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Versions: 00 01 02 03 04 05 06 RFC 3776

Network Working Group                                           J. Arkko
Internet-Draft                                                  Ericsson
Expires: August 19, 2003                                  V. Devarapalli
                                                   Nokia Research Center
                                                               F. Dupont
                                                           ENST Bretagne
                                                       February 18, 2003


 Using IPsec to Protect Mobile IPv6 Signaling between Mobile Nodes and
                              Home Agents
               draft-ietf-mobileip-mipv6-ha-ipsec-03.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at http://
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 19, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   Mobile IPv6 uses IPsec to protect signaling between the home agent
   and the mobile node.  Mobile IPv6 base document defines the main
   requirements these nodes must follow.  This document discusses these
   requirements in more depth, illustrates the used packet formats,
   describes suitable configuration procedures, and shows how
   implementations can process the packets in the right order.




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Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.    Terminology  . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.    Packet Formats . . . . . . . . . . . . . . . . . . . . . . .  8
         3.1   Binding Updates and Acknowledgements . . . . . . . . .  8
         3.2   Return Routability Signaling . . . . . . . . . . . . .  9
         3.3   Prefix Discovery . . . . . . . . . . . . . . . . . . . 10
         3.4   Payload Packets  . . . . . . . . . . . . . . . . . . . 10
   4.    Requirements . . . . . . . . . . . . . . . . . . . . . . . . 12
         4.1   Mandatory Support  . . . . . . . . . . . . . . . . . . 12
         4.2   Policy Requirements  . . . . . . . . . . . . . . . . . 12
         4.3   IPsec Protocol Processing  . . . . . . . . . . . . . . 14
         4.4   Dynamic Keying . . . . . . . . . . . . . . . . . . . . 16
   5.    Example Configurations . . . . . . . . . . . . . . . . . . . 18
         5.1   Format . . . . . . . . . . . . . . . . . . . . . . . . 18
         5.2   Manual Configuration . . . . . . . . . . . . . . . . . 19
               5.2.1 Binding Updates and Acknowledgements . . . . . . 19
               5.2.2 Return Routability Signaling . . . . . . . . . . 20
               5.2.3 Prefix Discovery . . . . . . . . . . . . . . . . 21
               5.2.4 Payload Packets  . . . . . . . . . . . . . . . . 22
         5.3   Dynamic Keying . . . . . . . . . . . . . . . . . . . . 24
               5.3.1 Binding Updates and Acknowledgements . . . . . . 24
               5.3.2 Return Routability Signaling . . . . . . . . . . 25
               5.3.3 Prefix Discovery . . . . . . . . . . . . . . . . 26
               5.3.4 Payload Packets  . . . . . . . . . . . . . . . . 26
   6.    Processing Steps within a Node . . . . . . . . . . . . . . . 28
         6.1   Binding Update to the Home Agent . . . . . . . . . . . 28
         6.2   Binding Update from the Mobile Node  . . . . . . . . . 29
         6.3   Binding Acknowledgement to the Mobile Node . . . . . . 29
         6.4   Binding Acknowledgement from the Home Agent  . . . . . 30
         6.5   Home Test Init to the Home Agent . . . . . . . . . . . 31
         6.6   Home Test Init from the Mobile Node  . . . . . . . . . 32
         6.7   Home Test to the Mobile Node . . . . . . . . . . . . . 32
         6.8   Home Test from the Home Agent  . . . . . . . . . . . . 33
         6.9   Prefix Solicitation Message to the Home Agent  . . . . 33
         6.10  Prefix Solicitation Message from the Mobile Node . . . 33
         6.11  Prefix Advertisement Message to the Mobile Node  . . . 33
         6.12  Prefix Advertisement Message from the Home Agent . . . 34
         6.13  Payload Packet to the Home Agent . . . . . . . . . . . 34
         6.14  Payload Packet from the Mobile Node  . . . . . . . . . 34
         6.15  Payload Packet to the Mobile Node  . . . . . . . . . . 34
         6.16  Payload Packet from the Home Agent . . . . . . . . . . 34
         6.17  Establishing New Security Associations . . . . . . . . 34
         6.18  Rekeying Security Associations . . . . . . . . . . . . 35
         6.19  Movements and Dynamic Keying . . . . . . . . . . . . . 36
   7.    Implementation Considerations  . . . . . . . . . . . . . . . 38
   8.    Security Considerations  . . . . . . . . . . . . . . . . . . 40



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         Normative References . . . . . . . . . . . . . . . . . . . . 41
         Informative References . . . . . . . . . . . . . . . . . . . 42
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 42
   A.    Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 43
   B.    Changes from Previous Version  . . . . . . . . . . . . . . . 44
         Intellectual Property and Copyright Statements . . . . . . . 45













































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1. Introduction

   This document illustrates the use of IPsec in securing control
   traffic relating to Mobile IPv6 [8].  In Mobile IPv6, a mobile node
   is always expected to be addressable at its home address, whether it
   is currently attached to its home link or is away from home.  The
   "home address" is an IP address assigned to the mobile node within
   its home subnet prefix on its home link.  While a mobile node is at
   home, packets addressed to its home address are routed to the mobile
   node's home link.

   While a mobile node is attached to some foreign link away from home,
   it is also addressable at a care-of addresses.  A care-of address is
   an IP address associated with a mobile node that has the subnet
   prefix of a particular foreign link.  The association between a
   mobile node's home address and care-of address is known as a
   "binding" for the mobile node.  While away from home, a mobile node
   registers its primary care-of address with a router on its home link,
   requesting this router to function as the "home agent" for the mobile
   node.  The mobile node performs this binding registration by sending
   a "Binding Update" message to the home agent.  The home agent replies
   to the mobile node by returning a "Binding Acknowledgement" message.

   Any other nodes communicating with a mobile node are referred to as
   "correspondent nodes".  Mobile nodes can provide information about
   their current location to correspondent nodes, again using Binding
   Updates and Acknowledgements.  Additionally, return routability test
   is performed between the mobile node, home agent, and the
   correspondent node in order to authorize the establishment of the
   binding.  Packets between the mobile node and the correspondent node
   are either tunneled via the home agent, or sent directly if a binding
   exists in the correspondent node for the current location of the
   mobile node.

   Mobile IPv6 tunnels payload packets between the mobile node and the
   home agent in both directions.  This tunneling uses IPv6
   encapsulation [7].  Where these tunnels need to be secured, they are
   replaced by IPsec tunnels [2].

   Mobile IPv6 also provides support for the reconfiguration of the home
   network.  Here the home subnet prefixes may change over time.  Mobile
   nodes can learn new information about home subnet prefixes through
   the "prefix discovery" mechanism.

   This document discusses security mechanisms for the control traffic
   between the mobile node and the home agent.  If this traffic is not
   protected, mobile nodes and correspondent nodes are vulnerable to
   Man-in-the-Middle, Hijacking, Confidentiality, Impersonation, and



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   Denial-of-Service attacks.  Any third parties are also vulnerable to
   Denial-of-Service attacks.  These threats are discussed in more
   detail in Section 15.1 of the Mobile IPv6 base specification [8].

