MIP6 Working Group                                       Basavaraj Patil
Internet-Draft                                    Nokia Siemens Networks
Intended status: Standards Track                           Gopal Dommety
Expires: August 28, 2008                                           Cisco
                                                       February 25, 2008


          Why Authentication Data suboption is needed for MIP6
                  draft-ietf-mip6-whyauthdataoption-05

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

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

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

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 28, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   Mobile IPv6 defines a set of messages that enable the mobile node
   (MN) to authenticate and perform registration with its home agent
   (HA).  These authentication signaling messages between the mobile
   node and home agent are secured by an IPsec SA that is established
   between the MN and HA.  The MIP6 working group has specified a
   mechanism to secure the binding update and binding acknowledgement
   messages using an authentication option, similar to the



Patil & Dommety          Expires August 28, 2008                [Page 1]


Internet-Draft        Why authdata option for MIP6         February 2008


   authentication option in Mobile IPv4, carried within the messages
   that are exchanged between the MN and HA to establish a binding.
   This document provides the justifications as to why the
   authentication option mechanism was needed for Mobile IPv6 deployment
   in certain environments.


Table of Contents

   1.  Conventions used in this document  . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  4
   5.  Justification for the use of the authentication option . . . .  5
     5.1.  Motivation for use of authentication option in
           cdma2000 wireless networks . . . . . . . . . . . . . . . .  5
     5.2.  Additional arguments for the use of Authentication
           option . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Solution Proposal  . . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  IPv4 based mobility architecture in cdma2000 networks  . .  9
     6.2.  IPv6 based mobility architecture in cdma2000 networks  . . 10
       6.2.1.  Overview of the mobility operation in IPv6 based
               cdma2000 networks  . . . . . . . . . . . . . . . . . . 11
       6.2.2.  Authentication and Security details  . . . . . . . . . 11
   7.  Limitations of the Authentication Protocol option  . . . . . . 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   10. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     12.2. Informative References . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 17

















Patil & Dommety          Expires August 28, 2008                [Page 2]


Internet-Draft        Why authdata option for MIP6         February 2008


1.  Conventions used in this document

   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 RFC 2119 [RFC2119].


2.  Introduction

   Mobile IPv6 relies on the IPsec Security Association between the
   Mobile Node (MN) and the Home Agent (HA) for authentication of the MN
   to its HA before a binding cache can be created at the HA.  An
   alternate mechanism that does not rely on the existence of the IPsec
   SA between the MN and HA for authenticating the MN is needed in
   certain deployment environments.  This document outlines some of the
   reasons why such a mechanism is essential to ensure the applicability
   of MIP6 as a protocol for wider deployment.  It should be noted that
   the alternate solution does not imply that the IPsec based solution
   would be deprecated.  It simply means that in certain deployment
   scenarios there is a need for supporting MIP6 without an IPsec SA
   between the MN and HA.  So the alternate solution would be in
   addition to the IPsec based mechanism specified in the base RFCs, RFC
   3775 [RFC3775], RFC 3776 [RFC3776] and RFC 4877 [RFC4877].  It should
   be noted that some of the challenges of deploying MIP6 in certain
   types of networks arise from the dependence on IKE which does not
   integrate will with a AAA backend infrastructure.  IKEv2 does address
   this problem.  However at the time of discussion on the need for the
   authentication protocol, the specification for using Mobile IPv6
   Operation with IKEv2 and the revised IPsec Architecture [RFC4877] was
   still work in progress at the time of this writing and as a result an
   alternative solution needed.  This document is intended to capture
   for archival purposes the reasoning behind the need for the
   authentication protocol which is specified in [RFC4285].  It should
   be noted that some of the arguments for justifying the specification
   of the authentication protocol have been made redundant as a result
   of the specification of Mobile IPv6 operation with IKEv2 [RFC4877].
   However some of the arguments discussed in this document are still
   applicable and justify usage of the authentication protocol in
   certain deployment environments.


3.  Background

   Mobile IPv6 signaling involves several messages.  These include:

   o  The binding update/Binding ACK between the mobile node and the
      home agent.




