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Versions: (draft-deng-mip4-generic-notification-message) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 6098

MIP4 Working Group                                               H. Deng
Internet-Draft                                              China Mobile
Intended status: Standards Track                            H. Levkowetz
Expires: April 28, 2011                                           Netnod
                                                          V. Devarapalli
                                                                WiChorus
                                                           S. Gundavelli
                                                           Cisco Systems
                                                                B. Haley
                                                 Hewlett-Packard Company
                                                        October 25, 2010


              Generic Notification Message for Mobile IPv4
            draft-ietf-mip4-generic-notification-message-16

Abstract

   This document specifies protocol enhancements that allow Mobile IPv4
   entities to send and receive explicit notification messages using a
   Mobile IPv4 message type designed for this purpose.

Status of this Memo

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

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

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

   This Internet-Draft will expire on April 28, 2011.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.


































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Notification Message - Usage Scenarios . . . . . . . . . . . .  7
     3.1.  Notification Message - Examples  . . . . . . . . . . . . .  7
     3.2.  Notification Message - Topology  . . . . . . . . . . . . .  7
       3.2.1.  Notification Message between a Home Agent and a
               Mobile Node  . . . . . . . . . . . . . . . . . . . . .  8
       3.2.2.  Notification Message between a Foreign Agent and a
               Mobile Node  . . . . . . . . . . . . . . . . . . . . .  8
       3.2.3.  Notification Message between a Home Agent and a
               Foreign Agent  . . . . . . . . . . . . . . . . . . . .  9
   4.  Generic Notification Message and Considerations  . . . . . . . 10
     4.1.  Generic Notification Message . . . . . . . . . . . . . . . 10
     4.2.  Generic Notification Acknowledgment Message  . . . . . . . 13
     4.3.  Notification Retransmission  . . . . . . . . . . . . . . . 16
     4.4.  General Implementation Considerations  . . . . . . . . . . 17
     4.5.  Mobile Node Considerations . . . . . . . . . . . . . . . . 17
       4.5.1.  Receiving Generic Notification Messages  . . . . . . . 17
       4.5.2.  Sending Generic Notification Acknowledgement
               Messages . . . . . . . . . . . . . . . . . . . . . . . 19
       4.5.3.  Sending Generic Notification Messages  . . . . . . . . 19
       4.5.4.  Receiving Generic Notification Acknowledgement
               Messages . . . . . . . . . . . . . . . . . . . . . . . 20
     4.6.  Foreign Agent Consideration  . . . . . . . . . . . . . . . 21
       4.6.1.  Receiving Generic Notification Messages  . . . . . . . 21
       4.6.2.  Sending Generic Notification Acknowledgement
               Messages . . . . . . . . . . . . . . . . . . . . . . . 23
       4.6.3.  Sending Generic Notification Messages  . . . . . . . . 24
       4.6.4.  Receiving Generic Notification Acknowledgement
               Messages . . . . . . . . . . . . . . . . . . . . . . . 24
     4.7.  Home Agent Consideration . . . . . . . . . . . . . . . . . 25
       4.7.1.  Sending Generic Notification Messages  . . . . . . . . 25
       4.7.2.  Receiving Generic Notification Acknowledgement
               Messages . . . . . . . . . . . . . . . . . . . . . . . 26
       4.7.3.  Receiving Generic Notification Messages  . . . . . . . 26
       4.7.4.  Sending Generic Notification Acknowledgement
               Messages . . . . . . . . . . . . . . . . . . . . . . . 28
   5.  Future Extensibility . . . . . . . . . . . . . . . . . . . . . 29
     5.1.  Examples of Possible Extensions  . . . . . . . . . . . . . 29
     5.2.  Extension Specification  . . . . . . . . . . . . . . . . . 29
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 31
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 32
     7.1.  Replay Protection for GNM, GNAM messages . . . . . . . . . 32
       7.1.1.  Replay Protection using Timestamps . . . . . . . . . . 33
       7.1.2.  Replay Protection using Nonces . . . . . . . . . . . . 34
     7.2.  Non-authentication Extensions Handling in Foreign Agent  . 34



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   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 35
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 36
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 36
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37














































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1.  Introduction

   In some situations, there is a need for Mobile IPv4 entities, such as
   the home agent(HA), foreign agent(FA) and mobile node(MN) to send and
   receive asynchronous notification messages during a mobility session.
   'Asynchronous messages' in this context is used to mean messages
   which are not synchronous with the Registration Request and
   Registration Reply messages of the base Mobile IP Specification
   [RFC3344].  The base Mobile IP Specification does not have a
   provision for this.

   This document defines a generic message and a notification model that
   can be used by Mobile IPv4 entities to send various notifications.
   It also defines a corresponding acknowledgement message to allow for
   reliable delivery of notifications.  Only the following extensions
   may be present in these new messages, as defined by this document:

      - MN-HA Authentication Extension

      - MN-FA Authentication Extension

      - FA-HA Authentication Extension

      - Message String Extension

   The semantics of receiving a generic notification message with a
   Message String Extension are null; i.e., it has no effect on the
   state of a mobile node's existing registration.  See Section 3.1 for
   some application examples that motivate the new messages defined in
   this document.





















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2.  Terminology

   It is assumed that the reader is familiar with the terminology used
   in [RFC4917], [RFC3344].  In addition, this document frequently uses
   the following terms:

   Notification Message
             A message from a mobility agent to a MN or other mobility
             agent to asynchronously notify it about an event that is
             relevant to the mobility service it is currently providing.

   Generic Notification Message
             A Notification Message in the context of Mobile IPv4 with a
             well-defined envelope format and extensibility, and with
             certain limitations on how extensions may be defined and
             used, but otherwise generally available for notification
             purposes within the Mobile IPv4 protocol.  Abbreviated
             'GNM' in this document.

   Generic Notification Acknowledgement Message
             An acknowledgement of a received Generic Notification
             Message.  Abbreviated 'GNAM' in this document.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119, [RFC2119].

























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3.  Notification Message - Usage Scenarios

3.1.  Notification Message - Examples

   The simplest usage scenario for a notification message is one where
   the notification has no semantic meaning within the protocol; it is
   only carrying a message which can be displayed to a user or an
   operator (depending on which is the receiving entity -- see more on
   this below, in Section 3.2).  Examples of such usage is messages from
   operator to user about billing or service related events ("You have
   used nearly all of your prepaid quota; there is only XX MB left --
   please purchase further service if you are going to need it."; or
   "You have now used data transfer services for the amount of $XXX
   since your last bill; this is above the notification threshold for
   your account.") or messages about service interruptions, and more.
   These examples are all supported by the use of the Mobile IPv4
   Generic Notification Message together with the Message String
   Extension, as defined in this document.

   There are also other examples, which cannot be implemented solely
   using the messages and extensions defined in this document.  Some of
   these are described briefly below, and covered slightly more
   extensively in Section 5.

   One example of an application of an extended Generic Notification
   Message is that during handover between CDMA 2000 1x EV-DO and
   Wireless LAN, the PPP resource on the CDMA side has to be removed on
   the FA (PDSN) to avoid over-charging subscribers.  To address this,
   the Registration Revocation Message was defined in [RFC3543], but it
   would have been preferable to have had it defined as a separate
   message (i.e., the Generic Notification Message) with a Registration
   Revocation extension.

