





Internet Engineering Task Force (IETF)                       G. Tsirtsis
Request for Comments: 6626                                       V. Park
Updates: 5177                                               V. Narayanan
Category: Standards Track                                       Qualcomm
ISSN: 2070-1721                                                 K. Leung
                                                                   Cisco
                                                                May 2012


                     Dynamic Prefix Allocation for
               Network Mobility for Mobile IPv4 (NEMOv4)

Abstract

   The base Network Mobility for Mobile IPv4 (NEMOv4) specification
   defines extensions to Mobile IPv4 for mobile networks.  This
   specification defines a dynamic prefix allocation mechanism for
   NEMOv4.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6626.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.




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Table of Contents

   1. Introduction ....................................................2
   2. Requirements Notation ...........................................2
   3. Dynamic Mobile Prefix Allocation ................................2
      3.1. Mobile Client Considerations ...............................2
      3.2. Home Agent Considerations ..................................3
   4. Security Considerations .........................................4
   5. IANA Considerations .............................................4
   6. Acknowledgements ................................................4
   7. Normative References ............................................4

1.  Introduction

   The base NEMOv4 specification [RFC5177] defines extensions to Mobile
   IPv4 [RFC5944] for mobile networks.  This specification adds support
   for dynamic allocation of mobile prefixes by the home agent.

2.  Requirements Notation

   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 [RFC2119].

3.  Dynamic Mobile Prefix Allocation

   The following extension is defined according to this specification.

3.1.  Mobile Client Considerations

   According to this specification, the Prefix field of the Mobile
   Network Request extension MUST be set to zero to indicate that the
   Mobile Router requests mobile network prefix(es) be assigned to it by
   the home agent.  In this case, the Mobile Router MAY set the prefix
   length field of such extensions to zero or to a length of its choice
   as a hint to the home agent.  According to this specification, Mobile
   Network Request extensions with the Prefix field set to zero MAY be
   included in a registration request message either during initial
   registration or during a subsequent registration.

   When a Mobile Router receives a registration reply, it MUST process
   it as defined in Mobile IPv4 [RFC5944] and [RFC5177].  If one or more
   network acknowledgement extensions are included with the Code field
   set to "Success", the Mobile Router SHOULD treat the prefixes in the
   corresponding Prefix fields as allocated prefixes and create the
   appropriate bindings as defined in [RFC5177].





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   In response to a registration request with a Mobile Network Request
   extension with the Prefix field set to zero, if a Mobile Router
   receives a registration reply with a network acknowledgement
   extension including Code field set to 1 "invalid prefix", it may use
   it as a hint that the home agent does not support dynamic prefix
   allocation.

3.2.  Home Agent Considerations

   A home agent receiving a Mobile Network Request extension with the
   Prefix field set to zero MAY return a Mobile Network Acknowledgement
   extension [RFC5177] with the Prefix field set to the prefix allocated
   to the Mobile Router.  The length of that prefix is at the discretion
   of the home agent.  The home agent MAY take into account the prefix
   length hint if one is included in the Mobile Network Request
   extension.  Once the home agent allocates a prefix, it MUST maintain
   the prefix registration table as defined in [RFC5177].
   Alternatively, the home agent MAY return a Mobile Network
   Acknowledgement extension with the Code field set to one of the
   negative codes defined in [RFC5177].

   Dynamic mobile prefix allocation, as defined in this specification,
   MAY be combined with dynamic home address allocation, as defined in
   [RFC5177].  In other words, the home address field of the
   registration request message MAY be set to zero while the message
   also includes one or more Mobile Network Request extensions with the
   Prefix field also set to zero.

   Once the home agent allocates a prefix, it MUST maintain the prefix
   registration table as defined in [RFC5177].  The lifetime of the
   allocated prefix will be equal to the lifetime of the binding cache
   entry.  The Mobile Router may request for multiple mobile network
   prefixes to be assigned by the home agent.  For a Mobile Network
   Prefix for which the assignment was unsuccessful, the Code field in
   the corresponding Mobile Network Acknowledgement extension should be
   set to 4 (MOBNET_UNASSIGNED).

   For dynamic prefix allocation, the Mobile Router's home address MAY
   be used to identify the client if it is not set to zero.  Otherwise,
   as defined in the Network Access Identifier (NAI) extension [RFC2794]
   of Mobile IPv4 [RFC2794], the NAI extension needs to be included in
   the registration request, in which case the same extension SHOULD be
   used to identify the Mobile Router for prefix allocation purposes.








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4.  Security Considerations

   This specification operates in the security constraints and
   requirements of Mobile IPv4 [RFC5944], NAI [RFC2794], and [RFC5177].

   Home agent implementations SHOULD take steps to prevent address
   exhaustion attacks.  One way to limit the effectiveness of such an
   attack is to limit the number and size of prefixes any one Mobile
   Router can be allocated.

5.  IANA Considerations

   A new value has been assigned in the Mobile Network Acknowledgement
   Extension registry: 4 - Home Agent cannot assign a mobile network
   prefix (MOBNET_UNASSIGNED).

6.  Acknowledgements

   The authors would like to thank Pete McCann, Alexandru Petrescu,
   Ralph Droms, and Jari Arkko for their reviews and comments.

7.  Normative References

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

   [RFC2794]  Calhoun, P. and C. Perkins, "Mobile IP Network Access
              Identifier Extension for IPv4", RFC 2794, March 2000.

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

   [RFC5944]  Perkins, C., "IP Mobility Support for IPv4, Revised",
              RFC 5944, November 2010.
















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Authors' Addresses

   George Tsirtsis
   Qualcomm

   EMail: tsirtsis@googlemail.com


   Vincent Park
   Qualcomm

   Phone: +908-443-8141
   EMail: vpark@qualcomm.com


   Vidya Narayana
   Qualcomm

   Phone: +858-845-2483
   EMail: vidyan@qualcomm.com


   Kent Leung
   Cisco

   Phone: +408-526-5030
   EMail: kleung@cisco.com
























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