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AAA Working Group                                        Pat R. Calhoun
Internet Draft                                                Airespace
draft-ietf-aaa-diameter-mobileip-20.txt                  Tony Johansson
                                                         Bytemobile Inc
                                                     Charles E. Perkins
                                                  Nokia Research Center
                                                    Tom Hiller (editor)
                                                        Peter J. McCann
                                                    Lucent Technologies
                                                            August 2004


                    Diameter Mobile IPv4 Application


Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668.

   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.


Abstract

   This document specifies a Diameter application that allows a Diameter
   server to authenticate, authorize and collect accounting information
   for Mobile IPv4 services rendered to a mobile node.  Combined with
   the Inter-Realm capability of the base protocol, this application
   allows mobile nodes to receive service from foreign service
   providers.  Diameter Accounting messages will be used by the foreign
   and home agents to transfer usage information to the Diameter
   servers.






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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 [KEYWORDS].


Table of Contents

   1. Introduction.....................................................3
     1.1. Entities and Relationships...................................4
     1.2. Mobility Security Associations...............................4
     1.3. Handoff......................................................6
     1.4. Structure of the Document....................................6
   2. Acronyms.........................................................7
   3. Scenarios and Message Flows......................................7
     3.1. Inter-Realm Mobile IPv4......................................7
     3.2. Allocation of Home Agent in Foreign Network.................13
     3.3. Co-located Mobile Node......................................16
     3.4. Key Distribution............................................18
   4. Diameter Protocol Considerations................................20
     4.1. Diameter Session Management.................................20
   5. Command-Code Values.............................................23
     5.1. AA-Mobile-Node-Request......................................23
     5.2. AA-Mobile-Node-Answer.......................................24
     5.3. Home-Agent-MIP-Request......................................25
     5.4. Home-Agent-MIP-Answer.......................................26
   6. Result-Code AVP Values..........................................27
     6.1. Transient Failures..........................................27
     6.2. Permanent Failures..........................................28
   7. Mandatory AVPs..................................................28
     7.1. MIP-Reg-Request AVP.........................................29
     7.2. MIP-Reg-Reply AVP...........................................29
     7.3. MIP-Mobile-Node-Address AVP.................................29
     7.4. MIP-Home-Agent-Address AVP..................................30
     7.5. MIP-Feature-Vector AVP......................................30
     7.6. MIP-MN-AAA-Auth AVP.........................................31
     7.7. MIP-FA-Challenge AVP........................................32
     7.8. MIP-Filter-Rule AVP.........................................32
     7.9. MIP-Candidate-Home-Agent-Host...............................33
     7.10. MIP-Originating-Foreign-AAA AVP............................33
     7.11. MIP-Home-Agent-Host AVP....................................33
   8. Key Distribution................................................33
     8.1. Authorization Lifetime vs. MIP Key Lifetime.................34
     8.2. Nonce vs. Session Key.......................................34
     8.3. Distributing the Mobile-Home Session Key....................35
     8.4. Distributing the Mobile-Foreign Session Key.................36
     8.5. Distributing the Foreign-Home Session Key...................36
   9. Key Distribution AVPs...........................................37
     9.1. MIP-FA-to-MN-MSA AVP........................................38
     9.2. MIP-FA-to-HA-MSA AVP........................................39
     9.3. MIP-HA-to-FA-MSA AVP........................................39
     9.4. MIP-HA-to-MN-MSA AVP........................................39

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     9.5. MIP-MN-to-FA-MSA AVP........................................40
     9.6. MIP-MN-to-HA-MSA AVP........................................40
     9.7. MIP-Session-Key AVP.........................................40
     9.8. MIP-Algorithm-Type AVP......................................41
     9.9. MIP-Replay-Mode AVP.........................................41
     9.10. MIP-FA-to-MN-SPI AVP.......................................41
     9.11. MIP-FA-to-HA-SPI AVP.......................................41
     9.12. MIP-Nonce AVP..............................................41
     9.13. MIP-MSA-Lifetime AVP.......................................42
     9.14. MIP-HA-to-FA-SPI AVP.......................................42
   10. Accounting AVPs................................................42
     10.1. Accounting-Input-Octets AVP................................42
     10.2. Accounting-Output-Octets AVP...............................42
     10.3. Acct-Session-Time AVP......................................42
     10.4. Accounting-Input-Packets AVP...............................43
     10.5. Accounting-Output-Packets AVP..............................43
     10.6. Event-Timestamp AVP........................................43
   11. AVP Occurrence Tables..........................................43
     11.1. Mobile IP Command AVP Table................................44
     11.2. Accounting AVP Table.......................................45
   12. IANA Considerations............................................45
     12.1. Command Codes..............................................45
     12.2. AVP Codes..................................................45
     12.3. Result-Code AVP Values.....................................46
     12.4. MIP-Feature-Vector AVP Values..............................46
     12.5. MIP-Algorithm-Type AVP Values..............................46
     12.6. MIP-Replay-Mode AVP Values.................................46
     12.7. Application Identifier.....................................46
   13. Security Considerations........................................46
   14. References.....................................................48
     14.1. Normative..................................................48
     14.2. Informative................................................49
   15. Acknowledgements...............................................49
   16. Authors' Addresses.............................................50


1. Introduction

   Mobile IPv4 [MOBILEIP] allows a Mobile Node (MN) to change its point
   of attachment to the Internet while maintaining its fixed home
   address.  Packets directed to the home address are intercepted by a
   Home Agent (HA), encapsulated in a tunnel, and forwarded to the MN at
   its current point of attachment.  Optionally, a Foreign Agent (FA)
   may be deployed at this point of attachment, which can serve as the
   tunnel endpoint and may also provide access control for the visited
   network link.  In this role, the FA needs to authenticate each MN
   that may attach to it, whether the MN is from the same or a different
   administrative domain.  The FA needs to verify that the MN is
   authorized to attach and use resources in the foreign domain.  Also,
   the FA must provide information to the home administrative domain
   about the resources used by the MN while it is attached in the
   foreign domain.


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   The Authentication, Authorization, and Accounting requirements for
   Mobile IPv4 are described in detail in other documents [MIPREQ,
   CDMA2000].  This document specifies a Diameter application to meet
   these requirements.  This application is not applicable to the Mobile
   IPv6 protocol.


1.1. Entities and Relationships

   The Diameter Mobile IPv4 Application supports the HA and FA in
   providing Mobile IPv4 service to MNs.  Both the HA and FA act as
   Diameter clients.  The MNs interact with the HA and FA using only
   Mobile IPv4, and therefore do not implement Diameter.

   The FA, when present, is always assumed to exist in the visited
   administrative domain.  The HA may be statically or dynamically
   allocated to the MN in the home administrative domain, or may be
   dynamically allocated to the MN in a visited administrative domain.
   The home domain contains a home AAA server (AAAH) and the visited
   domain contains a foreign AAA server (AAAF).  When the MN is "at
   home" (present on its home network), the AAAH and AAAF may be the
   same.


1.2. Mobility Security Associations

   The base Mobile IPv4 protocol [MOBILEIP] assumes the existence of a
   Mobility Security Association (MSA) between the MN and HA (MN-HA
   MSA).  The MN-HA MSA is used to authenticate, using a keyed hash
   style algorithm, the Mobile IP Registration Request that is sent from
   the MN to the HA.  It is important to authenticate Registration
   Requests because they serve to inform the HA about the MN's current
   Care-of-Address, which is the destination for tunneled packets from
   the home network.  Without authentication, malicious attackers would
   be able to redirect packets to anywhere on the Internet.  The MSA
   comprises an agreement on a Security Parameters Index (SPI, a 32-bit
   number) that will be used to refer to the MSA, an algorithm that will
   be used to compute keyed hashes over messages, and a shared secret
   key.  To enable authentication of a message, the sender appends a
   Mobile IP Authentication Extension that contains the SPI and the
   result of running the keyed hash over the entire previous contents of
   the message.  The recipient checks the Authentication Extension by
   looking up the MSA based on the SPI, re-computing the keyed hash, and
   verifying that the result is equal to the contents of the received
   Authentication Extension.

   The base Mobile IPv4 protocol also supports an optional MSA between
   the MN and FA (MN-FA MSA).  If available, the MN-FA MSA is used by
   the FA to authenticate each Registration Request passing through it
   on the way to the HA.  While not critical to the operation of the
   base protocol, the MN-FA MSA is useful when the FA needs to know the

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   authenticity of a Registration Request, e.g., when it will be
   generating accounting records for a session.  The MN-FA MSA may also
   be useful in future work related to handoff optimization.

   Similarly, Mobile IPv4 supports an optional MSA between the FA and HA
   (FA-HA MSA).  The FA-HA MSA is useful for authenticating messages
   between the FA and HA, such as when the HA wants to inform the FA
   that it has revoked a Mobile IP registration.

   Note that configuration of MSAs that involve FAs is substantially
   more difficult than configuring the one between the MN and HA,
   because the MN and HA are often in the same administrative domain and
   the MN will retain the same HA for long periods of time.  In
   contrast, the MN is likely to encounter many FAs over time and may
   often find itself in foreign administrative domains.

   The base Mobile IPv4 protocol assumes that MNs are identified by
   their static home IP addresses, and assumes that all MSAs are
   statically preconfigured.  The Diameter Mobile IPv4 application,
   together with extensions [MIPNAI, MIPCHAL, MIPKEY, AAANAI] to the
   base Mobile IPv4 protocol, allows an MN to be dynamically assigned a
   home address and/or home agent when it attaches to the Internet.
   This set of specifications also supports the dynamic configuration of
   the MN-HA, MN-FA, and FA-HA MSAs.  The dynamic configuration of these
   relationships is important to support deployments where the MN can
   attach to a visited network without having a pre-established
   relationship with it.

   Initially, the MN is assumed to have a long-term AAA security
   association only with the AAAH.  This security association is indexed
   by the MN's NAI, and, like the MSAs, comprises an agreement on a SPI,
   algorithm, and shared secret key.  The MN enters a visited network
   and requests service from some FA by sending a Mobile IPv4
   Registration Request.  The FA contacts a AAAF in its own
   administrative domain to authenticate and authorize the request for
   service.  The AAAF and AAAH may establish a Diameter session directly
   with each other, such as via a Diameter Redirect, or may pass
   messages via a network of Diameter proxies.  Where the AAAF and AAAH
   route messages to each other through proxies, rather than a direct
   connection, transitive trust is assumed.  MNs can include their
   Network Access Identifier (NAI) in a Mobile IPv4 Registration Request
   [MIPNAI], which serves in place of the home address to identify the
   MN.  The NAI is used to route Diameter messages towards the correct
   AAAH.  This use of the NAI is consistent with the roaming model
   defined by the ROAMOPS Working Group [EVALROAM, RFC2607].

   The AAAH can authenticate the Registration Request with the use of
   the MN-AAA security association [MIPCHAL].  If authentication is
   successful, the AAAH then generates and distributes MSAs to the MN,
   HA, and FA.  For each of the MSA pairs that involve the MN (i.e., MN-
   HA/HA-MN MSAs and MN-FA/FA-MN MSAs), the AAAH generates a nonce and
   then hashes that together with the MN-AAA shared key to derive the
   session key for the MSA pair.  The nonces are sent to the HA which

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   includes them in the Registration Reply, which enables the MN to
   derive the same keys [MIPKEY].  At the same time, the AAAH must
   distribute the MN-HA/HA-MN MSAs and the FA-HA/HA-FA MSAs to the HA
   and must distribute the MN-FA/FA-MN MSAs and the FA-HA/HA-FA MSAs to
   the FA.  These are sent in Diameter AVPs and must be independently
   secured using IPSec or TLS between the AAAH and the FA and between
   the AAAH and the HA.  See Section 8 for more information on key
   derivation and distribution.

   Note that MSAs in Mobile IP are unidirectional in that, e.g., the MN-
   HA MSA (used to protect traffic from the MN to the HA) and the HA-MN
   MSA (used to protect traffic from the HA to the MN) can use different
   SPIs, algorithms, and shared secrets.  This is true of the base
   Mobile IP protocol despite common existing practice during manual
   configuration of MSAs in which all parameters are set to the same
   value in both directions.  This document supports the use of
   different SPIs in each direction; however, it only supports the
   distribution of a single session key for each pair of MSAs between
   two nodes.  The security implications of this fact are discussed in
   Section 13.  This document sometimes names only one of the two
   unidirectional MSAs when referring to the distribution of the single
   shared secret and pair of SPIs for the pair of MSAs between two
   entities.


1.3. Handoff

   In addition to supporting the derivation and transport of the MN-HA,
   MN-FA and FA-HA MSAs, this application also supports MIPv4 handoff.
   When an MN moves from one point of attachment to another, the MN can
   continue the same Mobile IPv4 session using its existing HA and home
   address.

   The MN accomplishes this by sending a Mobile IPv4 Registration
   Request from its new point of attachment.  To enable a single set of
   accounting records to be maintained for the entire session, including
   handoffs, it is necessary to allow the AAAH to bind the new
   registration to the pre-existing session.  To enable the Mobile IPv4
   Registration Request to be routed to the same AAAH, the MN SHOULD
   include the AAAH NAI [AAANAI] in such re-registrations.  Also, to
   assist the AAAH in routing the messages to the MN's existing HA the
   mobile node SHOULD include the HA NAI [AAANAI] in such re-
   registrations.  If the mobile node does not support the Mobile IPv4
   AAA NAI extension [AAANAI], this functionality is not available.


