GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc6098

Internet Engineering Task Force (IETF) H. Deng Request for Comments: 6098 China Mobile Category: Standards Track H. Levkowetz ISSN: 2070-1721 Netnod

                                                        V. Devarapalli
                                                       Vasona Networks
                                                         S. Gundavelli
                                                                 Cisco
                                                              B. Haley
                                               Hewlett-Packard Company
                                                            April 2012
            Generic Notification Message for Mobile IPv4

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 is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6098.

Copyright Notice

 Copyright (c) 2012 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
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must

Deng, et al. Standards Track [Page 1] RFC 6098 MIP4 Generic Notification Message April 2012

 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.

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................4
 3. Notification Message - Usage Scenarios ..........................4
    3.1. Notification Message - Examples ............................4
    3.2. Notification Message - Topology ............................5
         3.2.1. Notification Message between a Home Agent
                and a Mobile Node ...................................6
         3.2.2. Notification Message between a Foreign Agent
                and a Mobile Node ...................................6
         3.2.3. Notification Message between a Home Agent
                and a Foreign Agent .................................7
 4. Generic Notification Message and Considerations .................7
    4.1. Generic Notification Message ...............................7
    4.2. Generic Notification Acknowledgement Message ..............11
    4.3. Notification Retransmission ...............................14
    4.4. General Implementation Considerations .....................15
    4.5. Mobile Node Considerations ................................15
         4.5.1. Receiving Generic Notification Messages ............15
         4.5.2. Sending Generic Notification
                Acknowledgement Messages ...........................16
         4.5.3. Sending Generic Notification Messages ..............17
         4.5.4. Receiving Generic Notification
                Acknowledgement Messages ...........................18
    4.6. Foreign Agent Consideration ...............................18
         4.6.1. Receiving Generic Notification Messages ............19
         4.6.2. Sending Generic Notification
                Acknowledgement Messages ...........................21
         4.6.3. Sending Generic Notification Messages ..............21
         4.6.4. Receiving Generic Notification
                Acknowledgement Messages ...........................22

Deng, et al. Standards Track [Page 2] RFC 6098 MIP4 Generic Notification Message April 2012

    4.7. Home Agent Consideration ..................................23
         4.7.1. Sending Generic Notification Messages ..............23
         4.7.2. Receiving Generic Notification
                Acknowledgement Messages ...........................24
         4.7.3. Receiving Generic Notification Messages ............24
         4.7.4. Sending Generic Notification
                Acknowledgement Messages ...........................26
 5. Future Extensibility ...........................................26
    5.1. Examples of Possible Extensions ...........................26
    5.2. Extension Specification ...................................27
 6. IANA Considerations ............................................28
 7. Security Considerations ........................................28
    7.1. Replay Protection for GNMs and GNAMs ......................29
         7.1.1. Replay Protection Using Timestamps .................29
         7.1.2. Replay Protection Using Nonces .....................30
    7.2. Non-Authentication Extensions Handling in the
         Foreign Agent .............................................31
 8. Acknowledgements ...............................................31
 9. References .....................................................32
    9.1. Normative References ......................................32
    9.2. Informative References ....................................32

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.  In this context, 'Asynchronous messages' is used to mean
 messages that are not synchronous with the Registration Request and
 Registration Reply messages of the base Mobile IP (MIP) specification
 [RFC5944].  The base Mobile IP specification does not have a
 provision for this.
 In order to rectify that, this document defines a generic
 notification 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 make it possible to ensure
 reliable delivery of notifications.  Only the following extensions
 may be present in these new messages, as defined by this document:
  1. MN-HA Authentication Extension
  1. MN-FA Authentication Extension
  1. FA-HA Authentication Extension
  1. Message String Extension

Deng, et al. Standards Track [Page 3] RFC 6098 MIP4 Generic Notification Message April 2012

 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.

2. Terminology

 It is assumed that the reader is familiar with the terminology used
 in [RFC4917] and [RFC5944].  In addition, this document frequently
 uses the following terms:
 Notification Message
    A message from a mobility agent to a an MN or other mobility
    agent, or from an MN to a 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].

