PMIPv6 MAG Multipath: Mobile Access Gateway (MAG) Multipath Options

Internet Engineering Task Force (IETF)                          P. Seite
Request for Comments: 8278                                        Orange
Category: Standards Track                                       A. Yegin
ISSN: 2070-1721                                                 Actility
                                                           S. Gundavelli
                                                                   Cisco
                                                            January 2018


             Mobile Access Gateway (MAG) Multipath Options

Abstract

   This specification defines extensions to the Proxy Mobile IPv6
   (PMIPv6) protocol that allow a mobile access gateway (MAG) to
   register more than one proxy care-of address (pCoA) with the local
   mobility anchor (LMA) and to simultaneously establish multiple IP
   tunnels with the LMA.  This capability allows the MAG to utilize all
   the available access networks to route the mobile node's IP traffic.
   This document defines the following two new mobility header options:
   the MAG Multipath Binding option and the MAG Identifier option.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8278.

Copyright Notice

   Copyright (c) 2018 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
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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.  Conventions and Terminology . . . . . . . . . . . . . . . . .   4
     2.1.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Example Call Flow . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Traffic Distribution Schemes  . . . . . . . . . . . . . .   6
   4.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  MAG Multipath Binding Option  . . . . . . . . . . . . . .   7
     4.2.  MAG Identifier Option . . . . . . . . . . . . . . . . . .  10
     4.3.  New Status Code for Proxy Binding Acknowledgement . . . .  11
     4.4.  Signaling Considerations  . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Multihoming support on IP hosts can greatly improve the user
   experience.  With the simultaneous use of multiple access networks,
   multihoming brings better network connectivity, reliability, and
   improved quality of communication.  The following are some of the
   goals and benefits of multihoming support:

   o  Redundancy/Fault-Recovery

   o  Load balancing

   o  Load sharing

   o  Preference settings

   According to [RFC4908], users of small-scale networks can benefit
   from a mobile and fixed multihomed architecture using mobile IP
   [RFC6275] and Network Mobility (NEMO) [RFC3963].

   The motivation for this work is to extend the PMIPv6 protocol with
   multihoming extensions [RFC4908] for realizing the following
   capabilities:

   o  Using GRE as mobile tunneling, possibly with its key extension
      [RFC5845].

   o  Using UDP encapsulation [RFC5844] in order to support NAT
      traversal in an IPv4 networking environment.

   o  Using the prefix delegation mechanism [RFC7148].

   o  Using the Vendor Specific Mobility Option [RFC5094], for example,
      to allow the MAG and LMA to exchange information (e.g., WAN
      interface QoS metrics), which allows the appropriate traffic-
      steering decisions to be made.

   PMIPv6 relies on two mobility entities: the MAG, which acts as the
   default gateway for the end node (either a mobile or a fixed node)
   attached to the MAG's access links, and the LMA, which acts as the
   topological anchor point.  IP tunnel is created with any one of the
   supported encapsulation mode between the MAG and the LMA.  Then, the
   MAG and LMA distribute the end node's traffic over these tunnels.
   All PMIPv6 operations are performed on behalf of the end node and its
   correspondent node.  Thus, it makes PMIPv6 well adapted to multihomed
   architecture as considered in [RFC4908].  Taking the LTE and WLAN
   networking environments as examples, the PMIPv6-based multihomed
   architecture is depicted in Figure 1.  In this example, IP flows,
   Flow-1 and Flow-3 are routed over Tunnel-1 and Flow-2 is routed over
   Tunnel-2.  However, IP traffic belonging to Flow-4 is distributed on
   both Tunnel-1 and Tunnel-2 paths.

     Flow-1
      |
      |Flow-2              _----_
      | |         CoA-1  _(      )_   Tunnel-1  Flow-1
      | |    .---=======(   LTE    )========\   Flow-3
      | |    |           (_      _)          \  Flow-4
      | |    |             '----'             \
      | | +=====+                              \  +=====+    _----_
      | '-|     |                               \ |     |  _(      )_
      '---| MAG |                                 | LMA |-( Internet )--
      .---|     |                                 |     |  (_      _)
      | .-|     |                               / |     |    '----'
      | | +=====+                              /  +=====+
      | |    |             _----_             /
      | |    |    CoA-2  _(      )_ Tunnel-2 /
      | |    .---=======(   WLAN  )========/    Flow-2
      | |                (_     _)              Flow-4
      | |                  '----'
      |Flow-3
      |
     Flow0-4

             Figure 1: Multihomed MAG Using Proxy Mobile IPv6

   The current version of PMIPv6 does not allow a MAG to register more
   than one pCoA to the LMA.  In other words, only one MAG/LMA link,
   i.e., IP-in-IP tunnel, can be used at the same time.  This document
   overcomes this limitation by defining the multiple pCoAs extension
   for PMIPv6.

