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rfc:rfc8818



Internet Engineering Task Force (IETF) H. Chan, Ed. Request for Comments: 8818 CIHE Category: Informational X. Wei ISSN: 2070-1721 Huawei Technologies

                                                                J. Lee
                                                     Sejong University
                                                               S. Jeon
                                               Sungkyunkwan University
                                                    CJ. Bernardos, Ed.
                                                                  UC3M
                                                          October 2020
                   Distributed Mobility Anchoring

Abstract

 This document defines distributed mobility anchoring in terms of the
 different configurations and functions to provide IP mobility
 support.  A network may be configured with distributed mobility
 anchoring functions for both network-based or host-based mobility
 support, depending on the network's needs.  In a distributed mobility
 anchoring environment, multiple anchors are available for mid-session
 switching of an IP prefix anchor.  To start a new flow or to handle a
 flow not requiring IP session continuity as a mobile node moves to a
 new network, the flow can be started or restarted using an IP address
 configured from the new IP prefix anchored to the new network.  If
 the flow needs to survive the change of network, there are solutions
 that can be used to enable IP address mobility.  This document
 describes different anchoring approaches, depending on the IP
 mobility needs, and how this IP address mobility is handled by the
 network.

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 candidates for any level of Internet
 Standard; see 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/rfc8818.

Copyright Notice

 Copyright (c) 2020 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
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction
 2.  Conventions and Terminology
 3.  Distributed Mobility Anchoring
   3.1.  Configurations for Different Networks
     3.1.1.  Network-Based DMM
     3.1.2.  Client-Based DMM
 4.  IP Mobility Handling in Distributed Anchoring Environments:
         Mobility Support Only When Needed
   4.1.  Nomadic Case
   4.2.  Mobility Case with Traffic Redirection
   4.3.  Mobility Case with Anchor Relocation
 5.  Security Considerations
 6.  IANA Considerations
 7.  References
   7.1.  Normative References
   7.2.  Informative References
 Acknowledgements
 Contributors
 Authors' Addresses

1. Introduction

 A key requirement in distributed mobility management (DMM) [RFC7333]
 is to enable traffic to avoid traversing a single mobility anchor far
 from an optimal route.  This document defines different
 configurations, functional operations, and parameters for distributed
 mobility anchoring and explains how to use them to avoid
 unnecessarily long routes when a mobile node moves.
 Other distributed mobility management documents already address
 source address selection [RFC8653] and control-plane and data-plane
 signaling [FPC-DMM-PROTOCOL].  A number of distributed mobility
 solutions have also been proposed, for example, in [DMM-DMA],
 [RFC8885], [DMM-WIFI], [DMM-ENHANCED-ANCHORING], and
 [STATELESS-UPLANE-VEPC].
 Distributed mobility anchoring employs multiple anchors in the data
 plane.  In general, control-plane functions may be separated from
 data-plane functions and be centralized but may also be co-located
 with the data-plane functions at the distributed anchors.  Different
 configurations of distributed mobility anchoring are described in
 Section 3.1.
 As a Mobile Node (MN) attaches to an access router and establishes a
 link between them, a /64 IPv6 prefix anchored to the router may be
 assigned to the link for exclusive use by the MN [RFC6459].  The MN
 may then configure a global IPv6 address from this prefix and use it
 as the source IP address in a flow to communicate with its
 Correspondent Node (CN).  When there are multiple mobility anchors
 assigned to the same MN, an address selection for a given flow is
 first required before the flow is initiated.  Using an anchor in an
 MN's network of attachment has the advantage that the packets can
 simply be forwarded according to the forwarding table.  However,
 after the flow has been initiated, the MN may later move to another
 network that assigns a new mobility anchor to the MN.  Since the new
 anchor is located in a different network, the MN's assigned prefix
 does not belong to the network where the MN is currently attached.
 When the MN wants to continue using its assigned prefix to complete
 ongoing data sessions after it has moved to a new network, the
 network needs to provide support for the MN's IP address and session
 continuity, since routing packets to the MN through the new network
 deviates from applying default routes.  The IP session continuity
 needs of a flow (application) determine how the IP address used by
 this flow has to be anchored.  If the ongoing IP flow can cope with
 an IP prefix/address change, the flow can be reinitiated with a new
 IP address anchored in the new network.  On the other hand, if the
 ongoing IP flow cannot cope with such change, mobility support is
 needed.  A network supporting a mix of flows both requiring and not
 requiring IP mobility support will need to distinguish these flows.