   Other applications are HA switch over (before HA decide to go off-
   line it would like to notify the MNs to register with another
   candidate HA), NEMO prefix changes (MN is notified by HA about NEMO
   prefix changes and service or billing related events, which is an
   operational requirement), Load balancing (HA wants to move some of
   the registered MNs to other HAs), Service Termination (due to end of
   prepaid time), and Service Interruption (due to system maintenance).

3.2.  Notification Message - Topology

   There are several scenarios where a mobility agent could initiate
   notification events.  Some of these are described in the following
   Sections.





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3.2.1.  Notification Message between a Home Agent and a Mobile Node

3.2.1.1.  Mobile Registered using a Foreign Agent Care-of Address

   In this case, the HA cannot directly notify the MN, but must send the
   notification via the FA, vice versa.

           +----+    notification  +----+ notification  +----+
           | MN |<================>| FA |<=============>| HA |
           +----+                  +----+               +----+


           Figure 1: HA notifies MN or MN notifies HA through FA

3.2.1.2.  Mobile Registered using a Co-located Care-of Address

   In this case, the MN has registered with the home agent directly, so
   the notification message can go directly to the MN.

   The notification mechanism as specified here does not support the
   case of Co-located CoA mode with registration through a FA (due to
   the 'R' bit being set in the FA's advertisement messages).

           +----+               notification          +----+
           | MN |<===================================>| HA |
           +----+                                     +----+


       Figure 2: HA directly notifies MN or MN directly notifies HA

3.2.2.  Notification Message between a Foreign Agent and a Mobile Node

   There are two cases where a FA may send notification messages to a
   MN, one where it is relaying a message, the other where the
   notification is triggered by a message from another network entity,
   for example a AAA node(notification messages between a AAA entity and
   the FA could be based on RADIUS or Diameter, but this is out of scope
   for this document).  If the notification is initiated by a FA, the FA
   may need to also notify the HA about the event.

   +----+    notification  +----+    trigger   +--------+
   | MN |<================>| FA |<=============|   AAA  |
   +----+                  +----+              +--------+
                             ||   notification +----+
                              ================>| HA |
                                               +----+





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                         Figure 3: FA notifies MN

3.2.3.  Notification Message between a Home Agent and a Foreign Agent

   The HA may also need to send a notification to the FA, but not to the
   MN, The FA may also need to send a notification to the HA, as
   illustrated below:

                       +----+ notification  +----+
                       | FA |<=============>| HA |
                       +----+               +----+


                Figure 4: HA notifies FA or FA notifies HA





































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4.  Generic Notification Message and Considerations

   This section describes in detail the Generic Notification Message
   (GNM), Generic Notification Acknowledgement Message (GNAM), and some
   considerations related to the handling of these messages in the MN,
   FA and HA.

   The MN and HA MUST maintain the following information, FA also needs
   to maintain both the HA's and MN's direction the below information:

      - the IP source address of the Registration Request/Reply

      - the IP destination address of the Registration Request/Reply

      - the UDP source port of the Registration Request/Reply

      - the UDP destination port of the Registration Request/Reply

   The sending node always sends the GNM message following the same
   procedure for sending Registration Request as in Section 3.3 of
   [RFC3344] and the receiving node follows the same procedure for
   Registration Reply as in Section 3.4. of [RFC3344] when sending GNAM.

4.1.  Generic Notification Message

   A GNM is sent by a mobility agent to inform another mobility agent,
   or a MN, of MIP-related information in the form of a Message String
   Extension [RFC4917].  These messages MUST use the same IP and UDP
   headers as any previous Registration Request(RRQ) or Reply (RRP)
   message to the same entity.  This would support NAT traversal and
   ensure same security association used for GNM/GNAM and RRQ/RRP.  The
   GNM is defined as follows:

   IP Fields:

     Source Address         Typically copied from the destination
                            address of the last Registration Reply/
                            Request message that the agent received from
                            the agent to which it is sending the GNM.

     Destination Address    Copied from the source address of the last
                            Registration Reply/Request message that the
                            agent received from the agent to which it is
                            sending the GNM.

   UDP Fields:





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     Source Port            Typically copied from the destination port
                            of the last Registration Reply/Request
                            message that the agent received from the
                            agent to which it is sending the GNM.

     Destination Port       Copied from the source port of the last
                            Registration Reply/Request message that the
                            agent received from the agent to which it is
                            sending the GNM.

   The UDP header is followed by the Mobile IP fields shown below:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |      MD       |A|  Reserved                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Home Address                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Home Agent Address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Care-of Address                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                       Identification                          +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Extensions...
      +-+-+-+-+-+-+-+-+-+-+-+-+-


   Type (To be assigned by IANA)

   MD: Message Direction

      This memo defines the semantics of the following MD field value:

      0 -- Message sent by the HA to the MN

      1 -- Message sent by the HA to the FA

      2 -- Message sent by the MN to the HA

      3 -- Message sent by the MN to the FA

      4 -- Message sent by the FA to the MN





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      5 -- Message sent by the FA to the HA

   A

      This bit indicates whether the notification message MUST be
      acknowledged by the recipient.  If "A" bit has been set during the
      message, but the sender doesn't receive any acknowledgement
      message, then the sender will have to re-send the notification
      message again.

      Set to "1" to indicate that acknowledgement is REQUIRED.

      Set to "0" to indicate that acknowledgement is OPTIONAL.

   Reserved

      MUST be sent as 0, and ignored when received.

   Home Address

      The home IP address of the mobile node.

   Home Agent Address

      The IP address of the mobile node's HA.

   Care-of Address

      The mobile node's care-of address, either the Co-located Care-of
      Address or the foreign agent care-of address.

   Identification

      A 64-bit number, constructed by the sender, used for matching GNM
      with GNAM, and for protecting against replay attacks of
      notification messages.  See Section 7.1.1 and Section 7.1.2 for
      more on the use of timestamps and nonces in this field.  Support
      for the use of timestamps is REQUIRED and support for nonces is
      OPTIONAL.

   Extensions

      The fixed portion of the GNM is followed by one or more extensions
      which may be used with this message, and by one or more
      authentication extensions as defined in Section 3.5 of [RFC3344].

      Apart from the Authentication Extensions mentioned below, only one
      extension is defined in this document as permitted for use with



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      the GNM: the Message String Extension defined in [RFC4917].

      This document requires the MN-HA Authentication Extension (AE) to
      be used when this message is sent between the MN and the HA; MN-FA
      AE and FA-HA AE are OPTIONAL.  This document also requires the use
      of the MN-FA AE when this message is sent between the MN and the
      FA; where the MN-HA AE and FA-HA AE are not needed.  This document
      finally require the use of the FA-HA AE when this message is sent
      between the FA and the HA, and the MN-HA AE and MN-FA AE are not
      needed.  This could be determined based on the "MD" value.
      See Sections 3.6.1.3 and 3.7.2.2 of [RFC3344] for the rules on the
      order of these extensions as they appear in Mobile IPv4 RRQ and
      RRP messages.  The same rules are applicable to GNM and GNAM.