   In order to avoid these attacks, the base specification uses IPsec
   [2] to protect control traffic between the home agent and the mobile
   node.  This control traffic consists of various messages carried by
   the Mobility Header protocol in IPv6 [6].  The traffic takes the
   following forms:

   o  Binding Update and Acknowledgement messages exchanged between the
      mobile node and the home agent, as described in Sections 10.3.1,
      10.3.2, 11.7.1, and 11.7.3 of the base specification [8].

   o  Return routability messages Home Test Init and Home Test that pass
      through the home agent on their way to a correspondent node, as
      described in Section 10.4.6 of the base specification [8].

   o  ICMPv6 messages exchanged between the mobile node and the home
      agent for the purposes of prefix discovery, as described in
      Sections 10.6 and 11.4 of the base specification [8].

   The nodes may also optionally protect payload traffic passing through
   the home agent, as described in Section 5.3 of the base specification
   [8].  If multicast group membership control protocols or stateful
   address autoconfiguration protocols are supported, payload data
   protection support is required.

   The control traffic between the mobile node and the home agent
   requires message authentication, integrity, correct ordering and
   replay protection.  The mobile node and the home agent must have a
   security association to protect this traffic.  Furthermore, great
   care is needed when using IKE [5] to establish security associations
   to Mobile IPv6 home agents.  The right kind of addresses must be used
   for transporting IKE.  This is necessary to avoid circular
   dependencies in which the use of a Binding Update triggers the need
   for an IKE exchange that cannot complete prior to the Binding Update
   having been completed.

   The mobile IPv6 base document defines the main requirements the
   mobile nodes and home agents must follow when securing the above
   traffic.  This document discusses these requirements in more depth,
   illustrates the used packet formats, describes suitable configuration
   procedures, and shows how implementations can process the packets in
   the right order.

   We begin our description by showing the required wire formats for the
   protected packets in Section 3.  Section 4 describes rules which



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   associated Mobile IPv6, IPsec, and IKE implementations must observe.
   Section 5 discusses how IPsec can be configured to use either manual
   or automatically established security associations.  Section 6 shows
   examples of how packets are processed within the nodes.

   All implementations of Mobile IPv6 mobile node and home agent MUST
   support at least the formats described in Section 3 and obey the
   rules in Section 4.  The configuration and processing sections are
   informative, and should only be considered as one possible way of
   providing the required functionality.









































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2. Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].














































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3. Packet Formats

3.1 Binding Updates and Acknowledgements

   When the mobile node is away from its home, the BUs sent by it to the
   home agent MUST support at least the following headers in the
   following order:

      IPv6 header (source = care-of address,
                   destination = home agent)
      Destination Options header
         Home Address option (home address)
      ESP header
      Mobility header
         Binding Update
            Alternative Care-of Address option (care-of address)

   Note that the Alternative Care-of Address option is used to ensure
   that the care-of address is protected by ESP.  The home agent
   considers the address within this option as the current care-of
   address for the mobile node.

   The Binding Acknowledgements sent back to the mobile node when it is
   away from home MUST have at least the following headers in the
   following order:

      IPv6 header (source = home agent,
                   destination = care-of address)
      Routing header (type 2)
         home address
      ESP header
      Mobility header
         Binding Acknowledgement

   When the mobile node is at home, the above rules are different as the
   mobile node can use its home address as a source address.  This
   typically happens for the de-registration Binding Update when the
   mobile is returning home.  In this situation, the Binding Updates
   MUST support at least the following headers in the following order:

      IPv6 header (source = home address,
                   destination = home agent)
      ESP header
      Mobility header
         Binding Update
            Alternative Care-of Address option (care-of address)

   The Binding Acknowledgement messages sent to the home address MUST



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   support at least the following headers in the following order:

      IPv6 header (source = home agent,
                   destination = home address)
      ESP header
      Mobility header
         Binding Acknowledgement


3.2 Return Routability Signaling

   When the Home Test Init messages tunneled to the home agent are
   protected by IPsec, they MUST support at least the following headers
   in the following order:

      IPv6 header (source = care-of address,
                   destination = home agent)
      ESP header
      IPv6 header (source = home address,
                   destination = correspondent node)
      Mobility Header
         Home Test Init

   This format assumes that the mobile node's current care-of address is
   used as one of the gateway addresses in the security association.  As
   discussed in Section 4.3, this requires the home agent to update the
   gateway address when the mobile node moves.  Policy entries and
   security association selectors stay the same, however, as the inner
   packets do not change upon movements.

   Similarly, when the Home Test messages tunneled from the home agent
   are protected by IPsec, they MUST support at least the following
   headers in the following order:

      IPv6 header (source = home agent,
                   destination = care-of address)
      ESP header
      IPv6 header (source = correspondent node,
                   destination = home address)
      Mobility Header
         Home Test

   The format used to protect return routability packets relies on the
   destination of the tunnel packets to change for the mobile node as it
   moves.  The home agent's address stays the same, but the mobile
   node's address changes upon movements, as if the security
   association's tunnel gateway address had changed.  When the mobile
   node adopts a new care-of address, its source address selection rules



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   will automatically adopt a new source address for outgoing tunnel
   packets.  (The home agent accepts packets sent like this, as the
   outer source address in tunnel packets is not checked.)

   The process is more complicated in the home agent side, as the home
   agent has stored the previous care-of address in its Security
   Association Database as the gateway address.  When IKE is being used,
   the mobile node runs it on top of its then current care-of address,
   and the resulting tunnel-mode security associations will use the same
   addresses as IKE was transported on.  In order for the home agent to
   be able to tunnel a Home Test message to the mobile node, it uses the
   current care-of address as the destination of the tunnel packets, as
   if the home agent had modified the gateway address of the security
   association used for this protection.  This implies that the same
   security association can be used in multiple locations, and no new
   configuration or IKE rekeying is needed per movement.

3.3 Prefix Discovery

   If IPsec is used to protect prefix discovery, requests for prefixes
   from the mobile node to the home agent MUST support at least the
   following headers in the following order.

      IPv6 header (source = care-of address,
                   destination = home agent)
      Destination Options header
         Home Address option (home address)
      ESP header
      ICMPv6
         Mobile Prefix Solicitation

   Again if IPsec is used, solicited and unsolicited prefix information
   advertisements from the home agent to the mobile node MUST support at
   least the following headers in the following order.

      IPv6 header (source = home agent,
                   destination = care-of address)
      Routing header (type 2)
         home address
      ESP header
      ICMPv6
         Mobile Prefix Advertisement


3.4 Payload Packets

   If IPsec is used to protect payload packets tunneled to the home
   agent from the mobile node, a similar format is used as in the case



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   of tunneled Home Test Init messages.  However, instead of the
   Mobility Header these packets may contain any legal IPv6 protocol(s):

      IPv6 header (source = care-of address,
                   destination = home agent)
      ESP header
      IPv6 header (source = home address,
                   destination = correspondent node)
      Any protocol

   Similarly, when the payload packets are tunneled from the home agent
   to the mobile node with IPsec protection, they MUST support at least
   the following headers in the following order:

      IPv6 header (source = home agent,
                   destination = care-of address)
      ESP header
      IPv6 header (source = correspondent node,
                   destination = home address)
      Any protocol































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4. Requirements

   This section describes mandatory rules for all Mobile IPv6 mobile
   nodes and home agents.  These rules are necessary in order for it to
   be possible to enable IPsec communications despite movements,
   guarantee sufficient security, and to ensure correct processing order
   of packets.

