and
   destination addresses are applied in an independent fashion.

5.1.2.3.  Outgoing traffic

   When an outgoing IPsec protected packet is handled by IRO, the SPI is
   used as the main key to find existing source and destination
   addresses remapping rules for that traffic (at most one for each).
   The expected address is checked against the one found in the IPv6



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   header of the packet.  If it matches, the remapping occurs.  Note
   that the remapping rules for source and destination addresses are
   applied in an independent fashion.

5.1.2.4.  Related traffic (ICMPv6 error traffic, fragments)

5.1.3.  MH traffic

   MH traffic emitted and received by a MIPv6 entity using IRO has
   specific additional requirements compared to common data traffic
   exchanged between those MIPv6 entities.

   Basically, the checks and settings on source and destination
   addresses are relaxed to allow IPsec-protected traffic sent from a
   new non-registered CoA to pass through.  In the MIPv6 stack of the
   CN, checks are done using an ancillary path that allows the on-wire
   address to be passed for verification.

   Here, we only consider IPsec-protected traffic associated with
   transport mode SAs whose selectors provide protection of MH traffic.
   Granularity considerations are covered below.

   The search for remapping rules is done in the same fashion as
   previously described for data traffic.  Only checks and application
   of the rules are changed as described below.

5.1.3.1.  Incoming traffic

   If a remapping rule is found for source address, which contains the
   unspecified address as check, the remapping is performed without
   checking the source address of the packet.  The unspecified address
   is used as a wildcard.

   In source rule case, the on-wire address found in the packet is
   stored as an ancillary data for further processing and decision by
   the MIPv6 stack (commonly in userland).

   Note that this specification does not explicitly mandate when the
   unspecified address should be used in the source remapping rule, and
   leave that to implementors, as it is highly dependent of following
   facts:

   o  if the system does not support fine-grained SP/SA or simply does
      not use them for MH traffic with a peer, then the use of the
      unspecified address will be required.
   o  if fine-grained SA are used, the MIPv6 stack will use the
      unspecified address if the traffic received protected by that SA
      can't be reliably mapped to a specific CoA for the peer, i.e. if



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      it is expected and authorized that the peer sends traffic from
      another [possibly to be registered] CoA.  This is the case for BU,
      AOTO, AOTR traffic for instance.
   o  if the MIPv6 stack supports extensions to [RFC3775]-defined MH
      messages, the use of IRO will still remain possible with those
      extensions.

   Note that this decision is not expected to create interoperability
   issues, as the use of the unspecified address is based on non-
   ambiguous criteria defined in the documents specifying the purpose of
   MH traffic.

   Also note that the use of the unspecified address for checks and the
   passing of the on-wire address to the MIPv6 stack for further
   processing is equivalent from a security standpoint to the decision
   that occurs in common MIPv6 processing of HAO extension.

5.2.  Rules syntax

   To avoid long descriptive sentences in following section, a simple
   syntax for expressing remapping rules is provided here.

5.2.1.  Remapping rules content

   A remapping rule is made of:

   o  a direction, describing the kind of traffic it will potentially be
      applied to.  Possible values are "incoming" or "outgoing"
   o  an SPI value, distinguishing the IPsec packets, encountered in
      that direction, to which the rules might apply.
   o  a value for expected source address or destination address, that
      will be respectively compared with the content of the source or
      destination address field in the IPv6 header.
   o  For a source address, the unspecified address (::) is used as a
      wildcard, in which cases all addresses are allowed.
   o  a value for source or destination address, that will be used for
      remapping the associated address in the packet.  If a single
      address is provided, it is used for remapping after checks have
      been performed.

      If the special keyword "ancillary" is used for remapping a source
      address, the address to be used is found as an ancillary data in
      the packet.

      If the keyword "(ancillary)" appears next to the address to be
      used for remapping a destination, the remapped address should be
      copied as ancillary data in the packet (see example 4 in next
      subsection).



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5.2.2.  Remapping rules simple syntax

   This subsection defines a simple syntax for providing the content
   described in previous subsection.  Those are given as a set of
   examples with few comments.

   1.  A typical set of remapping rules found on a MN (HoA, CoA) for a
       protected data flow with a CN available at address A:

       dir: out, SPI: 42, exp. src: HoA, remap. src: CoA
       dir: in , SPI: 43, exp. dst: CoA, remap. dst: HoA

   2.  A typical set of remapping rules found on a MN (HoA, CoA) for
       protected MH flows with a CN available at address A:

       dir: out, SPI: 44, exp. src: HoA, remap. src: CoA
       dir: in , SPI: 45, exp. dst: CoA, remap. dst: HoA

   3.  A typical set of remapping rules found on a MN (HoA1, CoA1) for a
       protected data flow with another MN (HoA2, CoA2):

       dir: out, SPI: 46, exp. src: HoA1, remap. src: CoA1
       dir: in , SPI: 47, exp. dst: CoA1, remap. dst: HoA1
       dir: out, SPI: 46, exp. dst: HoA2, remap. dst: CoA2
       dir: in , SPI: 47, exp. src: CoA2, remap. src: HoA2

   4.  A typical set of remapping rules found on a MN (HoA1, CoA1) for
       protected MH flows with another MN (HoA2, CoA2):

       dir: out, SPI: 48, exp. src: HoA1, remap. src: ancillary
       dir: in , SPI: 49, exp. dst: CoA1, remap. dst: HoA1
       dir: out, SPI: 50, exp. dst: HoA2, remap. dst: CoA2
       dir: in , SPI: 51, exp. src:   ::, remap. src: HoA2 (ancillary)

   Note that in example 4, last rule expresses the "blind" remapping of
   source address to HoA2; the remapped address is passed as ancillary
   data for further check by the MIPv6 process.


6.  Tracking SPI changes

   [ Following discussions are only geared towards unicast traffic and
   the whole section will certainly get more accurate/interesting
   information during implementation of the mechanism ]

   With IRO, the SPI values referencing SAs are of primary importance:
   their correct collect and tracking in the time is a requirement to
   allow remapping rules to be kept in sync with the changes that can



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   occur in the IPsec stack or MIPv6 stack.  One important remark is
   that the actions performed by the IRO part of the MIPv6 stack on
   incoming and outgoing IPsec protected packets is completely
   transparent for the IPsec stack.  There is no initial requirement for
   the IPsec stack associated with the use of IRO (even if having IRO
   implemented in the IPsec stack might be beneficial).