2. Conventions and Terminology

 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.
 All general mobility-related terms and their acronyms used in this
 document are to be interpreted as defined in the Mobile IPv6 (MIPv6)
 base specification [RFC6275], the Proxy Mobile IPv6 (PMIPv6)
 specification [RFC5213], the Mobility Terminology document [RFC3753],
 and the DMM Current Practices and Gap Analysis document [RFC7429].
 These include terms such as Mobile Node (MN), Correspondent Node
 (CN), Home Agent (HA), Home Address (HoA), Care-of-Address (CoA),
 Local Mobility Anchor (LMA), and Mobile Access Gateway (MAG).
 In addition, this document uses the following terms and definitions:
 IP session continuity:  The ability to maintain an ongoing transport
    interaction by keeping the same local endpoint IP address
    throughout the lifetime of the IP socket despite the mobile host
    changing its point of attachment within the IP network topology.
    The IP address of the host may change after closing the IP socket
    and before opening a new one, but that does not jeopardize the
    ability of applications using these IP sockets to work flawlessly.
    Session continuity is essential for mobile hosts to maintain
    ongoing flows without any interruption [RFC8653].
 Higher-layer session continuity:  The ability to maintain an ongoing
    transport- or higher-layer (e.g., application) interaction by
    keeping the session identifiers throughout the lifetime of the
    session despite the mobile host changing its point of attachment
    within the IP network topology.  This can be achieved by using
    mechanisms at the transport or higher layers.
 IP address reachability:  The ability to maintain the same IP address
    for an extended period of time.  The IP address stays the same
    across independent sessions, even in the absence of any session.
    The IP address may be published in a long-term registry (e.g.,
    DNS) and is made available for serving incoming (e.g., TCP)
    connections.  IP address reachability is essential for mobile
    hosts to use specific/published IP addresses [RFC8653].
 IP mobility:  The combination of IP address reachability and session
    continuity.
 Anchoring (of an IP prefix/address):  An IP prefix (i.e., Home
    Network Prefix (HNP)) or address (i.e., HoA) assigned for use by
    an MN is topologically anchored to an anchor node when the anchor
    node is able to advertise a route into the routing infrastructure
    for the assigned IP prefix.  The traffic using the assigned IP
    address/prefix must traverse the anchor node.  We can refer to the
    function performed by the IP anchor node as anchoring, which is a
    data-plane function.
 Location Management (LM) function:  A control-plane function that
    keeps and manages the network location information 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 of a node that can forward packets destined to the MN.
    When the MN is a Mobile Router (MR), the location information will
    also include the Mobile Network Prefix (MNP), which is the
    aggregate IP prefix delegated to the MR to assign IP prefixes for
    use by the Mobile Network Nodes (MNNs) in the mobile network.
    In a client-server protocol model, secure (i.e., authenticated and
    authorized) location query and update messages may be exchanged
    between a Location Management client (LMc) and a Location
    Management server (LMs), where the location information can be
    updated or queried from the LMc.  Optionally, there may be a
    Location Management proxy (LMp) between LMc and LMs.
    With separation of control plane and data plane, the LM function
    is in the control plane.  It may be a logical function at the
    control-plane node, control-plane anchor, or mobility controller.
    It may be distributed or centralized.
 Forwarding Management (FM) function:  Packet interception and
    forwarding to/from the IP address/prefix assigned for use by 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.
    This function may be used to achieve traffic indirection.  With
    separation of control plane and data plane, the FM function may
    split into an FM function in the data plane (FM-DP) and an FM
    function in the control plane (FM-CP).
    FM-DP may be distributed with distributed mobility management.  It
    may be a function in a data-plane anchor or data-plane node.
    FM-CP may be distributed or centralized.  It may be a function in
    a control-plane node, control-plane anchor, or mobility
    controller.
 Home Control-Plane Anchor (Home-CPA or H-CPA):  The Home-CPA function
    hosts the MN's mobility session.  There can be more than one
    mobility session for a mobile node, and those sessions may be
    anchored on the same or different Home-CPA's.  The Home-CPA will
    interface with the Home-DPA for managing the forwarding state.
 Home Data-Plane Anchor (Home-DPA or H-DPA):  The Home-DPA is the
    topological anchor for the MN's IP address/prefix(es).  The Home-
    DPA is chosen by the Home-CPA on a session basis.  The Home-DPA is
    in the forwarding path for all the mobile node's IP traffic.
 Access Control-Plane Node (Access-CPN or A-CPN):  The Access-CPN is
    responsible for interfacing with the mobile node's Home-CPA and
    with the Access-DPN.  The Access-CPN has a protocol interface to
    the Home-CPA.
 Access Data-Plane Node (Access-DPN or A-DPN):  The Access-DPN
    function is hosted on the first-hop router where the mobile node
    is attached.  This function is not hosted on a Layer 2 bridging
    device such as an eNode(B) or Access Point.

