DMM Working Group CJ. Bernardos
Internet-Draft A. de la Oliva
Intended status: Standards Track UC3M
Expires: September 14, 2012 F. Giust
IMDEA Networks and UC3M
T. Melia
R. Costa
Alcatel-Lucent
March 13, 2012
A PMIPv6-based solution for Distributed Mobility Management
draft-bernardos-dmm-pmip-01
Abstract
The number of mobile users and their traffic demand is expected to be
ever-increasing in future years, and this growth can represent a
limitation for deploying current mobility management schemes that are
intrinsically centralized, e.g., Mobile IPv6 and Proxy Mobile IPv6.
For this reason it has been waved a need for distributed and dynamic
mobility management approaches, with the objective of reducing
operators' burdens, evolving to a cheaper and more efficient
architecture.
This draft describes multiple solutions for network-based distributed
mobility management inspired by the well known Proxy Mobile IPv6.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on September 14, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. PMIPv6-based solution . . . . . . . . . . . . . . . . . . . . 6
3.1. Initial registration . . . . . . . . . . . . . . . . . . . 7
3.2. The CMD as PBU/PBA relay . . . . . . . . . . . . . . . . . 8
3.3. The CMD as MAAR locator . . . . . . . . . . . . . . . . . 10
3.4. The CMD as MAAR proxy . . . . . . . . . . . . . . . . . . 11
3.5. De-registration . . . . . . . . . . . . . . . . . . . . . 12
3.6. Message Format . . . . . . . . . . . . . . . . . . . . . . 12
3.6.1. Previous MAAR Option . . . . . . . . . . . . . . . . . 12
3.6.2. Serving MAAR Option . . . . . . . . . . . . . . . . . 14
4. DHCPv6-based solution . . . . . . . . . . . . . . . . . . . . 14
4.1. Using DHCPv6's database . . . . . . . . . . . . . . . . . 15
4.2. Protocol Operation . . . . . . . . . . . . . . . . . . . . 15
4.3. De-Registration . . . . . . . . . . . . . . . . . . . . . 17
4.4. Non-supported nodes and DHCPv6 . . . . . . . . . . . . . . 18
5. Fully distributed solution . . . . . . . . . . . . . . . . . . 18
5.1. Solution Example . . . . . . . . . . . . . . . . . . . . . 19
5.2. Work Flow . . . . . . . . . . . . . . . . . . . . . . . . 19
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Normative References . . . . . . . . . . . . . . . . . . . 22
9.2. Informative References . . . . . . . . . . . . . . . . . . 22
Appendix A. Implementation experience . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
Current IP mobility solutions, standardized with the names of Mobile
IPv6 [RFC6275], or Proxy Mobile IPv6 [RFC5213], just to cite the two
most relevant examples, offer mobility support at the cost of
handling operations at a cardinal point, the mobility anchor, and
burdening it with data forwarding and control mechanisms for a great
amount of users. As stated in [I-D.chan-distributed-mobility-ps],
centralized mobility solutions are prone to several problems and
limitations: longer (sub-optimal) routing paths, scalability
problems, signaling overhead (and most likely a longer associated
handover latency), more complex network deployment, higher
vulnerability due to the existence of a potential single point of
failure, and lack of granularity on the mobility management service
(i.e., mobility is offered on a per-node basis, not being possible to
define finer granularity policies, as for example per-application).
The purpose of Distributed Mobility Management is to overcome the
limitations of the traditional centralized mobility management; the
main concept behind DMM solutions is indeed bringing the mobility
anchor closer to the MN. Following this idea, in our proposal, the
central anchor is moved to the edge of the network, being deployed in
the default gateway of the mobile node. That is, the first elements
that provide IP connectivity to a set of MNs are also the mobility
managers for those MNs. In the following, we will call these
entities Mobility Anchor and Access Routers (MAARs).
This document focuses on network-based DMM, hence the starting point
is making PMIPv6 working in a distributed manner. In our proposal,
as in PMIPv6, mobility is handled by the network without the MNs
involvement, but, differently from PMIP, when the MN moves from one
access network to another, it also changes anchor router, hence
requiring signaling between the anchors to retrieve the MN's previous
location(s). Also, a key-aspect of network-based DMM, is that a
prefix pool belongs exclusively to each MAAR, in the sense that those
prefixes are assigned by the MAAR to the MNs attached to it, and they
are routable at that MAAR.
In the following, we consider two main approaches to design our DMM
solutions:
o Partially distributed schemes, where the data plane only is
distributed among access routers similar to MAGs, whereas the
control plane is kept centralized towards a cardinal node used as
information store, but relieved from any route management and MN's
data forwarding task. We describe in this document two different
approaches: one based on extending PMIPv6 signaling and the use of
a centralized database entity (when stateless address
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configuration is used by the mobile node), and one based on
extending DHCPv6 (when stateful address configuration is used by
the mobile node).
o Fully distributed schemes, where both data and control planes are
distributed among the access routers.