Patil & Dommety          Expires August 28, 2008                [Page 3]


Internet-Draft        Why authdata option for MIP6         February 2008


   o  The route optimization signaling messages which include HoTI/Hot,
      CoTI/CoT and BU/BAck between the MN and CN.  HoTI and HoT
      signaling messages are routed through the MNs HA.
   o  Mobile prefix solicitation and advertisements between the MN and
      HA.
   o  Home agent discovery by MNs.

   The signaling messages between the MN and HA are secured using the
   IPsec SA that is established between these entities.  The exception
   to this are the messages involved in the home agent discovery
   process.  [RFC4877] specifies the establishment of the IPsec SA using
   IKEv2.


4.  Applicability Statement

   The authentication option specified in the Authentication Protocol
   for MIP6 [RFC4285] provides a solution for MIP6 deployment in
   environments which an operator may not require IPsec based security
   for the signaling.  The reasons for an operator choosing to deploy
   MIP6 without mandating IPsec based security for signaling messages
   between the MN and HA could be many.  Some of these are for example:

   1.  Operators deploying MIP6 in cellular networks may consider IPsec
       and IKEv2 as adding overhead to the limited bandwidth over the
       air interface.  The overhead here is in terms of the bytes that
       IPsec and IKEv2 introduce to the signaling.
   2.  Operators may consider the number of messages between the MN and
       HA that are required to establish the IPsec SA as too many.  The
       number of transactions chew into the capacity of limited
       bandwidth air interfaces when MIP6 is used in such environments.
       It also adds additional latency to the establishment of the
       binding.
   3.  In many deployments the authentication credentials already exist
       in a AAA server.  These credentials are used for authenticating a
       user and authorizing network access.  The same credentials and
       security parameters can be reused for MIP6 security as well.
   4.  Dynamic assignment of home agents is needed in certain
       deployments to minmize the latency of the backhaul.  This is done
       by allocating an HA in a visited network for example.  Requiring
       IPsec SAs with home agents that are dynamically assigned is an
       overhead especially when the HA is in a visited network.
   5.  Signaling messages between the MN and HA may be in certain
       deployments over secure link-layers.  The lower layers provide
       ciphering and security for the messages and hence the need for
       IPsec to do the same for MIP6 messages does not exist.

   One such example of networks that have such characteristics are cdma



Patil & Dommety          Expires August 28, 2008                [Page 4]


Internet-Draft        Why authdata option for MIP6         February 2008


   networks as defined in the 3GPP2 X.S0011-D [3GPP2 X.S0011-D]
   specification.  Other networks which have similar deployment
   requirements are IEEE 802.16e based Mobile WiMAX networks and
   potentially 3GPP based HSPA (High speed Packet access) type of
   networks.


5.  Justification for the use of the authentication option

   The following two sections provide the reasoning for standardizing
   the authentication option based registration process for Mobile IPv6.
   Section 5.1 provides the key arguments for the use of authentication
   option.  Section 5.2 provides further explanation and additional
   motivations for the authentication option.

5.1.  Motivation for use of authentication option in cdma2000 wireless
      networks

   cdma2000 networks deployed and operational today use Mobile IPv4 for
   IP mobility.  Operators have gained a significant amount of
   operational experience in the process of deploying and operating
   these networks. 3GPP2 has specified Mobile IPv6 in Revision D of the
   3GPP2 X.S0011-D [3GPP2 X.S0011-D] specification (which specifies the
   packet data architecture).  The following are the deployment
   constraints that existing CDMA networks have to deal with when
   deploying Mobility service based on IPv6:

   o  Operators intend to leverage the Mobile IPv4 deployment and
      operational experience by ensuring that Mobile IPv6 has a similar
      deployment and operating model.
   o  Operators will have two parallel networks, one that offers IPv4
      mobility with MIP4 and another providing IPv6 mobility using MIP6.
   o  The same backend subscriber profile database, security keys etc.
      are intended to be used for both Mobile IPv4 and, Mobile IPv6
      service.
   o  The same user configuration information, i.e the identity and keys
      associated with a user will be used for IP mobility service in
      IPv4 and/or IPv6 networks.  The only security association that is
      preconfigured is a shared secret between the mobile node and the
      home-AAA server.  This is in contrast with the currently specified
      Mobile IPv6 model which requires an IPsec SA between the MN and
      HA.  At the time of this writing the IKEV2 based solution for
      establishing an IPsec SA [RFC4877] was not available.  IKEv2 does
      enable integration with a a AAA backend.
   o  At the time of specifying the authentication protocol, the Mobile
      IPv6 specification did not support the dynamic assignment of home
      agent and home address.  However work done in the MIP6 working
      group on bootstrapping of Mobile IPv6 as specified in [RFC5026]



Patil & Dommety          Expires August 28, 2008                [Page 5]


Internet-Draft        Why authdata option for MIP6         February 2008


      and MIP6-bootstrapping for the Integrated Scenario
      [I-D.ietf-mip6-bootstrapping-integrated-dhc] addresses this
      deficiency.  The mechanism defined in Authentication protocol for
      Mobile IPv6 [RFC4285] is capable of handling authentication even
      in the case of dynamic assignments (and is similar to what is used
      in current MIPv4 deployments).

   Consequently, MIP6 as specified at the time the authentication
   protocol was being specifid did not satisfy many of the deployment
   requirements.  The Authentication protocol for MIP6 [RFC4285] along
   with the MN Identifier option for MIP6 [RFC4283] are enabling the
   deployment of Mobile IPv6 in a manner that is similar to what is
   deployed in cdma2000 networks today.  This authentication model is
   very similar to the one adopted by the MIPv4 WG.  This is explained
   in detail in the 3GPP2 X.S0011-D [3GPP2 X.S0011-D] specification.

   Hence, with the MIP6 specifications and architecture that relies on
   IPsec as the sole means for securing the signaling between the MN and
   HA, it is not possible to accomplish a deployment that mirrors that
   of MIP4 for cdma deployments.

5.2.  Additional arguments for the use of Authentication option

   The use of IPsec for performing Registration with a home agent is not
   always an optimal solution.  While it is true that IPsec is an
   integral part of the IPv6 stack, it is still a considerable overhead
   from a deployment perspective of using IPsec as the security
   mechanism for the signaling messages between the MN and HA.  This
   statement is a result of experience gained from deployment of Mobile
   IPv4.  MIP4 does not rely on IPsec for securing the Registration
   signaling messages.

   Deployment of Mobile IPv6 on a large scale is possible only when the
   protocol is flexible for being adapted to various scenarios.  The
   scenario being considered is the deployment in cdma2000 net- works or
   WiMAX networks. cdma2000 networks are currently deployed in many
   countries today and WiMAX deployments are beginning.  The packet data
   network architecture of cdma2000 [3GPP2 X.S0011-D] includes a MIP4
   foreign agent/Home agent and a Radius based AAA infrastrucutre for
   authentication, authorization and accounting purposes.  The AAA
   infrastructure provides the authentication capability in the case of
   Mobile IPv4.

   Typically, the Mobile Node shares a security association with the
   AAA-Home entity.  This is the preferred mode of operation over having
   a shared secret between the MN and HA because the AAA-Home entity
   provides a central location for provisioning and administering the
   shared secrets for a large number of mobiles (millions).  This mode



Patil & Dommety          Expires August 28, 2008                [Page 6]


Internet-Draft        Why authdata option for MIP6         February 2008


   of operation also makes dynamic home address and dynamic home agent
   assignment easier.  A similar approach is needed for the deployment
   of Mobile IPv6 in these networks.  There is no practical mechanism to
   use IPsec directly with the AAA infrastructure with out the use of
   IKE or some other mechanism that enables the establishment of the
   IPsec SA between the MN and HA.