1.4. Structure of the Document

   The remainder of this document is structured as follows.   Section 2
   provides acronym definitions.  Section 3 provides some examples and
   message flows illustrating both the Mobile IPv4 and Diameter messages
   that occur when a mobile node attaches to the Internet.  Section 4

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   defines the relationship of this application to the Diameter Base
   Protocol.  Section 5 defines the new command codes used by this
   application.  Section 6 defines the new result codes used by this
   application.  Section 7 defines the set of mandatory Attribute-Value-
   Pairs (AVPs) used by this application.  Section 8 gives an overview
   of the key distribution capability, and Section 9 defines the key
   distribution AVPs used by this application.  Section 10 defines the
   accounting AVPs, and Section 11 contains a listing of all AVPs and
   their occurrence in Diameter commands.  Finally, Sections 12 and 13
   give IANA and Security considerations, respectively.


2. Acronyms

   AAAH         Authentication, Authorization, and Accounting Home
   AAAF         Authentication, Authorization, and Accounting Foreign
   AMA          AA-Mobile-Node-Answer
   AMR          AA-Mobile-Node-Request
   ASR          Abort-Session-Request
   AVP          Attribute Value Pair
   CoA          Care-of-Address
   FA           Foreign Agent
   FQDN         Fully Qualified Domain Name
   HA           Home Agent
   HAA          Home-Agent-MIP-Answer
   HAR          Home-Agent-MIP-Request
   MN           Mobile Node
   MSA          Mobility Security Association
   NAI          Network Authentication Identity
   RRQ          Registration Request
   SPI          Security Parameters Index
   STR          Session-Termination-Request


3. Scenarios and Message Flows

   This section presents four scenarios illustrating Diameter Mobile
   IPv4 application, and describes the operation of key distribution.

   In this document, the role of the "attendant" [MIPREQ] is performed
   by either the FA (when present in a visited network) or the HA (for
   co-located mobile nodes not registering via an FA), and these terms
   will be used interchangeably in the following scenarios.


3.1. Inter-Realm Mobile IPv4

   When a mobile node requests service by issuing a Registration Request
   to the foreign agent, the foreign agent creates the AA-Mobile-Node-
   Request (AMR) message, which includes the AVPs defined in section 7.
   The Home Address, Home Agent, Mobile Node NAI and other important
   fields are extracted from the registration messages for possible

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   inclusion as Diameter AVPs.  The AMR message is then forwarded to the
   local Diameter server, known as the AAA-Foreign, or AAAF.


                        Visited Realm                   Home Realm
                   +-----------+                     +-----------+
                   |example.net|       AMR/AMA       |example.org|
                   |   AAAF    |<------------------->|    AAAH   |
                +->|  server   |    server-server    |   server  |
                |  +-----------+    communication    +-----------+
                |           ^                           ^
                | AMR/AMA   |    client-server          | HAR/HAA
                |           |    communication          |
                v           v                           v
          +---------+    +---------+                +---------+
          | Foreign |    | Foreign |                |  Home   |
          |  Agent  |    |  Agent  |                |  Agent  |
          +---------+    +---------+                +---------+
                            ^
                            | Mobile IP
                            |
                            v
                         +--------+
                         | Mobile |
                         | Node   | mn@example.org
                         +--------+

                      Figure 1: Inter-Realm Mobility

   Upon receiving the AMR, the AAAF follows the procedures outlined in
   [DIAMBASE] to determine whether the AMR should be processed locally,
   or if it should be forwarded to another Diameter server, known as the
   AAA-Home, or AAAH.  Figure 1 shows an example in which a mobile node
   (mn@example.org) requests service from a foreign provider
   (example.net).  The request received by the AAAF is forwarded to
   example.org's AAAH server.

   Figure 2 shows the message flows involved when the foreign agent
   invokes the AAA infrastructure to request that a mobile node be
   authenticated and authorized.  Note that it is not required that the
   foreign agent invoke AAA services every time a Registration Request
   is received from the mobile, but rather only when the prior
   authorization from the AAAH expires.  The expiration time of the
   authorization is communicated through the Authorization-Lifetime AVP
   in the AA-Mobile-Node-Answer (AMA, see section 5.2) from the AAAH.








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      Mobile Node   Foreign Agent       AAAF          AAAH      Home
                                                                Agent
      -----------   -------------   ------------   ----------   -------
                    Advertisement &
           <--------- Challenge

      Reg-Req&MN-AAA  ---->

                         AMR------------>
                         Session-Id = foo

                                        AMR------------>
                                        Session-Id = foo

                                                      HAR----------->
                                                      Session-Id = bar

                                                        <----------HAA
                                                      Session-Id = bar

                                          <-----------AMA
                                          Session-Id = foo

                           <------------AMA
                           Session-Id = foo

           <-------Reg-Reply

              Figure 2: Mobile IPv4/Diameter Message Exchange


   The foreign agent (as shown in Figure 2) MAY provide a challenge,
   which gives it direct control over the replay protection in the
   Mobile IPv4 registration process, as described in [MIPCHAL].  The
   mobile node includes the Challenge and MN-AAA authentication
   extension to enable authorization by the AAAH.  If the authentication
   data supplied in the MN-AAA extension is invalid, the AAAH returns
   the response (AMA) with the Result-Code AVP set to
   DIAMETER_AUTHENTICATION_REJECTED.

   The above scenario causes the MN-FA and MN-HA keys to be exposed to
   Diameter agents all along the Diameter route.  If this is a concern,
   a more secure approach is to eliminate the AAAF and other Diameter
   agents as in Figure 3:









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                                         Redirect
        FA                AAAF             Agent             AAAH
               AMR
          ---------------->
                                  AMR
                            ---------------->
                              AMA (Redirect)
                            <----------------
            AMA (Redirect)
          <----------------

                         Setup Security Association
          <-------------------------------------------------->

                                  AMR
           -------------------------------------------------->
                             AMA (MN-FA key)
          <---------------------------------------------------

              Figure 3: Use of a Redirect Server with AMR/AMA

   In Figure 3, the FA sets up a TLS [TLS] or IPSec [IPSEC] based
   security association with the AAAH directly and runs the AMR/AMA
   exchange over it.  This provides end-to-end security for secret keys
   that may need to be distributed.

   Figure 4 shows the interaction between the AAAH and HA with the help
   of a redirect agent.  When the AAAH and HA are in the same network,
   it is likely that the AAAH knows the IP address of the HA, so the
   redirect server would therefore not be needed; however, it is shown
   anyway for completeness.  The redirect server will most likely be
   used in the case where the HA is allocated in a foreign network (see
   Section 3.2 for more details of HA allocation in foreign networks).




















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                                  Redirect
               HA                  Agent               AAAH
                                              HAR
                                     <--------------------
                                          HAA (Redirect)
                                     -------------------->
                          Setup Security Association
                <---------------------------------------->
                               HAR (MN-HA key)
                <-----------------------------------------
                                     HAA
                ----------------------------------------->

              Figure 4: Use of a Redirect Server with HAR/HAA

   As in Figure 2, the FA of Figure 3 would still provide the challenge
   and the mobile sends the RRQ, etc.; however, these were eliminated
   from Figure 3 to reduce clutter.  The redirect server eliminates the
   AAAF and any other Diameter agents from seeing the keys as they are
   transported to the FA and HA.  Note that the message flows in Figure
   3 and Figure 4 apply only to the initial authentication and key
   exchange.  Accounting messages would still be sent via Diameter
   agents, not the direct connection, unless network policies dictate
   otherwise.

   A mobile node that supports the AAA NAI extension [AAANAI], which has
   been previously authenticated and authorized, MUST always include the
   assigned home agent in the HA Identity subtype of the AAA NAI
   extension, and the authorizing Home AAA server in the AAAH Identity
   subtype of the AAA NAI extension, when re-authenticating.  So, in the
   event that the AMR generated by the FA is for a session that was
   previously authorized, it MUST include the Destination-Host AVP, with
   the identity of the AAAH found in the AAAH-NAI, and the MIP-Home-
   Agent-Host AVP with the identity and realm of the assigned HA found
   in the HA-NAI.  If on the other hand the mobile node does not support
   the AAA NAI extension, the FA may not have the identity of the AAAH
   and the identity and realm of the assigned HA.  This means that
   without support of the AAA NAI extension, the FA may not be able to
   guarantee that the AMR will be destined to the same AAAH, which
   previously authenticated and authorized the mobile node, since the FA
   may not know the identity of the AAAH.

   If the mobile node was successfully authenticated, the AAAH then
   determines which Home Agent to use for the session.  First, the AAAH
   checks if an HA has been requested by the MN, by checking the MIP-
   Home-Agent-Address AVP and the MIP-Home-Agent-Host AVP.  The
   administrative domain owning the HA may be determined from the realm
   portion of the MIP-Home-Agent-Host AVP, or by checking the Home-
   Agent-In-Foreign-Network flag of the MIP-Feature-Vector AVP and the
   value of the MIP-Originating-Foreign-AAA AVP.  If the requested HA
   belongs to a permitted administrative domain, the AAAH SHOULD use the


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   given HA for the session.  Otherwise, the AAAH returns the response
   (AMA) with the Result-Code AVP set to either
   DIAMETER_ERROR_NO_FOREIGN_HA_SERVICE or
   DIAMETER_ERROR_HA_NOT_AVAILABLE.

   If the MN has not requested any particular HA, then an HA MUST be
   dynamically allocated.  In this case the MIP-Feature-Vector will have
   the Home-Agent-Requested flag set.  If the Home-Address-Allocatable-
   Only-in-Home-Realm flag is not set, and if the Foreign-Home-Agent-
   Available flag is set, then the AAAH SHOULD allow the foreign realm
   to allocate the HA (see Section 3.2) but MAY allocate one itself in
   the home realm if dictated by local policy.  If the Home-Address-
   Allocatable-Only-in-Home-Realm flag is set, then the AAAH MUST
   allocate an HA in the home realm on behalf of the MN.  Allocation of
   the HA can be done in a variety of ways, including using a load-
   balancing algorithm in order to keep the load on all home agents
   equal.  The actual algorithm used and the method of discovering the
   home agents is outside the scope of this specification.

   The AAAH then sends a Home-Agent-MIP-Request (HAR), which contains
   the Mobile IPv4 Registration Request message data encapsulated in the
   MIP-Reg-Request AVP, to the assigned or requested Home Agent.  Refer
   to Figure 4 if the HA does not have a direct path to the HA.  The
   AAAH MAY allocate a home address for the mobile node, while the Home
   Agent MUST support home address allocation.  In the event the AAAH
   handles address allocation, it includes it in a MIP-Mobile-Node-
   Address AVP within the HAR.  The absence of this AVP informs the Home
   Agent to perform the home address allocation.

   Upon receipt of the HAR, the home agent first processes the Diameter
   message.  The home agent processes the MIP-Reg-Request AVP and
   creates the Registration Reply, encapsulating it within the MIP-Reg-
   Reply AVP.  In the creation of the Registration Reply the Home Agent
   MUST include the HA NAI and the AAAH NAI, which will be created from
   the Origin-Host AVP and Origin-Realm AVP of the HAR.  If a home
   address is needed, the home agent MUST also assign one, as well as
   include the address in both the Registration Reply and the MIP-
   Mobile-Node-Address AVP.

   Upon receipt of the HAA, the AAAH creates the AA-Mobile-Node-Answer
   (AMA) message, includes the Acct-Multi-Session-Id that was present in
   the HAA, and the MIP-Home-Agent-Address, MIP-Mobile-Node-Address AVPs
   in the AMA message.  See Figure 3 and Figure 4 for the use of the
   redirect agent for the secure transport of the HAA and AMA messages.

   See Section 4.1 for information on the management of sessions and
   session identifiers by the Diameter Mobile IPv4 entities.







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3.2. Allocation of Home Agent in Foreign Network

   The Diameter Mobile IPv4 application allows a home agent to be
   allocated in a foreign network, as required in [MIPREQ, CDMA2000].
   When a foreign agent detects that the mobile node has a home agent
   address equal to 0.0.0.0 or 255.255.255.255 in the Registration
   Request message, it MUST add a MIP-Feature-Vector AVP with the Home-
   Agent-Requested flag set to one.  If the home agent address is set to
   255.255.255.255, the foreign agent MUST set the Home-Address-
   Allocatable-Only-in-Home-Realm flag equal to one.  If the home agent
   address is set to 0.0.0.0, the foreign agent MUST set the Home-
   Address-Allocatable-Only-in-Home-Realm flag equal to zero.

   When the AAAF receives an AMR message with the Home-Agent-Requested
   flag set to one, and the Home-Address-Allocatable-Only-in-Home-Realm
   flag equal to zero, the AAAF MAY set the Foreign-Home-Agent-Available
   flag in the MIP-Feature-Vector AVP to inform the AAAH that it is
   willing and able to assign a Home Agent for the mobile node.  When
   doing so, the AAAF MUST include the MIP-Candidate-Home-Agent-Host AVP
   and the MIP-Originating-Foreign-AAA-AVP.  The MIP-Candidate-Home-
   Agent-Host AVP contains the identity (i.e., a DiameterIdentity, which
   is an FQDN) of the home agent that would be assigned to the mobile
   node and the MIP-Originating-Foreign-AAA AVP contains the identity of
   the AAAF.  The AAAF now sends the AMR to the AAAH.  However, as
   discussed above, the use of Diameter agents between the FA and AAAH
   in this exchange would expose the MN-FA key.  If this is deemed
   undesirable, a redirect server approach SHOULD be utilized to
   communicate the AMR to the AAAH.  This causes the FA to communicate
   the AMR directly to the AAAH via a security association.

