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Internet Engineering Task Force (IETF) H. Yokota
Request for Comments: 5949 KDDI Lab
Category: Standards Track K. Chowdhury
ISSN: 2070-1721 R. Koodli
Cisco Systems
B. Patil
Nokia
F. Xia
Huawei USA
September 2010
Fast Handovers for Proxy Mobile IPv6
Abstract
Mobile IPv6 (MIPv6; RFC 3775) provides a mobile node with IP mobility
when it performs a handover from one access router to another, and
fast handovers for Mobile IPv6 (FMIPv6) are specified to enhance the
handover performance in terms of latency and packet loss. While
MIPv6 (and FMIPv6 as well) requires the participation of the mobile
node in the mobility-related signaling, Proxy Mobile IPv6 (PMIPv6;
RFC 5213) provides IP mobility to nodes that either have or do not
have MIPv6 functionality without such involvement. Nevertheless, the
basic performance of PMIPv6 in terms of handover latency and packet
loss is considered no different from that of MIPv6.
When the fast handover is considered in such an environment, several
modifications are needed to FMIPv6 to adapt to the network-based
mobility management. This document specifies the usage of fast
handovers for Mobile IPv6 (FMIPv6; RFC 5568) when Proxy Mobile IPv6
is used as the mobility management protocol. Necessary extensions
are specified for FMIPv6 to support the scenario when the mobile node
does not have IP mobility functionality and hence is not involved
with either MIPv6 or FMIPv6 operations.
Yokota, et al. Standards Track [Page 1]
RFC 5949 Proxy-Based Fast Handover September 2010
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5949.
Copyright Notice
Copyright (c) 2010 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.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Yokota, et al. Standards Track [Page 2]
RFC 5949 Proxy-Based Fast Handover September 2010
Table of Contents
1. Introduction ....................................................3
2. Requirements Notation ...........................................4
3. Terminology .....................................................4
4. Proxy-Based FMIPv6 Protocol Overview ............................5
4.1. Protocol Operation .........................................7
4.2. Inter-AR Tunneling Operation ..............................14
4.3. IPv4 Support Considerations ...............................16
5. PMIPv6-Related Fast Handover Issues ............................16
5.1. Manageability Considerations ..............................16
5.2. Expedited Packet Transmission .............................17
6. Message Formats ................................................18
6.1. Mobility Header ...........................................18
6.1.1. Handover Initiate (HI) .............................18
6.1.2. Handover Acknowledge (HAck) ........................20
6.2. Mobility Options ..........................................22
6.2.1. Context Request Option .............................22
6.2.2. Local Mobility Anchor Address (LMAA) Option ........23
6.2.3. Mobile Node Link-Local Address Interface
Identifier (MN LLA-IID) Option .....................24
6.2.4. Home Network Prefix Option .........................25
6.2.5. Link-Local Address Option ..........................25
6.2.6. GRE Key Option .....................................25
6.2.7. IPv4 Address Option ................................25
6.2.8. Vendor-Specific Mobility Option ....................25
7. Security Considerations ........................................26
8. IANA Considerations ............................................26
9. Acknowledgments ................................................28
10. References ....................................................28
10.1. Normative References .....................................28
10.2. Informative References ...................................29
Appendix A. Applicable Use Cases ..................................30
A.1. PMIPv6 Handoff Indication .................................30
A.2. Local Routing .............................................31
1. Introduction
Proxy Mobile IPv6 (PMIPv6) [RFC5213] provides IP mobility to a mobile
node that does not support Mobile IPv6 (MIPv6) [RFC3775] mobile node
functionality. A proxy agent in the network performs the mobility
management signaling on behalf of the mobile node. This model
transparently provides mobility for nodes within a PMIPv6 domain.
Nevertheless, the basic performance of PMIPv6 in terms of handover
latency and packet loss is considered no different from that of
Mobile IPv6.
Yokota, et al. Standards Track [Page 3]
RFC 5949 Proxy-Based Fast Handover September 2010
Fast handovers for Mobile IPv6 (FMIPv6) [RFC5568] describes the
protocol to reduce the handover latency for Mobile IPv6 by allowing a
mobile node to send packets as soon as it detects a new subnet link
and by delivering packets to the mobile node as soon as its
attachment is detected by the new access router. This document
extends FMIPv6 for Proxy MIPv6 operation to minimize handover delay
and packet loss as well as to transfer network-resident context for a
PMIPv6 handover. [RFC5568] is normative for this document, except
where this document specifies new or revised functions and messages.
2. Requirements Notation
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 [RFC2119].
3. Terminology
This document reuses terminology from [RFC5213], [RFC5568], and
[RFC3775]. The following terms and abbreviations are additionally
used in this document.
Access Network (AN):
A network composed of link-layer access devices such as access
points or base stations providing access to a Mobile Access
Gateway (MAG) connected to it.
Previous Access Network (P-AN):
The access network to which the Mobile Node (MN) is attached
before handover.
New Access Network (N-AN):
The access network to which the Mobile Node (MN) is attached after
handover.
Previous Mobile Access Gateway (PMAG):
The MAG that manages mobility-related signaling for the mobile
node before handover. In this document, the MAG and the Access
Router are co-located.
New Mobile Access Gateway (NMAG):
The MAG that manages mobility-related signaling for the mobile
node after handover. In this document, the MAG and the Access
Router (AR) are co-located.
Yokota, et al. Standards Track [Page 4]
RFC 5949 Proxy-Based Fast Handover September 2010
Local Mobility Anchor (LMA):
The topological anchor point for the mobile node's home network
prefix(es) and the entity that manages the mobile node's binding
state. This specification does not alter any capability or
functionality defined in [RFC5213].
Handover indication:
A generic signaling message, sent from the P-AN to the PMAG, that
indicates a mobile node's handover. While this signaling is
dependent on the access technology, it is assumed that Handover
indication can carry the information to identify the mobile node
and to assist the PMAG in resolving the NMAG (and the new access
point or base station) to which the mobile node is moving. The
details of this message are outside the scope of this document.