2. Terminology
The following terms used in this document are defined in the Proxy
Mobile IPv6 specification [RFC5213]:
Local Mobility Anchor (LMA)
Mobile Access Gateway (MAG)
Mobile Node (MN)
Binding Cache Entry (BCE)
Proxy Care-of Address (P-CoA)
Proxy Binding Update (PBU)
Proxy Binding Acknowledgement (PBA)
The following terms are defined and used in this document:
MAAR (Mobility Anchor and Access Router). First hop router where the
mobile nodes attach to. It also plays the role of mobility
manager for the IPv6 prefixes it anchors, running the
functionalities of PMIP's MAG and LMA.
CMD (Central Mobility Database). Node that stores the BCEs allocated
for the MNs in the mobility domain.
P-MAAR (Previous MAAR). MAAR which was previously visited by the MN
and is still involved in an active flow using an IPv6 prefix it
has advertised to the MN (i.e., MAAR where that IPv6 prefix is
anchored). There might be multiple P-MAARs for an MN's mobility
session.
S-MAAR (Serving MAAR). MAAR which the MN is currently attached to.
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3. PMIPv6-based solution
The following solution belongs to the partially distributed category,
and it consists in de-coupling the entities that participates in the
data and the control planes: the data plane becomes distributed and
managed by the MAARs near the edge of the network, while the control
plane, besides on the MAARs, relies on a central entity called
Central Mobility Database (CMD). In the proposed architecture, the
hierarchy present in PMIP between LMA and MAG is preserved, but with
the following substantial variations:
o The LMA is relieved from the data forwarding role, only the
Binding Cache and its management operations are maintained. Hence
the LMA is renamed into Central Mobility Database (CMD). Also,
the CMD is able to send and parse both PBU and PBA messages.
o The MAG is enriched with the LMA functionalities, hence the name
Mobility Anchor and Access Router (MAAR). It maintains a local
Binding Cache for the MNs that are attached to it and it is able
to send and parse PBU and PBA messages.
o The binding cache will have to be extended to include information
regarding previous MAARs where the mobile node was anchored and
still retains active data sessions, see Appendix A for further
details.
o Each MAAR has a unique set of global prefixes (which are
configurable), that can be allocated by the MAAR to the MNs, but
must be exclusive to that MAAR, i.e. no other MAAR can allocate
the same prefixes.
The MAARs leverage on the Central Mobility Database (CMD) to access
and update information related to the MNs, stored as mobility
sessions; hence, a centralized node maintains a global view on the
status of the network. The CMD is queried whenever a MN is detected
to join/leave the mobility domain. It might be a fresh attachment, a
detachment or a handover, but as MAARs are not aware of past
information related to a mobility session, they contact the CMD to
retrieve the data of interest and eventually take the appropriate
action. The procedure adopted for the query and the messages
exchange sequence might vary to optimize the update latency and/or
the signaling overhead. Here is presented one method for the initial
registration, and three different approaches to update the mobility
sessions using PBUs and PBAs. Each approach assigns a different role
to the CMD:
o The CMD is a PBU/PBA relay;
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o The CMD is only a MAAR locator;
o The CMD is a PBU/PBA proxy.
3.1. Initial registration
Upon the MN's attachment to a MAAR, say MAAR1, if the MN is
authorized for the service, an IPv6 global prefix belonging to the
MAAR's prefix pool is reserved for it (Pref1) into a temporal Binding
Cache Entry (BCE) allocated locally. The prefix is sent in a
[RFC5213] PBU with the MN's Identifier (MN-ID) to the CMD, which,
since the session is new, stores a permanent BCE containing as main
fields the MN-ID, the MN's prefix and MAAR1's address as Proxy-CoA.
The CMD replies to MAAR1 with a PBA including the usual options
defined in PMIP/RFC5213, meaning that the MN's registration is fresh
and no past status is available. MAAR1 definitely stores the
temporal BCE previously allocated and unicasts a Router Advertisement
(RA) to the MN including the prefix reserved before, that can be used
by the MN to configure an IPv6 address (e.g., with stateless auto-
configuration). The address is routable at the MAAR, in the sense
that it is on the path of packets addressed to the MN. Moreover, the
MAAR acts as plain router for those packets, as no encapsulation nor
special handling takes place. Figure 1 illustrates this scenario.