3. Distributed Mobility Anchoring

3.1. Configurations for Different Networks

 We next describe some configurations with multiple distributed
 anchors.  To cover the widest possible spectrum of scenarios, we
 consider architectures in which the control and data planes are
 separated.  We analyze where LM and FM functions, which are specific
 sub-functions involved in mobility management, can be placed when
 looking at the different scenarios with distributed anchors.

3.1.1. Network-Based DMM

 Figure 1 shows a general scenario for network-based distributed
 mobility management.
 The main characteristics of a network-based DMM solution are:
  • There are multiple data-plane anchors, each with an FM-DP

function.

  • The control plane may either be distributed (not shown in the

figure) or centralized (as shown in the figure).

  • The Control-Plane Anchor (CPA) and the Data Plane Anchor (DPA) may

or may not be co-located. If the CPA is co-located with the

    distributed DPAs, then there are multiple co-located CPA-DPA
    instances (not shown in the figure).
  • An IP prefix/address IP1 (anchored to the DPA with IP address

IPa1) is assigned for use to an MN. The MN uses this IP1 address

    to communicate with CNs (not shown in the figure).
  • The location management (LM) function may be co-located or split

(as shown in the figure) into a separate server (LMs) and a client

    (LMc).  In this case, the LMs may be centralized whereas the LMc
    may be distributed or centralized.
            ____________  Network
        ___/            \___________
       /      +-----+                \___
      (       |LMs  |    Control-        \
     /        +-.---+    plane            \
    /  +--------.---+    functions         \
   (   |CPA:    .   |    in the             )
   (   |FM-CP, LMc  |    network            )
   (   +------------+                        \
  /          . .                              \
 (           .     .                           )
 (           .         .                       )
 (           .             .                   \
  \    +------------+ +------------+Distributed )
   (   |DPA(IPa1):  | |DPA(IPa2):  |DPAs        )
   (   |anchors IP1 | |anchors IP2 |          _/
    \  |FM-DP       | |FM-DP       | etc.    /
     \ +------------+ +------------+        /
      \___                Data-plane  _____/
          \______         functions  /
                 \__________________/
       +------------+
       |MN(IP1)     | Mobile node attached
       |flow(IP1,..)| to the network
       +------------+
               Figure 1: Network-Based DMM Configuration

3.1.2. Client-Based DMM

 Figure 2 shows a general scenario for client-based distributed
 mobility management.  In this configuration, the mobile node performs
 Control-Plane Node (CPN) and Data-Plane Node (DPN) mobility
 functions, namely the forwarding management and location management
 (client) roles.
        +-----+
        |LMs  |
        +-.---+
 +--------.---+
 |CPA:    .   |
 |FM-CP, LMp  |
 +------------+
       . .
       .     .
       .         .
       .             .
 +------------+ +------------+ Distributed
 |DPA(IPa1):  | |DPA(IPa2):  | DPAs
 |anchors IP1 | |anchors IP2 |
 |FM-DP       | |FM-DP       |  etc.
 +------------+ +------------+
 +------------+
 |MN(IP1)     |Mobile node
 |flow(IP1,..)|using IP1
 |FM,    LMc  |anchored to
 +------------+DPA(IPa1)
                Figure 2: Client-Based DMM Configuration

4. IP Mobility Handling in Distributed Anchoring Environments: Mobility

  Support Only When Needed
 IP mobility support may be provided only when needed instead of being
 provided by default.  Three cases can be considered:
  • Nomadic case: No address continuity is required. The IP address

used by the MN changes after a movement and traffic using the old

    address is disrupted.  If session continuity is required, then it
    needs to be provided by a solution running at Layer 4 or above.
  • Mobility case with traffic redirection: Address continuity is

required. When the MN moves, the previous anchor still anchors

    the traffic using the old IP address and forwards it to the new
    MN's location.  The MN obtains a new IP address anchored to the
    new location and preferably uses it for new communications
    established while connected at the new location.
  • Mobility case with anchor relocation: Address continuity is