4. Proxy-Based FMIPv6 Protocol Overview
This specification describes fast handover protocols for the network-
based mobility management protocol called Proxy Mobile IPv6 (PMIPv6)
[RFC5213]. The core functional entities defined in PMIPv6 are the
Local Mobility Anchor (LMA) and the Mobile Access Gateway (MAG). The
LMA is the topological anchor point for the mobile node's home
network prefix(es). The MAG acts as an access router (AR) for the
mobile node and performs the mobility management procedures on its
behalf. The MAG is responsible for detecting the mobile node's
movements to and from the access link and for initiating binding
registrations to the mobile node's local mobility anchor. If the
MAGs can be informed of the detachment and/or attachment of the
mobile node in a timely manner via, e.g., lower-layer signaling, it
will become possible to optimize the handover procedure, which
involves establishing a connection on the new link and signaling
between mobility agents, compared to the baseline specification of
PMIPv6.
In order to further improve the performance during the handover, this
document specifies a bidirectional tunnel between the Previous MAG
(PMAG) and the New MAG (NMAG) to tunnel packets meant for the mobile
node. In order to enable the NMAG to send the Proxy Binding Update
(PBU), the Handover Initiate (HI) and Handover Acknowledge (HAck)
messages in [RFC5568] are extended for context transfer, in which
parameters such as the mobile node's Network Access Identifier (NAI),
Home Network Prefix (HNP), and IPv4 Home Address are transferred from
the PMAG. New flags, 'P' and 'F', are defined for the HI and HAck
messages to distinguish from those in [RFC5568] and to request packet
forwarding, respectively.
Yokota, et al. Standards Track [Page 5]
RFC 5949 Proxy-Based Fast Handover September 2010
In this document, the Previous Access Router (PAR) and New Access
Router (NAR) are interchangeable with the PMAG and NMAG,
respectively. The reference network is illustrated in Figure 1. The
access networks in the figure (i.e., P-AN and N-AN) are composed of
Access Points (APs) defined in [RFC5568], which are often referred to
as base stations in cellular networks.
Since a mobile node is not directly involved with IP mobility
protocol operations, it follows that the mobile node is not directly
involved with fast handover procedures either. Hence, the messages
involving the mobile node in [RFC5568] are not used when PMIPv6 is in
use. More specifically, the Router Solicitation for Proxy
Advertisement (RtSolPr), the Proxy Router Advertisement (PrRtAdv),
Fast Binding Update (FBU), Fast Binding Acknowledgment (FBack), and
the Unsolicited Neighbor Advertisement (UNA) messages are not
applicable in the PMIPv6 context. A MAG that receives a RtSolPr or
FBU message from a mobile node SHOULD behave as if they do not
implement FMIPv6 as defined in [RFC5568] at all -- continuing to
operate according to this specification within the network -- or
alternatively, start serving that particular mobile node as specified
in [RFC5568].
+----------+
| LMA |
| |
+----------+
/ \
/ \
/ \
+........../..+ +..\..........+
. +-------+-+ .______. +-+-------+ .
. | PMAG |()_______)| NMAG | .
. | (PAR) | . . | (NAR) | .
. +----+----+ . . +----+----+ .
. | . . | .
. ___|___ . . ___|___ .
. / \ . . / \ .
. ( P-AN ) . . ( N-AN ) .
. \_______/ . . \_______/ .
. | . . | .
. +----+ . . +----+ .
. | MN | ----------> | MN | .
. +----+ . . +----+ .
+.............+ +.............+
Figure 1: Reference Network for Fast Handover
Yokota, et al. Standards Track [Page 6]
RFC 5949 Proxy-Based Fast Handover September 2010
4.1. Protocol Operation
There are two modes of operation in FMIPv6 [RFC5568]. In the
predictive mode of fast handover, a bidirectional tunnel between the
PMAG (PAR) and NMAG (NAR) is established prior to the mobile node's
attachment to the NMAG. In the reactive mode, this tunnel
establishment takes place after the mobile node attaches to the NMAG.
In order to alleviate the packet loss during a mobile node's handover
(especially when the mobile node is detached from both links), the
downlink packets for the mobile node need to be buffered either at
the PMAG or NMAG, depending on when the packet forwarding is
performed. It is hence REQUIRED that all MAGs have the capability
and enough resources to buffer packets for the mobile nodes
accommodated by them. The buffer size to be prepared and the rate at
which buffered packets are drained are addressed in Section 5.4 of
[RFC5568]. Note that the protocol operation specified in the
document is transparent to the local mobility anchor (LMA); hence
there is no new functional requirement or change on the LMA.
Unlike MIPv6, the mobile node in the PMIPv6 domain is not involved
with IP mobility signaling; therefore, in order for the predictive
fast handover to work effectively, it is REQUIRED that the mobile
node is capable of reporting lower-layer information to the AN at a
short enough interval, and that the AN is capable of sending the
Handover indication to the PMAG at an appropriate timing. The
sequence of events for the predictive fast handover is illustrated in
Figure 2.
Yokota, et al. Standards Track [Page 7]
RFC 5949 Proxy-Based Fast Handover September 2010
PMAG NMAG
MN P-AN N-AN (PAR) (NAR) LMA
| | | | | |
(a) |--Report-->| | | | |
| | | | | |
| | Handover | | |
(b) | |------indication------>| | |
| | | | | |
| | | | | |
(c) | | | |----HI---->| |
| | | | | |
| | | | | |
(d) | | | |<---HAck---| |
| | | | | |
| | | | | |
| | | |HI/HAck(optional) |
(e) | | | |<- - - - ->| |
| | | #=|<===================|
(f) | | | #====DL data=>| |
| Handover | Handover | | |
(g) |<-command--|<------command---------| | |
~~~ | | | | |
~~~ | | | | |
| MN-AN connection | AN-MAG connection | |
(h) |<---establishment---->|<----establishment----->| |
| | | (substitute for UNA) | |
| | | | | |
(i) |<==================DL data=====================| |
| | | | | |
(j) |===================UL data====================>|=# |
| | | #=|<============# |
| | | #=====================>|
/ | | | | | | \
|(k) | | | | |--PBU-->| |
| | | | | | | |
|(l) | | | | |<--PBA--| |
| |<==================DL data=====================|<=======| |
| | | | | | | |
\ |===================UL data====================>|=======>| /
UL Uplink
DL Downlink
PBA Proxy Binding Acknowledgment
Figure 2: Predictive Fast Handover for PMIPv6 (Initiated by PMAG)
Yokota, et al. Standards Track [Page 8]
RFC 5949 Proxy-Based Fast Handover September 2010
The detailed descriptions are as follows:
(a) The mobile node detects that a handover is imminent and reports
its identifier (MN ID) and the New Access Point Identifier (New
AP ID) [RFC5568] to which the mobile node is most likely to
move. The MN ID could be the NAI, link-layer address, or any
other suitable identifier, but the MAG SHOULD be able to map any
access-specific identifier to the NAI as the MN ID. In some
cases, the previous access network (P-AN) will determine the New
AP ID for the mobile node. This step is access technology
specific, and details are outside the scope of this document.