+-----+ +---+ +--+
|MAAR1| |CMD| |CN|
+-----+ +---+ +*-+
| | *
MN | * +---+
attach. | ***** _|CMD|_
detection | flow1 * / +-+-+ \
| | * / | \
local BCE | * / | \
allocation | * / | \
|--- PBU -->| +---*-+-' +--+--+ `+-----+
| BCE | * | | | | |
| creation |MAAR1+------+MAAR2+-----+MAAR3|
|<-- PBA ---| | * | | | | |
local BCE | +---*-+ +-----+ +-----+
finalized | *
| | Pref1 *
| | +*-+
| | |MN|
| | +--+
Operations sequence Packets flow
Figure 1: First attachment to the network
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3.2. The CMD as PBU/PBA relay
When the MN moves from its current access and associates to MAAR2
(now the S-MAAR), MAAR2 reserves another IPv6 prefix (Pref2), it
stores a temporal BCE, and it sends a plain PBU to the CMD for
registration. Upon PBU reception and BC lookup, the CMD retrieves an
already existing entry for the MN, binding the MN-ID to its former
location; thus, the CMD forwards the PBU to the MAAR indicated as
Proxy CoA (MAAR1), including a new mobility option to communicate the
S-MAAR's global address to MAAR1, defined as Serving MAAR Option in
Section 3.6.2. The CMD updates the P-CoA field in the BCE related to
the MN with the S-MAAR's address.
Upon PBU reception, MAAR1 can install a tunnel on its side towards
MAAR2 and the related routes for Pref1. Then MAAR1 replies to the
CMD with a PBA (including the option mentioned before) to ensure that
the new location has successfully changed, containing the prefix
anchored at MAAR1 in the Home Network Prefix option. The CMD, after
receiving the PBA, updates the BCE populating an instance of the
P-MAAR list. The P-MAAR list is an additional field on the BCE that
contains an element for each P-MAAR involved in the MN's mobility
session. The list element contains the P-MAAR's global address and
the prefix it has delegated (see Appendix A for further details).
Also, the CMD send a PBA to the new S-MAAR, containing the previous
Proxy-CoA and the prefix anchored to it embedded into a new mobility
option called Previous MAAR Option (defined in Section 3.6.1), so
that, upon PBA arrival, a bi-directional tunnel can be established
between the two MAARs and new routes are set appropriately to recover
the IP flow(s) carrying Pref1.
Now packets destined to Pref1 are first received by MAAR1,
encapsulated into the tunnel and forwarded to MAAR2, which finally
delivers them to their destination. In uplink, when the MN transmits
packets using Pref1 as source address, they are sent to MAAR2, as it
is MN's new default gateway, then tunneled to MAAR1 which routes them
towards the next hop to destination. Conversely, packets carrying
Pref2 are routed by MAAR2 without any special packet handling both
for uplink and downlink. The procedure is depicted in Figure 2.
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+-----+ +---+ +-----+ +--+ +--+
|MAAR1| |CMD| |MAAR2| |CN| |CN|
+-----+ +---+ +-----+ +*-+ +*-+
| | | * *
| | MN * +---+ *
| | attach. ***** _|CMD|_ *
| | det. flow1 * / +-+-+ \ *flow2
| |<-- PBU ---| * / | \ *
| BCE | * / | *******
| check+ | * / | * \
| update | +---*-+-? +--+-*+ `+-----+
|<-- PBU*---| | | * | | *| | |
route | | |MAAR1|______|MAAR2+-----+MAAR3|
update | | | **(______)** *| | |
|--- PBA*-->| | +-----+ +-*--*+ +-----+
| BCE | * *
| update | Pref1 * *Pref2
| |--- PBA*-->| +*--*+
| | route ---move-->|*MN*|
| | update +----+
Operations sequence Data Packets flow
PBU/PBA Messages with * contain
a new mobility option
Figure 2: Scenario after a handover, CMD as relay
For next MN's movements the process is repeated except for the number
of P-MAARs involved, that rises accordingly to the number of prefixes
that the MN wishes to maintain. Indeed, once the CMD receives the
first PBU from the new S-MAAR, it forwards copies of the PBU to all
the P-MAARs indicated in the BCE as current P-CoA (i.e., the MAAR
prior to handover) and in the P-MAARs list. They reply with a PBA to
the CMD, which aggregates them into a single one to notify the
S-MAAR, that finally can establish the tunnels with the P-MAARs.
It should be noted that this design separates the mobility management
at the prefix granularity, and it can be tuned in order to erase old
mobility sessions when not required, while the MN is reachable
through the latest prefix acquired. Moreover, the latency associated
to the mobility update is bound to the PBA sent by the furthest
P-MAAR, in terms of RTT, that takes the longest time to reach the
CMD. The drawback can be mitigated introducing a timeout at the CMD,
by which, after its expiration, all the PBAs so far collected are
transmitted, and the remaining are sent later upon their arrival.
