Mobile IPv6 Fast Handovers
draft-ietf-mipshop-fmipv6-rfc4068bis-07
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 5268.
|
|
|---|---|---|---|
| Author | Rajeev Koodli | ||
| Last updated | 2015-10-14 (Latest revision 2008-04-17) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 5268 (Proposed Standard) | |
| Action Holders |
(None)
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||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Jari Arkko | ||
| Send notices to | (None) |
draft-ietf-mipshop-fmipv6-rfc4068bis-07
MIPSHOP Working Group Rajeev. Koodli (Editor)
Internet-Draft Starent Networks
Intended status: Standards Track April 17, 2008
Expires: October 19, 2008
Mobile IPv6 Fast Handovers
draft-ietf-mipshop-fmipv6-rfc4068bis-07.txt
Status of this Memo
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Abstract
Mobile IPv6 enables a Mobile Node to maintain its connectivity to the
Internet when moving from one Access Router to another, a process
referred to as handover. During handover, there is a period during
which the Mobile Node is unable to send or receive packets because of
link switching delay and IP protocol operations. This "handover
latency" resulting from standard Mobile IPv6 procedures, namely
movement detection, new Care of Address configuration, and Binding
Update, is often unacceptable to real-time traffic such as Voice over
IP. Reducing the handover latency could be beneficial to non-real-
time, throughput-sensitive applications as well. This document
specifies a protocol to improve handover latency due to Mobile IPv6
procedures. This document does not address improving the link
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switching latency.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Addressing the Handover Latency . . . . . . . . . . . . . 7
3.2. Protocol Operation . . . . . . . . . . . . . . . . . . . . 9
3.3. Protocol Operation during Network-initiated Handover . . . 12
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 12
5. Other Considerations . . . . . . . . . . . . . . . . . . . . . 16
5.1. Handover Capability Exchange . . . . . . . . . . . . . . . 16
5.2. Determining New Care of Address . . . . . . . . . . . . . 17
5.3. Prefix Management . . . . . . . . . . . . . . . . . . . . 17
5.4. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 18
5.5. DAD Handling . . . . . . . . . . . . . . . . . . . . . . . 18
5.6. Fast or Erroneous Movement . . . . . . . . . . . . . . . . 19
6. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 20
6.1. New Neighborhood Discovery Messages . . . . . . . . . . . 20
6.1.1. Router Solicitation for Proxy Advertisement
(RtSolPr) . . . . . . . . . . . . . . . . . . . . . . 20
6.1.2. Proxy Router Advertisement (PrRtAdv) . . . . . . . . . 22
6.2. Inter-Access Router Messages . . . . . . . . . . . . . . . 25
6.2.1. Handover Initiate (HI) . . . . . . . . . . . . . . . . 25
6.2.2. Handover Acknowledge (HAck) . . . . . . . . . . . . . 27
6.3. New Mobility Header Messages . . . . . . . . . . . . . . . 29
6.3.1. Fast Binding Update (FBU) . . . . . . . . . . . . . . 29
6.3.2. Fast Binding Acknowledgment (FBack) . . . . . . . . . 31
6.4. Unsolicited Neighbor Advertisement (UNA) . . . . . . . . . 32
6.5. New Options . . . . . . . . . . . . . . . . . . . . . . . 33
6.5.1. IP Address/Prefix Option . . . . . . . . . . . . . . . 33
6.5.2. Link-layer Address (LLA) Option . . . . . . . . . . . 35
6.5.3. Mobility Header Link-layer Address (MH-LLA) Option . . 36
6.5.4. Binding Authorization Data for FMIPv6 (BADF) . . . . . 36
6.5.5. Neighbor Advertisement Acknowledgment (NAACK) . . . . 37
7. Related Protocol and Device Considerations . . . . . . . . . . 38
8. Evolution from and Compatibility with RFC 4068 . . . . . . . . 39
9. Configurable Parameters . . . . . . . . . . . . . . . . . . . 40
10. Security Considerations . . . . . . . . . . . . . . . . . . . 40
10.1. Peer Authorization Database Entries when using IKEv2 . . . 42
10.2. Security Policy Database Entries . . . . . . . . . . . . . 43
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 44
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
13.1. Normative References . . . . . . . . . . . . . . . . . . . 45
13.2. Informative References . . . . . . . . . . . . . . . . . . 46
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Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 46
Appendix B. Changes Since RFC 4068 . . . . . . . . . . . . . . . 46
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 47
Intellectual Property and Copyright Statements . . . . . . . . . . 48
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1. Introduction
Mobile IPv6 [rfc3775] describes the protocol operations for a mobile
node to maintain connectivity to the Internet during its handover
from one access router to another. These operations involve link
layer procedures, movement detection, IP address configuration, and
location update. The combined handover latency is often sufficient
to affect real-time applications. Throughput-sensitive applications
can also benefit from reducing this latency. This document describes
a protocol to reduce the handover latency.
This specification addresses the following problem: how to allow a
mobile node to send packets as soon as it detects a new subnet link,
and how to deliver packets to a mobile node as soon as its attachment
is detected by the new access router. The protocol defines IP
protocol messages necessary for its operation regardless of link
technology. It does this without depending on specific link-layer
features while allowing link-specific customizations. By definition,
this specification considers handovers that interwork with Mobile IP:
once attached to its new access router, an MN engages in Mobile IP
operations including Return Routability [rfc3775]. There are no
special requirements for a mobile node to behave differently with
respect to its standard Mobile IP operations.