2.  Conventions and Terminology

2.1.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.2.  Terminology

   All mobility-related terms used in this document are to be
   interpreted as defined in [RFC5213], [RFC5844], and [RFC7148].
   Additionally, this document uses the following term:

   IP-in-IP

      IP-within-IP encapsulation [RFC2473] [RFC4213]

3.  Overview

3.1.  Example Call Flow

   Figure 2 is the call flow detailing multi-access support with PMIPv6.
   The MAG in this example scenario is equipped with both WLAN and LTE
   interfaces and is also configured with the multihoming functionality.
   The steps of the call flow are as follows:

   Steps (1) and (2): The MAG attaches to both WLAN and LTE networks.
   Then, the MAG obtains two different pCoAs, respectfully.

   Step (3): The MAG sends, over the LTE access, a Proxy Binding Update
   (PBU) message with the new MAG Multipath Binding (MMB) and MAG
   Network Access Identifier (MAG-NAI) options to the LMA.  The request
   can be for a physical mobile node attached to the MAG or for a
   logical mobile node configured on the mobile access gateway.  A
   logical mobile node is a logical representation of a mobile node in
   the form of a configuration that is always enabled on the MAG.  The
   mobility session that is created (i.e., create a Binding Cache Entry
   (BCE)) on the LMA will be marked with multipath support.

   Step (4): The LMA sends back a Proxy Binding Acknowledgement (PBA)
   including the Home Network Prefix (HNP) and other session parameters
   allocated for that mobility session.

   Step (5): IP tunnel is created between the MAG and the LMA over LTE
   access with any one of the supported encapsulation modes.

   Steps (6) to (8): The MAG repeats steps (3) to (5) on the WLAN
   access.  The MAG includes the HNP, received on step (4) in the PBU.
   The LMA updates its binding cache by creating a new mobility session
   for this MAG.

   Steps (9) and (10): The IP hosts MN_1 and MN_2 are assigned IP
   addresses from the mobile network prefix delegated to the MAG by the
   LMA.

   +=====+ +=====+     +=====+      +=====+      +=====+         +=====+
   | MN_1| | MN_2|     | MAG |      | WLAN|      | LTE |         | LMA |
   +=====+ +=====+     +=====+      +=====+      +=====+         +=====+
      |       |           |            |            |               |
      |       |           |            |            |               |
      |       |           | (1) ATTACH |            |               |
      |       |           | <--------> |            |               |
      |       |           | (2) ATTACH              |               |
      |       |           | <---------------------->|               |
      |       |           | (3) PBU (MAG-NAI, MMB, ...)             |
      |       |           | ------------------------*-------------->|
      |       |           |                                         |
      |       |           |                                   Accept PBU
      |       |           |                               (allocate HNP,
      |       |           |                                  create BCE)
      |       |           | (4) PBA (MMB, ...)                      |
      |       |           | <-----------------------*---------------|
      |       |           | (5) TUNNEL INTERFACE CREATION over LTE  |
      |       |           |-============== TUNNEL ==*==============-|
      |       |           |                                         |
      |       |           | (6) PBU (MAG-NAI, MMB, ...)             |
      |       |           | -----------*--------------------------->|
      |       |           |                                         |
      |       |           |                                   Accept PBU
      |       |           |                                 (update BCE)
      |       |           | (7) PBA (MMB, ...)                      |
      |       |           | <----------*--------------------------- |
      |       |           | (8) TUNNEL INTERFACE CREATION over WLAN |
      |       |           |-===========*== TUNNEL =================-|
      |   (9) ATTACH      |                                         |
      | <---------------> |                                         |
      |       |(10) ATTACH|                                         |
      |       |<--------> |                                         |

      Figure 2: Functional Separation of the Control and User Planes

3.2.  Traffic Distribution Schemes

   When the MAG has registered a multipath binding with the LMA, there
   will be multiple established overlay tunnels between them.  The MAG
   and the LMA can use any one, or more, of the available tunnel paths
   for routing the mobile node's IP traffic.  This specification does
   not recommend or define any specific traffic distribution scheme.
   However, it identifies two well-known approaches that implementations
   can potentially use.  These approaches are per-flow and per-packet
   traffic distribution schemes.