required. In this case, the route followed by the traffic is

    optimized by using some means for traffic indirection to deviate
    from default routes.
 A straightforward choice of mobility anchoring is the following: the
 MN chooses, as a source IP address for packets belonging to an IP
 flow, an address allocated by the network the MN is attached to when
 the flow was initiated.  As such, traffic belonging to this flow
 traverses the MN's mobility anchor [DMM-DMA] [RFC8885].
 The IP prefix/address at the MN's side of a flow may be anchored to
 the Access Router (AR) to which the MN is attached.  For example,
 when an MN attaches to a network (Net1) or moves to a new network
 (Net2), an IP prefix from the attached network is assigned to the
 MN's interface.  In addition to configuring new link-local addresses,
 the MN configures from this prefix an IP address that is typically a
 dynamic IP address (meaning that this address is only used while the
 MN is attached to this access router, so the IP address configured by
 the MN dynamically changes when attaching to a different access
 network).  It then uses this IP address when a flow is initiated.
 Packets from this flow addressed to the MN are simply forwarded
 according to the forwarding table.
 There may be multiple IP prefixes/addresses that an MN can select
 when initiating a flow.  They may be from the same access network or
 different access networks.  The network may advertise these prefixes
 with cost options [PREFIX-COST] so that the mobile node may choose
 the one with the least cost.  In addition, the IP prefixes/addresses
 provided by the network may be of different types regarding whether
 mobility support is supported [RFC8653].  An MN will need to choose
 which IP prefix/address to use for each flow according to whether or
 not it needs IP mobility support, for example, using the mechanisms
 described in [RFC8653].

4.1. Nomadic Case

 When IP mobility support is not needed for a flow, the LM and FM
 functions are not utilized so that the configurations in Section 3.1
 are simplified as shown in Figure 3.
 Net1                                                Net2
 +---------------+                                   +---------------+
 |AR1            |            AR is changed          |AR2            |
 +---------------+              ------->             +---------------+
 |CPA:           |                                   |CPA:           |
 |---------------|                                   |---------------|
 |DPA(IPa1):     |                                   |DPA(IPa2):     |
 |anchors IP1    |                                   |anchors IP2    |
 +---------------+                                   +---------------+
 +...............+                                   +---------------+
 .MN(IP1)        .              MN moves             |MN(IP2)        |
 .flow(IP1,...)  .              =======>             |flow(IP2,...)  |
 +...............+                                   +---------------+
             Figure 3: Changing to a New IP Address/Prefix
 When there is no need to provide IP mobility to a flow, the flow may
 use a new IP address acquired from a new network as the MN moves to
 the new network.
 Regardless of whether or not IP mobility is needed, if the flow has
 not terminated before the MN moves to a new network, the flow may
 subsequently restart using the new IP address assigned from the new
 network.
 When IP session continuity is needed, even if an application flow is
 ongoing as the MN moves, it may still be desirable for the
 application flow to change to using the new IP prefix configured in
 the new network.  The application flow may then be closed at the IP
 level and then be restarted using a new IP address configured in the
 new network.  Such a change in the IP address used by the application
 flow may be enabled using a higher-layer mobility support that is not
 in the scope of this document.
 In Figure 3, a flow initiated while the MN was using the IP prefix
 IP1, anchored to a previous access router AR1 in network Net1, has
 terminated before the MN moves to a new network Net2.  After moving
 to Net2, the MN uses the new IP prefix IP2, anchored to a new access
 router AR2 in network Net2, to start a new flow.  Packets may then be
 forwarded without requiring IP-layer mobility support.
 An example call flow is outlined in Figure 4.  An MN attaches to AR1,
 which sends a router advertisement (RA) including information about
 the prefix assigned to the MN, from which the MN configures an IP
 address (IP1).  This address is used for new communications, for
 example, with a correspondent node (CN).  If the MN moves to a new
 network and attaches to AR2, the process is repeated (the MN obtains
 a new IP address, IP2, from AR2).  Since the IP address (IP1)
 configured at the previously visited network is not valid at the
 current attachment point, any existing flows have to be reestablished
 using IP2.
 Note that in these scenarios, if there is no mobility support
 provided by Layer 4 or above, application traffic would stop.
  MN                    AR1           AR2                           CN
   |MN attaches to AR1:  |             |                             |
   |acquires MN-ID and profile         |                             |
   |--RS---------------->|             |                             |
   |                     |             |                             |
   |<----------RA(IP1)---|             |                             |
   |                     |             |                             |
 Assigned prefix IP1     |             |                             |
 IP1 address configuration             |                             |
   |                     |             |                             |
   |<-Flow(IP1,IPcn,...)-+------------------------------------------>|
   |                     |             |                             |
   |MN detaches from AR1 |             |                             |
   |MN attaches to AR2   |             |                             |
   |                     |             |                             |
   |--RS------------------------------>|                             |
   |                     |             |                             |
   |<--------------RA(IP2)-------------|                             |
   |                     |             |                             |
 Assigned prefix IP2     |             |                             |
 IP2 address configuration             |                             |
   |                     |             |                             |
   |<-new Flow(IP2,IPcn,...)-----------+---------------------------->|
   |                     |             |                             |
         Figure 4: Restarting a Flow with New IP Prefix/Address