(b) The previous access network, to which the mobile node is
currently attached, indicates the handover of the mobile node to
the previous mobile access gateway (PMAG), with the MN ID and
New AP ID. Detailed definition and specification of this
message are outside the scope of this document.
(c) The previous MAG derives the new mobile access gateway (NMAG)
from the New AP ID, which is a similar process to that of
constructing an [AP ID, AR-Info] tuple in [RFC5568]. The
previous MAG then sends the Handover Initiate (HI) message to
the new MAG. The HI message MUST have the 'P' flag set and
include the MN ID, the HNP(s), and the address of the local
mobility anchor that is currently serving the mobile node. If
there is a valid (non-zero) MN Link-layer Identifier (MN LL-ID),
that information MUST also be included. With some link layers,
the MN Link-local Address Interface Identifier (MN LLA-IID) can
also be included (see Section 6.2.3).
(d) The new MAG sends the Handover Acknowledge (HAck) message back
to the previous MAG with the 'P' flag set.
(e) If it is preferred that the timing of buffering or forwarding
should be later than step (c), the new MAG MAY optionally
request that the previous MAG buffer or forward packets at a
later and appropriate time, by setting the 'U' flag [RFC5568] or
the 'F' flag in the HI message, respectively.
(f) If the 'F' flag is set in the previous step, a bidirectional
tunnel is established between the previous MAG and new MAG, and
packets destined for the mobile node are forwarded from the
previous MAG to the new MAG over this tunnel. After
decapsulation, those packets MAY be buffered at the new MAG. If
the connection between the new access network and new MAG has
already been established, those packets MAY be forwarded towards
Yokota, et al. Standards Track [Page 9]
RFC 5949 Proxy-Based Fast Handover September 2010
the new access network, which then becomes responsible for them
(e.g., buffering or delivering, depending on the condition of
the mobile node's attachment); this is access technology
specific.
(g) When handover is ready on the network side, the mobile node is
triggered to perform handover to the new access network. This
step is access technology specific, and details are outside the
scope of this document.
(h) The mobile node establishes a physical-layer connection with the
new access network (e.g., radio channel assignment), which in
turn triggers the establishment of a link-layer connection
between the new access network and new MAG if not yet
established. An IP-layer connection setup may be performed at
this time (e.g., PPP IPv6 Control Protocol) or at a later time
(e.g., stateful or stateless address autoconfiguration). This
step can be a substitute for the Unsolicited Neighbor
Advertisement (UNA) in [RFC5568]. If the new MAG acquires a
valid new MN LL-ID via the new access network and a valid old MN
LL-ID from the previous MAG at step (c), these IDs SHOULD be
compared to determine whether the same interface is used before
and after handover. When the connection between the mobile node
and new MAG is PPP and the same interface is used for the
handover, the new MAG SHOULD confirm that the same interface
identifier is used for the mobile node's link-local address
(this is transferred from the previous MAG using the MN LLA-IID
option at step (c), and sent to the mobile node during the
Configure-Request/Ack exchange).
(i) The new MAG starts to forward packets destined for the mobile
node via the new access network.
(j) The uplink packets from the mobile node are sent to the new MAG
via the new access network, and the new MAG forwards them to the
previous MAG. The previous MAG then sends the packets to the
local mobility anchor that is currently serving the mobile node.
(k) The new MAG sends the Proxy Binding Update (PBU) to the local
mobility anchor, whose address is provided in step (c). Steps
(k) and (l) are not part of the fast handover procedure but are
shown for reference.
(l) The local mobility anchor sends back the Proxy Binding
Acknowledgment (PBA) to the new MAG. From this time on, the
packets to/from the mobile node go through the new MAG instead
of the previous MAG.
Yokota, et al. Standards Track [Page 10]
RFC 5949 Proxy-Based Fast Handover September 2010
According to Section 4 of [RFC5568], the previous MAG establishes a
binding between the Previous Care-of Address (PCoA) and New Care-of
Address (NCoA) to forward packets for the mobile node to the new MAG,
and the new MAG creates a proxy neighbor cache entry to receive those
packets for the NCoA before the mobile node arrives. In the case of
PMIPv6, however, the only address that is used by the mobile node is
the Mobile Node's Home Address (MN-HoA), so the PMAG forwards the
mobile node's packets to the NMAG instead of the NCoA. The NMAG then
simply decapsulates those packets and delivers them to the mobile
node. FMIPv4 [RFC4988] specifies forwarding when the mobile node
uses the home address as its on-link address rather than the care-of
address. The usage in PMIPv6 is similar to that in FMIPv4, where the
address(es) used by the mobile node is/are based on its HNP(s).
Since the NMAG can obtain the link-layer address (MN LL-ID) and
HNP(s) via the HI message (also the interface identifier of the
mobile node's link-local address (MN LLA-ID), if available), it can
create a neighbor cache entry for the link-local address and the
routes for the whole HNP(s), even before the mobile node performs
Neighbor Discovery. For the uplink packets from the mobile node
after handover in step (j), the NMAG forwards the packets to the PMAG
through the tunnel established in step (f). The PMAG then
decapsulates and sends them to the local mobility anchor.
The timing of the context transfer and that of packet forwarding may
be different. Thus, a new flag 'F' and Option Code values for it in
the HI and HAck messages are defined to request forwarding. To
request buffering, the 'U' flag has already been defined in
[RFC5568]. If the PMAG receives the HI message with the 'F' flag
set, it starts forwarding packets for the mobile node. The HI
message with the 'U' flag set MAY be sent earlier if the timing of
buffering is different from that of forwarding. If packet forwarding
is completed, the PMAG MAY send the HI message with the 'F' flag set
and the Option Code value set to 2. Via this message, the ARs on
both ends can tear down the forwarding tunnel synchronously.