   The rules in the following sections apply only to the communications
   between home agents and mobile nodes.  They should not be taken as
   requirements on how IPsec in general is used by mobile nodes.

4.1 Mandatory Support

   The following requirements apply to both home agents and mobile
   nodes:

   o  Manual configuration of security associations MUST be supported.
      The configuration of the keys is expected to take place
      out-of-band, for instance at the time the mobile node is
      configured to use its home agent.

   o  Automatic key management with IKE [5] MAY be supported.  Only
      IKEv1 is discussed in this document, even if it is expected that
      the next version of IKE can also be used and that it offers
      several improvements in this specific application.

   o  IPsec protection for Binding Updates and Acknowledgements between
      the mobile node and home agent MUST be supported and MUST be used.

   o  IPsec protection for the Home Test Init and Home Test messages
      tunneled between the mobile node and home agent MUST be supported
      and SHOULD be used.

   o  IPsec protection for the ICMPv6 messages related to prefix
      discovery MUST be supported and SHOULD be used.

   o  IPsec protection of the payload packets tunneled between the
      mobile node and home agent MAY be supported and used.

   o  If multicast group membership control protocols or stateful
      address autoconfiguration protocols are supported, payload data
      protection MUST be supported for those protocols.


4.2 Policy Requirements

   The following requirements apply to both home agents and mobile



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   nodes:

   o  When a packet is matched against IPsec security policy or
      selectors of a security association, an address appearing in a
      Home Address destination option MUST be considered as the source
      address of the packet.

   o  Similarly, a home address within a Type 2 Routing header MUST be
      considered as the destination address of the packet, when a packet
      is matched against IPsec security policy or selectors of a
      security association.

   o  When IPsec is used to protect return routability signaling or
      payload packets, the security policy database entries SHOULD be
      defined specifically for the tunnel interface between the mobile
      node and the home agent.  That is, the policy entries are not
      generally applied on all traffic on the physical interface(s) of
      the nodes, but rather only on traffic that enters this tunnel.

   o  The authentication of mobile nodes MAY be based either on machine
      or user credentials.  Note that multi-user operating systems
      typically allow all users of a node to use any of the IP addresses
      assigned to the node.  This limits the capability of the home
      agent to restrict the use of a home address to a particular user
      in such environment.  Where user credentials are applied in a
      multi-user environment, the configuration should authorize all
      users of the node to control all home addresses assigned to the
      node.

   o  When the mobile node returns home and de-registers with the Home
      Agent, the tunnel between the home agent and the mobile node's
      care-of address is torn down.  The SPD entries, which were used
      for protecting tunneled traffic between the mobile node and the
      home agent become inactive.  The corresponding security
      associations could be stored or deleted depending on how they were
      created.  If the security associations were created dynamically
      using IKE, they are automatically deleted when they expire.  If
      the security associations were created through manual
      configuration, they MUST be retained and used later when the
      mobile node moves aways from home again.  The security
      associations protecting Binding Updates and Acknowledgements, and
      prefix discovery SHOULD not be deleted as they do not depend on
      care-of addresses and can be used again.

   The following rules apply to mobile nodes:

   o  The mobile node MUST use the Home Address destination option in
      Binding Updates and Mobile Prefix Solicitations, sent to the home



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      agent from a care-of address.

   o  When the mobile node receives a changed set of prefixes from the
      home agent during prefix discovery, there is a need to configure
      new security policy entries, and there may be a need to configure
      new security associations.  It is outside the scope of this
      specification to discuss automatic methods for this.

   The following rules apply to home agents:

   o  The home agent MUST use the Type 2 Routing header in Binding
      Acknowledgements and Mobile Prefix Advertisements sent to the
      mobile node, again due to the need to have the home address
      visible when the policy checks are made.

   o  It is necessary to avoid the possibility that a mobile node could
      use its security association to send a Binding Update on behalf of
      another mobile node using the same home agent.  In order to do
      this, the security policy database entries MUST unequivocally
      identify a single security association for any given home address
      and home agent when manual keying is used.  When dynamic keying is
      used, the security policy database entries MUST unequivocally
      identify the IKE phase 1 credentials which can be used to
      authorize the creation of security associations for a particular
      home address.  How these mappings are maintained is outside the
      scope of this specification, but they may be maintained, for
      instance, as a locally administered table in the home agent.  If
      the phase 1 identity is a FQDN, secure forms of DNS may also be
      used.

   o  When the set of prefixes advertised by the home agent changes,
      there is a need to configure new security policy entries, and
      there may be a need to configure new security associations.  It is
      outside the scope of this specification to discuss automatic
      methods for this, if new home addresses are required.


4.3 IPsec Protocol Processing

   The following requirements apply to both home agents and mobile
   nodes:

   o  When securing Binding Updates, Binding Acknowledgements, and
      prefix discovery, both the mobile nodes and the home agents SHOULD
      use the Encapsulating Security Payload (ESP) [4] header in
      transport mode and MUST use a non-null payload authentication
      algorithm to provide data origin authentication, connectionless
      integrity and optional anti-replay protection.  Note that



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      Authentication Header (AH) [3] is also possible but for brevity is
      not discussed in this specification.

      Mandatory support for encryption and integrity protection
      algorithms is as defined in RFC 2401 [2], RFC 2402 [3], and RFC
      2406 [4].  Care is needed when selecting suitable encryption
      algorithms for ESP, however.  Currently available integrity
      protection algorithms are in general considered to be secure.  The
      encryption algorithm, DES, mandated by the current IPsec standards
      is not, however.  This is particularly problematic when security
      associations are configured manually, as the same key is used for
      a long time.

   o  Tunnel mode IPsec ESP MUST be supported and SHOULD be used for the
      protection of packets belonging to the return routability
      procedure.  A non-null encryption transform and authentication
      algorithm MUST be applied.

   o  IPsec AH [3] authenticator calculation MUST be performed as if a
      packet with a Type 2 Routing header would have the home address in
      the IPv6 destination address field and the care-of address in the
      Routing header.  Type 2 Routing header should be treated by IPsec
      in the same manner as Type 0 Routing header.

   o  Similarly, the authenticator calculation MUST be performed as if a
      packet with a Home Address destination option would have the home
      address in the IPv6 source address field and the care-of address
      in the destination option.

   The following rules apply to mobile nodes:

   o  When ESP is used to protect Binding Updates, there is no
      protection for the care-of address which appears in the IPv6
      header outside the area protected by ESP.  It is important for the
      home agent to verify that the care-of address has not been
      tampered.  As a result, the attacker would have redirected the
      mobile node's traffic to another address.  In order to prevent
      this, Mobile IPv6 implementations MUST use the Alternate Care-of
      Address mobility option in all Binding Updates sent to the home
      agent.  (Note that AH protects also the IPv6 header, and some
      implementations might avoid the option if they know AH is being
      used.)

   o  When IPsec is used to protect return routability signaling or
      payload packets, the mobile node MUST set the source address it
      uses for the outgoing tunnel packets to the current primary
      care-of address.  The mobile node starts to use a new primary
      care-of address immediately after sending a Binding Update to the



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      home agent to register this new address.