4.2. Mobility Case with Traffic Redirection

 When IP mobility is needed for a flow, the LM and FM functions in
 Section 3.1 are utilized.  There are two possible cases: (i) the
 mobility anchor remains playing that role and forwards traffic to a
 new locator in the new network, and (ii) the mobility anchor (data-
 plane function) is changed but binds the MN's transferred IP address/
 prefix.  The latter enables optimized routes but requires some data-
 plane node that enforces traffic indirection.  We focus on the first
 case in this section.  The second case is addressed in Section 4.3.
 Mobility support can be provided by using mobility management
 methods, such as the approaches surveyed in the following academic
 papers: [IEEE-DISTRIBUTED-MOBILITY], [PMIP-DMA], and
 [DMM-MOBILE-INTERNET].  After moving, a certain MN's traffic flow may
 continue using the IP prefix from the prior network of attachment.
 Yet, some time later, the application generating this traffic flow
 may be closed.  If the application is started again, the new flow may
 not need to use the prior network's IP address to avoid having to
 invoke IP mobility support.  This may be the case where a dynamic IP
 prefix/address, rather than a permanent one, is used.  Packets
 belonging to this flow may then use the new IP prefix (the one
 allocated in the network where the flow is being initiated).  Routing
 is again kept simpler without employing IP mobility and will remain
 so as long as the MN, which is now in the new network, does not move
 again to another network.
 An example call flow in this case is outlined in Figure 5.  In this
 example, the AR1 plays the role of the FM-DP entity and redirects the
 traffic (e.g., using an IP tunnel) to AR2.
  MN                    AR1           AR2                           CN
   |MN attaches to AR1:  |             |                             |
   |acquires MN-ID and profile         |                             |
   |--RS---------------->|             |                             |
   |                     |             |                             |
   |<----------RA(IP1)---|             |                             |
   |                     |             |                             |
 Assigned prefix IP1     |             |                             |
 IP1 address configuration             |                             |
   |                     |             |                             |
   |<-Flow(IP1,IPcn,...)-+------------------------------------------>|
   |                     |             |                             |
   |MN detaches from AR1 |             |                             |
   |MN attaches to AR2   |             |                             |
   |                     |             |                             |
   |--RS------------------------------>|                             |
    (some IP mobility support solution)
   |<--------------RA(IP2,IP1)---------|                             |
   |                     |             |                             |
   |                     +<-Flow(IP1,IPcn,...)---------------------->|
   |                     +<===========>+                             |
   |<-Flow(IP1,IPcn,...)-------------->+                             |
   |                     |             |                             |
 Assigned prefix IP2     |             |                             |
 IP2 address configuration             |                             |
   |                     |             |                             |
 Flow(IP1,IPcn) terminates             |                             |
   |                     |             |                             |
   |<-new Flow(IP2,IPcn,...)-----------+---------------------------->|
   |                     |             |                             |
  Figure 5: Flow Using IP Prefix from Home Network after MN has Moved
 Another solution could be to place an FM-DP entity closer to the CN
 network to perform traffic steering to deviate from default routes
 (which will bring the packet to AR1 per default routing).  The LM and
 FM functions are implemented as shown in Figure 6.
 Net1                                                Net2
 +---------------+                                   +---------------+
 |AR1            |                                   |AR2            |
 +---------------+                                   +---------------+
 |CPA:           |                                   |CPA:           |
 |               |                                   |LM:IP1 at IPa1 |
 |---------------|      IP1 (anchored to Net1)       |---------------|
 |DPA(IPa1):     |      is redirected to Net2        |DPA(IPa2):     |
 |anchors IP1    |              =======>             |anchors IP2    |
 |FM:IP1 via IPa2|                                   |FM:IP1 via IPa1|
 +---------------+                                   +---------------+
 +...............+                                   +---------------+
 .MN(IP1)        .              MN moves             |MN(IP2,IP1)    |
 .flow(IP1,...)  .              =======>             |flow(IP1,...)  |
 .               .                                   |flow(IP2,...)  |
 +...............+                                   +---------------+
                      Figure 6: Anchor Redirection
 Multiple instances of DPAs (at access routers), which are providing
 IP prefixes to the MNs, are needed to provide distributed mobility
 anchoring in an appropriate configuration such as those described in
 Figure 1 (Section 3.1.1) for network-based distributed mobility or in
 Figure 2 (Section 3.1.2) for client-based distributed mobility.