This specification is applicable when a mobile node has to perform IP
layer operations as a result of handovers. This specification does
not address improving the link switching latency. It does not modify
or optimize procedures related to signaling with the home agent of a
mobile node. Indeed, while targeted for Mobile IPv6, it could be
used with any mechanism that allows communication to continue despite
movements. Finally, this specification does not address bulk
movement of nodes using aggregate prefixes.
2. Terminology
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].
The use of the term, "silently ignore" is not defined in RFC 2119.
However, the term is used in this document and can be similarly
construed.
The following terminology and abbreviations are used in this document
in addition to those defined in [rfc3775]. The reference handover
scenario is illustrated in Figure 1.
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v +--------------+
+-+ | Previous | <
| | ------------ | Access | ------- >-----\
+-+ | Router | < \
MN | (PAR) | \
| +--------------+ +---------------+
| ^ IP | Correspondent |
| | Network | Node |
V | +---------------+
v /
v +--------------+ /
+-+ | New | < /
| | ------------ | Access | ------- >-----/
+-+ | Router | <
MN | (NAR) |
+--------------+
Figure 1: Reference Scenario for Handover
Mobile Node (MN): A Mobile IPv6 host
Access Point (AP): A Layer 2 device connected to an IP subnet that
offers wireless connectivity to a MN. An Access Point Identifier
(AP-ID) refers the AP's L2 address. Sometimes, AP-ID is also
referred to as a Basic Service Set IDentifier (BSSID).
Access Router (AR): The MN's default router
Previous Access Router (PAR): The MN's default router prior to its
handover
New Access Router (NAR): The MN's anticipated default router
subsequent to its handover
Previous CoA (PCoA): The MN's Care of Address valid on PAR's
subnet
New CoA (NCoA): The MN's Care of Address valid on NAR's subnet
Handover: A process of terminating existing connectivity and
obtaining new IP connectivity
Router Solicitation for Proxy Advertisement (RtSolPr): A message
from the MN to the PAR requesting information for a potential
handover
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Proxy Router Advertisement (PrRtAdv): A message from the PAR to
the MN that provides information about neighboring links
facilitating expedited movement detection. The message can also
act as a trigger for network-initiated handover.
(AP-ID, AR-Info) tuple: Contains an access router's L2 and IP
addresses, and prefix valid on the interface to which the Access
Point (identified by AP-ID) is attached. The triplet [Router's L2
address, Router's IP address and Prefix] is called "AR-Info". See
also Section 5.3.
Neighborhood Discovery: The process of resolving neighborhood AP-
IDs to AR-Info
Assigned Addressing: A particular type of NCoA configuration in
which the NAR assigns an IPv6 address for the MN. The method by
which NAR manages its address pool is not specified in this
document.
Fast Binding Update (FBU): A message from the MN instructing its
PAR to redirect its traffic (toward NAR)
Fast Binding Acknowledgment (FBack): A message from the PAR in
response to FBU
Predictive Fast Handover: The fast handover in which an MN is able
to send FBU when it is attached to the PAR, which then establishes
forwarding for its traffic (even before the MN attaches to the
NAR)
Reactive Fast Handover: The fast handover in which an MN is able
to send the FBU only after attaching to the NAR
Unsolicited Neighbor Advertisement (UNA): The message in [rfc4861]
with 'O' bit cleared
Fast Neighbor Advertisement (FNA): This message from RFC4068
[rfc4068] is deprecated. The UNA message above is the preferred
message in this specification.
Handover Initiate (HI): A message from the PAR to the NAR
regarding an MN's handover
Handover Acknowledge (HAck): A message from the NAR to the PAR as
a response to HI
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3. Protocol Overview
3.1. Addressing the Handover Latency
The ability to immediately send packets from a new subnet link
depends on the "IP connectivity" latency, which in turn depends on
the movement detection latency and the new CoA configuration latency.
Once an MN is IP-capable on the new subnet link, it can send a
Binding Update to its Home Agent and one or more correspondents.
Once its correspondents successfully process the Binding Update,
which typically involves the Return Routability procedure, the MN can
receive packets at the new CoA. So, the ability to receive packets
from correspondents directly at its new CoA depends on the Binding
Update latency as well as the IP connectivity latency.
The protocol enables an MN to quickly detect that it has moved to a
new subnet by providing the new access point and the associated
subnet prefix information when the MN is still connected to its
current subnet (i.e., PAR in Figure 1). For instance, an MN may
discover available access points using link-layer specific mechanisms
(e.g., a "scan" in WLAN) and then request subnet information
corresponding to one or more of those discovered access points. The
MN may do this after performing router discovery or at any time while
connected to its current router. The result of resolving an
identifier associated with an access point is a [AP-ID, AR-Info]
tuple, which an MN can use in readily detecting movement: when
attachment to an access point with AP-ID takes place, the MN knows
the corresponding new router's coordinates including its prefix, IP
address and L2 address. The "Router Solicitation for Proxy
Advertisement (RtSolPr)" and "Proxy Router Advertisement (PrRtAdv)"
messages in Section 6.1 are used for aiding movement detection.
