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RFC 7429

Informational
Pages: 34
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Distributed Mobility Management: Current Practices and Gap Analysis

 


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Internet Engineering Task Force (IETF)                       D. Liu, Ed.
Request for Comments: 7429                                  China Mobile
Category: Informational                                  JC. Zuniga, Ed.
ISSN: 2070-1721                                             InterDigital
                                                                P. Seite
                                                                  Orange
                                                                 H. Chan
                                                     Huawei Technologies
                                                           CJ. Bernardos
                                                                    UC3M
                                                            January 2015


  Distributed Mobility Management: Current Practices and Gap Analysis

Abstract

   This document analyzes deployment practices of existing IP mobility
   protocols in a distributed mobility management environment.  It then
   identifies existing limitations when compared to the requirements
   defined for a distributed mobility management solution.

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/rfc7429.

Page 2 
Copyright Notice

   Copyright (c) 2015 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Functions of Existing Mobility Protocols  . . . . . . . . . .   4
   4.  DMM Practices . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Assumptions . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  IP Flat Wireless Network  . . . . . . . . . . . . . . . .   6
       4.2.1.  Host-Based IP DMM Practices . . . . . . . . . . . . .   7
       4.2.2.  Network-Based IP DMM Practices  . . . . . . . . . . .  12
     4.3.  Flattening 3GPP Mobile Network Approaches . . . . . . . .  15
   5.  Gap Analysis  . . . . . . . . . . . . . . . . . . . . . . . .  19
     5.1.  Distributed Mobility Management - REQ1  . . . . . . . . .  19
     5.2.  Bypassable Network-Layer Mobility Support for Each
           Application Session - REQ2  . . . . . . . . . . . . . . .  21
     5.3.  IPv6 Deployment - REQ3  . . . . . . . . . . . . . . . . .  22
     5.4.  Considering Existing Mobility Protocols - REQ4  . . . . .  23
     5.5.  Coexistence with Deployed Networks/Hosts and Operability
           across Different Networks - REQ5  . . . . . . . . . . . .  23
     5.6.  Operation and Management Considerations - REQ6  . . . . .  23
     5.7.  Security Considerations - REQ7  . . . . . . . . . . . . .  24
     5.8.  Multicast Considerations - REQ8  . . .  . . . . . . . . .  25
     5.9.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  25
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  28
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  28
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  33
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  33

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1.  Introduction

   Existing network-layer mobility management protocols have primarily
   employed a mobility anchor to ensure connectivity of a mobile node by
   forwarding packets destined to, or sent from, the mobile node after
   the node has moved to a different network.  The mobility anchor has
   been centrally deployed in the sense that the traffic of millions of
   mobile nodes in an operator network is typically managed by the same
   anchor.  This centralized deployment of mobility anchors to manage IP
   sessions poses several problems.  In order to address these problems,
   a distributed mobility management (DMM) architecture has been
   proposed.  This document investigates whether it is feasible to
   deploy current IP mobility protocols in a DMM scenario in a way that
   can fulfill the requirements as defined in [RFC7333], discusses
   current deployment practices of existing mobility protocols, and
   identifies the limitations (gaps) in these practices from the
   standpoint of satisfying DMM requirements.  The analysis is primarily
   towards IPv6 deployment but can be seen to also apply to IPv4
   whenever there are IPv4 counterparts equivalent to the IPv6 mobility
   protocols.

   The rest of this document is organized as follows: Section 3 analyzes
   existing IP mobility protocols by examining their functions and how
   these functions can be configured and used to work in a DMM
   environment, Section 4 presents the current practices of IP wireless
   networks and 3GPP architectures (both network- and host-based
   mobility protocols are considered), and Section 5 presents the gap
   analysis with respect to the current practices.

2.  Terminology

   All general mobility-related terms and their acronyms used in this
   document are to be interpreted as defined in the Mobile IPv6 base
   specification [RFC6275], in the Proxy Mobile IPv6 specification
   [RFC5213], and in the Distributed Mobility Management Requirements
   [RFC7333].  These terms include mobile node (MN), correspondent node
   (CN), home agent (HA), local mobility anchor (LMA), mobile access
   gateway (MAG), centrally deployed mobility anchors, distributed
   mobility management, hierarchical mobile network, flatter mobile
   network, and flattening mobile network.

   In addition, this document also introduces some definitions of IP
   mobility functions in Section 3.

   In this document there are also references to a "distributed mobility
   management environment."  By this term, we refer to a scenario in
   which the IP mobility, access network, and routing solutions allow

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   for setting up IP networks so that traffic is distributed in an
   optimal way without relying on centrally deployed mobility anchors to
   manage IP mobility sessions.

3.  Functions of Existing Mobility Protocols

   The host-based Mobile IPv6 (MIPv6) [RFC6275] and its network-based
   extension, Proxy Mobile IPv6 (PMIPv6) [RFC5213], as well as
   Hierarchical Mobile IPv6 (HMIPv6) [RFC5380], are logically
   centralized mobility management approaches addressing primarily
   hierarchical mobile networks.  Although these approaches are
   centralized, they have important mobility management functions
   resulting from years of extensive work to develop and to extend these
   functions.  It is therefore useful to take these existing functions
   and examine them in a DMM scenario in order to understand how to
   deploy the existing mobility protocols to provide distributed
   mobility management.

   The main mobility management functions of MIPv6, PMIPv6, and HMIPv6
   are the following:

   1.  Anchoring Function (AF): allocation to a mobile node of an IP
       address, i.e., Home Address (HoA), or prefix, i.e., Home Network
       Prefix (HNP), topologically anchored by the advertising node.
       That is, the anchor node is able to advertise a connected route
       into the routing infrastructure for the allocated IP prefixes.
       This function is a control-plane function.

   2.  Internetwork Location Management (LM) function: managing and
       keeping track of the internetwork location of an MN.  The
       location information may be a binding of the advertised IP
       address/prefix, e.g., HoA or HNP, to the IP routing address of
       the MN, or it may be a binding of a node that can forward packets
       destined to the MN.  It is a control-plane function.

       In a client-server protocol model, location query and update
       messages may be exchanged between a Location Management client
       (LMc) and a Location Management server (LMs).

   3.  Forwarding Management (FM) function: packet interception and
       forwarding to/from the IP address/prefix assigned to the MN,
       based on the internetwork location information, either to the
       destination or to some other network element that knows how to
       forward the packets to their destination.

       FM may optionally be split into the control plane (FM-CP) and
       data plane (FM-DP).

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   In Mobile IPv6, the home agent (HA) typically provides the AF; the
   LMs is at the HA, whereas the LMc is at the MN; the FM function is
   distributed between the ends of the tunnel at the HA and the MN.

   In Proxy Mobile IPv6, the local mobility anchor (LMA) provides the
   AF; the LMs is at the LMA, whereas the LMc is at the MAG; the FM
   function is distributed between the ends of the tunnel at the LMA and
   the MAG.

   In HMIPv6 [RFC5380], the Mobility Anchor Point (MAP) serves as a
   location information aggregator between the LMs at the HA and the LMc
   at the MN.  The MAP also provides the FM function to enable tunneling
   between HA and itself, as well as tunneling between the MN and
   itself.

4.  DMM Practices

   This section documents deployment practices of existing mobility
   protocols to satisfy distributed mobility management requirements.
   This description considers both IP wireless, e.g., evolved Wi-Fi
   hotspots, and 3GPP flattening mobile networks.

   While describing the current DMM practices, the section provides
   references to the generic mobility management functions described in
   Section 3 as well as some initial hints on the identified gaps with
   respect to the DMM requirements documented in [RFC7333].

