[Search] [txt|pdf|bibtex] [Tracker] [Email] [Nits]

Versions: 00                                                            
Network Working Group                                             D. Liu
Internet-Draft                                                   H. Deng
Intended status: Standards Track                            China Mobile
Expires: September 6, 2012                                        W. Luo
                                                                     ZTE
                                                           March 5, 2012


                     DMM Dynamic Anchor Discussion
               draft-liu-dmm-dynamic-anchor-discussion-00

Abstract

   Distributed mobility management aims to distribute the mobility
   anchor to the access network level to avoid the centralized mobility
   anchor problem.  By distributing the mobility anchor, the traffic can
   be distributed in an optimal way.  There are many different proposals
   for DMM solution, one of those types of solution is called "dynamic
   anchor".  This document analyses the limitations of current dynamic
   anchor solution and discusses the possible solution to overcome those
   limitations.

Requirements Language

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

Status of this Memo

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

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

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

   This Internet-Draft will expire on September 6, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the



Liu, et al.             Expires September 6, 2012               [Page 1]


Internet-Draft     draft-liu-dmm-dynamic-discussion-00        March 2012


   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.


Table of Contents

   1.  Problem of dynamic anchor and potential solution  . . . . . . . 3
     1.1.  Active session managment  . . . . . . . . . . . . . . . . . 3
     1.2.  Soure address selection . . . . . . . . . . . . . . . . . . 4
     1.3.  CN address selection  . . . . . . . . . . . . . . . . . . . 4
     1.4.  IPv4 support  . . . . . . . . . . . . . . . . . . . . . . . 4
     1.5.  Resource consumption consideration  . . . . . . . . . . . . 5
   2.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     5.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6























Liu, et al.             Expires September 6, 2012               [Page 2]


Internet-Draft     draft-liu-dmm-dynamic-discussion-00        March 2012


1.  Problem of dynamic anchor and potential solution

   As draft [I-D.draft-seite-dmm-dma-00] introduced, the main idea of
   dynamic anchor is distributing the mobility anchor function in the
   access router (MAR).  The newly initiated session is routed through
   the current MAR, only the original sessions that established before
   handover will be maintained at the previous anchor.  As the following
   figure shows, flow1 is anchored to MAR1, flow2 is anchored to MAR2.
   Two different prefixes are assigned to the MN.

                            +--------------+
                            | Policy Server|
                            +-.-'--+-----`.+
          +---+             .'     |       `. flow2 +----+
          |CN1|          .-'       |         `.____,| CN2|
          ++--+        .'          |    ,-'''' `.   +----+
       flow1\ +-----.-'--+    +----+--.'-+   +---`.-----+
              +-------.  |    |       |  |   |          |
              |   MAR1 `-+-'''''-..MAR2.'|   |    MRA3  |
              +----------+    +----+-+---+   +----------+
                                   | |
                             HNP1  | | HNP2
                                +--`-+-+
                                |  MN  |
                                +------+
   Figure 1 There are several potential problems for this solution

1.1.  Active session managment

   In this dynamic anchor solution, the MAR needs to know whether a
   prefix is active, if not, the MAR need to release the mobility
   binding.  For instance, when the MN attach to MAR1, MAR1 detects the
   attachment of MN and allocate HNP1 to the MN.  When the MN moves to
   MAR2, MAR2 needs to know that there is one on-going session in the MN
   and needs to trigger mobility binding update to MAR1 to update the
   binding.

   The question is how MAR2 know that there is an active session for
   HNP1 in MN?  The first approach is to use policy server to store the
   MN-ID and corresponding home network prefix that allocate to the MN.
   When MN moves to MAR2, as mentioned in [I-D.draft-seite-dmm-dma-00],
   MAR2 first check the policy server and find that MN is anchored to
   MAR1, then it can send binding update message to MAR1.  But only that
   is not enough.  MAR2/MAR1 has to have some mechanism to trigger the
   release HNP1, otherwise the MAR1 will always be occupied by the MN as
   one of its anchor point.  This will lead system capacity waste.  For
   example, after the on-going session is terminated, the MAR2 need to
   release the HNP1.