Through the RtSolPr and PrRtAdv messages, the MN also formulates a
prospective new CoA (NCoA), when it is still present on the PAR's
link. Hence, the latency due to new prefix discovery subsequent to
handover is eliminated. Furthermore, this prospective address can be
used immediately after attaching to the new subnet link (i.e., NAR's
link) when the MN has received a "Fast Binding Acknowledgment
(FBack)" (see Section 6.3.2) message prior to its movement. In the
event it moves without receiving an FBack, the MN can still start
using NCoA after announcing its attachment through an unsolicited
Neighbor Advertisement message (with the 'O' bit set to zero) message
[rfc4861]; NAR responds to to this UNA message in case it wishes to
provide a different IP address to use. In this way, NCoA
configuration latency is reduced.
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The information provided in the PrRtAdv message can be used even when
DHCP [rfc3315] is used to configure an NCoA on the NAR's link. In
this case, the protocol supports forwarding using PCoA, and the MN
performs DHCP once it attaches to the NAR's link. The MN still
formulates an NCoA for FBU processing; however, it MUST NOT send data
packets using the NCoA in the FBU.
In order to reduce the Binding Update latency, the protocol specifies
a binding between the Previous CoA (PCoA) and NCoA. A MN sends a
"Fast Binding Update" (see Section 6.3.1) message to its Previous
Access Router to establish this tunnel. When feasible, the MN SHOULD
send FBU from PAR's link. Otherwise, the MN should send the FBU
immediately after detecting attachment to NAR. An FBU message MUST
contain the Binding Authorization Data for FMIPv6 (BADF) option (see
Section 6.5.4) in order to ensure that only a legitimate MN that owns
the PCoA is able to establish a binding. Subsequent sections
describe the protocol mechanics. In any case, the result is that PAR
begins tunneling packets arriving for PCoA to NCoA. Such a tunnel
remains active until the MN completes the Binding Update with its
correspondents. In the opposite direction, the MN SHOULD reverse
tunnel packets to PAR, again until it completes Binding Update. And,
PAR MUST forward the inner packet in the tunnel to its destination
(i.e., to the MN's correspondent). Such a reverse tunnel ensures
that packets containing PCoA as source IP address are not dropped due
to ingress filtering. Even though the MN is IP-capable on the new
link, it cannot use NCoA directly with its correspondents without the
correspondents first establishing a binding cache entry (for NCoA).
Forwarding support for PCoA is provided through a reverse tunnel
between the MN and the PAR.
Setting up a tunnel alone does not ensure that the MN receives
packets as soon as it is attached to a new subnet link, unless the
NAR can detect the MN's presence. A neighbor discovery operation
involving a neighbor's address resolution (i.e., Neighbor
Solicitation and Neighbor Advertisement) typically results in
considerable delay, sometimes lasting multiple seconds. For
instance, when arriving packets trigger NAR to send Neighbor
Solicitation before the MN attaches, subsequent retransmissions of
address resolution are separated by a default period of one second
each. In order to circumvent this delay, an MN announces its
attachment immediately with an UNA message that allows NAR to forward
packets to the MN right away. Through tunnel establishment for PCoA
and fast advertisement, the protocol provides expedited forwarding of
packets to the MN.
The protocol also provides the following important functionalities.
The access routers can exchange messages to confirm that a proposed
NCoA is acceptable. For instance, when an MN sends an FBU from PAR's
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link, FBack can be delivered after the NAR considers the NCoA
acceptable for use. This is especially useful when addresses are
assigned by the access router. The NAR can also rely on its trust
relationship with PAR before providing forwarding support for the MN.
That is, it may create a forwarding entry for the NCoA subject to
"approval" from PAR which it trusts. In addition, buffering for
handover traffic at NAR may be desirable. Even though the Neighbor
Discovery protocol provides a small buffer (typically one or two
packets) for packets awaiting address resolution, this buffer may be
inadequate for traffic such as VoIP already in progress. The routers
may also wish to maintain a separate buffer for servicing the
handover traffic. Finally, the access routers could transfer
network-resident contexts, such as access control, QoS, and header
compression, in conjunction with handover (although the context
transfer process itself is not specified in this document). For all
these operations, the protocol provides "Handover Initiate (HI)" and
"Handover Acknowledge (HAck)" messages (see Section 6.2). Both of
these messages SHOULD be used. The access routers MUST have
necessary security association established by means outside the scope
of this document.
3.2. Protocol Operation
The protocol begins when an MN sends an RtSolPr message to its access
router to resolve one or more Access Point Identifiers to subnet-
specific information. In response, the access router (e.g., PAR in
Figure 1) sends a PrRtAdv message containing one or more [AP-ID, AR-
Info] tuples. The MN may send a RtSolPr at any convenient time, for
instance as a response to some link-specific event (a ``trigger'') or
simply after performing router discovery. However, the expectation
is that prior to sending RtSolPr, the MN will have discovered the
available APs by link-specific methods. The RtSolPr and PrRtAdv
messages do not establish any state at the access router; their
packet formats are defined in Section 6.1.
With the information provided in the PrRtAdv message, the MN
formulates a prospective NCoA and sends an FBU message to the PAR.