4.1.  Assumptions

   There are many different approaches that can be considered to
   implement and deploy a distributed anchoring and mobility solution.
   The focus of the gap analysis is on certain current mobile network
   architectures and standardized IP mobility solutions, considering any
   kind of deployment options that do not violate the original protocol
   specifications.  In order to limit the scope of our analysis of DMM
   practices, we consider the following list of technical assumptions:

   1.  Both host- and network-based solutions are considered.

   2.  Solutions should allow selecting and using the most appropriate
       IP anchor among a set of available candidates.

   3.  Mobility management should be realized by the preservation of the
       IP address across the different points of attachment (i.e.,
       provision of IP address continuity).  This is in contrast to
       certain transport-layer-based approaches such as Stream Control
       Transmission Protocol (SCTP) [RFC4960] or application-layer
       mobility.

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   Applications that can cope with changes in the MN's IP address do not
   depend on IP mobility management protocols such as DMM.  Typically, a
   connection manager, together with the operating system, will
   configure the source address selection mechanism of the IP stack.
   This might involve identifying application capabilities and
   triggering the mobility support accordingly.  Further considerations
   on application management and source address selection are out of the
   scope of this document, but the reader might consult [RFC6724].

4.2.  IP Flat Wireless Network

   This section focuses on common IP wireless network architectures and
   how they can be flattened from an IP mobility and anchoring point of
   view using common and standardized protocols.  We take Wi-Fi as a
   useful wireless technology since it is widely known and deployed
   nowadays.  Some representative examples of Wi-Fi deployment
   architectures are depicted in Figure 1.

                      +-------------+             _----_
     +---+            |   Access    |           _(      )_
     |AAA|. . . . . . | Aggregation |----------( Internet )
     +---+            |   Gateway   |           (_      _)
                      +-------------+             '----'
                         |  |   |
                         |  |   +-------------+
                         |  |                 |
                         |  |              +-----+
         +---------------+  |              | AR  |
         |                  |              +--+--+
      +-----+            +-----+         *----+----*
      | RG  |            | WLC |        (    LAN    )
      +-----+            +-----+         *---------*
         .                /   \            /     \
        / \          +-----+ +-----+  +-----+   +-----+
       /   \         |Wi-Fi| |Wi-Fi|  |Wi-Fi|   |Wi-Fi|
     MN1   MN2       | AP1 | | AP2 |  | AP3 |   | AP4 |
                     +-----+ +-----+  +-----+   +-----+
                        .                .
                       / \              / \
                      /   \            /   \
                     MN3  MN4         MN5  MN6

                 Figure 1: IP Wi-Fi Network Architectures

   In Figure 1, three typical deployment options are shown
   [COMMUNITY-WIFI].  On the left-hand side of the figure, mobile nodes
   MN1 and MN2 directly connect to a Residential Gateway (RG) at the
   customer premises.  The RG hosts the 802.11 Access Point (AP)

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   function to enable wireless Layer 2 access connectivity and also
   provides Layer 3 routing functions.  In the middle of the figure,
   mobile nodes MN3 and MN4 connect to Wi-Fi access points AP1 and AP2
   that are managed by a Wireless LAN Controller (WLC), which performs
   radio resource management on the APs, domain-wide mobility policy
   enforcement, and centralized forwarding function for the user
   traffic.  The WLC could also implement Layer 3 routing functions or
   attach to an access router (AR).  Last, on the right-hand side of the
   figure, access points AP3 and AP4 are directly connected to an access
   router.  This can also be used as a generic connectivity model.

   IP mobility protocols can be used to provide heterogeneous network
   mobility support to users, e.g., handover from Wi-Fi to cellular
   access.  Two kinds of protocols can be used: Proxy Mobile IPv6
   [RFC5213] or Mobile IPv6 [RFC5555], with the role of mobility anchor
   (e.g., local mobility anchor or home agent) typically being played by
   the edge router of the mobile network [SDO-3GPP.23.402].

   Although this section has made use of the example of Wi-Fi networks,
   there are other flattening mobile network architectures specified,
   such as Worldwide Interoperability for Microwave Access (WiMAX)
   [IEEE.802-16.2009], which integrates both host- and network-based IP
   mobility functions.

   Existing IP mobility protocols can also be deployed in a flatter
   manner so that the anchoring and access aggregation functions are
   distributed.  We next describe several practices for the deployment
   of existing mobility protocols in a distributed mobility management
   environment.  The analysis in this section is limited to protocol
   solutions based on existing IP mobility protocols, either host- or
   network-based, such as Mobile IPv6 [RFC6275] [RFC5555], Proxy Mobile
   IPv6 (PMIPv6) [RFC5213] [RFC5844], and Network Mobility (NEMO) Basic
   Support Protocol [RFC3963].  Extensions to these base protocol
   solutions are also considered.  The analysis is divided into two
   parts: host- and network-based practices.

4.2.1.  Host-Based IP DMM Practices

   Mobile IPv6 (MIPv6) [RFC6275] and its extension to support mobile
   networks, the NEMO Basic Support protocol (hereafter, simply referred
   to as NEMO) [RFC3963], are well-known, host-based IP mobility
   protocols.  They depend on the function of the home agent (HA), a
   centralized anchor, to provide mobile nodes (hosts and routers) with
   mobility support.  In these approaches, the home agent typically
   provides the AF, FM function, and Location Management server (LMs)
   functions.  The mobile node possesses the Location Management client
   (LMc) function and the FM function to enable tunneling between the HA

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   and itself.  We next describe some practices that show how MIPv6/NEMO
   and several other protocol extensions can be deployed in a
   distributed mobility management environment.

   One approach to distribute the anchors can be to deploy several HAs
   (as shown in Figure 2), and assign the topologically closest anchor
   to each MN [RFC4640] [RFC5026] [RFC6611].  In the example shown in
   Figure 2, the mobile node MN1 is assigned to the home agent HA1 and
   uses a home address anchored by HA1 to communicate with the
   correspondent node CN1.  Similarly, the mobile node MN2 is assigned
   to the home agent HA2 and uses a home address anchored by HA2 to
   communicate with the correspondent node CN2.  Note that MIPv6/NEMO
   specifications do not prevent the simultaneous use of multiple home
   agents by a single mobile node.  In this deployment model, the mobile
   node can use several anchors at the same time, each of them anchoring
   IP flows initiated at a different point of attachment.  However,
   there is currently no mechanism specified in IETF standard to enable
   an efficient dynamic discovery of available anchors and the selection
   of the most suitable one.

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    <-INTERNET-> <- HOME NETWORK -> <------- ACCESS NETWORK ------->
     +-----+                            +-----+       +--------+
     | CN1 |---                      ===| AR1 |=======|   MN1  |
     +-----+   \   +-----------+   //   +-----+       |(FM,LMc)|
                ---|    HA1    |===                   +--------+
                   |(AF,FM,LMs)|        +-----+       (anchored
                   +-----------+        | AR2 |          at HA1)
                                        +-----+
     +-----+       +-----------+
     | CN2 |-------|    HA2    |===
     +-----+       |(AF,FM,LMs)|   \\   +-----+=======+--------+
                   +-----------+     ===| AR3 |       |   MN2  |
                                        +-----+-------|(FM,LMc)|
     +-----+                              /           +--------+
     | CN3 |-----------------------------/            (anchored
     +-----+                                             at HA2)
                                        +-----+
                                        | AR4 |
                                        +-----+

    CN1   CN2  CN3   HA1   HA2         AR1   AR3      MN1    MN2
     |     |    |     |     |           |     |        |      |
     |<-------------->|<======tunnel====+=============>|      | BT mode
     |     |    |     |     |           |     |        |      |
     |     |<-------------->|<======tunnel====+==============>| BT mode
     |     |    |     |     |           |     |        |      |
     |     |    |<----------------------------+-------------->| RO mode
     |     |    |     |     |           |     |        |      |

      Figure 2: Distributed Operation of Mobile IPv6 (BT and RO)/NEMO

   One goal of the deployment of mobility protocols in a distributed
   mobility management environment is to avoid the suboptimal routing
   caused by centralized anchoring.  Here, the Route Optimization (RO)
   support provided by Mobile IPv6 can be used to achieve a flatter IP
   data forwarding.  By default, Mobile IPv6 and NEMO use the so-called
   Bidirectional Tunnel (BT) mode, in which data traffic is always
   encapsulated between the MN and its HA before being directed to any
   other destination.  The RO mode allows the MN to update its current
   location on the CNs and then use the direct path between them.  Using
   the example shown in Figure 2, MN1 and MN2 are using BT mode with CN1
   and CN2, respectively, while MN2 is in RO mode with CN3.  However,
   the RO mode has several drawbacks:

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   o  The RO mode is only supported by Mobile IPv6.  There is no route
      optimization support standardized for the NEMO protocol because of
      the security problems posed by extending return routability tests
      for prefixes, although many different solutions have been proposed
      [RFC4889].

   o  The RO mode requires signaling that adds some protocol overhead.

   o  The signaling required to enable RO involves the home agent and is
      repeated periodically for security reasons [RFC4225].  Therefore,
      the HA remains a single point of failure.

   o  The RO mode requires support from the CN.