   The following rules apply to home agents:

   o  When IPsec is used to protect return routability signaling or
      payload packets, IPsec security associations are needed to provide
      this protection.  When the care-of address for the mobile node
      changes as a result of an accepted Binding Update, special
      treatment is needed for the next packets sent using these security
      associations.  The home agent MUST set the new care-of address as
      the destination address of these packets, as if the destination
      gateway address in the security association had changed.


4.4 Dynamic Keying

   The following requirements apply to both home agents and mobile
   nodes:

   o  If replay protection is required, dynamic keying MUST be used.
      IPsec can provide replay protection only if dynamic keying is
      used.  This may not always be possible, and manual keying would be
      preferred in some cases.  IPsec also does not guarantee correct
      ordering of packets, only that they have not been replayed.
      Because of this, sequence numbers within the Mobile IPv6 messages
      ensure correct ordering.  However, if a home agent reboots and
      loses its state regarding the sequence numbers, replay attacks
      become possible.  The use of a key management mechanism together
      with IPsec can be used to prevent such replay attacks.

   o  If IKE version 1 is used with preshared secrets in main mode, it
      determines the shared secret to use from the IP address of the
      peer.  With Mobile IPv6, however, this may be a care-of address
      and does not indicate which mobile node attempts to contact the
      home agent.  Therefore, if preshared secret authentication is used
      in IKEv1 between the mobile node and the home agent then
      aggressive mode MUST be used.  Note also that care needs to be
      taken with phase 1 identity selection.  Where the ID_IPV6_ADDR
      Identity Payloads is used, unambiguous mapping of identities to
      keys is not possible.  (The next version of IKE may not have these
      limitations.)

   The following rules apply to mobile nodes:

   o  Where dynamic keying is used, the key management protocol MUST use
      the care-of address as the source address in the protocol
      exchanges with the mobile node's home agent.




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   o  Conversely, the IPsec security associations with the mobile node's
      home agent MUST be requested from the key management protocol with
      the home address as the mobile node's address.

      The security associations for protecting Binding Updates and
      Acknowledgements are requested for the Mobility header protocol in
      transport mode and for specific IP addresses as endpoints.
      Similarly, the security associations for protecting prefix
      discovery are requested for the ICMPv6 protocol.  Payload and
      return routability protection requests security associations for a
      specific tunnel interface and either the payload protocol or the
      Mobility header protocol, in tunnel mode.  In this case one
      requested endpoint is an IP address and another one is a wildcard.

   o  If the mobile node has used IKE to establish security associations
      with its home agent, it should follow the procedures discussed in
      Section 11.7.1 and 11.7.3 of the base specification to determine
      whether the IKE endpoints can be moved or if rekeying is needed.

   The following rules apply to home agents:

   o  If the home agent has used IKE to establish security associations
      with the mobile node, it should follow the procedures discussed in
      Section 10.3.1 and 10.3.2 of the base specification to determine
      whether the IKE endpoints can be moved or if rekeying is needed.


























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5. Example Configurations

   In the following we describe the Security Policy Database (SPD) and
   Security Association Database (SAD) entries necessary to protect
   Binding Updates and Binding Acknowledgements exchanged between the
   mobile node and the home agent.  Our examples assume the use of ESP,
   but a similar configuration could also be used to protect the
   messages with AH.

   Section 5.1 introduces the format we use in the description of the
   SPD and the SAD.  Section 5.2 describes how to configure manually
   keyed security associations, and Section 5.3 describes how to use
   dynamic keying.

5.1 Format

   The format used in the examples is as follows.  The SPD description
   has the format

     <node> "SPD OUT:"
       "-" <spdentry>
       "-" <spdentry>
       ...
       "-" <spdentry>

     <node> "SPD IN:"
       "-" <spdentry>
       "-" <spdentry>
       ...
       "-" <spdentry>

   Where <node> represents the name of the node, and <spdentry> has the
   following format:

     "IF" <condition> "THEN USE" <sa> |
     "IF" <condition> "THEN CREATE" <pattern> |

   Where <condition> is an boolean expression about the fields of the
   IPv6 packet, <sa> is the name of a security association, and
   <pattern> is a specification for a security association to be
   negotiated via IKE [5].  The SAD description has the format

     <node> "SAD:"
       "-" <sadentry>
       "-" <sadentry>
       ...
       "-" <sadentry>




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   Where <node> represents the name of the node, and <sadentry> has the
   following format:

     <sa> "(" <dir> ","
              <spi> ","
              <destination> ","
              <ahesp> ","
              <mode> ")" ":"
          <selectors>

   Where <dir> is "IN" or "OUT", <spi> is the SPI of the security
   association, <destination> is its destination, <ahesp> is normally
   "ESP" in our case but could also be "AH", <mode> is either "TUNNEL"
   or "TRANSPORT", and <selectors> is a boolean expression about the
   fields of the IPv6 packet.

   We will be using an example mobile node in this section with the home
   address "home_address_1".  The user's identity in this mobile node is
   "user_1".  The home agent's address is "home_agent_1".

5.2 Manual Configuration

5.2.1 Binding Updates and Acknowledgements

   Here are the contents of the SPD and SAD for protecting Binding
   Updates and Acknowledgements:

























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     mobile node SPD OUT:
       - IF source = home_address_1 & destination = home_agent_1 &
            proto = MH
         THEN USE SA1

     mobile node SPD IN:
       - IF source = home_agent_1 & destination = home_address_1 &
            proto = MH
         THEN USE SA2

     mobile node SAD:
       - SA1(OUT, spi_a, home_agent_1, ESP, TRANSPORT):
         source = home_address_1 & destination = home_agent_1 &
         proto = MH
       - SA2(IN, spi_b, home_address_1, ESP, TRANSPORT):
         source = home_agent_1 & destination = home_address_1 &
         proto = MH

     home agent SPD OUT:
       - IF source = home_agent_1 & destination = home_address_1 &
            proto = MH
         THEN USE SA2

     home agent SPD IN:
       - IF source = home_address_1 & destination = home_agent_1 &
            proto = MH
         THEN USE SA1

     home agent SAD:
       - SA2(OUT, spi_b, home_address_1, ESP, TRANSPORT):
         source = home_agent_1 & destination = home_address_1 &
         proto = MH
       - SA1(IN, spi_a, home_agent_1, ESP, TRANSPORT):
         source = home_address_1 & destination = home_agent_1 &
         proto = MH

   In the above, "MH" refers to the protocol number for the Mobility
   Header [8].

5.2.2 Return Routability Signaling

   In the following we describe the necessary SPD and SAD entries to
   protect return routability signaling between the mobile node and the
   home agent.  Note that the rules in the SPD are ordered, and the ones
   in the previous section must take precedence over these ones:






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     mobile node SPD OUT:
       - IF interface = tunnel to home_agent_1 &
            source = home_address_1 & destination = any &
            proto = MH
         THEN USE SA3

     mobile node SPD IN:
       - IF interface = tunnel from home_agent_1 &
            source = any & destination = home_address_1 &
            proto = MH
         THEN USE SA4

     mobile node SAD:
       - SA3(OUT, spi_c, home_agent_1, ESP, TUNNEL):
         source = home_address_1 & destination = any & proto = MH
       - SA4(IN, spi_d, home_address_1, ESP, TUNNEL):
         source = any & destination = home_address_1 & proto = MH

     home agent SPD OUT:
       - IF interface = tunnel to home_address_1 &
            source = any & destination = home_address_1 &
            proto = MH
         THEN USE SA4

     home agent SPD IN:
       - IF interface = tunnel from home_address_1 &
            source = home_address_1 & destination = any &
            proto = MH
         THEN USE SA3

     home agent SAD:
       - SA4(OUT, spi_d, home_address_1, ESP, TUNNEL):
         source = any & destination = home_address_1 & proto = MH
       - SA3(IN, spi_c, home_agent_1, ESP, TUNNEL):
         source = home_address_1 & destination = any & proto = MH


5.2.3 Prefix Discovery

   In the following we describe some additional SPD and SAD entries to
   protect prefix discovery.