4.2.  Generic Notification Acknowledgment Message

   A GNAM is sent by mobility agents or MNs to indicate the successful
   receipt of a GNM.

   IP Fields:

     Source Address         Typically copied from the destination
                            address of the GNM to which the agent is
                            replying.

     Destination Address    Copied from the source address of the GNM to
                            which the agent is replying.

   UDP Fields:

     Source Port            Copied from the destination port of the
                            corresponding GNM.

     Destination Port       Copied from the source port of the
                            corresponding GNM.

   The UDP header is followed by the Mobile IP fields shown below:














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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |      MD       |     code      | Reserved      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Home Address                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Home Agent Address                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Care-of Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                       Identification                          +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Extensions...
   +-+-+-+-+-+-+-+-+-+-+-+-+-


   Type (To be assigned by IANA)

   MD: Message Direction

      This memo defines the semantics of the following MD field value:

      0 -- Message sent by the HA to the MN

      1 -- Message sent by the HA to the FA

      2 -- Message sent by the MN to the HA

      3 -- Message sent by the MN to the FA

      4 -- Message sent by the FA to the MN

      5 -- Message sent by the FA to the HA

   code

      A value indicating the result of the GNM.  See below for a list of
      currently defined Code values.

   Notification successful

      0 -- notification accepted

   Notification denied by the HA




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      128 -- reason unspecified

      129 -- administratively prohibited

      130 -- insufficient resources

      131 -- mobile node failed authentication

      132 -- foreign agent failed authentication

      133 -- notification Identification mismatch

   Notification denied by the FA

      64 -- reason unspecified

      65 -- administratively prohibited

      66 -- insufficient resources

      67 -- mobile node failed authentication

      68 -- home agent failed authentication

      69 -- notification Identification mismatch

   Notification denied by the mobile node

      192 -- reason unspecified

      193 -- administratively prohibited

      194 -- insufficient resources

      195 -- foreign agent failed authentication

      196 -- home agent failed authentication

      197 -- notification Identification mismatch

   Home Address

      The home IP address of the mobile node.

   Home Agent Address

      The IP address of the sender's home agent.




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   Care-of Address

      The mobile node's care-of address, either the Co-located Care-of
      Address or the foreign agent care-of address.

   Identification

      A 64-bit number used for matching GNM message with GNAM message
      and for protecting against replay attacks of registration
      messages.  See Section 7.1.1 and Section 7.1.2 for more on the use
      of timestamps and nonces in this field.  Support for the use of
      timestamps is REQUIRED and support for nonces is OPTIONAL.  The
      value is based on the Identification field from the GNM message
      from the sender, and on the style of replay protection used in the
      security context between the sender and its receiver (defined by
      the mobility security association between them, and SPI value in
      the authorization-enabling extension).

   Extensions

      The fixed portion of the GNAM is followed by one or more
      extensions which may be used with this message, and by one or more
      authentication extensions as defined in Section 3.5 of [RFC3344].

      This document REQUIRES the MN-HA Authentication Extension (AE) to
      be used when this message is sent between the MN and the HA; MN-FA
      AE and FA-HA AE are OPTIONAL.  This document also requires the use
      of the MN-FA AE when this message is sent between the MN and the
      FA; where the MN-HA AE and FA-HA AE are not needed.  This document
      finally requires the use of the FA-HA AE when this message is sent
      between the FA and the HA, and the MN-HA AE and MN-FA AE are not
      needed.  This could be determined based on the "MD" value.
      See Sections 3.6.1.3 and 3.7.2.2 of [RFC3344] for the rules on the
      order of these extensions as they appear in Mobile IPv4 RRQ and
      RRP messages.  The same rules are applicable to GNM and GNAM.

4.3.  Notification Retransmission

   If "A" flag has been set during the GNM message, but the sender
   doesn't receive any GNAM message within a reasonable time, then
   another GNM will be retransmitted.  When timestamps are used, a new
   registration Identification is chosen for each retransmission; Thus
   it counts as a new GNM.  When nonces are used, the unanswered GNM
   message is retransmitted unchanged; thus the retransmission does not
   count as a new GNM (Section 7.1).  In this way a retransmission will
   not require the receiver to re-synchronize with the sender by issuing
   another nonce in the case in which the original GNM message (rather
   than its GNAM message) was lost by the network.



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   The maximum time until a new GNM message is sent SHOULD be no greater
   than the requested Lifetime of the last GNM message.  The minimum
   value SHOULD be large enough to account for the size of the messages,
   twice the round trip time for transmission to the receiver, and at
   least an additional 100 milliseconds to allow for processing the
   messages before responding.  The round trip time for transmission to
   the receiver will be at least as large as the time REQUIRED to
   transmit the messages at the link speed of the sender's current point
   of attachment.  Some circuits add another 200 milliseconds of
   satellite delay in the total round trip time to the receiver.  The
   minimum time between GNM MUST NOT be less than 1 second.  Each
   successive retransmission timeout period SHOULD be at least twice the
   previous period, as long as that is less than the maximum as
   specified above.

4.4.  General Implementation Considerations

   Implementations of this specifications should provide support for
   management of the various settings related to the notification
   messages.  In particular, it should be possible to do the following:

      * List the notification messages supported

      * Show enabled/disabled status for notification message support,
      overall and in detail.

      * Show the value of the maximum and minimum retransmission times.

      * Enable and disable notification support entirely.

      * Enable and disable the individual notification messages
      supported.

      * Set the value of the maximum and minimum retransmission times
      described in Section 4.3.

4.5.  Mobile Node Considerations

   It is possible that the MN MAY receive a GNM from a FA or HA.  Both
   in the case of FA-CoA and Co-located CoA, the MN MAY reply with a
   GNAM based on the "A" flag in the GNM message.

4.5.1.  Receiving Generic Notification Messages

   When the MN is using FA-CoA and receives a Notification message, if
   the "MD" value is 0, it means that the notification message came from
   the HA.  If the "MD" value is 4, the notification came from the FA.




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   If this notification message came from a FA and the MN accepts the
   FA's GNM, then it will process the notification extension according
   to the specific rules for that extension.

   The MN MUST check for the presence of an authorization-enabling
   extension, and perform the indicated authentication.  Exactly one
   authorization-enabling extension MUST be present in the GNM, if this
   message came from a FA, then MN-FA AE MUST be present.  If no MN-FA
   AE is found, or if more than one MN-FA AE is found, or if the
   Authenticator is invalid, then the MN MUST reject the GNM and MAY
   send a GNAM to the FA with Code 195, including an Identification
   field computed in accordance with the rules specified in Section 7.1.
   The MN MUST do no further processing with such a notification, though
   it SHOULD log the error as a security exception.

   The MN MUST check that the Identification field is correct using the
   context selected by the SPI within mandatory authentication extension
   like MN-FA AE or MN-HA AE.  See Section 7.1 for a description of how
   this is performed.  If incorrect, the MN MUST reject the GNM and MAY
   send a GNAM to the initiator with Code 197, including an
   Identification field computed in accordance with the rules specified
   in Section 7.1.  The MN MUST do no further processing with such a
   notification, though it SHOULD log the error as a security exception.