4.3. Mobility Case with Anchor Relocation

 We focus next on the case where the mobility anchor (data-plane
 function) is changed but binds the MN's transferred IP address/
 prefix.  This enables optimized routes but requires some data-plane
 node that enforces traffic indirection.
 IP mobility is invoked to enable IP session continuity for an ongoing
 flow as the MN moves to a new network.  The anchoring of the IP
 address of the flow is in the home network of the flow (i.e.,
 different from the current network of attachment).  A centralized
 mobility management mechanism may employ indirection from the anchor
 in the home network to the current network of attachment.  Yet, it
 may be difficult to avoid using an unnecessarily long route (when the
 route between the MN and the CN via the anchor in the home network is
 significantly longer than the direct route between them).  An
 alternative is to move the IP prefix/address anchoring to the new
 network.
 The IP prefix/address anchoring may move without changing the IP
 prefix/address of the flow.  The LM function in Figure 1 of
 Section 3.1.1 is implemented as shown in Figure 7.
 Net1                                              Net2
 +---------------+                                 +---------------+
 |AR1            |                                 |AR2            |
 +---------------+                                 +---------------+
 |CPA:           |                                 |CPA:           |
 |LM:IP1 at IPa1 |                                 |LM:IP1 at IPa2 |
 |   changes to  |                                 |               |
 |   IP1 at IPa2 |                                 |               |
 |---------------|                                 |---------------|
 |DPA(IPa1):     | IP1 anchoring effectively moved |DPA(IPa2):     |
 |anchored IP1   |            =======>             |anchors IP2,IP1|
 +---------------+                                 +---------------+
 +...............+                                 +---------------+
 .MN(IP1)        .            MN moves             |MN(IP2,IP1)    |
 .flow(IP1,...)  .            =======>             |flow(IP1,...)  |
 +...............+                                 +---------------+
                      Figure 7: Anchor Relocation
 As an MN with an ongoing session moves to a new network, the flow may
 preserve IP session continuity by moving the anchoring of the
 original IP prefix/address of the flow to the new network.
 One way to accomplish such a move is to use a centralized routing
 protocol, but such a solution may present some scalability concerns
 and its applicability is typically limited to small networks.  One
 example of this type of solution is described in [BGP-ATN-IPS].  When
 an MN associates with an anchor, the anchor injects the MN's prefix
 into the global routing system.  If the MN moves to a new anchor, the
 old anchor withdraws the /64 and the new anchor injects it instead.

5. Security Considerations

 As stated in [RFC7333], "a DMM solution MUST support any security
 protocols and mechanisms needed to secure the network and to make
 continuous security improvements".  It "MUST NOT introduce new
 security risks".
 There are different potential deployment models of a DMM solution.
 The present document has presented three different scenarios for
 distributed anchoring: (i) nomadic case, (ii) mobility case with
 traffic redirection, and (iii) mobility case with anchor relocation.
 Each of these cases has different security requirements, and the
 actual security mechanisms depend on the specifics of each solution/
 scenario.
 As general rules, for the first distributed anchoring scenario
 (nomadic case), no additional security consideration is needed, as
 this does not involve any additional mechanism at Layer 3.  If
 session connectivity is required, the Layer 4 or above solution used
 to provide it MUST also provide the required authentication and
 security.
 The second and third distributed anchoring scenarios (mobility case)
 involve mobility signaling among the mobile node and the control-
 plane and data-plane anchors.  The control-plane messages exchanged
 between these entities MUST be protected using end-to-end security
 associations with data-integrity and data-origination capabilities.
 IPsec [RFC8221] Encapsulating Security Payload (ESP) in transport
 mode with mandatory integrity protection SHOULD be used for
 protecting the signaling messages.  Internet Key Exchange Protocol
 Version 2 (IKEv2) [RFC8247] SHOULD be used to set up security
 associations between the data-plane and control-plane anchors.  Note
 that in scenarios in which traffic indirection mechanisms are used to
 relocate an anchor, authentication and authorization mechanisms MUST
 be used.
 Control-plane functionality MUST apply authorization checks to any
 commands or updates that are made by the control-plane protocol.