   IRO acts at the lowest possible level, theoretically just outside the
   IPsec stack, directly on the IPsec protected packets, and only
   requires access to three pieces of information to track and filter
   that packets: SPI, source and destination addresses.

   This section covers that tracking and associated actions based on the
   availability of PF_KEYv2 API [RFC2367].  The intent is to base the
   discussion on a standard interface but it generally apply in a system
   dependent fashion to other interfaces (Netlink/XFRM, ...).  It
   obviously rely on the synchronisation between the two IPsec stacks on
   peers (SADB mainly, expected to be done by IKE).

6.1.  Initial collect ?

   [The need for initial collect _clearly_ depends on the location of
   IRO engine is implemented and how remapping rules are pushed/changed]

   The way remapping rules are put in place and maintained on the system
   implementing IRO is a local matter.  The only requirement is that the
   externally understood behavior be in sync with the description
   provided in the document.  This is especially important with changes
   associated with registration/deregistration and movement.

   In that context, if IRO engine is running in userland, there might be
   a need for maintaining a limited local version of system's SADB to be
   able to efficiently manage changes (removal, addition, CoA change)
   against a set of SA.  For instance, when an IRO registration is
   accepted for a peer, remapping rules are put in place to have its HoA
   remapped to the CoA for incoming IPsec traffic (and the reverse for
   outgoing IPsec traffic).  Upon movement, all those remapping rules
   must be updated to reflect the change of CoA.

   In that case, the use of PF_KEY SADB_DUMP message is possible to get
   access to the whole SADB content, filter interesting SA, load
   required remapping rules for those SA (as described for PF_KEY
   SADB_UPDATE message in 6.2.1) and initially populate some initial IRO
   SA state table.

   Then, if used, this table could be updated when receiving PF_KEY
   messages described in following subsection (addition or removal of
   entries), during movement (access to all impacted SA whose remapping



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   rules should be remapped), or during registration/deregistration
   (addition/removal of associated remapping rules).

6.2.  SADB related PF_KEY events

   This subsection covers the actions performed by IRO when receiving SA
   related PF_KEY events.  Those actions deal with the filtering of
   interesting SAs and installation/removal of associated remapping
   rules.  If another interface than PF_KEY is used to track SA related
   events (or IRO logic is not implemented in userland), the behavior of
   IRO must remain the same with regard to the addition/removal of
   remapping rules.

6.2.1.  Overview

   A fundamental need of IRO is associated with the ability to setup
   remapping rules _before_ traffic that use those rules is emitted.  A
   direct impact of this requirement is the need to access the SPI of
   the SA that will protect the traffic _before_ that SA is used.  In
   practice, when dynamic keying is used, this creates an interesting
   challenge: because SA negotiation is usually triggered by a packet
   matching a SP, and IRO does not modifies IKE processing, some care is
   required in the implementation to ensure that the SPI information is
   gathered and the associated remapping rule installed _before_ the
   triggering packets is IPsec- and then IRO-processed.

   When dynamic keying is implemented using PF_KEY framework, the
   sequence of events performed by the key manager allows to implement
   that behavior, basically by monitoring SADB_GETSPI messages from the
   kernel in order to access SPI value and install the remapping rule
   while the SA is being negotiated.

   It is an implementation issue to ensure that IRO will be able to
   access the SPI and install the remapping rules before they are used.
   This highly depends on the location of IRO implementation (userland,
   kernel space), framework (PF_KEY, ...), ...

6.2.2.  Reception of a PF_KEY SADB_GETSPI message

   When the kernel returns a PF_KEY SADB_GETSPI message to all listening
   processes, IRO processing engine considers this kernel message.
   After validation (kernel emitted, errno not set, ...), it extracts
   the interesting information from the message (SA, Addresses, SPI) in
   order to decide if remapping rules are needed for this SPI.







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6.2.3.  Reception of a PF_KEY SADB_UPDATE message

   When the kernel returns a PF_KEY SADB_UPDATE message to all
   listeners, following reception of the message from a key manager, IRO
   processing engine considers this kernel message.  After validation
   (kernel emitted, errno not set, ...), it extracts from it the Source
   and Destination address extensions along with the direction and the
   SPI value found in the association header.

   Direction allows to decide if the remapping rule is an incoming or
   outgoing one. proto values (should match) allow to decide if wildcard
   rules are required (MH case).  As there is more granularity available
   with IKEv2 selectors, this implies more cases and more specific rules
   (based on MH Type).  [This part will get the required level of
   precision during the implementation].  Addresses allow to decide if
   an address is our HoA for which a peer has registered our CoA, or the
   HoA of a peer for which we have registered its CoA.

6.2.4.  Reception of a PF_KEY SADB_ADD message

   From IRO standpoint, SADB_ADD message is processed in the same
   fashion as SADB_UPDATE message.  The message returned by the kernel
   to all listening processes contains the required SPI (in association
   header) along with the source and destination address extensions.

6.2.5.  Reception of a PF_KEY SADB_DELETE message

   The reception of a PF_KEY SADB_DELETE message from the kernel must
   trigger the removal of associated remapping rules for the SA if any
   (i.e. having that SPI).

6.2.6.  Reception of a PF_KEY SADB_EXPIRE message

   When IRO engine receives a PF_KEY SADB_EXPIRE message from the kernel
   for a SA for which it has loaded some remapping rules, the associated
   action depends on the kind of expiration (hard or soft limit):

   o  In soft case, nothing is done as the SA is still valid.
   o  In hard case, the SA may already have been deleted from the SADB
      and IRO engine must remove associated remapping rules.

6.3.  Rekeying

6.3.1.  Phase 2

   When dynamic keying is used, negotiated IPsec SA have limited
   lifetime.  With IKEv1, the lifetime is negotiated and the rekeying is
   performed by the initiator.  In the context of MIPv6, this is



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   expected to be the peer.