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 that 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 are messages
 from operator to user about billing- or service-related events ("You
 have used nearly all of your prepaid quota; there are only XX MB left
 -- please purchase further service if you are going to need it."; or

Deng, et al. Standards Track [Page 4] RFC 6098 MIP4 Generic Notification Message April 2012

 "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 (Packet Data Serving Node) 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:
 o  HA switch-over (before the HA decides to go off-line, it would
    like to notify the MNs to register with another candidate HA),
 o  Network Mobility (NEMO) prefix changes (an MN is notified by the
    HA about NEMO prefix changes and service- or billing-related
    events; this is an operational requirement),
 o  load balancing (the HA wants to move some of the registered MNs to
    other HAs),
 o  service termination (due to end of prepaid time), and
 o  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.

Deng, et al. Standards Track [Page 5] RFC 6098 MIP4 Generic Notification Message April 2012

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, and 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 Care-of Address (CoA) mode with registration
 through an 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 an FA may send notification messages to an
 MN -- one where it is relaying a message, the other where the
 notification is triggered by a message from another network entity,
 for example, an Authentication, Authorization, and Accounting (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 an FA, the FA may
 also need to notify the HA about the event.

Deng, et al. Standards Track [Page 6] RFC 6098 MIP4 Generic Notification Message April 2012

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

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:
  1. the IP source address of the Registration Request/Reply
  1. the IP destination address of the Registration Request/Reply
  1. the UDP source port of the Registration Request/Reply
  1. the UDP destination port of the Registration Request/Reply
 The sending node always sends the GNM following the same procedure
 for sending a Registration Request as in Section 3.3 of [RFC5944],
 and the receiving node follows the same procedure for Registration
 Reply as in Section 3.4 of [RFC5944] when sending GNAM.

4.1. Generic Notification Message

 A GNM is sent by a mobility agent to inform another mobility agent,
 or an MN, of MIP-related information in the form of a Message String
 Extension [RFC4917].  These messages MUST use the same IP and UDP

Deng, et al. Standards Track [Page 7] RFC 6098 MIP4 Generic Notification Message April 2012

 headers as any previous Registration Request (RRQ) or Reply (RRP)
 message to the same entity.  This would support NAT traversal and
 ensure the 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:
 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.

Deng, et al. Standards Track [Page 8] RFC 6098 MIP4 Generic Notification Message April 2012

 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 22
 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
 A
    This bit indicates whether the notification message MUST be
    acknowledged by the recipient.  If the "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.

Deng, et al. Standards Track [Page 9] RFC 6098 MIP4 Generic Notification Message April 2012

    Set to "0" to indicate that acknowledgement is OPTIONAL.
 Reserved
    MUST be sent as 0, and ignored when received.
 Home Address
    The home 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 Sections 7.1.1 and 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
    that may be used with this message, and by one or more
    authentication extensions as defined in Section 3.5 of [RFC5944].
    Apart from the Authentication Extensions mentioned below, only one
    extension is defined in this document as permitted for use with
    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 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 3.8.3.3 of [RFC5944] 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.

Deng, et al. Standards Track [Page 10] RFC 6098 MIP4 Generic Notification Message April 2012

4.2. Generic Notification Acknowledgement 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:
  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...
 +-+-+-+-+-+-+-+-+-+-+-+-+-

Deng, et al. Standards Track [Page 11] RFC 6098 MIP4 Generic Notification Message April 2012

 Type 23
 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
    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

Deng, et al. Standards Track [Page 12] RFC 6098 MIP4 Generic Notification Message April 2012

    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 address of the mobile node.
 Home Agent Address
    The IP address of the sender's home agent.
 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 the GNM with the GNAM and for
    protecting against replay attacks of notification messages.  See
    Sections 7.1.1 and 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 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 the Security Parameter
    Index (SPI) value in the authorization-enabling extension).