   Mobile IPv6 as specified in RFC3775 and RFC3776 is based on a very
   specific model for deployment.  It anticipates the Mobile nodes
   having a static home IPv6 address and a designated home agent.  This
   is not practical in most deployment scenarios being considered.  An
   IPsec SA is expected to be created, either via manual keying or
   established dynamically by using IKE or IKEv2.  These assumptions do
   not necessarily fit in very well for the deployment model envisioned
   in cdma2000 or WiMAX networks.  These limitations have however been
   overcome as a result of the bootstrapping specifications as per
   [RFC5026] and MIP6-bootstrapping for the Integrated Scenario
   [I-D.ietf-mip6-bootstrapping-integrated-dhc]

   cdma2000 and WiMAX networks would prefer to allocate home addresses
   to MNs on a dynamic basis.  The advantage of doing so is the fact
   that the HA can be assigned on a link that is close to the MNs point
   of attachment.  While route-optimization negates the benefit of
   having a home-agent on a link close to the MN, it cannot be always
   guaranteed that the MN and CN will use or support route optimization.
   There may also be instances where the operator prefers to not allow
   route optimization for various reasons such as accounting aggregation
   or enforcing service contracts.  In such cases an HA that is close to
   the MNs point of attachment reduces the issues of latency etc. of
   forward and reverse tunnelling of packets between the MN and HA.

   cdma2000 networks that are operational today have large numbers of
   subscribers who are authenticated via the AAA infrastrucure.
   Deployment of Mobile IPv6 should leverage the existing AAA
   infrastructure.  The security model needed in these networks is an SA
   between the MN and AAA-Home entity.  This is the primary security
   association that should be used for authenticating and authorizing
   users to utilize MIPv6 service.  This SA is then used for
   establishing session keys between the MN and the dynamically assigned
   HA for authenticating subsequent binding updates and binding
   acknowledgements between them.  Establishing an IPsec SA between the
   MN and HA using AAA infrastrucure was not specified for Mobile IPv6
   at the time the Authentication protocol was being specified.  RFC3776
   explains how IKE is used for establishing the SA between the MN and
   HA.  [RFC4877] has been published subsequently and hence the issue of
   establishing an IPsec SA dynamically between the MN and HA no longer
   exists. cdma2000 network operators would prefer to assign home
   addresses to the MN on a dynamic basis and do this preferably using



Patil & Dommety          Expires August 28, 2008                [Page 7]


Internet-Draft        Why authdata option for MIP6         February 2008


   the AAA infrastrucutre which contains subscriber profile and
   capability information.  This was not possible prior to the
   specification of the bootstrapping mechanism in [RFC5026].

   A large subset of MNs in cdma2000 networks do not have IKE
   capability.  As a result the use of RFC3776 for setting up the MN-HA
   IPsec SA is not an option.  It should also be noted that IKE requires
   several transactions before it is able to establish the IPsec SA.
   [RFC4877] specifies the establishment of an IPsec SA between the MN
   and HA using IKEv2.  It is possible that not all MNs in a deployment
   will support IKEv2 and hence an alternative mechanism provides the
   needed flexibility.

   cdma2000 network operators are extremely conscious in terms of the
   number of messages sent and received over the air-interface for
   signaling.  The overhead associated with sending/receiving a large
   number of signaling messages over the air interface has a direct
   impact on the overall capacity and cost for the operator.
   Optimization of the number of messages needed for using a service
   like Mobile IPv6 is of great concern.  As a result the use of IKE for
   Mobile IPv6 deployment is detrimental to the operators bottom line.

   Another downside of IKE for setting up the IPsec SA between the MN
   and HA is that IKE does not integrate very well with the Radius based
   AAA back-end.  Since operators rely on the AAA infrastrucure to
   provision subscribers as well as define profiles, keys etc. in the
   AAA-Home, there is no getting away from the use of AAA in cdma2000
   networks.  IKEv2 does address this problem.  However from a timeline
   perspective the availability of IKEv2 specifications for Mobile IPv6
   Operation with IKEv2 and the revised IPsec Architecture [RFC4877] and
   implementations did not meet the need of operators that were relying
   on 3GPP2 specifications.  With the specification of IKEv2 and
   publication of RFC4877 the integration with AAA backends is no longer
   an issue.

