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RFC 6279

Proxy Mobile IPv6 (PMIPv6) Localized Routing Problem Statement

Pages: 14
Informational

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Internet Engineering Task Force (IETF)                   M. Liebsch, Ed.
Request for Comments: 6279                                           NEC
Category: Informational                                         S. Jeong
ISSN: 2070-1721                                                     ETRI
                                                                   Q. Wu
                                                                  Huawei
                                                               June 2011


     Proxy Mobile IPv6 (PMIPv6) Localized Routing Problem Statement

Abstract

Proxy Mobile IPv6 is the IETF Standard for network-based mobility management. In Proxy Mobile IPv6, mobile nodes are topologically anchored at a Local Mobility Anchor, which forwards all data for registered mobile nodes. The setup and maintenance of localized routing, which allows forwarding of data packets between two mobile nodes' Mobility Access Gateways without involvement of their Local Mobility Anchor in forwarding, is not considered. This document describes the problem space of localized routing in Proxy Mobile IPv6. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. 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). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see 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/rfc6279.
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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
   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 ....................................................2 2. Conventions and Terminology .....................................3 3. Problem Statement for Localized Routing in PMIPv6 ...............4 3.1. General Observation ........................................4 3.2. Use Cases Analysis .........................................5 3.3. IPv4 Considerations ........................................8 3.3.1. Localized Routing for Communication between IPv4 Home Addresses .................................8 3.3.2. IPv4 Transport Network Considerations ...............9 4. Functional Requirements for Localized Routing ...................9 5. Roaming Considerations .........................................10 6. Security Considerations ........................................11 7. Acknowledgments ................................................12 8. References .....................................................13 8.1. Normative References ......................................13 8.2. Informative References ....................................13

1. Introduction

The IETF has specified Proxy Mobile IPv6 (PMIPv6) [RFC5213] as the base protocol for network-based localized mobility management (NetLMM). The scope of the base protocol covers the setup and maintenance of a tunnel between a Mobile Node's (MN's) Mobile Access Gateway (MAG) and its selected Local Mobility Anchor (LMA). Data packets will always traverse the MN's MAG and its LMA, irrespective of the location of the MN's remote communication endpoint. Even though an MN may be attached to the same MAG or a different MAG as its Correspondent Node (CN) within the same provider domain, packets being associated with their communication will traverse the MN's and the CN's LMA, which can be located topologically far away from the MN's and the CN's MAG or even in a separate provider domain.
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   [RFC5213] addresses the need to enable local routing of traffic
   between two nodes being attached to the same MAG, but does not
   specify the complete procedure to establish such localized routing
   state on the shared MAG.

   The NetLMM Extensions (NetExt) Working Group has an objective to
   design a solution for localized routing in PMIPv6.  This objective
   includes the specification of protocol messages and associated
   protocol operation between PMIPv6 components to support the setup of
   a direct routing path for data packets between the MN's and the CN's
   MAG, while both hosts receive mobility service according to the
   PMIPv6 protocol [RFC5213].  As a result of localized routing, these
   packets will be forwarded between the two associated MAGs without
   traversing the MN's and the CN's LMA(s).  In cases where one or both
   nodes hand over to a different MAG, the localized routing protocol
   maintains the localized routing path.  Relevant protocol interfaces
   may include the interface between associated MAGs, between a MAG and
   an LMA, and between LMAs.  The setup of localized routing with CNs
   not registered with a PMIPv6 network is out of scope of the NetExt
   solution and this problem statement.

   This document analyzes and discusses the problem space of always
   using the default route through two communicating mobile nodes' local
   mobility anchors.  Furthermore, the problem space of enabling
   localized routing in PMIPv6 is analyzed and described, while
   different communication and mobility scenarios are taken into
   account.  Based on the analysis, a list of key functional
   requirements is provided, serving as input to the design of the
   protocol solution.