6. IANA Considerations

 This document has no IANA actions.

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>.
 [RFC3753]  Manner, J., Ed. and M. Kojo, Ed., "Mobility Related
            Terminology", RFC 3753, DOI 10.17487/RFC3753, June 2004,
            <https://www.rfc-editor.org/info/rfc3753>.
 [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>.
 [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>.
 [RFC7333]  Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J.
            Korhonen, "Requirements for Distributed Mobility
            Management", RFC 7333, DOI 10.17487/RFC7333, August 2014,
            <https://www.rfc-editor.org/info/rfc7333>.
 [RFC7429]  Liu, D., Ed., Zuniga, JC., Ed., Seite, P., Chan, H., and
            CJ. Bernardos, "Distributed Mobility Management: Current
            Practices and Gap Analysis", RFC 7429,
            DOI 10.17487/RFC7429, January 2015,
            <https://www.rfc-editor.org/info/rfc7429>.
 [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>.
 [RFC8221]  Wouters, P., Migault, D., Mattsson, J., Nir, Y., and T.
            Kivinen, "Cryptographic Algorithm Implementation
            Requirements and Usage Guidance for Encapsulating Security
            Payload (ESP) and Authentication Header (AH)", RFC 8221,
            DOI 10.17487/RFC8221, October 2017,
            <https://www.rfc-editor.org/info/rfc8221>.
 [RFC8247]  Nir, Y., Kivinen, T., Wouters, P., and D. Migault,
            "Algorithm Implementation Requirements and Usage Guidance
            for the Internet Key Exchange Protocol Version 2 (IKEv2)",
            RFC 8247, DOI 10.17487/RFC8247, September 2017,
            <https://www.rfc-editor.org/info/rfc8247>.

7.2. Informative References

 [BGP-ATN-IPS]
            Templin, F., Saccone, G., Dawra, G., Lindem, A., and V.
            Moreno, "A Simple BGP-based Mobile Routing System for the
            Aeronautical Telecommunications Network", Work in
            Progress, Internet-Draft, draft-ietf-rtgwg-atn-bgp-06, 30
            June 2020,
            <https://tools.ietf.org/html/draft-ietf-rtgwg-atn-bgp-06>.
 [DMM-DMA]  Seite, P., Bertin, P., and J. Lee, "Distributed Mobility
            Anchoring", Work in Progress, Internet-Draft, draft-seite-
            dmm-dma-07, 6 February 2014,
            <https://tools.ietf.org/html/draft-seite-dmm-dma-07>.
 [DMM-ENHANCED-ANCHORING]
            Kim, Y. and S. Jeon, "Enhanced Mobility Anchoring in
            Distributed Mobility Management", Work in Progress,
            Internet-Draft, draft-yhkim-dmm-enhanced-anchoring-05, 8
            July 2016, <https://tools.ietf.org/html/draft-yhkim-dmm-
            enhanced-anchoring-05>.
 [DMM-MOBILE-INTERNET]
            Chan, H., Yokota, H., Xie, J., Seite, P., and D. Liu,
            "Distributed and Dynamic Mobility Management in Mobile
            Internet: Current Approaches and Issues", Journal of
            Communications, Vol. 6, No. 1, February 2011.
 [DMM-WIFI] Sarikaya, B. and L. Li, "Distributed Mobility Management
            Protocol for WiFi Users in Fixed Network", Work in
            Progress, Internet-Draft, draft-sarikaya-dmm-for-wifi-05,
            30 October 2017, <https://tools.ietf.org/html/draft-
            sarikaya-dmm-for-wifi-05>.
 [FPC-DMM-PROTOCOL]
            Matsushima, S., Bertz, L., Liebsch, M., Gundavelli, S.,
            Moses, D., and C. Perkins, "Protocol for Forwarding Policy
            Configuration (FPC) in DMM", Work in Progress, Internet-
            Draft, draft-ietf-dmm-fpc-cpdp-14, 22 September 2020,
            <https://tools.ietf.org/html/draft-ietf-dmm-fpc-cpdp-14>.
 [IEEE-DISTRIBUTED-MOBILITY]
            Lee, J., Bonnin, J., Seite, P., and H. A. Chan,
            "Distributed IP mobility management from the perspective
            of the IETF: motivations, requirements, approaches,
            comparison, and challenges", IEEE Wireless Communications,
            vol. 20, no. 5, pp. 159-168, October 2013.
 [PMIP-DMA] Chan, H., "Proxy mobile IP with distributed mobility
            anchors", IEEE Globecom Workshops Miami, FL, 2010, pp.
            16-20, December 2010.
 [PREFIX-COST]
            McCann, P. and J. Kaippallimalil, "Communicating Prefix
            Cost to Mobile Nodes", Work in Progress, Internet-Draft,
            draft-mccann-dmm-prefixcost-03, 11 April 2016,
            <https://tools.ietf.org/html/draft-mccann-dmm-prefixcost-
            03>.
 [RFC6459]  Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
            T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
            Partnership Project (3GPP) Evolved Packet System (EPS)",
            RFC 6459, DOI 10.17487/RFC6459, January 2012,
            <https://www.rfc-editor.org/info/rfc6459>.
 [RFC8653]  Yegin, A., Moses, D., and S. Jeon, "On-Demand Mobility
            Management", RFC 8653, DOI 10.17487/RFC8653, October 2019,
            <https://www.rfc-editor.org/info/rfc8653>.
 [RFC8885]  Bernardos, CJ., de la Oliva, A., Giust, F., Zúñiga, JC.,
            and A. Mourad, "Proxy Mobile IPv6 Extensions for
            Distributed Mobility Management", RFC 8885,
            DOI 10.17487/RFC8885, October 2020,
            <https://www.rfc-editor.org/info/rfc8885>.
 [STATELESS-UPLANE-VEPC]
            Matsushima, S. and R. Wakikawa, "Stateless user-plane
            architecture for virtualized EPC (vEPC)", Work in
            Progress, Internet-Draft, draft-matsushima-stateless-
            uplane-vepc-06, 21 March 2016,
            <https://tools.ietf.org/html/draft-matsushima-stateless-
            uplane-vepc-06>.

