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MEXT Working Group                                  R. Wakikawa (Editor)
Internet-Draft                                           Toyota ITC USA.
Intended status: Standards Track                            May 10, 2011
Expires: November 11, 2011


                 Home Agent Reliability Protocol (HARP)
                  draft-ietf-mip6-hareliability-09.txt

Abstract

   The home agent can be a single point of failure when Mobile IPv6 and
   its associated supporting protocols are operated in a system.  It is
   critical to provide home agent reliability in the event of a home
   agent crashing or becoming unavailable.  This would allow another
   home agent to take over and continue providing service to the mobile
   nodes.  This document describes the problem scope briefly, and
   provides mechanisms of home agent failure detection, home agent state
   transfer, and home agent switching for home agent redundancy and
   reliability.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 11, 2011.

Copyright Notice

   Copyright (c) 2011 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



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   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Problem Statement and Requirements . . . . . . . . . . . .  6

   2.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  8

   3.  Home Agent Configuration . . . . . . . . . . . . . . . . . . . 11
     3.1.  Network Configuration  . . . . . . . . . . . . . . . . . . 12
     3.2.  Home Agent Address Configuration . . . . . . . . . . . . . 13

   4.  Home Agent Operations  . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Home Agent List Management . . . . . . . . . . . . . . . . 13
     4.2.  Detecting Home Agent Failure . . . . . . . . . . . . . . . 14
     4.3.  Processing the HARP Messages . . . . . . . . . . . . . . . 15
       4.3.1.  IP field and Security Descriptions of HARP message . . 15
       4.3.2.  Processing Home Agent Hello (HA-HELLO) . . . . . . . . 16
       4.3.3.  Processing Home Agent Switch Over (SWO-REQ/REP)  . . . 17
       4.3.4.  Processing Home Agent Switch Back (SWB-REQ/REP)  . . . 19
     4.4.  State Synchronization  . . . . . . . . . . . . . . . . . . 20
       4.4.1.  Binding Cache Information Management . . . . . . . . . 21
       4.4.2.  IP field and Security Descriptions of State
               Synchronization message  . . . . . . . . . . . . . . . 21
       4.4.3.  Requesting State of Mobile Nodes (SS-REQ)  . . . . . . 21
       4.4.4.  Sending State Information (SS-REP) . . . . . . . . . . 22
       4.4.5.  Synchronizing State (SS-REP and SS-ACK)  . . . . . . . 23
     4.5.  Switching the Active Home Agent  . . . . . . . . . . . . . 24
     4.6.  Consideration of Routing and Neighbor Discovery
           Protocol (VHARP) . . . . . . . . . . . . . . . . . . . . . 25
     4.7.  Interworking with VRRP . . . . . . . . . . . . . . . . . . 26
     4.8.  Retransmissions and Rate Limiting  . . . . . . . . . . . . 26

   5.  Mobile Node Operation  . . . . . . . . . . . . . . . . . . . . 27
     5.1.  Home Agent Addresses Discovery . . . . . . . . . . . . . . 27
     5.2.  IPsec/IKE Establishment to Home Agents . . . . . . . . . . 28
     5.3.  Synchronizing State: K-bit treatment . . . . . . . . . . . 28
     5.4.  Receiving Home Agent Switch message  . . . . . . . . . . . 29

   6.  Messages Format  . . . . . . . . . . . . . . . . . . . . . . . 29
     6.1.  New Mobility Header Messages . . . . . . . . . . . . . . . 29
       6.1.1.  HARP Message Format  . . . . . . . . . . . . . . . . . 29



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       6.1.2.  State Synchronization Message Format . . . . . . . . . 33
       6.1.3.  Home Agent Rekey Message . . . . . . . . . . . . . . . 35
     6.2.  New Mobility Options . . . . . . . . . . . . . . . . . . . 36
       6.2.1.  Binding Cache Information Option . . . . . . . . . . . 36
       6.2.2.  State Synchronization Status Option  . . . . . . . . . 38
       6.2.3.  AAA Information Option . . . . . . . . . . . . . . . . 39

   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 40

   8.  Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 40

   9.  Protocol Configuration Variables . . . . . . . . . . . . . . . 40

   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 40

   11. Additional Authors . . . . . . . . . . . . . . . . . . . . . . 41

   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 42

   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 42
     13.2. Informative References . . . . . . . . . . . . . . . . . . 43

   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 44



























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1.  Introduction

   In Mobile IPv6 [RFC-3775, ID-3775bis] and its derivative protocols
   like NEMO Basic Support [RFC-3963] and Dual Stack Mobile IPv6 [RFC-
   5555], if a home agent loses binding cache state or even network
   connectivity due to its failure, or some other reason, the result is
   a loss of service for the mobile nodes.  It is beneficial to provide
   high availability and redundancy for a home agent so that mobile
   nodes can have uninterrupted service even when one home agent crashes
   or loses state.  The Home Agent Reliability Protocol (HARP) is
   designed to manage standby home agents, and switch service from an
   active to a standby home agent in the case of an active home agent
   failure.

1.1.  Terminology

   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].

   In this document, the term mobile node refers both to a mobile host
   [RFC-3775] and a mobile router [RFC-3963].

   Mobility related terms used in this document are defined in [RFC-
   3775] and [RFC-3753].  In addition or in replacement of these, the
   following terms are defined or redefined:

   Home Agent Reliability Protocol (HARP)

      A protocol between Mobile IPv6 home agents that provides
      reliability by moving state and service from an active home agent
      to a standby, in the case of an active home agent failure.  HARP
      can accomodate multiple home agents being placed on the same home
      link, or on different links, by grouping them into a redundant
      home agent set.  One of home agents is selected as an active home
      agent.  If the active home agent fails, a standby home agent can
      take over and become the active home agent.  Since each home agent
      is assigned individual home agent addresses, a mobile node is
      aware of home agent failures and needs to register its binding to
      the new active home agent again.

   Virtual Home Agent Reliability Protocol (VHARP)

      A protocol between Mobile IPv6 home agents which provides
      reliability by cloning an active home agent.  Unlike HARP, the
      standby home agents are an exact copy of the active home agent,
      including home agent IP address.  It is similar to the virtual
      router concept of VRRP [RFC-3768, RFC-5798] and HSRP [RFC-2281].



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      The VHARP operations are transparent to a mobile node.

   Active Home Agent

      A home agent that is currently serving the mobile nodes.

   Standby Home Agent

      A home agent which can serve the mobile nodes when the active home
      agent fails.

   Failed Home Agent

      A home agent that is not available due to hardware or software
      failure, system maintenance, etc.

   Active Home Agent Address

      An IPv6 address of the Active Home Agent.

   Standby Home Agent Address

      An IPv6 address of the Standby Home Agent.

   Redundant Home Agent Set

      A grouping which includes an active and standby home agent(s).
      The Group Identifier is used to identify a redundant home agent
      set.  Operators need to configure a unique value per redundant
      home agent set.

   Virtual Home Agent Address

      A home agent address shared among home agents in a redundant home
      agent set.  It is similar to virtual router address specified in
      VRRP [RFC-3768, RFC-5798].  The address is only activated on an
      active home agent.

   Home Agent Preference

      This preference value was originally defined for Dynamic Home
      Agent Address Discovery (DHAAD) in RFC3775.  This protocol re-uses
      this preference value for home agent selection when an active home
      agent has failed.  A home agent SHOULD NOT share the same
      preference value with other home agents.  Meanwhile, operators can
      also define an independent value for the home agent reliability
      protocol.  It is useful when operators want to assign different
      operational policies to the preference values of DHAAD and the



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      Home Agent Reliability Protocol.

   New Messages

         Home Agent Reliability Protocol (HARP) message defined in
         Section 6.1.1:

            SwitchOver Request (SWO-REQ)

            SwitchOver Reply (SWO-REP)

            SwitchBack Request (SWB-REQ)

            SwitchBack Reply (SWB-REP)

            Switch Complete (SW-COMP)

            Home Agent HELLO (HA-HELLO)

         State Synchronization (SS) message defined in Section 6.1.2:

            State Synchronization Request (SS-REQ)

            State Synchronization Reply (SS-REP)

            State Synchronization Reply-Ack (SS-ACK)

1.2.  Problem Statement and Requirements

   In Mobile IPv6 [RFC-3775, RFC-4877], a mobile node registers and
   establishes a binding with only one home agent.  The home agent
   represents the possibility of a single point of failure for Mobile
   IPv6.  A home agent is responsible for multiple mobile nodes on its
   home link.  The failure of the home agent may then result in the loss
   of connectivity for numerous mobile nodes located throughout the
   Internet.  To overcome this problem, Mobile IPv6 allows deployment of
   multiple home agents on the home link so that upon the failure of a
   home agent, a mobile node can re-establish its connection through a
   new home agent.  However, the base Mobile IPv6 specification does not
   address home agent fail-over and dynamic transfer of service from one
   home agent to another.  This transfer of service from the failed home
   agent to a new active home agent requires coordination or pre-
   configuration among the home agents regarding security associations,
   transfer of mobile node bindings, and other service information for
   reliable Mobile IPv6 service in a deployment scenario.