2. Conventions and 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 [RFC2119]. This document uses the terminology of [RFC5213]. In addition, the following terms are used in the context of this problem statement: o Mobile Node (MN): Mobile Node without IP mobility support, which is attached to a Mobile Access Gateway (MAG) and registered with a Local Mobility Anchor (LMA) according to the PMIPv6 specification [RFC5213].
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   o  Correspondent Node (CN): Correspondent Node according to its
      definition in [RFC3775] with or without IP mobility support.  The
      CN represents the communication peer of an MN that is attached to
      a MAG and registered with an LMA according to the PMIPv6
      specification.

   o  Localized Routing: Result of signaling to set up routing states on
      relevant network entities to allow forwarding of data packets
      between an MN and a CN, which are attached to MAGs sharing the
      same provider domain, without intervention of the MN's LMA and the
      CN's LMA in data forwarding.

   o  Localized Routing States: Information for localized routing on
      relevant forwarding entities on the optimized data path between an
      MN and a CN.  Such information includes route entries and tunnel
      endpoints and may include further information about the MN and the
      CN, such as the communicating nodes' Mobile Node Identifier and
      their assigned Home Network Prefix.

   o  Provider Domain: A network domain in which network components are
      administered by a single authority, e.g., the mobile operator.

3. Problem Statement for Localized Routing in PMIPv6

3.1. General Observation

The Mobile IPv6 (MIPv6) protocol [RFC3775] has built-in mechanisms for direct communication between an MN and a CN. Mechanisms for route optimization in MIPv6 cannot be directly applied in PMIPv6. Following the paradigm of PMIPv6, MNs are not involved in mobility signaling and hence cannot perform signaling to set up localized routes. Instead, the solution for localized routing must consider functions in the network to find out whether or not a localized route is to be used and then control the setup and maintenance of localized routing states accordingly without any assistance from the MN and the CN. In the case of communication between two nodes attached to the PMIPv6 network infrastructure and where each node is registered with an LMA, data packets between these two nodes will always traverse the responsible LMA(s). At least some deployments would benefit from having such communication localized, rather than having packets traverse the core network to the LMA(s). In the context of this document, such localized communication comprises offloading traffic from LMAs and establishing an optimized forwarding path between the two communication endpoints. Localized routing is understood in [RFC5213] as optimization of traffic between an MN and a CN that are attached to an access link connected to the same MAG. In such a case, the MAG forwards traffic
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   directly between the MN and the CN, assuming the MAG is enabled to
   support this feature (setting of the EnableMAGLocalRouting flag on
   the MAG) and the MN's LMA enforces this optimization.  [RFC5213] does
   not specify how an LMA can enforce optimization for such local
   communication.  Maintaining local forwarding between the MN and the
   regular IPv6 CN gets more complex in the case where the MN performs a
   handover to a different MAG.  Such a use case is not considered in
   the specification and is out of scope of this problem statement.
   This document focuses on use cases where both nodes, the MN and the
   CN, are within a PMIPv6 network and served by an LMA in a domain of
   LMAs.

   With localized routing, operators have the possibility of offloading
   traffic from LMAs and from the core network.  Establishment of a
   direct path between the MN's and the CN's MAG can be beneficial for
   the following reasons: First, by limiting the communication to the
   access nodes, the data traffic traversing the MAG - LMA path
   (network) can be reduced.  This is significant, considering that the
   transport network between the access and the core is often the
   bottleneck in terms of costs and performance.  Second, there may be
   performance benefits for data flows between the MN and the CN in
   terms of delay and packet loss, especially when the MN and the CN are
   attached to the same MAG and the LMA is topologically far away from
   that MAG.  Even when the MN and the CN are attached to different
   MAGs, there could be benefit in limiting the communication to the
   access network only, rather than traversing the transport network to
   the LMA.  Furthermore, offloading traffic from the LMA by means of
   localized routing can improve scalability of the LMA, as it
   represents a bottleneck for traffic being forwarded by many MAGs.