   As stated in Section 2.8 of [RFC4306], a "difference between IKEv1
   and IKEv2 is that in IKEv1 SA lifetimes were negotiated.  In IKEv2,
   each end of the SA is responsible for enforcing its own lifetime
   policy on the SA and rekeying the SA when necessary.  If the two ends
   have different lifetime policies, the end with the shorter lifetime
   will end up always being the one to request the rekeying".  Again, in
   the context of MIPv6, it is expected that the MN will be the
   initiator that will perform the rekeying (i.e. having the shortest
   lifetime).

   In both cases, independently of the specific details of rekeying
   process, new SA will be put in place with new SPI values.  When this
   event occurs on one side, IRO implementation will get _live_
   information regarding the installation of new SAs by receiving PF_KEY
   SADB_ADD messages.  It will be followed after some time by the
   reception of PF_KEY SADB_EXPIRE messages indicating the expiration of
   a "hard lifetime" for old SAs.

   From IRO's perspective, IPsec SA rekeying process is only seen
   through the reception of specific PF_KEY messages for which
   associated actions have previously been described.


7.  Extending advantages of IRO to the HA

7.1.  Rationale and expected advantages

   IRO's primary purpose is to improve security and efficiency of MIPv6
   communications in IPsec environments.  Because most of them are
   expected to occur directly between peers, IRO is oriented towards
   MN-CN and MN-MN flows.

   But the flows between a MN and its HA can also benefit from the
   improvements: using the SPI information available on both sides to
   perform the remapping of incoming and outgoing IPsec traffic, the
   need of RH2 and HAO extensions between the MN and its HA simply
   disappears.  This provides anonymity (See Appendix J) of the MN on a
   foreign link by hiding its HoA to eavesdropper on the path (if IKE
   does not leak that information).  It also makes the MN fully capable
   in networks were only IPsec is allowed to flow (500/udp is required
   for the initial negotiation of SA and infrequently for rekeying).

7.2.  Changes to HA processing

   IRO does not mandates a detection mechanism (Appendix I) and
   transparently reuses most of [RFC3775]-defined messages.  For that



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   reason, MN and HA must be explicitly configured to use IRO.

   The changes to HA processing for the peer, required by the use of
   IRO, are simply the use of remapping rules instead of HAO and RH2
   extensions.

   With IRO, the relationship between a MN and one of its CN is
   basically the same as the relationship between the MN and its HA,
   with the following simple differences:

   o  HA and MN never exchange AOT* messages as the MN is always trusted
      regarding the CoA information it provides in its BU.
   o  HA and MN have a larger set of possible messages they can
      exchange.  Remapping rules should be able to handle that.
   o  Chances are high that an IPsec tunnel be used for protecting
      traffic relayed through the HA.  Remapping rules do not interfere
      with that as the associated SA is not tracked.  This is due to the
      fact that the SA references the CoA of the MN as the source (on-
      wire) address of the communication and not the HoA.

7.3.  Changes to MN processing

   The changes to MN processing for IRO to be used with its HA are quite
   comparable to the one previously described for the MN, i.e. they are
   naturally deduced from the basic requirement that RH2 and HAO must be
   replaced by the use of remapping rules.


8.  Implementation Notes

   The content of this section is not meant to be normative but only
   informative.

   This section provides some explicit feedback associated with the
   implementation of IRO on Linux (Linux kernel, UMIP mobility daemon
   and racoon IKE daemon).  Based on the specific targeted system, some
   of the points discussed in this section may be completely irrelevant.

8.1.  Nested SA

8.1.1.  Problem

   The main purpose of IRO is to route optimize IPsec traffic exchanged
   between the MN (from its HoA) and its CN.  Before that optimization
   takes places (i.e. before the AOT* exchanges), that traffic is
   expected to follow the natural path, i.e. be routed via the tunnel to
   the HA.




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   In IPsec environments, chances are high the data path to the HA will
   be IPsec protected, using IPsec in tunnel mode as (optionally)
   expected by MIPv6 specifications.  In that case, before the
   optimization is effective, traffic sent by the MN to the remote IPsec
   peer will have to undergo both the protection of the specific SA
   protecting the end-to-end traffic with the peer and the tunnel one
   protecting the data traffic to the HA.  This is required (at least
   for topological reasons) because the HoA is only valid as an inner
   address for tunneled traffic.  This is basically the kind of setup
   described in Appendix E of [RFC4301].

   Supporting that kind of nested IPsec configuration, even temporarily
   before the route optimization is in place, is not straightforward.
   Obviously, this usually does not require anything specific on the HA
   or the CN, but the MN case may be trickier.

   In the specific context of IRO, there may be a need for both
   previously described IPsec SP/SA to exist separately.  The main
   reason is that, even if the traffic to the CN initially needs to
   undergo both SP (and in the end protection provided by associated
   SAs), this need disappears when the optimization is in place.  At
   that moment, the traffic only undergo the end-to-end SP and the
   protection of associated SA.

8.1.2.  Selected solution

   XXX FIXME

8.2.  Having IKE traffic flow via the IPsec tunnel to the HA

8.2.1.  Problem

   Traffic generated by an IKE daemon needs to bypass the system's
   security policies in order to avoid chicken and eggs issues.  Unix
   IKE daemons implementation usually achieve that using a specific
   IPsec bypass setsockopt() call on their sockets.

   In common situations, previous method works just fine.  But when an
   IPsec data tunnel already exist on the system as it is usually the
   case for corporate VPN clients, this method prevents the use of the
   inner tunnel address for IKE negotiation with remote peers accessible
   only via the remote security gateway (e.g. hosts in the corporate
   network).  Stated differently, this prevents the setup of end-to-end
   IPsec protection via the IPsec tunnel.

   More precisely, if the IKE daemon tries and use the inner address for
   negotiation with a peer, the IPsec bypass setsockopt() call on
   associated socket prevents associated IKE traffic to flow correctly.



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   This is because, from a topological standpoint, the only valid path
   for traffic originating from that address is via the IPsec tunnel.

   When MIPv6 data traffic between the MN and its HA is required by
   policy to undergo IPsec tunnel protection, the same limitation as
   described above exists.  For the specific needs of IRO, this is an
   issue because the HoA is used for the IKE negotiation with the CN
   (whose side effect is also to prove HoA ownership to the peer).