   For the home agent reliability solution, we define the following
   generic requirements:



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   Reliable Home Agent service

      Multiple home agents are available for a home prefix, and one of
      them actively serves the mobile nodes.  A standby home agent takes
      over when the active home agent becomes unavailable.  The transfer
      of the MN-HA association should be transparent to applications and
      should not take longer than the care-of-addresses update procedure
      described in Mobile IPv6 [RFC-3775].

   Availability of a Redundant Home Agent Set

      Availability of an active home agent address and a standby home
      agent address at the bootstrapping period for the mobile node is
      assumed.

   State Synchronization

      The information for mobile nodes must be able to be synchronized
      between an active home agent and standby home agent(s).  This
      includes the Binding Cache, AAA information, and other Mobile IPv6
      and NEMO related information.  Note that the Home Agent
      Reliability Protocol only exchanges state information for active
      mobile nodes.  Therefore, we do not have any specific operation
      for synchronizing the configuration information.  For instance,
      when Mobile IPv6 is operated with Authentication protocol [RFC-
      4285], synchronizing the configurations of the Authentication
      protocol is out of scope in this document.  Operators MAY
      correctly set the configuration information in multiple home
      agents.

   Consideration of IPsec/IKE Transfer

      An active home agent maintains several IPsec and IKE states for
      mobile nodes.  These states are synchronized within the redundant
      home agent set.  (Note this is out of scope in this document.)

   Secured Message Exchanges

      The messages used between the home agents to transfer binding
      cache information MAY be authenticated and encrypted.

   Failure Detection

      Redundant home agents must actively check for possible failure of
      an active home agent.  If a home agent supports an existing
      failure detection mechanism such as VRRP [RFC-3768, RFC-5798] or
      HSRP [RFC-2281], it can re-use that mechanism to detect home agent
      failure.  In addition, periodic Hello messages are introduced in



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      this document to detect active an home agent's service
      availability.

   Failure Notification

      If necessary, a mobile node is notified about the active home
      agent failure by the standby home agent.


2.  Protocol Overview

   HARP works when one or more home agents are provisioned on a home
   link, or different links, and these are grouped into a redundant home
   agent set.  One home agent is selected as the active home agent and
   receives binding updates from mobile nodes.  According to [RFC- 3775,
   RFC-4877], an active home agent maintains not only binding cache
   information, but also IPsec/IKEv2 states per mobile node, because
   Mobile IPv6 relies on IPsec for securing the signaling, and
   optionally user plane traffic.

   If the active home agent fails, all state information associated with
   a mobile node is lost.  As a result, all mobile nodes served by the
   failed home agent will be disconnected.  In HARP, other home agents,
   called standby home agents, exchange the required information with
   the active home agent.  In case of a failure of the active home
   agent, HARP can let a standby home agent take over for the failed
   home agent with this information about the active mobile nodes.


     MN          HA1         HA2
      |       [HA1-addr]   [HA2-addr]
      |           |           |
      |        (active)    (standby)
      |           |           |
      |           |<--------->| 1. Hello exchanges
      |<--------->|           | 2. Binding Registration to HA1
      |           |<--------->| 3. State exchanges
      |           |           |
      |           X           |  HA1 FAILURE
      |           X           |
      |           X           | 4. Failure Detection
      |<----------------------| 5. Sending Home Agent Switch message
      |<--------------------->| 6. Binding Registration to HA2
      |           X       (active) RECOVERY COMPLETE
      |           X           |


       Figure 1: Overview of Home Agent Reliability Protocol (HARP)



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   Figure 1 shows an example of the HARP operations.  HA1 and HA2 belong
   to the same redundant home agent set and are assigned with an
   individual IP address (HA1-addr and HA2-addr) at the home link.  Each
   home agent can be seen as an individual home agent by mobile nodes.
   All the home agents periodically send a Hello message (named HA-
   HELLO) to exchange the home agent information, as well as monitor the
   state of the active home agent (1).  The mobile node registers its
   binding with only the active home agent (2).  The active home agent
   synchronizes the active mobile node information with the other
   standby home agents periodically (3).

   HARP introduces the new HA-HELLO message for failure detection, but
   it may use any type of information to detect that failure.  After
   detecting the failure of the active home agent (4), the standby home
   agent whose preference value is the highest takes over for the failed
   home agent.  Once completed, the standby home agent sends a Home
   Agent Switch message to all the mobile nodes that were registered at
   the failed home agent (5).  The standby home agent puts its own
   address in the Home Agent Address field of the Home Agent Switch
   message so that it will receive the binding update from the mobile
   node as an acknowledgment of the sent Home Agent Switch message.  The
   home agent switch-over is complete when it receives binding updates
   from all the mobile nodes (6).  For protecting the Home Agent Switch
   message, the mobile node should have an IPsec Security Association
   (SA) with the standby home agent before the failover.  The mobile
   node may pre-establish multiple IPsec SAs with all the home agents.

   Although the active home agent manages IPsec/IKEv2 states per mobile
   node, HARP does not offer any recovery mechanism of these states by
   itself.  IPsec/IKE state synchronization is out of scope in this
   document.  If IPsec/IKEv2 state can be recovered from the active home
   agent on the standby home agent, HARP can be operated in a slightly
   different manner called Virtual-HARP (VHARP).  Unlike HARP, the
   standby home agents are an exact copy of the active home agent.  It
   is similar to the virtual router concept of VRRP [RFC-3768, RFC-5798]
   and HSRP [RFC- 2281].  Note that HARP is mandatory and VHARP is
   optional in this document.  VHARP is shown in Figure 2.














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     MN          HA1         HA2
      |        [HA-addr]   [HA-addr']
      |           |           :
      |        (active)    (standby)
      |<--------->|           : 1. Binding Registration to HA1
      |           |<--------->: 2. State exchanges
      |           |           :
      |           X           :  HA1 FAILURE
      |           X           :
      |           X           : 3. Failure Detection
      |           X           | 4. HA2 takes over the HA1
      |           X       (active) RECOVERY COMPLETE
      |           X           |


   Figure 2: Overview of Virtual Home Agent Reliability Protocol (VHARP)

   All the home agents (HA1 and HA2) in the redundant home agent set
   share a virtual home agent address (HA-addr), and routing ensures
   only the active home agent will be reachable using that virtual home
   agent address.  After a mobile node's binding registration (1), the
   active home agent pushes the states of all of its mobile nodes to the
   other standby home agents (2).  In VHARP, all the states of a mobile
   node need to be synchronized.  For example, information such as the
   Binding Cache, and Authentication, Authorization, and Accounting
   (AAA) information.

   After detecting the active home agent has failed (3), the standby
   home agent whose preference value is the highest takes over the
   failed home agent.  The standby home agent activates the virtual home
   agent address on its interface attached to the home link.  The
   virtual home agent address activation can be operated by VRRP.  Since
   all the necessary states of mobile nodes have already been
   transferred to this standby home agent, the standby home agent can
   immediately start acting as the active home agent (4).  Unlike HARP,
   the mobile node is not required to re-register its binding to a new
   active home agent.  The mobile node may use the IKEv2 resumption
   mechanism [RFC-5723] to resume it's IPsec SA with the new active home
   agent.

   This document offers a new management mechanism of active and standby
   home agents by using a new Mobility Header (MH) message called a HARP
   message as shown in Figure 3.  This mechanism can be used in both
   HARP and VHARP.  Each home agent exchanges its own home agent
   information with the other home agents in its redundant home agent
   set by a Home Agent HELLO message (HA-HELLO) (1).  The HA-HELLO
   message can also be used to monitor the availability of the active
   home agent.