   In the event that the mobile node with AAA NAI extension support
   [AAANAI] has been previously authorized by the AAAH and now needs to
   be re-authenticated, and requests to keep the assigned home agent in
   the foreign network, the mobile node MUST include the HA NAI and the
   AAAH NAI in the registration request to the FA.  Upon receipt, the FA
   will create the AMR including the MIP-Home-Agent-Address AVP, the
   Destination-Host AVP based on the AAAH NAI and include the MIP-Home-
   Agent-Host AVP based on the home agent NAI.  If the AAAF authorizes
   the use of the requested home agent, the AAAF MUST set the Home-
   Agent-In-Foreign-Network bit in the MIP-Feature-Vector AVP.

   In the event that the mobile node needs to be re-authenticated but
   does not support the AAA NAI extension, it sends a registration
   request without the AAA NAI and the HA NAI, even though it has been
   previously authorized by the AAAH and requests to keep the assigned
   home agent in the foreign network.  Upon receipt, the FA will create
   the AMR including the MIP-Home-Agent-Address AVP.  If the AAAF
   authorizes the use of the requested home agent, and if it has
   knowledge that the requested home agent is in its own domain, the
   AAAF MUST set the Home-Agent-In-Foreign-Network bit in the MIP-
   Feature-Vector AVP.



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   When the AAAH receives an AMR message, it first checks the
   authentication data supplied by the mobile node, according to the
   MIP-Reg-Request AVP and MIP-MN-AAA-Auth AVP, and determines whether
   to authorize the mobile node.  If the AMR indicates that the AAAF has
   offered to allocate a Home Agent for the mobile node, i.e. the
   Foreign-Home-Agent-Available is set in the MIP-Feature-Vector AVP, or
   the AMR indicates that the AAAF has offered a previously allocated
   Home Agent for the mobile node, i.e. the Home-Agent-In-Foreign-
   Network is set in the MIP-Feature-Vector AVP, then the AAAH must
   decide whether its local policy would allow the user to have or keep
   a home agent in the foreign network.  Assuming the mobile node is
   permitted to have or keep a home agent in the foreign network, the
   AAAH determines the IP address of the HA based upon the FQDN of the
   HA using DNS, or learns it via an MIP-Home-Agent-Address AVP in a
   redirect response to an HAR (i.e., if the redirect server adds this
   AVP to the HAA), and sends an HAR message to Home Agent by including
   the Destination-Host AVP set to the value found in the AMR's MIP-
   Candidate-Home-Agent-Host AVP or MIP-Home-Agent-Host AVP.  If DNS is
   used to determine the HA IP address, this specification makes the
   assumption that the HA has a public address and it can be resolved by
   DNS.

   Security considerations may require that the HAR be sent directly
   from the AAAH to the HA without the use of intermediary Diameter
   agents.  This requires that a security association between the AAAH
   and HA be established, as in Figure 4.  If no security association
   can be established, the AAAH MUST return an AMA with the Result-Code
   AVP set to DIAMETER_ERROR_END_TO_END_MIP_KEY_ENCRYPTION.

   If Diameter agents are being used (i.e., there is no redirect server,
   etc.) the AAAH sends the HAR to the originating AAAF.  In this HAR
   the Destination-Host AVP is set to the value found in the AMR's MIP-
   Originating-Foreign-AAA AVP, and the MIP-Home-Agent-Host AVP or the
   MIP-Candidate-Home-Agent-Host AVP found in the AMR are copied into
   the HAR.

   Therefore, the AAAH MUST always copy the MIP-Originating-Foreign-AAA
   AVP from the AMR message to the HAR message.  In cases when another
   AAAF receives the HAR, this new AAAF will send the HAR to the HA.















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                              Visited                           Home
                               Realm                           Realm
                             +--------+ ------- AMR -------> +--------+
                             |  AAAF  | <------ HAR -------- |  AAAH  |
                             |        |                      |        |
                        +--->| server | ------- HAA -------> | server |
                        |    +--------+ <------ AMA -------- +--------+
                        |         ^  |
                        |         |  |
                HAR/HAA |     AMR |  | AMA
                        v         |  v
                +---------+       +---------+
                |   Home  |       | Foreign |
                |  Agent  |       |  Agent  |
                +---------+       +---------+
                                          ^
                     +--------+           |
                     | Mobile |<----------+
                     | Node   |  Mobile IP
                     +--------+

              Figure 5: Home Agent allocated in Visited Realm

   Upon receipt of an HAA from the Home Agent in the visited realm, the
   AAAF forwards the HAA to the AAAH in the home realm.  The AMA is then
   constructed, and issued to the AAAF, and finally to the FA.  If the
   Result-Code indicates success, the HAA and AMA MUST include the MIP-
   Home-Agent-Address and the MIP-Mobile-Node-Address AVPs.

   If exposing keys to the Diameter Agents along the way represents an
   unacceptable security risk, then the redirect approach depicted in
   Figure 3 and Figure 4 MUST be used instead.





















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      Mobile Node   Foreign Agent    Home Agent     AAAF       AAAH
      -----------   -------------  ------------- ---------- ----------

         <----Challenge----
       Reg-Req (Response)->
                            ------------AMR------------->
                                                        -----AMR---->
                                                        <----HAR-----
                                         <-----HAR------
                                         ------HAA------>

                                                        -----HAA---->
                                                        <----AMA-----
                          <-------------AMA------------
          <---Reg-Reply----

          Figure 6: MIP/Diameter Exchange for HA is allocated in
                               Visited Realm


   If the mobile node moves to another foreign Network, it MAY either
   request to keep the same Home Agent within the old foreign network,
   or request to get a new one in the new foreign network.  If the AAAH
   is willing to provide the requested service, the AAAH will have to
   provide services for both visited networks, e.g., key refresh.


3.3. Co-located Mobile Node

   In the event that a mobile node registers with the Home Agent as a
   co-located mobile node, there is no foreign agent involved.
   Therefore, when the Home Agent receives the Registration Request, an
   AMR message is sent to the local AAAH server, with the Co-Located-
   Mobile-Node bit set in the MIP-Feature-Vector AVP.  The Home Agent
   also includes the Acct-Multi-Session-Id AVP in the AMR sent to the
   AAAH, as the AAAH may find this a useful piece of session-state or
   log entry information.















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                                             Home
                                            Realm
                                          +--------+
                                          |  AAAH  |
                                          |        |
                                          | server |
                                          +--------+
                                            ^  |
                                            |  |
                                        AMR |  | AMA
                                            |  v
                +--------+               +---------+
                | Mobile | Registration  |  Home   |
                | Node   |-------------->|  Agent  |
                +--------+    Request    +---------+

                     Figure 7: Co-located Mobile Node


   If the MN-HA-Key-Requested bit was set in the AMR message from the
   Home Agent, the home agent and mobile node's session keys would be
   present in the AMA message.

   Figure 8 shows the secure solution using redirect servers.  In Figure
   8, the Proxy AAA represents any AAA server or servers that the HA may
   use.  This applies to the visited or home network.


                                       Local redirect
       HA           Proxy AAA              Agent              AAAH

         AMR
         --------------->
                             AMR (Redirect)
                         -------------------->
                             AMA (Redirect)
                        <---------------------
         AMA (Redirect)
         <----------------
                       Setup Security Association
         <------------------------------------------------------>
                                      AMR
         ------------------------------------------------------->
                              AMA (MN-HA key)
         <-------------------------------------------------------

          Figure 8: Use of Redirect Server for Co-located CoA and
                                  AMR/AMA



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3.4. Key Distribution

   In order to allow the scaling of wireless data access across
   administrative domains, it is necessary to minimize the number of
   pre-existing Mobility Security Associations (MSAs) required.  This
   means that each Foreign Agent should not be required have a pre-
   configured MSA with each Home Agent on the Internet, nor should the
   mobile node be required to have a pre-configured MSA with any
   specific home agent or any specific foreign agent, as defined in
   [MOBILEIP].

   The Diameter Mobile IPv4 application solves this by including key
   distribution functionality, which means that after a Mobile Node is
   authenticated the authorization phase includes the generation of
   session keys and nonces.  Specifically, three session keys and two
   nonces are generated:

     - K1 - the MN-HA Session Key, which will be part of the MSA between
           the Mobile Node and the Home Agent.  An associated nonce is
           generated that the Mobile Node uses to derive the
           (identical) session key.

     - K2 - the MN-FA Key, which will be part of the MSA between the
           Mobile Node and the Foreign Agent.  An associated nonce is
           generated that the Mobile Node uses to derive the
           (identical) session key.

     - K3 - the FA-HA Key, which will be part of the MSA between the
           Foreign Agent and the Home Agent.

   The same session key is used in both directions between two entities,
   e.g., the Mobile Node and the Foreign Agent use the same session key
   for the MN-FA and the FA-MN authentication extensions.  Security
   implications of this fact are examined in Section 13.  However, the
   SPIs may be different for the MN-FA and the FA-MN authentication
   extensions.  The SPI for the MN-FA MSA is used on messages sent from
   the MN to the FA, and the SPI for the FA-MN MSA is used on messages
   sent from the FA to the MN.

   All keys and nonces are generated by the AAAH, even if a Home Agent
   is dynamically allocated in the foreign network.

   Figure 9 depicts the MSAs used for Mobile-IPv4 message integrity
   using the keys created by the DIAMETER server.









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                  +--------+                      +--------+
                  |Foreign |          K3          | Home   |
                  |Agent   |<-------------------->| Agent  |
                  |        |                      |        |
                  +--------+                      +--------+
                          ^                        ^
                          | K2                  K1 |
                          |       +--------+       |
                          |       | Mobile |       |
                          +------>| Node   |<------+
                                  |        |
                                  +--------+

          Figure 9: Mobility Security Associations after Session
                        Key and Nonce Distribution

   The keys destined for the foreign and home agent are propagated to
   the mobility nodes via the Diameter protocol.  If exposing keys to
   the Diameter Agents along the way represents an unacceptable security
   risk, then the keys MUST be protected either by IPSec or TLS security
   associations that exist directly between the HA and AAAH or the FA
   and AAAF, as explained above.

   The keys destined for the mobile node MUST also be propagated via the
   Mobile IPv4 protocol and MUST therefore instead follow the mechanisms
   described in [MIPKEYS].  In [MIPKEYS], the keys distributed to the
   mobile node are instead sent as nonces, and the mobile node will use
   the nonce and the long-term shared secret to create the keys (see
   section 8).

   Once the session keys have been established and propagated, the
   mobility devices can exchange registration information directly as
   defined in [MOBILEIP] without the need of the Diameter
   infrastructure.  However, the session keys have a lifetime, after
   which the Diameter infrastructure MUST be invoked again to acquire
   new session keys and nonces.






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4. Diameter Protocol Considerations

   This section details the relationship of the Diameter Mobile IPv4
   application to the Diameter base protocol.

   This document specifies Diameter Application-ID 2.  Diameter nodes
   conforming to this specification MAY advertise support by including
   the value of two (2) in the Auth-Application-Id or the Acct-
   Application-Id AVP of the Capabilities-Exchange-Request and
   Capabilities-Exchange-Answer command [DIAMBASE].  The value of two
   (2) MUST be used as the Application-Id in all AMR/AMA and HAR/HAA
   commands.  The value of two (2) MUST be used as the Application-Id in
   all ACR/ACA commands, because this application defines new, mandatory
   AVPs for accounting.  The value of zero (0) SHOULD be used as the
   Application-Id in all STR/STA and ASR/ASA commands, because these are
   defined in the Diameter base protocol and no additional mandatory
   AVPs for those commands are defined in this document.

   Given the nature of Mobile IPv4, re-authentication can only be
   initiated by a mobile node, which does not participate in the
   Diameter message exchanges.  Therefore, Diameter server initiated re-
   auth does not apply to this application and RAR/RAA commands MUST NOT
   be sent for Diameter Mobile IPv4 sessions.


4.1. Diameter Session Management

   The AAAH and AAAF MAY maintain session-state or MAY be session-
   stateless.  AAA redirect agents and AAA relay agents MUST NOT
   maintain session-state.  The AAAH, AAAF, proxies and relays agents
   MUST maintain transaction state.

   A mobile node's session is identified via its identity in the User-
   Name AVP, the MIP-Mobile-Node-Address, and the MIP-Home-Agent-Address
   AVPs.  This is necessary in order to allow the session state machine,
   defined in the base protocol [DIAMBASE], to be used unmodified with
   this application.  However, because the MN may interact with more
   than one FA during the life of its session, it is important for the
   Diameter Mobile IPv4 application to distinguish the two pieces of the
   session (some state at the FA, some state at the HA) and to manage
   them independently.  The following sub-sections give further details.