   Per-Flow Traffic Distribution:

   o  In this approach, the MAG and the LMA associate each of the IP
      flows (upstream and downstream) with a specific tunnel path.  The
      packets in a given IP flow are always routed on the same overlay
      tunnel path; they are never split and routed concurrently on more
      than one tunnel path.  It is possible for a given flow to be moved
      from one tunnel path to another, but the flow is never split.  The
      decision to bind a given IP flow to a specific tunnel path is
      based on the traffic distribution policy.  This traffic
      distribution policy is either statically configured on both the
      MAG and the LMA or dynamically negotiated over PMIPv6 signaling.
      The Flow Binding extension [RFC6089] and Traffic Selectors for
      Flow Bindings [RFC6088] define the mechanism and the semantics for
      exchanging the traffic policy between two tunnel peers; the same
      mechanism and the mobility options are used here.

   Per-Packet Traffic Distribution:

   o  In this approach, packets belonging to a given IP flow will be
      split and routed across more than one tunnel path.  The exact
      approach for traffic distribution or the distribution weights is
      outside the scope of this specification.  In a very simplistic
      approach, assuming that the established tunnel paths have
      symmetric characteristics, the packets can be equally distributed
      on all the available tunnel paths.  In a different scenario, when
      the links have different speeds, the chosen approach can be based
      on weighted distribution (e.g., n:m ratio).  However, in any of
      these chosen approaches, implementations have to be sensitive to
      issues related to asymmetric link characteristics and the
      resulting issues such as reordering, buffering, and the impact on
      application performance.  Care must be taken to ensure that there
      is no negative impact on the application performance due to the
      use of this approach.

4.  Protocol Extensions

4.1.  MAG Multipath Binding Option

   The MAG Multipath Binding option is a new mobility header option
   defined for use with PBU and PBA messages exchanged between the LMA
   and the MAG.

   This mobility header option is used for requesting multipath support.
   It indicates that the MAG is requesting that the LMA register the
   current CoA associated with the request as one of the many CoAs
   through which the MAG can be reached.  It is also used for carrying
   the information related to the access network associated with the
   CoA.

   The MAG Multipath Binding option does not have any alignment
   requirement.  Its format is as shown in Figure 3:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |   Length      |    If-ATT     |    If-Label   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Binding ID   |B|O|             Reserved                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 3: MAG Multipath Binding Option

   Type

      Type: MAG Multipath Binding (63)

   Length

      8-bit unsigned integer indicating the length of the option in
      octets, excluding the Type and Length fields.

   Interface Access-Technology Type (If-ATT)

      This 8-bit field identifies the Access-Technology type of the
      interface through which the mobile node is connected.  The
      permitted values for this are from the Access Technology Type
      registry <https://www.iana.org/assignments/mobility-parameters/>
      defined in [RFC5213].

   Interface Label (If-Label)

      This 8-bit unsigned integer represents the interface label.

      The interface label is an identifier configured on the WAN
      interface of the MAG.  All the WAN interfaces of the MAG that are
      used for sending PBU messages are configured with a label.  The
      labels merely identify the type of WAN interface and are primarily
      used in application-routing policies.  For example, a Wi-Fi
      interface can be configured with a label "9" and an LTE interface
      with a label "11".  Furthermore, the same label may be configured
      on two WAN interfaces of similar characteristics (e.g., two
      Ethernet interfaces with the same label).

      Interface labels are signaled from the MAG to the LMA in the PBU
      messages and both the LMA and MAG will be able to mark each of the
      dynamically created Binding/Tunnel with the associated label.
      These labels are used in generating consistent application-routing
      rules on the both the LMA and the MAG.  For example, there can be
      a policy requiring HTTP packets to be routed over an interface
      that has the interface label of "9", and if any of the interfaces
      with interface label "9" are not available, the traffic needs to
      be routed over the interface with the interface label "11".  The
      MAG and the LMA will be able to apply this routing rule with the
      exchange of interface labels in PBU messages and by associating
      the application flows to tunnels with the matching interface
      labels.

   Binding Identifier (BID)

      This 8-bit unsigned integer is used for identifying the binding.
      The permitted values are 1 through 254.  The values 0 and 255 are
      reserved.

      The MAG identifies each of the mobile node's bindings with a
      unique identifier.  The MAG includes the identifier in the PBU
      message; when the PBU request is accepted by the LMA, the
      resulting binding is associated with this BID in the mobile node's
      Binding Cache entry.