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       HA1(active)  HA2    HA3 .. HAn
           |        |      |      |
           |<------>|<---->|<---->| 1. HELLO exchange
           |------->|      |      | 2. HA1 sends SWB-REQ
           |<-------|      |      | 3. HA2 sends SWB-REP
           |------->|      |      | 4. HA2 sends SW-COMP
       (standby) (active)  |      | HA2 BECOMES ACTIVE HA
           |        |      |      |
              SYSTEM MAINTENANCE, ETC.
           |        |      |      |
           |------->|      |      | 5. HA1 sends SWO-REQ
           |<-------|      |      | 6. HA2 sends SWO-REP
           |------->|      |      | 7. HA1 sends SW-COMP (optional)
       (active) (standby)  |      | 8. HA1 returns to active HA
           |        |      |      | HA1 BECOMES ACTIVE AGAIN


                      Figure 3: Home Agent Management

   In some scenarios, the active home agent may need to stop serving
   mobile nodes for system maintenance.  This specification enables
   manual intervention for home agent management.  As shown in Figure 3,
   the active home agent (HA1) sends a SwitchBack Request message (SWB-
   REQ) to a standby home agent (HA2) (2).  HA2 will acknowledge the
   message by sending a SwitchBack Reply message (SWB-REP) to HA1 (3).
   In HARP operation, it could take a long time to complete home agent
   failover since all mobile nodes must re-register with the new home
   agent.  During this failover operation, HA1 may continue serving the
   mobile nodes until the switch-over is completed.  When HA2 decides
   the switch-over has completed, it MAY send an optional message, SW-
   COMP, to HA1 (4).  As soon as HA2 sends the SW-COMP, it becomes the
   active home agent.  HA1 becomes a standby home agent when it receives
   SW-COMP.  If SW-COMP is not used, HA2 and HA1 change their status
   appropriately.

   After maintenance is complete and HA1 is back online, HA1 sends a
   SwitchOver Request (SWO-REQ) to HA2 in order to become the active
   home agent again (5).  HA2 acknowledges it by sending a SwitchOver
   Reply (SWO-REP) back to HA1 (6).  HA1 now starts the home agent
   failover operation.  After the switch-over is complete, HA1 sends a
   SW-COMP to HA2 (7).  Then, HA1 becomes the active home agent and HA2
   becomes a standby home agent (8).


3.  Home Agent Configuration






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3.1.  Network Configuration

   HARP supports two different configurations for standby home agents.
   Standby home agents can be placed on the same home link or on
   different links.  Figure 4 depicts the configuration where home
   agents serving the same home network are located on the same link as
   defined in [RFC-3775].


                 HA1    HA2    HA3    HA4 .... HAn
                  |      |      |      |        |
          --------+------+------+------+--------+---------
                             Home Link


                  Figure 4: Local Recovery Configuration

   Figure 5 illustrates when standby home agents are located on
   different links (illustrated as Recovery Link in Figure 5).  Most
   large operators have a very stringent requirement on network
   availability even in the worst type of disaster or outage.  This
   configuration can achieve home agent recovery even if the entire home
   link fails.  This is called geographic redundancy, and is a well-
   known configuration for Telecommunications operators.  In Figure 5,
   home agents (HA1-HA4) are placed in geographically separated regions
   (region-1 and region-2).  If region-1 suffers down time for any
   reason, all the sessions will be seamlessly taken over by the nodes
   in region-2.  Note that HA3 and HA4 cannot receive packets meant for
   the home network until the route on the Routers is changed.  The
   routing must also be updated to direct the packets meant for the home
   link to the recovery link.


           ---------IGP------>|<---BGP--->|<-----IGP---------

                HA1    HA2                     HA3    HA4
                 |      |                       |      |
         --------+------+-----+ R---R---R +-----+------+-------
               Home Link          Routers     Recovery Link
              (region-1)                       (region-2)


                  Figure 5: Global Recovery Configuration








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3.2.  Home Agent Address Configuration

   In HARP, each home agent obtains its individual IPv6 address from its
   serving home prefix.  In VHARP, all the home agents use a virtual
   home agent address generated from the home prefix.

   In addition, each home agent running VHARP needs to obtain its
   individual IPv6 address from its attached link.  This IPv6 address is
   used only for VHARP operations between home agents and is not
   revealed to mobile nodes for binding registration.

   All the home agents MUST join the ALL_HA_MULTICAST_ADDR.  In VHARP,
   each home agent joins the multicast group with its individual IPv6
   address, but not with the virtual home agent address.  This multicast
   address can be used to exchange HA-HELLO messages among the home
   agents.  Alternatively, if a remote home recovery link is defined,
   each home agent unicasts the HARP messages to home agents configured
   at the remote recovery link.


4.  Home Agent Operations

4.1.  Home Agent List Management

   In Mobile IPv6, each home agent periodically sends router
   advertisements with the Home Address Information option [RFC-3775].
   HARP introduces a HARP HA-HELLO message to replace the router
   advertisement.  There are several reasons to use HA-HELLO messages
   instead of a Router Advertisement such as:

   o  A HA-HELLO message can be sent beyond the link, while a router
      advertisement cannot.  In case of geographic redundancy, Router
      Advertisements cannot be sent to the recovery link unless the home
      link and the recovery link are virtually connected, for example,
      by L2TP.

   o  A HA-HELLO message is defined to manage additional information,
      such as Group ID and Active/Standby Status of the home agents in
      the home agent list.

   o  A HA-HELLO message is exchanged only between home agents, while a
      Router Advertisement is also processed by mobile nodes attached to
      a home link.  A HA-HELLO does not introduce any burden to the
      mobile nodes even if it is frequently sent on the home link.

   When a HA-HELLO is used to exchange home agent information, each home
   agent SHOULD NOT process the Home Agent Information option carried by
   a Router Advertisement.  Router Advertisements are only processed by



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   mobile nodes.  Operators may define different configuration values to
   the parameters of the home agent information for a HA-HELLO and a
   Router Advertisement.

   This document requires additional information to be added the
   conceptual Home Agents list defined in [RFC-3775].  The additional
   information is learned through HA-HELLO message exchange.

   o  Group ID of a redundant home agent set.  It is learned through the
      Group ID field of the HA-HELLO.

   o  HA-HELLO Interval.  This value is locally configured at every home
      agent by operators, and is learned through the Hello Interval
      field of the HA-HELLO.

   o  Individual home agent addresses used in the VHARP operation.  This
      information is only required when VHARP is used in addition to the
      virtual home agent address.  It is learned through the Source
      Address of the HA-HELLO message.

   o  VHARP capability.  This information is learned through the V flag
      of the HA-HELLO message.

   o  Current mode (HARP or VHARP).  This information is learned through
      the M flag of the HA-HELLO message.

   o  Active status.  This information is learned through the A flag of
      the HA-HELLO message.

4.2.  Detecting Home Agent Failure

   Active and standby home agents can monitor each other in several
   ways.  One method is to reuse other failure detection mechanisms
   defined in VRRP [RFC-3768, RFC-5798] and HSRP [RFC-2281].  However,
   VRRP and HSRP are not sufficient since they cannot detect the case
   where the system is running, but the Mobile IPv6 stack is not
   operational.  Failure events used in HARP/VHARP are listed below.

   Loss of HA-HELLO

      HARP/VHARP is an extension to Mobile IPv6, and can monitor the
      availability of Mobile IPv6 services on each home agent by
      periodically sending a HA-HELLO as a heart-beat.  This HA-HELLO
      can be exchanged frequently enough to detect a failure without any
      additional overhead to mobile nodes attached to the home link.  In
      the event that a standby home agent does not receive any HA-HELLOs
      from its peer for a configurable duration of time, the standby
      home agent assumes the peer home agent has failed.  Details of the



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      Hello message are described in Section 4.3.2.

   Monitored Server Failure by the Active Home Agent

      There may be a number of critical servers, such as an AAA, in the
      network that are essential for ongoing Mobile IPv6 sessions at the
      home agent.  Operators can have a policy in place for which the
      active home agent is treated as a failed home agent upon detecting
      that the link to such servers has failed.

   Routing Peer/Link Failure

      Operators may require the home agent to detect its next-hop
      routing peer failure.  If the next-hop routing failure is fatal in
      nature, or due to some other routing policies, the active home
      agent is treated as a failed home agent and the recovery operation
      should be started.

4.3.  Processing the HARP Messages

4.3.1.  IP field and Security Descriptions of HARP message

   The HARP message format is defined in Section 6.1.1.  If a HARP
   message is unicast, the destination address MUST be one of the Home
   Agents in the same Redundant Home Agent set.  If it is a HA-HELLO
   message, designated by setting the type field to 4, it can be
   multicast.  The destination address MUST be set to the
   ALL_HA_MULTICAST_ADDR address.  The source address MUST be set to the
   sender's home agent address.  Note that in VHARP, the virtual home
   agent address SHOULD NOT be set to the source or destination address.
   Instead, the IP address of the interface the packet is being sent
   from SHOULD be used.

   If a HARP message is unicast, it SHOULD be secured by IPsec ESP.  If
   a HA-HELLO message is multicast, multicast extensions to IPsec [RFC-
   5374] SHOULD be applied.  If all the home agents are placed in a
   secure transport network to exchange a HARP message, authentication
   and encryption MAY be omitted.  Which security verification is used
   depends on operational policy.  If security verification fails for a
   received HA-HELLO, the HA-HELLO MUST be discarded.