4.1.1. Session Identifiers

   During creation of the AMR, the FA will choose a session identifier.
   During the creation of the HAR, the AAAH MUST use a different session
   identifier than the one used in the AMR/AMA.  If the AAAH is session-
   stateful, it MUST send the same session identifier for all HARs
   initiated on behalf of a given mobile node's session.  Otherwise, if
   the AAAH is session-stateless, it will manufacture a unique session-
   id for every HAR.

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   When the HA is first allocated, it MUST create and include an Acct-
   Multi-Session-Id AVP in the HAA returned to the AAAH.  This
   identifier will be kept constant for the life of the Mobile IPv4
   session, as detailed in the next subsection.

4.1.2. Managing Sessions During Mobile IPv4 Handoffs

   Given the nature of Mobile IPv4, a mobile node MAY receive service
   from many foreign agents during a period of time.  However, the home
   realm should not view these handoffs as different sessions, since
   this could affect billing systems.  Furthermore, foreign agents
   usually do not communicate between each other, which implies AAA
   information cannot be exchanged between these entities.  Therefore,
   it MUST be assumed that a foreign agent is not aware that a
   registration request from a mobile node has been previously
   authorized.

   A handoff registration request from a mobile node will cause the FA
   to send an AMR to its AAAF.  The AMR will include a new session
   identifier, and MAY be sent to a new AAAF (i.e., a AAAF different
   from the one used by the previous FA).  However, assuming the MN
   supports the AAA NAI, the AMR shall be received by the AAAH to which
   the user is currently registered (possibly via the redirect mechanism
   depicted in Figure 3).

   Since the AAAH may be session-stateless, it is necessary for the
   resulting HAR received by the HA to be identified as a continuation
   of an existing session.  If the HA receives an HAR for a mobile node
   with a new session identifier, and the HA can guarantee that this
   request is to extend service for an existing service, then the HA
   MUST be able to modify its internal session state information to
   reflect the new session identifier.

   It is necessary for accounting records to have some commonality
   across handoffs in order for correlation to occur.  Therefore, the
   home agent MUST send the same Acct-Multi-Session-Id AVP value in all
   HAAs for the mobile's session.  That is, the HA generates a unique
   Acct-Multi-Session-Id when receiving an HAR for a new session, and
   returns this same value in every HAA for the session.  This Acct-
   Multi-Session-Id AVP will be returned to the foreign agent by the
   AAAH in the AMA.  Both the foreign and home agents MUST include the
   Acct-Multi-Session-Id in the accounting messages.











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              ACR, Session-Id = foo         ACR, Session-Id = bar
              Acct-Multi-Session-Id = a     Acct-Multi-Session-Id = a
              --------------------->      <--------------------
         +----+      +------+      +------+                    +----+
         | FA |      | AAAF |      | AAAH |                    | HA |
         +----+      +------+      +------+                    +----+
              <---------------------      --------------------->
              ACA, Session-Id = foo       ACA, Session-Id = bar

               Figure 10: Accounting messages w/ Mobile IPv4
                                Application

4.1.3. Diameter Session Termination

   A foreign and home agent following this specification MAY expect
   their respective Diameter servers to maintain session state
   information for each mobile node in their networks.  In order for the
   Diameter Server to release any resources allocated to a specific
   mobile node, the mobility agents MUST send a Session-Termination-
   Request (STR) to the Diameter server that authorized the service.
   The mobility agents MUST issue the Session-Termination-Request (STR)
   if the Authorization Lifetime has expired and no subsequent MIP
   registration request has been received.

   The AAAH SHOULD only deallocate all resources after the STR is
   received from the home agent.  This ensures that a mobile node that
   moves from one foreign agent to another (hand-off) does not cause the
   Home Diameter Server to free all resources for the mobile node.
   Therefore, an STR from a foreign agent would free the session from
   the foreign agent, but not the one towards the home agent (see Figure
   11).

              STR, Session-Id = foo       STR, Session-Id = bar
              --------------------->      <--------------------
         +----+      +------+      +------+                    +----+
         | FA |      | AAAF |      | AAAH |                    | HA |
         +----+      +------+      +------+                    +----+
              <---------------------      --------------------->
              STA, Session-Id = foo       STA, Session-Id = bar

                Figure 11: Session Termination and Session Identifiers


   When deallocating all of the mobile node's resources the home
   Diameter server (and the foreign Diameter server in case of HA
   allocated in foreign network) MUST destroy all session keys that may
   still be valid.

   In the event that the AAAF wishes to terminate a session, its Abort-
   Session-Request (ASR) [DIAMBASE] message SHOULD be sent to the FA.
   Similarly, the AAAH SHOULD send its message to the Home Agent.

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5. Command-Code Values

   This section defines Command-Code [DIAMBASE] values that MUST be
   supported by all Diameter implementations conforming to this
   specification.  The following Command Codes are defined in this
   specification:

         Command-Name             Abbreviation    Code       Section
         -----------------------------------------------------------
         AA-Mobile-Node-Request       AMR         260          5.1
         AA-Mobile-Node-Answer        AMA         260          5.2
         Home-Agent-MIP-Request       HAR         262          5.3
         Home-Agent-MIP-Answer        HAA         262          5.4


5.1. AA-Mobile-Node-Request

   The AA-Mobile-Node-Request (AMR), indicated by the Command-Code field
   set to 260 and the 'R' bit set in the Command Flags field, is sent by
   an attendant, acting as a Diameter client, to a AAAH in order to
   request the authentication and authorization of a mobile node.  The
   foreign agent (or home agent in the case of a co-located Mobile Node)
   uses information found in the Registration Request to construct the
   following AVPs that are to be included as part of the AMR:

             Home Address (MIP-Mobile-Node-Address AVP)
             Home Agent address (MIP-Home-Agent-Address AVP)
             Mobile Node NAI (User-Name AVP [DIAMBASE])
             MN-HA Key Request (MIP-Feature-Vector AVP)
             MN-FA Key Request (MIP-Feature-Vector AVP)
             MN-AAA Authentication Extension (MIP-MN-AAA-Auth AVP)
             Foreign Agent Challenge Extension (MIP-FA-Challenge AVP)
             Home Agent NAI (MIP-Home-Agent-Host AVP)
             Home AAA server NAI (Destination-Host AVP [DIAMBASE])
             Home Agent to Foreign Agent SPI (MIP-HA-to-FA-SPI AVP)

   If the mobile node's home address is zero, the foreign or home agent
   MUST NOT include a MIP-Mobile-Node-Address AVP in the AMR.  If the
   home agent address is zero or all ones, the MIP-Home-Agent-Address
   AVP MUST NOT be present in the AMR.

   If a home agent is used in a visited network, the AAAF MAY set the
   Foreign-Home-Agent-Available flag in the MIP-Feature-Vector AVP in
   the AMR message to indicate that it is willing to assign a Home Agent
   in the visited realm.

   If the mobile node's home address is all ones, the foreign or home
   agent MUST include a MIP-Mobile-Node-Address AVP, set to all ones.



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   If the mobile node includes the home agent NAI and the home AAA
   server NAI [AAANAI], the foreign agent MUST include the MIP-Home-
   Agent-Host AVP and the Destination-Host AVP in the AMR.

      Message Format

         <AA-Mobile-Node-Request> ::= < Diameter Header: 260, REQ, PXY >
                                      < Session-ID >
                                      { Auth-Application-Id }
                                      { User-Name }
                                      { Destination-Realm }
                                      { Origin-Host }
                                      { Origin-Realm }
                                      { MIP-Reg-Request }
                                      { MIP-MN-AAA-Auth }
                                      [ Acct-Multi-Session-Id ]
                                      [ Destination-Host ]
                                      [ Origin-State-Id ]
                                      [ MIP-Mobile-Node-Address ]
                                      [ MIP-Home-Agent-Address ]
                                      [ MIP-Feature-Vector ]
                                      [ MIP-Originating-Foreign-AAA ]
                                      [ Authorization-Lifetime ]
                                      [ Auth-Session-State ]
                                      [ MIP-FA-Challenge ]
                                      [ MIP-Candidate-Home-Agent-Host ]
                                      [ MIP-Home-Agent-Host ]
                                      [ MIP-HA-to-FA-SPI ]
                                    * [ Proxy-Info ]
                                    * [ Route-Record ]
                                    * [ AVP ]


5.2. AA-Mobile-Node-Answer

   The AA-Mobile-Node-Answer (AMA), indicated by the Command-Code field
   set to 260 and the 'R' bit cleared in the Command Flags field, is
   sent by the AAAH in response to the AA-Mobile-Node-Request message.
   The User-Name MAY be included in the AMA if present in the AMR.  The
   Result-Code AVP MAY contain one of the values defined in section 6,
   in addition to the values defined in [DIAMBASE].

   An AMA message with the Result-Code AVP set to DIAMETER_SUCCESS MUST
   include the MIP-Home-Agent-Address AVP, MUST include the MIP-Mobile-
   Node-Address AVP, and includes the MIP-Reg-Reply AVP if and only if
   the Co-Located-Mobile-Node bit was not set in the MIP-Feature-Vector
   AVP.  The MIP-Home-Agent-Address AVP contains the Home Agent assigned
   to the mobile node, while the MIP-Mobile-Node-Address AVP contains
   the home address that was assigned.  The AMA message MUST contain the
   MIP-FA-to-HA-MSA, MIP-FA-to-MN-MSA if they were requested in the AMR,
   and they were present in the HAR.  The MIP-MN-to-HA-MSA and MIP-HA-
   to-MN-MSA AVPs MUST be present if the session keys were requested in


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   the AMR, and the Co-Located-Mobile-Node bit was set in the MIP-
   Feature-Vector AVP.


      Message Format

         <AA-Mobile-Node-Answer> ::= < Diameter Header: 260, PXY >
                                     < Session-Id >
                                     { Auth-Application-Id }
                                     { Result-Code }
                                     { Origin-Host }
                                     { Origin-Realm }
                                     [ Acct-Multi-Session-Id ]
                                     [ User-Name ]
                                     [ Authorization-Lifetime ]
                                     [ Auth-Session-State ]
                                     [ Error-Message ]
                                     [ Error-Reporting-Host ]
                                     [ Re-Auth-Request-Type ]
                                     [ MIP-Feature-Vector ]
                                     [ MIP-Reg-Reply ]
                                     [ MIP-MN-to-FA-MSA ]
                                     [ MIP-MN-to-HA-MSA ]
                                     [ MIP-FA-to-MN-MSA ]
                                     [ MIP-FA-to-HA-MSA ]
                                     [ MIP-HA-to-MN-MSA ]
                                     [ MIP-MSA-Lifetime ]
                                     [ MIP-Home-Agent-Address ]
                                     [ MIP-Mobile-Node-Address ]
                                   * [ MIP-Filter-Rule ]
                                     [ Origin-State-Id ]
                                   * [ Proxy-Info ]
                                   * [ AVP ]


5.3. Home-Agent-MIP-Request

   The AAA sends the Home-Agent-MIP-Request (HAR), indicated by the
   Command-Code field set to 262 and the 'R' bit set in the Command
   Flags field, to the Home Agent.  If the Home Agent is to be assigned
   in a foreign network, the HAR is issued by the AAAH and forwarded by
   the AAAF to the HA if no redirect servers are involved.  If redirect
   servers are involved the HAR is sent directly to the HA via a
   security association.  If the HAR message does not include a MIP-
   Mobile-Node-Address AVP, and the Registration Request has 0.0.0.0 for
   the home address, and the HAR is successfully processed, the Home
   Agent MUST allocate the mobile nodes address.  If on the other hand
   the home agent's local AAA server allocates the mobile node's home
   address, the local AAA server MUST include the assigned address in an
   MIP-Mobile-Node-Address AVP.




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   When session keys are requested for use by the mobile node, the AAAH
   MUST create them and include them in the HAR message.  When a FA-HA
   session key is requested, it will be created and distributed by the
   AAAH server.

      Message Format

         <Home-Agent-MIP-Request> ::= < Diameter Header: 262, REQ, PXY >
                                      < Session-Id >
                                      { Auth-Application-Id }
                                      { Authorization-Lifetime }
                                      { Auth-Session-State }
                                      { MIP-Reg-Request }
                                      { Origin-Host }
                                      { Origin-Realm }
                                      { User-Name }
                                      { Destination-Realm }
                                      { MIP-Feature-Vector }
                                      [ Destination-Host ]
                                      [ MIP-MN-to-HA-MSA ]
                                      [ MIP-MN-to-FA-MSA ]
                                      [ MIP-HA-to-MN-MSA ]
                                      [ MIP-HA-to-FA-MSA ]
                                      [ MIP-MSA-Lifetime ]
                                      [ MIP-Originating-Foreign-AAA ]
                                      [ MIP-Mobile-Node-Address ]
                                      [ MIP-Home-Agent-Address ]
                                    * [ MIP-Filter-Rule ]
                                      [ Origin-State-Id ]
                                    * [ Proxy-Info ]
                                    * [ Route-Record ]
                                    * [ AVP ]


5.4. Home-Agent-MIP-Answer

   The Home Agent sends the Home-Agent-MIP-Answer (HAA), indicated by
   the Command-Code field set to 262 and the 'R' bit cleared in the
   Command Flags field, to its local AAA server in response to a Home-
   Agent-MIP-Request.  The User-Name MAY be included in the HAA if
   present in the HAR.  If the home agent allocated a home address for
   the mobile node, the address MUST be included in the MIP-Mobile-Node-
   Address AVP.  The Result-Code AVP MAY contain one of the values
   defined in section 6 instead of the values defined in [DIAMBASE].