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     mobile node SPD OUT:
       - IF source = home_address_1 & destination = home_agent_1 &
            proto = ICMPv6
         THEN USE SA5.

     mobile node SPD IN:
       - IF source = home_agent_1 & destination = home_address_1 &
            proto = ICMPv6
         THEN USE SA6

     mobile node SAD:
       - SA5(OUT, spi_e, home_agent_1, ESP, TRANSPORT):
         source = home_address_1 & destination = home_agent_1 &
         proto = ICMPv6
       - SA6(IN, spi_f, home_address_1, ESP, TRANSPORT):
         source = home_agent_1 & destination = home_address_1 &
         proto = ICMPv6

     home agent SPD OUT:
       - IF source = home_agent_1 & destination = home_address_1 &
            proto = ICMPv6
         THEN USE SA6

     home agent SPD IN:
       - IF source = home_address_1 & destination = home_agent_1 &
            proto = ICMPv6
         THEN USE SA5

     home agent SAD:
       - SA6(OUT, spi_f, home_address_1, ESP, TRANSPORT):
         source = home_agent_1 & destination = home_address_1 &
         proto = ICMPv6
       - SA5(IN, spi_e, home_agent_1, ESP, TRANSPORT):
         source = home_address_1 & destination = home_agent_1 &
         proto = ICMPv6

   Note that the SPDs described above protect all ICMPv6 traffic between
   the mobile node and the home agent.

5.2.4 Payload Packets

   It is also possible to perform some additional, optional, protection
   of tunneled payload packets.  This protection takes place in a
   similar manner to the return routability protection above, but
   requires a different value for the protocol field.  The necessary SPD
   and SAD entries are shown below.  It is assumed that the entries for
   protecting Binding Updates and Acknowledgements, and the entries to
   protect Home Test Init and Home Test messages take precedence over



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   these entries.

     mobile node SPD OUT:
       - IF interface = tunnel to home_agent_1 &
            source = home_address_1 & destination = any &
            proto = X
         THEN USE SA7

     mobile node SPD IN:
       - IF interface = tunnel from home_agent_1 &
            source = any & destination = home_address_1 &
            proto = X
         THEN USE SA8

     mobile node SAD:
       - SA7(OUT, spi_g, home_agent_1, ESP, TUNNEL):
         source = home_address_1 & destination = any & proto = X
       - SA8(IN, spi_h, home_address_1, ESP, TUNNEL):
         source = any & destination = home_address_1 & proto = X

     home agent SPD OUT:
       - IF interface = tunnel to home_address_1 &
            source = any & destination = home_address_1 &
            proto = X
         THEN USE SA8

     home agent SPD IN:
       - IF interface = tunnel from home_address_1 &
            source = home_address_1 & destination = any &
            proto = X
         THEN USE SA7

     home agent SAD:
       - SA8(OUT, spi_h, home_address_1, ESP, TUNNEL):
         source = any & destination = home_address_1 & proto = X
       - SA7(IN, spi_g, home_agent_1, ESP, TUNNEL):
         source = home_address_1 & destination = any & proto = X

   If multicast group membership control protocols such as MLDv1 [9] or
   MLDv2 [12] need to be protected, these packets may use a link-local
   address rather than the home address of the mobile node.  In this
   case the source and destination can be left as a wildcard and the SPD
   entries will work solely based on the used interface and the
   protocol, which is ICMPv6 for both MLDv1 and MLDv2.

   Similar problems are encountered when stateful address
   autoconfiguration protocols such as DHCPv6 [10] are used.  The same
   approach is applicable for DHCPv6 as well.  DHCPv6 uses the UDP



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   protocol.

   Support for multiple layers of encapsulation (such as ESP
   encapsulated in ESP) is not required by RFC 2401 [2] and is also
   otherwise often problematic.  It is therefore useful to avoid setting
   the protocol X in the above entries to either AH or ESP.

5.3 Dynamic Keying

   In this section we show an example configuration that uses IKE to
   negotiate security associations.

5.3.1 Binding Updates and Acknowledgements

   Here are the contents of the SPD for protecting Binding Updates and
   Acknowledgements:

     mobile node SPD OUT:
       - IF source = home_address_1 & destination = home_agent_1 &
            proto = MH
         THEN CREATE ESP TRANSPORT SA: local phase 1 identity = user_1

     mobile node SPD IN:
       - IF source = home_agent_1 & destination = home_address_1 &
            proto = MH
         THEN CREATE ESP TRANSPORT SA: local phase 1 identity = user_1

     home agent SPD OUT:
       - IF source = home_agent_1 & destination = home_address_1 &
            proto = MH
         THEN CREATE ESP TRANSPORT SA: peer phase 1 identity = user_1

     home agent SPD IN:
       - IF source = home_address_1 & destination = home_agent_1 &
            proto = MH
         THEN CREATE ESP TRANSPORT SA: peer phase 1 identity = user_1

   We have omitted details of the proposed transforms in the above, and
   all details related to the particular authentication method such as
   certificates beyond listing a specific identity that must be used.

   We require IKE to be run using the care-of addresses but still
   negotiate IPsec SAs that use home addresses.  The extra conditions
   set by the home agent SPD for the peer phase 1 identity to be
   "user_1" must be verified by the home agent.  The purpose of the
   condition is to ensure that the IKE phase 2 negotiation for a given
   user's home address can't be requested by another user.  In the
   mobile node, we simply set our local identity to be "user_1".



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   These checks also imply that the configuration of the home agent is
   user-specific: every user or home address requires a specific
   configuration entry.  It would be possible to alleviate the
   configuration tasks by using certificates that have home addresses in
   the Subject AltName field.  However, it isn't clear if all IKE
   implementations allow one address to be used for carrying the IKE
   negotiations when another address is mentioned in the used
   certificates.  In any case, even this approach would have required
   user-specific tasks in the certificate authority.