   The following operations MUST be performed when transmitting a HARP
   message:

   o  The incremented latest Sequence Number MUST be set in the Sequence
      Number field.  The Sequence Number SHOULD be initialized to zero
      for the first Hello message.  To accomplish sequence number
      rollover, if the sequence number has already been assigned to be



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      the largest possible number representable as a 16-bit unsigned
      integer, then when it is incremented it will then have a value of
      zero (0).

   o  The sender's Group ID MUST be set in the Group ID field.

   o  The V-flag MUST be set if the sender is capable of VHARP.

   o  The M-flag MUST be unset if the sender is operating in HARP mode.

   o  The M-flag MUST be set if the sender is operating in VHARP mode.

   o  The A-flag MUST be set if the sender is the active home agent.

   The following functions MUST be performed when a HARP message is
   received:

   o  The Group ID in the HARP message MUST match the receiver's Group
      ID.

   o  The source address of the HARP message MUST belong to a home agent
      in the receiver's redundant home agent set.

   o  The M-flag MUST match the receiver's operating mode.

   o  The Sequence Number value in the HARP message MUST be larger than
      the last received Sequence Number value.  When the sequence number
      rollover occurrs, the sequence number value in the HA-HELLO MUST
      be zero.

   If any one of the above checks fails, the receiver SHOULD discard the
   HARP message.

4.3.2.  Processing Home Agent Hello (HA-HELLO)

4.3.2.1.  Sending HA-Hello Messages

   Each home agent MUST send a HA-HELLO in the following cases:

   o  UNSOLICITED: Each home agent SHOULD periodically send a HA-HELLO.
      The time interval is configured locally at each home agent.

   o  UNSOLICITED: When a home agent detects its local information has
      changed it should immediately send a HA-HELLO.

   o  SOLICITED: When a home agent receives a HA-HELLO with the R-flag
      set, the HA-HELLO can be sent to the destination home agent.




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   A home agent can solicit a HA-HELLO from a particular home agent(s)
   in the same redundant home agent set by unicasting or multicasting a
   HA- HELLO with the R-flag set.  Soliciting a HA-HELLO happens when:

   o  A new home agent boots up.  The new home agent SHOULD solicit HA-
      Hello messages by multicasting a HA-Hello message with the R-flag
      set to 1.

   o  If a HA-HELLO has not been received after the specified Hello
      Interval, a HA-HELLO MAY be solicited to the home agent.

   o  A home agent entry in the redundant home agent set is about to be
      removed due to home agent lifetime expiration.  A HA-HELLO SHOULD
      be solicited from the home agent whose lifetime is soon expired.

   In addition to Section 4.3.1, the following operations MUST be
   performed when transmitting a HA-HELLO.

   o  The Type field MUST be set to 4.

   o  The R-flag MUST be set if the sender is soliciting a HA-HELLO from
      the other home agent(s).

   o  The appropriate home agent configuration values MUST be copied to
      the Home Agent Preference, the Home Agent Lifetime, and Hello
      Interval fields.

4.3.2.2.  Receiving Hello Messages

   The receiver MUST perform the verification of the HA-HELLO described
   in Section 4.3.1.  After the verification, the receiver copies the
   values stored in the HA-HELLO message to the corresponding home agent
   list entry according to Section 4.1.

   If the home agent lifetime field in the HA-HELLO is set to 0, the
   receiver MUST remove the sending home agent from the home agents
   list.

   If the R-flag is set in the received HA-HELLO, the receiver MUST send
   a new HA-HELLO to the originator as described in Section 4.3.2.1.

4.3.3.  Processing Home Agent Switch Over (SWO-REQ/REP)

   When a standby home agent decides to become an active home agent, the
   standby home agent sends a SwitchOver Request (SWO-REQ) to the
   current active home agent in the following way:





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   o  It MUST be unicast to only the current active home agent.

   o  It MUST be sent from a standby home agent.  The active home agent
      MUST NOT generate this message.

   When an active home agent receives a SWO-REQ, it MUST do the
   following verifications and operations, in addition to what is
   described in Section 4.3.1

   o  If the receiver of the SWO-REQ is not an active home agent, it
      MUST send a SWO-REP with the Status field set to 130 (Not active
      home agent).

   o  If the sending home agent does not belong to the same redundant
      home agent set, a SWO-REP message MUST be sent to the sender with
      the Status field set to 132 (Not in same redundant home agent
      set).

   o  If there are any other reasons that the receiver cannot accept the
      SWO-REP, the active home agent MUST reply a SWO-REP with the
      Status field set to 129 (Administratively prohibited).

   o  Otherwise, the active home agent MUST become a standby home agent
      and reply with a SWO-REP message with the Status field set to 0
      (Success).

   When a standby home agent receives a SWO-REP, it MUST do the
   following verifications and operations, in addition to what is
   described in Section 4.3.1:

   o  If the receiver is an active home agent, the SWO-REP MUST be
      discarded.

   o  If the standby home agent receives an unsolicited SWO-REP which is
      not in reply to an SWO-REQ it has sent, it MUST ignore the SWO-
      REP.

   o  Otherwise, if the Status field of the SWO-REP is 0 (Success), the
      standby home agent (the receiver of the SWO-REP) immediately
      becomes an active home agent.

   o  If the value in the Status field is greater than 128, an error has
      occurred.  In this case, the receiver MUST NOT attempt to be an
      active home agent.







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4.3.4.  Processing Home Agent Switch Back (SWB-REQ/REP)

   When an active home agent decides to become a standby home agent, it
   sends a SWB-REQ to one of the standby home agents.  The reason for
   the active home agent sending this message might be due to an
   administrative intervention, or an event like Monitored Server
   Failure by the active home agent, or due to a Routing Peer/Link
   Failure.  The following operations MUST be performed when SWB-REQ is
   sent:

   o  It MUST be unicast to only one of the standby home agents in the
      same redundant home agent set.

   o  It MUST be sent from an active home agent.  A standby home Agent
      MUST NOT generate this message.

   When a home agent receives a SWB-REQ message, it verifies the message
   as follows:

   o  If the sending home agent of the SWB-REQ is not an active home
      agent, a SWB-REP MUST be sent in which the Status field is set to
      130 (Not active home agent).

   o  If the sending home agent does not belong to the same redundant
      home agent set, a SWB-REP MUST be sent in which the Status field
      is set to 132 (Not in same redundant home agent set).

   o  Otherwise, the receiving home agent MUST send a SWB-REP with the
      Status field set to 0 (Success).

   o  After sending the SWB-REP, the standby home agent MUST NOT become
      an active home agent immediately.  This is because the active home
      agent is still active until it receives the SWB-REP acknowledging
      the SWB-REQ it sent.  The standby home agent SHOULD change to
      active after LINK_TRAVERSAL_TIME.  The default value of
      LINK_TRAVERSAL_TIME is defined in Section 9.

   When a home agent receives a SWB-REP message, it verifies the message
   as follows:

   o  If the standby home agent received an unsolicited SWB-REP not in
      reply to it's own SWB-REQ, it SHOULD ignore the SWO-REP.

   o  If the Status field of the SWB-REP is 0 (Success), the active home
      agent should immediately become a standby home agent.  The sending
      home agent of SWB-REP becomes an active home agent after
      LINK_TRAVERSAL_TIME.




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   o  If the value in the Status field is greater than 128, the receiver
      of the SWB-REP (active home agent) cannot become a standby home
      agent and MUST continue to be an active home agent.

4.4.  State Synchronization

   The State Synchronization (SS) message format is defined in
   Section 6.1.2.  It can carry multiple aspects of the state
   information associated with a mobile node by setting mobility options
   in the Mobility Options field.  The following list shows examples of
   the mobility options which can be specified in the state
   synchronization message:

   o  IPv6 Home Address (Binding Cache Option)

   o  Binding Cache Information (Binding Cache Option)

   o  NEMO Mobile Network Prefix (Mobile Network Prefix Option [RFC-
      3963])

   o  IPv4 Care-of Address (IPv4 Care-of Address Option [RFC-5555])

   o  IPv4 Home Address (IPv4 Home Address Option [RFC-5555])

   o  Binding Identifier (Binding Identifier Option [RFC-5648]

   o  AAA states (AAA Information Option)

   o  Miscellaneous states (Vendor Specific Mobility Option [RFC-5094])

   When a home agent needs to send the state of multiple mobile nodes in
   a single state synchronization message (SS-REQ or SS-REP), a Binding
   Cache Information option is used as a separator.  For each mobile
   node, a Binding Cache Information option is placed first, followed by
   any other options related to the mobile node, if necessary.

   In HARP, since a mobile node will re-register to the new active home
   agent after a home agent failover, it is not necessary for the
   standby home agents to synchronize all the mobile nodes' state
   information.  The standby home agents only need to collect the home
   address information of all the mobile nodes served by the active home
   agent.  The information is used to send Home Agent Switch messages to
   all the mobile nodes when a home agent failure occurs.