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      Message Format

         <Home-Agent-MIP-Answer> ::= < Diameter Header: 262, PXY >
                                     < Session-Id >
                                     { Auth-Application-Id }
                                     { Result-Code }
                                     { Origin-Host }
                                     { Origin-Realm }
                                     [ Acct-Multi-Session-Id ]
                                     [ User-Name ]
                                     [ Error-Reporting-Host ]
                                     [ Error-Message ]
                                     [ MIP-Reg-Reply ]
                                     [ MIP-Home-Agent-Address ]
                                     [ MIP-Mobile-Node-Address ]
                                     [ MIP-FA-to-HA-SPI ]
                                     [ MIP-FA-to-MN-SPI ]
                                     [ Origin-State-Id ]
                                   * [ Proxy-Info ]
                                   * [ AVP ]


6. Result-Code AVP Values

   This section defines new Result-Code [DIAMBASE] values that MUST be
   supported by all Diameter implementations that conform to this
   specification.

6.1. Transient Failures

   Errors that fall within the transient failures category are used to
   inform a peer that the request could not be satisfied at the time it
   was received, but may be able to satisfy the request in the future.

         DIAMETER_ERROR_MIP_REPLY_FAILURE    4005
            This error code is used by the home agent when processing of
            the Registration Request has failed.

         DIAMETER_ERROR_HA_NOT_AVAILABLE     4006
            This error code is used to inform the foreign agent that the
            requested Home Agent cannot be assigned to the mobile node
            at this time.  The foreign agent MUST return a Mobile IPv4
            Registration Reply to the mobile node with an appropriate
            error code.

         DIAMETER_ERROR_BAD_KEY              4007
            This error code is used by the home agent to indicate to the
            local Diameter server that the key generated is invalid.





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         DIAMETER_ERROR_MIP_FILTER_NOT_SUPPORTED   4008
            This error code is used by a mobility agent to indicate to
            the home Diameter server that the requested packet filter
            Rules cannot be supported.


6.2. Permanent Failures

   Errors that fall within the permanent failures category are used to
   inform the peer that the request failed, and SHOULD NOT be attempted
   again.

         DIAMETER_ERROR_NO_FOREIGN_HA_SERVICE 5024
            This error is used by the AAAF to inform the AAAH that
            allocation of a home agent in the foreign domain is not
            permitted at this time.

         DIAMETER_ERROR_END_TO_END_MIP_KEY_ENCRYPTION 5025

            This error is used by the AAAF / AAAH to inform the peer
            that the requested Mobile IPv4 session keys could not be
            delivered via a security association.



7. Mandatory AVPs

   The following table describes the Diameter AVPs defined in the Mobile
   IPv4 application, their AVP Code values, types, possible flag values
   and whether the AVP MAY be encrypted.

   Due to space constraints, the short form IPFiltrRule is used to
   represent IPFilterRule and DiamIdent is used to represent
   DiameterIdentity.



















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                                            +--------------------------+
                                            |    AVP Flag rules        |
                                            |----+-----+----+-----|----+
                   AVP  Section             |    |     |SHLD| MUST|MAY |
   Attribute Name  Code Defined  Value Type |MUST| MAY | NOT|  NOT|Encr|
   -----------------------------------------|----+-----+----+-----|----|
   MIP-Reg-Request  320  7.1     OctetString| M  |  P  |    |  V  | Y  |
   MIP-Reg-Reply    321  7.2     OctetString| M  |  P  |    |  V  | Y  |
   MIP-MN-AAA-Auth  322  7.6     Grouped    | M  |  P  |    |  V  | Y  |
   MIP-Mobile-Node- 333  7.3     Address    | M  |  P  |    |  V  | Y  |
     Address
   MIP-Home-Agent-  334  7.4     Address    | M  |  P  |    |  V  | Y  |
     Address
   MIP-Candidate-   336  7.9     DiamIdent  | M  |  P  |    |  V  | N  |
     Home-Agent-Host
   MIP-Feature-     337  7.5     Unsigned32 | M  |  P  |    |  V  | Y  |
     Vector
   MIP-Auth-Input-  338  7.6.2   Unsigned32 | M  |  P  |    |  V  | Y  |
     Data-Length
   MIP-             339  7.6.3   Unsigned32 | M  |  P  |    |  V  | Y  |
     Authenticator-Length
   MIP-             340  7.6.4   Unsigned32 | M  |  P  |    |  V  | Y  |
     Authenticator-Offset
   MIP-MN-AAA-SPI   341  7.6.1   Unsigned32 | M  |  P  |    |  V  | Y  |
   MIP-Filter-Rule  342  7.8     IPFiltrRule| M  |  P  |    |  V  | Y  |
   MIP-FA-Challenge 344  7.7     OctetString| M  |  P  |    |  V  | Y  |

   MIP-Originating- 347  7.10    Grouped    | M  |  P  |    |  V  | Y  |
   Foreign-AAA
   MIP-Home-Agent-  348  7.9     DiamIdent  | M  |  P  |    |  V  | N  |
     Host


7.1. MIP-Reg-Request AVP

   The MIP-Reg-Request AVP (AVP Code 320) is of type OctetString and
   contains the Mobile IPv4 Registration Request [MOBILEIP] sent by the
   mobile node to the foreign agent.


7.2. MIP-Reg-Reply AVP

   The MIP-Reg-Reply AVP (AVP Code 321) is of type OctetString and
   contains the Mobile IPv4 Registration Reply [MOBILEIP] sent by the
   home agent to the foreign agent.


7.3. MIP-Mobile-Node-Address AVP

   The MIP-Mobile-Node-Address AVP (AVP Code 333) is of type Address and
   contains the mobile node's home IP address.


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7.4. MIP-Home-Agent-Address AVP

   The MIP-Home-Agent-Address AVP (AVP Code 334) is of type Address and
   contains the mobile node's home agent IP address.


7.5. MIP-Feature-Vector AVP

   The MIP-Feature-Vector AVP (AVP Code 337) is of type Unsigned32 and
   is added with flag values set by the foreign agent or by the AAAF
   owned by the same administrative domain as the foreign agent.  The
   foreign agent SHOULD include MIP-Feature-Vector AVP within the AMR
   message it sends to the AAAF.

      Flag values currently defined include:
            1   Mobile-Node-Home-Address-Requested
            2   Home-Address-Allocatable-Only-in-Home-Realm
            4   Home-Agent-Requested
            8   Foreign-Home-Agent-Available
            16  MN-HA-Key-Request
            32  MN-FA-Key-Request
            64  FA-HA-Key-Request
            128 Home-Agent-In-Foreign-Network
            256 Co-Located-Mobile-Node

   The flags are set according to the following rules.

   If the mobile node includes a valid home address (i.e., not equal to
   0.0.0.0 or 255.255.255.255) in its Registration Request, the foreign
   agent sets the Mobile-Node-Home-Address-Requested flag in the MIP-
   Feature-Vector AVP to zero.

   If the mobile node sets the home address field equal to 0.0.0.0 in
   its Registration Request, the foreign agent sets the Mobile-Node-
   Home-Address-Requested flag to one.

   If the mobile node sets the home agent field equal to 255.255.255.255
   in its Registration Request, the foreign agent sets both the Home-
   Agent-Requested flag and the Home-Address-Allocatable-Only-in-Home-
   Realm flag to one in the MIP-Feature-Vector AVP.

   If the mobile node sets the home agent field equal to 0.0.0.0 in its
   Registration Request, the foreign agent sets the Home-Agent-Requested
   flag to one, and zeroes the Home-Address-Allocatable-Only-in-Home-
   Realm flag in the MIP-Feature-Vector AVP.

   Whenever the foreign agent sets either the Mobile-Node-Home-Address-
   Requested flag or the Home-Agent-Requested flag to one, it MUST set
   the MN-HA-Key-Request flag to one.  The MN-HA-Key-Request flag is
   also set to one if the mobile node includes a "Generalized MN-HA Key
   Nonce Generation Request" [MIPKEYS] extension, with the subtype set
   to AAA.

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   If the mobile node includes a "Generalized MN-FA Key Nonce Generation
   Request" [MIPKEYS] extension with the AAA subtype in its Registration
   Request, the foreign agent sets the MN-FA-Key-Request flag to one in
   the MIP-Feature-Vector AVP.

   If the mobile node requests a home agent in the foreign network
   either by setting the home address field to all ones, or by
   specifying a home agent in the foreign network, and the AAAF
   authorizes the request, the AAAF MUST set the Home-Agent-In-Foreign-
   Network bit to one.

   If the Home Agent receives a Registration Request from the mobile
   node indicating that the MN is acting as a co-located mobile node,
   the home agent sets the Co-Located-Mobile-Node bit to one.

   If the foreign agent's local policy allows it to receive AAA session
   keys, and it does not have any existing FA-HA key with the home
   agent, the foreign agent MAY set the FA-HA-Key-Request flag

   The foreign agent MUST NOT set the Foreign-Home-Agent-Available and
   Home-Agent-In-Foreign-Network flag both to one.

   When the AAAF receives the AMR message, it MUST first verify that the
   sender was an authorized foreign agent.  The AAAF then takes any
   actions indicated by the settings of the MIP-Feature-Vector AVP
   flags.  The AAAF then MAY set additional flags.  Only the AAAF may
   set the Foreign-Home-Agent-Available and Home-Agent-In-Foreign-
   Network flags to one.  This is done according to local administrative
   policy.  When the AAAF has finished setting additional flags
   according to its local policy, then the AAAF transmits the AMR with
   the possibly modified MIP-Feature-Vector AVP to the AAAH.


7.6. MIP-MN-AAA-Auth AVP

   The MN-AAA-Auth AVP (AVP Code 322) is of type Grouped and contains
   some ancillary data to simplify processing of the authentication data
   in the Mobile IPv4 Registration Request [MOBILEIP, MIPCHAL] by the
   target AAA server.  Its value has the following ABNF grammar:

         MIP-MN-AAA-Auth ::= < AVP Header: 322 >
                             { MIP-MN-AAA-SPI }
                             { MIP-Auth-Input-Data-Length }
                             { MIP-Authenticator-Length }
                             { MIP-Authenticator-Offset }
                           * [ AVP ]







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7.6.1. MIP-MN-AAA-SPI AVP

   The MIP-MN-AAA-SPI AVP (AVP Code 341) is of type Unsigned32 and
   indicates the MSA by which the targeted AAA server (AAAH) should
   attempt to validate the Authenticator computed by the mobile node
   over the Registration Request data.


7.6.2. MIP-Auth-Input-Data-Length AVP

   The MIP-Auth-Input-Data-Length AVP (AVP Code 338) is of type
   Unsigned32 and contains the length, in bytes, of the Registration
   Request data (data portion of MIP-Reg-Request AVP)that should be used
   as input to the algorithm, as indicated by the MN-AAA-SPI AVP, used
   to determine whether the Authenticator Data supplied by the mobile
   node is valid.


7.6.3. MIP-Authenticator-Length AVP

   The MIP-Authenticator-Length AVP (AVP Code 339) is of type Unsigned32
   and contains the length of the authenticator to be validated by the
   targeted AAA server (i.e., AAAH).


7.6.4. MIP-Authenticator-Offset AVP

   The MIP-Authenticator-Offset AVP (AVP Code 340) is of type Unsigned32
   and contains the offset into the Registration Request Data, of the
   authenticator to be validated by the targeted AAA server (i.e.,
   AAAH).


7.7. MIP-FA-Challenge AVP

   The MIP-FA-Challenge AVP (AVP Code 344) is of type OctetString and
   contains the challenge advertised by the foreign agent to the mobile
   node.  This AVP MUST be present in the AMR if the mobile node used
   the RADIUS-style MN-AAA computation algorithm.


7.8. MIP-Filter-Rule AVP

   The MIP-Filter-Rule AVP (AVP Code 342) is of type IPFilterRule, and
   provides filter rules that need to be configured on the foreign or
   home agent for the user.  The packet filtering rules are set by the
   AAAH by adding one or more MIP-Filter-Rule AVPs in the HAR if
   destined for the home agent and/or in the AMA if destined for the
   foreign agent.




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7.9. MIP-Candidate-Home-Agent-Host

   The MIP-Candidate-Home-Agent-Host AVP (AVP Code 336) is of type
   DiameterIdentity and contains the identity of a home agent in the
   foreign network that the AAAF proposes be dynamically assigned to the
   mobile node.


7.10. MIP-Originating-Foreign-AAA AVP

   The MIP-Originating-Foreign-AAA AVP (AVP Code 347) if of type
   Grouped, and contains the identity of the AAAF, which issues the AMR
   to the AAAH.  The MIP- Originating-Foreign-AAA AVP MUST only be used
   in cases when the home agent is or may be allocated in a foreign
   domain.  If present in the AMR, the AAAH MUST copy the MIP-
   Originating-Foreign-AAA AVP into the HAR.

         MIP-Originating-Foreign-AAA ::= < AVP Header: 347 >
                                          { Origin-Realm }
                                          { Origin-Host }
                                        * [ AVP ]


7.11. MIP-Home-Agent-Host AVP

      The MIP-Home-Agent-Host AVP (AVP Code 348) is of type Grouped, and
      contains the identity of the assigned Home Agent.  If present in
      the AMR, the AAAH MUST copy the MIP-Home-Agent-Host AVP into the
      HAR.