3.2. Use Cases Analysis

This problem statement focuses on local communication between PMIPv6 managed nodes, which attach to MAGs sharing the same provider domain. The following list analyzes different use cases, which consider the existence of multiple LMAs. Figure 1 depicts a PMIPv6-based network with two mobility anchors. According to [RFC5213], the MN moves in the PMIPv6 domain being built by its LMA and MAG. The same applies to the CN, which moves in the PMIPv6 domain built by the CN's LMA and MAG. The analysis takes no assumption on whether the MN and the CN share the same PMIPv6 domain or not.
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                              Internet Backbone
                             :                  :
                             +------------------+
                             |                  |
                          +----+              +----+
                          |LMA1|              |LMA2|
                          +----+              +----+
                             |                  |
                             |                  |
                        +----+------------------+----+
                        |                            |
                     +----+                       +----+
                     |MAG1|                       |MAG2|
                     +----+                       +----+
                     :    :                          :
                   +---+ +---+                     +---+
                   |MN | |CN1|                     |CN2|
                   +---+ +---+                     +---+

     Figure 1: Reference Architecture for Localized Routing in PMIPv6

   All "A" use cases below assume that both the MN and the CN are
   registered with an LMA according to the PMIPv6 protocol.  Whereas
   MAG1 is always considered as the MN's current Proxy Care-of Address,
   the CN can be either connected to the same MAG or to a different MAG
   or LMA as the MN.  Accordingly, these topological differences are
   denoted as follows:

   A[number of MAGs][number of LMAs]

   A11: The MN and the CN (CN1) connect to the same MAG (MAG1) and are
      registered with the same LMA (LMA).  The common MAG may forward
      data packets between the MN and the CN directly without forwarding
      any packet to the LMA.  [RFC5213] addresses this use case, but
      does not specify the complete procedure to establish such
      localized routing state on the shared MAG.

   A12: The MN and the CN (CN1) connect to the same MAG (MAG1) and are
      registered with different LMAs (LMA1 and LMA2).  The common MAG
      may forward data packets between the MN and the CN directly
      without forwarding any packet to the LMAs.  Following the policy
      of [RFC5213] and enforcement of the setup of a localized
      forwarding path, potential problems exist in the case where LMA1
      and LMA2 differ in their policy to control the MAG.

   A21: The CN (CN2) connects to a different MAG (MAG2) than the MN
      (MAG1), but the MN and the CN are registered with the same LMA
      (LMA1).  The result of localized routing should be the existence
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      of routing information at MAG1 and MAG2, which allows direct
      forwarding of packets between the MN's MAG1 and the CN's MAG2.  As
      LMA1 is the common anchor for the MN and the CN and maintains
      location information for both nodes, no major race condition and
      instability in updating the states for localized routing is
      expected.

   A22: The CN (CN2) connects to a different MAG (MAG2) and a different
      LMA (LMA2) than the MN (MAG1, LMA1).  The result of localized
      routing should be the existence of routing information at MAG1 and
      MAG2, which allows direct forwarding of packets between the MN's
      MAG1 and the CN's MAG2.  As the location information of the CN and
      the MN is maintained at different LMAs, both LMAs need to be
      involved in the procedure to set up localized routing.  In the
      case of a handover of the MN and/or the CN to a different MAG,
      non-synchronized control of updating the states for localized
      routing may result in race conditions, superfluous signaling, and
      packet loss.