   The MN MUST also check that the extensions present in the Generic
   Notification Message are permitted for use with the GNM.  If not, the
   MN MUST silently discard the message.  It MUST NOT do any further
   processing with such a notification, though it SHOULD log the error.

   After this, the MN MAY reply GNAM back to the FA.  If the "A" flag is
   set in the GNM, then the MN MUST send the GNAM.

   If this notification message came from the HA, relayed by the FA, or
   is a Co-located CoA, then the MN-HA AE MUST be checked and the MN
   MUST check the Authenticator value in the Extension.  If no MN-HA AE
   is found, or if more than one MN-HA AE is found, or if the
   Authenticator is invalid, then the MN MUST reject the GNM and MAY
   send a GNAM to the initiator with Code 196, including an
   Identification field computed in accordance with the rules specified
   in Section 7.1.  The MN MUST do no further processing with such a
   notification, though it SHOULD log the error as a security exception.
   If the MN accepts the HA's GNM, then it will process it according to
   the specific rules for that extension.  After that, the MN MAY reply
   with a GNAM with Code 0 back to the HA based on the "A" flag in the
   GNM.






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4.5.2.  Sending Generic Notification Acknowledgement Messages

   Both in the case of a Co-located CoA and FA-CoA, the MN MAY reply
   with a GNAM based on the "A" flag in the GNM as follows:

   If the GNM was initiated from the FA to the MN ("MD" value is set to
   4), then MN-FA AE MUST be the last extension in order to protect all
   other non-authentication extensions as defined in Section 3.5.3 of
   [RFC3344].

   In the case of a FA-CoA, the source address is the MN's address, the
   destination address is the FA's address.

   The Code field of the GNAM is chosen in accordance with the rules
   specified in Section 4.2.  When replying to an accepted notification,
   a MN SHOULD respond with Code 0.

   There are a number of reasons the MN might reject a notification such
   as administrative in nature returning a GNAM with a code of 193,
   similarly and provides the Code value 192 or 194 for the unspecified
   reason and insufficient resources.

   If the GNM was initiated from the HA to the MN ("MD" value is set to
   0) and in the case of Co-located CoA, then MN-HA AE MUST be the last
   extension in order to protect all other non-authentication extensions
   as defined in Section 3.5.2 of [RFC3344]

   In the case of a FA-CoA, the source address is the MN's HoA address
   and the destination address is the FA's address ("MD" value is set to
   2), the ordering of the extension is: any non-authentication
   Extensions used only by the HA, followed by the MN-HA AE defined in
   Section 3.5.2 of [RFC3344], followed by any non-authentication
   Extensions used only by the FA, followed by the MN-FA AE defined in
   Section 3.5.3 of [RFC3344].

4.5.3.  Sending Generic Notification Messages

   The MN may either send a GNM to notify the FA or HA.

   If the message is sent to the FA, then the source address is the MN's
   address, and the destination address is the FA's address

   If the FA is the target of this notification message, then the "MD"
   value is set to 3, MN-FA AE MUST be the last extension in order to
   protect all other non-authentication extensions.  Computing
   Authentication Extension Value is the same as Section 3.5.1 of
   [RFC3344].




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   If the FA is working only as a relay agent, then the "MD" value is
   set to 2, and the ordering of the extension is: the notification
   extension, followed by any non-authentication extension expected to
   be used by HA, followed by MN-HA AE defined in Section 3.5.2 of
   [RFC3344], followed by any non-authentication Extensions used only by
   the FA, followed by The MN-FA AE defined in Section 3.5.3 of
   [RFC3344].  Computing Authentication Extension Value is the same as
   Section 3.5.1 of [RFC3344].

   In the case of a Co-located CoA, the MN MAY send a notification
   message directly to the HA if it needs to be notified.  The "MD"
   value is set to 2, and the ordering of the extension is: the
   notification extension, followed by any non-authentication extension
   expected to be used by HA, followed by MN-HA AE defined in Section
   3.5.2 of [RFC3344].

   The MN chooses the Identification field in accordance with the style
   of replay protection it uses with its HA.  This is part of the
   mobility security association the MN shares with its HA.  See
   Section 7.1 for the method by which the MN computes the
   Identification field.

4.5.4.  Receiving Generic Notification Acknowledgement Messages

   In the case of a FA-CoA, if the MN receives this message, and the
   "MD" value is set to 0, it means that the GNAM came from HA

   If the "MD" value is set to 4, then the MN-FA AE MUST be checked, and
   the MN MUST check the Authenticator value in the Extension.  If no
   MN-FA AE is found, or if more than one MN-FA AE is found, or if the
   Authenticator is invalid, then the MN MUST silently discard the GNAM.

   In addition, the low-order 32 bits of the Identification field in the
   GNAM MUST be compared to the low-order 32 bits of the Identification
   field in the most recent GNM sent to the replying agent.  If they do
   not match, then the GNAM MUST be silently discarded.

   If the "MD" value is set to 0, then the MN-HA AE MUST be checked, and
   the MN MUST check the Authenticator value in the Extension.  If no
   MN-HA AE is found, or if more than one MN-HA AE is found, or if the
   Authenticator is invalid, then the MN MUST silently discard the GNAM.
   If the MN accepted this message, then the MN MAY also process it
   based on the notification event.

   In the case of a Co-located CoA, if the MN received this message,
   then the MN-HA AE MUST be checked, and the MN MUST check the
   Authenticator value in the Extension.  If no MN-HA AE is found, or if
   more than one MN-HA AE is found, or if the Authenticator is invalid,



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   then the MN MUST silently discard the Notification Acknowledgement
   message.

4.6.  Foreign Agent Consideration

   The FA may initiate a GNM to the MN or the HA.  Additionally, the FA
   also relays GNM and GNAM messages between the MN and its HA as long
   as there is an active binding for the MN at the FA.

4.6.1.  Receiving Generic Notification Messages

   If the FA receives a GNM, and the "MD" value is set to 0, then it
   means that the HA is asking the FA to relay the message to the MN.
   If the "MD" value is set to 1, then it means that the target of the
   notification is the FA.  If the "MD" value is set to 2, then it means
   that the MN is asking the FA to relay the message to the HA.  If the
   "MD" value is set to 3, then it means that the notification came from
   the MN to the FA.

   If the "MD" value is set to 0, then the FA MAY validate the FA-HA AE
   if present.  If the FA-HA AE is invalid, then all extensions between
   the HA-MN AE and the HA-FA AE MUST be removed, FA SHOULD relay the
   GNM to the MN's home address as specified in the Home Address field
   of the GNM, MN will eventually validate the MN-HA AE to ensure that
   all information sent to the MN is integrity protected.  If the FA-HA
   AE is valid, FA MUST relay the GNM to the MN's home address as
   specified in the Home Address field of the GNM.  The FA MUST NOT
   modify any of the fields beginning with the fixed portion of the GNM
   through the MN-HA AE or other authentication extension supplied by
   the HA as an authorization-enabling extension for the MN.

   Furthermore, the FA MUST process and remove any extensions following
   the MN-HA AE.  If the FA shares a mobility security association with
   the MN, the FA MAY append any of its own non-authentication
   extensions which of relevance to the MN.  In this case, the FA MUST
   append the MN-FA AE after these non-authentication extensions.

