draft-ietf-dmm-distributed-mobility-anchoring-10.xml

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     docName="draft-ietf-dmm-distributed-mobility-anchoring-10"
     ipr="trust200902">
<front>
<title abbrev="distributed mobility anchoring">Distributed Mobility
    Anchoring</title>

<author fullname="H. Anthony Chan" initials="H" surname="Chan" role="editor">
  <organization>Huawei Technologies</organization>
  <address>
    <postal>
      <street>5340 Legacy Dr. Building 3</street>
      <city>Plano, TX 75024</city>
      <country>USA</country>
    </postal>
    <email>h.a.chan@ieee.org</email>
  </address>
</author>

<author fullname="Xinpeng Wei" initials="X" surname="Wei">
  <organization>Huawei Technologies</organization>
  <address>
    <postal>
      <street>Xin-Xi Rd. No. 3, Haidian District</street>
      <city>Beijing, 100095</city>
      <country>P. R. China</country>
    </postal>
    <email>weixinpeng@huawei.com</email>
  </address>
</author>

<author fullname="Jong-Hyouk Lee" initials="J" surname="Lee">
  <organization>Sangmyung University</organization>
  <address>
    <postal>
      <street>31, Sangmyeongdae-gil, Dongnam-gu</street>
      <city>Cheonan 31066</city>
      <country>Republic of Korea</country>
    </postal>
    <email>jonghyouk@smu.ac.kr</email>
  </address>
</author>

<author fullname="Seil Jeon" initials="S" surname="Jeon">
  <organization>Sungkyunkwan University</organization>
  <address>
    <postal>
      <street>2066 Seobu-ro, Jangan-gu</street>
      <city>Suwon, Gyeonggi-do</city>
      <country>Republic of Korea</country>
    </postal>
    <email>seiljeon@skku.edu</email>
  </address>
</author>

<author fullname="Carlos J. Bernardos"
        initials="CJ."
        surname="Bernardos"
        role="editor">
  <organization abbrev="UC3M">
    Universidad Carlos III de Madrid
  </organization>
  <address>
    <postal>
      <street>Av. Universidad, 30</street>
      <city>Leganes, Madrid</city>
      <code>28911</code>
      <country>Spain</country>
    </postal>
    <phone>+34 91624 6236</phone>
    <email>cjbc@it.uc3m.es</email>
    <uri>http://www.it.uc3m.es/cjbc/</uri>
  </address>
</author>

<date year="2018" month="July" />
<area/>

<workgroup>DMM</workgroup>

<abstract>
<t>
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 according to the needs of mobility support. In
the 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 re-started using a new IP address
configured from the new IP prefix which is anchored to the new network. The
mobility functions and their operations and parameters are general for different
configurations.
</t>
</abstract>
</front>

<middle>

<!-- Introduction -->

<section anchor="intro" title="Introduction">
<t>
A key requirement in distributed mobility management <xref target="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 make the route changes to avoid unnecessarily long routes.
</t>

<t>
Companion distributed mobility management documents are already addressing the
architecture and deployment <xref target="I-D.ietf-dmm-deployment-models"/>,
source address selection <xref target="I-D.ietf-dmm-ondemand-mobility"/>, and
control-plane data-plane signaling <xref target="I-D.ietf-dmm-fpc-cpdp"/>. A
number of distributed mobility solutions have also been proposed, for example,
in <xref target="I-D.seite-dmm-dma"/>, <xref
target="I-D.bernardos-dmm-pmipv6-dlif"/>, <xref
target="I-D.sarikaya-dmm-for-wifi"/>, <xref
target="I-D.yhkim-dmm-enhanced-anchoring"/>, and <xref
target="I-D.matsushima-stateless-uplane-vepc"/>.
</t>


<t>
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 <xref target="sec:distributed-anchoring-configurations"/>.
</t>

<t>
As an 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 <xref target="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 which assigns a new mobility anchor to the MN.
Since the new anchor is located in a different network, the MN's assigned prefix
and the built MN IP address does not belong to the network where the MN is
currently attached.
</t>

<t>
When the MN wants to continue using its assigned prefix and IP address, e.g., to
complete ongoing data sessions after it moved to a new network, the network
needs to provide support for 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) determines the how the
IP address used by the traffic of 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. 
</t>

</section>


<!-- Conventions and terminoloty (begin section)-->
<section anchor="sec:definitions"
title="Conventions and Terminology">

<t>
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 <xref target="RFC6275"/>, 
the Proxy Mobile IPv6 (PMIPv6) specification <xref target="RFC5213"/>,
the "Mobility Related Terminologies" <xref target="RFC3753"/>,
and the DMM current practices and gap analysis <xref target="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).
</t>