   In summary the model of Mobile IPv6 deployment which mandated the
   existence of an IPsec SA between the MN and HA, as specified in RFCs
   3775 and 3776, was too rigid and did not meet the requirements of
   operators building networks based on the cdma2000 [3GPP2 X.S0011-D]
   specifications.  To address this shortcoming, the authentication
   protocol [RFC4285] was specified.


6.  Solution Proposal

   The above issues can be addressed by developing a solution that
   allows MIPv6 deployment that does not mandate the use of IPsec for
   securing the binding update and binding acknowledgment messages



Patil & Dommety          Expires August 28, 2008                [Page 8]


Internet-Draft        Why authdata option for MIP6         February 2008


   between the MN and HA.  A solution similar to the one that is used in
   Mobile IPv4 today can be applied to Mobile IPv6 as well.  The
   experience gained in deploying Mobile IPv4 in cdma2000 networks on a
   large scale can be reused for Mobile IPv6 also.  The technical
   arguments against the use of IPsec for the registration process have
   been described in the previous sections which are primarily: message
   overhead, number of round trips required to establish an SA,
   keepalives etc.  The only con- sideration is that the alternative
   solution should not be vulner- able to attacks that are otherwise
   prevented by the use of IPsec.  Sections 4.1 and 4.2 describe the
   IPv4 based mobility architecture in cdma networks and IPv6 based
   mobility architecture in cdma Net- works respectively.

6.1.  IPv4 based mobility architecture in cdma2000 networks

   The figure below shows a high level view of the key network elements
   that play a role in providing IP mobility using Mobile IPv4.

                 +--------------+           +----------------------+
                 |   +------+   |           |   +------+           |
                 |   |      |   |           |   |      |           |
                 |   |F-AAA |   |           |   |H-AAAH|           |
                 |   |      +-------------------+      |           |
                 |   +---+--+   |           |   +--+---+           |
                 |       |      |           |      |               |
                 |       |      |           |      |               |
      +------+   |   +---+--+   |           |   +--+---+           |
      |      |   |   |      |   |           |   |      |           |
      |  MN  +- -|- -+ PDSN + --  --  --  --  - +  HA  |           |
      |      |   |   |  /FA |   |           |   |      |           |
      +------+   |   +------+   |           |   +------+           |
                 |              |           |                      |
                 +--------------+           +----------------------+


   Figure 1: cdma2000 packet data network architecture with Mobile IPv4

   The cdma mobility architecture based on MIPv4 is explained below.  In
   this architecture, mobility is tightly integrated with the AAA
   infrastructure.  The Mobile is configured with a NAI (Network Access
   Identifier) and a MN-AAA Key. The MN-AAA key is a shared Key that is
   shared between the MN and the Home AAA server.

   Below is the access link setup procedure:

   1.   Bring up PPP on MN/PDSN (access router link).  PPP
        authentication is skipped.  Mobile IP Authentication is
        performed via the FA.



Patil & Dommety          Expires August 28, 2008                [Page 9]


Internet-Draft        Why authdata option for MIP6         February 2008


   2.   PDSN sends a Mobile IP challenge to the MN on PPP link (RFC
        3012).
   3.   MN sends a MIP registration request (RRQ), which includes the
        users NAI, challenge and a MN-AAA extension which has challenge
        response and a MN-HA extension which is generated based on the
        MN-HA key.
   4.   PDSN extracts the MIP NAI/Challenge and response from MIP MN-AAA
        extension sends an Access Request to F-AAA (challenge/response
        using MD5).
   5.   F-AAA may forward it to H-AAA if needed (based on realm).
   6.   AAA authenticates the chap-challenge/response and returns
        "success" if authentication succeeds.
   7.   PDSN forwards Registration Request (RRQ) to HA.
   8.   HA authenticates the RRQ (MHAE extension).  HA may optionally
        authenticate with AAA infrastructure (just like PDSN as in #4).
   9.   If authentication is successful, HA creates a binding and sends
        a success Registration Reply (RRP) to PDSN.
   10.  PDSN creates a visitor entry and forwards the RRP to MN.