   If the "MD" value is set to 1, the FA-HA AE MUST be checked, and the
   FA MUST check the Authenticator value in the Extension.  If no FA-HA
   AE is found, or if more than one FA-HA AE is found, or if the
   Authenticator is invalid, the FA MUST reject the GNM and MAY send a
   GNAM to the HA with Code 68, including an Identification field
   computed in accordance with the rules specified in Section 7.1.  The
   FA MUST do no further processing with such a notification, though it
   SHOULD log the error as a security exception.

   The FA MUST check that the Identification field is correct using the
   context selected by the SPI within mandatory FA-HA AE.  See



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   Section 7.1 for a description of how this is performed.  If
   incorrect, the FA MUST reject the GNM and MAY send a GNAM to the
   initiator with Code 69, including an Identification field computed in
   accordance with the rules specified in Section 7.1.  The FA MUST do
   no further processing with such a notification, though it SHOULD log
   the error as a security exception.

   The FA MUST also check that the extensions present in the Generic
   Notification Message are permitted for use with the GNM.  If not, the
   FA MUST silently discard the message.  It MUST NOT do any further
   processing with such a notification, though it SHOULD log the error.

   If FA accepts the HA's GNM, it will process it based on the specific
   rules for that extension.  The FA MAY then reply with a GNAM with
   Code 0 back to the MN based on the "A" flag in the GNM.

   In the case of a FA-CoA and if the "MD" value is set to 2, if the FA
   received this message, and if the MN-FA AE is present, the MN-FA AE
   MUST be checked, and the FA MUST check the Authenticator value in the
   Extension.  If no MN-FA AE is found, or if more than one MN-FA AE is
   found, or if the Authenticator is invalid, the FA MUST silently
   discard the GNM message.  If MN-FA is valid, FA MUST relay the GNM to
   the HA's address as specified in the Home Agent Address field of the
   GNM, HA will eventually validate the MN-HA AE to ensure that all
   information sent to the HA is integrity protected.  The FA MUST NOT
   modify any of the fields beginning with the fixed portion of the GNM
   through the MN-HA AE or other authentication extension supplied by
   the MN as an authorization-enabling extension for the HA.

   Furthermore, the FA MUST process and remove any Extensions following
   the MN-HA AE, and MAY append any of its own non-authentication
   Extensions of relevance to the HA if applicable, and MUST append the
   FA-HA AE, if the FA shares a mobility security association with the
   HA.

   If the "MD" value is set to 3, the MN-FA AE MUST be checked, and the
   FA MUST check the Authenticator value in the Extension which is the
   same as the Section 3.7.2.1 of [RFC3344].  If no MN-FA AE is found,
   or if more than one MN-FA AE is found, or if the Authenticator is
   invalid, the FA MUST reject the GNM and MAY send a GNAM to the MN
   with Code 67, including an Identification field computed in
   accordance with the rules specified in Section 7.1.  The FA MUST do
   no further processing with such a notification, though it SHOULD log
   the error as a security exception.

   The FA MUST check that the Identification field is correct using the
   context selected by the SPI within mandatory MN-FA AE.  See
   Section 7.1 for a description of how this is performed.  If



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   incorrect, the FA MUST reject the GNM and MAY send a GNAM to the
   initiator with Code 69, including an Identification field computed in
   accordance with the rules specified in Section 7.1.  The FA MUST do
   no further processing with such a notification, though it SHOULD log
   the error as a security exception.

   If FA accepts the MN's GNM, it will process it based on the specific
   rules for that extension.  The FA MAY then reply with a GNAM with
   Code 0 back to the MN based on the "A" flag in the GNM.

4.6.2.  Sending Generic Notification Acknowledgement Messages

   The FA may need to either relay a GNAM message between the MN and the
   HA or send one as a response to a GNM message that was sent to it.
   In both cases, the GNAM message is defined as follows:

   The source address is the FA address, the destination address is HA's
   or MN's home address.

   The Code field of the GNAM is chosen in accordance with the rules
   specified in Section 4.2.  When replying to an accepted notification,
   a FA SHOULD respond with Code 0.

   There are a number of reasons the FA might reject a notification such
   as administrative in nature returning a GNAM with a code of 65,
   similarly and provides the Code value 64 or 66 for the unspecified
   reason and insufficient resources.

   If the FA is only relaying this message to the HA, the FA MUST NOT
   modify any of the fields beginning with the fixed portion of the GNAM
   through the including the MN-HA AE or other authentication extension
   supplied by the MN as an authorization-enabling extension for the MN.
   Furthermore, the foreign agent MUST process and remove any Extensions
   following the MN-HA AE.  If the FA shares a mobility security
   association with the HA, the FA MAY append any of its own non-
   authentication extensions which of relevance to the HA, In this case
   the FA MUST append the FA-HA AE after these non-authentication
   extensions.

   If the notification message is from the HA to the FA then the "MD"
   value is set to 5 and the ordering of the extension is: any non-
   authentication Extensions used only by the FA, followed by The FA-HA
   AE defined in Section 3.5.4 of [RFC3344].

   If the notification message is from the MN to the FA then the "MD"
   value is set to 4 and the ordering of the extension is: any non-
   authentication Extensions used only by the FA, followed by The MN-FA
   AE defined in Section 3.5.3 of [RFC3344].



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4.6.3.  Sending Generic Notification Messages

   If the FA is initiating a notification to the MN using the GNM, it
   MAY also notify the HA as well.

   In the message to the MN, the source address is the FA address, the
   destination address is the MN's address, the "MD" value is set to 4,
   and the ordering of the extension is: the notification extension,
   followed by any non-authentication Extensions used only by the MN,
   followed by The MN-FA AE defined in Section 3.5.3 of [RFC3344].
   Computing Authentication Extension Value is the same as Section 3.5.1
   of [RFC3344] except the payload is the notification other than
   registration.

   In the message to the HA, the source address is the FA's address, the
   destination address is the HA's address (the "MD" value is set to 5),
   and the ordering of the extension is: notification extension,
   followed by any non-authentication Extensions used only by the HA,
   followed by The FA-HA AE defined in Section 3.5.4 of [RFC3344].
   Computing Authentication Extension Value is the same as Section 3.5.1
   of [RFC3344] except the payload is the notification other than
   registration.

4.6.4.  Receiving Generic Notification Acknowledgement Messages

   In the case of a FA-CoA, if the FA receives this message, and the
   "MD" value is set to 3, it means that the notification
   acknowledgement message came from the MN, otherwise it came from the
   HA.

   If the "MD" value is set to 1, the FA-HA AE MUST be checked, and the
   FA MUST check the Authenticator value in the Extension.  If no FA-HA
   AE is found, or if more than one FA-HA AE is found, or if the
   Authenticator is invalid, the FA MUST silently discard the
   Notification Acknowledgement message.  If the FA accepted this
   message, the FA MAY also process it based on the notification event.

   If the "MD" value is set to 3, if the MN-FA AE is present, it MUST be
   checked, and the FA MUST check the Authenticator value in the
   Extension.  If no MN-FA AE is found, or if more than one MN-FA AE is
   found, or if the Authenticator is invalid, the FA MUST silently
   discard the GNAM message.  If the FA accepted this message, the FA
   MAY also process it based on the notification event.