The purpose of FBU is to authorize PAR to bind PCoA to NCoA, so that
arriving packets can be tunneled to the new location of the MN. The
FBU should be sent from PAR's link whenever feasible. For instance,
an internal link-specific trigger could enable FBU transmission from
the previous link.
When it is not feasible, FBU is sent from the new link.
The format and semantics of FBU processing are specified in
Section 6.3.1. The FBU message MUST contain the BADF option (see
Section 6.5.4) to secure the message.
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Depending on whether an FBack is received on the previous link (which
clearly depends on whether FBU was sent in the first place), there
are two modes of operation.
1. The MN receives FBack on the previous link. This means that
packet tunneling is already in progress by the time the MN
handovers to NAR. The MN SHOULD send UNA immediately after
attaching to NAR, so that arriving as well as buffered packets can
be forwarded to the MN right away.
Before sending FBack to MN, PAR can determine whether NCoA is
acceptable to NAR through the exchange of HI and HAck messages.
When assigned addressing (i.e., addresses are assigned by the
router) is used, the proposed NCoA in FBU is carried in HI (from
PAR to NAR), and NAR MAY assign the proposed NCoA. Such an
assigned NCoA MUST be returned in HAck (from NAR to PAR), and PAR
MUST in turn provide the assigned NCoA in FBack. If there is an
assigned NCoA returned in FBack, the MN MUST use the assigned
address (and not the proposed address in FBU) upon attaching to
NAR.
2. The MN does not receive the FBack on the previous link because
the MN has not sent the FBU or the MN has left the link after
sending the FBU (which itself may be lost), but before receiving
an FBack. Without receiving an FBack in the latter case, the MN
cannot ascertain whether PAR has successfully processed the FBU.
Hence, the MN (re)sends the FBU message to PAR immediately after
sending the UNA message. If NAR chooses to supply a different IP
address to use than the NCoA, it MAY sends a Router Advertisement
with "Neighbor Advertisement Acknowledge (NAACK)" option in which
it includes an alternate IP address for the MN to use. Detailed
UNA processing rules are specified in Section 6.4.
The scenario in which an MN sends an FBU and receives an FBack on
PAR's link is illustrated in Figure 2. For convenience, this
scenario is characterized as "predictive" mode of operation. The
scenario in which the MN sends an FBU from NAR's link is illustrated
in Figure 3. For convenience, this scenario is characterized as
"reactive" mode of operation. Note that the reactive mode also
includes the case in which an FBU has been sent from PAR's link but
an FBack has not been received yet. The Figure is intended to
illustrate that the FBU is forwarded through NAR, but it is processed
only by the PAR.
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MN PAR NAR
| | |
|------RtSolPr------->| |
|<-----PrRtAdv--------| |
| | |
|------FBU----------->|----------HI--------->|
| |<--------HAck---------|
| <--FBack---|--FBack---> |
| | |
disconnect forward |
| packets ===============>|
| | |
| | |
connect | |
| | |
|------------UNA --------------------------->|
|<=================================== deliver packets
| |
Figure 2: Predictive Fast Handover
MN PAR NAR
| | |
|------RtSolPr------->| |
|<-----PrRtAdv--------| |
| | |
disconnect | |
| | |
| | |
connect | |
|-------UNA-----------|--------------------->|
|-------FBU-----------|---------------------)|
| |<-------FBU----------)|
| |----------HI--------->|
| |<-------HAck--------->|
| |(HI/HAck if necessary)|
| forward |
| packets(including FBAck)=====>|
| | |
|<=================================== deliver packets
| |
Figure 3: Reactive Fast Handover
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Finally, the PrRtAdv message may be sent unsolicited, i.e., without
the MN first sending a RtSolPr. This mode is described in
Section 3.3.
3.3. Protocol Operation during Network-initiated Handover
In some wireless technologies, the handover control may reside in the
network even though the decision to undergo handover may be mutually
arrived at between the MN and the network. In such networks, the PAR
can send an unsolicited PrRtAdv containing the link layer address, IP
address and subnet prefix of the NAR when the network decides that a
handover is imminent. The MN MUST process this PrRtAdv to configure
a new care of address on the new subnet, and MUST send an FBU to PAR
prior to switching to the new link. After transmitting PrRtAdv, the
PAR MUST continue to forward packets to the MN on its current link
until the FBU is received. The rest of the operation is the same as
that described in Section 3.2.
The unsolicited PrRtAdv also allows the network to inform the MN
about geographically adjacent subnets without the MN having to
explicitly request that information. This can reduce the amount of
wireless traffic required for the MN to obtain a neighborhood
topology map of links and subnets. Such usage of PrRtAdv is
decoupled from the actual handover; see Section 6.1.2.
4. Protocol Details
All descriptions refer to Figure 1.
After discovering one or more nearby access points, the MN sends
RtSolPr to PAR in order to resolve access point identifiers to subnet
router information. A convenient time to do this is after performing
router discovery. However, the MN can send RtSolPr at any time,
e.g., when one or more new access points are discovered. The MN can
also send RtSolPr more than once during its attachment to PAR. The
trigger for sending RtSolPr can originate from a link-specific event,
such as the promise of a better signal strength from another access
point coupled with fading signal quality with the current access
point. Such events, often broadly referred to as "L2 triggers", are
outside the scope of this document. Nevertheless, they serve as
events that invoke this protocol. For instance, when a "link up"
indication is obtained on the new link, protocol messages (e.g., UNA)
can be immediately transmitted. Implementations SHOULD make use of
such triggers whenever available.