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3.3. The CMD as MAAR locator
The handover latency experienced in the approach shown before can be
reduced if the P-MAARs are allowed to signal directly their
information to the new S-MAAR. This procedure reflect what was
described in Section 3.2 up to the moment the P-MAAR receives the PBU
with the P-MAAR option. At that point a P-MAAR is aware of the new
MN's location (because of the S-MAAR's address in the S-MAAR option),
and, besides sending a PBA to the CMD, it also sends a PBA to the
S-MAAR including the prefix it is anchoring. This latter PBA does
not need to include new options, as the prefix is embedded in the HNP
option and the P-MAAR's address OS taken from the message's source
address. The CMD is relieved from forwarding the PBA to the S-MAAR,
as the latter receives a copy directly from the P-MAAR with the
necessary information to build the tunnels and set the appropriate
routes. In Figure 3 is illustrated the new messages sequence, while
the data forwarding is unaltered.
+-----+ +---+ +-----+ +--+ +--+
|MAAR1| |CMD| |MAAR2| |CN| |CN|
+-----+ +---+ +-----+ +*-+ +*-+
| | | * *
| | MN * +---+ *
| | attach. ***** _|CMD|_ *
| | det. flow1 * / +-+-+ \ *flow2
| |<-- PBU ---| * / | \ *
| BCE | * / | *******
| check+ | * / | * \
| update | +---*-+-? +--+-*+ `+-----+
|<-- PBU*---| | | * | | *| | |
route | | |MAAR1|______|MAAR2+-----+MAAR3|
update | | | **(______)** *| | |
|--------- PBA -------->| +-----+ +-*--*+ +-----+
|--- PBA*-->| route * *
| BCE update Pref1 * *Pref2
| update | +*--*+
| | | ---move-->|*MN*|
| | | +----+
Operations sequence Data Packets flow
PBU/PBA Messages with * contain
a new mobility option
Figure 3: Scenario after a handover, CMD as locator
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3.4. The CMD as MAAR proxy
A further enhancement of previous solutions can be achieved when the
CMD sends the PBA to the new S-MAAR before notifying the P-MAARs of
the location change. Indeed, when the CMD receives the PBU for the
new registration, it is already in possess of all the information
that the new S-MAAR requires to set up the tunnels and the routes.
Thus the PBA is sent to the S-MAAR immediately after a PBU is
received, including also in this case the P-MAAR option. In
parallel, a PBU is sent by the CMD to the P-MAARs containing the
S-MAAR option, to notify them about the new MN's location, so they
receive the information to establish the tunnels and routes on their
side. When P-MAARs complete the update, they send a PBA to the CMD
to indicate that the operation is concluded and the information are
updated in all network nodes. This procedure is obtained from the
first one re-arranging the order of the messages, but the parameters
communicated are the same. This scheme is depicted in Figure 4,
where, again, the data forwarding is kept untouched.
+-----+ +---+ +-----+ +--+ +--+
|MAAR1| |CMD| |MAAR2| |CN| |CN|
+-----+ +---+ +-----+ +*-+ +*-+
| | | * *
| | MN * +---+ *
| | attach. ***** _|CMD|_ *
| | det. flow1 * / +-+-+ \ *flow2
| |<-- PBU ---| * / | \ *
| BCE | * / | *******
| check+ | * / | * \
| update | +---*-+-? +--+-*+ `+-----+
|<-- PBU*---x--- PBA*-->| | * | | *| | |
route | route |MAAR1|______|MAAR2+-----+MAAR3|
update | update | **(______)** *| | |
|--- PBA*-->| | +-----+ +-*--*+ +-----+
| BCE | * *
| update | Pref1 * *Pref2
| | | +*--*+
| | | ---move-->|*MN*|
| | | +----+
Operations sequence Data Packets flow
PBU/PBA Messages with * contain
a new mobility option
Figure 4: Scenario after a handover, CMD as proxy
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3.5. De-registration
The de-registration mechanism devised for PMIPv6 is no longer valid
in the Partial DMM architecture. This is motivated by the fact that
each MAAR handles an independent mobility session (i.e., a single or
a set of prefixes) for a given MN, whereas the aggregated session is
stored at the CMD. Indeed, when a previous MAAR initiates a de-
registration procedure, because the MN is no longer present on the
MAAR's access link, it removes the routing state for that (those)
prefix(es), that would be deleted by the CMD as well, hence defeating
any prefix continuity attempt. The simplest approach to overcome
this limitation is to deny an old MAAR to de-register a prefix, that
is, allowing only a serving MAAR to de-register the whole MN session.