   In the case of a FA-CoA and if the "MD" value is set to 2, if the FA
   received this message, and if the MN-FA AE is present, the MN-FA AE
   MUST be checked, and the FA MUST check the Authenticator value in the
   Extension.  If no MN-FA AE is found, or if more than one MN-FA AE is



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   found, or if the Authenticator is invalid, the FA MUST silently
   discard the GNAM message.  If FA accepted the MN's GNAM message, it
   MUST relay this message to the HA.  The FA MUST NOT modify any of the
   fields beginning with the fixed portion of the GNAM message through
   the including the MN-HA AE or other authentication extension supplied
   by the HA as an authorization-enabling extension for the MN.
   Furthermore, the FA MUST process and remove any Extensions following
   the MN-HA AE and MAY append any of its own non-authentication
   Extensions of relevance to the HA, if applicable, and MUST append the
   FA-HA AE, if the FA shares a mobility security association with the
   HA.

4.7.  Home Agent Consideration

   The HA MAY initiate a GNM message to both the mobile node and FA, and
   it also MAY receive a GNAM message from both the FA and MN.  The HA
   also MAY receive a GNM message from the FA, but only when there is a
   binding for a MN.  If the HA receives a GNM from a FA and there is no
   corresponding MN registration, the HA SHOULD drop the GNM message.

4.7.1.  Sending Generic Notification Messages

   In the case of a FA-CoA, the HA may either send a GNM to notify the
   FA, or have the FA relay the GNM to the MN if the MN needs to be
   notified.

   If the message is from the HA to the FA, the source address is the
   HA's address, and the destination address is the FA's address

   If the FA is working only as a relay agent, the "MD" value is set to
   0, and the ordering of the extension is: the notification extension,
   followed by any non-authentication extension expected to be used by
   MN, followed by MN-HA AE defined in Section 3.5.2 of [RFC3344],
   followed by any non-authentication Extensions used only by the FA,
   followed by The FA-HA AE defined in Section 3.5.4 of [RFC3344].
   Computing Authentication Extension Value is the same as Section 3.5.1
   of [RFC3344].

   If the FA is the target of this notification message, then the "MD"
   value is set to 1, and the ordering of the extension is: the
   notification extension, followed by any non-authentication Extensions
   used only by the FA, followed by The FA-HA AE defined in Section
   3.5.4 of [RFC3344].  Computing Authentication Extension Value is the
   same as Section 3.5.1 of [RFC3344].

   In the case of a Co-located CoA, the HA MAY send a notification
   message directly to the MN if it needs to be notified.  The "MD"
   value is set to 0, and the ordering of the extension is: the



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   notification extension, followed by any non-authentication extension
   expected to be used by MN, followed by MN-HA AE defined in Section
   3.5.2 of [RFC3344].

4.7.2.  Receiving Generic Notification Acknowledgement Messages

   In the case of a FA-CoA, if the HA receives this message, and the
   "MD" value is set to 2, it means that the GNAM message came from MN.

   If the "MD" value is set to 5, and the HA accepted this message, the
   HA MAY also process it based on the notification event.  The FA-HA AE
   MUST be checked, and the HA MUST check the Authenticator value in the
   Extension.  If no FA-HA AE is found, or if more than one FA-HA AE is
   found, or if the Authenticator is invalid, the HA MUST silently
   discard the GNAM message.

   If the "MD" value is set to 2, in the case of a FA-CoA, and if FA-HA
   AE is present, the FA-HA AE MUST be checked, and the HA MUST check
   the Authenticator value in the Extension.  If more than one FA-HA AE
   is found, or if the Authenticator is invalid, the HA MUST silently
   discard the GNAM message.  Anyway, MN-HA AE MUST be checked, and the
   HA MUST check the Authenticator value in the Extension.  If no MN-HA
   AE is found, or if more than one MN-HA AE is found, or if the
   Authenticator is invalid, the HA MUST silently discard the GNAM.  If
   the HA accepted this message, the HA MAY also process it based on the
   notification event.

   If the "MD" value is set to 2, in the case of a Co-located CoA, MN-HA
   AE MUST be checked, and the HA MUST check the Authenticator value in
   the Extension.  If no MN-HA AE is found, or if more than one MN-HA AE
   is found, or if the Authenticator is invalid, the HA MUST silently
   discard the GNAM.  If the HA accepted this message, the HA MAY also
   process it based on the notification event.

4.7.3.  Receiving Generic Notification Messages

   The HA MAY receive a GNM message sent from the FA.  When the HA
   receives this message, if the the "MD" value is set to 5, this
   message came from FA.  FA-HA AE MUST be checked, and the HA MUST
   check the Authenticator value in the Extension.  If no FA-HA AE is
   found, or if more than one FA-HA AE is found, or if the Authenticator
   is invalid, the HA MUST reject the GNM and MAY send a GNAM to the FA
   with Code 132, including an Identification field computed in
   accordance with the rules specified in Section 7.1.  The HA MUST do
   no further processing with such a notification, though it SHOULD log
   the error as a security exception.

   The HA MUST check that the Identification field is correct using the



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   context selected by the SPI within mandatory authentication extension
   like MN-HA AE or FA-HA AE.  See Section 7.1 for a description of how
   this is performed.  If incorrect, the HA MUST reject the GNM and MAY
   send a GNAM to the initiator with Code 133, including an
   Identification field computed in accordance with the rules specified
   in Section 7.1.  The HA MUST do no further processing with such a
   notification, though it SHOULD log the error as a security exception.
   If HA accepts the FA's GNM message, it will process it based on the
   notification extension.  Furthermore, the HA MAY reply with a GNAM
   message with Code 0 back to the FA based on the "A" flag in the GNM
   message.

   If the the "MD" value is set to 2, this message come from MN, in the
   case of FA-COA, if FA-HA AE is present, it MUST be checked, and the
   HA MUST check the Authenticator value in the Extension.  If more than
   one FA-HA AE Extension is found, or if the Authenticator is invalid,
   the HA MUST reject the GNM and MAY send a GNAM to the FA with Code
   132, including an Identification field computed in accordance with
   the rules specified in Section 7.1.  The HA MUST do no further
   processing with such a notification, though it SHOULD log the error
   as a security exception.  And MN-HA AE MUST be checked, and the HA
   MUST check the Authenticator value in the Extension.  If no MN-HA AE
   is found, or if more than one MN-HA AE is found, or if the
   Authenticator is invalid, the HA MUST reject the GNM and MAY send a
   GNAM to the MN with Code 131, including an Identification field
   computed in accordance with the rules specified in Section 7.1.  The
   HA MUST do no further processing with such a notification, though it
   SHOULD log the error as a security exception.  If HA accepts the MN's
   GNM message, it will process it based on the notification extension.
   Furthermore, the HA MAY reply with a GNAM message back to the MN with
   Code 0 based on the "A" flag in the GNM message.