5.3.2 Return Routability Signaling

   Protection for the return routability signaling can be configured in
   a similar manner as above.

     mobile node SPD OUT:
       - IF interface = tunnel to home_agent_1 &
            source = home_address_1 & destination = any &
            proto = MH
         THEN CREATE ESP TUNNEL SA: gateway = home_agent_1 &
                                    local phase 1 identity = user_1

     mobile node SPD IN:
       - IF interface = tunnel from home_agent_1 &
            source = any & destination = home_address_1 &
            proto = MH
         THEN CREATE ESP TUNNEL SA: gateway = home_agent_1 &
                                    local phase 1 identity = user_1

     home agent SPD OUT:
       - IF interface = tunnel to home_address_1 &
            source = any & destination = home_address_1 &
            proto = MH
         THEN CREATE ESP TUNNEL SA: gateway = home_address_1 &
                                    peer phase 1 identity = user_1

     home agent SPD IN:
       - IF interface = tunnel from home_address_1 &
            source = home_address_1 & destination = any &
            proto = MH
         THEN CREATE ESP TUNNEL SA: gateway = home_address_1 &
                                    peer phase 1 identity = user_1

   Here we specified the gateway address for the security association as
   the home address for the mobile node.  However, as required by
   Section 4.3 the packets will actually be sent to the current care-of
   address.  In order to avoid writing dynamically changing information
   to the SPD entries, the above has been written with the home address



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   as the gateway.

5.3.3 Prefix Discovery

   In the following we describe some additional SPD entries to protect
   prefix discovery with IKE.  (Note that when actual new prefixes are
   discovered, there may be a need to enter new manually configured SPD
   entries to specify the authorization policy for the resulting new
   home addresses.)

     mobile node SPD OUT:
       - IF source = home_address_1 & destination = home_agent_1 &
            proto = ICMPv6
         THEN CREATE ESP TRANSPORT SA: local phase 1 identity = user_1

     mobile node SPD IN:
       - IF source = home_agent_1 & destination = home_address_1 &
            proto = ICMPv6
         THEN CREATE ESP TRANSPORT SA: local phase 1 identity = user_1

     home agent SPD OUT:
       - IF source = home_agent_1 & destination = home_address_1 &
            proto = ICMPv6
         THEN CREATE ESP TRANSPORT SA: peer phase 1 identity = user_1

     home agent SPD IN:
       - IF source = home_address_1 & destination = home_agent_1 &
            proto = ICMPv6
         THEN CREATE ESP TRANSPORT SA: peer phase 1 identity = user_1


5.3.4 Payload Packets

   Protection for the payload packets happens similarly to the
   protection of return routability signaling.  As in the manually keyed
   case, these SPD entries have lower priority than the above ones.















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     mobile node SPD OUT:
       - IF interface = tunnel to home_agent_1 &
            source = home_address_1 & destination = any &
            proto = X
         THEN CREATE ESP TUNNEL SA: gateway = home_agent_1 &
                                    local phase 1 identity = user_1

     mobile node SPD IN:
       - IF interface = tunnel from home_agent_1 &
            source = any & destination = home_address_1 &
            proto = X
         THEN CREATE ESP TUNNEL SA: gateway = home_agent_1 &
                                    local phase 1 identity = user_1

     home agent SPD OUT:
       - IF interface = tunnel to home_address_1 &
            source = any & destination = home_address_1 &
            proto = X
         THEN CREATE ESP TUNNEL SA: gateway = home_address_1 &
                                    peer phase 1 identity = user_1

     home agent SPD IN:
       - IF interface = tunnel from home_address_1 &
            source = home_address_1 & destination = any &
            proto = X
         THEN CREATE ESP TUNNEL SA: gateway = home_address_1 &
                                    peer phase 1 identity = user_1
























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6. Processing Steps within a Node

6.1 Binding Update to the Home Agent

   Step 1.  At the mobile node, Mobile IPv6 module first produces the
   following packet:

      IPv6 header (source = home address,
                   destination = home agent)
      Mobility header
         Binding Update

   Step 2.  This packet is matched against the IPsec policy data base on
   the mobile node and we make a note that IPsec must be applied.

   Step 3.  Then, we add the necessary Mobile IPv6 options but do not
   change the addresses yet, as described in Section 11.2.2 of the base
   specification [8].  This results in:

      IPv6 header (source = home address,
                   destination = home agent)
      Destination Options header
         Home Address option (care-of address)
      Mobility header
         Binding Update

   Step 4.  Finally, IPsec headers are added and the necessary
   authenticator values are calculated:

      IPv6 header (source = home address,
                   destination = home agent)
      Destination Options header
         Home Address option (care-of address)
      ESP header (SPI = spi_a)
      Mobility header
         Binding Update

   Step 5.  Before sending the packet, the addresses in the IPv6 header
   and the Destination Options header are changed:

      IPv6 header (source = care-of address,
                   destination = home agent)
      Destination Options header
         Home Address option (home address)
      ESP header (SPI = spi_a)
      Mobility header
         Binding Update




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6.2 Binding Update from the Mobile Node

   Step 1.  The following packet is received at the home agent:

      IPv6 header (source = care-of address,
                   destination = home agent)
      Destination Options header
         Home Address option (home address)
      ESP header (SPI = spi_a)
      Mobility header
         Binding Update

   Step 2.  The home address option is processed first, which results in

      IPv6 header (source = home address,
                   destination = home agent)
      Destination Options header
         Home Address option (care-of address)
      ESP header (SPI = spi_a)
      Mobility header
         Binding Update

   Step 3.  ESP header is processed next, resulting in

       IPv6 header (source = home address,
                    destination = home agent)
       Destination Options header
          Home Address option (care-of address)
       Mobility header
          Binding Update

   Step 4.  This packet matches the security association selectors
   (source = home address, destination = home agent, proto = MH).

   Step 5.  Mobile IPv6 processes the Binding Update.  The Binding
   Update is delivered to the Mobile IPv6 module.

6.3 Binding Acknowledgement to the Mobile Node

   Step 1.  Mobile IPv6 produces the following packet:

      IPv6 header (source = home agent,
                   destination = home address)
      Mobility header
         Binding Acknowledgement

   Step 2.  This packet matches the IPsec policy entries, and we
   remember that IPsec has to be applied.



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   Step 3.  Then, we add the necessary Route Headers but do not change
   the addresses yet, as described in Section 9.6 of the base
   specification [8].  This results in:

      IPv6 header (source = home agent,
                   destination = home address)
      Routing header (type 2)
         care-of address
      Mobility header
         Binding Acknowledgement

   Step 4.  We apply IPsec:

      IPv6 header (source = home agent,
                   destination = home address)
      Routing header (type 2)
         care-of address
      ESP header (SPI = spi_b)
      Mobility header
         Binding Acknowledgement

   Step 5.  Finally, before sending the packet out we change the
   addresses in the IPv6 header and the Route header:

      IPv6 header (source = home agent,
                   destination = care-of address)
      Routing header (type 2)
         home address
      ESP header (SPI = spi_b)
      Mobility header
         Binding Acknowledgement


6.4 Binding Acknowledgement from the Home Agent

   Step 1.  The following packet is received at the mobile node

      IPv6 header (source = home agent,
                   destination = care-of address)
      Routing header (type 2)
         home address
      ESP header (SPI = spi_b)
      Mobility header
         Binding Acknowledgement

   Step 2.  After the routing header is processed the packet becomes





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      IPv6 header (source = home agent,
                   destination = home address)
      Routing header (type 2)
         care-of address
      ESP header (SPI = spi_b)
      Mobility header
         Binding Acknowledgement

   Step 3.  ESP header is processed next, resulting in:

      IPv6 header (source = home agent,
                   destination = home address)
      Routing header (type 2)
         care-of address
      Mobility header
         Binding Acknowledgement

   Step 4.  This packet matches the security association selectors
   (source = home agent, destination = home address, proto = MH).