The RtSolPr message contains one or more AP-IDs. A wildcard requests
all available tuples.
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As a response to RtSolPr, PAR sends a PrRtAdv message which indicates
one of the following possible conditions.
1. If the PAR does not have an entry corresponding to the new
access point, it MUST respond indicating that the new access point
is unknown. The MN MUST stop fast handover protocol operations on
the current link. The MN MAY send an FBU from its new link.
2. If the new access point is connected to the PAR's current
interface (to which MN is attached), the PAR MUST respond with a
Code value indicating that the new access point is connected to
the current interface, but not send any prefix information. This
scenario could arise, for example, when several wireless access
points are bridged into a wired network. No further protocol
action is necessary.
3. If the new access point is known and the PAR has information
about it, then the PAR MUST respond indicating that the new access
point is known and supply the [AP-ID, AR-Info] tuple. If the new
access point is known, but does not support fast handover, the PAR
MUST indicate this with Code 3 (see Section 6.1.2).
4. If a wildcard is supplied as an identifier for the new access
point, the PAR SHOULD supply neighborhood [AP-ID, AR-Info] tuples
that are subject to path MTU restrictions (i.e., provide any 'n'
tuples without exceeding the link MTU).
When further protocol action is necessary, some implementations MAY
choose to begin buffering copies of incoming packets at the PAR. If
such FIFO buffering is used, the PAR MUST continue forwarding the
packets to PCoA (i.e., buffer and forward). While the protocol does
not forbid such an implementation support, care must be taken to
ensure that the PAR continues forwarding packets to the PCoA (i.e.,
uses a buffer and forward approach). The PAR SHOULD stop buffering
once it begins forwarding packets to the NCoA.
The method by which Access Routers exchange information about their
neighbors and thereby allow construction of Proxy Router
Advertisements with information about neighboring subnets is outside
the scope of this document.
The RtSolPr and PrRtAdv messages MUST be implemented by an MN and an
access router that supports fast handovers. However, when the
parameters necessary for the MN to send packets immediately upon
attaching to the NAR are supplied by the link layer handover
mechanism itself, use of above messages is optional on such links.
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After a PrRtAdv message is processed, the MN sends an FBU at a time
determined by link-specific events, and includes the proposed NCoA.
The MN SHOULD send the FBU from PAR's link whenever "anticipation" of
handover is feasible. When anticipation is not feasible or when it
has not received an FBack, the MN sends an FBU immediately after
attaching to NAR's link. In response to the FBU, the PAR establishes
a binding between PCoA ("Home Address") and NCoA, and sends the FBack
to the MN. Prior to establishing this binding, PAR SHOULD send an HI
message to NAR, and receive HAck in response. In order to determine
the NAR's address for the HI message, the PAR can perform the longest
prefix match of NCoA (in FBU) with the prefix list of neighboring
access routers. When the source IP address of the FBU is PCoA, i.e.,
the FBU is sent from the PAR's link, the HI message MUST have a Code
value set to 0; see Section 6.2.1. When the source IP address of the
FBU is not PCoA, i.e., the FBU is sent from the NAR's link, the HI
message MUST have a Code value of 1; see Section 6.2.1.
The HI message contains the PCoA, Link-Layer Address and the NCoA of
the MN. In response to processing an HI message with Code 0, the NAR
1. determines whether NCoA supplied in the HI message is unique
before beginning to defend it. It sends a DAD probe [rfc4862] for
NCoA to verify uniqueness. However, in deployments where the
probability of address collisions is considered extremely low (and
hence not an issue), the parameter DupAddrDetectTransmits (see
[rfc4862]) is set to zero on NAR, allowing it to avoid performing
DAD on NCoA. The NAR similarly sets DupAddrDetectTransmits to
zero in other deployments where DAD is not a concern. Once NCoA
is determined to be unique, NAR starts proxying [rfc4861] the
address for PROXY_ND_LIFETIME during which the MN is expected to
connect to NAR. In case there is already an NCoA present in its
data structure (for instance, it has already processed a HI
message earlier), NAR MAY verify if the LLA is the same as its own
or that of the MN itself. If so, NAR MAY allow the use of NCoA.
2. allocates NCoA for the MN when assigned addressing is used,
creates a proxy neighbor cache entry and begins defending it. The
NAR MAY allocate the NCoA proposed in HI.
3. MAY create a host route entry for PCoA (on the interface to
which the MN is attaching to) in case NCoA cannot be accepted or
assigned. This host route entry SHOULD be implemented such that
until the MN's presence is detected, either through explicit
announcement by the MN or by other means, arriving packets do not
invoke neighbor discovery. The NAR SHOULD also set up a reverse
tunnel to the PAR in this case.
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4. provides the status of the handover request in the Handover
Acknowledge (HAck) message to the PAR.
When the Code value in HI is 1, NAR MUST skip the above operations.