   If the the "MD" value is set to 2, in the case of a Co-located CoA,
   the MN-HA AE MUST be checked, and the HA MUST check the Authenticator
   value in the Extension.  If no MN-HA AE is found, or if more than one
   MN-HA AE is found, or if the Authenticator is invalid, the HA MUST
   reject the GNM and MAY send a GNAM to the MN with Code 131, including
   an Identification field computed in accordance with the rules
   specified in Section 7.1.  The HA MUST do no further processing with
   such a notification, though it SHOULD log the error as a security
   exception.  If HA accepts the MN's GNM message, it will process it
   based on the notification extension.  Furthermore, the HA MAY reply
   with a GNAM message back to the MN with Code 0 based on the "A" flag
   in the GNM message.

   The HA MUST also check that the extensions present in the Generic
   Notification Message are permitted for use with the GNM.  If not, the
   HA MUST silently discard the message.  It MUST NOT do any further



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   processing with such a notification, though it SHOULD log the error.

4.7.4.  Sending Generic Notification Acknowledgement Messages

   If the GNM message came from the FA only, and if the "A" flag is set
   in the GNM message, then the HA MUST send a GNAM message.  The
   message is as follows: The source address is HA's address, the
   destination address is the FA's address, the "MD" value is set to 1.
   The ordering of the extension is: any non-authentication Extensions
   used only by the FA, followed by The Foreign-Home Authentication
   extension defined in Section 3.5.4 of [RFC3344].

   The Code field of the GNAM is chosen in accordance with the rules
   specified in Section 4.2.  When replying to an accepted GNM, a MN
   SHOULD respond with Code 0.

   If the GNM message came from the MN, and if the "A" flag is set in
   the GNM message, then the HA MUST send a GNAM message.  The message
   is as follows: The source address is HA's address, the destination
   address is the FA's address, the "MD" value is set to 0.  The
   ordering of the extension is: any non-authentication Extensions used
   only by the MN, followed by the MN-HA AE defined in Section 3.5.2 of
   [RFC3344], optionally followed by any non-authentication Extensions
   used only by the FA, optionally followed by The MN-FA AE defined in
   Section 3.5.3 of [RFC3344]


























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5.  Future Extensibility

   This document defines the Generic Notification Message used with the
   Message String Extension [RFC4917].

   It is however possible to define new notification-related extensions
   for use with the Generic Notification Message, for cases where the
   notification is intended to have a semantic content and is intended
   for the HA, FA or MN, rather than for the user.

5.1.  Examples of Possible Extensions

   One example of such usage, which would have been defined in this
   document if it hadn't already been defined as a separate message is
   the Registration Revocation Message [RFC3543].  This is a message
   sent from the HA to FA(s) or MN to notify the receiving node that a
   currently active registration is being revoked.  The use case for
   this is clearly laid out in [RFC3543].

   Another example would be managed maintenance switch-over between HA
   instances, where a HA due to go down for maintenance could direct the
   MNs registered with it to re-register with another specified HA.
   Such a message could also be used for managed load balancing.  There
   is currently no support for such forced switch-over in the Mobile
   IPv4 protocol.

   Yet another example is when the prefix set handled by an MIPv4 NEMO
   [RFC5177] HA changes; to ensure proper routing, the mobile router
   needs to be notified about the change so that its internal routing
   rules may be updated.

   One final example is home network changes which require host
   configuration changes, for instance a change of address for the DNS
   server or another network server; again this is a case where the HA
   would want to notify the MN of the change, so that service
   interruptions can be avoided.

5.2.  Extension Specification

   In order to avoid making the MIPv4 Generic Notification Message a
   generic protocol extension mechanism by which new protocol mechanisms
   could be implemented without appropriate discussion and approval, any
   new extensions which are to be used with the Generic Notification
   Message must be registered with IANA, where registration is limited
   by the 'RFC Required' policy defined in [RFC5226]

   If additional extensions are specified for use with the Generic
   Notification Message, the practice exemplified in [RFC3344] and



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   related specification should be followed.  Generally it has not been
   necessary so far to provide versioning support within individual
   extensions; in a few cases it has been necessary to define new
   extensions with new extension numbers where a generalizations of a
   pre-existing extension has been needed, and with the current rate of
   extension number consumption that seems to be an acceptable approach.

   If at some point extensions are specified for use with the Generic
   Notification Message which overlap pre-existing notification
   messages, the authors of the specification should consider providing
   a method to flag which notification messages are supported, and which
   notification message usage is requested, in a manner similar to the
   way tunnelling method capabilities and usage requests are flagged in
   the Mobile IPv4 Base Specification [RFC3344].

   Encoded in the extension number of Mobile IPv4 extensions is the
   notion of 'skippable' and 'not skippable' extensions; see Section 1.8
   of [RFC3344].  This notion is also applicable when extensions are
   used with the Generic Notification Message: It is not required that a
   receiver understand a skippable extension, but a non-skippable
   extension needs to be handled according to Section 1.8 of [RFC3344]
   (i.e., the message must be silently discarded if the extension is not
   recognized).  This document does not specify any change from the
   Mobile IPv4 Base Specification [RFC3344] in this respect.



























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6.  IANA Considerations

   This document defines two new messages, the Generic Notification
   Message described in Section 4.1, and the Generic Notification
   Acknowledgement Message, described in Section 4.2.  The message
   numbers for these two message numbers are to be allocated from the
   same number space used by the Registration Request and Registration
   Reply messages in [RFC3344].

   The Generic Notification Message may only carry extensions which are
   explicitly permitted for use with this message.  This document
   defines 4 extensions which are permitted, in Section 4.1.  IANA must
   establish a register of Mobile IPv4 extensions which are permitted
   for use with the Generic Notification Message.  Approval of new
   extensions which are permitted for use with the Generic Notification
   Message requires that they be defined in an RFC according to the 'RFC
   Required' policy described in [RFC5226].

   The Generic Notification Acknowledgement message, specified in
   Section 4.2, has a Code field.  The number space for the Code field
   values is new, and also specified in Section 4.2.  The Code number
   space is structured according to whether the notification was
   successful, or whether the HA denied the notification, or whether FA
   denied the notification, or whether MN denied the notification, as
   follows:

             0       Success Code
             64-69   Error Codes from the FA
             128-133 Error Codes from the HA
             192-197 Error Codes from the MN

   Approval of new Code values require expert review.



















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7.  Security Considerations

   This specification operates with the security constraints and
   requirements of [RFC3344].  This means that when these message is
   transmitted between the MN and the HA, MN-HA AE is REQUIRED, when
   this message is transmitted between the MN and the FA, MN-FA AE is
   REQUIRED, when this message is transmitted between the FA and the HA,
   FA-HA AE is REQUIRED.  It extends the operations of MN, HA and FA
   defined in [RFC3344] to notify each other about some events.  The GNM
   message defined in the specification could carry information that
   modifies the mobility bindings.  Therefore the message MUST be
   integrity protected.  Replay protection MUST also be guaranteed.

   RFC 3344 provides replay protection only for registration requests
   sent by the MN.  There is no mechanism for replay protection for
   messages initiated by a FA or a HA.  The 64-bit Identification field
   specified in this document (Section 4.1 and 4.2) for the GNM message
   is used to provide replay protection for the notification messages
   initiated by the FA or HA.