8.2.2.  Selected solution

   For the sake of the discussion, we consider the existence of some
   wide IPsec SP requiring protection of all traffic from the HoA to a
   given peer behind the HA.  To make things clear, IKE traffic (500/
   udp) between the HoA and the address of the peer matches this SP's
   selectors.

   Obviously, the simple removal of the IPsec bypass setsockopt() on the
   socket associated with the HoA is not sufficient to make things work.
   This would have initially been sufficient to have associated IKE
   traffic undergo the IPsec tunnel mode SP (protecting data traffic
   between the MN and its HA).  But the existence of the additional SP
   creates a chicken and eggs situation and prevents things to work that
   easily.

   But once the IPsec bypass setsockopt() call is removed for the IKE
   socket associated with the HoA, associated traffic basically undergo
   the system security policies.  Then, the addition of a high priority
   SP with selectors specifically suited for IKE traffic from the HoA to
   the address of the peer is sufficient to have the IKE traffic be
   IPsec tunneled using the existing SA already protecting MIPv6 data
   traffic.

   From an implementation perspective, the removal of the IPsec bypass
   setsockopt() call has been implemented by adding a simple option
   ('no_bypass') to the racoon IKE daemon allowing the user to specify
   an address for which associated socket should not undergo the
   setsockopt() call.

   With regard to the addition of the high priority IPsec security
   policy matching IKE traffic between the HoA and the address of the
   peer, it was easier to have that job done inside UMIP.  This is
   basically because UMIP is already the one handling the installation
   of other security policies for MIPv6 and data traffic.  Another
   reason is that UMIP will need to update the tunnel mode SP after a
   handover. (via [MIGRATE]).





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8.3.  Remapping rules and old IPsec architecture

8.3.1.  Problem

   XXX FIXME: the old IPsec architecture expected SAD lookups to be
   performed by SPI and destination address.  If an IPsec stack only
   implements such kind of lookups when handling IPsec traffic, this may
   require additional work to support the implementation of IRO
   remapping rules.  [RFC4301] changed that behavior and now expects SAD
   lookups for unicast SA to be performed by SPI, which is expected to
   simplify the implementation of IRO remapping process.

8.3.2.  Selected solution

   XXX FIXME


9.  Security Considerations

9.1.  Proof of address ownership

9.1.1.  Position of the problem

   As a CN, registering a binding between a CoA and a HoA is not
   something harmless.  This can be seen as a modification of local
   routing table, like an order from a peer to direct traffic to a
   specific address.  For that reason, the CN needs some proof regarding
   this binding.  In MIPv6, RRP has been designed with the hypothesis
   that there is no initial trust relationship between a MN and its CN.
   The solution to provide confidence to the CN in the HoA and CoA
   binding has consisted in showing the ability for the MN to send _and_
   receive traffic both at the HoA and CoA.

   With IRO, there is an initial trust relationship between a MN and the
   CN it will contact.  This is expected to take the form of
   cryptographic credentials (X.509 certificates, ...) that will allow
   an IKE negotiation to occur to setup SAs to protect the binding.
   Static keying case is covered in Appendix G.  Those SA only
   references the HoA of the MN and not at all its CoA.

   The point here is that the existence of SAs does not directly provide
   to the CN any _live_ proof of address ownership as it occurs with
   RRP.

   Furthermore, as summarized in section 6.2 of [RFC4866] paragraph 4,
   the trust relationship between a HA and its MN is very different from
   the one between a MN and a CN, even if both use IPsec/IKE to
   authenticate.



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9.1.2.  Home Address ownership

   The proof of HoA ownership to the CN is one of the reason behind the
   design decision to have MN and CN perform the IKE negotiation via the
   tunnel to the HA (i.e. using the HoA).  That way, the existence of
   the SAs gets bound to a successful initial exchange between the CN
   and the MN.  This proves to the CN the ability for the MN to send/
   receive traffic from/at that address.

   Nonetheless, as IKE basically allows negotiation to be performed from
   a different address than the one the SA contain ([MIGRATE] has such
   an use), this behavior MUST be prevented on the CN for the purpose of
   negotiations of the initial SAs that will protect MH traffic for
   IRO's binding between the MN and the CN.

   While MN and CN are able to perform an IKE exchange between them
   using a set of credentials, there are many possible reasons for which
   those credentials might in fact be invalid at the time the
   negotiation occur.  This might for instance be the case if the CN has
   not up to date revocation information.  This can also result from the
   use by the MN of a different set of credentials for the purpose of
   protecting its HA registration and the registration with its CN.

   Mandating the IKE negotiation to be routed through the tunnel to the
   HA provides the proof that the MN is still granted ownership of the
   address by the network it belongs to at the time of negotiation.  It
   should be noted that the proof of HoA ownership occurs at SA setup
   time and remains valid till the SA is rekeyed, i.e. each rekeying
   providing a new live proof.  This specification does not mandates
   regular check of HoA ownership between rekeying.  Appendix C provides
   arguments on that topic.

   The case of static keying is covered in Appendix G.

9.1.3.  Care-of Address ownership

   The proof of CoA ownership by the CN is an especially important point
   in the security of large scale deployments of IRO.  As stated in the
   introduction of this section, the acceptance of a binding by a CN for
   a CoA is a local modification of local routing table to send current
   and future traffic to that address when it is destined to the HoA.

   The proof by the MN that it is able to both send and receive traffic
   at this address is a primary concern in the security of the protocol.
   Appendix A covers the reasons why the only ability to send is an
   insufficient proof of CoA ownership, even in the context of IRO.





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9.2.  Remapping (comparison with explicit HAO/RH2 inclusion)

   For every remapping, the practical impact is the same as the explicit
   one resulting from the inclusion of a RH2 or HAO.

9.3.  Anonymity

   At the moment, this section is empty.  See Appendix J.

9.4.  Limiting attack surface

   IRO can provide the ability to have port 500/udp open for remote
   negotiations on the HoA for the purpose of the inbound contacts and
   not on the CoA.  CoA is only used for the discussion between the MN
   and its HoA, which allow to put some specific firewalling rules in
   place for that purpose.