6.2.  IPv6 based mobility architecture in cdma2000 networks

   Due to the need for co-existence with MIPv4, and having the same
   operational model, the 3GPP2 standards body is adopting the following
   mobility architecture for MIPv6.


                        Access Domain                  Home Domain
                  +--------------+           +----------------------+
                  |   +------+   |           |   +------+           |
                  |   |      |   |           |   |      |           |
                  |   |F-AAA |   |           |   |H-AAA |           |
                  |   |      +-------------------+      |           |
                  |   +---+--+   |           |   +--+---+           |
                  |       |      |           |      |               |
                  |       |      |           |      |               |
       +------+   |   +---+--+   |           |   +--+---+           |
       |      |   |   |      |   |           |   |      |           |
       |  MN  +- -|- -+ PDSN + --  --  --  --  - +  HA  |           |
       |      |   |   |  /AR |   |           |   |      |           |
       +------+   |   +------+   |           |   +------+           |
                  |              |           |                      |
                  +--------------+           +----------------------+



   Figure 2: cdma2000 packet data network architecture with Mobile IPv6

   The Mobile is configured with an NAI (Network Access Identifier) and



Patil & Dommety          Expires August 28, 2008               [Page 10]


Internet-Draft        Why authdata option for MIP6         February 2008


   a MN-AAA Key. The MN-AAA key is a shared Key between the MN and the
   Home AAA server.

6.2.1.  Overview of the mobility operation in IPv6 based cdma2000
        networks

   The following steps explain at a very generic level the operation of
   IP mobility in cdma2000 networks:

   1.  The MN performs Link Layer establishment.  This includes setting
       up the PPP link.  PPP-Chap authentication is performed.  This is
       authenticated by the PDSN/AR by sending an Access Request to the
       F-AAA (and to the H-AAA when/if needed).  Optionally, the MN
       acquires bootstrap information from the Home Network (via the
       PDSN; PDSN receives this information in Access Accept).  The
       bootstrap information includes Home address and Home agent
       assignment.  The MN uses stateless DHCPv6 [RFC3736] to obtain the
       bootstrap information from the PDSN.
   2.  The MN begins to use the HoA that was assigned in step 1.  If no
       HoA was assigned at step 1, the MN generates (auto-configures) an
       IPv6 global unicast address based on the prefix information
       received at step 1.
   3.  At this step the MN sends a Binding Update to the selected Home
       Agent.  In the BU, the MN includes the NAI option, timestamp
       option and MN-AAA auth option.
   4.  The HA extracts the NAI, authenticator etc. from the BU and sends
       an access request to the Home RADIUS server.
   5.  The Home RADIUS server authenticates and authorizes the user and
       sends back a RADIUS Access-Accept to the HA indicating successful
       authentication and authorization.
   6.  At this step the HA performs a replay check with the ID field in
       the received BU.  The HA also performs proxy Duplicate Address
       Detection (DAD) on the MN's home address (global) using proxy
       Neighbor Solicitation as specified in RFC 2461.
   7.  Assuming that proxy DAD is successful, the HA sends back a
       Binding Acknowledgment to the MN.  In this BA message the HA
       includes the MN-HA mobility option, NAI mobility option and the
       ID mobility option.

6.2.2.  Authentication and Security details

   Access Link Setup, Access Authentication and Bootstrapping:

   1.  MN brings up PPP session.  PDSN triggers the MN to perform CHAP
       authentication, as part of access authentication, while bringing
       up PPP link.





Patil & Dommety          Expires August 28, 2008               [Page 11]


Internet-Draft        Why authdata option for MIP6         February 2008


   2.  The MN is authenticated using PPP-CHAP by the H-AAA (Home AAA),
       via the F-AAA (Foreign AAA).
   3.  H-AAA may optionally send HoA and HA IP address to the PDSN for
       bootstrapping the MN (skipping details).