   In the case of VHARP, home agent fail-over is accomplished without
   the mobile nodes having to perform re-registration.  Therefore,
   standby home agents need to copy the complete state information of
   each mobile node registered with the active home agent.



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4.4.1.  Binding Cache Information Management

   In HARP, each standby home agent learns the partial binding cache
   information such as a pair of a home address and a mobile node's
   registering home agent address.

   In VHARP, a standby home agent ideally copies the received binding
   cache information and other mobile node's information into the
   appropriate database so that it can act as an active home agent as
   soon as it takes over the failed home agent.

4.4.2.  IP field and Security Descriptions of State Synchronization
        message

   A state synchronization message is unicast.  The destination address
   MUST be one of the home agents in the same Redundant Home Agent set.
   The source address MUST be set to the sender's home agent address.
   Note, that in VHARP, the virtual home agent address MUST NOT be set
   to the source address, the IP address of the interface the packet is
   being sent from SHOULD be used.

   The message SHOULD be secured by IPsec ESP.  If all the home agents
   are placed in a secure transport network to exchange the state
   synchronization message, authentication and encryption MAY be
   omitted.  If security verification fails for a received state
   synchronization message, the message MUST be discarded.  The choice
   of security mechanism used depends on the operational model of the
   network.

4.4.3.  Requesting State of Mobile Nodes (SS-REQ)

   When a home agent needs the state information for a particular mobile
   node, or a subset of mobile nodes, it sends a SS-REQ message
   constructed as follows:

   o  It MUST set the Type field to 0 (Request).

   o  It MUST set a random value in the Identifier field that does not
      coincide with any other currently pending Requests.

   o  It MUST include a Binding Cache Information option(s) in which the
      Home Address field is set to the target home address.  Other
      fields of the Binding Cache Information option can be omitted.

   o  If the request is for the state of all the mobile nodes registered
      at the destination home agent for the SS-REQ message, it MUST set
      the Home Address field of the Binding Cache Information option to
      the unspecified address (::).



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   o  If the sender is requesting information about multiple mobile
      nodes, it MUST include multiple binding cache information options
      in a single SS-REQ.  The sender SHOULD NOT send multiple SS-REQs
      per mobile node.

   o  It MUST send a SS-REQ to the active home agent of the target
      mobile node(s).

   When a home agent receives a SS-REQ, it MUST perform the verification
   described in Section 4.4.2 and the following:

   o  If the receiver does not have binding cache information for the
      target mobile node(s) specified in the received Binding Cache
      Information option(s), it MUST ignore the SS-REQ and MUST NOT
      reply with a SS-REQ.

   o  Otherwise, the receiver MUST reply with a SS-REP, including all
      the state information of the target mobile node(s).

4.4.4.  Sending State Information (SS-REP)

   An SS-REP message(s) SHOULD be sent when:

   1.  The active home agent receives an SS-REQ.

   2.  The active home agent creates or deletes a binding cache entry
       for a particular mobile node.

   The active home agent MAY additionally send an SS-REP message in the
   following cases:

   1.  The active home agent updates the state information for all
       sessions that have changed since the last update in a periodic
       interval.

   2.  Often in VHARP, the active home agent MAY update a binding cache
       entry for a particular mobile node whenever the binding cache
       entry is updated.  If an active home agent sends an SS-REP
       message whenever the local state information changes, such as a
       binding cache change, the number of the SS-REP messages can be
       quite large.

   The following rules must be applied when the active home agent
   constructs a SS-REP:

   o  It MUST copy the Identifier field of the SS-REQ to the same field
      of the SS-REP, if the SS-REP is sent in response to the SS-REQ.




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   o  It MUST set the Identifier field to zero (0) if the SS-REP is sent
      without solicitation (no SS-REQ).

   o  It MUST include the required mobility options in the SS-REP.

      *  In HARP, a partial Binding Cache Information option (the Home
         Address Field only) MUST be included in the SS-REP.

      *  In VHARP, a full Binding Cache Information option, and other
         required options shown in Section 6.1.2, MUST be included in
         the SS-REP.

   o  It MUST include the state of all the active mobile nodes
      registered at the active home agent in the SS-REP when the
      unspecified address is found in the Home Address mobility option
      carried with the SS-REQ.  The message may be fragmented depending
      on the total size needed to carry all states.

4.4.5.  Synchronizing State (SS-REP and SS-ACK)

   When a home agent receives a SS-REP, it MUST take the following
   operations:

   o  If no options are carried in the SS-REP, the home agent MUST
      ignore the SS-REP.

   o  If the sender of SS-REP is not in the same global home agent set,
      the home agent MUST reject the SS-REP and MUST send SS-ACK with
      the Status Synchronization Status option in which status value is
      set to [130: Not in same global home agent set]

   o  The receiver MUST record the IPv6 address of the sender as the
      active home agent of the mobile node in its local binding cache.

   o  The receiver MUST update its binding cache, and all other
      necessary information, in its database(s).

   o  If the A-flag is set in the SS-REP, the receiver MUST reply with
      an SS-ACK.

   If an active home agent requires an acknowledgment of a SS-REP, it
   MUST set the A-flag (Ack) in the SS-REP.  The receiver of the SS-REP
   will send back an SS-ACK.  The receiver MUST copy the Identifier
   value received in the SS-REP into the SS-ACK in order to match the
   SS-REP and SS-ACK.






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4.5.  Switching the Active Home Agent

   In HARP, the standby home agent which is going to be active MUST send
   a Home Agent Switch message [RFC-5142] to all the mobile nodes that
   were being served by the failed home agent.  The following rules MUST
   be applied when transmitting a Home Agent Switch message.

   o  MUST use IPsec ESP to protect the Home Agent Switch message.

   o  MUST set the address of the standby home agent address who is the
      sender of this Home Agent Switch message in the Home Agent Address
      field of the Home Agent Switch message [RFC-5142].

   If there are a large number of mobile nodes served by the failed home
   agent, the overhead of sending Home Agent Switch messages is high.
   This overhead cannot be avoided if the active home agent suddenly
   stopped serving mobile nodes due to an unexpected reason (crash,
   network trouble, etc).  However, if this switch-over is an
   administrative operation (maintenance, etc), the previous active home
   agent may continue serving the mobile nodes until the switch-over is
   complete.  Until the mobile node sends a binding update to the new
   active home agent, it still sends packets to the previous home agent.

   When the new active home agent completes the switch-over, it SHOULD
   send a SW-COMP to the previous active home agent.  Until the previous
   home agent receives this message, it SHOULD continue serving any
   mobile nodes that are registered with it.  Once the previous home
   agent receives the SW-COMP message, it can be shutdown or detached
   from the network safely.

   In VHARP, after detecting the active home agent has failed, the
   standby home agent whose preference value is the highest MUST take
   over for the failed home agent.  The standby home agent MUST activate
   the virtual home agent address and its virtual MAC address.  A
   virtual MAC address as introduced in [RFC-3768, RFC-5798] SHOULD be
   used in VHARP.  If VHARP is run with VRRP and HSRP as described in
   Section 4.7, the virtual home agent address can be treated as a
   virtual router address in VRRP and HSRP.  Therefore, VRRP and HSRP
   can automatically activate the virtual home agent address on the
   standby home agent after their election mechanism has completed.
   Since all the necessary state has already been transferred to this
   standby home agent before the active home agent failed, it can
   immediately start acting as the active home agent.

   When the failed home agent is restarted and wants to become the
   active home agent again, it MUST re-establish an IPsec SA with each
   mobile node, as all the mobile nodes will have purged their IPsec SA
   with the home agent when the failure occurred.  Otherwise, it cannot



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   be a standby or active home agent for the mobile nodes.  Therefore,
   as soon as the active home agent detects the recovery of the failed
   home agent, it sends a Home Agent Rekey message to all the mobile
   nodes served by other home agents in the same redundant home agent
   set, and includes the recovered home agent address in the Home Agent
   Addresses field.  The detail of the Home Agent Rekey message is
   described in Section 6.1.3.  The mobile node will re-key the SA by
   using The IKEv2 resumption mechanism [RFC-5723].  Alternatively, the
   mobile node MAY start a new IKE session with the recovered home
   agent.

4.6.  Consideration of Routing and Neighbor Discovery Protocol (VHARP)

   This section gives a brief explanation of how a home agent interacts
   with routing and Neighbor Discovery when VHARP is used.