   Notwithstanding these considerations, the RO mode does offer the
   possibility of substantially reducing traffic through the home agent,
   in cases when it can be supported by the relevant correspondent
   nodes.  Note that a mobile node can also use its Care-of Address
   (CoA) directly [RFC5014] when communicating with CNs on the same link
   or anywhere in the Internet, although no session continuity support
   would be provided by the IP stack in this case.

   HMIPv6 [RFC5380], as shown in Figure 3, is another host-based IP
   mobility extension that can be considered as a complement to provide
   a less centralized mobility deployment.  It allows the reduction of
   the amount of mobility signaling as well as improving the overall
   handover performance of Mobile IPv6 by introducing a new hierarchy
   level to handle local mobility.  The Mobility Anchor Point (MAP)
   entity is introduced as a local mobility handling node deployed
   closer to the mobile node.  It provides LM intermediary function
   between the LMs at the HA and the LMc at the MN.  It also performs
   the FM function to tunnel with the HA and also with the MN.

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    <INTERNET> <- HOME NETWORK -> <---------- ACCESS NETWORK ---------->
                                                   LCoA anchored
                                                      at AR1
                                                       +---+  +--------+
                                                    ===|AR1|==|   MN1  |
     +-----+    +-----------+      +----------+   //   +---+  |(FM,LMc)|
     | CN1 |----|    HA1    |======|   MAP1   |===            +--------+
     +-----+    |(AF,FM,LMs)|     /|(AF,FM,LM)|        +---+        HoA,
                +-----------+    / +----------+        |AR2|       RCoA,
                 HoA anchored   /  RCoA anchored       +---+       LCoA
                    at HA1     /      at MAP1
                              /                        +---+
                             /                         |AR3|
     +-----+                /      +----------+        +---+
     | CN2 |----------------       |   MAP2   |
     +-----+                       |(AF,FM,LM)|        +---+
                                   +----------+        |AR4|
                                                       +---+
    CN1   CN2        HA1               MAP1             AR1     MN1
     |     |          |                 |                |       |
     |<-------------->|<===============>|<====tunnel============>| HoA
     |     |          |                 |                |       |
     |     |<-------------------------->|<====tunnel============>| RCoA
     |     |          |                 |                |       |

                    Figure 3: Hierarchical Mobile IPv6

   When HMIPv6 is used, the MN has two different temporary addresses:
   the Regional Care-of Address (RCoA) and the Local Care-of Address
   (LCoA).  The RCoA is anchored at one MAP, which plays the role of
   local home agent, while the LCoA is anchored at the access-router
   level.  The mobile node uses the RCoA as the CoA that is signaled to
   its home agent.  Therefore, while roaming within a local domain
   handled by the same MAP, the mobile node does not need to update its
   home agent, i.e., the mobile node does not change its RCoA.

   The use of HMIPv6 enables a form of route optimization, since a
   mobile node may decide to directly use the RCoA as the source address
   for a communication with a given correspondent node, particularly if
   the MN does not expect to move outside the local domain during the
   lifetime of the communication.  This can be seen as a potential DMM
   mode of operation, though it fails to provide session continuity if
   and when the MN moves outside the local domain.  In the example shown
   in Figure 3, MN1 is using its global HoA to communicate with CN1,
   while it is using its RCoA to communicate with CN2.

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   Furthermore, a local domain might have several MAPs deployed, thus
   enabling different kinds of HMIPv6 deployments that are flattening
   and distributed.  The HMIPv6 specification supports a flexible
   selection of the MAP, including selections based on the expected
   mobility pattern of the MN or on the distance between the MN and the
   MAP.

   Another extension that can be used to help with distributing mobility
   management functions is the Home Agent switch specification
   [RFC5142], which defines a new mobility header to signal to a mobile
   node that it should acquire a new home agent.  [RFC5142] does not
   specify the case of changing the mobile node's home address, as that
   might imply loss of connectivity for ongoing persistent connections.
   Nevertheless, that specification could be used to force the change of
   home agent in those situations where there are no active persistent
   data sessions that cannot cope with a change of home address.

   There are other host-based approaches standardized that can be used
   to provide mobility support.  For example, IKEv2 Mobility and
   Multihoming (MOBIKE) [RFC4555] allows a mobile node encrypting
   traffic through Internet Key Exchange Protocol Version 2 (IKEv2)
   [RFC7296] to change its point of attachment while maintaining a
   Virtual Private Network (VPN) session.  The MOBIKE protocol allows
   updating the VPN Security Associations (SAs) in cases where the base
   connection initially used is lost and needs to be re-established.
   The use of the MOBIKE protocol avoids having to perform an IKEv2
   renegotiation.  Similar considerations to those made for Mobile IPv6
   can be applied to MOBIKE; though MOBIKE is best suited for situations
   where the address of at least one endpoint is relatively stable and
   can be discovered using existing mechanisms such as DNS.

   Extensions have been defined to the mobility protocol to optimize the
   handover performance.  Mobile IPv6 Fast Handovers (FMIPv6) [RFC5568]
   is the extension to optimize handover latency.  It defines new access
   router discovery mechanism before handover to reduce the new network
   discovery latency.  It also defines a tunnel between the previous
   access router and the new access router to reduce the packet loss
   during handover.  The Candidate Access Router Discovery (CARD)
   [RFC4066] and Context Transfer Protocol (CXTP) [RFC4067] protocols
   were standardized to improve the handover performance.  The DMM
   deployment practice discussed in this section can also use those
   extensions to improve the handover performance.

4.2.2.  Network-Based IP DMM Practices

   Proxy Mobile IPv6 (PMIPv6) [RFC5213] is the main network-based IP
   mobility protocol specified for IPv6.  Proxy Mobile IPv4 [RFC5844]
   defines some IPv4 extensions.  With network-based IP mobility

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   protocols, the LMA typically provides the AF, FM function, and
   Location Management server (LMs) function.  The mobile access gateway
   (MAG) provides the Location Management client (LMc) function and FM
   function to tunnel with LMA.  PMIPv6 is architecturally almost
   identical to MIPv6, as the mobility signaling and routing between LMA
   and MAG in PMIPv6 is similar to those between the HA and MN in MIPv6.
   The required mobility functionality at the MN is provided by the MAG
   so that the involvement in mobility support by the MN is not
   required.

   We next describe some practices that show how network-based mobility
   protocols and several other protocol extensions can be deployed in a
   distributed mobility management environment.

   One way to decentralize Proxy Mobile IPv6 operation can be to deploy
   several LMAs and use some selection criteria to assign LMAs to
   attaching mobile nodes.  An example of this type of assignment is
   shown in Figure 4.  As with the client-based approach, a mobile node
   may use several anchors at the same time, each of them anchoring IP
   flows initiated at a different point of attachment.  This assignment
   can be static or dynamic.  The main advantage of this simple approach
   is that the IP address anchor, i.e., the LMA, could be placed closer
   to the mobile node.  Therefore, the resulting paths are close to
   optimal.  On the other hand, as soon as the mobile node moves, the
   resulting path will start deviating from the optimal one.