<t>In addition, this document uses the following terms:</t>

<t><list style="hanging">
<t hangText="Home network of a home address:">
the network that has assigned the HoA 
used as the session identifier by the application running in an MN. 
The MN may be running multiple application sessions, 
and each of these sessions can have a different home network. 
<vspace blankLines="1"/>
</t>

<t hangText="Anchor (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 connected 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 IP anchor
node as anchoring, which is a data plane function.
<vspace blankLines="1"/>
</t>

<t hangText="Location Management (LM) function:">
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. 
<vspace blankLines="1"/> 

When the MN is a mobile router (MR)
carrying a mobile network of mobile network nodes (MNN),
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 MNNs in the mobile network.
<vspace blankLines="1"/> 
 
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), 
where
the location information can be updated to or queried from the LMc.

Optionally, there may be a Location Management proxy (LMp)
between LMc and LMs.
<vspace blankLines="1"/> 

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. 
<vspace blankLines="1"/> 

It may be distributed or centralized. 
<vspace blankLines="1"/>
</t>

<t hangText="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. 
<vspace blankLines="1"/>

This function may be used to achieve traffic indirection. 
With separation of control plane and data plane, 
the FM function may split into a FM function in the data plane (FM-DP) 
and a FM function in the control plane (FM-CP).
<vspace blankLines="1"/> 

FM-DP may be distributed with distributed mobility management. 
It may be a function in a data plane anchor or data plane node. 
<vspace blankLines="1"/> 

FM-CP may be distributed or centralized. 
It may be a function in a control plane node,
control plane anchor or mobility controller. 
<vspace blankLines="1"/>
</t>

</list></t>

</section>
<!-- Conventions and terminology (end section) -->

<!-- distributed mobility anchoring (begin section) -->
<section anchor="sec:distributed-anchoring"
          title="Distributed Mobility Anchoring">

<!-- distributed anchoring configurations (begin section) -->
<section anchor="sec:distributed-anchoring-configurations"
 title="Configurations for Different Networks">

<t>
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, as described in <xref
target="I-D.ietf-dmm-deployment-models"/>.
</t>


<!-- distributed anchoring network based flat begin section) -->
<section anchor="sec:distributed-anchoring-network-based"
          title="Network-based DMM">

<t>
<xref target="fig:dmm_net-based" /> shows a general scenario for network-based
distributed mobility management.
</t>

<t>
The main characteristics of a network-based DMM solution are:
</t>

<t>

<list style="symbols">

<t>
There are multiple data plane anchors (i.e., DPA instances), each with an FM-DP
function.
</t>

<t>
The control plane may either be distributed (not shown in the figure) or
centralized (as shown in the figure).
</t>

<t>
The control plane and the data plane (Control Plane Anchor -- CPA -- and Data
Plane Anchor -- DPA) may be co-located or not. If the CPA is co-located with the
distributed DPAs, then there are multiple co-located CPA-DPA instances (not
shown in the figure).
</t>

<t>
An IP prefix/address IP1 (anchored to the DPA with IP address IPa1) is assigned
for use by an MN. The MN uses this IP1 address to communicate with CNs (not
shown in the figure).
</t>

<t>
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.
<!-- Deleted (due to Marco's comment) -->
<!-- ,according to whether the CPA is distributed or centralized. -->
</t>

</list>

</t>

<figure anchor="fig:dmm_net-based" title="Network-based DMM configuration">
  <artwork><![CDATA[
           ____________  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
      +------------+
  ]]></artwork>
</figure>

</section>
<!-- distributed anchoring network based flat (end section) -->

<!-- distributed anchoring host based (begin section) -->
<section anchor="sec:distributed-anchoring-host-based"
          title="Client-based DMM">

<t>
<xref target="fig:dmm_client-based" /> 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 role) ones.
</t>

<figure anchor="fig:dmm_client-based" title="Client-based DMM configuration">
  <artwork><![CDATA[
       +-----+
       |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)               
  ]]></artwork>
</figure>

</section>
<!-- distributed anchoring host based (end section) -->

</section>
<!-- distributed anchoring configuratitons (end section) -->

<!-- distributed mobility anchoring (end section) -->
</section>

<!-- IP mobility support only when needed (begin section) -->
<section anchor="sec:on-demand"
 title="IP Mobility Handling in Distributed Anchoring Environments
- Mobility Support Only When Needed">

<t>
IP mobility support may be provided only when needed instead of being provided
by default. Three cases can be considered:

<list style="symbols"> 

<t>
Nomadic case: no address continuity is required. The IP address used by the MN
changes after movement and traffic using old address is disrupted. If session
continuity is required, then it needs to be provided by a solution running at L4
or above.
</t>

<t>
Mobility case, traffic redirection: address continuity is required. When the MN
moves, the previous anchor still anchors traffic using the old IP address, and
forwards it to the new MN's location. The MN obtains a new IP address anchored
at the new location, and preferably uses it for new communications, established
while connected at the new location.
</t>

<t>
Mobility case, 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.
</t>

</list>

</t>

<t>
A straightforward choice of mobility anchoring is the following: the MN's choses
as source IP address of 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 <xref
target="I-D.seite-dmm-dma"/> <xref target="I-D.bernardos-dmm-pmipv6-dlif"/>. 
</t>

<t>
The IP prefix/address at the MN's side of a flow may be anchored at the access
router 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 which is
typically a dynamic IP address. It then uses this IP address when a flow is
initiated. Packets to the MN in this flow are simply forwarded according to the
forwarding table.
</t>

<t>
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 <xref
target="I-D.mccann-dmm-prefixcost"/> so that the mobile node may choose the one
with the least cost. In addition, these IP prefixes/addresses may be of
different types regarding whether mobility support is needed <xref
target="I-D.ietf-dmm-ondemand-mobility"/>. A flow will need to choose the
appropriate one according to whether it needs IP mobility support.
</t>


<!-- Changing to the new IP prefix/address (begin section) -->
<section anchor="sec:changing-anchor"
 title="Nomadic case (no need of IP mobility): Changing to new IP prefix/address">

<t>
When IP mobility support is not needed for a flow, the LM and FM functions are
not utilized so that the configurations in <xref
target="sec:distributed-anchoring-configurations"/> are simplified as shown in
<xref target="fig:change-net" />.
</t>

<figure anchor="fig:change-net" title="Changing to a new IP address/prefix">
  <artwork><![CDATA[
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,...)  |
+...............+                                   +---------------+
  ]]></artwork>
</figure>

<t>
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.
</t>

<t>
Regardless of whether IP mobility is needed, if the flow has terminated before
the MN moves to a new network, the flow may subsequently restart using the new
IP address assigned from the new network.
</t>

<t>
When IP session continuity is needed, even if a flow is ongoing as the MN moves,
it may still be desirable for the flow to change to using the new IP prefix
configured in the new network. The flow may then close and then restart using a
new IP address configured in the new network. Such a change in the IP address of
the flow may be enabled using a higher layer mobility support which is not in
the scope of this document.
</t>

<t>
In <xref target="fig:change-net" />, 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. The packets may then be forwarded without requiring IP
layer mobility support.
</t>

<t>An example call flow is outlined in <xref target="fig:change-net-flow" /></t>

<figure anchor="fig:change-net-flow" title="Re-starting a flow with new IP prefix/address">
  <artwork><![CDATA[
 MN                    AR1           AR2                           CN
  |MN attaches to AR1:  |             |                             |
  |acquire 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,...)-----------+---------------------------->|
  |                     |             |                             |
  ]]></artwork>
</figure>

</section>
<!-- Changing to the new IP prefix/address (end section) -->

<!-- Mobility case, traffic redirection (begin section) -->
<section anchor="sec:traffic_redirection" title="Mobility case, traffic redirection">

<!-- needs to be changed: here we focus on (i) -->
<t>
When IP mobility is needed for a flow, the LM and FM functions in <xref
target="sec:distributed-anchoring-configurations"/> are utilized. There are two
possible cases: (i) the initial anchor remains the anchor 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
rules for traffic indirection. Next, we focus on the first case.
</t>

<t>
Mobility support can be provided by using mobility management methods such as
(<xref target="Paper-Distributed.Mobility"/>, <xref
target="Paper-Distributed.Mobility.PMIP"/> and <xref
target="Paper-Distributed.Mobility.Review"/>). 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 user application for the 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. The flow may then use the new IP prefix 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
has not moved again and left to another new network.
</t>

<t>
An example call flow in this case is outlined in <xref
target="fig:flow-continuity" />. In this example, the AR1 plays the role of
FM-DP entity and redirects the traffic (e.g., using an IP tunnel) to AR2.
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 <xref target="fig:anchor-redirection" />.
</t>

<figure anchor="fig:anchor-redirection" title="Anchor redirection">
  <artwork><![CDATA[
Net1                                                Net2     