   Mobile IPv6 Authentication:

   The Call Flow for the initial authentication (the number in the
   parenthesis corresponds to the explanation below)


     MN                                    HA                    H-AAA
      |              BU to HA (4)           | RADIUS Access-ReQ(5)
      |------------------------------------>|------------------->|(6)
      | (includes NAI option, MN-ID option, |                    |
      | Mesg ID option, MN-AAA Auth Option) |RADIUS Access-Accept|(7)
      |
                                            |<-------------------|
      |                                     |                    |
      |                             HA/AAAH authenticates MN
      |
      |                                     |(8)
      |
      |                                     |
      |
      |              BA to MN    (9)        |
      |
      |<------------------------------------|--------------------|
      | (including MN-ID option,            | (10)
      |  Message ID option,                 |
      |  MN-HA auth options)                |                    |


             Figure 3: Flow diagram for initial authentication

   4.  MN sends Binding Update (BU) to the HA.  Binding Update is
       authenticated using MN-AAA option.  The authenticator in MN-AAA
       option is calculated using hash of BU and MN-AAA shared key.  It
       uses HMAC_SHA1 algorithm.  The SPI field in MN-AAA is set to 3
       (defined in the draft) BU also includes NAI and timestamp among
       other details.  The hash of BU includes the 'timestamp' option
       and thus provides proof of liveness to prevent replay.
   5.  HA on receiving the BU, extracts the NAI, timestamp,
       authenticator from MN-AAA option and generates hash of BU.  HA
       sends an Access Request to the AAA and puts this information in
       3gpp2 defined VSAs (Vendor Specific Attributes).  The NAI is put
       in username in Access Request.  The other attributes sent are:
       timestamp option, hash of the BU (till SPI field of MN-AAA auth



Patil & Dommety          Expires August 28, 2008               [Page 12]


Internet-Draft        Why authdata option for MIP6         February 2008


       option) and the authentication data from MN-AAA auth option.
   6.  AAA (Radius server which interprets these attributes),
       authenticates the MN based on the hash of BU and authenticator.
       Proceed to step 7
   7.  AAA calculates a session key based on MN-AAA shared secret and
       timestamp and sends this to HA in Access-Accept (in a 3gpp2
       defined VSA).
   8.  (skipping details for timestamp processing at HA) HA creates a
       binding and a security association per Authentication Protocol
       for MIP6 [RFC4285].  The key for this association is retrieved
       from Access Accept and is referred to as session key.  HA
       associates a fixed SPI of 5 with this SA and is associated with
       the binding for the MN
   9.  HA sends a Binding Acknowledgement (BA) to the MN.  BA has the
       MN-HA authentication option, authenticated using the session key.
       This option has the SPI set to 5.
   10.  On receiving a BA, MN calculates the session-key (using same
       method as AAA) and associates it with SPI value of 5.

   MN derives the session key and SA using the timestamp in the BU that
   the MN sent and the MN-AAA shared key.  The MN uses this key to
   authenticate the MN-HA option in Binding Ack. If authentication is
   successful, MN creates a security association with SPI=5.  This key
   is used to authenticate further BU to the HA using the MN-HA auth
   option.  Once the binding lifetime expires and binding is deleted,
   the binding as well as the security association based on the
   Integrity Key is removed at the MN and HA.

   Migration from MobileIPv4 to MobileIPv6 utilizes the same network
   architecture and specially the same AAA infrastructure.  Thus, it is
   natural to have similar signaling in MIP6 as in MIP4, specifically
   the authentication with AAA infrastructure.


7.  Limitations of the Authentication Protocol option

   While the authentication protocol as specified in [RFC4285] provides
   Mobile IPv6 [RFC3775] deployments a certain degree of flexibility it
   does have several disadvantages as well.  Some of them are:

   1.  Route optimization is not supported.  Since route optimization
       signaling messages between the MN and HA are secured by IPsec ESP
       an equivalent solution will have to be specfied or the deployment
       will have to rely on link-layer security mechanisms.
   2.  Bootstrapping of the MN home address is possible when using
       IKEv2.  DHCPv6 or other mechanisms will have to be relied on in
       the absence of IKEv2 with IPsec for MIP6 signaling.