Sending an HI message with Code 1 allows NAR to validate the neighbor
cache entry it creates for the MN during UNA processing. That is,
NAR can make use of the knowledge that its trusted peer (i.e., PAR)
has a trust relationship with the MN.
If HAck contains an assigned NCoA, the FBack MUST include it, and the
MN MUST use the address provided in the FBack. The PAR MAY send the
FBack to the previous link as well to facilitate faster reception in
the event that the MN is still present. The result of the FBU and
FBack processing is that PAR begins tunneling the MN's packets to
NCoA. If the MN does not receive an FBack message even after
retransmitting the FBU for FBU_RETRIES, it must assume that fast
handover support is not available and stop the protocol operation.
As soon as the MN establishes link connectivity with the NAR, it
1. sends a UNA message (see Section 6.4). If the MN has not
received an FBack by the time UNA is being sent, it SHOULD send an
FBU message following the UNA message.
2. joins the all-nodes multicast group and the solicited-node
multicast group corresponding to the NCoA
3. starts a DAD probe for NCoA. See [rfc4862].
When a NAR receives a UNA message, it
1. deletes its proxy neighbor cache entry, if it exists, updates
the state to STALE [rfc4861], and forwards arriving and buffered
packets.
2. updates an entry in INCOMPLETE state [rfc4861], if it exists,
to STALE and forwards arriving and buffered packets. This would
be the case if NAR had previously sent a Neighbor Solicitation
which went unanswered perhaps because the MN had not yet attached
to the link.
The buffer for handover traffic should be linked to this UNA
processing. The exact mechanism is implementation dependent.
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The NAR may choose to provide different IP address other than the
NCoA. This is possible if it is proxying the NCoA. In such a case,
it
1. MAY send a Router Advertisement with the NAACK option in which
it includes an alternate IP address for use. This message MUST be
sent to the source IP address present in UNA using the same Layer
2 address present in UNA.
If the MN receives an IP address in the NAACK option, it MUST use it
and send an FBU using the new CoA. As a special case, the address
supplied in NAACK could be PCoA itself, in which case the MN MUST NOT
send any more FBUs. The Status codes for NAACK option are specified
in Section 6.5.5.
Once the MN has confirmed its NCoA (either through DAD or when
provided for by the NAR), it SHOULD send a Neighbor Advertisement
message with the 'O' bit set, to the all-nodes multicast address.
This message allows MN's neighbors to update their neighbor cache
entries.
For data forwarding, the PAR tunnels packets using its global IP
address valid on the interface to which the MN was attached. The MN
reverse tunnels its packets to the same global address of PAR. The
tunnel end-point addresses must be configured accordingly. When PAR
receives a reverse tunneled packet, it must verify if a secure
binding exists for the MN identified by PCoA in the tunneled packet,
before forwarding the packet.
5. Other Considerations
5.1. Handover Capability Exchange
The MN expects a PrRtAdv in response to its RtSolPr message. If the
MN does not receive a PrRtAdv message even after RTSOLPR_RETRIES, it
must assume that PAR does not support the fast handover protocol and
stop sending any more RtSolPr messages.
Even if an MN's current access router is capable of providing fast
handover support, the new access router to which the MN attaches may
be incapable of fast handover. This is indicated to the MN during
"runtime", through the PrRtAdv message with a Code value of 3 (see
Section 6.1.2).
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5.2. Determining New Care of Address
Typically, the MN formulates its prospective NCoA using the
information provided in a PrRtAdv message and sends the FBU. The PAR
MUST use the NCoA present in the FBU in its HI message. The NAR MUST
verify if the NCoA present in HI is already in use. In any case, NAR
MUST respond to HI using a HAck, in which it may include another NCoA
to use, especially when assigned address configuration is used. If
there is a CoA present in HAck, the PAR MUST include it in the FBack
message. However, the MN itself does not have to wait on PAR's link
for this exchange to take place. It can handover any time after
sending the FBU message; sometimes it may be forced to handover
without sending the FBU. In any case, it can still confirm using
NCoA from NAR's link by sending the UNA message.
If a PrRtAdv message carries an NCoA, the MN MUST use it as its
prospective NCoA.
When DHCP is used, the protocol supports forwarding for PCoA only.
In this case, the MN MUST perform DHCP operations once it attaches to
the NAR even though it formulates an NCoA for transmitting the FBU.
This is indicated in the PrRtAdv message with Code = 5.
5.3. Prefix Management
As defined in Section 2, the Prefix part of ``AR-Info'' is the prefix
valid on the interface to which the AP is attached. This document
does not specify how this Prefix is managed, it's length and
assignment policies. The protocol operation specified in this
document works regardless of these considerations. Often, but not
necessarily always, this Prefix may be the aggregate prefix (such as
/48) valid on the interface. In some deployments, each MN may have
its own per-mobile prefix (such as a /64) used for generating the
NCoA. Some point-to-point links may use such a deployment.
When per-mobile prefix assignment is used, the ``AR-Info'' advertised
in PrRtAdv still includes the (aggregate) prefix valid on the
interface to which the target AP is attached, unless the access
routers communicate with each other (using HI and HAck messages) to
manage per-mobile prefix. The MN still formulates an NCoA using the
aggregate prefix. However, an alternate NCoA based on the per-mobile
prefix is returned by NAR in the HAck message. This alternate NCoA
is provided to the MN in either the FBack message or in the NAACK
option.