         MIP-Home-Agent-Host ::= < AVP Header: 348 >
                                  { Destination-Realm }
                                  { Destination-Host }
                                * [ AVP ]


8. Key Distribution

   The mobile node and mobility agents use session keys (i.e., the MN-
   FA, FA-HA and MN-HA session keys) to compute authentication
   extensions applied to MIP registration messages, as defined in
   [MOBILEIP].  If session keys are requested the AAAH MUST return the
   keys and nonces after the mobile node is successfully authenticated
   and authorized.

   The SPI values are used as key identifiers, each session key has its
   own SPI value; nodes that share a key can have different SPIs.  The
   mobile node allocates SPIs for use in the mobility security
   associations of the MN-FA and MN-HA authentication extensions, via
   the Mobile IPv4 AAA Key Request extensions [MIPKEYS].  The home agent
   allocates SPIs for the MN-HA and FA-HA mobility security association.

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   The foreign agent chooses a SPI for the MN-FA and HA-FA mobility
   security association.  In all cases, the entity that receives an
   authentication extension (i.e., verifies the authentication
   extension) is providing the entity that sends the authentication
   extension (i.e., computes the authentication extension) the value of
   the SPI to use for that key and extension.  Note that the keys in
   this regime are symmetric in the sense they are used in both
   directions, even though the SPIs do not have to be symmetric.

   Once the session keys and nonces have been distributed, subsequent
   Mobile IPv4 registrations need not invoke the AAA infrastructure
   until the keys expire.  These registrations MUST include the MN-HA
   authentication extension.  In addition, subsequent registrations MUST
   also include MN-FA authentication extension if the MN-FA session key
   was generated and distributed by AAA; similarly for subsequent use of
   the FA-HA authentication extensions.


8.1. Authorization Lifetime vs. MIP Key Lifetime

   The Diameter Mobile IPv4 application makes use of two timers - the
   Authorization-Lifetime AVP [DIAMBASE] and the MIP-MSA-Lifetime AVP.

   The Authorization-Lifetime contains the number of seconds before the
   mobile node must issue a subsequent MIP registration request.  The
   content of the Authorization-Lifetime AVP corresponds to the Lifetime
   field in the MIP header [MOBILEIP].

   The MIP-MSA-Lifetime AVP contains the number of seconds before
   session keys destined for the mobility agents and the mobile node
   expire.  A value of zero indicates infinity (no timeout).  If not
   zero, the value of the MIP-MSA-Lifetime AVP MUST is at least equal to
   the value in the Authorization Lifetime AVP.


8.2. Nonce vs. Session Key

   As described in section 3.4, the AAAH generates session keys and
   transmits them to the home agent and foreign agent.  The AAAH
   generates nonces that correspond to the same keys and transmits them
   to the mobile node.  Where it is necessary to protect the session
   keys and SPIs from un-trusted Diameter agents, end-to-end security
   mechanisms such as TLS or IPSec are required to eliminate the all
   Diameter Agents between the FA or HA and the AAAH, as outlined above.

   In [MIPKEYS] the mobility security associations are established via
   nonces transmitted to the mobile node via Mobile IPv4.  To provide
   the nonces, the AAAH must generate a random [RANDOM] value of at
   least 128 bits [MIPKEYS].  The mobile node then uses the nonce to
   derive the MN-HA and MN-FA session keys.



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   More details of the MN-HA and the MN-FA session key creation
   procedure are found in [MIPKEYS].

   It is important that the hashing algorithm used by the mobile node to
   construct the session key is the same as the one used by the AAAH in
   the session key generation procedure.  The AAAH therefore indicates
   the algorithm used along with the nonce.

   The FA-HA and HA-FA session key is shared between the FA and HA.  The
   AAAH generates a random [RANDOM] value of at least 128 bits for use
   as this session key.

   See sections 9 for details about the format of the AVPs used to
   transport the session keys.


8.3. Distributing the Mobile-Home Session Key

   If the mobile node does not have a MN-HA session key, then the AAAH
   is likely to be the only entity trusted that is available to the
   mobile node.  Thus, the AAAH has to generate the MN-HA session key.

   The distribution of the HA-MN (session) key to the HA has been
   specified above.  The HA and AAAH establish a security association
   (IPSec or TLS) and transport the key over that security association.
   If no security association exists between the AAAH and the home
   agent, and a security association cannot be established the AAAH MUST
   return a Result-Code AVP with
   DIAMETER_ERROR_END_TO_END_MIP_KEY_ENCRYPTION.

   The AAAH also has to arrange for the key to be delivered to the
   mobile node.  Unfortunately, the AAAH only knows about Diameter
   messages and AVPs, and the mobile node only knows about Mobile IPv4
   messages and extensions [MOBILEIP].  For this purpose, AAAH includes
   the MN-HA MIP-nonce AVP into a MIP-MN-to-HA-MSA AVP, which is added
   to the HAR for FA COA style Mobile IPv4 or AMA for collocated COA
   style Mobile IPv4 messages, and delivered either to a local home
   agent or a home agent in the visited network.  Recall the mobile node
   will use the nonce to create the MN-HA session key using the MN-AAA
   key it shares with the AAAH [MIPKEYS].  The AAAH has to rely on the
   home agent (that also understands Diameter) to transfer the nonce
   into a Mobile IPv4 "Generalized MN-HA Key Generation Nonce Reply"
   extension [MIPKEYS] in the Registration Reply message.  The HA
   includes the SPIs proposed by the mobile node and the home agent in
   the "Generalized MN-HA Key Generation Nonce Request" extension.  The
   home agent can format the Reply message and extensions correctly for
   eventual delivery to the mobile node.  The resulting Registration
   Reply is added to the HAA's MIP-Reg-Reply AVP.

   The AAAH parses the HAA message, transforms it into an AMA message
   containing an MIP-Reg-Reply AVP, and sends the AMA message to the
   foreign agent.  The foreign agent then uses that AVP to recreate a


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   Registration Reply message containing the "Generalized MN-HA Key
   Generation Nonce Reply" extension for delivery to the mobile node.

   In summary, the AAAH generates the MN-HA nonce, which is added to the
   MIP-MN-to-HA-MSA AVP, and a session key, which is added to the MIP-
   HA-to-MN-MSA AVP.  These AVPs are delivered to the home agent in HAR
   or AMA messages.  The home agent retains the session key for its own
   use, and copies the nonce from the MIP-MN-to-HA-MSA AVP into a
   "Generalized MN-HA Key Generation Nonce Reply"  extension, which is
   appended to the Mobile IPv4 Registration Reply message.  This
   Registration Reply message MUST also include the HA-MN authentication
   extension, which is created using the newly allocated HA-MN session
   key.  The home agent then includes the Registration Reply message and
   extensions into a MIP-Reg-Reply AVP as part of the HAA message to be
   sent back to the AAA server.

   The key derived by the MN from the MN-HA session nonce is identical
   to the HA-MN session key provided to the HA.


8.4. Distributing the Mobile-Foreign Session Key

   The MN-FA session nonce is also generated by AAAH (upon request) and
   is added to the MIP-MN-to-FA-MSA AVP, which is added to the HAR, and
   copied by the home agent into a "Generalized MN-FA Key Generation
   Nonce Reply"  extension [MIPKEYS] to the Mobile IPv4 Registration
   Reply message.  The HA also includes the SPIs proposed by the mobile
   node and foreign agent in the "MN-FA Key Generation Nonce Request"
   extension.  The AAAH includes the FA-MN session key in the MIP-FA-to-
   MN-MSA AVP in the AMA, to be used by the foreign agent in the
   computation of the FA-MN authentication extension.

   The key derived by the MN from the MN-FA session nonce is identical
   to the FA-MN session key provided to the FA.


8.5. Distributing the Foreign-Home Session Key

   If the foreign agent requests an FA-HA session key, it also includes
   a MIP-HA-to-FA-SPI AVP in the AMR to convey the SPI to be used by the
   home agent for this purpose.  The AAAH generates the  FA-HA session
   key, which is identical to the HA-FA session key, and distributes
   that to both the HA and the FA over respective security associations
   to each using the MIP-HA-to-FA-MSA and MIP-FA-to-HA-MSA AVPs.  The HA
   conveys the SPI the FA MUST use in the HAA; this is similar to the
   way that the FA conveys the SPI the HA MUST use in the AMR.  The AAAH
   later includes these SPIs in the MIP-FA-HA-MSA and MIP-HA-FA-MSA
   AVPs, respectively, along with the session key.

   Refer to Figure 2, Figure 3, Figure 4 and Figure 6 for the messages
   involved.


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   Note that if multiple MNs are registered on the same pair of FA and
   HA, then multiple mobility security associations would be
   distributed.  However, only one is required to protect the Mobile IP
   control traffic between FA and HA.  This creates an unacceptable
   level of state (i.e., to store the two SPIs and shared key for each
   FA-HA mobility security association).  To improve scalablity the FA
   and HA may discard FA-HA mobility security associations prior to the
   time they actually expire.  However, if a proper discard policy is
   not chosen, this could cause Mobile IP messages in transit or waiting
   in queues for transmission to fail authentication.

   The FA MUST always use the FA-HA security association with the latest
   expiry time when computing authentication extensions on outgoing
   messages.  The FA MAY discard HA-FA mobility security associations 10
   seconds after a new HA-FA mobility security association arrives with
   a later expiry time.

   The HA SHOULD use the HA-FA mobility security association that has
   the latest expiry time when computing authentication extensions in
   outgoing messages.  However, when the HA receives a new HA-FA
   mobility security association with a later expiry time, the HA SHOULD
   wait 4 seconds for the AMA to propagate to the FA before using the
   new association.  Note that the HA always uses the mobility security
   association from the HAR when constructing the Mobile IP Registration
   Reply in the corresponding HAA.  The HA may discard an FA-HA mobility
   security association once it receives a message authenticated by a
   FA-HA mobility security association with a later expiry time.


9. Key Distribution AVPs

   The Mobile-IP protocol defines a set of mobility security
   associations shared between the mobile node, foreign agent and home
   agent.  These three mobility security associations (MN-HA, MN-FA, and
   FA-HA) are dynamically created by the AAAH, and has previously been
   described in section 3.4 and section 8.  AAA servers supporting the
   Diameter Mobile IP Application MUST implement the key distribution
   AVPs defined in this document.

   The names of the key distribution AVPs indicate the two entities
   sharing the mobility security association.  The first named entity in
   the AVP name will use the mobility security association to create
   authentication extensions using the given SPI and key.  The second
   named entity in the AVP name will use the mobility security
   association to verify the authentication extensions of received
   Mobile IP messages.

   So for instance, the MIP-MN-to-HA-MSA AVP contains the MN-HA nonce,
   which the mobile node will use to derive the MN-HA Key, and the MIP-
   HA-to-MN-MSA AVP contains the MN-HA key for the home agent.  Note
   that mobility security associations are unidirectional, however, this
   application delivers only one key that is shared between both


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   unidirectional security associations that exist between two peers.
   The security considerations of using the same key in each direction
   are given in Section 13.  The SPIs are however unique to each
   unidirectional security association and are chosen by the peer that
   will receive the Mobile IP messages authenticated with that security
   association.

   The following table describes the Diameter AVPs defined in the Mobile
   IP application, their AVP Code values, types, and possible flag
   values.