Patil & Dommety          Expires August 28, 2008               [Page 13]


Internet-Draft        Why authdata option for MIP6         February 2008


8.  Security Considerations

   When MIP6 signaling messages use IPsec with ESP encapsulation, they
   are accorded privacy on the links over which the messages traverse.
   When MIP6 signaling messages are secured using the authentication
   protocol, such ciphering capability will have to be enabled by the
   underlying link layers.  It should be noted that the MIP6 signaling
   messages are susceptible to snooping/sniffing when the authentication
   protocol [RFC4285] is used.  Route optimization messages need to be
   secured between the MN and HA and this is not possible with the
   authentication protocol.  Howver route optimization is not supported
   in the current specification of the authentication protocol in
   [RFC4285].


9.  IANA Considerations

   This document has no actions for IANA.


10.  Conclusion

   Mobile IPv6 has been standardized only recently.  Deployment of this
   protocol on a large scale is in the interest of the IETF and the
   working group as well as the many people who have worked on this.  A
   rigid model for deployment will cause the protocol to be limited to
   an academic exercise only.  It is extremely critical that the working
   group consider the needs of the industry and the deployment scenarios
   and address them accordingly.  This document captures the reasoning
   behind the need for the authentication protocol which has been
   published as RFC 4285.  It should be noted that the key length
   proposed in RFC 4285 was 16 octets in length.  This was considered as
   being weak.  The issue is being corrected by increasing the key
   length to 20 octets at a minimum in Authentication Protocol for
   Mobile IPv6 [I-D.ietf-mip6-rfc4285bis].


11.  Acknowledgements

   The authors would like to thank Alpesh Patel, AC Mahendra, Kuntal
   Chowdhury and Vijay Devarapalli for their input and discussions.
   Jari Arkko has reviewed the ID and provided valuable feedback.
   Thomas Narten has provided valuable reviews and made significant
   improvements to the text in this document.  In his role as the IETF
   liaison to 3GPP2, Thomas Narten has ensured that the IETF understands
   the 3GPP2 requirements.





Patil & Dommety          Expires August 28, 2008               [Page 14]


Internet-Draft        Why authdata option for MIP6         February 2008


12.  References

12.1.  Normative References

   [I-D.ietf-mip6-rfc4285bis]
              Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
              Chowdhury, "Authentication Protocol for Mobile IPv6",
              draft-ietf-mip6-rfc4285bis-02 (work in progress),
              December 2007.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement  Levels", RFC 2119, March 1997,
              <ftp://ftp.isi.edu/in-notes/rfc2119>.

   [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
              (DHCP) Service for IPv6", RFC 3736, April 2004.

   [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.

   [RFC4283]  Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
              Chowdhury, "Mobile Node Identifier Option for Mobile IPv6
              (MIPv6)", RFC 4283, November 2005.

12.2.  Informative References

   [3GPP2 X.S0011-D]
              "3GPP2 X.S0011-D "cdma2000 Wireless IP Network Standard",
              March 2006.

   [I-D.ietf-mip6-bootstrapping-integrated-dhc]
              Chowdhury, K. and A. Yegin, "MIP6-bootstrapping for the
              Integrated Scenario",
              draft-ietf-mip6-bootstrapping-integrated-dhc-05 (work in
              progress), July 2007.

   [RFC4285]  Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
              Chowdhury, "Authentication Protocol for Mobile IPv6",
              RFC 4285, January 2006.

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




Patil & Dommety          Expires August 28, 2008               [Page 15]


Internet-Draft        Why authdata option for MIP6         February 2008


   [RFC5026]  Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6
              Bootstrapping in Split Scenario", RFC 5026, October 2007.


Authors' Addresses

   Basavaraj Patil
   Nokia Siemens Networks
   6000 Connection Drive
   Irving, TX  75039
   USA

   Email: basavaraj.patil@nsn.com


   Gopal Dommety
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: gdommety@cisco.com





























Patil & Dommety          Expires August 28, 2008               [Page 16]


Internet-Draft        Why authdata option for MIP6         February 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





Patil & Dommety          Expires August 28, 2008               [Page 17]