   Step 5.  The Binding Acknowledgement is delivered to the Mobile IPv6
   module.

6.5 Home Test Init to the Home Agent

   Step 1.  The mobile node constructs a Home Test Init message:

      IPv6 header (source = home address,
                   destination = correspondent node)
      Mobility header
         Home Test Init

   Step 2.  Mobile IPv6 determines that this packet should go to the
   tunnel to the home agent.

   Step 3.  The packet is matched against IPsec policy entries for the
   interface, and we find that IPsec needs to be applied.

   Step 4.  IPsec tunnel mode headers are added.  Note that we use a
   care-of address as a source address for the tunnel packet.

      IPv6 header (source = care-of address,
                   destination = home agent)
      ESP header (SPI = spi_c)
      IPv6 header (source = home address,
                   destination = correspondent node)
      Mobility header
         Home Test Init



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   Step 5.  The packet no longer satisfies the criteria that made it
   enter the tunnel, and it is sent directly to the home agent.

6.6 Home Test Init from the Mobile Node

   Step 1.  The home agent receives the following packet:

      IPv6 header (source = care-of address,
                   destination = home agent)
      ESP header (SPI = spi_c)
      IPv6 header (source = home address,
                   destination = correspondent node)
      Mobility Header
         Home Test Init

   Step 2.  IPsec processing is performed, resulting in:

      IPv6 header (source = home address,
                   destination = correspondent node)
      Mobility Header
         Home Test Init

   Step 3.  The resulting packet matches the selectors and the packet
   can be processed further.

   Step 4.  The packet is then forwarded to the correspondent node.

6.7 Home Test to the Mobile Node

   Step 1.  The home agent receives a Home Test packet from the
   correspondent node:

      IPv6 header (source = correspondent node,
                   destination = home address)
      Mobility Header
         Home Test Init

   Step 2.  The home agent determines that this packet is destined to a
   mobile node that is away from home, and decides to tunnel it.

   Step 3.  The packet matches the IPsec policy entries for the tunnel
   interface, and we note that IPsec needs to be applied.

   Step 4.  IPsec is applied, resulting in a new packet.  Note that the
   home agent must keep track of the location of the mobile node, and
   update the tunnel gateway address in the security association(s)
   accordingly.




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      IPv6 header (source = home agent,
                   destination = care-of address)
      ESP header (SPI = spi_d)
      IPv6 header (source = correspondent node,
                   destination = home address)
      Mobility Header
         Home Test Init

   Step 5.  The packet no longer satisfies the criteria that made it
   enter the tunnel, and it is sent directly to the care-of address.

6.8 Home Test from the Home Agent

   Step 1.  The mobile node receives the following packet:

      IPv6 header (source = home agent,
                   destination = care-of address)
      ESP header (SPI = spi_d)
      IPv6 header (source = correspondent node,
                   destination = home address)
      Mobility Header
         Home Test Init

   Step 2.  IPsec is processed, resulting in:

      IPv6 header (source = correspondent node,
                   destination = home address)
      Mobility Header
         Home Test Init

   Step 3.  This matches the security association selectors (source =
   any, destination = home address).

   Step 4.  The packet is given to Mobile IPv6 processing.

6.9 Prefix Solicitation Message to the Home Agent

   This procedure is similar to the one presented in Section 6.1.

6.10 Prefix Solicitation Message from the Mobile Node

   This procedure is similar to the one presented in Section 6.2.

6.11 Prefix Advertisement Message to the Mobile Node

   This procedure is similar to the one presented in Section 6.3.





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6.12 Prefix Advertisement Message from the Home Agent

   This procedure is similar to the one presented in Section 6.4.

6.13 Payload Packet to the Home Agent

   This procedure is similar to the one presented in Section 6.5.

6.14 Payload Packet from the Mobile Node

   This procedure is similar to the one presented in Section 6.6.

6.15 Payload Packet to the Mobile Node

   This procedure is similar to the one presented in Section 6.7.

6.16 Payload Packet from the Home Agent

   This procedure is similar to the one presented in Section 6.8.

6.17 Establishing New Security Associations

   Step 1.  The mobile node wishes to send a Binding Update to the home
   agent.

     IPv6 header (source = home address,
                  destination = home agent)
     Mobility header
        Binding Update

   Step 2.  There is no existing security association to protect the
   Binding Update, so IKE is initiated.  The IKE packets are sent as
   shown in the following examples.  The first packet is an example of
   an IKE packet sent from the mobile node, and the second one is from
   the home agent.  The examples shows also that the phase 1 identity
   used for the mobile node is a FQDN.

     IPv6 header (source = care-of address,
                  destination = home agent)
        UDP
        IKE
           ... IDii = ID_FQDN mn123.ha.net ...


     IPv6 header (source = home agent
                  destination = care-of address)
        UDP
        IKE



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           ... IDir = ID_FQDN ha.net ...

   Step 3.  IKE phase 1 completes, and phase 2 is initiated to request
   security associations for protecting traffic between the mobile
   node's home address and the home agent.  This involves sending and
   receiving additional IKE packets.  The below example shows again one
   packet sent by the mobile node and another sent by the home agent.
   The example shows also that the phase 2 identity used for the mobile
   node is the mobile node's home address.

     IPv6 header (source = care-of address,
                  destination = home agent)
        UDP
        IKE
           ... IDci = ID_IPV6_ADDR home address ...

     IPv6 header (source = home agent,
                  destination = care-of address)
        UDP
        IKE
           ... IDcr = ID_IPV6_ADDR home agent ...

   Step 4.  The remaining steps are as shown in Section 6.1.

6.18 Rekeying Security Associations

   Step 1.  The mobile node and the home agent have existing security
   associations.  Either side may decide at any time that the security
   associations need to be rekeyed, for instance, because the specified
   lifetime is approaching.

   Step 2.  Mobility header packets sent during rekey may be protected
   by the existing security associations.

   Step 3.  When the rekeying is finished, new security associations are
   established.  In practice there is a time interval during which an
   old, about-to-expire security association and newly established
   security association will both exist.  The new ones should be used as
   soon as they become available.

   Step 4.  A notification of the deletion of the old security
   associations is received.  After this, only the new security
   associations can be used.

   Note that there is no requirement that the existence of the IPsec and
   IKE security associations is tied to the existence of bindings.  It
   is not necessary to delete a security association if a binding is
   removed, as a new binding may soon be established after this.



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   Since cryptographic acceleration hardware may only be able to handle
   a limited number of active security associations, security
   associations may be deleted via IKE in order to keep the number of
   active cryptographic contexts to a minimum.  Such deletions should
   not be interpreted as a sign of losing a contact to the peer or as a
   reason to remove a binding.  Rather, if additional traffic needs to
   be sent, it is preferable to bring up another security association to
   protect it.

6.19 Movements and Dynamic Keying

   In this section we describe the sequence of events that relate to
   movement with IKE-based security associations.  In the initial state,
   the mobile node is not registered in any location and has no security
   associations with the home agent.  Depending on whether the peers
   will be able to move IKE endpoints to new care-of addresses, the
   actions taken in Step 9 and 10 are different.

   Step 1.  Mobile node with the home address A moves to care-of address
   B.

   Step 2.  Mobile node runs IKE from care-of address B to the home
   agent, establishing a phase 1.