The IP addresses in the headers of those user packets are summarized
below:
In step (f),
Inner source address: IP address of the correspondent node
Inner destination address: HNP or Mobile Node's IPv4 Home Address
(IPv4-MN-HoA)
Outer source address: IP address of the PMAG
Outer destination address: IP address of the NMAG
Yokota, et al. Standards Track [Page 11]
RFC 5949 Proxy-Based Fast Handover September 2010
In step (i),
Source address: IP address of the correspondent node
Destination address: HNP or IPv4-MN-HoA
In step (j),
- from the mobile node to the NMAG,
Source address: HNP or IPv4-MN-HoA
Destination address: IP address of the correspondent node
- from the NMAG to the PMAG,
Inner source address: HNP or IPv4-MN-HoA
Inner destination address: IP address of the correspondent node
Outer source address: IP address of the NMAG
Outer destination address: IP address of the PMAG
- from the PMAG to the LMA,
Inner source address: HNP or IPv4-MN-HoA
Inner destination address: IP address of the correspondent node
Outer source address: IP address of the PMAG
Outer destination address: IP address of the LMA
In the case of the reactive handover for PMIPv6, since the mobile
node does not send either the FBU or UNA, it would be more natural
that the NMAG send the HI message to the PMAG after the mobile node
has moved to the new link. The NMAG then needs to obtain the
information of the PMAG beforehand. Such information could be
provided, for example, by the mobile node sending the AP-ID on the
old link and/or by the lower-layer procedures between the P-AN and
N-AN. The exact method is not specified in this document. Figure 3
illustrates the reactive fast handover procedures for PMIPv6, where
the bidirectional tunnel establishment is initiated by the NMAG.
Yokota, et al. Standards Track [Page 12]
RFC 5949 Proxy-Based Fast Handover September 2010
PMAG NMAG
MN P-AN N-AN (PAR) (NAR) LMA
| | | | | |
(a) ~~~ | | | | |
~~~ | | | | |
| MN-AN connection | AN-MAG connection | |
(b) |<--establishment-->|<-------establishment------>| |
| | |(substitute for UNA and FBU)| |
| | | | | |
| | | | | |
(c) | | | |<-----HI-------| |
| | | | | |
| | | | | |
(d) | | | |-----HAck----->| |
| | | | | |
| | | | | |
(e) | | | #=|<=======================|
| | | #================>|=# |
|<====================DL data======================# |
| | | | | |
(f) |=====================UL data===================>|=# |
| | | #=|<================# |
| | | #=========================>|
| | | | | |
/ | | | | | | \
|(g) | | | | |--PBU-->| |
| | | | | | | |
|(h) | | | | |<--PBA--| |
| |<====================DL data====================|<=======| |
| | | | | | | |
\ |=====================UL data===================>|=======>| /
Figure 3: Reactive Fast Handover for PMIPv6 (Initiated by NMAG)
The detailed descriptions are as follows:
(a) The mobile node undergoes handover from the previous access
network to the new access network.
(b) The mobile node establishes a connection (e.g., radio channel)
with the new access network, which triggers the establishment of
the connection between the new access network and new MAG. The
MN ID is transferred to the new MAG at this step for the
subsequent procedures. The AP-ID on the old link (Old AP ID),
which will be provided by either the mobile node or the new
access network, is also transferred to the new MAG to help
identify the previous MAG on the new link. This can be regarded
as a substitute for the UNA and FBU.
Yokota, et al. Standards Track [Page 13]
RFC 5949 Proxy-Based Fast Handover September 2010
(c) The new MAG sends the HI message to the previous MAG. The HI
message MUST have the 'P' flag set and include the MN ID. The
Context Request option MAY be included to request additional
context information on the mobile node to the previous MAG.
(d) The previous MAG sends the HAck message back to the new MAG with
the 'P' flag set. The HAck message MUST include the HNP(s)
and/or IPv4-MN-HoA that corresponds to the MN ID in the HI
message and SHOULD include the MN LL-ID, only if it is valid
(non-zero), and the local mobility anchor address that is
currently serving the mobile node. The context information
requested by the new MAG MUST be included. If the requested
context is not available for some reason, the previous MAG MUST
return the HAck message with the Code value 131. If the 'F'
flag is set in the HI message at step (c) and forwarding is
nevertheless not executable for some reason, the previous MAG
MUST return the HAck message with the Code value 132.
(e) If the 'F' flag in the HI message is set at step (c), a
bidirectional tunnel is established between the previous MAG and
new MAG, and packets destined for the mobile node are forwarded
from the previous MAG to the new MAG over this tunnel. After
decapsulation, those packets are delivered to the mobile node
via the new access network.
(f) The uplink packets from the mobile node are sent to the new MAG
via the new access network, and the new MAG forwards them to the
previous MAG. The previous MAG then sends the packets to the
local mobility anchor that is currently serving the mobile node.
Steps (g)-(h) are the same as steps (k)-(l) in the predictive fast
handover procedures.
In step (c), the IP address of the PMAG needs to be resolved by the
NMAG to send the HI message to the PMAG. This information may come
from the N-AN or some database that the NMAG can access.
4.2. Inter-AR Tunneling Operation
When the PMAG (PAR) or NMAG (NAR), depending on the fast handover
mode, receives the HI message with the 'F' flag set, it prepares to
send/receive the mobile node's packets to/from the other MAG and
returns the HAck message with the same sequence number. Both MAGs
SHOULD support the following encapsulation modes for the user
packets, which are also defined for the tunnel between the local
mobility anchor and MAG:
Yokota, et al. Standards Track [Page 14]
RFC 5949 Proxy-Based Fast Handover September 2010
o IPv4-or-IPv6-over-IPv6 [RFC5844]
o IPv4-or-IPv6-over-IPv4 [RFC5844]
o IPv4-or-IPv6-over-IPv4-UDP [RFC5844]
o TLV-header UDP tunneling [RFC5845]
o Generic Routing Encapsulation (GRE) tunneling with or without GRE
key(s) [RFC5845]
The PMAG and the NMAG MUST use the same tunneling mechanism for the
data traffic tunneled between them. The encapsulation mode to be
employed SHOULD be configurable. It is RECOMMENDED that:
1. As the default behavior, the inter-MAG tunnel uses the same
encapsulation mechanism as that for the PMIPv6 tunnel between the
local mobility anchor and the MAGs. The PMAG and NMAG
automatically start using the same encapsulation mechanism
without a need for a special configuration on the MAGs or a
dynamic tunneling mechanism negotiation between them.