                                            +--------------------------+
                                            |       AVP Flag Rules     |
                                            |----+-----+----+-----|----+
                   AVP  Section             |    |     |SHLD| MUST|MAY |
   Attribute Name  Code Defined  Value Type |MUST| MAY | NOT|  NOT|Encr|
   -----------------------------------------|----+-----+----+-----|----|
   MIP-FA-to-HA-SPI 318  9.11    Unsigned32 | M  |  P  |    |  V  | Y  |
   MIP-FA-to-MN-SPI 319  9.10    Unsigned32 | M  |  P  |    |  V  | Y  |
   MIP-HA-to-FA-SPI 323  9.14    Unsigned32 | M  |  P  |    |  V  | Y  |
   MIP-MN-to-FA-MSA 325  9.5     Grouped    | M  |  P  |    |  V  | Y  |
   MIP-FA-to-MN-MSA 326  9.1     Grouped    | M  |  P  |    |  V  | Y  |
   MIP-FA-to-HA-MSA 328  9.2     Grouped    | M  |  P  |    |  V  | Y  |
   MIP-HA-to-FA-MSA 329  9.3     Grouped    | M  |  P  |    |  V  | Y  |
   MIP-MN-to-HA-MSA 331  9.6     Grouped    | M  |  P  |    |  V  | Y  |
   MIP-HA-to-MN-MSA 332  9.4     Grouped    | M  |  P  |    |  V  | Y  |
   MIP-Nonce        335  9.12    OctetString| M  |  P  |    |  V  | Y  |
   MIP-Session-Key  343  9.7     OctetString| M  |  P  |    |  V  | Y  |
   MIP-Algorithm-   345  9.8     Enumerated | M  |  P  |    |  V  | Y  |
     Type
   MIP-Replay-Mode  346  9.9     Enumerated | M  |  P  |    |  V  | Y  |
   MIP-MSA-Lifetime 367  9.13    Unsigned32 | M  |  P  |    |  V  | Y  |


9.1. MIP-FA-to-MN-MSA AVP

   The MIP-FA-to-MN-MSA AVP (AVP Code 326) is of type Grouped, and
   contains the FA-MN session key.  This AVP is conveyed to the FA in an
   AMA message.  The MN allocates the MIP-FA-to-MN-SPI.  The FA creates
   an FA-MN authentication extension using the session key and
   algorithm, and the MN verifies that extension using the same session
   key and algorithm.  The data field of this AVP has the following ABNF
   grammar:

         MIP-FA-to-MN-MSA ::= < AVP Header: 326 >
                              { MIP-FA-to-MN-SPI }
                              { MIP-Algorithm-Type }
                              { MIP-Session-Key }
                            * [ AVP ]



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9.2. MIP-FA-to-HA-MSA AVP

   The MIP-FA-to-HA-MSA AVP (AVP Code 328) is of type Grouped, and
   contains the FA-HA session key.  This AVP is conveyed to the FA in an
   AMA message.  The HA allocates the MIP-FA-to-HA-SPI.  The FA creates
   the FA-HA authentication extension using the session key and
   algorithm, and the HA verifies that extension using the same session
   key and algorithm.  The AVP's  data field has the following ABNF
   grammar:

         MIP-FA-to-HA-MSA ::= < AVP Header: 328 >
                              { MIP-FA-to-HA-SPI }
                              { MIP-Algorithm-Type }
                              { MIP-Session-Key }
                            * [ AVP ]


9.3. MIP-HA-to-FA-MSA AVP

   The MIP-HA-to-FA-MSA AVP (AVP Code 329) is of type Grouped, and
   contains the Home Agent's session key, which it shares with the
   foreign agent.  This AVP is conveyed to the HA in an HAR message.
   The FA allocates the MIP-HA-to-FA-SPI.  The HA creates the HA-FA
   authentication extension using the session key and algorithm, and the
   FA verifies that extension using the same session key and algorithm.
   The AVP's data field has the following ABNF grammar:

         MIP-HA-to-FA-MSA ::= < AVP Header: 329 >
                              { MIP-HA-to-FA-SPI   }
                              { MIP-Algorithm-Type }
                              { MIP-Session-Key }
                            * [ AVP ]


9.4. MIP-HA-to-MN-MSA AVP

   The MIP-HA-to-MN-MSA AVP (AVP Code 332) is of type Grouped, and
   contains the HA-MN session key.  This AVP is conveyed to the HA in an
   HAR for the case of FA COA Mobile IPv4 and in an AMA for the case of
   collocated COA Mobile IPv4.  The MN allocates the MIP-HA-to-MN-SPI.
   The HA creates the HA-MN authentication extension using the session
   key and algorithm, and the MN verifies that extension using the same
   session key and algorithm.  The AVP's  field has the following ABNF
   grammar:

         MIP-HA-to-MN-MSA ::= < AVP Header: 332 >
                              { MIP-HA-to-MN-SPI   }
                              { MIP-Algorithm-Type }
                              { MIP-Replay-Mode }
                              { MIP-Session-Key }
                            * [ AVP ]

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9.5. MIP-MN-to-FA-MSA AVP

   The MIP-MN-to-FA-MSA AVP (AVP Code 325) is of type Grouped, and
   contains the MN-FA session nonce, which the mobile node uses to
   derive the MN-FA session key.  This AVP is conveyed to the HA in an
   HAR message.  The FA allocates the MIP-MN-to-FA-SPI.  The MN creates
   the MN-FA authentication extension using the session key and
   algorithm, and the FA verifies that extension using the same session
   key and algorithm.

   The home agent uses this AVP in the construction of the Mobile IP
   "Generalized MN-FA Key Generation Nonce Reply" extension [MIPKEYS].

         MIP-MN-to-FA-MSA ::= < AVP Header: 325 >
                              { MIP-MN-FA-SPI }
                              { MIP-Algorithm-Type }
                              { MIP-nonce }
                            * [ AVP ]


9.6. MIP-MN-to-HA-MSA AVP

   The MIP-MN-to-HA-MSA AVP (AVP Code 331) is of type Grouped, and
   contains the MN-HA session nonce, which the mobile node uses to
   derive the MN-HA session key.  This AVP is conveyed to the HA in an
   HAR message for the case of FA COA Mobile IPv4 and in an AMR for the
   case of collocated Mobile IPv4.   The HA allocates the MIP-MN-to-HA-
   SPI.  The MN creates the MN-FA authentication extension using the
   session key and algorithm, and the HA verifies that extension using
   the same session key and algorithm.

   The Home Agent uses this AVP in the construction of the Mobile IP
   "Generalized MN-HA Key Generation Nonce Reply" extension [MIPKEYS].

         MIP-MN-to-HA-MSA ::= < AVP Header: 331 >
                              { MIP-MN-HA-SPI }
                              { MIP-Algorithm-Type }
                              { MIP-Replay-Mode }
                              { MIP-nonce }
                            * [ AVP ]


9.7. MIP-Session-Key AVP

   The MIP-Session-Key AVP (AVP Code 343) is of type OctetString and
   contains the Session Key for the associated Mobile IPv4
   authentication extension.  The HAAA selects the session key.




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9.8. MIP-Algorithm-Type AVP

   The MIP-Algorithm-Type AVP (AVP Code 345) is of type Enumerated, and
   contains the Algorithm identifier for the associated Mobile IPv4
   authentication extension.  The HAAA selects the algorithm type.  The
   following values are currently defined:


         2   HMAC-SHA-1 [HMAC]


9.9. MIP-Replay-Mode AVP

   The MIP-Replay-Mode AVP (AVP Code 346) is of type Enumerated and
   contains the replay mode the Home Agent for authenticating the mobile
   node.  The HAAA selects the replay mode.

   The following values are supported (see [MOBILEIP] for more
   information):

         1   None
         2   Timestamps
         3   Nonces


9.10. MIP-FA-to-MN-SPI AVP

   The MIP-FA-to-MN-SPI AVP (AVP Code 319) is of type Unsigned32, and it
   contains the Security Parameter Index the FA and MN use to refer to
   the FA-MN session key.  The MN allocates the SPI, and it  MUST NOT
   have a value between zero (0) and 255, which is the reserved
   namespace defined in [MOBILEIP].


9.11. MIP-FA-to-HA-SPI AVP

   The MIP-FA-to-HA-SPI AVP (AVP Code 318) is of type Unsigned32, and
   contains the Security Parameter Index the FA and HA   use to refer to
   the FA-HA session key.  The HA allocates the SPI , and it MUST NOT
   have a value between zero (0) and 255, which is the reserved
   namespace defined in [MOBILEIP].


9.12. MIP-Nonce AVP

   The MIP-Nonce AVP (AVP Code 335) is of type OctetString and contains
   the nonce sent to the mobile node for the associated authentication
   extension.  The mobile node follows the procedures in [MIPKEYS] to
   generate the session key used to authenticate Mobile IPv4
   registration messages.  The HAAA selects the nonce.



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9.13. MIP-MSA-Lifetime AVP

   The MIP-MSA-Lifetime AVP (AVP Code 367) is of type Unsigned32 and
   represents the period of time (in seconds) for which the session key
   or nonce is valid.  The associated session key or nonce, as the case
   may be, MUST NOT be used if the lifetime has expired; if the session
   key or nonce lifetime expires while the session to which it applies
   is still active, either the session key or nonce MUST be changed or
   the association Mobile IPv4 session MUST be terminated.


9.14. MIP-HA-to-FA-SPI AVP

   The MIP-HA-to-FA-SPI AVP (AVP Code 323) is of type Unsigned32, and
   contains the Security Parameter Index the HA and FA use to refer to
   the HA-FA session key.  The FA allocates the SPI, and it MUST NOT
   have a value between zero (0) and 255, which is the reserved
   namespace defined in [MOBILEIP].


10. Accounting AVPs


10.1. Accounting-Input-Octets AVP

   The Accounting-Input-Octets AVP (AVP Code 363) is of type Unsigned64,
   and contains the number of octets in IP packets received from the
   user.  This AVP MUST be included in all Accounting-Request messages
   and MAY be present in the corresponding Accounting-Answer messages as
   well.


10.2. Accounting-Output-Octets AVP

   The Accounting-Output-Octets AVP (AVP Code 364) is of type
   Unsigned64, and contains the number of octets in IP packets sent to
   the user.  This AVP MUST be included in all Accounting-Request
   messages and MAY be present in the corresponding Accounting-Answer
   messages as well.


10.3. Acct-Session-Time AVP

   The Acct-Time AVP (AVP Code 46) is of type Unsigned32, and indicates
   the length of the current session in seconds.  This AVP MUST be
   included in all Accounting-Request messages and MAY be present in the
   corresponding Accounting-Answer messages as well.






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10.4. Accounting-Input-Packets AVP

   The Accounting-Input-Packets (AVP Code 365) is of type Unsigned64,
   and contains the number of IP packets received from the user.  This
   AVP MUST be included in all Accounting-Request messages and MAY be
   present in the corresponding Accounting-Answer messages as well.


10.5. Accounting-Output-Packets AVP

   The Accounting-Output-Packets (AVP Code 366) is of type Unsigned64,
   and contains the number of IP packets sent to the user.  This AVP
   MUST be included in all Accounting-Request messages and MAY be
   present in the corresponding Accounting-Answer messages as well.


10.6. Event-Timestamp AVP

   The Event-Timestamp (AVP Code 55) is of type Time, and MAY be
   included in an Accounting-Request message to record the time that
   this event occurred on the mobility agent, in seconds since January
   1, 1970 00:00 UTC.


11. AVP Occurrence Tables

   The following tables presents the AVPs defined in this document and
   their occurrences in Diameter messages.  Note that AVPs that can only
   be present within a Grouped AVP are not represented in this table.

   The table uses the following symbols:
         0      The AVP MUST NOT be present in the message.
         0+     Zero or more instances of the AVP MAY be present in the
                message.
         0-1    Zero or one instance of the AVP MAY be present in the
                message.
         1      One instance of the AVP MUST be present in the message.
















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11.1. Mobile IP Command AVP Table

   The table in this section is limited to the Command Codes defined in
   this specification.

                                    +-----------------------+
                                    |      Command-Code     |
                                    |-----+-----+-----+-----+
      Attribute Name                | AMR | AMA | HAR | HAA |
      ------------------------------|-----+-----+-----+-----+
      Authorization-Lifetime        | 0-1 | 0-1 | 1   | 0   |
      Auth-Application-Id           | 1   | 1   | 1   | 1   |
      Auth-Session-State            | 0-1 | 0-1 | 1   | 0   |
      Acct-Multi-Session-Id         | 0-1 | 0-1 | 0   | 0-1 |
      Destination-Host              | 0-1 | 0   | 0-1 | 0   |
      Destination-Realm             | 1   | 0   | 1   | 0   |
      Error-Message                 | 0   | 0-1 | 0   | 0-1 |
      Error-Reporting-Host          | 0   | 0-1 | 0   | 0-1 |
      MIP-Candidate-Home-Agent-Host | 0-1 | 0   | 0-1 | 0   |
      MIP-Home-Agent-Host           | 0-1 | 0   | 0-1 | 0   |
      MIP-Originating-Foreign-AAA   | 0-1 | 0   | 0-1 | 0   |
      MIP-FA-Challenge              | 0-1 | 0   | 0   | 0   |
      MIP-FA-to-MN-MSA              | 0   | 0-1 | 0   | 0   |
      MIP-FA-to-HA-MSA              | 0   | 0-1 | 0   | 0   |
      MIP-HA-to-FA-MSA              | 0   | 0   | 0-1 | 0   |
      MIP-HA-to-MN-MSA              | 0   | 0-1 | 0-1 | 0   |
      MIP-MN-to-FA-MSA              | 0   | 0   | 0-1 | 0   |
      MIP-MN-to-HA-MSA              | 0   | 0-1 | 0-1 | 0   |
      MIP-FA-to-HA-SPI              | 0   | 0   | 0   | 0-1 |
      MIP-HA-to-FA-SPI              | 0   | 0   | 0   | 0-1 |

      MIP-FA-to-MN-SPI              | 0   | 0   | 0   | 0-1 |
      MIP-MN-to-FA-SPI              | 0   | 0   | 0   | 0-1 |

      MIP-HA-to-MN-SPI              | 0   | 0   | 0   | 0-1 |
      MIP-MN-to-HA-SPI              | 0   | 0   | 0   | 0-1 |
      MIP-Feature-Vector            | 0-1 | 0-1 | 1   | 0   |
      MIP-Filter-Rule               | 0   | 0+  | 0+  | 0   |
      MIP-Home-Agent-Address        | 0-1 | 0-1 | 0-1 | 0-1 |
      MIP-MSA-Lifetime              | 0   | 0-1 | 0-1 | 0   |
      MIP-MN-AAA-Auth               | 1   | 0   | 0   | 0   |
      MIP-Mobile-Node-Address       | 0-1 | 0-1 | 0-1 | 0-1 |
      MIP-Reg-Reply                 | 0   | 0-1 | 0   | 0-1 |
      MIP-Reg-Request               | 1   | 0   | 1   | 0   |
      Origin-Host                   | 1   | 1   | 1   | 1   |
      Origin-Realm                  | 1   | 1   | 1   | 1   |
      Origin-State-Id               | 0-1 | 0-1 | 0-1 | 0-1 |
      Proxy-Info                    | 0+  | 0+  | 0+  | 0+  |
      Redirect-Host                 | 0   | 0+  | 0   | 0+  |
      Redirect-Host-Usage           | 0   | 0-1 | 0   | 0-1 |
      Redirect-Max-Cache-Time       | 0   | 0-1 | 0   | 0-1 |
      Result-Code                   | 0   | 1   | 0   | 1   |


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      Re-Auth-Request-Type          | 0   | 0-1 | 0   | 0   |
      Route-Record                  | 0+  | 0   | 0+  | 0   |
      Session-Id                    | 1   | 1   | 1   | 1   |
      User-Name                     | 1   | 0-1 | 1   | 0-1 |
      ------------------------------|-----+-----+-----+-----|


11.2. Accounting AVP Table

   The table in this section is used to represent which AVPs defined in
   this document are to be present in the Accounting messages, defined
   in [DIAMBASE].