Acknowledgements

 The work of Jong-Hyouk Lee was supported by the MSIT (Ministry of
 Science and ICT), Korea, under the ITRC (Information Technology
 Research Center) support program (IITP-2020-2015-0-00403) supervised
 by the IITP (Institute for Information & communications Technology
 Planning & Evaluation).

Contributors

 Alexandre Petrescu and Fred Templin had contributed to earlier draft
 versions of this document regarding distributed anchoring for
 hierarchical networks and for network mobility, although these
 extensions were removed to keep the document within reasonable
 length.
 This document has benefited from other work on mobility support in
 SDN networks, on providing mobility support only when needed, and on
 mobility support in enterprise networks.  These works have been
 referenced.  While some of these authors have taken the work to
 jointly write this document, others have contributed at least
 indirectly by writing these works.  The latter include Philippe
 Bertin, Dapeng Liu, Satoru Matushima, Pierrick Seite, Jouni Korhonen,
 and Sri Gundavelli.
 For completeness, some terminology from draft-ietf-dmm-deployment-
 models-04 has been incorporated into this document.
 Valuable comments have been received from John Kaippallimalil,
 ChunShan Xiong, Dapeng Liu, Fred Templin, Paul Kyzivat, Joseph
 Salowey, Yoshifumi Nishida, Carlos Pignataro, Mirja Kuehlewind, Eric
 Vyncke, Qin Wu, Warren Kumari, Benjamin Kaduk, Roman Danyliw, and
 Barry Leiba.  Dirk von Hugo, Byju Pularikkal, and Pierrick Seite have
 generously provided careful review with helpful corrections and
 suggestions.  Marco Liebsch and Lyle Bertz also performed very
 detailed and helpful reviews of this document.

Authors' Addresses

 H. Anthony Chan (editor)
 Caritas Institute of Higher Education
 2 Chui Ling Lane, Tseung Kwan O
 N.T.
 Hong Kong
 Email: h.a.chan@ieee.org
 Xinpeng Wei
 Huawei Technologies
 Xin-Xi Rd. No. 3, Haidian District
 Beijing, 100095
 China
 Email: weixinpeng@huawei.com
 Jong-Hyouk Lee
 Sejong University
 209, Neungdong-ro, Gwangjin-gu
 Seoul
 05006
 Republic of Korea
 Email: jonghyouk@sejong.ac.kr
 Seil Jeon
 Sungkyunkwan University
 2066 Seobu-ro, Jangan-gu
 Suwon, Gyeonggi-do
 Republic of Korea
 Email: seiljeon.ietf@gmail.com
 Carlos J. Bernardos (editor)
 Universidad Carlos III de Madrid
 Av. Universidad, 30
 28911 Leganes, Madrid
 Spain
 Phone: +34 91624 6236
 Email: cjbc@it.uc3m.es
 URI:   http://www.it.uc3m.es/cjbc/
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