10.  IANA Considerations

   The values for following mobility header messages MUST be assigned by
   IANA:

   o  Address Ownership Test Offer message (AOTO, see Section 4.4.1)
   o  Address Ownership Test Challenge message (AOTC, see Section 4.4.2)
   o  Address Ownership Test Response message (AOTR, see Section 4.4.3)
   o  Address Ownership Test Status message (AOTS, see Section 4.4.4)

   The values for following mobility option MUST be assigned by IANA:

   o  Nonce Option (see Section 4.3.1)


11.  Acknowledgements

   The author acknowledge the comments and correction of Guillaume
   Valadon on the initial version of the document.

   This document was generated by xml2rfc.


12.  References

12.1.  Normative References

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




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

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [RFC4835]  Manral, V., "Cryptographic Algorithm Implementation
              Requirements for Encapsulating Security Payload (ESP) and
              Authentication Header (AH)", RFC 4835, April 2007.

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

12.2.  Informative References

   [CNIPsec]  Dupont, F. and JM. Combes, "Using IPsec between Mobile and
              Correspondent IPv6 Nodes", draft-ietf-mip6-cn-ipsec-08
              (work in progress), August 2008.

   [MIGRATE]  Ebalard, A. and S. Decugis, "PF_KEY Extension as an
              Interface between Mobile IPv6 and IPsec/IKE",
              draft-ebalard-mext-pfkey-enhanced-migrate-00 (work in
              progress), August 2008.

   [RFC4225]  Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E.
              Nordmark, "Mobile IP Version 6 Route Optimization Security
              Design Background", RFC 4225, December 2005.

   [RFC4651]  Vogt, C. and J. Arkko, "A Taxonomy and Analysis of
              Enhancements to Mobile IPv6 Route Optimization", RFC 4651,
              February 2007.




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   [RFC4866]  Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route
              Optimization for Mobile IPv6", RFC 4866, May 2007.

   [RFC4882]  Koodli, R., "IP Address Location Privacy and Mobile IPv6:
              Problem Statement", RFC 4882, May 2007.


Appendix A.  Ability to send does not prove CoA ownership

   With IRO, negotiation of the protection for the registration traffic
   between the peers is done using the tunnel to the Home Agent (i.e.
   the HoA).  Then, the protected Binding Update message is emitted by
   the MN.  It locally uses the HoA but a remapping process makes the
   CoA the address appearing on the wire for this packet.  When the CN
   receives that packet, the address is remapped to the HoA of the MN by
   the MIPv6 stack.  The remapped address appearing as source of the
   packet is passed as ancillary data to the MIPv6 process where a check
   will be performed during parsing against the content of the required
   Alternate Care-of Address option.

   This process proves the CN that the MN is able to _send_ traffic
   using the CoA.

   Then, IRO requires additional steps for the MN to prove its ability
   to receive traffic at that address.  This appendix covers the threats
   prevented by the addition of this proof of reception capability in
   IRO.

   The trust model between the MN and its HA is based on the existence
   of the IPsec protection between the two.  The only requirement for
   the update of the tunnel endpoint when a movement occur is the
   reception by the HA of a protected Binding Update message containing
   the new CoA in the Alternate CoA option.  The use of the new CoA as
   source of the packet is not even mandatory.

   One would argue that the same kind of trust relationship exists
   between the MN and its CN as they already have an established trust
   relationship, materialized by the pair of SA protecting MH traffic.
   Nonetheless there are many difference between the two situations.

   The first and main one is that all the traffic emitted by the HA to
   the CoA provided by the MN has a traceable source: the address of the
   HA, which belongs to the home network.  It allows to track the source
   of the traffic emitted to the CoA back to the Home Network.  In the
   context of the flow from the CN to the MN, the source address might
   possibly be that of a foreign network (if the CN is also acting as a
   MN) and the destination is the one that would be provided by the MN.




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   Now consider the following, still in the context of a proof of
   address ownership based solely on the ability of the MN to emit
   traffic from the CoA.  A MN has been compromised by an attacker that
   has the ability to emit traffic with the address of a target (no
   ingress-filtering by its provider).  The attacker would now be able
   to mount connections with the HA and then, using IRO, with all the
   peers that trust the MN.  At the moment, it still uses some valid
   address where it can emit/receive traffic from/to.  After having some
   traffic intensive connection running with a peer, it simply warns the
   peer of a change of CoA by advertising the address of the target.  As
   the CN does not require a proof of reception capability, all the
   IPsec traffic gets redirected to the target.  This might not be a
   problem with a single peer and some connected protocol but it is
   expected that the protocol be used in vast trust domains where the
   number of peer is not directly limited.

   In the end, requiring that the proof of CoA ownership includes a
   proof of reception capability by the MN at the CoA prevents that
   compromise of a MN by an attacker provides her with a potentially
   unlimited number of anonymous and unwilling "bots" to DoS a target
   other than herself.

   In the design of IRO, to maintain the efficiency of the protocol in
   term of latency associated with movement, the proof of reception
   capability is not required to occur before the CN can emit traffic to
   the CoA.


Appendix B.  IKE exchanges use the HoA and the tunnel to the HA

   Remainder: in this appendix, we still consider that the data tunnel
   between the HA and the MN is IPsec protected.  Some security
   arguments in this appendix should be modulated if this hypothesis is
   known to be invalid.

   We provide here some arguments regarding the use of the HoA for
   performing the IKE exchanges with the peers, using the tunnel through
   the HA.

   The first simple rule which always applies with IRO is that no
   connection happens directly if it is not IPsec-protected.  No
   difference is made for IKE exchanges even if those flows have
   intrinsic protection mechanisms.