Deng, et al. Standards Track [Page 13] RFC 6098 MIP4 Generic Notification Message April 2012

 Extensions
    The fixed portion of the GNAM is followed by one or more
    extensions that may be used with this message, and by one or more
    authentication extensions as defined in Section 3.5 of [RFC5944].
    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 3.8.3.3 of [RFC5944] 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 the "A" flag has been set during the GNM, but the sender doesn't
 receive any GNAM within a reasonable time, then the GNM SHOULD be
 retransmitted.  When timestamps are used, a new notification
 Identification is chosen for each retransmission; thus, it counts as
 a new GNM.  When nonces are used, the unanswered GNM 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 (rather than its GNAM) was lost
 by the network.
 The maximum time until a new GNM is sent SHOULD be no greater than
 the requested Lifetime of the last GNM.  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 GNMs 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.

Deng, et al. Standards Track [Page 14] RFC 6098 MIP4 Generic Notification Message April 2012

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:
 o  List the notification messages supported.
 o  Show enabled/disabled status for notification message support,
    overall and in detail.
 o  Show the value of the maximum and minimum retransmission times.
 o  Enable and disable notification support entirely.
 o  Enable and disable the individual notification messages supported.
 o  Set the values 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 an 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.

4.5.1. Receiving Generic Notification Messages

 When the MN is using an 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.  If the MN is using a co-located CoA and receives a notification
 message, the "MD" value will be 0, indicating that the notification
 message came from the HA.
 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 an FA, then an 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.

Deng, et al. Standards Track [Page 15] RFC 6098 MIP4 Generic Notification Message April 2012

 If this notification message came from the HA, relayed by the FA, or
 if the MN is using 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.
 The MN MUST check that the Identification field is correct using the
 context selected by the SPI within a mandatory authentication
 extension like the 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.
 If the MN accepts a GNM, then it will process it according to the
 specific rules for the extensions.  After that, the MN MAY reply to
 the originator with a GNAM with Code 0 based on the "A" flag in the
 GNM.

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 the 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 [RFC5944].
 In the case of an 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,
 an MN SHOULD respond with Code 0.

Deng, et al. Standards Track [Page 16] RFC 6098 MIP4 Generic Notification Message April 2012

 There are a number of reasons why the MN might reject a notification,
 such as for example not being permitted to receive notifications,
 which could be for a number of reasons, causing the return of a GNAM
 with Code value 193 (administratively prohibited); or being unable to
 act on or display the notification, or otherwise being resource
 constrained, causing the use of Code value 194 (insufficient
 resources); or other reasons for which no other specific Code value
 is available, which would cause the use of Code value 192 (reason
 unspecified).
 If the GNM was initiated from the HA to the MN ("MD" value is set to
 0) and in the case of a co-located CoA, then the 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 [RFC5944].
 When replying to a GNM from an HA to an MN with an FA-CoA, the source
 address is the MN's home 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 intended for the HA, followed
 by the MN-HA AE defined in Section 3.5.2 of [RFC5944], followed by
 any non-authentication Extensions intended for the FA, followed by
 the MN-FA AE defined in Section 3.5.3 of [RFC5944].

4.5.3. Sending Generic Notification Messages

 The MN may send a GNM to notify either 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, and the MN-FA AE MUST be the last extension in
 order to protect all other non-authentication extensions.  Computing
 the Authentication Extension Values is done in the same manner as in
 Section 3.5.1 of [RFC5944].
 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 the MN-HA AE defined in Section 3.5.2 of
 [RFC5944], followed by any non-authentication Extensions intended for
 the FA, followed by the MN-FA AE defined in Section 3.5.3 of
 [RFC5944].  Computing the Authentication Extension Values is done in
 the same manner as in Section 3.5.1 of [RFC5944].
 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

Deng, et al. Standards Track [Page 17] RFC 6098 MIP4 Generic Notification Message April 2012

 notification extension, followed by any non-authentication extension
 expected to be used by HA, followed by the MN-HA AE defined in
 Section 3.5.2 of [RFC5944].
 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 an FA-CoA, if the MN receives this message, and the
 "MD" value is set to 0, it means that the GNAM came from the 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,
 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 GNMs and GNAMs between the MN and its HA as long as there
 is an active binding for the MN at the FA.