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5.4. Packet Loss
Handover involves link switching, which may not be exactly co-
ordinated with fast handover signaling. Furthermore, the arrival
pattern of packets is dependent on many factors, including
application characteristics, network queuing behaviors etc. Hence,
packets may arrive at NAR before the MN is able to establish its link
there. These packets will be lost unless they are buffered by the
NAR. Similarly, if the MN attaches to NAR and then sends an FBU
message, packets arriving at PAR until FBU is processed will be lost
unless they are buffered. This protocol provides an option to
indicate request for buffering at the NAR in the HI message. When
the PAR requests this feature (for the MN), it SHOULD also provide
its own support for buffering.
Whereas buffering can enable a smooth handover, the buffer size and
the rate at which buffered packets are eventually forwarded are
important considerations when providing buffering support. For
instance, an application such as Voice over IP typically needs
smaller buffers compared to high-resolution streamig video, which has
larger packet sizes and higher arrival rates. This specification
does not restrict implementations to providing buffering support for
any specific application. However, the implementations should
recognize that the buffer size requirements are dependent on the
application characteristics (including the arrival rate, arrival
process, perceived performance loss in the event buffering is not
offered, and so on), and arrive at their own policy decisions.
Particular attention must be paid to the rate at which buffered
packets are forwarded to the MN once attachment is complete. Just as
in any network event where a router buffers packets, forwarding
buffered packets in a handover at a rate inconsistent with the policy
governing the outbound interface can cause performance degradation to
the existing sessions and connections. Implementations must take
care to prevent such occurances, just as routers do with buffered
packets on the Internet.
5.5. DAD Handling
Duplicate Address Detection (DAD) was defined in [rfc4862] to avoid
address duplication on links when stateless address auto-
configuration is used. The use of DAD to verify the uniqueness of an
IPv6 address configured through stateless auto-configuration adds
delays to a handover. The probability of an interface identifier
duplication on the same subnet is very low, however it cannot be
ignored. Hence, the protocol specified in this document SHOULD only
be used in deployments where the probability of such address
collisions is extremely low or it is not a concern (because of the
address management procedure deployed). The protocol requires the
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NAR to send a DAD probe before it starts defending NCoA. However,
this DAD delay can be turned off by setting DupAddrDetectTransmits to
zero on NAR ([rfc4862]).
This document specifies messages which can be used to provide
duplicate-free addresses but the document does not specify how to
create or manage such duplicate-free addresses. In some cases the
NAR may already have the knowledge required to assess whether the
MN's address is a duplicate or not before the MN moves to the new
subnet. For example, in some deployments, the NAR may maintain a
pool of duplicate-free addresses in a list for handover purposes. In
such cases, the NAR can provide this disposition in the HAck message
(see Section 6.2.2) or in the NAACK option (see Section 6.5.5).
5.6. Fast or Erroneous Movement
Although this specification is for fast handover, the protocol is
limited in terms of how fast an MN can move. A special case of fast
movement is ping-pong, where an MN moves between the same two access
points rapidly. Another instance of the same problem is erroneous
movement i.e., the MN receives information prior to a handover that
it is moving to a new access point but it either moves to a different
one or it aborts movement altogether. All of the above behaviors are
usually the result of link layer idiosyncrasies and thus are often
resolved at the link layer itself.
IP layer mobility, however, introduces its own limits. IP layer
handovers should occur at a rate suitable for the MN to update the
binding of, at least, its Home Agent and preferably that of every CN
with which it is in communication. An MN that moves faster than
necessary for this signaling to complete, which may be of the order
of few seconds, may start losing packets. The signaling cost over
the air interface and in the network may increase significantly,
especially in the case of rapid movement between several access
routers. To avoid the signaling overhead, the following measures are
suggested.
An MN returning to the PAR before updating the necessary bindings
when present on the NAR MUST send a Fast Binding Update with the Home
Address equal to the MN's PCoA and a lifetime of zero to the PAR.
The MN should have a security association with the PAR since it
performed a fast handover to the NAR. The PAR,up on receiving this
Fast Binding Update, will check its set of outgoing (temporary fast
handover) tunnels. If it finds a match, it SHOULD terminate that
tunnel; i.e., start delivering packets directly to the node instead.
In order for PAR to process such an FBU, the lifetime of the security
association has to be at least that of the tunnel itself.
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Temporary tunnels for the purposes of fast handovers should use short
lifetimes (of the order of atmost few tens of seconds or less). The
lifetime of such tunnels should be enough to allow a MN to update all
its active bindings. The default lifetime of the tunnel should be
the same as the lifetime value in the FBU message.
The effect of erroneous movement is typically limited to the loss of
packets since routing can change and the PAR may forward packets
toward another router before the MN actually connects to that router.
If the MN discovers itself on an unanticipated access router, it
SHOULD send a new Fast Binding Update to the PAR. This FBU
supersedes the existing binding at PAR and the packets will be
redirected to the newly confirmed location of the MN.
6. Message Formats
All the ICMPv6 messages have a common Type specified in [rfc2463].
The messages are distinguished based on the Subtype field (see
below). For all the ICMPv6 messages, the checksum is defined in
[rfc2463].