   The need for performing IRO to get direct routing between the peers
   is motivated by the net performance impact in terms of bandwidth,
   delay and jitter by avoiding triangular routing and the bottleneck of
   HA.  This is of interest for specific flows like VoIP, direct file



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   exchanges, ... but are mainly useless for infrequent flows like IKE
   negotiations.  When a MN performs IKE negotiation with a peer, having
   IKE_SA (or ISAKMP SA for IKEv1) set up is only a matter of few
   packets (IKEv1 Main mode exchange uses six).  Then, all next CHILD_SA
   (or IPsec SA for IKEv1) will reuse the same IKE_SA and generally
   complete after a three packet exchange.  As rekeying is supposed to
   occur extremely infrequently and does not need the advantage of
   direct routing, this is unneeded.  The argument regarding the loss
   associated by the routing through the tunnel gets the same answer:
   the impact is very limited given the amount of traffic.  Furthermore,
   when certificates are used, IKE packets already get fragmented even
   with a full 1500 bytes PMTU.

   In fact, the advantage of using the HoA and the IPsec tunnel to the
   HA for performing IKE negotiation with peers is the stability
   guaranteed by the migration process when movement occurs.  MIPv6
   simply makes things transparent for all IKE daemon connections from
   the HoA.

   To conclude and after all previous functional arguments, there are
   also some security advantages in performing IKE negotiations with
   peers using the protected IPsec tunnel to the HA.

   The most important one is anonymity.  A positive side effect of
   having the negotiation performed through the IPsec tunnel to the HA
   (ESP with meaningful encryption is assumed) is that it hides
   everything to people in MN's network.  IKE traffic is only accessible
   on the path between the HA and the peer.  In fact, in the MN-MN
   situation eavesdroppers on both foreign networks are unable to get
   the HoA of the peer on the other network.  It requires being on the
   path between the two HA.  The same is also true for the identity
   information that might appear during the IKE negotiation depending on
   the modes peers use.

   Another security advantage with that policy is that a peer is able to
   statefully filter 500/udp traffic received on its CoA and allow only
   outbound initiated connections addressed to the HoA.  This policy
   simply allows reducing the network attack surface of the node in the
   foreign network.


Appendix C.  Arguments for no regular check of HoA ownership

   As presented in Section 9.1.2, when dynamic keying is used, the
   initial IKE negotiation protecting the registration traffic between
   the MN and the CN provides to the CN the proof of HoA ownership by
   the MN.  This proof remains valid till this SA is rekeyed.  This is
   also true for further SA negotiated between the MN and the CN.



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   The initial proof of HoA ownership is easily obtained as it results
   from a positive information: packets exchanged with the MN at this
   address.  Note that the inability for the MN or the CN to get traffic
   routed to the HA at that moment results in the inability to get
   direct connectivity as the IKE negotiation cannot be performed.  In
   the same fashion, after the initial proof, there is no defined way to
   track a loss of HoA ownership through a positive event: the CN is
   simply not warned that the MN has been removed ownership of its HoA
   by its home network (resulting from a compromise, change of network
   prefix, ...).  Discovery of a loss of HoA ownership cannot be tracked
   by a negative event either, such as the inability to exchange traffic
   with the MN at a specific moment.  In fact, a crash of the HA, the
   loss of connectivity between the MN and its HA, or between the CN and
   the HA are to be expected.  In that context, such a mechanism would
   simply amplify the existence of points of failure or allow DoS to
   occur.  Avoiding that provides resilience and allow direct
   communications to survive previous failure conditions related to the
   HA.

   Another reason to prevent regular proof of HoA ownership is the use
   of the HoA in IRO.  It acts as a local identifier on both peers.  It
   allows the MN to acquire movement independence and can be seen as a
   convenience in the relationship between the peers, to find themselves
   initially, no matter where they are located.  With IRO, the HoA never
   appears anymore in packet exchanged directly between the peers (due
   to removal of HAO and RH2).  It is only understood locally in the
   context of ongoing IPsec communications between the peers.

   The last argument for not including this requirement (capability is
   provided, see Section 4.5.3) in the protocol is that different CN or
   MN might have different more efficient methods for performing that
   tracking.  For instance, inside a home network, instead of using a
   constant regular polling by all MNs, an administrator revoking the
   credentials of a MN will easily be able to request all MNs to update
   their revocation information, before shutting down communications
   with associated MN (i.e. replacing polling by push).

   In the context of IRO, no mechanism to perform regular checks of HoA
   ownership is included.  This capability is outside the scope of this
   specification.


Appendix D.  Lack of encryption between MN and HA

   In this specification, the use of IPsec tunnel protection of data
   traffic is expected.  Note that section 5.5 of [RFC3775] only
   specifies that:




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      For traffic tunneled via the home agent, additional IPsec ESP
      encapsulation MAY be supported and used. If multicast group
      membership control protocols or stateful address
      autoconfiguration protocols are supported, payload data
      protection MUST be supported.

   The logic behind previous expectation is associated with the
   availability of credentials between the MN and HA, and also the kind
   of environment in which it will get deployed.

   However, the lack of IPsec protection of tunneled data does not
   prevent IRO; it only removes some security advantages of this
   protection.  This loss is covered in this appendix.

   When negotiating IRO, the MN uses the tunnel to its HA for routing
   IKE negotiation with the peer.  As IKE is designed for robustness,
   the advantage of the privacy when IPsec is used for protecting the
   data tunnel (i.e. non NULL encryption) is the insurance that the
   address of the peer or its cryptographic credentials are not
   disclosed on MN's network.  Note that MN's HoA and associated
   identity are expected to be disclosed to eavesdroppers during
   registration of the MN to its HA (if IRO is not extended to HA-MN
   exchanges).

   As a conclusion, removing the hypothesis of privacy for data tunneled
   to the HA removes the anonymity provided to peer's identity (HoA or
   CoA, and possibly cryptographic identity appearing during IKE
   exchange).


Appendix E.  What if I don't need protection?

   IRO mandates the use of IPsec for all direct communications between
   MIPv6 peers.  As IPsec is only a framework, the level of protection
   might vary, along with the additional requirements, environments and
   capabilities of end devices.

   There will certainly be some very specific and limited cases where
   people will see a need in downgrading the security for performance or
   other reasons.  To be fair, except in some very specific conditions,
   achieving performance while still keeping security is possible.  For
   instance, if authentication is a real requirement but privacy is not
   (but it is still activated by default), and CPU limits the
   throughput, keeping only authentication services of IPsec as provided
   by ESP with NULL encryption or by AH will clearly boost performance.

