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Mobile IPv4 Dynamic Home Agent (HA) Assignment
RFC 4433

Network Working Group                                        M. Kulkarni
Request for Comments: 4433                                      A. Patel
Category: Standards Track                                       K. Leung
                                                      Cisco Systems Inc.
                                                              March 2006

            Mobile IPv4 Dynamic Home Agent (HA) Assignment

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   Mobile IPv4 (RFC 3344) uses the home agent (HA) to anchor sessions of
   a roaming mobile node (MN).  This document proposes a messaging
   mechanism for dynamic home agent assignment and HA redirection.  The
   goal is to provide a mechanism to assign an optimal HA for a Mobile
   IP session while allowing any suitable method for HA selection.

Kulkarni, et al.            Standards Track                     [Page 1]
RFC 4433                 Dynamic HA Assignment                March 2006

Table of Contents

   1. Introduction ....................................................3
   2. Requirements Terminology ........................................3
   3. Problem Statement ...............................................5
      3.1. Scope ......................................................5
      3.2. Dynamic Home Agent Discovery in Mobile IPv4 ................5
      3.3. NAI Usage and Dynamic HA Assignment ........................6
      3.4. Dynamic HA Extension .......................................6
           3.4.1. Requested HA Extension ..............................7
           3.4.2. Redirected HA Extension .............................7
   4. Messaging Mechanism for Dynamic HA Assignment/Redirection .......7
      4.1. Messaging for Dynamic HA Assignment ........................7
           4.1.1. Example with Message Flow Diagram ...................8
      4.2. Messaging for HA Redirection ..............................10
           4.2.1. Example with Message Flow Diagram ..................12
   5. Mobility Agent Considerations ..................................14
      5.1. Mobile Node Considerations ................................14
           5.1.1. MN Using FA CoA ....................................14
           5.1.2. MN Using Co-Located CoA ............................15
           5.1.3. Refreshing Assigned HA Address on Mobile Node ......16
      5.2. Foreign Agent Considerations ..............................16
      5.3. Home Agent Considerations .................................17
           5.3.1. Assigned Home Agent Considerations .................17
   6. Requested Home Agent Selection .................................19
   7. Error Values ...................................................20
   8. IANA Considerations ............................................20
   9. Security Considerations ........................................20
   10. Backward-Compatibility Considerations .........................21
   11. Acknowledgements ..............................................23
   12. Normative References ..........................................23

Kulkarni, et al.            Standards Track                     [Page 2]
RFC 4433                 Dynamic HA Assignment                March 2006

1.  Introduction

   This document adds to the Mobile IP protocol [1], by proposing a
   messaging mechanism for dynamic home agent assignment and home agent
   redirection during initial registration.  The goal is to assign an
   optimal HA for a Mobile IP session.  The mobile node MUST use the
   Network Access Identifier (NAI) extension [2] when requesting a
   dynamically assigned HA.

   The MN requests a dynamically assigned HA by setting the HA field in
   the initial Registration Request to ALL-ZERO-ONE-ADDR (defined in
   Section 2).  If the request is accepted, the HA sends a successful
   Registration Reply containing the HA's own address.  The requested HA
   can suggest an alternate HA and if so, the Registration Reply is
   rejected with a new error code REDIRECT-HA-REQ and the alternate HA
   address is specified in a new extension (Redirected HA Extension).

   This document also defines a new Requested HA Extension for use in
   Registration Requests when the HA field is set to ALL-ZERO-ONE-ADDR.
   The Requested HA address is a hint to the network about the MN's

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