+---------------+                                   +---------------+
|AR1            |                                   |AR2            |
+---------------+                                   +---------------+
|CPA:           |                                   |CPA:           |
|               |                                   |LM:IP1 at IPa1 |
|---------------|      IP1 (anchored at Net1)       |---------------|
|DPA(IPa1):     |      is redirected to Net2        |DPA(IPa2):     |
|anchors IP1    |              =======>             |anchors IP2    |
+---------------+                                   +---------------+

+...............+                                   +---------------+
.MN(IP1)        .              MN moves             |MN(IP2,IP1)    |
.flow(IP1,...)  .              =======>             |flow(IP1,...)  |
.               .                                   |flow(IP2,...)  |
+...............+                                   +---------------+
  ]]></artwork>
</figure>

<figure anchor="fig:flow-continuity" title="A flow continues to use the IP prefix from its home network after MN has moved to a new network">
  <artwork><![CDATA[
 MN                    AR1           AR2                           CN
  |MN attaches to AR1:  |             |                             |
  |acquire MN-ID and profile          |                             |
  |--RS---------------->|             |                             |
  |                     |             |                             |
  |<----------RA(IP1)---|             |                             |
  |                     |             |                             |
Assigned prefix IP1     |             |                             |
IP1 address configuration             |                             |
  |                     |             |                             |
  |<-Flow(IP1,IPcn,...)-+------------------------------------------>|
  |                     |             |                             |
  |MN detach from AR1   |             |                             |
  |MN attach to AR2     |             |                             |
  |                     |             |                             |
  |--RS------------------------------>|                             |
IP mobility support such as that described in next sub-section
  |<--------------RA(IP2,IP1)---------|                             |
  |                     |             |                             |
  |                     +<-Flow(IP1,IPcn,...)---------------------->|
  |                     +<===========>+                             |
  |<-Flow(IP1,IPcn,...)-------------->+                             |
  |                     |             |                             |
Assigned prefix IP2     |             |                             |
IP2 address configuration             |                             |
  |                     |             |                             |
Flow(IP1,IPcn) terminates             |                             |
  |                     |             |                             |
  |<-new Flow(IP2,IPcn,...)-----------+---------------------------->|
  |                     |             |                             |
  ]]></artwork>
</figure>

<t>
Multiple instances of DPAs (at access routers), which are providing IP prefix to
the MNs, are needed to provide distributed mobility anchoring in an appropriate
configuration such as those described in <xref target="fig:dmm_net-based" />
(<xref target="sec:distributed-anchoring-network-based" />) for network-based
distributed mobility or in <xref target="fig:dmm_client-based" /> (<xref
target="sec:distributed-anchoring-host-based" />) for client-based distributed
mobility.
</t>

</section>
<!-- Mobility case, traffic redirection (end section) -->

<!-- Mobility case, anchor relocation (begin section) -->
<section anchor="sec:anchor_relocation" title="Mobility case, anchor relocation">

<t>
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 rules for traffic
indirection.
</t>

<t>
IP mobility is invoked to enable IP session continuity for an ongoing flow as
the MN moves to a new network. Here the anchoring of the IP address of the flow
is in the home network of the flow, which is not in 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 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 switch the IP prefix/address
anchoring to the new network.
</t>

<t>
The IP prefix/address anchoring may move 
without changing the IP prefix/address of the flow.
Here the LM and FM functions in <xref target="fig:dmm_net-based" /> in 
<xref target="sec:distributed-anchoring-configurations"/>
are implemented as shown in <xref target="fig:anchor-mobility" />.
</t>

<figure anchor="fig:anchor-mobility" title="Anchor mobility">
  <artwork><![CDATA[
Net1                                                Net2     

+---------------+                                   +---------------+
|AR1            |                                   |AR2            |
+---------------+                                   +---------------+

|CPA:           |                                   |CPA:           |

|LM:IP1 at IPa1 |                                   |LM:IP1 at IPa2 |
|   changes to  |                                   |               |
|   IP1 at IPa2 |                                   |               |
|---------------|                                   |---------------|
|DPA(IPa1):     | IP1 anchoring is effectively moved|DPA(IPa2):     |
|anchored IP1   |              =======>             |anchors IP2,IP1|
+---------------+                                   +---------------+

+...............+                                   +---------------+
.MN(IP1)        .              MN moves             |MN(IP2,IP1)    |
.flow(IP1,...)  .              =======>             |flow(IP1,...)  |
+...............+                                   +---------------+
  ]]></artwork>
</figure>

<t>
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. 
</t>

<t>
One way to accomplish such move is to use a centralized routing protocol, but
note that this solution presents some scalability concerns and its applicability
is typically limited to small networks.
</t>