2. Configuration on the MAGs can override the default mechanism
specified in scenario #1 above. The PMAG and NMAG MUST be
configured with the same mechanism, and this configuration is
most likely to be uniform throughout the PMIPv6 domain. If the
packets on the PMIPv6 tunnel cannot be uniquely mapped on to the
configured inter-MAG tunnel, this scenario is not applicable, and
scenario #3 below SHOULD directly be applied.
3. An implicit or explicit tunnel negotiation mechanism between the
MAGs can override the default mechanism specified in scenario #1
above. The employed tunnel negotiation mechanism is outside the
scope of this document.
The necessary information MUST be transferred in the HI/HAck messages
to determine whether a mobile node's packets should be forwarded
immediately or at a later time. Such information includes the HNP(s)
(or IPv4-MN-HoA) and/or GRE key(s). In the case of GRE tunneling
with GRE keys being used, for each mobility session, the NMAG selects
the GRE key for the downlink packets, and the PMAG selects the GRE
key for the uplink packets. These GRE keys are exchanged between the
PMAG and the NMAG using the GRE Key option as described in [RFC5845];
e.g., in the case of the reactive mode as shown in Figure 3, the DL
GRE key is communicated in the HI message while the UL GRE key is
sent in the HAck message. In the case of downlink packets, the PMAG
redirects the mobile node's packets from the local mobility anchor
towards the NMAG, and if the mobile node is ready to receive those
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packets or the N-AN can handle them regardless of the state of the
mobile node, the NMAG SHOULD immediately send them towards the N-AN;
otherwise, it SHOULD buffer them until the mobile node is ready. In
the case of uplink packets, the NMAG SHOULD reverse-tunnel them from
the mobile node towards the PMAG, and the PMAG will then send them to
the local mobility anchor.
When the PMAG or NMAG receives the HI message with the 'U' flag set,
it prepares to buffer the mobile node's packets and returns the HAck
message with the same sequence number. It MUST be followed by
another HI message with the 'F' flag set at an appropriate time to
forward the buffered packets.
If the MAG that received the HI message encounters an erroneous
situation (e.g., insufficient buffer space), it SHOULD immediately
send the HAck message with the cause of the error and cancel all
tunneling operations.
4.3. IPv4 Support Considerations
The motivation and usage scenarios of IPv4 protocol support by PMIPv6
are described in [RFC5844]. The scope of IPv4 support covers the
following two features:
o IPv4 Home Address Mobility Support, and
o IPv4 Transport Support.
As for IPv4 Home Address Mobility Support, the mobile node acquires
the IPv4 Home Address (IPv4-MN-HoA), and in the case of handover, the
PMAG needs to transfer IPv4-MN-HoA to the NMAG, which is the inner
destination address of the packets forwarded on the downlink. For
this purpose, the IPv4 Address option described in Section 6.2.7 is
used. In order to provide IPv4 Transport Support, the NMAG needs to
know the IPv4 address of the local mobility anchor (IPv4-LMAA) to
send PMIPv6 signaling messages to the local mobility anchor in the
IPv4 transport network. For this purpose, a new option called the
LMA Address (LMAA) option is defined in Section 6.2.2 so as to convey
IPv4-LMAA from the PMAG to the NMAG.
5. PMIPv6-Related Fast Handover Issues
5.1. Manageability Considerations
This specification does not require any additional IP-level
functionality on the local mobility anchor and the mobile node
running in the PMIPv6 domain. A typical network interface that the
mobile node could be assumed to have is one with the cellular
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network, where the network controls the movement of the mobile node.
Different types of interfaces could be involved, such as different
generations (3G and 3.9G) or different radio access systems. This
specification supports a mobile node with the single radio mode,
where only one interface is active at any given time. The assigned
IP address is preserved whether the physical interface changes or
not, and the mobile node can identify which interface should be used
if there are multiple ones.
5.2. Expedited Packet Transmission
The protocol specified in this document enables the NMAG to obtain
parameters that would otherwise be available only by communicating
with the local mobility anchor. For instance, the HNP(s) and/or
IPv4-MN-HoA of a mobile node are made available to the NMAG through
context transfer. This allows the NMAG to perform some procedures
that may be beneficial. The NMAG, for example, SHOULD send a Router
Advertisement (RA) with prefix information to the mobile node as soon
as its link attachment is detected (e.g., via receipt of a Router
Solicitation message). Such an RA is recommended, for example, in
scenarios where the mobile node uses a new radio interface while
attaching to the NMAG; since the mobile node does not have
information regarding the new interface, it will not be able to
immediately send packets without first receiving an RA with HNP(s).
Especially in the reactive fast handover, the NMAG gets to know the
HNP(s) assigned to the mobile node on the previous link at step (d)
in Figure 3. In order to reduce the communication disruption time,
the NMAG SHOULD expect the mobile node to keep using the same HNP and
to send uplink packets before that step upon the mobile node's
request. However, if the HAck message from the PMAG returns a
different HNP or the subsequent PMIPv6 binding registration for the
HNP fails for some reason, then the NMAG MUST withdraw the advertised
HNP by sending another RA with zero prefix lifetime for the HNP in
question. This operation is the same as that described in
Section 6.12 of [RFC5213].
The protocol specified in this document is applicable regardless of
whether link-layer addresses are used between a mobile node and its
MAG. A mobile node should be able to continue sending packets on the
uplink even when it changes link. When link-layer addresses are
used, the mobile node performs Neighbor Unreachability Detection
(NUD) [RFC4861], after attaching to a new link, probing the
reachability of its default router. The new router should respond to
the NUD probe, providing its link-layer address in the solicited
Neighbor Advertisement, which is common in the PMIPv6 domain.