   The following list summarizes general problems with setting up and
   maintaining localized routing between an MN and a CN.  In the context
   of this problem statement, the MN and the CN are always assumed to be
   registered at an LMA according to the PMIPv6 protocol [RFC5213].

   o  MNs do not participate in mobility management and hence cannot
      perform binding registration at a CN on their own.  Rather,
      entities in the network infrastructure must take over the role of
      MNs to set up and maintain a direct route.  Accordingly, a
      solution for localized routing in PMIPv6 must specify protocol
      operation between relevant network components, such as between a
      MAG and an LMA, to enable localized routing for data traffic
      without traversing the MN's and the CN's LMA(s).

   o  In the case where the MN and the CN are both registered with
      different LMAs according to the PMIPv6 protocol, relevant
      information for the setup of a localized routing path, such as the
      current MAG of the MN and the CN, is distributed between these
      LMAs.  This may complicate the setup and stable maintenance of
      states enabling localized routing.

   o  In the case where localized routing between an MN and a CN has
      been successfully set up and both nodes move and attach to a new
      access router simultaneously, signaling the new location and
      maintenance of states for localized routing at relevant routers
      may run into a race condition situation.  This can happen in the
      case where coordination of signaling for localized routing and
      provisioning of relevant state information is distributed between
      different network entities, e.g., different LMAs.  In such a case,
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      as a result of the MN's handover, updated information about the
      MN's location may arrive at the CN's previous MAG, while the CN
      has already moved to a new MAG.  The same applies to the other
      direction, where the system may update the MN's previous MAG about
      the CN's new location, while the MN has moved to a new MAG in the
      meantime.  The protocol solution must deal with such exceptional
      handover cases efficiently to avoid or resolve such problems.

3.3. IPv4 Considerations

According to [RFC5844], the basic configuration requirements for supporting IPv4 in PMIPv6 are that LMAs and MAGs are both IPv4 and IPv6 enabled. Also, LMAs and MAGs must have a globally unique IPv6 address configured, irrespective of enabled support for IPv6 routing between these components. This requirement should also apply to configuration requirements of localized routing. Additional issues emerge when localized routing is considered for PMIPv6 with IPv4 support. These can be classified into two general groups: issues with localized routing between an MN's and a CN's IPv4 Home Addresses, and transport plane issues. The following subsections analyze these two groups.

3.3.1. Localized Routing for Communication between IPv4 Home Addresses

In the case where an LMA and a MAG hold a registration to support IPv4 Home Address mobility for an MN, the MAG and the LMA must support appropriate encapsulation of IPv4 packets. To enable localized routing, the MN's MAG must encapsulate and forward routing path optimized packets to the CN's MAG and needs to ensure that the chosen encapsulation mode is supported by the correspondent MAG. Incompatibility in a selected encapsulation mode causes failure in setting up a localized route. When localized routing is used for IPv4 traffic, the conceptual data structures on associated MAGs must be augmented with appropriate parameters for forwarding localized traffic. MAGs may need to maintain a routing state for each MN-CN-pair and make routing decisions for uplink traffic based on the packet's complete IPv4 source and destination address. Hence, conceptual data structures to handle states for localized routes need to comprise this address tuple for unique identification.
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   As a known constraint, IPv4 addresses of two nodes that hold
   addresses from a private address space may overlap.  To uniquely
   identify both nodes, the IPv4 address of the MN and the CN must not
   overlap.  To cope with overlapping address spaces, the localized
   routing solution could use additional mechanisms to tag and uniquely
   identify the MN and the CN.

3.3.2. IPv4 Transport Network Considerations

The transport network between the LMA and the MAG may be based on IPv6 or IPv4. Deployments may ensure that the same transport mechanism (i.e., IPv6 or IPv4) is used for operational consistency. Similar to the encapsulation requirement stated in the previous section, the IP version used for localized routing is also assumed, by configuration, to be consistent across all MAGs within the associated provider domain. The design of optional mechanisms for negotiating the IP version to use as well as the encapsulation mode to use are outside the scope of the NetExt WG's solution for localized routing.