Deng, et al. Standards Track [Page 18] RFC 6098 MIP4 Generic Notification Message April 2012

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, the FA SHOULD relay
 the GNM to the MN's home address as specified in the Home Address
 field of the GNM, and the 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, the 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 that are relevant 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 the mandatory FA-HA AE.  See
 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.

Deng, et al. Standards Track [Page 19] RFC 6098 MIP4 Generic Notification Message April 2012

 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 the FA accepts the HA's GNM, it will process it based on the
 specific rules for the extensions it contains.  The FA MAY then reply
 to the HA with a GNAM with Code 0 based on the "A" flag in the GNM.
 In the case of an 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.  If the MN-FA is valid, the FA MUST relay the GNM to
 the HA's address as specified in the Home Agent Address field of the
 GNM.  The 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.  Also, it 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, as described
 in Section 3.7.2.1 of [RFC5944].  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
 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.

Deng, et al. Standards Track [Page 20] RFC 6098 MIP4 Generic Notification Message April 2012

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

4.6.2. Sending Generic Notification Acknowledgement Messages

 The FA may need either to relay a GNAM between the MN and the HA or
 to send one as a response to a GNM that was sent to it.  In both
 cases, the GNAM is defined as follows.
 The source address is the FA address, and the destination address is
 the 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,
 an FA SHOULD respond with Code 0.
 The FA might reject a notification by returning a GNAM with the Code
 value 65 (administratively prohibited), which could be for a number
 of reasons; 64 (reason unspecified); or 66 (insufficient resources).
 If the FA is relaying this message to only the HA, the FA MUST NOT
 modify any of the fields beginning with the fixed portion of the GNAM
 up through and 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 that are relevant 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 intended for the FA, followed by the FA-HA
 AE defined in Section 3.5.4 of [RFC5944].
 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 intended for the FA, followed by the MN-FA
 AE defined in Section 3.5.3 of [RFC5944].

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.

Deng, et al. Standards Track [Page 21] RFC 6098 MIP4 Generic Notification Message April 2012

 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 intended for the MN,
 followed by the MN-FA AE defined in Section 3.5.3 of [RFC5944].
 Computing the Authentication Extension Values is done in the same
 manner as in Section 3.5.1 of [RFC5944] except the payload is the
 notification rather than the 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 intended for the HA,
 followed by the FA-HA AE defined in Section 3.5.4 of [RFC5944].
 Computing the Authentication Extension Value is done in the same
 manner as described in Section 3.5.1 of [RFC5944], except that the
 payload is the notification instead of the registration.

4.6.4. Receiving Generic Notification Acknowledgement Messages

 In the case of an FA-CoA, if the FA receives this message, and the
 "MD" value is set to 2, it means that the notification
 acknowledgement message is from the MN to the HA; if the "MD" value
 is set to 3, the message is from the MN to the FA; 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, and if the MN-FA AE is present, the 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 GNAM.  If the FA accepted this message, the FA MAY also
 process it based on the notification event.
 In the case of an 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 GNAM.  If the FA accepted the MN's GNAM, 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 up through and including

Deng, et al. Standards Track [Page 22] RFC 6098 MIP4 Generic Notification Message April 2012

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

4.7.1. Sending Generic Notification Messages

 In the case of an 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 the MN-HA AE defined in Section 3.5.2 of [RFC5944],
 followed by any non-authentication extensions intended for the FA,
 followed by the FA-HA AE defined in Section 3.5.4 of [RFC5944].
 Computing the Authentication Extension Value is done in the same
 manner as in Section 3.5.1 of [RFC5944].
 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
 intended for the FA, followed by the FA-HA AE defined in Section
 3.5.4 of [RFC5944].  Computing the Authentication Extension Values is
 done in the same manner as in Section 3.5.1 of [RFC5944].
 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
 notification extension, followed by any non-authentication extension
 expected to be used by the MN, followed by the MN-HA AE defined in
 Section 3.5.2 of [RFC5944].