   Now, if there is a desperate need to suppress security services
   between MIPv6 peers for some reason, the best thing is to use another



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   route optimization like common RO as specified in [RFC3775], instead
   of trying to circumvent them.

   For those with some imagination, who still think the author is wrong
   and think about simply negotiating NULL authentication and NULL
   encryption, next paragraph might be worth reading.

   [RFC4835] defines mandatory-to-implement cryptographic algorithms for
   use with ESP (and AH).  NULL encryption algorithm and NULL
   authentication algorithm must both be implemented.  In section 3.2 of
   [RFC4303], some requirements are specified on those algorithms,
   preventing their simultaneous uses:


        Note that although both confidentiality and integrity are
        optional, at least one of these services MUST be selected, hence
        both algorithms MUST NOT be simultaneously NULL.


Appendix F.  MTU Gains

   Standard RO is based on the use of RH2 and HAO to explicitly carry
   the HoA of the MN, respectively as real destination or final source
   of the packet sent directly between the nodes:

   o  From MN to CN: HAO
   o  From CN to MN: RH2
   o  From MN to MN: HAO and RH2, simultaneously.

   The inclusion of these explicit containers generates a loss of MTU.
   In common case, where no other specific extensions or options are
   used (to remove padding considerations), HAO and RH2 each consume 24
   bytes.

   The loss of MTU associated with those MIPv6 extension for direct
   MN-CN communications is 24 bytes.  For direct MN-MN communications,
   it is 48 bytes.  As an initial comparison, unprotected routing via
   the HA through an IPv6-in-IPv6 tunnel consumes 40 bytes.  When an
   IPsec tunnel is used, the loss of MTU depends on the authentication
   and encryption algorithm, negotiation of ESN, padding requirement.

   As IRO has been designed to provide secure IPsec-protected direct
   communications between MIPv6 peers, it is difficult (and does not
   make that much sense) to compare the loss of MTU associated with IRO
   and the one of standard unprotected RO.  In term of header inclusion,
   IRO neither use RH2 nor HAO but require AH or ESP.  Depending on the
   size of ESP or AH header(s) and the specific type of communication
   (MN-MN or MN-CN), one route optimization type might consume more



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   bandwidth than the other:

   o  ESP in transport mode using HMAC-SHA1-96 (required in all
      implementation) as authentication algorithm, NULL for encryption
      and no ESN consumes 24 bytes (with 2 bytes of padding).  Adding a
      meaningful encryption algorithm will make that higher.
   o  AH in transport mode also using HMAC-SHA1-96 and no ESN will give
      a similar value.

   To make things simple, using IRO with some ESP with NULL encryption
   or with AH for MN-CN communications provides similar MTU loss as
   standard RO.  Having a meaningful encryption algorithm (expected)
   with ESP give a little advantage to standard RO regarding MTU loss.

   When considering MN-MN, IRO will clearly consumes less bandwidth than
   standard RO in all possible combinations of algorithms for AH or ESP.

   Now, considering the same level of protection, i.e. by using IPsec
   for standard RO carried packets (we do not take into account padding
   variations), IRO simply gets a direct advantage: 24 bytes for MN-CN
   communications and 48 bytes for MN-MN communications.  It is due to
   the complete removal of HAO and RH2 from packets exchanged directly
   between peers.

   In fact, regarding MTU considerations, IRO provides a zero cost
   mobility service to IPsec protected connections between end nodes.


Appendix G.  Compatibility with static keying

   IRO has been designed for enabling direct secure communications
   between MIPv6 entities belonging to a common trust domain.
   Scalability was a primary concern; This is the reason why the
   specification covers SA negotiation under the hypothesis that IKE is
   used for that purpose.  But IRO is also fully compatible with static
   keying.

   In fact, the specification is not specifically bound to the use of
   either static or dynamic keying for SA setup; it is left as a local
   configuration decision to domain administrators.

   This appendix quickly covers the differences regarding the use of
   static keying with IRO.

   One great difference between static and dynamic keying is the removal
   of the IKE negotiation.  For IRO, the first negotiation performed
   with the peer provides an additional information to the CN: a live
   proof of address (HoA) ownership by the MN.  The removal of this step



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   also removes the live check.  This is a fact administrators should be
   aware of.

   The question of rekeying is of primary interest for the maintenance
   of SPI information on MN and CN that use IRO.  This changes somehow
   with static keying as the rekeying is done ... by the user.  Even if
   it is expected to happen less often, tracking of SA removal and
   addition, along with their associated SPI is still required.  It is
   expected that the same mechanism (PF_KEY is one of them) used for
   tracking addition and deletion of SA by IKE be used for that purpose.

   There should be no specific reason preventing the simultaneous use of
   static and dynamic keying with IRO.


Appendix H.  Compatibility with the use of CoA in SP/SA

   SP and SA are not changed at any moment by MIPv6 stack when IRO is
   used.  Only incoming and outgoing IPsec packets can undergo source or
   destination address modifications, mainly based on SPI information.

   When using IRO, MIPv6 stack tracks SA addition and deletion looking
   for local HoA or IRO peers' HoAs (MN) as source or destination
   addresses of those SA (endpoints for tunnel mode SA).  Associated SPI
   are used for tracking IPsec packets.

   Outgoing IPsec packets are only possibly modified to change the HoA
   into the CoA.  CoA of outgoing IPsec packets are never modified by
   MIPv6 stack, when IRO is used.

   Incoming IPsec packets will have their source modified (from CoA to
   peer's MN HoA) iif the SPI is the one of a tracked SA that expect the
   HoA of an IRO peer.  This implies that no incoming packet with a CoA
   source will be modified if the SA associated with its SPI references
   that CoA (and not peer's HoA).  Regarding destination address of an
   incoming IPsec packet, remapping of a CoA will occur if the SA
   associated with the SPI expects an HoA.  This implies that no
   incoming packet with a CoA destination will be modified if the rules
   associated with its SPI references that CoA (and not our HoA).

   As a conclusion, the work of IRO is compatible with the use of CoA as
   destination or source address (endpoint addresses for tunnel mode) of
   any SP/SA.


Appendix I.  Rationale for not specifying a new BU

   IRO is not designed as a fallback mode for IPsec communications



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   between MIPv6 entities but as an improved alternative.