This can be achieved by first removing any layer-2 detachment event,
so that de-registration is triggered only when the session lifetime
expires, hence providing a guard interval for the MN to connect to a
new MAAR. Then, a change in the MAAR operations is required, and at
this stage two possible solutions can be deployed:
o A previous MAAR stops the BCE timer upon receiving a PBU from the
CMD containing a "Serving MAAR" option. In this way only the
Serving MAAR is allowed to de-register the mobility session,
arguing that the MN left definitely the domain.
o Previous MAARs can, upon BCE expiry, send de-registration messages
to the CMD, which, instead of acknowledging the message with a 0
lifetime, send back a PBA with a non-zero lifetime, hence re-
newing the session, if the MN is still connected to the domain.
The evaluation of these methods is left for future work.
3.6. Message Format
This section defines two Mobility Options to be used in the PBU and
PBA messages:
Previous MAAR Option
Serving MAAR Option
In the current draft the messages reflect IPv6 format only. IPv4
compatibility will be added in next release.
3.6.1. Previous MAAR Option
This new option is defined for use with the Proxy Binding
Acknowledgement messages exchanged by the CMD to a MAAR. This option
is used to notify the S-MAAR about the previous MAAR's global address
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and the prefix anchored to it. There can be multiple Previous MAAR
options present in the message. Its format is as follows:
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 | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ P-MAAR's address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Network Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
To be assigned by IANA.
Length
8-bit unsigned integer indicating the length of the option in
octets, excluding the type and length fields. This field MUST be
set to 34.
Prefix Length
8-bit unsigned integer indicating the prefix length of the IPv6
prefix contained in the option.
Previous MAAR's address
A sixteen-byte field containing the P-MAAR's IPv6 global address.
Home Network Prefix
A sixteen-byte field containing the mobile node's IPv6 Home
Network Prefix.
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3.6.2. Serving MAAR Option
This new option is defined for use with the Proxy Binding Update and
Proxy Binding Acknowledgement messages exchanged between the CMD and
a Previous MAAR. This option is used to notify the P-MAAR about the
current Serving MAAR's global address. Its format is as follows:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ S-MAAR's address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
To be assigned by IANA.
Length
8-bit unsigned integer indicating the length of the option in
octets, excluding the type and length fields. This field MUST be
set to 16.
Serving MAAR's address
A sixteen-byte field containing the S-MAAR's IPv6 global address.
4. DHCPv6-based solution
As the solution presented before, next scheme follows the partially
distributed approach. Instead of using a dedicated entity such as
the CMD, in this proposal we leverage on the collaboration between
PMIPv6 and DHCPv6 [RFC3315] to provide the control plane, while the
data plane is distributed among the MAARs. To be clearer, in the
following key points we present the similarities and differences
between this solution and the ones before:
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o The CMD is removed from the architecture.
o The MAAR entity is present, but an emphasis in given to the DCHP
relay component running along with the LMA and MAG
functionalities.
o The set of global prefixes assigned to each MAAR must be
synchronized with the domain's DHCPv6 server as defined in
[RFC5213]. This means, we push the prefix management operations
to the DHCP domain server, providing in the MAAR just the mobility
control.
o All MAARs must have global routable IPv6 addresses (one per
prefix) on the access link, which are built in the exact same way
(derived from the link-local address), and maintain the same link-
local address principle as in PMIPv6 (i.e. all MAARs are
configured with the same link-local address on the access link).
(Note: in the first version of this document no DHCP options are
defined for P-MAAR recognition, it is work for furhter study).
o Each MAAR may or may not have knowledge of other MAARs, and may or
may not have had previous contact with other MAARs.
4.1. Using DHCPv6's database
An issue to be albe to perform the PBU/PBA signaling among MAARs is
how to know the address of the P-MAAR(s) from where the mobile node
came from and has other anchored data flows, so to direct the PBU to
the right P-MAAR(s) and subsequently tunnel the data flows.
To solve the issue we intend to gather the information required to
address the PBU/PBA message sequence to the corresponding P-MAARs in
a simple way. By slightly adapting the work flow of the protocols,
we allow the MAARs to learn the node's P-MAARs from the address
configuration process of DHCPv6. Since the PMIPv6 protocol standard
has specific mechanisms in place that already adapt DHCPv6 to be able
to cope with PMIPv6 specifications, we take advantage of these DHCPv6
mechanisms and enhance them to fit our needs.