4. Functional Requirements for Localized Routing

Several tasks need to be performed by the network infrastructure components before relevant information for such direct communication is discovered and associated states for localized routing can be set up. The following list summarizes some key functions that need to be performed by the PMIPv6-enabled network infrastructure to substitute mobile nodes in setting up a direct route. o Detection of the possibility to perform localized routing. This function includes looking at a data packet's source and destination address. o Initiation of a procedure that sets up a localized routing path. o Discovery of stateful entities (i.e., the LMA(s) and/or the MAG(s)) that maintain and can provide relevant information needed to set up a localized routing path. Such information may include the routable address of an LMA or MAG, where one or both mobile nodes are connected to and registered with that LMA or MAG. o Control in setting up and maintaining (e.g., during handover) the localized routing path. Control is also needed to terminate the use of a localized routing path and to delete associated states, whereas a trigger for the termination may come from a non-PMIPv6- related component.
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   o  Enforcement of administrative policy rules to localized routing.
      Such policies allow operators to have further control of the setup
      of a localized route and enable the possibility to disallow
      localized routing, for example, to ensure that traffic traverses
      charging-related functions on the LMA.  Explicit authorization of
      localized routing is, for example, discussed in [PMIP6-LR].  As a
      further example, mobile-node- and operator-specific policy rules
      can be established on PMIPv6 components during PMIPv6
      bootstrapping according to [RFC5779].

5. Roaming Considerations

Figure 2 shows PMIPv6 roaming cases where PMIPv6 components (e.g., LMAs, MAGs) tied by the MN and the CN may be distributed between different provider domains (i.e., domain A, B, C) and the MN and/or CN moves from one provider domain to another one. In order to support localized routing when roaming occurs, it is required that MAGs to which the MN and CN connect be within the same provider domain, and each MAG has a security relationship with the corresponding LMA, which maintains the registration of the MN or the CN, respectively. According to the roaming model as depicted in Figure 2, the MN's PMIPv6 domain is characterized by its MAG (MAG1/MAG1') and its LMA (LMA1), whereas the CN's PMIPv6 domain is characterized by the CN's MAG (MAG2/MAG2') and its LMA (LMA2/LMA2'). A solution for localized routing cannot take any assumption about whether or not the MN and CN share the same PMIPv6 domain; hence, MAG1/MAG1' may not share a security association with LMA2/LMA2', and MAG2/MAG2' may not share a security association with LMA1, respectively. It is not required that LMAs, which hold the registration for the MN and the CN, respectively, be part of the same provider domain as the MAGs where the MN and CN attach. When the MN's MAG and LMA belong to different provider domains (A and C), localized routing is subject to policy governing the service level agreements between these domains. The same applies to the provider domains that provide the CN's MAG and LMA. Based on the above requirements, four PMIPv6 roaming and non-roaming cases can be taken into account. o Case 1: The MN's MAG (MAG1), the CN's MAG (MAG2), the MN's LMA (LMA1), and the CN's LMA (LMA2) are located in the same provider domain A. o Case 2: The MN's MAG (MAG1), the CN's MAG (MAG2), and the MN's LMA (LMA1) are located in the same domain A, while the CN's LMA (LMA2') is located in provider domain B.
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   o  Case 3: The MN's MAG (MAG1') and the CN's MAG (MAG2') are located
      in domain C, while the MN's LMA (LMA1) and the CN's LMA (LMA2) are
      located in provider domain A.

   o  Case 4: The MN's MAG (MAG1') and the CN's MAG (MAG2') are located
      in provider domain C, while the MN's LMA (LMA1) is located in
      provider domain A and the CN's LMA (LMA2') is located in provider
      domain B.

   In these roaming cases, the MN can be allowed to roam within its
   domain (e.g., the MN's home domain in which the MN's LMA is located)
   or over different domains (e.g., the MN moves from its home domain to
   a visited domain).  During mobility, the CN and MN should remain
   attached to MAGs of the same provider domain to maintain efficient
   routing of traffic between their MAGs.