   When a standby home agent becomes active in VHARP, it MUST start to
   advertise the home agent address, and the home prefix of the home
   addresses serviced by the redundant home agent set, into the routing
   infrastructure.  This operation is normally done using a route
   selector such as BGP, or an OSPF modifier.  For example, we can use
   the AS_Path prepend operation for BGP, and the Metric field in OSPF
   for the route selection.  When each home agent participates in OSPF
   routing, each home agent should be configured with the appropriate
   metric matched to the home agent preference value.  When the active
   home agent fails, OSPF detects the failure and can dynamically switch
   the route to the standby home Agent based on the OSPF cost value.  If
   this creates conflicts with the home agent preference value due to
   configuration errors, the routers on the home link may not route
   packets to the desired standby home agent.  In order to change the
   OSPF cost correctly and dynamically, the operator would use its
   existing approaches.  For example, most router vendors have a private
   MIB to set the OSPF cost via SNMP, though this is a vendor- specific
   function.

   When an active home agent activates a home agent address, it SHOULD
   use a virtual MAC address as introduced in [RFC-3768, RFC-5798].
   When the active home agent is changed, the neighbor cache of the
   active home agent is not necessarily updated on mobile nodes located
   on the home link.  Otherwise, the new home agent MUST update the
   neighbor cache entry for the home agent address on all the mobile
   nodes located on the home link.  In addition, Mobile IPv6 uses proxy
   Neighbour Discovery to intercept packets meant for mobile nodes which
   are away from the home link.  However, it is unnecessary for the new
   active home agent to overwrite the existing proxy neighbor entries of
   the mobile nodes.





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4.7.  Interworking with VRRP

   VRRP and HSRP specify an election protocol that dynamically assigns
   responsibility for a virtual router to one of the VRRP routers on a
   LAN.  This operation is similar to VHARP.  For example, the VRRP
   router controlling the IP address(es) associated with a virtual
   router is called the Master, and forwards packets sent to these IP
   addresses.  The election process provides dynamic failover in the
   forwarding responsibility should the Master become unavailable.
   Although VRRP is used to guarantee home agent address reachability,
   it cannot be used for state synchronization and explicit switching of
   Master and Backup.  Thus, the Home Agent Reliability Protocol cannot
   be replaced by VRRP.  This section explains how VRRP can interwork
   with HARP/VHARP.

   When VRRP is available, VRRP can replace the Hello message described
   in Section 6.1.1.  However, some information is missing by using just
   VRRP.  After receiving a VRRP message, each home agent SHOULD process
   the message and store the information as if it had received a Home
   Agent Hello message, as described in Section 4.3.2.2.  The message
   format of VRRP can be found in Section 5.1 of [RFC-5798].  Each field
   is mapped as follows:

   o  Virtual Rtr ID: Group ID is stored in the Virtual Rtr ID field.

   o  Priority: Home Agent Preference is stored in the Priority field.
      Note that VRRP only has 8 bits for the Priority field.  Therefore,
      values larger than 255 MUST NOT be assigned to the preference
      value.

   o  Count IPv6 IPv6 Addr: This field MUST be always be 1.

   o  Max Advert Int: This field MUST be mapped to the Hello Interval
      field of the Home Agent Hello message, though it only has 12
      bytes.

   o  IPv6 address: A home agent address is stored in this field.

   Home Agent Lifetime, Sequence Number and Flags fields are not present
   in the VRRP packet format.  Therefore, operators SHOULD use the same
   statically configured value for Home Agent Lifetime.  Each home agent
   does not check the freshness of received VRRP message because there
   is no sequence number.

4.8.  Retransmissions and Rate Limiting

   Home agents are responsible for retransmissions and rate limiting of
   SS-REQ, SWO-REQ, SWB-REQ messages for which they expect a response.



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   The home agent MUST determine a value for the initial transmission
   timer:

   o  If the home agent sends a SS-REQ message, it SHOULD use an initial
      retransmission interval of INITIAL_STATE_SYNC_REQ_TIMER.

   o  If a home agent sends a SWO-REQ or SWB-REQ message, it SHOULD use
      an initial retransmission interval of INITIAL_SWITCH_REQ_TIMER.

   If the sending home agent fails to receive a valid matching response
   within the selected initial retransmission interval, it SHOULD
   retransmit the message until a response is received.  All of the
   above constants are specified in Section 8.

   The retransmission MUST use an exponential backoff process as
   described in [RFC-3775] until either the home agent receives a
   response, or the timeout period reaches the value
   MAC_HARELIABILITY_TIMEOUT.  The home agent SHOULD use a separate
   back-off process for different message types and different
   destinations.  The rate limiting of Mobility Header messages is the
   same as one in [RFC-3775].  A home agent MUST NOT send Mobility
   Header Messages to a particular home agent more than MAX_UPDATE_RATE
   (3) times a second, which is specified in [RFC-3775].


5.  Mobile Node Operation

   This section describes the operations of a mobile node only when HARP
   is used.  None of the operations in this section are required with
   VHARP.

5.1.  Home Agent Addresses Discovery

   A mobile node authenticates itself to two or more home agents and
   creates IPsec SAs with them during bootstrapping.  When the active
   home agent fails, another home agent can use the pre-existing SA to
   notify the mobile node about the failure by sending a Home Agent
   Switch message.

   In order to discover multiple home agent addresses, two different
   mechanisms are defined in the bootstrapping solution in the split
   scenario [RFC-5026].  One is DNS lookup by home agent Name, the other
   is DNS lookup by Service Name.  DHCPv6 can also be used in the
   integrated scenario [ID-BOOTINT] to provide home agent provisioning
   to mobile nodes.

   In the split scenario, a mobile node can use DNS lookup by Service
   Name to discover the home agents, as defined in [RFC-5026].  For



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   example, if home agent reliability is required by a mobile node, DNS
   lookup by Service Name method is recommended for the mobile node to
   discover multiple home agent addresses.  Therefore, mobile nodes will
   query the DNS SRV records with a service name of mip6 and protocol
   name of ipv6.  The DNS SRV records includes multiple home agent
   addresses and different preference values and weights.  The mobile
   node SHOULD choose two or more home agents from the home agents list
   according to their preference value.  Then the mobile node should
   authenticate itself to these home agents via an IKEv2 exchange.

   In the integrated scenario, a mobile node can use DHCPv6 to get home
   agent provisioning from an MSP or ASP, as already defined in [ID-
   BOOTINT].  The only requirement is that the DHCPv6 response must
   include multiple home agents' information in order to support home
   agent reliability.

5.2.  IPsec/IKE Establishment to Home Agents

   In this document, a mobile node needs to manage an IPsec SA with a
   home agent(s).  The following mechanisms can be used to manage the
   IPsec SA(s) with a home agent(s):

   o  IKEv1/v2 running per home agent (HARP) to establish multiple IPsec
      SAs for home agents.

   o  The IKEv2 resumption mechanism [RFC-5723] to update an IPsec SA
      with the new home agent (VHARP)

   If an IPsec/IKEv2 state synchronization mechanism is available in
   Virtual Private Network (VPN) products, none of above is required for
   the VHARP operation.  The IPsec SAs per mobile node are seamlessly
   copied among multiple home agents.

   The mobile node MUST follow the standard IKEv2 exchange in the
   bootstrapping solution of the split scenario [RFC-5026].  If multiple
   IKEv2 operations are run per home agent, the mobile node MUST NOT
   attempt the home address assignment to standby home agents.

5.3.  Synchronizing State: K-bit treatment

   When a mobile node moves and the care-of address changes, it can use
   the Key Management Mobility Capability (K) bit in the Binding Update
   in order to update the peer endpoint of the key management protocol,
   for example, the IKE Security Association.

   If an active home agent receives a Binding Update with the K-bit set,
   it MUST process the Binding Update as specified in [RFC-3775].  In
   addition, the active home agent MUST notify the other standby home



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   agents of the care-of address change.  To do so, it MUST send a State
   Synchronization Reply message, including a Binding Cache Information
   option, to all the other standby home agents.  The flags of the
   Binding Update MUST be copied to the flags field of the Binding Cache
   Information option.  The standby home agents will update the peer
   endpoint of the key management protocol upon detecting the K-bit it
   set in the Flag field of the Binding Cache Information option.

   If the K-bit is not set in the Binding Update, an active home agent
   needs to rerun the key management protocol.  The active home agent
   MUST send State Synchronization Reply messages, including Binding
   Cache Information options, to all the other standby home agents.  The
   flags of the Binding Update MUST be copied to the flags field of the
   Binding Cache Information option.  The standby home agents that
   receive the State Synchronization Reply message will detect the
   care-of address change and rerun the key management protocol.

5.4.  Receiving Home Agent Switch message

   A mobile node must follow the verification and operations specified
   in [RFC-5142] when it receives a Home Agent Switch message.

   The Home Agent Switch message MUST be securely exchanged between a
   mobile node and a home agent by using IPsec ESP.