Deng, et al. Standards Track [Page 23] RFC 6098 MIP4 Generic Notification Message April 2012

4.7.2. Receiving Generic Notification Acknowledgement Messages

 In the case of an FA-CoA, if the HA receives this message, and the
 "MD" value is set to 2, it means that the GNAM came from the 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.
 If the "MD" value is set to 2, in the case of an FA-CoA, and if the
 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.  No matter what, 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 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, 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
 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 sent from the FA.  When the HA receives this
 message, if the "MD" value is set to 5, this message came from FA.
 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
 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
 context selected by the SPI within a 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,

Deng, et al. Standards Track [Page 24] RFC 6098 MIP4 Generic Notification Message April 2012

 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 the HA accepts the FA's GNM, it will process
 it based on the notification extension.  Furthermore, the HA MAY
 reply to the FA with a GNAM with Code 0 based on the "A" flag in the
 GNM.
 If the "MD" value is set to 2, this message comes from the 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.  Also, 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 the HA accepts the MN's GNM, it will process it based on the
 notification extension.  Furthermore, the HA MAY reply to the MN with
 a GNAM back with Code 0 based on the "A" flag in the GNM.
 If 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 the HA accepts the MN's GNM, it will process it based
 on the notification extension.  Furthermore, the HA MAY reply to the
 MN with a GNAM with Code 0 based on the "A" flag in the GNM.
 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
 processing with such a notification, though it SHOULD log the error.

Deng, et al. Standards Track [Page 25] RFC 6098 MIP4 Generic Notification Message April 2012

4.7.4. Sending Generic Notification Acknowledgement Messages

 If the GNM came from the FA only, and if the "A" flag is set in the
 GNM, then the HA MUST send a GNAM.  The message is as follows: The
 source address is the HA's address, the destination address is the
 FA's address, and the "MD" value is set to 1.  The ordering of the
 extension is: any non-authentication Extensions intended for the FA,
 followed by the Foreign-Home Authentication extension defined in
 Section 3.5.4 of [RFC5944].
 The Code field of the GNAM is chosen in accordance with the rules
 specified in Section 4.2.  When replying to an accepted GNM, an MN
 SHOULD respond with Code 0.
 If the GNM came from the MN, and if the "A" flag is set in the GNM,
 then the HA MUST send a GNAM.  The message is as follows: The source
 address is the HA's address, the destination address is the FA's
 address, and the "MD" value is set to 0.  The ordering of the
 extension is: any non-authentication extensions intended for the MN,
 followed by the MN-HA AE defined in Section 3.5.2 of [RFC5944],
 optionally followed by any non-authentication extensions intended for
 the FA, optionally followed by the MN-FA AE defined in Section 3.5.3
 of [RFC5944].

5. Future Extensibility

 This document defines the Generic Notification Message used with the
 Message String Extension [RFC4917].
 However, it is 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 the 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 an HA due to go down for maintenance could direct
 the MNs registered with it to re-register with another specified HA.

Deng, et al. Standards Track [Page 26] RFC 6098 MIP4 Generic Notification Message April 2012

 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 that 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 that 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 [RFC5944] and
 related specifications 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 generalization of a
 pre-existing extension has been needed.  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 that overlap with 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 tunneling method capabilities and usage requests are flagged in
 the Mobile IPv4 base specification [RFC5944].
 Encoded in the extension number of Mobile IPv4 extensions is the
 notion of 'skippable' and 'not skippable' extensions; see Section 1.8
 of [RFC5944].  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 [RFC5944]

Deng, et al. Standards Track [Page 27] RFC 6098 MIP4 Generic Notification Message April 2012

 (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 [RFC5944] in this respect.

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 messages have been allocated from the same
 number space used by the Registration Request and Registration Reply
 messages in [RFC5944].
 The Generic Notification Message may only carry extensions that are
 explicitly permitted for use with this message.  Section 4.1 of this
 document defines 4 extensions that are permitted.  IANA has added a
 column to the registry of Mobile IPv4 extensions, which will indicate
 for each extension if it is permitted for use with the Generic
 Notification Message.  Approval of new extensions that 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, the HA denied the notification, the FA denied the
 notification, or the 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 requires expert review.