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    <INTERNET> <--- HOME NETWORK ---> <------ ACCESS NETWORK ------->
                                                +--------+      +---+
                                         =======|  MAG1  |------|MN1|
     +-----+       +-----------+       //       |(FM,LMc)|      +---+
     | CN1 |-------|    LMA1   |=======         +--------+
     +-----+       |(AF,FM,LMs)|
                   +-----------+                +--------+
     +-----+                                    |  MAG2  |
     | CN2 |---                                 |(FM,LMc)|
     +-----+   \   +-----------+                +--------+
                ---|    LMA2   |=======
     +-----+       |(AF,FM,LMs)|       \\       +--------+      +---+
     | CN3 |       +-----------+         =======|  MAG3  |------|MN2|
     +-----+                                    |(FM,LMc)|      +---+
                                                +--------+
    CN1   CN2        LMA1  LMA2                  MAG1 MAG3     MN1  MN2
     |     |          |     |                     |    |        |    |
     |<-------------->|<===========tunnel========>|<----------->|    |
     |     |          |     |                     |    |        |    |
     |     |<-------------->|<=====tunnel=============>|<----------->|
     |     |          |     |                     |    |        |    |

           Figure 4: Distributed Operation of Proxy Mobile IPv6

   In a similar way to the host-based IP mobility case, network-based IP
   mobility has some extensions defined to mitigate the suboptimal
   routing issues that may arise due to the use of a centralized anchor.
   The Local Routing extensions [RFC6705] enable optimal routing in
   Proxy Mobile IPv6 in three cases: i) when two communicating MNs are
   attached to the same MAG and LMA, ii) when two communicating MNs are
   attached to different MAGs but to the same LMA, and iii) when two
   communicating MNs are attached to the same MAG but have different
   LMAs.  In these three cases, data traffic between the two mobile
   nodes does not traverse the LMA(s), thus providing some form of path
   optimization, since the traffic is locally routed at the edge.  The
   main disadvantage of this approach is that it only tackles the MN-to-
   MN communication scenario and only under certain circumstances.

   An interesting extension that can also be used to facilitate the
   deployment of network-based mobility protocols in a distributed
   mobility management environment is the support of an LMA runtime
   assignment described in [RFC6463].  This extension specifies a
   runtime LMA assignment functionality and corresponding mobility
   options for Proxy Mobile IPv6.  This runtime LMA assignment takes
   place during the Proxy Binding Update / Proxy Binding Acknowledgment
   message exchange between a mobile access gateway and an LMA.  While
   this mechanism is mainly aimed for load-balancing purposes, it can
   also be used to select an optimal LMA from the routing point of view.

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   A runtime LMA assignment can be used to change the assigned LMA of an
   MN, for example, in cases when the mobile node does not have any
   active session or when the running sessions can survive an IP address
   change.  Note that several possible dynamic LMA discovery solutions
   can be used, as described in [RFC6097].

4.3.  Flattening 3GPP Mobile Network Approaches

   The 3GPP is the standards development organization that specifies the
   3rd generation mobile network and the Evolved Packet System (EPS)
   [SDO-3GPP.23.402], which mainly comprises the Evolved Packet Core
   (EPC) and a new radio access network, usually referred to as LTE
   (Long Term Evolution).

   Architecturally, the 3GPP EPC network is similar to an IP wireless
   network running PMIPv6 or MIPv6, as it relies on the Packet Data
   Network Gateway (P-GW) anchoring services to provide mobile nodes
   with mobility support (see Figure 5).  There are client-based and
   network-based mobility solutions in 3GPP, which for simplicity will
   be analyzed together.  We next describe how 3GPP mobility protocols
   and several other completed or ongoing extensions can be deployed to
   meet some of the DMM requirements [RFC7333].

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             +---------------------------------------------------------+
             |                           PCRF                          |
             +-----------+--------------------------+----------------+-+
                         |                          |                |
    +----+   +-----------+------------+    +--------+-----------+  +-+-+
    |    |   |          +-+           |    |  Core Network      |  |   |
    |    |   | +------+ |S|__         |    | +--------+  +---+  |  |   |
    |    |   | |GERAN/|_|G|  \        |    | |  HSS   |  |   |  |  |   |
    |    +-----+ UTRAN| |S|   \       |    | +---+----+  |   |  |  | E |
    |    |   | +------+ |N|  +-+-+    |    |     |       |   |  |  | x |
    |    |   |          +-+ /|MME|    |    | +---+----+  |   |  |  | t |
    |    |   | +---------+ / +---+    |    | |  3GPP  |  |   |  |  | e |
    |    +-----+ E-UTRAN |/           |    | |  AAA   |  |   |  |  | r |
    |    |   | +---------+\           |    | | SERVER |  |   |  |  | n |
    |    |   |             \ +----+   |    | +--------+  |   |  |  | a |
    |    |   |   3GPP AN    \|S-GW+---- S5---------------+ P |  |  | l |
    |    |   |               +----+   |    |             | - |  |  |   |
    |    |   +------------------------+    |             | G |  |  | I |
    | UE |                                 |             | W |  |  | P |
    |    |   +------------------------+    |             |   +-----+   |
    |    |   |+-------------+ +------+|    |             |   |  |  | n |
    |    |   || Untrusted   +-+ ePDG +-S2b---------------+   |  |  | e |
    |    +---+| non-3GPP AN | +------+|    |             |   |  |  | t |
    |    |   |+-------------+         |    |             |   |  |  | w |
    |    |   +------------------------+    |             |   |  |  | o |
    |    |                                 |             |   |  |  | r |
    |    |   +------------------------+    |             |   |  |  | k |
    |    +---+  Trusted non-3GPP AN   +-S2a--------------+   |  |  | s |
    |    |   +------------------------+    |             |   |  |  |   |
    |    |                                 |             +-+-+  |  |   |
    |    +--------------------------S2c--------------------|    |  |   |
    |    |                                 |                    |  |   |
    +----+                                 +--------------------+  +---+

     where E-UTRAN - Evolved Universal Terrestrial Radio Access Network
           GERAN   - GSM EDGE Radio Access Network
           HSS     - Home Subscriber Server
           MME     - Mobility Management Entity
           PCRF    - Policy and Charging Rule Function
           SGSN    - Serving GPRS Support Node
           UTRAN   - Universal Terrestrial Radio Access Network

             Figure 5: EPS (Non-roaming) Architecture Overview

   The GPRS Tunneling Protocol (GTP) [SDO-3GPP.29.060] [SDO-3GPP.29.281]
   [SDO-3GPP.29.274] is a network-based mobility protocol specified for
   3GPP networks (S2a, S2b, S5, and S8 interfaces).  In a similar way to
   PMIPv6, it can handle mobility without requiring the involvement of

Top      ToC       Page 17 
   the mobile nodes.  In this case, the mobile node functionality is
   provided in a proxy manner by the Serving Data Gateway (S-GW),
   Evolved Packet Data Gateway (ePDG), or Trusted Wireless Access
   Gateway (TWAG [SDO-3GPP.23.402]) .

   3GPP specifications also include client-based mobility support, based
   on adopting the use of Dual-Stack Mobile IPv6 (DSMIPv6) [RFC5555] for
   the S2c interface [SDO-3GPP.24.303].  In this case, the User
   Equipment (UE) implements the binding update functionality, while the
   home agent role is played by the P-GW.

   A Local IP Access (LIPA) and Selected IP Traffic Offload (SIPTO)
   enabled network [SDO-3GPP.23.401] allows offloading some IP services
   at the local access network above the Radio Access Network (RAN)
   without the need to travel back to the P-GW (see Figure 6).