Implementations should allow the mobile node to continue to send
uplink packets while it is performing NUD.
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6. Message Formats
This document defines new Mobility Header messages for the extended
HI and HAck, and new mobility options for conveying context
information.
6.1. Mobility Header
6.1.1. Handover Initiate (HI)
This section defines extensions to the HI message in [RFC5568]. The
format of the Message Data field in the Mobility Header 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
+-------------------------------+
| Sequence # |
+-+-+-+-+-------+---------------+-------------------------------+
|S|U|P|F|Resv'd | Code | |
+-+-+-+-+-------+---------------+ |
| |
. .
. Mobility options .
. .
| |
+---------------------------------------------------------------+
(Note: P=1)
IP Fields:
Source Address
The IP address of the PMAG or NMAG
Destination Address
The IP address of the peer MAG
Message Data:
Sequence # Same as [RFC5568].
'S' flag Defined in [RFC5568], and MUST be set to zero in this
specification.
'U' flag Buffer flag. Same as [RFC5568].
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'P' flag Proxy flag. Used to distinguish the message from that
defined in [RFC5568], and MUST be set in all new message
formats defined in this document when using this protocol
extension.
'F' flag Forwarding flag. Used to request to forward the packets
for the mobile node.
Reserved Same as [RFC5568].
Code [RFC5568] defines this field and its values, 0 and 1. In
this specification, with the 'P' flag set, this field can
be set to zero by default, or to the following values:
2: Indicate the completion of forwarding
3: All available context transferred
Code value 3 is set when the transfer of all necessary
context information is completed with this message. This
Code value is used both in cases where the context
information is fragmented into several pieces and the
last fragment is contained in this message, and where the
whole information is transferred in one piece.
Mobility options:
This field contains one or more mobility options, whose encoding and
formats are defined in [RFC3775].
Required option
In order to uniquely identify the target mobile node, the mobile
node identifier MUST be contained in the Mobile Node Identifier
option.
The transferred context MUST be for one mobile node per message. In
addition, the NMAG can request necessary mobility options via the
Context Request option defined in this document.
Context Request Option
This option MAY be present to request context information,
typically by the NMAG to the PMAG in the NMAG-initiated fast
handover.
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6.1.2. Handover Acknowledge (HAck)
This section defines extensions to the HAck message in [RFC5568].
The format of the Message Data field in the Mobility Header 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
+-------------------------------+
| Sequence # |
+-+-+-+---------+---------------+-------------------------------+
|U|P|F|Reserved | Code | |
+-+-+-+---------+---------------+ |
| |
. .
. Mobility options .
. .
| |
+---------------------------------------------------------------+
(Note: P=1)
IP Fields:
Source Address
Copied from the destination address of the Handover Initiate
message to which this message is a response.
Destination Address
Copied from the source address of the Handover Initiate message to
which this message is a response.
Message Data:
The usages of Sequence # and Reserved fields are exactly the same as
those in [RFC5568].
'U' flag Same as defined in Section 6.1.1.
'P' flag Same as defined in Section 6.1.1. Used to distinguish
the message from that defined in [RFC5568], and MUST be
set in all new message formats defined in this document
when using this protocol extension.
'F' flag Same as defined in Section 6.1.1.
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Code Code values 0 through 4 and 128 through 130 are defined
in [RFC5568]. When the 'P' flag is set, the meaning of
Code value 0 is as defined in this specification; 128
through 130 are reused; and 5, 6, 131, and 132 are newly
defined.
0: Handover Accepted or Successful
5: Context Transfer Accepted or Successful
6: All available Context Transferred
128: Handover Not Accepted, reason unspecified
129: Administratively prohibited
130: Insufficient resources
131: Requested Context Not Available
132: Forwarding Not Available
Mobility options:
This field contains one or more mobility options, whose encoding and
formats are defined in [RFC3775]. The mobility option that uniquely
identifies the target mobile node MUST be copied from the
corresponding HI message, and the transferred context MUST be for one
mobile node per message.
Required option(s)
All the context information requested by the Context Request
option in the HI message SHOULD be present in the HAck message.
The other cases are described below.
In the case of the PMAG-initiated fast handover, when the PMAG sends
the HI message to the NMAG with the context information and the NMAG
successfully receives it, the NMAG returns the HAck message with Code
value 5. In the case of the NMAG-initiated fast handover, when the
NMAG sends the HI message to the PMAG with or without the Context
Request option, the PMAG returns the HAck message with the requested
or default context information (if any). If all available context
information is transferred, the PMAG sets the Code value in the HAck
message to 6. If more context information is available, the PMAG
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sets the Code value in the HAck message to 5, and the NMAG MAY send
new HI message(s) to retrieve the rest of the available context
information. If none of the requested context information is
available, the PMAG returns the HAck message with Code value 131
without any context information.
6.2. Mobility Options
6.2.1. Context Request Option
This option is sent in the HI message to request context information
on the mobile node. If a default set of context information is
defined and always sufficient, this option is not used. This option
is more useful to retrieve additional or dynamically selected context
information.
The Context Request option is typically used for the reactive (NMAG-
initiated) fast handover mode to retrieve the context information
from the PMAG. When this option is included in the HI message, all
the requested context information SHOULD be included in the HAck
message in the corresponding mobility option(s) (e.g., HNP, LMAA, or
MN LL-ID mobility options).
The default context information to request is the Home Network Prefix
option. If the Mobile Node link layer is available and used, the
Mobile Node Link-layer Identifier option MUST also be requested.
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
+---------------+---------------+---------------+---------------+
| Option-Type | Option-Length | Reserved |
+---------------+---------------+-------------------------------+
| Req-type-1 | Req-length-1 | Req-type-2 | Req-length-2 |
+---------------------------------------------------------------+
| Req-type-3 | Req-length-3 | Req-option-3 |
+---------------------------------------------------------------+
| ... |
Option-Type 40
Option-Length The length in octets of this option, not including the
Option Type and Option Length fields.
Reserved This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Req-type-n The type value for the nth requested option.
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Req-length-n The length of the nth requested option, excluding the
Req-type-n and Req-length-n fields.
Req-option-n The optional data to uniquely identify the requested
context for the nth requested option.