                                           +-------------+
                                           | Command-Code|
                                           |------+------+
      Attribute Name                       |  ACR |  ACA |
      -------------------------------------|------+------+
      Accounting-Input-Octets              |  1   |  0-1 |
      Accounting-Input-Packets             |  1   |  0-1 |
      Accounting-Output-Octets             |  1   |  0-1 |
      Accounting-Output-Packets            |  1   |  0-1 |
      Acct-Multi-Session-Id                |  1   |  0-1 |
      Acct-Session-Time                    |  1   |  0-1 |
      MIP-Feature-Vector                   |  1   |  0-1 |
      MIP-Home-Agent-Address               |  1   |  0-1 |
      MIP-Mobile-Node-Address              |  1   |  0-1 |
      Event-Timestamp                      | 0-1  |   0  |
      -------------------------------------|------+------+


12. IANA Considerations

   This section contains the namespaces that have either been created in
   this specification, or the values assigned to existing namespaces
   managed by IANA.


12.1. Command Codes

   This specification assigns the values 260 and 262 from the Command
   Code namespace defined in [DIAMBASE].  See section 5 for the
   assignment of the namespace in this specification.


12.2. AVP Codes

   This specification assigns the values 318-348 and 363-366 from the
   AVP Code namespace defined in [DIAMBASE].  See sections 7, 9, and 10
   for the assignment of the namespace in this specification.



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12.3. Result-Code AVP Values

   This specification assigns the values 4005-4008, and 5024-5025 from
   the Result-Code AVP (AVP Code 268) value namespace defined in
   [DIAMBASE].  See section 6 for the assignment of the namespace in
   this specification.


12.4. MIP-Feature-Vector AVP Values

   There are 32 bits in the MIP-Feature-Vector AVP (AVP Code 337) that
   are available for assignment.  This document assigns bits 1-9, as
   listed in section 7.5.  The remaining bits should only be assigned
   via Standards Action [IANA].


12.5. MIP-Algorithm-Type AVP Values

   As defined in Section 9.8, the MIP-Algorithm-Type AVP (AVP Code 345)
   defines the value 2.  All remaining values, except zero, are
   available for assignment via Designated Expert [IANA].


12.6. MIP-Replay-Mode AVP Values

   As defined in Section 9.9, the MIP-Replay-Mode AVP (AVP Code 346)
   defines the values 1-3.  All remaining values, except zero, are
   available for assignment via Designated Expert [IANA].


12.7. Application Identifier

   This specification assigns the value two (2) to the Application
   Identifier namespace defined in [DIAMBASE].  See section 4 for more
   information.


13. Security Considerations

   This specification describes a Mobile IPv4 Diameter Application for
   authenticating and authorizing a Mobile IPv4 mobile node.  The
   authentication algorithm used is dependent upon the transforms used
   within the Mobile IPv4 protocol, and [MIPCHAL].  This specification,
   in conjunction with [MIPKEYS], also defines a method by which the
   home Diameter server can create and distribute session keys and
   nonces for use in authenticating and integrity-protecting Mobile IPv4
   registration messages [MOBILEIP].  The key distribution is asymmetric
   since communication with the mobile node occurs via the Mobile IPv4
   protocol [AAAKEY, MOBILEIP], while communication to the Home Agent
   and Foreign Agent occurs via the Diameter protocol.  Where untrusted
   Diameter agents are present, end-to-end security MUST be used.  The
   end-to-end security takes the form of TLS or IPSec security

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   associations between the AAAH and the FA and between the AAAH and the
   HA.  These connections will be authenticated with the use of public
   keys and certificates; however, the identities that appear in the
   certificates must be authorized and bound to a particular Mobile IPv4
   Diameter session before the AAAH can safely begin distribution of
   keys.

   Note that the direct connections are established as a result of
   Diameter redirect messages.  For example, in Figure 3, the FA gets a
   redirect response containing the Redirect-Host AVP of the AAAH.  This
   is the identity that should be matched against the certificate
   presented by the AAAH when the secure connection is established.  In
   this case, the network of Diameter proxies and redirect agents is
   trusted with the task of returning the correct AAAH identity to the
   FA.

   The AAAH must also make an authorization decision at the time the FA
   establishes the connection.  If the AAAH is one and the same with the
   redirect server, then it may have observed and noted the original AMR
   message that contained the identity of the FA, and so may authorize
   the establishment of a TLS or IPSec connection from the same entity.
   Otherwise, the AAAH would need to maintain a list of all authorized
   visited domains (roaming partners) and authorize TLS or IPSec
   connections based on this list.  Note that establishment of the
   connection is only the first step, and the AAAH has another
   opportunity to deny service upon receipt of the AMR message itself.
   At this step, the AAAH can check the internal AVPs of the AMR to
   ensure that the FA is valid; for example, it can check that the
   Mobile IP COA is equal to the IP address used as the endpoint of the
   TLS or IPSec connection.  However, such a policy would prevent the FA
   from using different interfaces for AAA and Mobile IP tunnel packets,
   and may not be desirable in every deployment situation.

   A similar set of considerations applies to the connection between
   AAAH and HA when those entities are in different administrative
   domains.  However, here the roles are reversed because it is the AAAH
   that contacts the HA via the HAR.  The identity of the candidate HA
   is given to the AAAH in the AMR, and the AAAH should expect to
   receive the same identity in the public key certificates during TLS
   or IPSec negotiation.  The HA may authorize individual connections by
   acting as its own redirect server or it may maintain a list of
   trusted roaming partners.

   This application creates and distributes a single session key for
   each pair of MSAs between two entities, e.g., the same session key is
   used for the MN-HA MSA and the HA-MN MSA.  It is safe to do so from a
   security perspective because the session keys are only used with
   keyed hash functions to generate authenticator values that protect
   the integrity of each Mobile IP control message.  Mobile IP messages
   have built in replay protection with the use of timestamps or nonces
   [MOBILEIP] and, due to the nature of the protocol, requests are
   always bitwise different from responses at least in the message type
   code.  This avoids problems that might arise in other situations

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   where an attacker could mount a replay or reflection attack if the
   same key were used to, e.g., encrypt otherwise unprotected traffic on
   more than one connection leg in the network.

   Nonces are sent to the mobile node, which are used to generate the
   session keys via the HMAC-SHA-1 one-way function.  Because the nonces
   and authentication extensions may be observed by anyone with access
   to a clear-text copy of the Registration Reply, the pre-shared key
   between the mobile node and the home Diameter server would be
   vulnerable to an offline dictionary attack if it does not contain
   enough entropy.  To prevent this, the pre-shared key between the
   mobile node and the home Diameter server SHOULD be a randomly chosen
   quantity of at least 96 bits.

   Because the session key is determined by the long-term secret and the
   nonce, the nonce SHOULD be temporally and globally unique; if the
   nonce were to repeat, then so would the session key.  To prevent
   this, a nonce is strongly recommended to be a random [RANDOM] value
   of at least 128 bits.  The long-term secret between the MN and AAAH
   MUST be periodically refreshed, to guard against recovery of the
   long-term secret due to nonce reuse or other factors.  This is
   accomplished using out-of-band mechanisms, which are not specified in
   this document.

   It should also be noted that it is not recommended to set the MIP-
   MSA-Lifetime AVP value equal to zero, since keeping session keys for
   a long time (no refresh) increases the level of vulnerability.


14. References

14.1. Normative

   [DIAMBASE]     P. Calhoun, H. Akhtar, J. Arkko, E. Guttman, A.
                  Rubens,"Diameter Base Protocol", RFC 3588, September
                  2003.

   [IANA]         Narten, Alvestrand, "Guidelines for Writing an IANA C
                  Considerations Section in RFCs", BCP 26, RFC 2434,
                  October 1998

   [MOBILEIP]     C. Perkins, Editor. IP Mobility Support. RFC 3344,
                  August 2002.

   [MIPCHAL]      C. Perkins, P. Calhoun, "Mobile IP Challenge/Response
                  Extensions", Request
                  For Comments 3021, December 2000.

   [NAI]          B. Aboba, M. Beadles "The Network Access Identifier."
                  Request For Comments 2486, January 1999.

   [HMAC]         H. Krawczyk, M. Bellare, and R. Cannetti.  HMAC:

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                  Keyed Hashing for Message Authentication.  RFC 2104,
                  February 1997.

   [MIPKEYS]      C. Perkins, P. Calhoun, "AAA Registration Keys for
                  Mobile IP", draft-ietf-mipv4-aaa-key-04.txt,
                  IETF work in progress, November 2003.

   [AAANAI]       F. Johansson, T. Johansson, "AAA NAI for Mobile IP
                  Extension", draft-mip4-aaa-nai-02.txt, IETF work
                  December 2003. (approved for
                  publication)_

   [IPSEC]        S. Kent, Security Architecture for the Internet, RFC
                  2401, November 1998.

   [TLS]          Blake-Wilson, Transport Layer Security Extensions, RFC
                  3546, June 2003.

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


14.2. Informative

   [MIPREQ]       S. Glass, S. Jacobs, C. Perkins, "Mobile IP
                  Authentication, Authorization, and Accounting
                  Requirements". RFC 2977. October 2000.

   [CDMA2000]     T. Hiller and al, "CDMA2000 Wireless Data Requirements
                  for AAA", RFC 3141, June 2001.

   [EVALROAM]     B. Aboba, G. Zorn, "Criteria for Evaluating Roaming
                  Protocols", RFC 2477, January 1999.

   [MIPNAI]       P. Calhoun, C. Perkins, "Mobile IP Network Address
                  Identifier Extension", RFC 2794, March 2000.

   [RANDOM]       D. Eastlake, 3rd, S. Crocker, and J. Schiller.
                  Radomness Recommendations for Security. RFC 1750,
                  Internet Engineering Task Force, December 1994.



15. Acknowledgements

   The authors would like to thank Nenad Trifunovic, Haseeb Akhtar and
   Pankaj Patel for their participation in the pre-IETF Document Reading
   Party, to Erik Guttman for his very useful proposed text, and to
   Fredrik Johansson, Martin Julien and Bob Kopacz for their very useful
   contributed text.



Calhoun et al.          Expires February 2005                      49 
                             Diameter MIP                  August 2004


   The authors would also like to thank the participants of 3GPP2's TSG-
   X working group for their valuable feedback and also the following
   people for their contribution in the development of the protocol:

   Kevin Purser, Thomas Panagiotis, Mark Eklund, Paul Funk, Michael
   Chen, Henry Haverinen, Johan Johansson.  General redirect server text
   due to Pasi Eronen was borrowed from Diameter-EAP.

   Pat Calhoun would like to thank Sun Microsystems since most of the
   effort put into this document was done while he was in their employ.


16. Authors' Addresses

   Questions about this memo can be directed to:


   Pat Calhoun                      Tony Johansson
   Airespace                        Bytemobile, Inc.
   110 Nortech Parkway              2029 Stierlin Court
   San Jose, CA 95154               Mountain View, CA 94043
   USA                              USA

   Phone: +1 408-635-2023           Phone: +1 650-641-7817
   Email: pcalhoun@airespace.com      Fax: +1 650-641-7701
                                    Email: tony.johansson@bytemobile.com


   Charles E. Perkins               Tom Hiller
   Nokia Research Center            Lucent Technologies
   313 Fairchild Drive              1960 Lucent Lane
   Mountain View, CA 94043          Naperville, IL 60566
   USA                              USA

   Phone: +1 650-625-2986           Phone: +1 630-979-7673
     Fax: +1 650-625-2502           Email: tomhiller@lucent.com
   Email: charliep@iprg.nokia.com


   Peter J. McCann
   Lucent Technologies
   1960 Lucent Lane
   Naperville, IL 60563
   USA

   Phone: +1 630-713-9359
     Fax: +1 630-713-1921
   Email: mccap@lucent.com






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                             Diameter MIP                  August 2004


A. Change Log (to be removed before publication)

   Changes since draft-18:

     - Added text to section 4 to clarify the value of the Application
      ID used with each of the various Diameter commands.

     - Removed spurious "MIP-Type-Algorithm" AVP, which was not defined
      anywhere in the document, from the answer commands.

   Changes since draft-19:

     - Changed Application ID from 4 to 2, as specified in the base
      Diameter protocol

     - Reserved MIP-Algorithm-Type zero from future Designated Expert
      allocation in Section 12.5.





































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                             Diameter MIP                  August 2004


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