      +---------+ IP traffic to mobile operator's CN
      |  User   |....................................(Operator's CN)
      | Equipm. |..................
      +---------+                 . Local IP traffic
                                  .
                            +-----------+
                            |Residential|
                            |enterprise |
                            |IP network |
                            +-----------+

                          Figure 6: LIPA Scenario

   SIPTO enables an operator to offload certain types of traffic at a
   network node close to the UE's point of attachment to the access
   network.  This is done by selecting a set of GWs (S-GW and P-GW1 in
   the figure below) that are geographically/topologically close to the
   UE's point of attachment.

                         SIPTO Traffic
                              |
                              .
                              .
                          +-------+        +------+
                          | P-GW1 |   ---- | MME  |
                          +-------+  /     +------+
                               |    /
    +------+     +-----+   +------+/       +-------+
    |  UE  |.....| eNB |...| S-GW |........| P-GW2 |... CN Traffic
    +------+     +-----+   +------+        +-------+

                       Figure 7: SIPTO Architecture

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   LIPA, on the other hand, enables an IP addressable UE connected via a
   Home evolved Network B (HeNB) to access other IP addressable entities
   in the same residential/enterprise IP network without traversing the
   mobile operator's network core in the user plane.  In order to
   achieve this, a Local GW (L-GW) collocated with the HeNB is used.  To
   establish LIPA, the UE requests a new Public Data Network (PDN)
   connection to an access point name for which LIPA is permitted, the
   network selects the Local GW associated with the HeNB, and the
   network enables a direct user-plane path between the Local GW and the
   HeNB.

    +------------+  +------+  +----------+  +-------------+    =====
    |Residential |  | HeNB |  | Backhaul |  |Mobile       |   ( IP  )
    |Enterprise  |..|------|..|          |..|Operator     |..(Network)
    |Network     |  | L-GW |  |          |  |Core network |   =======
    +------------+  +------+  +----------+  +-------------+
                       /
                       |
                       /
                   +-----+
                   | UE  |
                   +-----+

                        Figure 8: LIPA Architecture

   The 3GPP architecture specifications also provide mechanisms to allow
   discovery and selection of gateways [SDO-3GPP.29.303].  These
   mechanisms enable decisions that take into consideration topological
   location and gateway collocation aspects, by relying upon the DNS as
   a "location database."

   Both SIPTO and LIPA have a very limited mobility support, especially
   in 3GPP specifications up to Rel-12.  Briefly, LIPA mobility support
   is limited to handovers between HeNBs that are managed by the same
   L-GW (i.e., mobility within the local domain).  There is no guarantee
   of IP session continuity for SIPTO.

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5.  Gap Analysis

   This section identifies the limitations in the current practices,
   described in Section 4, with respect to the DMM requirements listed
   in [RFC7333].

5.1.  Distributed Mobility Management - REQ1

   According to requirement REQ1 stated in [RFC7333], IP mobility,
   network access, and forwarding solutions provided by DMM must make it
   possible for traffic to avoid traversing a single mobility anchor far
   from the optimal route.

   From the analysis performed in Section 4, a DMM deployment can meet
   the requirement "REQ1 Distributed mobility management" usually
   relying on the following functions:

   o  Multiple (distributed) anchoring: ability to anchor different
      sessions of a single mobile node at different anchors.  In order
      to provide improved routing, some anchors might need to be placed
      closer to the mobile node or the corresponding node.

   o  Dynamic anchor assignment/re-location: ability to i) assign the
      initial anchor, and ii) dynamically change the initially assigned
      anchor and/or assign a new one (this may also require the transfer
      of mobility context between anchors).  This can be achieved either
      by changing anchor for all ongoing sessions or by assigning new
      anchors just for new sessions.

   GAP1-1:  Both the main client- and network-based IP mobility
            protocols (namely, MIPv6, DSMIPv6, and PMIPv6) allow
            deploying multiple anchors (i.e., home agents and localized
            mobility anchors), thereby providing the multiple anchoring
            function.  However, existing solutions only provide an
            initial anchor assignment, thus the lack of dynamic anchor
            change/new anchor assignment is a gap.  Neither the HA
            switch nor the LMA runtime assignment allows changing the
            anchor during an ongoing session.  This actually comprises
            several gaps: ability to perform anchor assignment at any
            time (not only at the initial MN's attachment), ability of
            the current anchor to initiate/trigger the relocation, and
            ability to transfer registration context between anchors.

   GAP1-2:  Dynamic anchor assignment may lead the MN to manage
            different mobility sessions served by different mobility
            anchors.  This is not an issue with client-based mobility
            management, where the mobility client natively knows the
            anchor associated with each of its mobility sessions.

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            However, there is one gap, as the MN should be capable of
            handling IP addresses in a DMM-friendly way, meaning that
            the MN can perform smart source address selection (i.e.,
            deprecating IP addresses from previous mobility anchors so
            they are not used for new sessions).  Besides, managing
            different mobility sessions served by different mobility
            anchors may raise issues with network-based mobility
            management.  In this case, the mobile client located in the
            network, e.g., MAG, usually retrieves the MN's anchor from
            the MN's policy profile, as described in Section 6.2 of
            [RFC5213].  Currently, the MN's policy profile implicitly
            assumes a single serving anchor and thus does not maintain
            the association between home network prefix and anchor.

   GAP1-3:  The consequence of the distribution of the mobility anchors
            is that there might be more than one available anchor for a
            mobile node to use, which leads to an anchor discovery and
            selection issue.  Currently, there is no efficient mechanism
            specified to allow the dynamic discovery of the presence of
            nodes that can play the anchor role, the discovery of their
            capabilities, and the selection of the most suitable one.
            There is also no mechanism to allow selecting a node that is
            currently anchoring a given home address/prefix (capability
            sometimes required to meet REQ#2).  However, there are some
            mechanisms that could help to discover anchors, such as the
            Dynamic Home Agent Address Discovery (DHAAD) [RFC6275], the
            use of the home agent flag (H) in Router Advertisements
            (which indicates that the router sending the Router
            Advertisement is also functioning as a Mobile IPv6 home
            agent on the link) or the MAP option in Router
            Advertisements defined by HMIPv6.  Note that there are 3GPP
            mechanisms providing that functionality defined in
            [SDO-3GPP.29.303].

   Regarding the ability to transfer registration context between
   anchors, there are already some solutions that could be reused or
   adapted to fill that gap, such as Fast Handovers for Mobile IPv6
   [RFC5568] to enable traffic redirection from the old to the new
   anchor, the Context Transfer Protocol [RFC4067] to enable the
   required transfer of registration information between anchors, or the
   Handover Keying architecture solutions [RFC6697] to speed up the re-
   authentication process after a change of anchor.  Note that some
   extensions might be needed in the context of DMM, as these protocols
   were designed in the context of centralized client IP mobility
   (focusing on the access reattachment and authentication).

Top      ToC       Page 21 
   GAP1-4:  Also note that REQ1 is intended to prevent the data-plane
            traffic from taking a suboptimal route.  Distributed
            processing of the traffic may then be needed only in the
            data plane.  Provision of this capability for distributed
            processing should not conflict with the use of a centralized
            control plane.  Other control-plane solutions (such as
            charging, lawful interception, etc.) should not be
            constrained by the DMM solution.  On the other hand,
            combining the control-plane and data-plane FM function may
            limit the choice of solutions to those that distribute both
            data plane and control plane together.  In order to enable
            distribution of only the data plane without distributing the
            control plane, it would be necessary to split the forwarding
            management function into the control-plane (FM-CP) and data-
            plane (FM-DP) components; there is currently a gap here.