4.2. Protocol Operation
When the managed network is using DHCPv6 and a new mobile node
attaches to a MAAR, a Binding Cache Entry is created, and a prefix is
allocated to the mobile node. Since the node is using statefull IP
address configuration, the mobile node will shortly send a DHCP-
Request message to the proper address and port on the MAAR where a
DHCP-Relay will be listening. The DHCP-Relay will act according to
the specified behavior in [RFC5213] and on reception and treatment of
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the DHCP-Request by the DHCP server, we propose adding the following
enhancements:
o Once the DHCP server receives a DHCP-Request message from the
mobile node, it will reply not only with the same prefixes already
existent in the previous lease, but will also allocate the new
prefixes corresponding to the new link.
o The prefixes belonging to any P-MAARs will have their lifetime set
to zero, establishing them as deprecated and to be used only for
ongoing data flows, while new data flows should use the newly
allocated prefixes.
When the DHCP-Relay co-located with the MAAR receives the DHCP-Reply
message, it will pass the information contained in the message to the
MAAR. If there were no other previous prefixes then this is a new
registration, and the MAAR BCE is updated, the DHCP-Reply relayed to
the mobile node, allowing the address configuration based on the
allocated prefix.
Otherwise if there were older prefixes, the MAAR must send PBUs to
the P-MAARs. The MAAR will first look for any known P-MAAR addresses
related to the prefixes received from the DHCP-Relay. If the query
is unsuccessful, a P-MAAR address can still be built based on three
pieces of information: i) the previous prefixes allocated to the
mobile node by the DHCP server, known through the DHCP-Relay; ii) the
fact that the IP addresses of the MAARs on the link access are all
built the same way; iii) the fact that the the IP addresses of the
MAARs on the link access are reachable through the core network.
The PBUs are sent to the P-MAARs in order to update their BCEs,
routing and establish new data tunnels if any flows for this mobile
node are anchored in that P-MAAR. The P-MAARs will reply back with
PBAs accordingly, using as source address not the access link address
but their own core network interface address. Upon reception, this
enables the MAAR to learn the right address for the P-MAAR and update
it's BCE information, routing and to create a data tunnel if
necessary.
Meanwhile the DHCP Relay on the MAAR had relayed the DHCP-Reply
message to the mobile node, triggering it's IP address configuration.
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+-------+ +-------+ +-------+ +-----------+ +--+ +--+
|DHCP CL| |DHCP RL| |DHCP RL| |DHCP Server| |CN| |CN|
+-------+ +-------+ +-------+ +-----------+ +*-+ +*-+
| MN | | P-MAAR| | MAAR | | * *
+-------+ +-------+ +-------+ | flow1* flow2 *
| | | | * *
| | MN attach. | .*-'-.-'-.-*.
|------- DHCP REQ ----->| | / * * \
| | BCE create+ | \ * Core * /
| | Prefix Alloc | / * Network * \
| | | | \ * * /
| | |--DHCP RL REQ->| '*'-.-'-.-'*'
| | | | * *
| | | Renews old +-----------+ * *
| | | prefix(s)+ adds |DHCP Server| * *
| | | new prefix(s) +----:------+ * *
| | | | :............. *
| | |<-DHCP RL REP--| : * : *
| | BCE | +----:-+ * +-:----+*
| | update | |DHCP | * |DHCP |*
|<------ DHCP REP ------| | |Relay | ****** |Relay |*
| | build | +------+-*+ +------+*+
| | P-MAAR | | P-MAAR *|_____| MAAR *|
| | address | | *(_____)* *|
| |<-- PBU ---| | +---------+ +*------*+
| BCE | | * *
| update | | +*------*+
| +route | | |* MN *|
| update | | --- move --> +--------+
| |--- PBA -->| | |DHCP CL |
| | BCE | +--------+
| | update |
| | +route |
| | update |
Control Signalling Data Flow
Figure 5: Work flow of the DHCPv6 partially distributed approach.
4.3. De-Registration
The PMIPv6 protocol already includes the case in which the need to
revoke or delete an allocated prefix to a mobile node arises. It
uses the DHCP's mechanism to do so and it is complemented, in this
case, by the MAAR sending to the mobile a Route Advertisement with
the mentioned prefix's lifetime set to zero.
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4.4. Non-supported nodes and DHCPv6
It may happen that network wishes to allow terminals that the network
does not have support for mobility (e.g. roaming terminals that do
not belong to this domain), to enjoy the benefit of using stateful
address configuration. To these nodes regular DHCPv6 behavior can
still be attained. Upon identification of the node and it's status,
any mobility related procedures can be skipped, allowing the regular
procedures of DHCPv6 to take place.
5. Fully distributed solution
Following the logical sense of the approaches described in previous
sections of this document, the next logical step would be to
introduce a fully distributed solution. We present it in order to
show that our previous proposals can be reused to tackle with the
enormous restriction of depending on the use of a centralized control
entity, and so we decided to also cover this possibility as the final
step of an evolving mobility architecture.