   Bulk Re-registration Flag (B)

      If set to a value of (1), this flag notifies the LMA to consider
      this as a request to update the binding lifetime of all the mobile
      node's bindings upon accepting this specific request.  The (B)
      flag MUST NOT be set to a value of (1) if the value of the
      Registration Overwrite (O) flag is set to a value of (1).

   Registration Overwrite (O)

      This flag, if set to a value of (1), notifies the LMA that upon
      accepting this request, it should replace all of the mobile node's
      existing bindings with this binding.  This flag MUST NOT be set to
      a value of (1) if the value of the Bulk Re-registration Flag (B)
      is set to a value of (1).  This flag MUST be set to a value of (0)
      in De-Registration requests.

   Reserved

      This field is unused in this specification.  The value MUST be set
      to zero (0) by the sender and MUST be ignored by the receiver.

4.2.  MAG Identifier Option

   The MAG Identifier option is a new mobility header option defined for
   use with PBU and PBA messages exchanged between the LMA and the MAG.
   This mobility header option is used for conveying the MAG's identity.

   This option does not have any alignment requirements.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |   Length      |  Subtype      |  Reserved     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Identifier ...                      ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 4: MAG Identifier Option

   Type

      Type: MAG Identifier (64)

   Length

      8-bit unsigned integer indicating the length of the option in
      octets, excluding the Type and Length fields.

   Subtype

      One-byte unsigned integer used for identifying the type of the
      Identifier field.  Accepted values for this field are the
      registered type values from the "Mobile Node Identifier Option
      Subtypes" registry <https://www.iana.org/assignments/mobility-
      parameters/>.

   Reserved

      This field is unused in this specification.  The value MUST be set
      to zero (0) by the sender and MUST be ignored by the receiver.

   Identifier

      A variable-length identifier of the type indicated in the Subtype
      field.

4.3.  New Status Code for Proxy Binding Acknowledgement

   This document defines the following new Status Code value for use in
   PBA messages.

   The LMA SHOULD use this error code when rejecting a PBU message from
   a MAG requesting a multipath binding.  The following is the potential
   reason for rejecting the request:

   o  The LMA does not support multipath binding.

   CANNOT_SUPPORT_MULTIPATH_BINDING (Cannot Support Multipath Binding):
   180

4.4.  Signaling Considerations

   o  The MAG, when requesting multipath support, MUST include the MAG
      Multipath Binding option (Section 4.1) in each of the PBU messages
      that it sends through the different WAN interfaces.  The inclusion
      of this option serves as a hint that the MAG is requesting
      multipath support.  Furthermore, the MAG Identifier option MUST
      also be present in the PBU message.

   o  If the MAG is aware that the LMA supports the multipath binding
      option defined in this specification and if it chooses to use
      multiple paths, then it can send the PBU packets for each of the
      paths, either sequentially or concurrently.  However, if the MAG
      is not aware of the LMA capability, then it SHOULD first discover
      the LMA capability by sending PBU packets with multipath on only
      one path first.  This will ensure that the LMA will not be
      overwriting the binding of one path with the other path.

   o  If the LMA supports multipath capability as defined in this
      specification and if it enables the same for a mobile node's
      session per the MAG's request, then the LMA MUST include the
      Multipath Binding option (Section 4.1) without the MAG-NAI option
      (Section 4.2) in the corresponding PBA reply.

   o  If the LMA is a legacy LMA that does not support this
      specification, the LMA will skip the MAG Multipath Binding option
      (and MAG-NAI option) and process the rest of the message as
      specified in the base PMIPv6 specification ([RFC5213]).
      Furthermore, the LMA will not include the MAG Multipath Binding
      option (or the MAG-NAI option) in the PBA message.  The MAG, upon
      receiving the PBA message without the MAG Multipath Binding
      option, SHOULD disable multipath support for the mobile node.

   o  If the mobile node is not authorized for multipath support, then
      the LMA will reject the request by sending a PBA message with the
      Status field value set to CANNOT_SUPPORT_MULTIPATH_BINDING
      (Section 4.3).  The LMA MUST echo the MAG Multipath Binding option
      (without the MAG-NAI option) in the PBA message.  The MAG, upon
      receiving this message, SHOULD disable multipath support for the
      mobile node.

5.  IANA Considerations

   This specification defines a new mobility option: the MAG Multipath
   Binding option.  The format of this option is described in
   Section 4.1.  The type value 63 has been allocated for this mobility
   option from the "Mobility Options" registry at
   <http://www.iana.org/assignments/mobility-parameters>.

   This specification defines a new mobility option: the MAG Identifier
   option.  The format of this option is described in Section 4.2.  The
   type value 64 has been allocated for this mobility option from the
   "Mobility Options" registry at <http://www.iana.org/assignments/
   mobility-parameters>.