5.2.  Bypassable Network-Layer Mobility Support for Each Application
      Session - REQ2

   The requirement REQ2 for "bypassable network-layer mobility support
   for each application session" introduced in [RFC7333] requires
   flexibility in determining whether network-layer mobility support is
   needed.  This requirement enables one to choose whether or not to use
   network-layer mobility support.  The following two functions are also
   needed:

   o  Dynamically assign/relocate anchor: A mobility anchor is assigned
      only to sessions that use the network-layer mobility support.  The
      MN may thus manage more than one session; some of them may be
      associated with anchored IP address(es), while the others may be
      associated with local IP address(es).

   o  Multiple IP address management: This function is related to the
      preceding item and is about the ability of the mobile node to
      simultaneously use multiple IP addresses and select the best one
      (from an anchoring point of view) to use on a per-
      session/application/service basis.  This requires MN to acquire
      information regarding the properties of the available IP
      addresses.

   GAP2-1:  The dynamic anchor assignment/relocation needs to ensure
            that IP address continuity is guaranteed for sessions that
            use such mobility support (e.g., in some scenarios, the
            provision of mobility locally within a limited area might be
            enough from the point of view of the mobile node or the
            application) at the relocated anchor.  Implicitly, DMM may
            release the needed resources when no applications are using
            the network-layer mobility support.  DMM is then potentially

Top      ToC       Page 22 
            required to know which sessions at the mobile node are
            active and are using the mobility support.  Typically, this
            is known only by the MN (e.g., by its connection manager)
            and would require some signaling support, such as socket API
            extensions, from applications to indicate to the IP stack
            whether or not mobility support is required.  This may imply
            having the knowledge of which sessions at the mobile node
            are active and are using the mobility support.  This is
            something typically known only by the MN, e.g., by its
            connection manager, and would also typically require some
            signaling support, such as socket API extensions, from
            applications to indicate to the IP stack whether mobility
            support is required or not.  Therefore, (part of) this
            knowledge might need to be transferred to/shared with the
            network.

   GAP2-2:  Management of multiple IP addresses provides the MN with the
            choice to pick the correct address (e.g., from those
            provided or not provided with mobility support) depending on
            the application requirements.  When using client-based
            mobility management, the MN is itself aware of the anchoring
            capabilities of its assigned IP addresses.  This is not
            necessarily the case with network-based IP mobility
            management, as current mechanisms do not allow the MN to be
            aware of the properties of its IP addresses.  For example,
            the MN does not know whether or not the allocated IP
            addresses are anchored.  However, there are proposals such
            as [CLASS-PREFIX], [PREFIX-PROPERTIES], and [MULTI-ARCH],
            where the network could indicate such properties during IP
            address assignment procedures.  These proposals could be
            considered as attempts to fix the gap.

   GAP2-3:  The handling of mobility management to the granularity of an
            individual session of a user/device needs proper session
            identification in addition to user/device identification.

5.3.  IPv6 Deployment - REQ3

   This requirement states that DMM solutions should primarily target
   IPv6 as the primary deployment environment.  IPv4 support is not
   considered mandatory and solutions should not be tailored
   specifically to support IPv4.

   All analyzed DMM practices support IPv6.  Some of them, such as
   MIPv6/NEMO (including the support of dynamic HA selection), MOBIKE,
   and SIPTO also have IPv4 support.  Some solutions, e.g., PMIPv6, also
   have some limited IPv4 support.  In conclusion, this requirement is
   met by existing DMM practices.

Top      ToC       Page 23 
5.4.  Considering Existing Mobility Protocols - REQ4

   A DMM solution must first consider reusing and extending IETF-
   standardized protocols before specifying new protocols.

   As stated in [RFC7333], a DMM solution could reuse existing IETF and
   standardized protocols before specifying new protocols.  Besides,
   Section 4 of this document discusses various ways to flatten and
   distribute current mobility solutions.  Actually, nothing prevents
   the distribution of mobility functions within IP mobility protocols.
   However, as discussed in Sections 5.1 and 5.2, limitations exist.
   The 3GPP data-plane anchoring function, i.e., the P-GW, can also be
   distributed but with limitations such as no anchoring relocation and
   no context transfer between anchors and the centralized control
   plane.  The 3GPP architecture is also going in the direction of
   flattening with SIPTO and LIPA, though they do not provide full
   mobility support.  For example, mobility support for SIPTO traffic
   can be rather limited, and offloaded traffic cannot access operator
   services.  Thus, the operator must be very careful in selecting which
   traffic to offload.

5.5.  Coexistence with Deployed Networks/Hosts and Operability across
      Different Networks - REQ5

   According to [RFC7333], DMM implementations are required to coexist
   with existing network deployments, end hosts, and routers.
   Additionally, DMM solutions are expected to work across different
   networks, possibly operated as separate administrative domains, when
   the necessary mobility management signaling, forwarding, and network
   access are allowed by the trust relationship between them.  All
   current mobility protocols can coexist with existing network
   deployments and end hosts.  There is no gap between existing mobility
   protocols and this requirement.

5.6.  Operation and Management Considerations - REQ6

   This requirement actually comprises several aspects, as summarized
   below.

   o  A DMM solution needs to consider configuring a device, monitoring
      the current operational state of a device, responding to events
      that impact the device, possibly by modifying the configuration,
      and storing the data in a format that can be analyzed later.

   o  A DMM solution has to describe in what environment and how it can
      be scalably deployed and managed.

Top      ToC       Page 24 
   o  A DMM solution has to support mechanisms to test if the DMM
      solution is working properly.

   o  A DMM solution is expected to expose the operational state of DMM
      to the administrators of the DMM entities.

   o  A DMM solution, which supports flow mobility, is also expected to
      support means to correlate the flow routing policies and the
      observed forwarding actions.

   o  A DMM solution is expected to support mechanisms to check the
      liveness of the forwarding path.

   o  A DMM solution has to provide fault management and monitoring
      mechanisms to manage situations where update of the mobility
      session or the data path fails.

   o  A DMM solution is expected to be able to monitor the usage of the
      DMM protocol.

   o  DMM solutions have to support standardized configuration with
      Network Configuration Protocol (NETCONF) [RFC6241] using YANG
      [RFC6020] modules, which are expected to be created for DMM when
      needed for such configuration.

   GAP6-1:  Existing mobility management protocols have not thoroughly
            documented how, or whether, they support the above list of
            operation and management considerations.  Each of the above
            needs to be considered from the beginning in a DMM solution.

   GAP6-2:  Management Information Base (MIB) objects are currently
            defined in [RFC4295] for MIPv6 and in [RFC6475] for PMIPv6.
            Standardized configuration with NETCONF [RFC6241], using
            YANG [RFC6020] modules, is lacking.

5.7.  Security Considerations - REQ7

   As stated in [RFC7333], a DMM solution has to support any security
   protocols and mechanisms needed to secure the network and to make
   continuous security improvements.  In addition, with security taken
   into consideration early in the design, a DMM solution cannot
   introduce new security risks or privacy concerns, or amplify existing
   security risks that cannot be mitigated by existing security
   protocols and mechanisms.

   Any solutions that are intended to fill in gaps identified in this
   document need to meet this requirement.  At present, it does not
   appear that using existing solutions to support DMM has introduced

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   any new security issues.  For example, Mobile IPv6 defines security
   features to protect binding updates both to home agents and
   correspondent nodes.  It also defines mechanisms to protect the data
   packets transmission for Mobile IPv6 users.  Proxy Mobile IPv6 and
   other variations of mobile IP also have similar security
   considerations.

5.8.  Multicast Considerations - REQ8

   It is stated in [RFC7333] that DMM solutions are expected to allow
   the development of multicast solutions to avoid network inefficiency
   in multicast traffic delivery.

   Current IP mobility solutions address mainly the mobility problem for
   unicast traffic.  Solutions relying on the use of an anchor point for
   tunneling multicast traffic down to the access router, or to the
   mobile node, introduce the so-called "tunnel convergence problem".
   This means that multiple instances of the same multicast traffic can
   converge to the same node, diminishing the advantage of using
   multicast protocols.