Firstly, we reuse the concept of MAAR: the MAARs are, in a
distributed manner, located on the edge of the network near the
access, being the major difference here the lack of a centralized
control to share information between themselves. The information and
functionalities of both PMIP's MAG and LMA are now present on each
and every MAAR, giving each MAAR it's own micro domain and therefore
a view of only a subset that composes the local domain network,
namely the set of mobile nodes directly anchored to it.
We reuse as well some of the points enforced in previous sections of
this document:
o Any central control entity is removed from the architecture and
each MAAR will retain it's own cache for the mobile nodes directly
anchored to it.
o Both control and data planes are now entirely handled by the
MAARs, although data and control are decoupled.
o All MAARs must have global routable IPv6 addresses (one per
prefix) on the access link, which are built in the exact same way
(derived from the link-local address), and maintain the same link-
local address principle as in PMIPv6 (i.e. all MAARs are
configured with the same link-local address on the access link).
Because we aim for a fully distributed approach, the lack of
knowledge of other MAARs and their advertised prefixes becomes a
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serious obstacle. In this particular case, there are three main
pieces of information that a MAAR requires to know, to properly
assure a mobile node's mobility and continuity of it's data flows: i)
if the node has any P-MAARs; ii) if it has P-MAARs, how many are
there; and iii) the P-MAARs addresses.
There are several methods to achieve this:
o Layer 2 mechanisms with capability to retrieve the IP addresses
configured in the mobile node (MN to MAAR communication)
o A peer-to-peer communication service between the MAARs (either
unicast or multicast).
o A distibuted scheme that allows MAAR discovery (either unicast or
multicast)
o Extensions to layer three IP address configuration mechanisms
(e.g. ND)
o Other MN to MAAR communication protocol (e.g. IEEE 802.21)
5.1. Solution Example
The Node Information Queries (NIQ) [RFC4620] protocol fits nicely in
this situation, where it can allow the MAAR to obtain part of the
needed information from the mobile node. The NIQ protocol makes
possible for two entities to communicate at a simple level and
through a simple query-reply message sequence retrieves information
related to names and IP addresses. The protocol's applicability
statement clearly points out that the protocol can be used to learn
configured IP addresses and names on a point-to-point or medium-
shared link, such as the the connection between the MAAR and the
mobile node.
5.2. Work Flow
If the managed network is not using DHCPv6, then it falls to the use
of NIQ [RFC4620]. When When a new mobile node attaches to a MAAR, a
Binding Cache Entry is created, and a prefix is allocated to the
mobile node. Since the node is using stateless IP address
configuration, the mobile node will shortly send a IMCP Route
Solicitation message that will be listened by the MAAR.
The MAAR will then send a NI Query message to the mobile node's link-
local address with the Qtype field with set to 3, asking for the
mobile node's IPv6 addresses. The mobile node will reply with a NI
Reply message containing currently configured IP addresses.
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Upon the reception of the NI Reply, the MAAR will check the
configured addresses and extract the prefixes. Then it will first
look for any known P-MAAR addresses related to the prefixes. If any
prefix does not have a P-MAAR address the P-MAAR address can still be
built based on three pieces of information: i) the prefixes extracted
from the IP address belonging to the NI-Reply message; ii) the fact
that the IP addresses of the MAARs on the link access are all built
the same way; iii) the fact that the the IP addresses of the MAARs on
the link access are reachable through the core network.
Once all the required P-MAAR addresses are known, a PBU is sent to
each P-MAAR, updating their BCEs, routing and will establish new data
tunnels if any flows for this mobile node are anchored in that
P-MAAR. The P-MAARs will reply back with PBAs accordingly, using as
source address not the access link address but their own address.
Upon reception, this enables the MAAR to learn the right address for
the P-MAAR and update it's BCE information, routing and to create
it's endpoint of the data tunnel if necessary.
Finally the MAAR will send the unicast Route Advertisement message to
the mobile node, triggering it's new IP address configuration.
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+-----+ +-------+ +-----+ +--+ +--+
| MN | | P-MAAR| | MAAR| |CN| |CN|
+-----+ +-------+ +-----+ +*-+ +*-+
| | | * *
| | MN attach. * flow1 * flow2
| | BCE create+ * *
| | Prefix Alloc .*.-'-.-'-.-'-.-*.
|-------- RtSol ------->| / * * \
|<------ NI Query ------| | * Core Network * |
|------- NI Reply ----->| \ * * /
| | build '*-'-.-'-.-'-.-'*'
| | P-MAAR * *
| | address * *
| |<-- PBU ---| +--------*+ +-------*+
| BCE | | P-MAAR *|_____| MAAR *|
| update | | *(_____)* *|
| +route | +---------+ +*------*+
| update | * *
| |--- PBA -->| * *
| | BCE +*------*+
| | update --- move --> |* MN *|
| | +route +--------+
| | update
|<------- RtAdv --------|
Control Signalling Data Flow
Figure 6: Work flow of the fully distributed approach.