   When the mobile node receives a Home Agent Switch message, if the
   message contains the IPv6 address of a standby home agent, it MUST
   select the standby home agent as its active home agent and MUST send
   a new Binding Update message to it.

   The standby home agent address in the Home Agent Switch message MUST
   be equal to the sender of the Home Agent Switch message.  If the IPv6
   address stored in the Home Agent address field is different from the
   sender's source IPv6 address, the mobile node MUST send a binding
   update to the sender and MUST NOT use the IPv6 address in the Home
   Agent Switch message.


6.  Messages Format

6.1.  New Mobility Header Messages

6.1.1.  HARP Message Format

   The HARP message has the type field to identify different roles.  The
   HARP message has the MH Type value TBD.





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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      |   Group ID    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Sequence #           |A|R|V|M| Rsvd  |   Status      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Home Agent Preference    |      Home Agent Lifetime      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |        Hello Interval         |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
       |                                                               |
       .                        Mobility Options                       .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                    Figure 6: Home Agent Hello Message

   Type

      8-bit unsigned integer.  It can be assigned one of the following
      values:

         0: SwitchOver Request (SWO-REQ)

         Unicast by a standby home agent that desires to become the
         active home agent.  The receiver of the message MUST transition
         to standby state as soon as the message is received and
         validated successfully.

         1: SwitchOver Reply (SWO-REP)

         Used to acknowledge the receipt of the corresponding SWO-REQ.

         2: SwitchBack Request (SWB-REQ)

         Unicast by an active home agent that desires to become a
         standby home agent.  The receiver of this message SHOULD
         transition to active state as soon as the message is received
         and validated successfully.

         3: SwitchBack Reply (SWB-REP)

         Used to acknowledge the receipt of the corresponding SWB-REQ.






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         4: Switch Complete (SW-COMP)

         Used to indicate the completion of a switch-over, (i.e. sending
         Home Agent Switch messages, and receiving binding update
         messages from all the served mobile nodes).

         4: Home Agent HELLO (HA-HELLO)

         Used to carry home agent information among the redundant home
         agent set.  MUST be either unicast or multicast.  The HA-Hello
         message is defined for two purpose: 1) an alive check and 2)
         home agent information exchange.

   Group Identifier

      8-bit unsigned integer.  This value is used to identify a
      particular redundant home agent set.

   Sequence #

      16-bit unsigned integer.  The Sequence number of the HA-Hello
      message can be used to verify whether this Hello message is the
      latest one or not.

   (A)ctive flag

      Active Home Agent flag.  If this flag is set, the sender of this
      HA-Hello message is an active home agent.

   (R)equest flag

      HA-HELLO requesting flag.  If this flag is set, the receiver of
      this HA-Hello message must send back a HA-Hello message to the
      sender.

   (V)HARP capability flag

      VHARP capability Flag.  If a home agent is capable of IPsec/IKE
      state synchronization, it MUST set this flag.

   (M)ode flag

      A home agent MUST set this flag only when VHARP is used in the
      current operation.  If the flag is unset, the home agent currently
      operates HARP.  (HARP:0, VHARP:1)






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   Reserved

      This field is unused.  It MUST be initialized to zero by the
      sender and MUST be ignored by the receiver.

   Status

      8-bit unsigned integer indicating the disposition of a SWO-REQ or
      SWB-REQ.  This field is only valid in SWO-REP and SWB-REP
      messages.  The following Status values are defined:

         0: Success

         128: Reason unspecified

         129: Administratively prohibited

         130: Not active home agent (The receiver of SWO-REQ is not the
         active home agent)

         131: Not standby home agent (The receiver of SWB-REQ is already
         the active home agent)

         132: Not in same redundant home agent set

   Home Agent Preference

      16-bit unsigned integer.  The preference for the home agent
      sending the HA-Hello message.  This preference is the same as the
      Home Agent Preference value of the Home Agent Information option
      as defined in [RFC-3775].  However, operators MAY use a different
      preference value for this operation.

   Home Agent Lifetime

      16-bit unsigned integer.  The lifetime for the home agent sending
      the HA-Hello message.  This lifetime is the same as the Home Agent
      Lifetime value of the Home Agent Information option as defined in
      [RFC-3775].

   Hello Interval

      16-bit unsigned integer.  The interval for the home agent sending
      this Hello message.







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   Mobility Options

      Variable-length field of such length that the complete Mobility
      Header is an integer multiple of 8 octets long.  This field
      contains zero or more TLV-encoded mobility options.  The encoding
      and format of defined options are described in [RFC-3775].  The
      receiver MUST ignore and skip any options which it does not
      understand.  This specification does not define any options valid
      for the HARP message.

6.1.2.  State Synchronization Message Format

   This message is used to exchange state corresponding to a particular
   mobile node(s).  It MUST be unicast and MUST be authenticated by
   IPsec ESP.  This message has the MH Type value TBD.


        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      |A|   Reserved  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Identifier            |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
       .                                                               .
       .                        Mobility Options                       .
       .                                                               .
       .                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                  Figure 7: State Synchronization Message

   Type

      8-bit unsigned integer.  It can be assigned one of the following
      values:

         0: State Synchronization Request (SS-REQ)

         Used to solicit the active state corresponding to a particular
         mobile node.

         1: State Synchronization Reply (SS-REP)







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         Used between the home agents in the redundant home agent set to
         exchange binding cache and any other information related to
         providing mobility service to the mobile nodes.  Sent either
         periodically or in response to a SS-REQ.

         2: State Synchronization Reply-Ack (SS-ACK)

         This message is optional and is used only when the links
         between home agents are not reliable.

   (A)ck flag

      This flag is valid only for SS-REP.  If the sender requires
      explicit acknowledgment by an SS-ACK, it MUST set this flag.

   Reserved

      This field is unused.  It MUST be initialized to zero by the
      sender and MUST be ignored by the receiver.

   Identifier

      A 16-bit identifier to aid in matching state synchronization
      messages.  The identifier should never be set to 0.  It should
      always be more than 1.

   Mobility Options

      Variable-length field of such length that the complete Mobility
      Header is an integer multiple of 8 octets long.  This field
      contains zero or more TLV-encoded mobility options.  The encoding
      and format of defined options are described in [RFC-3775].  The
      receiver MUST ignore and skip any options which it does not
      understand.  This message requires at least one mobility option,
      therefore, there is no default length for this message.

      Binding Cache Information Option is mandatory in the SS-REQ
      message.  Multiple options can be stored in the same SS-REQ
      message.  A home agent includes the mobile node's home address in
      the Binding Cache Information option.  If a home agent wants to
      solicit all the active mobile nodes' states, it can include the
      unspecified address (::) in an IPv6 address option.

      Binding Cache Information option is mandatory in SS-REP.  SS-REP
      can carry many mobility options.  The following options are just
      examples.





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      *  AAA Information Option

      *  Vendor Specific Mobility Option [RFC-5094]

      *  Mobile Network Prefix Option [RFC-3963]

      *  IPv4 Care-of Address Option [RFC-5555]

      *  IPv4 Home Address Option [RFC-5555]

      *  Binding Identifier Option [RFC-5648]

6.1.3.  Home Agent Rekey Message

   This message is used to indicate that the mobile node SHOULD start an
   IPsec re-key with the home agent specified in the Home Agent
   Addresses field.  This message is used when a failed home agent
   recovers and needs to re-establish IPsec SA/IKE state with a mobile
   node.  This message MUST be unicast to a mobile node by the active
   home agent and MUST be authenticated and encrypted by IPsec ESP.  The
   Home Agent Rekey message has the MH Type value TBD.  If no options
   are present in this message, no padding is necessary and the Header
   Len field will be set to 2.


       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
                                      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                      |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      .                      Home Agent Addresses                     .
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                        Mobility options                       .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                    Figure 8: Home Agent Rekey Message

   Reserved

      A 16-bit field reserved for future use.  The value MUST be
      initialized to zero by the sender, and MUST be ignored by the
      receiver.




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   Home Agent Address

      The receiver of this message MUST re-key the security association
      with the specified home agent.

   When a mobile node receives a Home Agent Rekey message, it MUST
   verify the message as follows:

   o  The message MUST be sent from the receiver's active home agent.
      Otherwise, the message MUST be discarded.

   o  The message MUST be protected by IPsec ESP.  Otherwise, the
      message MUST be discarded.

   o  The message SHOULD contain one of the standby home agent's
      addresses.  If the home agent address is not known from the
      bootstrapping described in Section 5.1, the mobile node MUST NOT
      start an IKE re-key session with the unknown home agent.  Instead,
      it SHOULD re-start home agent discovery to update its home agent
      address information.

   If all the above verifications are satisfied, the mobile node MUST
   re-key the SA with the home agent addresses stored in the Home Agent
   Addresses field.