   You cannot use IRO and common mode with the same peer.  You either
   need the security advantages of IRO for communications with a peer or
   you can afford unprotected direct communications with it, for which
   common RO has been developed.  Parallel uses of common mode and IRO
   mode with different MIPv6 entities (including its HA) is not
   forbidden but strongly discouraged as it suppresses the anonymity of
   the MN on its foreign link.

   For that reasons, IRO does not come with some detection algorithm
   against peers that do not have IRO activated to perform a fallback to
   common mode.  Considering the setup associated with the protection
   mechanisms required by IRO and the kind of environments it is
   expected to be used in, requiring that entities be configured to
   specifically use IRO for a peer (or by default, preventing the common
   mode) is required.

   This has many positive impacts both on development costs, deployment
   and debugging.  This notably provides the ability to reuse messages
   without creating parallels versions where needed.  As only a few
   things changes when IRO is activated between two entities, most of
   the code remains usable.  In fact, the two mains changes introduced
   by IRO are:

   o  the removal of HAO/RH2 and the replacement by the remapping
      process on selected IPsec traffic.
   o  a simplified registration procedure with CN (AOT* framework)

   Let's go a little further.  One can think that it would have been
   possible to create specific mobility options to discriminate IRO mode
   from the common mode.  This was impossible for multiple reason.
   First, from a specification perspective, section 6.1.7 of [RFC3775]
   requires that "The receiver MUST ignore and skip any options which it
   does not understand", which prevents the reuse of MIPv6 messages with
   a slightly modified semantic if peers are not aware of that.  For
   options to have an interest, you have to be aware that the peer
   support it (not necessarily that it is activated).

   Anyway, there is a better reason that makes the use of common mode
   and IRO mode incompatible between peers: IRO remapping process must
   be activated on the receiver for the packets to be valid.  If a MN
   that uses IRO sends an IPsec protected Binding Update message to a
   peer that is not using IRO, no remapping will occur and the checksum
   will end up being invalid (if it passes the IPsec stack).  Section
   9.2 of [RFC3775] requires the following rule to be applied to such
   packet: "The checksum must be verified as per Section 6.1.
   Otherwise, the node MUST silently discard the message".



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Appendix J.  Anonymity

   There are mainly 2 kinds of identifiers that can appear during an
   IPsec protected communication in IKE/MIPv6 environments: addresses
   (HoA, CoA, CN addresses) and cryptographic identifiers (IKE
   credentials, i.e.  X.509 certificates).

   In MN-CN communications, the addresses of the CN and the CoA of the
   MN will obviously be disclosed, but they should not be meaningful.
   We see later that in MN-MN case, the address of the CN that appears
   on the wire might temporarily be the HoA, before registration has
   been performed by the second MN.

   In MIPv6, the use of explicit containers (HAO and RH2) makes the Home
   Address of the MN available in all cases.  With IRO, the complete
   removal of this extensions prevents the disclosure of the HoA during
   direct MN-CN communications and MN-HA communications.

   The removal applies to:

   o  the IPsec protected signaling traffic exchanged directly between
      the two peers (BU/BA for instance)
   o  the IPsec protected data traffic exchanged in MN-MN and MN-CN
      cases (when tunnel mode is not already used to avoid RH2/HAO).

   From the perspective of an eavesdropper on the FL of the MN, when IRO
   is used the visible exchanges that occur are (in order, for MN-MN
   case, with registrations performed on that link, i.e. worst case
   scenario):

   o  IKE negotiation between the CoA of the MN and its HA
   o  IPsec protected BU/BA exchanges using CoA and HA@ as on-wire
      addresses (remapping rules applied on both ends)
   o  IPsec protected (tunnel mode this time) traffic with peers
   o  IKE exchange from the HoA, IPsec tunneled to the HA, with a CN
   o  Direct IPsec-protected BU/BA exchanges using the CoA and the
      address of the the CN for on-wire addresses.
   o  Direct IPsec-protected data traffic exchange with the CN, between
      the CoA and the address of the CN.

   In all those exchanges, the only addresses that are disclosed to an
   eavesdropper on the FL of the MN (if ESP with a meaningful encryption
   is used for all IPsec exchanges) are the CoA, the address of MN's HA
   and the address of the CN.  The HoA of the MN never appears in those
   exchanges.

   For IKE case, even if it is used as an ID in Phase 2 for
   bootstrapping as described in [MIGRATE], the exchanges are encrypted



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   and the HoA does not appear.  For the negotiation with the CN,
   because the HoA is used for the exchanges, the IPsec tunnel to the HA
   protects traffic to/from the Home Network.

   Regarding cryptographic identifiers, the certificate of the MN is not
   expected to appear on the wire.  In all cases, the only information
   one can get are associated with the MN's Home Network (HA address and
   possibly certificate), but nothing more specific should be disclosed.

   Now, considering the specific case of MN-MN communications, on the
   network of the initiating MN1 (the first to register with its peer),
   after the IKE negotiation as been performed relayed by both Home
   Agents, the IPsec protected Binding Update packets is emitted with
   the HoA of MN2 as destination (the address of the CN in previous list
   is the HoA of MN2).  Let's consider associated SPI is 42.  The packet
   is sent directly with the CoA of MN1 on the wire and is routed to the
   Home Network of the peer, before it is tunneled to it.  The BA
   follows a reverse path but with a different SPI (say 43).  After the
   second registration is over, the MH traffic using those SPI values
   (42 and 43) flows directly (remapping rules are now in place on both
   ends).  From an eavesdropper perspective on the FL of MN1, this
   provides "a clue" about the association between the HoA and the CoA
   of the second MN2.  This is introduced in [RFC4882].

   Note that this is the only "leaking" that happens and only on the FL
   of the first MN.  It is no more the case on FL that are visited
   later.  Anyway, from the perspective of an eavesdropper monitoring
   that, the information will be that a Mobile Node from a known Home
   Network (HA@) has performed IPsec communications with a MN having a
   known HoA (no credentials).


Author's Address

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

   Phone: +33 1 46 97 30 28
   Email: arnaud.ebalard@eads.net









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