Liu, et al.             Expires September 6, 2012               [Page 3]


Internet-Draft     draft-liu-dmm-dynamic-discussion-00        March 2012


   The question is that the policy server does not know when to release
   HNP1.  One of possible solution is that MAR2 can inspect the traffic
   that has the source address prefix equals to HNP1.  When MAR2 finds
   that there is no traffic sourced from HNP1 for a certain time, it can
   send deregistration binding update to MAR1 and release the binding
   state for HNP1.  It seems that MAR2 needs a certain kind of timer to
   support the inspection for each sessions.  If in this way, system
   capacity consumed by those timers can not be ignored since the
   traffic from hundreds of mobile nodes which are in a same MAR may
   have many thousands of sessions.

1.2.  Soure address selection

   MN may be configured with multiple addresses.  For example, MN can
   have HNP1 and HNP2 at the same time.  In this case, the MN's
   application need to select the correct source address.  For example,
   there maybe a VoIP session running using HNP1 when MN attaches to
   MAR1.  When MN moves to MAR2 , the VoIP session need to continue.
   When the user start a web browser, MAR2 will allocate a new perfix:
   HNP2.  The VoIP software need to select HNP1 as the source address
   and the web browser need to select HNP2 as source address.  RFC3484
   specifies the source address selection rules for IPv6 but RFC3484 is
   not enough to cope with this situation since RFC3284 does not specify
   how to select source address for a particular application.

   To solve this problem, the host may use the following rules for
   source address selection:

   a.  For any on-going session, keep to use the original address even
       there is a newly address been configured for the same interface.

   b.  For any new session, always choose to use the newly allocated
       address.  The new MAR need to advertise the newly allocated
       prefix as the highest priority.

1.3.  CN address selection

   From the CN's perspective, the MN has multiple addresses, the CN
   needs to know which one it should use when it wants to initiate a
   session to MN.

1.4.  IPv4 support

   It will worse the IPv4 address depletion problem if use the dynamic
   anchor solution for IPv4 since each MN will need multiple IP
   addresses in that case.





Liu, et al.             Expires September 6, 2012               [Page 4]


Internet-Draft     draft-liu-dmm-dynamic-discussion-00        March 2012


1.5.  Resource consumption consideration

                 _.------.
           ,---''         `------------------.
         ,'         +----------+              `-.
        /           |Session DB|                 :
       (            +----------+                MARn
        \                                       /  ``---MN
         `.                              _.----'(HoA1,HoA2,HoA3,..,HoAn)
           'MAR1----MAR2------------MAR3'           ..+
           .'        \                     move _..-'/
         .'   move    \      move      __..--''
        MN  --------> MN   --------> MN
      (HoA1)       (HoA1,HoA2)    (HoA1,HoA2,HoA3)
   Figure2.  Resource consumption

   As illustrated in figure2, during the movement, mobile node gets more
   and more HoAs and more and more MARs will be occupied by this mobile
   node as its anchor points.  The mobile node could maintain its HoAs
   by keep on sending packets at very low data rate for each sessions.
   In this way, capacity of the network will be consumed, e.g. many
   tunnels should be maintained among those MARs, many mobility contexts
   for this mobile node should be maintained among those MARs, and the
   operator will gain almost nothing from this mobile node.
   Additionally, the scenario described above provides a possibility for
   attackers to consume network resource maliciously.


2.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.


3.  Security Considerations

   TBD


4.  Acknowledgements

   TBD


5.  References




Liu, et al.             Expires September 6, 2012               [Page 5]


Internet-Draft     draft-liu-dmm-dynamic-discussion-00        March 2012


5.1.  Normative References

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

5.2.  Informative References

   [I-D.draft-seite-dmm-dma-00]
              Seite , P. and P. Bertin, "Distributed Mobility Anchoring,
              draft-seite-dmm-dma-00", February 2012.


Authors' Addresses

   Dapeng Liu
   China Mobile
   32 Xuanwumen West Street
   Beijng, Xicheng District,   100053
   China

   Phone: +86-13911788933
   Email: liudapeng@chinamobile.com


   Hui Deng
   China Mobile
   32 Xuanwumen West Street
   Beijng, Xicheng District,   100053
   China

   Phone: +86-13911788933
   Email: denghui@chinamobile.com


   Wen Luo
   ZTE
   No.68, Zijinhua RD,Yuhuatai District
   Nanjing, Jiangsu  210012
   China

   Email: luo.wen@zte.com.cn










Liu, et al.             Expires September 6, 2012               [Page 6]