   Step 3.  Protected by this phase 1, mobile node establishes a pair of
   security associations for protecting Mobility Header traffic to and
   from the home address A.

   Step 4.  Mobile node sends a Binding Update and receives a Binding
   Acknowledgement using the security associations created in Step 3.

   Step 5.  Mobile node establishes a pair of security associations for
   protecting return routability packets.  These security associations
   are in tunnel mode and their endpoint in the mobile node side is
   care-of address B.  For the purposes of our example, this step uses
   the phase 1 connection established in Step 2.  Multiple phase 1
   connections are also possible.

   Step 6.  The mobile node uses the security associations created in
   Step 5 to run return routability.

   Step 7.  The mobile node moves to a new location and adopts a new
   care-of address C.

   Step 8.  Mobile node sends a Binding Update and receives a Binding
   Acknowledgement using the security associations created in Step 3.
   The home agent ensures that the next packets sent using the security
   associations created in Step 5 will have the new care-of address as



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   their destination address, as if the destination gateway address in
   the security association had changed.

   Step 9.  If the mobile node and the HA have the capability to change
   the IKE endpoints, they change the address to C.  If they dont have
   the capability, both nodes remove their phase 1 connections created
   on top of the care-of address B and establish a new IKE phase 1 on
   top of the care-of address C.  This capability to change the IKE
   phase 1 end points is indicated through setting the Key Management
   Mobility Capability (K) flag [8] in the Binding Update and Binding
   Acknowledgement messages.

   Step 10.  If a new IKE phase 1 connection was setup after movement,
   the MN will not be able to receive any notifications delivered on top
   of the old IKE phase 1 security association.  Notifications delivered
   on top of the new security association are received and processed
   normally.  If the mobile node and HA were able to update the IKE
   endpoints, they can continue using the same IKE phase 1 connection.

































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7. Implementation Considerations

   We have chosen to require an encapsulation format for return
   routability and payload packet protection which can only be realized
   if the destination of the IPsec packets sent from the home agent can
   be changed as the mobile node moves.  One of the main reasons for
   choosing such a format is that it removes the overhead of twenty four
   bytes when a home address option or routing header is added to the
   tunneled packet.  What is needed is that the home agent must act as
   if the gateway address of a security association to the mobile node
   would have changed.  Implementations are free to choose any
   particular method to make this change, such as using an API to the
   IPsec implementation to change the parameters of the security
   association, removing the security association and installing a new
   one, or modification of the packet after it has gone through IPsec
   processing.  The only requirement is that after registering a new
   binding at the home agent, the next IPsec packets sent on this
   security association will be addressed to the new care-of address.

   We have also chosen to require that a dynamic key management protocol
   must be able to make an authorization decision for IPsec security
   association creation with different addresses than with what the key
   management protocol is run.  We expect this to be done typically by
   configuring the allowed combinations of phase 1 user identities and
   home addresses.

   The base Mobile IPv6 specification sets high requirements for a
   so-called Bump-In-The-Stack (BITS) implementation model of IPsec.  As
   Mobile IPv6 specific modifications of the packets are required after
   IPsec processing, the BITS implementation has to perform also some
   tasks related to mobility.  This may increase the complexity of the
   implementation, even if it already performs some tasks of the IP
   layer (such as fragmentation).

   We have chosen to require policy entries that are specific to a
   tunnel interface.  This means that implementations have to regard the
   Home Agent - Mobile Node tunnel as a separate interface on which
   IPsec SPDs can be based.

   A further complication of the IPsec processing on a tunnel interface
   is that this requires access to the BITS implementation before the
   packet actually goes out.

   When certificate authentication is used, IKE fragmentation can be
   encountered.  This can occur when certificate chains are used, or
   even with single certificates if they are large.  Many firewalls do
   not handle fragments properly, and may drop them.  Routers in the
   path may also discard fragments after the initial one, since they



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   typically will not contain full IP headers that can be compared
   against an access list.  Where fragmentation occurs, the endpoints
   will not always be able to establish a security association.

   Fortunately, typical Mobile IPv6 deployment uses short certificate
   chains, as the mobile node is communicating directly with its home
   network.  Nevertheless, where the problem appears, one solution is to
   replace the firewalls or routers with equipment that can properly
   support fragments.  If this cannot be done, it may help to store the
   peer certificates locally, or to obtain them through other means.









































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8. Security Considerations

   The Mobile IPv6 base specification [8] requires strong security
   between the mobile node and the home agent.  This memo discusses how
   that security can be arranged in practice, using IPsec.














































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Normative References

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

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

   [3]  Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
        November 1998.

   [4]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
        (ESP)", RFC 2406, November 1998.

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

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

   [7]  Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6
        Specification", RFC 2473, December 1998.

   [8]  Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in
        IPv6", draft-ietf-mobileip-ipv6-21 (work in progress), February
        2003.

























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Informative References

   [9]   Deering, S., Fenner, W. and B. Haberman, "Multicast Listener
         Discovery (MLD) for IPv6", RFC 2710, October 1999.

   [10]  Droms, R., "Dynamic Host Configuration Protocol for IPv6
         (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress),
         November 2002.

   [11]  Kivinen, T., Huttunen, A., Swander, B. and V. Volpe,
         "Negotiation of NAT-Traversal in the IKE",
         draft-ietf-ipsec-nat-t-ike-04 (work in progress), November
         2002.

   [12]  Vida, R. and L. Costa, "Multicast Listener Discovery Version 2
         (MLDv2) for IPv6", draft-vida-mld-v2-06 (work in progress),
         December 2002.


Authors' Addresses

   Jari Arkko
   Ericsson
   Jorvas  02420
   Finland

   EMail: jari.arkko@ericsson.com


   Vijay Devarapalli
   Nokia Research Center
   313 Fairchild Drive
   Mountain View  CA 94043
   USA

   EMail: vijayd@iprg.nokia.com


   Francis Dupont
   ENST Bretagne
   Campus de Rennes 2, rue de la Chataigneraie
   BP 78
   Cesson-Sevigne Cedex  35512
   France

   EMail: Francis.Dupont@enst-bretagne.fr





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Appendix A. Acknowledgements

   The authors would like to thank Greg O'Shea, Michael Thomas, Kevin
   Miles, Cheryl Madson, Bernard Aboba, Erik Nordmark, and Gabriel
   Montenegro for interesting discussions in this problem space.














































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Appendix B. Changes from Previous Version

   The following changes have been made to this document from version
   02:

   o  It is now better explained why the mobile node can change its
      source address in security associations before such a change is
      told to the home agent (tracked issue 249).

   o  The support for protecting prefix discovery with IPsec has been
      made mandatory, but use is still a SHOULD (tracked issue 249).

   o  Requirements for security association and policy configuration for
      new home addresses received through prefix discovery have been
      specified (tracked issue 243).

   o  IPsec protocol and mode requirements have now been stated as
      minimal requirements and no longer prevent the use of other
      protocols (AH) and modes (tracked issue 228).

   o  The specification explicitly discourages the use of nested IPsec
      encapsulation (tracked issue 219).

   o  The different types of requests for phase 2 security associations
      have been explained in the requirements section.  This relates to
      using IKE for creating security associations for Binding Update
      protection or other tasks (tracked issue 219).

   o  Many editorial modifications have been performed.






















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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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