7.1.  Replay Protection for GNM, GNAM messages

   The Identification field is used to let the receiving node verify
   that a GNM has been freshly generated by the sending node, not
   replayed by an attacker from some previous registration.  Two methods
   are described in this section: timestamps (REQUIRED) and "nonces"
   (OPTIONAL).  All senders and receivers MUST implement timestamp-based
   replay protection.  These nodes MAY also implement nonce-based replay
   protection

   The style of replay protection in effect between any two peer nodes
   among MN, FA and HA is part of the mobile security association.  A
   sending node and its receiving node MUST agree on which method of
   replay protection will be used.  The interpretation of the
   Identification field depends on the method of replay protection as
   described in the subsequent subsections.

   Whatever method is used, the low-order 32 bits of the Identification
   MUST be copied unchanged from the GNM to the GNAM.  The receiver uses
   those bits (and the sender's source address) to match GNAM with
   corresponding replies.  The receiver MUST verify that the low-order
   32 bits of any GNAM are identical to the bits it sent in the GNM.

   The Identification in a new GNM MUST NOT be the same as in an
   immediately preceding GNM, and SHOULD NOT repeat while the same
   security context is being used between the MN and the HA.





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7.1.1.  Replay Protection using Timestamps

   The basic principle of timestamp replay protection is that the node
   generating a message inserts the current time of day, and the node
   receiving the message checks that this timestamp is sufficiently
   close to its own time of day.  Unless specified differently in the
   security association between the nodes, a default value of 7 seconds
   MAY be used to limit the time difference.  This value SHOULD be
   greater than 3 seconds.  Obviously the two nodes must have adequately
   synchronized time-of-day clocks.  As with any messages, time
   synchronization messages may be protected against tampering by an
   authentication mechanism determined by the security context between
   the two nodes.

   In this document, the timestamps are used, the sender MUST set the
   Identification field to a 64-bit value formatted as specified by the
   Network Time Protocol (NTP) [RFC5905].  The low-order 32 bits of the
   NTP format represent fractional seconds .  Note, however, that when
   using timestamps, the 64-bit Identification used in a GNM message
   from the sender MUST be greater than that used in any previous GNM
   message, as the receiver uses this field also as a sequence number.
   Without such a sequence number, it would be possible for a delayed
   duplicate of an earlier GNM message to arrive at the receiver (within
   the clock synchronization required by the receiver), and thus be
   applied out of order, mistakenly altering the sender's current
   status.

   Upon receipt of a GNM message with an authorization-enabling
   extension, the receiver MUST check the Identification field for
   validity.  In order to be valid, the timestamp contained in the
   Identification field MUST be close enough to the receiver's time of
   day clock and the timestamp MUST be greater than all previously
   accepted timestamps for the requesting sender.  Time tolerances and
   re-synchronization details are specific to a particular mobility
   security association.

   If the timestamp is valid, the receiver copies the entire
   Identification field into the GNAM it returns the GNAM message to the
   sender.  If the timestamp is not valid, the receiver copies only the
   low-order 32 bits into the GNAM, and supplies the high-order 32 bits
   from its own time of day.  In this latter case, the receiver MUST
   reject the registration by returning Code 69/133/197 (identification
   mismatch) in the GNAM message.

   Furthermore, the receiver MUST verify that the low-order 32 bits of
   the Identification in the GNAM are identical to those in the rejected
   GNM attempt, before using the high-order bits for clock re-
   synchronization.



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7.1.2.  Replay Protection using Nonces

   The basic principle of nonce replay protection is that node A
   includes a new random number in every message to node B, and checks
   that node B returns that same number in its next message to node A.
   Both messages use an authentication code to protect against
   alteration by an attacker.  At the same time node B can send its own
   nonces in all messages to node A (to be echoed by node A), so that it
   too can verify that it is receiving fresh messages.

   The receiver may be expected to have resources for computing pseudo-
   random numbers useful as nonces, according to [RFC4086].  It inserts
   a new nonce as the high-order 32 bits of the identification field of
   every GNAM message.  The receiver copies the low-order 32 bits of the
   Identification from the GNM message into the low-order 32 bits of the
   Identification in the GNAM message.  When the sender receives an
   authenticated GNAM message from the receiver, it saves the high-order
   32 bits of the identification for use as the high-order 32 bits of
   its next GNM message.

   The sender is responsible for generating the low-order 32 bits of the
   Identification in each GNM message.  Ideally it should generate its
   own random nonces.  However it may use any expedient method,
   including duplication of the random value sent by the receiver.  The
   method chosen is of concern only to the sender , because it is the
   node that checks for valid values in the GNAM message.  The high-
   order and low-order 32 bits of the identification chosen SHOULD both
   differ from their previous values.  The receiver uses a new high-
   order value and the sender uses a new low-order value for each
   registration message.

   If a GNM message is rejected because of an invalid nonce, the GNAM
   always provides the sender with a new nonce to be used in the next
   registration.  Thus the nonce protocol is self- synchronizing.

7.2.  Non-authentication Extensions Handling in Foreign Agent

   When the FA is relaying the GNM message between the MN and the HA,
   and if the FA does not share a mobility security association with the
   MN or HA, all non-authentication extensions between MN and FA, or FA
   and HA are not protected; In this case, all non-authentication
   extensions should be silently discarded.









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8.  Acknowledgments

   The author appreciate the efforts of Ahmad Muhanna for his detail
   reviewing of this document and his many contributions to the text of
   this document.  The author also wants to thank Kent Leung, Peng Yang
   and Peter McCann et al. for their helping developing this document.
   Thanks to Alexey Melnikov, Sean Turner, Ralph Droms, Charles E.
   Perkins, Russ Housley, Magnus Westerlund, Lars Eggert, Dan Romascanu,
   Tim Polk, Amanda Baber, Sebastian Thalanany, and Joseph Salowey's
   discussion and comments.  Thanks to Jari Arkko for each step of this
   document.








































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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3344]  Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
              August 2002.

   [RFC3543]  Glass, S. and M. Chandra, "Registration Revocation in
              Mobile IPv4", RFC 3543, August 2003.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4917]  Sastry, V., Leung, K., and A. Patel, "Mobile IPv4 Message
              String Extension", RFC 4917, June 2007.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

9.2.  Informative References

   [RFC5177]  Leung, K., Dommety, G., Narayanan, V., and A. Petrescu,
              "Network Mobility (NEMO) Extensions for Mobile IPv4",
              RFC 5177, April 2008.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.



















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Authors' Addresses

   Hui Deng
   China Mobile
   53A,Xibianmennei Ave.,
   Xuanwu District,
   Beijing  100053
   China

   Email: denghui02@gmail.com


   Henrik Levkowetz
   Netnod
   Franzengatan 5
   S-104 25, Stockholm
   SWEDEN

   Email: henrik@levkowetz.com


   Vijay Devarapalli
   WiChorus
   3590 North First St
   San Jose, CA
   USA

   Email: dvijay@gmail.com


   Sri Gundavelli
   Cisco Systems
   170 W.Tasman Drive
   San Jose, CA  95134
   USA

   Email: sgundave@cisco.com


   Brian Haley
   Hewlett-Packard Company
   110 Spitbrook Road
   Nashua, NH  03062
   USA

   Email: brian.haley@hp.com





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