   [RFC6224] documents a baseline solution for the previous issue, and
   [RFC7028] documents a routing optimization solution.  The baseline
   solution suggests deploying a Multicast Listener Discovery (MLD)
   proxy function at the MAG and either a multicast router or another
   MLD proxy function at the LMA.  The routing optimization solution
   describes an architecture where a dedicated multicast tree mobility
   anchor or a direct routing option can be used to avoid the tunnel
   convergence problem.

   Besides the solutions highlighted before, there are no other
   mechanisms for mobility protocols to address the multicast tunnel
   convergence problem.

5.9.  Summary

   We next list the main gaps identified from the analysis performed
   above:

   GAP1-1:  Existing solutions only provide an optimal initial anchor
            assignment, a gap being the lack of dynamic anchor change/
            new anchor assignment.  Neither the HA switch nor the LMA
            runtime assignment allows changing the anchor during an
            ongoing session.  MOBIKE allows change of GW, but its
            applicability has been scoped to a very narrow use case.

Top      ToC       Page 26 
   GAP1-2:  The MN needs to be able to perform source address selection.
            A proper mechanism to inform the MN is lacking, so there is
            not a basis for performing the correct selection.

   GAP1-3:  Currently, there is no efficient mechanism specified by the
            IETF that allows the dynamic discovery of the presence of
            nodes that can play the role of anchor, discover their
            capabilities, and allow the selection of the most suitable
            one.  However, the following mechanisms could help
            discovering anchors:

            Dynamic Home Agent Address Discovery (DHAAD): The use of the
            home agent flag (H) in Router Advertisements (which
            indicates that the router sending the Router Advertisement
            is also functioning as a Mobile IPv6 home agent on the link)
            and the MAP option in Router Advertisements defined by
            HMIPv6.

   GAP1-4:  While existing network-based DMM practices may allow the
            deployment of multiple LMAs and dynamically select the best
            one, this requires to still keep some centralization in the
            control plane to access the policy database (as defined in
            RFC 5213).  Although [RFC7389] allows a MAG to perform
            splitting of its control and user planes, there is a lack of
            solutions/extensions that support a clear control- and data-
            plane separation for IETF IP mobility protocols in a DMM
            context.

   GAP2-1:  The information of which sessions at the mobile node are
            active and are using the mobility support need to be
            transferred to, or shared with, the network.  Such mechanism
            has not been defined.

   GAP2-2:  The mobile node needs to simultaneously use multiple IP
            addresses with different properties.  There is a lack of
            mechanism to expose this information to the mobile node,
            which can then update accordingly its source address
            selection mechanism.

   GAP2-3:  The handling of mobility management has not been to the
            granularity of an individual session of a user/device
            before.  The combination of session identification and user/
            device identification may be lacking.

Top      ToC       Page 27 
   GAP6-1:  Mobility management protocols have not thoroughly documented
            how, or whether, they support the following list of
            operation and management considerations:

            *  A DMM solution needs to consider configuring a device,
               monitoring the current operational state of a device, and
               responding to events that impact the device possibly by
               modifying the configuration and storing the data in a
               format that can be analyzed later.

            *  A DMM solution has to describe in what environment, and
               how, it can be scalably deployed and managed.

            *  A DMM solution has to support mechanisms to test if the
               DMM solution is working properly.

            *  A DMM solution is expected to expose the operational
               state of DMM to the administrators of the DMM entities.

            *  A DMM solution, which supports flow mobility, is also
               expected to support means to correlate the flow routing
               policies and the observed forwarding actions.

            *  A DMM solution is expected to support mechanisms to check
               the liveness of the forwarding path.

            *  A DMM solution has to provide fault management and
               monitoring mechanisms to manage situations where update
               of the mobility session or the data path fails.

            *  A DMM solution is expected to be able to monitor the
               usage of the DMM protocol.

            *  DMM solutions have to support standardized configuration
               with NETCONF [RFC6241], using YANG [RFC6020] modules,
               which are expected to be created for DMM when needed for
               such configuration.

   GAP6-2:  Management Information Base (MIB) objects are currently
            defined in [RFC4295] for MIPv6 and in [RFC6475] for PMIPv6.
            Standardized configuration with NETCONF [RFC6241], using
            YANG [RFC6020] modules, is lacking.

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6.  Security Considerations

   The deployment of DMM using existing IP mobility protocols raises
   similar security threats as those encountered in centralized mobility
   management systems.  Without authentication, a malicious node could
   forge signaling messages and redirect traffic from its legitimate
   path.  This would amount to a denial-of-service attack against the
   specific node or nodes for which the traffic is intended.
   Distributed mobility anchoring, while keeping current security
   mechanisms, might require more security associations to be managed by
   the mobility management entities, potentially leading to scalability
   and performance issues.  Moreover, distributed mobility anchoring
   makes mobility security problems more complex, since traffic
   redirection requests might come from previously unconsidered origins,
   thus leading to distributed points of attack.  Consequently, the DMM
   security design needs to account for the distribution of security
   associations between additional mobility entities and fulfill the
   security requirement of [RFC7333].

7.  References

7.1.  Normative References

   [RFC6275]  Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
              in IPv6", RFC 6275, July 2011,
              <http://www.rfc-editor.org/info/rfc6275>.

   [RFC7333]  Chan, H., Liu, D., Seite, P., Yokota, H., and J. Korhonen,
              "Requirements for Distributed Mobility Management", RFC
              7333, August 2014,
              <http://www.rfc-editor.org/info/rfc7333>.

7.2.  Informative References

   [CLASS-PREFIX]
              Systems, C., Halwasia, G., Gundavelli, S., Deng, H.,
              Thiebaut, L., Korhonen, J., and I. Farrer, "DHCPv6 class
              based prefix", Work in Progress, draft-bhandari-dhc-class-
              based-prefix-05, July 2013.

   [COMMUNITY-WIFI]
              Gundavelli, S., Grayson, M., Seite, P., and Y. Lee,
              "Service Provider Wi-Fi Services Over Residential
              Architectures", Work in Progress, draft-gundavelli-v6ops-
              community-wifi-svcs-06, April 2013.

Top      ToC       Page 29 
   [IEEE.802-16.2009]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks Part 16: Air Interface for Broadband Wireless
              Access Systems", IEEE Standard 802.16, 2009,
              <http://standards.ieee.org/getieee802/
              download/802.16-2009.pdf>.

   [MULTI-ARCH]
              Anipko, D., Ed., "Multiple Provisioning Domain
              Architecture", Work in Progress, draft-ietf-mif-mpvd-arch-
              08, January 2015.

   [PREFIX-PROPERTIES]
              Korhonen, J., Patil, B., Gundavelli, S., Seite, P., and D.
              Liu, "IPv6 Prefix Properties", Work in Progress,
              draft-korhonen-6man-prefix-properties-02, July 2013.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, January 2005,
              <http://www.rfc-editor.org/info/rfc3963>.

   [RFC4066]  Liebsch, M., Singh, A., Chaskar, H., Funato, D., and E.
              Shim, "Candidate Access Router Discovery (CARD)", RFC
              4066, July 2005, <http://www.rfc-editor.org/info/rfc4066>.

   [RFC4067]  Loughney, J., Nakhjiri, M., Perkins, C., and R. Koodli,
              "Context Transfer Protocol (CXTP)", RFC 4067, July 2005,
              <http://www.rfc-editor.org/info/rfc4067>.

   [RFC4225]  Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E.
              Nordmark, "Mobile IP Version 6 Route Optimization Security
              Design Background", RFC 4225, December 2005,
              <http://www.rfc-editor.org/info/rfc4225>.

   [RFC4295]  Keeni, G., Koide, K., Nagami, K., and S. Gundavelli,
              "Mobile IPv6 Management Information Base", RFC 4295, April
              2006, <http://www.rfc-editor.org/info/rfc4295>.