6. IANA Considerations
TBD.
7. Security Considerations
TBD.
8. Acknowledgments
The authors would like to thank Marco Liebsch for his comments and
discussion on this document.
The research leading to these results has received funding from the
European Community's Seventh Framework Programme (FP7-ICT-2009-5)
under grant agreement n. 258053 (MEDIEVAL project). The work of
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Carlos J. Bernardos has also been partially supported by the Ministry
of Science and Innovation of Spain under the QUARTET project
(TIN2009-13992-C02-01).
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
[RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
in IPv6", RFC 6275, July 2011.
9.2. Informative References
[I-D.chan-distributed-mobility-ps]
Chan, A., "Problem statement for distributed and dynamic
mobility management",
draft-chan-distributed-mobility-ps-05 (work in progress),
October 2011.
[RFC4620] Crawford, M. and B. Haberman, "IPv6 Node Information
Queries", RFC 4620, August 2006.
Appendix A. Implementation experience
The solution described in section Section 3.4 has been implemented in
a real test-bed comprising 3 MAARs, one CMD, one MN and a CN. The CN
is connected to the DMM domain through a router, which simulates the
gateway to the internet cloud. All the machines used are Linux
UBUNTU 10.04 systems with kernel 2.26.32.
The code is developed from an existing implementation of PMIP
(OpenAirInterface Proxy Mobile IPv6: OAI PMIPv6) partially developed
within the framework of the MEDIEVAL EU project. The most relevant
changes are related to how to create the CMD and MAAR's state
machines from those of an LMA and a MAG; for this purpose, part of
the LMA code was copied to the MAG, in order to send PBA messages and
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parse PBU. Also, the LMA routing functions were removed completely,
and moved to the MAG, because MAARs need to route through the tunnels
in downlink (as an LMA) and in uplink (as a MAG).
Tunnel management is hence a relevant technical aspect, as multiple
tunnels are established by a single MAAR, which keeps their status
directly into the MN's BCE. Indeed, from the implementation
experience it was chosen to create an ancillary data structure as
field within a BCE: the data structure is called "MAAR list" and
stores the previous MAARs' address and the corresponding prefix(es)
assigned for the MN. Only the CMD and the serving MAAR store this
data structure, because the CMD maintains the global MN's mobility
session formed during the MN's roaming within the domain, and the
serving MAAR needs to know which previous MAARs were visited, the
prefix(es) they assigned and the tunnels established with them.
Conversely, a previous MAAR only needs to know which is the current
Serving MAAR and establish a single tunnel with it. For this reason,
a MAAR that receives a PBU from the CMD (meaning that the MN attached
to another MAAR), first sets up the routing state for the MN's
prefix(es) it is anchoring, then stop the BCE expiry timer and
deletes the MAAR list (if present) since it is no longer useful.
In order to have the MN totally unaware of the changes in the access
link, all MAARs exhibit the same L2 and L3 identifiers in the access
interface (as the PMIPv6 Fixed MAG Link Local Address feature). A
solution is under study to avoid this configuration and influence the
MN on the source address choice. Moreover, it should be noted that
the protocols designed in the document work only at the network layer
to handle the MNs joining or leaving the domain. This should
guarantee a certain independency to a particular access technology.
The implementation reflects this reasoning, but we argue that an
interaction with lower layers produces a more effective attachment
and detachment detection, therefore improving the performance, also
regarding de-registration mechanisms.
It was chosen to implement the "proxy" solution because it produces
the shortest handover latency, but a slight modification on the CMD
state machine can produce the first scenario described ("relay")
which guarantees a more consistent request/ack scheme between the
MAARS. By modifying also the MAAR's state machine it can be
implemented the second solution ("locator").
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Authors' Addresses
Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
Antonio de la Oliva
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Phone: +34 91624 8803
Email: aoliva@it.uc3m.es
URI: http://www.it.uc3m.es/aoliva/
Fabio Giust
Institute IMDEA Networks and Universidad Carlos III de Madrid
Av. del Mar Mediterraneo, 22
Leganes, Madrid 28918
Spain
Phone: +34 91481 6979
Email: fabio.giust@imdea.org
Telemaco Melia
Alcatel-Lucent Bell Labs
Route de Villejust
Nozay, Ile de France 91620
France
Email: telemaco.melia@alcatel-lucent.com
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Rui Pedro Ferreira da Costa
Alcatel-Lucent Bell Labs
Route de Villejust
Nozay, Ile de France 91620
France
Email: rui_pedro.ferreira_da_costa@alcatel-lucent.com
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