In the case where there are only Req-type-n and Req-length-n fields,
the value of Req-length-n is set to zero. If additional information
besides Req-type-n is necessary to uniquely specify the requested
context, such information follows after Req-length-n. For example,
when the requested contexts start with the HNP option (type=22), the
MN Link-layer ID option (type=25), and the Vendor-Specific option
(type=19), the required option format looks as follows:
| ... |
+---------------+---------------+---------------+---------------+
|Option-Type=CRO| Option-Length | Reserved |
+---------------+---------------+---------------+---------------+
| Req-type-n=22 | Req-length-n=0| Req-type-n=25 | Req-length-n=0|
+---------------+---------------+-------------------------------+
| Req-type-n=19 | Req-length-n=5| Vendor-ID |
+-------------------------------+---------------+---------------+
| Vendor-ID | Sub-Type | |
+-----------------------------------------------+ |
| ... |
Note: CRO = Context Request Option
The first two options can uniquely identify the requested contexts
(i.e., the HNP and MN Link-layer ID) by the Req-type, so the
Req-length is set to zero; however, the subsequent Vendor-Specific
option further needs the Vendor-ID and Sub-Type to identify the
requested context, so these parameters follow, and the Req-length is
set to 5. Note that the exact values in the Vendor-ID and Sub-Type
follow [RFC5094].
6.2.2. Local Mobility Anchor Address (LMAA) Option
This option is used to transfer the Local Mobility Anchor IPv6
Address (LMAA) or its IPv4 Address (IPv4-LMAA) with which the mobile
node is currently registered. The detailed definition of the LMAA is
described in [RFC5213].
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option-Type | Option-Length | Option-Code | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Mobility Anchor Address ... |
Option-Type 41
Option-Length 18 or 6
Option-Code 0 Reserved
1 IPv6 address of the local mobility anchor (LMAA)
2 IPv4 address of the local mobility anchor
(IPv4-LMAA)
Reserved This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Local Mobility Anchor Address
If the Option-Code is 1, the LMA IPv6 address (LMAA)
is inserted. If the Option-Code is 2, the LMA IPv4
address (IPv4-LMA) is inserted.
6.2.3. Mobile Node Link-Local Address Interface Identifier (MN LLA-IID)
Option
This option is used to transfer the interface identifier of the
mobile node's IPv6 Link-local Address that is used in the P-AN. In
deployments where the interface identifier is assigned by the network
or is known to the network, this option is used to transfer this
identifier from the PMAG to the NMAG.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option-Type | Option-Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Interface Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Option-Type 42
Option-Length 10
Reserved This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Interface Identifier
The Interface Identifier value used for the mobile
node's IPv6 Link-local address in the P-AN.
6.2.4. Home Network Prefix Option
This option, as defined in [RFC5213], is used to transfer the home
network prefix that is assigned to the mobile node in the P-AN.
6.2.5. Link-Local Address Option
This option, as defined in [RFC5213], is used to transfer the link-
local address of the PMAG.
6.2.6. GRE Key Option
This option is used to transfer the GRE Key for the mobile node's
data flow over the bidirectional tunnel between the PMAG and NMAG.
The message format of this option follows that of the GRE Key option
defined in [RFC5845]. The GRE Key value uniquely identifies each
flow, and the sender of this option expects to receive packets of the
flow from the peer AR with this value.
6.2.7. IPv4 Address Option
As described in Section 4.3, if the mobile node runs in IPv4-only
mode or dual-stack mode, it requires the IPv4 home address
(IPv4-MN-HoA). This option is used to transfer the IPv4 home address
if assigned on the previous link. The format of this option follows
that of the IPv4 Home Address Request option defined in [RFC5844].
6.2.8. Vendor-Specific Mobility Option
This option is used to transfer any other information defined in this
document. The format and used values of this option follow those of
the Vendor-Specific Mobility option defined in [RFC5094].
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7. Security Considerations
Security issues for this document follow those for PMIPv6 [RFC5213]
and FMIPv6 [RFC5568]. In PMIPv6, the MAG and local mobility anchor
are assumed to share security associations. In FMIPv6, the access
routers (i.e., the PMAG and NMAG in this document) are assumed to
share security associations.
The Handover Initiate (HI) and Handover Acknowledge (HAck) messages
exchanged between the PMAG and NMAG MUST be protected using end-to-
end security association(s) offering integrity and data origin
authentication. The PMAG and the NMAG MUST implement IPsec [RFC4301]
for protecting the HI and HAck messages. IPsec Encapsulating
Security Payload (ESP) [RFC4303] in transport mode with mandatory
integrity protection SHOULD be used for protecting the signaling
messages. Confidentiality protection SHOULD be used if sensitive
context related to the mobile node is transferred.
IPsec ESP [RFC4303] in tunnel mode SHOULD be used to protect the
mobile node's packets at the time of forwarding if the link between
the PMAG and NMAG exposes the mobile node's packets to more threats
than if they had followed their normal routed path.
8. IANA Considerations
This document defines new flags and status codes in the HI and HAck
messages, as well as three new mobility options. The Type values for
these mobility options are assigned from the same numbering space as
that allocated for the other mobility options defined in [RFC3775].
Those for the flags and status codes are assigned from the
corresponding numbering space defined in [RFC5568], and have been
created as new tables in the IANA registry (marked with asterisks).
New values for these registries can be allocated by Standards Action
or IESG approval [RFC5226].