   This document defines a new status value:
   CANNOT_SUPPORT_MULTIPATH_BINDING (180) for use in PBA messages, as
   described in Section 4.3.  This value has been assigned from the
   "Status Codes" registry at <http://www.iana.org/assignments/mobility-
   parameters>.

6.  Security Considerations

   This specification allows a MAG to establish multiple PMIPv6 tunnels
   with an LMA by registering a care-of address for each of its
   connected access networks.  This essentially allows the mobile node's
   IP traffic to be routed through any of the tunnel paths based on the
   negotiated flow policy.  This new capability has no impact on the
   protocol security.  Furthermore, this specification defines two new
   mobility header options: the MAG Multipath Binding option and the MAG
   Identifier option.  These options are carried like any other mobility
   header option as specified in [RFC5213].  Therefore, it inherits
   security guidelines from [RFC5213].  Thus, this specification does
   not weaken the security of the PMIPv6 Protocol and does not introduce
   any new security vulnerabilities.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, DOI 10.17487/RFC3963, January 2005,
              <https://www.rfc-editor.org/info/rfc3963>.

   [RFC5094]  Devarapalli, V., Patel, A., and K. Leung, "Mobile IPv6
              Vendor Specific Option", RFC 5094, DOI 10.17487/RFC5094,
              December 2007, <https://www.rfc-editor.org/info/rfc5094>.

   [RFC5213]  Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
              Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
              RFC 5213, DOI 10.17487/RFC5213, August 2008,
              <https://www.rfc-editor.org/info/rfc5213>.

   [RFC5844]  Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
              Mobile IPv6", RFC 5844, DOI 10.17487/RFC5844, May 2010,
              <https://www.rfc-editor.org/info/rfc5844>.

   [RFC5845]  Muhanna, A., Khalil, M., Gundavelli, S., and K. Leung,
              "Generic Routing Encapsulation (GRE) Key Option for Proxy
              Mobile IPv6", RFC 5845, DOI 10.17487/RFC5845, June 2010,
              <https://www.rfc-editor.org/info/rfc5845>.

   [RFC6088]  Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont,
              "Traffic Selectors for Flow Bindings", RFC 6088,
              DOI 10.17487/RFC6088, January 2011,
              <https://www.rfc-editor.org/info/rfc6088>.

   [RFC6089]  Tsirtsis, G., Soliman, H., Montavont, N., Giaretta, G.,
              and K. Kuladinithi, "Flow Bindings in Mobile IPv6 and
              Network Mobility (NEMO) Basic Support", RFC 6089,
              DOI 10.17487/RFC6089, January 2011,
              <https://www.rfc-editor.org/info/rfc6089>.

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <https://www.rfc-editor.org/info/rfc6275>.

   [RFC7148]  Zhou, X., Korhonen, J., Williams, C., Gundavelli, S., and
              CJ. Bernardos, "Prefix Delegation Support for Proxy Mobile
              IPv6", RFC 7148, DOI 10.17487/RFC7148, March 2014,
              <https://www.rfc-editor.org/info/rfc7148>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

7.2.  Informative References

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <https://www.rfc-editor.org/info/rfc2473>.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213,
              DOI 10.17487/RFC4213, October 2005,
              <https://www.rfc-editor.org/info/rfc4213>.

   [RFC4908]  Nagami, K., Uda, S., Ogashiwa, N., Esaki, H., Wakikawa,
              R., and H. Ohnishi, "Multi-homing for small scale fixed
              network Using Mobile IP and NEMO", RFC 4908,
              DOI 10.17487/RFC4908, June 2007,
              <https://www.rfc-editor.org/info/rfc4908>.

Acknowledgements

   The authors of this document would like to acknowledge the
   discussions and feedback on this topic from the members of the
   Distributed Mobility Management Working Group.  The authors would
   also like to thank Jouni Korhonen, Jong Hyouk Lee, Dirk Von-Hugo,
   Seil Jeon, Carlos Bernardos, Robert Sparks, Adam Roach, Kathleen
   Moriarty, Hilarie Orman, Ben Campbell, Warren Kumari, and Dhananjay
   Patki for their review feedback.  Special thanks to Mirja Kuehlewind
   for a very thorough review and suggesting many text improvements.

Authors' Addresses

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

   Email: pierrick.seite@orange.com


   Alper Yegin
   Actility
   Turkey

   Email: alper.yegin@actility.com


   Sri Gundavelli
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   United States of America

   Email: sgundave@cisco.com