7. Security Considerations

 This specification operates with the security constraints and
 requirements of [RFC5944].  This means that when this message is
 transmitted between the MN and the HA, the MN-HA AE is REQUIRED; when
 this message is transmitted between the MN and the FA, the MN-FA AE
 is REQUIRED; when this message is transmitted between the FA and the
 HA, the FA-HA AE is REQUIRED.  It extends the operations of the MN,
 HA, and FA defined in [RFC5944] to notify each other about some
 events.  The GNM defined in this specification could carry

Deng, et al. Standards Track [Page 28] RFC 6098 MIP4 Generic Notification Message April 2012

 information that modifies the mobility bindings.  Therefore, the
 message MUST be integrity protected.  Replay protection MUST also be
 guaranteed.
 RFC 5944 provides replay protection only for Registration Requests
 sent by the MN.  There is no mechanism for replay protection for
 messages initiated by an FA or HA.  The 64-bit Identification field
 specified in this document (Sections 4.1 and 4.2) for the GNM is used
 to provide replay protection for the notification messages initiated
 by the FA or HA.

7.1. Replay Protection for GNMs and GNAMs

 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 notification.  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 the 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
 field MUST be copied unchanged from the GNM to the GNAM.  The
 receiver uses those bits (and the sender's source address) to match
 the GNAM with corresponding replies.  The receiver MUST verify that
 the low-order 32 bits of any GNAM Identification field 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.

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

Deng, et al. Standards Track [Page 29] RFC 6098 MIP4 Generic Notification Message April 2012

 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, and 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 from
 the sender MUST be greater than that used in any previous GNM, 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 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 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, and it returns the GNAM 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 notification by returning Code 69, 133, or 197
 (notification Identification mismatch) in the GNAM.
 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.

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.

Deng, et al. Standards Track [Page 30] RFC 6098 MIP4 Generic Notification Message April 2012

 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.  The receiver copies the low-order 32 bits of the
 Identification field from the GNM into the low-order 32 bits of the
 Identification field in the GNAM.  When the sender receives an
 authenticated GNAM from the receiver, it saves the high-order 32 bits
 of the Identification field for use as the high-order 32 bits of its
 next GNM.
 The sender is responsible for generating the low-order 32 bits of the
 Identification field in each GNM.  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.  The high-order and low-
 order 32 bits of the Identification chosen SHOULD both differ from
 their previous values.  For each notification message, the receiver
 uses a new high-order value and the sender uses a new low-order
 value.
 If a GNM is rejected because of an invalid nonce, the GNAM always
 provides the sender with a new nonce to be used in the next message.
 Thus, the nonce protocol is self-synchronizing.

7.2. Non-Authentication Extensions Handling in the Foreign Agent

 When the FA is relaying a GNM 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 the MN and FA, or FA and
 HA, are not protected.  In this case, all non-authentication
 extensions should be silently discarded.

8. Acknowledgements

 The authors appreciate the efforts of Ahmad Muhanna for his detailed
 review of and his many contributions to the text of this document.
 The author also wants to thank Kent Leung, Peng Yang, 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 for their discussion
 and comments.  Thanks to Jari Arkko for help at each step of this
 document's development.

Deng, et al. Standards Track [Page 31] RFC 6098 MIP4 Generic Notification Message April 2012

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.
 [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.
 [RFC5944]  Perkins, C., "IP Mobility Support for IPv4, Revised",
            RFC 5944, November 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.

Deng, et al. Standards Track [Page 32] RFC 6098 MIP4 Generic Notification Message April 2012

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
 Vasona Networks
 2900 Lakeside Drive
 Santa Clara, CA  95054
 USA
 EMail: dvijay@gmail.com
 Sri Gundavelli
 Cisco
 170 W.Tasman Drive
 San Jose, CA  95134
 USA
 EMail: sgundave@cisco.com
 Brian Haley
 Hewlett-Packard Company
 165 Dascomb Road
 Andover, MA  01810
 USA
 EMail: brian.haley@hp.com

Deng, et al. Standards Track [Page 33]

/data/webs/external/dokuwiki/data/pages/rfc/rfc6098.txt · Last modified: 2012/04/13 17:35 (external edit)