Mobility Options
Value Description Reference
----- ------------------------------------- -------------
40 Context Request Option Section 6.2.1
41 Local Mobility Anchor Address Option Section 6.2.2
42 Mobile Node Link-local Address
Interface Identifier Option Section 6.2.3
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Handover Initiate Flags (*)
Registration Procedures: Standards Action or IESG Approval
Flag Value Description Reference
---- ----- ----------------------------------- -------------
S 0x80 Assigned Address Configuration flag [RFC5568]
U 0x40 Buffer flag [RFC5568]
P 0x20 Proxy flag Section 6.1.1
F 0x10 Forwarding flag Section 6.1.1
Handover Acknowledge Flags (*)
Registration Procedures: Standards Action or IESG Approval
Flag Value Description Reference
---- ----- ------------------------------- -------------
U 0x80 Buffer flag Section 6.1.2
P 0x40 Proxy flag Section 6.1.2
F 0x20 Forwarding flag Section 6.1.2
Handover Initiate Status Codes (*)
Registration Procedures: Standards Action or IESG Approval
Code Description Reference
---- -------------------------------------- -------------
0 FBU with the PCoA as source IP address [RFC5568]
1 FBU whose source IP address is not PCoA [RFC5568]
2 Indicate the completion of forwarding Section 6.1.1
3 All available context transferred Section 6.1.1
4-255 Unassigned
Handover Acknowledge Status Codes (*)
Registration Procedures: Standards Action or IESG Approval
Code Description Reference
---- --------------------------------------- -------------
0 Handover Accepted or Successful
(when 'P' flag is set) Section 6.1.2
Handover Accepted with NCoA valid [RFC5568]
1 Handover Accepted, NCoA not valid [RFC5568]
2 Handover Accepted, NCoA assigned [RFC5568]
3 Handover Accepted, use PCoA [RFC5568]
4 Message sent unsolicited [RFC5568]
5 Context Transfer Accepted or Successful Section 6.1.2
6 All available Context Transferred Section 6.1.2
7-127 Unassigned
128 Handover Not Accepted, reason unspecified [RFC5568]
129 Administratively prohibited [RFC5568]
130 Insufficient resources [RFC5568]
131 Requested Context Not Available Section 6.1.2
132 Forwarding Not Available Section 6.1.2
133-255 Unassigned
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9. Acknowledgments
The authors would like to specially thank Vijay Devarapalli and Sri
Gundavelli for their thorough reviews of this document.
The authors would also like to thank Charlie Perkins, Desire Oulai,
Ahmad Muhanna, Giaretta Gerardo, Domagoj Premec, Marco Liebsch, Fan
Zhao, Julien Laganier, and Pierrick Seite for their passionate
discussions in the MIPSHOP working group mailing list.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC5094] Devarapalli, V., Patel, A., and K. Leung, "Mobile IPv6
Vendor Specific Option", RFC 5094, December 2007.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury,
K., and B. Patil, "Proxy Mobile IPv6", RFC 5213,
August 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5568] Koodli, R., "Mobile IPv6 Fast Handovers", RFC 5568,
July 2009.
[RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
Mobile IPv6", RFC 5844, May 2010.
[RFC5845] Muhanna, A., Khalil, M., Gundavelli, S., and K. Leung,
"Generic Routing Encapsulation (GRE) Key Option for Proxy
Mobile IPv6", RFC 5845, June 2010.
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10.2. Informative References
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4988] Koodli, R. and C. Perkins, "Mobile IPv4 Fast Handovers",
RFC 4988, October 2007.
Yokota, et al. Standards Track [Page 29]
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Appendix A. Applicable Use Cases
A.1. PMIPv6 Handoff Indication
PMIPv6 [RFC5213] defines the Handoff Indicator option and also
describes the type of handoff and values that can be set for this
option. This document proposes one approach to determining the
handoff type by the NMAG when the handoff of the mobile node is
executed.
According to [RFC5213], the following handoff types are defined:
0) Reserved
1) Attachment over a new interface
2) Handoff between two different interfaces of the mobile node
3) Handoff between mobile access gateways for the same interface
4) Handoff state unknown
5) Handoff state not changed (Re-registration)
Assuming that there is a valid MN Link-layer Identifier (MN LL-ID),
the following solution can be considered. When the NMAG receives the
MN LL-ID from the PMAG in the MN LL-ID option via the HI or HAck
message, the NMAG compares it with the new MN LL-ID that is obtained
from the mobile node in the N-AN. If these two MN LL-IDs are the
same, the handoff type falls into type 3 (defined above) and the
Handoff Indicator value is set to 3. If these two MN LL-IDs are
different, the handoff is likely to be type 2 (defined above) since
the HI/HAck message exchange implies that this is a handoff rather
than a multihoming, and therefore the Handoff Indicator value can be
set to 2. If there is no HI/HAck exchange performed prior to the
network attachment of the mobile node in the N-AN, the NMAG may infer
that this is a multi-homing case and set the Handoff Indicator value
to 1. In the case of re-registration, the MAG, to which the mobile
node is attached, can determine if the handoff state is not changed,
so the MAG can set the HI value to 5 without any additional
information. If no handoff type can be assumed or if there is no
valid MN LL-ID available, the NMAG may set the value to 4.
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A.2. Local Routing
As described in Section 6.10.3 of [RFC5213], if the
EnableMAGLocalRouting flag is set, when two mobile nodes are attached
to one MAG, the traffic between them may be locally routed. If one
mobile node moves from this MAG (PMAG) to another MAG (NMAG) and if
the PMAG does not detect the mobile node's detachment, it will
continue to forward packets locally forever. This situation is more
likely to happen in the reactive fast handover with Wireless Local
Area Network (WLAN) access, which does not have the capability to
detect the detachment of the mobile node in a timely manner. This
specification can be applied to handle this case. When the mobile
node attaches to the NMAG, the NMAG sends the HI message to the PMAG
with the 'F' flag set, which makes the PMAG realize the detachment of
the mobile node and establish the inter-MAG tunnel. The PMAG
immediately stops the local routing and sends the packets for the
mobile node to the NMAG via that tunnel; the packets are then
delivered to the mobile node on the new link.
Yokota, et al. Standards Track [Page 31]
RFC 5949 Proxy-Based Fast Handover September 2010
Authors' Addresses
Hidetoshi Yokota
KDDI Lab
2-1-15 Ohara, Fujimino
Saitama 356-8502
Japan
EMail: yokota@kddilabs.jp
Kuntal Chowdhury
Cisco Systems
30 International Place
Tewksbury, MA 01876
USA
EMail: kchowdhu@cisco.com
Rajeev Koodli
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
EMail: rkoodli@cisco.com
Basavaraj Patil
Nokia
6000 Connection Drive
Irving, TX 75039
USA
EMail: basavaraj.patil@nokia.com
Frank Xia
Huawei USA
1700 Alma Dr. Suite 500
Plano, TX 75075
USA
EMail: xiayangsong@huawei.com
Yokota, et al. Standards Track [Page 32]