6.2.  New Mobility Options

6.2.1.  Binding Cache Information Option

   The Binding Cache Information option is used to carry Binding Cache
   Information of each mobile node.  This option is only valid in a
   State Synchronization message.  Its format is as follows:



















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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 = TBD  |     Length    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                        Home Address                           |
       +                                                               +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :                                                               :
       +                                                               +
       :                                                               :
       +                        Care-of Address                        +
       :                                                               :
       +                                                               +
       :                                                               :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :          Flags                :       Sequence Number         :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :          Lifetime             :          Reserved             :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                Figure 9: Binding Cache Information Option

   Length

      8-bit unsigned integer, representing the length in octets of the
      mobility option, not including the Option Type and Option Length
      fields.  There are two valid length values, 16 and 40, depending
      on the number of fields in use.  The alignment requirement is
      either 8n+6 (length 16) or 8n+2 (length 40).

   Home Address

      The Home Address of a mobile node.

   Care-of Address

   Flags







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   Sequence Number

   Lifetime

      Optional values only used in VHARP, in which case the
      corresponding value from the binding cache database of the active
      home agent is copied into each field.

   Reserved

      A 16-bit field reserved for future use.  The value MUST be
      initialized to zero by the sender, and MUST be ignored by the
      receiver.

6.2.2.  State Synchronization Status Option

   The State Synchronization Status option is used to carry the status
   value of an SS-ACK for a received SS-REP.  In [ID-HAHA], SS-ACK is
   mandatory in response of an SS-REP to update global binding
   registration status.


        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 = TBD  |  Length = 20  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Status       |                  Reserved                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                        Home Address                           |
       +                                                               +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


              Figure 10: State Synchronization Status Option

   Status

      8-bit unsigned integer indicating the status of the SS-REP.

      *  0: Success





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      *  128: Reason unspecified

      *  129: Malformed SS-REP

      *  130: Not in same global home agent set

   Reserved

      A 24-bit field reserved for future use.  The value MUST be
      initialized to zero by the sender, and MUST be ignored by the
      receiver.

   Home Address

      Corresponding home address of the mobile node.

6.2.3.  AAA Information Option

   This option is used to carry the AAA state of the mobile node's
   Mobile IPv6 sessions.  The AAA state information can be carried in
   RADIUS or Diameter AVP formats, including the user and session info.
   This information option is only valid in a State Synchronization
   message.


        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 = TBD  |   Length      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       .                                                               .
       .                        AAA AVPs                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 11: AAA Information Option

   Length

      8-bit unsigned integer, representing the length in octets of the
      mobility option, not including the Option Type and Option Length
      fields.

   AAA AVPs






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      A series of TLV-encoded AAA AVPs (including vendor specific AVPs)
      carrying AAA-related information for each Mobile IPv6 and IPsec/
      IKE session.


7.  Security Considerations

   All the messages newly defined in this document SHOULD be secured by
   IPsec ESP.  When a HA-HELLO message is multicast, the multicast
   extensions to IPsec [RFC-5374] is used.  In some operational
   scenarios, home agents are located deep in the core network and
   securely managed.  If there is a secure transport network between
   home agents, some of security mechanism can be disabled, depending on
   administrative policy.

   A Home Agent Switch message is reused for signaling between a home
   agent and a mobile node in HARP.  It is protected by IPsec ESP as
   defined in [RFC-5142].

   When an active home agent fails, mobile nodes using that home agent
   need to change their home agent to one of standby home agents.  The
   mobile node needs to update or establish the IPsec SA with the new
   home agent as described in Section 5.2.  Existing mechanisms
   [RFC5723] are applied to this operation.


8.  Protocol Constants

      INITIAL_STATE_SYNC_REQ_TIMER: 3sec

      INITIAL_SWITCH_REQ_TIMER: 1sec

      MAC_HARELIABILITY_TIMEOUT 16sec

      ALL_HA_MULTICAST_ADDR: TBD


9.  Protocol Configuration Variables

      LINK_TRAVERSAL_TIME: default 150msec


10.  IANA Considerations

   The following Extension Types MUST be assigned by IANA:

   o  Home Agent Reliability Protocol (HARP) Message




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   o  State Synchronization (SS) Message

   o  Binding Cache Information Option

   o  AAA Information Option

   o  A new link-local multicast address (ALL_HA_MULTICAST_ADDR) for all
      home agents will be assigned by the IANA.


11.  Additional Authors

   This document is a result of discussions in the Mobile IPv6 Home
   Agent Reliability Design Team.  The members of the design team that
   are listed below are authors that have contributed to this document:

   Samita Chakrabarti

      samita.chakrabarti@azairenet.com

   Kuntal Chowdhury

      kchowdhury@starentnetworks.com

   Hui Deng

      denghui@chinamobile.com

   Vijay Devarapalli

      vijay.devarapalli@azairenet.com

   Sri Gundavelli

      sgundave@cisco.com

   Brian Haley

      brian.haley@hp.com

   Behcet Sarikaya

      behcet.sarikaya@huawei.com

   Ryuji Wakikawa






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      ryuji.wakikawa@gmail.com


12.  Acknowledgements

   This document includes a lot of text from [ID-LOCALHAHA] and [ID-
   HAHA].  Therefore the authors of these two documents are
   acknowledged.  We would also like to thank the authors of the home
   agent reliability problem statement [ID-PS-HARELIABILITY] for
   describing the problem succinctly and Alice Qin for her work on the
   hello protocol.


13.  References


13.1.  Normative References

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

   [RFC-3775] Johnson, D., Perkins, C., Arkko, J., "Mobility Support in
   IPv6", RFC 3775, June 2004.

   [ID-3775bis] Perkins, C., Johnson, D., Arkko, J., "Mobility Support
   in IPv6", draft-ietf-mext-rfc3775bis-10.txt, Octover 2010.

   [RFC-3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
   Thubert, "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
   January 2005.

   [RFC-5026] Giaretta, G., "Mobile IPv6 bootstrapping in split
   scenario", RFC 5026, October 2007.

   [RFC-5094] Devarapalli, V., "Mobile IPv6 Vendor Specific Option", RFC
   5094, October 2007.

   [RFC-5142] Haley, B., "Mobility Header Home Agent Switch Message",
   RFC-5142, November 2007.

   [RFC-5374] B. Weis, G. GrossD.  Ignjatic, "Multicast Extensions to
   the Security Architecture for the Internet Protocol", RFC 5374,
   November 2008

   [RFC-5555] Soliman, H. et al, "Mobile IPv6 support for dual stack
   Hosts and Routers (DSMIPv6)", RFC-5555, June 2009.

   [RFC-5648] Wakikawa, R., Devarapalli, V., Tsirtsis, G., Ernst, T.,



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   and K. Nagami, "Multiple Care-of Addresses Registration", RFC 5648,
   October 2009.

   [ID-BOOTINT] Chowdhury, K. and A. Yegin, "MIP6-bootstrapping via
   DHCPv6 for the Integrated Scenario",
   draft-ietf-mip6-bootstrapping-integrated-dhc-06 (work in progress),
   April 2008.

13.2.  Informative References

   [RFC-2281] Li, T., Cole, B., Morton, P., and D. Li, "Cisco Hot
   Standby Router Protocol (HSRP)", RFC 2281, March 1998.

   [RFC-3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
   RFC 3753, June 2004.

   [RFC-3768] Hinden, R., "Virtual Router Redundancy Protocol (VRRP)",
   RFC 3768, April 2004.

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

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

   [RFC-5723] Y. Sheffer, H. Tschofenig, "Internet Key Exchange Protocol
   Version 2 (IKEv2) Session Resumption", RFC 5273, January 2010.

   [RFC-5798] S. Nadas, "Virtual Router Redundancy Protocol Version 3
   for IPv4 and IPv6", RFC 5798 (soon?), December 2009.

   [ID-HAHA] Wakikawa, R., "Inter Home Agents Protocol Specification",
   draft-wakikawa-mip6-nemo-haha-spec-01 (expired), March 2006.

   [ID-LOCALHAHA] Devarapalli, V., "Local HA to HA protocol",
   draft-devarapalli-mip6-nemo-local-haha-01 (expired), March 2006.

   [ID-PS-HARELIABILITY] Faizan, J., "Problem Statement: Home Agent
   Reliability", draft-jfaizan-mipv6-ha-reliability-01 (expired),
   February 2004.











Wakikawa (Editor)       Expires November 11, 2011              [Page 43]


Internet-Draft               HA Reliability                     May 2011


Author's Address

   Ryuji Wakikawa
   TOYOTA InfoTechnology Center, U.S.A., Inc.
   465 Bernardo Avenue
   Mountain View, CA  94043
   USA

   Email: ryuji.wakikawa@gmail.com










































Wakikawa (Editor)       Expires November 11, 2011              [Page 44]


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