   [RFC4555]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", RFC 4555, June 2006,
              <http://www.rfc-editor.org/info/rfc4555>.

   [RFC4640]  Patel, A. and G. Giaretta, "Problem Statement for
              bootstrapping Mobile IPv6 (MIPv6)", RFC 4640, September
              2006, <http://www.rfc-editor.org/info/rfc4640>.

Top      ToC       Page 30 
   [RFC4889]  Ng, C., Zhao, F., Watari, M., and P. Thubert, "Network
              Mobility Route Optimization Solution Space Analysis", RFC
              4889, July 2007, <http://www.rfc-editor.org/info/rfc4889>.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol", RFC
              4960, September 2007,
              <http://www.rfc-editor.org/info/rfc4960>.

   [RFC5014]  Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
              Socket API for Source Address Selection", RFC 5014,
              September 2007, <http://www.rfc-editor.org/info/rfc5014>.

   [RFC5026]  Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6
              Bootstrapping in Split Scenario", RFC 5026, October 2007,
              <http://www.rfc-editor.org/info/rfc5026>.

   [RFC5142]  Haley, B., Devarapalli, V., Deng, H., and J. Kempf,
              "Mobility Header Home Agent Switch Message", RFC 5142,
              January 2008, <http://www.rfc-editor.org/info/rfc5142>.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008,
              <http://www.rfc-editor.org/info/rfc5213>.

   [RFC5380]  Soliman, H., Castelluccia, C., ElMalki, K., and L.
              Bellier, "Hierarchical Mobile IPv6 (HMIPv6) Mobility
              Management", RFC 5380, October 2008,
              <http://www.rfc-editor.org/info/rfc5380>.

   [RFC5555]  Soliman, H., "Mobile IPv6 Support for Dual Stack Hosts and
              Routers", RFC 5555, June 2009,
              <http://www.rfc-editor.org/info/rfc5555>.

   [RFC5568]  Koodli, R., "Mobile IPv6 Fast Handovers", RFC 5568, July
              2009, <http://www.rfc-editor.org/info/rfc5568>.

   [RFC5844]  Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
              Mobile IPv6", RFC 5844, May 2010,
              <http://www.rfc-editor.org/info/rfc5844>.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010, <http://www.rfc-editor.org/info/rfc6020>.

   [RFC6097]  Korhonen, J. and V. Devarapalli, "Local Mobility Anchor
              (LMA) Discovery for Proxy Mobile IPv6", RFC 6097, February
              2011, <http://www.rfc-editor.org/info/rfc6097>.

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   [RFC6224]  Schmidt, T., Waehlisch, M., and S. Krishnan, "Base
              Deployment for Multicast Listener Support in Proxy Mobile
              IPv6 (PMIPv6) Domains", RFC 6224, April 2011,
              <http://www.rfc-editor.org/info/rfc6224>.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011, <http://www.rfc-editor.org/info/rfc6241>.

   [RFC6463]  Korhonen, J., Gundavelli, S., Yokota, H., and X. Cui,
              "Runtime Local Mobility Anchor (LMA) Assignment Support
              for Proxy Mobile IPv6", RFC 6463, February 2012,
              <http://www.rfc-editor.org/info/rfc6463>.

   [RFC6475]  Keeni, G., Koide, K., Gundavelli, S., and R. Wakikawa,
              "Proxy Mobile IPv6 Management Information Base", RFC 6475,
              May 2012, <http://www.rfc-editor.org/info/rfc6475>.

   [RFC6611]  Chowdhury, K. and A. Yegin, "Mobile IPv6 (MIPv6)
              Bootstrapping for the Integrated Scenario", RFC 6611, May
              2012, <http://www.rfc-editor.org/info/rfc6611>.

   [RFC6697]  Zorn, G., Wu, Q., Taylor, T., Nir, Y., Hoeper, K., and S.
              Decugis, "Handover Keying (HOKEY) Architecture Design",
              RFC 6697, July 2012,
              <http://www.rfc-editor.org/info/rfc6697>.

   [RFC6705]  Krishnan, S., Koodli, R., Loureiro, P., Wu, Q., and A.
              Dutta, "Localized Routing for Proxy Mobile IPv6", RFC
              6705, September 2012,
              <http://www.rfc-editor.org/info/rfc6705>.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012,
              <http://www.rfc-editor.org/info/rfc6724>.

   [RFC7028]  Zuniga, JC., Contreras, LM., Bernardos, CJ., Jeon, S., and
              Y. Kim, "Multicast Mobility Routing Optimizations for
              Proxy Mobile IPv6", RFC 7028, September 2013,
              <http://www.rfc-editor.org/info/rfc7028>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", RFC 7296, October 2014,
              <http://www.rfc-editor.org/info/rfc7296>.

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   [RFC7389]  Wakikawa, R., Pazhyannur, R., Gundavelli, S., and C.
              Perkins, "Separation of Control and User Plane for Proxy
              Mobile IPv6", RFC 7389, October 2014,
              <http://www.rfc-editor.org/info/rfc7389>.

   [SDO-3GPP.23.401]
              3GPP, "General Packet Radio Service (GPRS) enhancements
              for Evolved Universal Terrestrial Radio Access Network
              (E-UTRAN) access", 3GPP TS 23.401 10.10.0, March 2013.

   [SDO-3GPP.23.402]
              3GPP, "Architecture enhancements for non-3GPP accesses",
              3GPP TS 23.402 10.8.0, September 2012.

   [SDO-3GPP.24.303]
              3GPP, "Mobility management based on Dual-Stack Mobile
              IPv6; Stage 3", 3GPP TS 24.303 10.0.0, June 2013.

   [SDO-3GPP.29.060]
              3GPP, "General Packet Radio Service (GPRS); GPRS
              Tunnelling Protocol (GTP) across the Gn and Gp interface",
              3GPP TS 29.060 3.19.0, March 2004.

   [SDO-3GPP.29.274]
              3GPP, "3GPP Evolved Packet System (EPS); Evolved General
              Packet Radio Service (GPRS) Tunnelling Protocol for
              Control plane (GTPv2-C); Stage 3", 3GPP TS 29.274 10.11.0,
              June 2013.

   [SDO-3GPP.29.281]
              3GPP, "General Packet Radio System (GPRS) Tunnelling
              Protocol User Plane (GTPv1-U)", 3GPP TS 29.281 10.3.0,
              September 2011.

   [SDO-3GPP.29.303]
              3GPP, "Domain Name System Procedures; Stage 3", 3GPP TS
              29.303 10.4.0, September 2012.

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Contributors

   This document has benefited due to valuable contributions from

   Charles E. Perkins
   Huawei Technologies
   EMail: charliep@computer.org

   who produced a matrix to compare the different mobility protocols and
   extensions against a list of desired DMM properties.  They were
   useful inputs in the early work of gap analysis.  He continued to
   give suggestions as well as extensively review comments for this
   document.

Authors' Addresses

   Dapeng Liu (editor)
   China Mobile
   Unit 2, 28 Xuanwumenxi Ave, Xuanwu District
   Beijing  100053
   China

   EMail: liudapeng@chinamobile.com


   Juan Carlos Zuniga (editor)
   InterDigital Communications, LLC
   1000 Sherbrooke Street West, 10th floor
   Montreal, Quebec  H3A 3G4
   Canada

   EMail: JuanCarlos.Zuniga@InterDigital.com
   URI:   http://www.InterDigital.com/


   Pierrick Seite
   Orange
   4, rue du Clos Courtel, BP 91226
   Cesson-Sevigne  35512
   France

   EMail: pierrick.seite@orange.com

Top      ToC       Page 34 
   H Anthony Chan
   Huawei Technologies
   5340 Legacy Dr. Building 3
   Plano, TX  75024
   United States

   EMail: h.a.chan@ieee.org


   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911
   Spain

   Phone: +34 91624 6236
   EMail: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/