</section>
<!-- Mobility case, anchor relocation (end section) -->

</section>
<!-- IP mobility support only when needed (end section) -->

<section anchor="security" title="Security Considerations">

<t>
Security protocols and mechanisms are employed to secure the network and to make
continuous security improvements, and a DMM solution is required to support them
<xref target="RFC7333"/>.
</t>

<t>
In a DMM deployment <xref target="I-D.ietf-dmm-deployment-models"/> various
attacks such as impersonation, denial of service, man-in-the-middle attacks need
to be prevented. 
</t>

</section>

<section title="IANA Considerations">

<t>
This document presents no IANA considerations.
</t>

</section>

<section title="Contributors">

<t>
Alexandre Petrescu and Fred L. Templin had contributed to earlier versions of
this document regarding distributed anchoring for hierarchical network and for
network mobility, although these extensions were removed to keep the document
within reasonable length.
</t>

<t>
This document has benefited from other work on mobility support in SDN network,
on providing mobility support only when needed, and on mobility support in
enterprise network. 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 drafts. The latter include
Philippe Bertin, Dapeng Liu, Satoru Matushima, Pierrick Seite, Jouni Korhonen,
and Sri Gundavelli.
</t>

<t>
Valuable comments have been received from John Kaippallimalil, ChunShan Xiong,
and Dapeng Liu. Dirk von Hugo, Byju Pularikkal, Pierrick Seite
have generously provided careful review with helpful corrections and
suggestions. Marco Liebsch also performed a very detailed and helpful review of
this document.
</t>

</section>

</middle>

<back>
<references title="Normative References">
<?rfc include="reference.RFC.3753.xml" ?>
<?rfc include="reference.RFC.5213.xml" ?>
<?rfc include="reference.RFC.6275.xml" ?>
<?rfc include="reference.RFC.6459.xml" ?>
<?rfc include="reference.RFC.7333.xml" ?>
<?rfc include="reference.RFC.7429.xml" ?>

<?rfc include="reference.I-D.ietf-dmm-ondemand-mobility.xml"?>
<?rfc include="reference.I-D.ietf-dmm-fpc-cpdp.xml"?>
<?rfc include="reference.I-D.ietf-dmm-deployment-models.xml"?>
<?rfc include="reference.I-D.mccann-dmm-prefixcost.xml"?>

<?rfc include="reference.I-D.matsushima-stateless-uplane-vepc.xml"?>
<?rfc include="reference.I-D.seite-dmm-dma.xml"?>
<?rfc include="reference.I-D.bernardos-dmm-pmipv6-dlif.xml"?>
<?rfc include="reference.I-D.sarikaya-dmm-for-wifi.xml"?>
<?rfc include="reference.I-D.yhkim-dmm-enhanced-anchoring.xml"?>

</references>

<references title="Informative References">
<reference anchor="Paper-Distributed.Mobility.Review">
        <front>
          <title>Distributed and Dynamic Mobility Management in Mobile
          Internet: Current Approaches and Issues</title>

          <author initials="H" surname="Chan">
            <organization/>
          </author>

          <author initials="H" surname="Yokota">
            <organization/>
          </author>

          <author initials="J" surname="Xie">
            <organization/>
          </author>

          <author initials="P" surname="Seite">
            <organization/>
          </author>

          <author initials="D" surname="Liu">
            <organization/>
          </author>

          <date month="February" year="2011"/>
        </front>
</reference>

<reference anchor="Paper-Distributed.Mobility">
        <front>
          <title>Distributed IP Mobility Management from the Perspective of
          the IETF: Motivations, Requirements, Approaches, Comparison, and
          Challenges</title>

          <author initials="J" surname="Lee">
            <organization/>
          </author>

          <author initials="J" surname="Bonnin">
            <organization/>
          </author>

          <author initials="P" surname="Seite">
            <organization/>
          </author>

          <author initials="H" surname="Chan">
            <organization/>
          </author>

          <date month="October" year="2013"/>
        </front>

        <seriesInfo name="" value="IEEE Wireless Communications"/>
</reference>

<reference anchor="Paper-Distributed.Mobility.PMIP">
        <front>
          <title>Proxy Mobile IP with Distributed Mobility Anchors</title>

          <author initials="H" surname="Chan">
            <organization/>
          </author>

          <date month="December" year="2010"/>
        </front>

        <seriesInfo name=""
                    value="Proceedings of GlobeCom Workshop on Seamless Wireless Mobility"/>
      </reference>
</references>
</back>

</rfc>