                                     |
           +-----+       +-----+     |      +-----+
           |LMA1 |       |LMA2 |     |      |LMA2'|
           +-----+       +-----+     |      +-----+
                                     |
                                     |
                                     |
                                     |
           +-----+       +-----+     |
           |MAG1 |       |MAG2 |     |
           +-----+       +-----+     |
                                     |
                                     |
                  Provider Domain A  |  Provider Domain B
       ------------------------------+-------------------------------
                             Provider Domain C

                          +-----+        +-----+
                          |MAG1'|        |MAG2'|
                          +-----+        +-----+

      Figure 2: PMIPv6 Roaming Cases Considered for Localized Routing

6. Security Considerations

A protocol solution for localized routing in a PMIPv6 network must counter unauthorized change of a routing path. In particular, the control plane for localized routing must preclude the blocking or hijacking of mobile nodes' traffic by malicious or compromised network components. A security solution must support suitable mechanisms for authentication of control plane components of the localized routing functional architecture for both roaming and
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   non-roaming scenarios.  Any possibility for Internet hosts to
   interfere with the localized routing procedure in a malicious manner
   must be precluded.

   Since network entities other than MNs and CNs perform signaling to
   set up localized routing, the MIPv6 return routability test [RFC3775]
   is not suitable to authenticate associated signaling messages in
   PMIPv6.  Solutions for localized routing in PMIPv6 need to mitigate,
   or to provide sufficient defense against, possible security threats.
   When PMIPv6 participants are administered within the same domain,
   infrastructure-based authorization mechanisms, such as IPsec, may be
   usable to protect signaling for localized routing.

   Existing security associations according to [RFC5213] can be re-used
   to protect signaling for localized routing on the interface between a
   MAG and an LMA.  In the case where a protocol solution for localized
   routing in PMIPv6 relies on protocol operation between MAGs, means
   for protection of signaling between these MAGs must be provided.  The
   same applies for signaling on a possible protocol interface between
   two LMAs of the same domain.

7. Acknowledgments

Many aspects of the problem space for route optimization in PMIPv6 have been discussed in the context of a PMIPv6 Route Optimization Design Goals document, which was submitted to the NetLMM WG in November 2007. This group of contributors includes Sangjin Jeong, Christian Vogt, Ryuji Wakikawa, Marco Liebsch, Behcet Sarikaya, Shinta Sugimoto, Long Le, Alice Qinxia, and Jaehwoon Lee. Many thanks to Rajeev Koodli for his comments about the structure and scope of this problem statement for the NetExt WG. This problem statement reflects the results of the discussion in the NetExt group. Many thanks to Hidetoshi Yokota, Carlos Bernardos, Ashutosh Dutta, Sri Gundavelli, Mohana Jeyatharan, Jouni Korhonen, Glen Zorn, Dirk von Hugo, Frank Xia, Xiangsong Cui, and Basavaraj Patil for their comments and support to improve the quality of the problem statement.
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8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. [RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy Mobile IPv6", RFC 5844, May 2010.

8.2. Informative References

[PMIP6-LR] Zorn, G., Wu, Q., Liebsch, M., and J. Korhonen, "Diameter Support for Proxy Mobile IPv6 Localized Routing", Work in Progress, May 2011. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [RFC5779] Korhonen, J., Ed., Bournelle, J., Chowdhury, K., Muhanna, A., and U. Meyer, "Diameter Proxy Mobile IPv6: Mobile Access Gateway and Local Mobility Anchor Interaction with Diameter Server", RFC 5779, February 2010.
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Authors' Addresses

Marco Liebsch (editor) NEC Laboratories Europe NEC Europe Ltd. Kurfuersten-Anlage 36 69115 Heidelberg Germany Phone: +49 6221 4342146 EMail: liebsch@neclab.eu Sangjin Jeong ETRI 218 Gajeongno, Yuseong Daejeon 305-700 Korea Phone: +82 42 860 1877 EMail: sjjeong@etri.re.kr Qin Wu Huawei Technologies Co., Ltd 101 Software Avenue, Yuhua District Nanjing 210012 China Phone: +86 25 56623633 EMail: sunseawq@huawei.com