6.1. New Neighborhood Discovery Messages
6.1.1. Router Solicitation for Proxy Advertisement (RtSolPr)
Mobile Nodes send Router Solicitation for Proxy Advertisement in
order to prompt routers for Proxy Router Advertisements. All the
link-layer address options have the format defined in Section 6.5.2.
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype | Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 4: Router Solicitation for Proxy Advertisement (RtSolPr)
Message
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IP Fields:
Source Address: An IP address assigned to the sending interface
Destination Address: The address of the Access Router or the
all routers multicast address.
Hop Limit: 255. See RFC 2461.
ICMP Fields:
Type: To be assigned by IANA
Code: 0
Checksum: The ICMPv6 checksum.
Subtype: 2
Reserved: MUST be set to zero by the sender and ignored by the
receiver.
Identifier: MUST be set by the sender so that replies can be
matched to this Solicitation.
Valid Options:
Source Link-layer Address: When known, the link-layer address
of the sender SHOULD be included using the Link-Layer Address
option. See LLA option format below.
New Access Point Link-layer Address: The link-layer address or
identification of the access point for which the MN requests
routing advertisement information. It MUST be included in all
RtSolPr messages. More than one such address or identifier can
be present. This field can also be a wildcard address. See
LLA Option below.
Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options that they do not recognize
and continue processing the rest of the message.
Including the source LLA option allows the receiver to record the
sender's L2 address so that neighbor discovery can be avoided when
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the receiver needs to send packets back to the sender (of the RtSolPr
message).
When a wildcard is used for New Access Point LLA, no other New Access
Point LLA options must be present.
A Proxy Router Advertisement (PrRtAdv) message should be received by
the MN in response to a RtSolPr. If such a message is not received
in a timely manner (no less than twice the typical round trip time
(RTT) over the access link or 100 milliseconds if RTT is not known),
it SHOULD resend the RtSolPr message. Subsequent retransmissions can
be up to RTSOLPR_RETRIES, but MUST use an exponential backoff in
which the timeout period (i.e., 2xRTT or 100 milliseconds) is doubled
prior to each instance of retransmission. If Proxy Router
Advertisement is not received by the time the MN disconnects from the
PAR, the MN SHOULD send an FBU immediately after configuring a new
CoA.
When RtSolPr messages are sent more than once, they MUST be rate
limited with MAX_RTSOLPR_RATE per second. During each use of a
RtSolPr, exponential backoff is used for retransmissions.
6.1.2. Proxy Router Advertisement (PrRtAdv)
Access routers send Proxy Router Advertisement messages gratuitously
if the handover is network-initiated or as a response to a RtSolPr
message from an MN, providing the Link-Layer Address, IP address, and
subnet prefixes of neighboring routers. All the link-layer address
options have the format defined in 6.4.3.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype | Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 5: Proxy Router Advertisement (PrRtAdv) Message
IP Fields:
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Source Address: MUST be the link-local address assigned to the
interface from which this message is sent.
Destination Address: The Source Address of an invoking Router
Solicitation for Proxy Advertisement or the address of the node
the Access Router is instructing to handover.
Hop Limit: 255. See RFC 2461.
ICMP Fields:
Type: To be assigned by IANA
Code: 0, 1, 2, 3, 4 or 5. See below.
Checksum: The ICMPv6 checksum.
Subtype: 3
Reserved: MUST be set to zero by the sender and ignored by the
receiver.
Identifier: Copied from Router Solicitation for Proxy
Advertisement or set to Zero if unsolicited.
Valid Options in the following order:
Source Link-layer Address: When known, the link-layer address
of the sender SHOULD be included using the Link-Layer Address
option. See LLA option format below.
New Access Point Link-layer Address: The link-layer address or
identification of the access point is copied from RtSolPr
message. This option MUST be present.
New Router's Link-layer Address: The link-layer address of the
Access Router for which this message is proxied for. This
option MUST be included when Code is 0 or 1.
New Router's IP Address: The IP address of NAR. This option
MUST be included when Code is 0 or 1.
New Router Prefix Information Option: Specifies the prefix of
the Access Router the message is proxied for and is used for
address auto-configuration. This option MUST be included when
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Code is 0 or 1. However, when this prefix is the same as what
is used in the New Router's IP Address option (above), the
Prefix Information option need not be present.
New CoA Option: MAY be present when PrRtAdv is sent
unsolicited. PAR MAY compute new CoA using NAR's prefix
information and the MN's L2 address, or by any other means.
Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognize and
continue processing the message.
Currently, Code values 0, 1, 2, 3, 4 and 5 are defined.
A Proxy Router Advertisement with Code 0 means that the MN should use
the [AP-ID, AR-Info] tuple (present in the options above) for
movement detection and NCoA formulation. The Option-Code field in
the New Access Point LLA option in this case is 1 reflecting the LLA
of the access point for which the rest of the options are related.
Multiple tuples may be present.
A Proxy Router Advertisement with Code 1 means that the message is
sent unsolicited. If a New CoA option is present following the New
Router Prefix Information option, the MN MUST use the supplied NCoA
and send FBU immediately or else stand to lose service. This message
acts as a network-initiated handover trigger; see Section 3.3. The
Option-Code field in the New Access Point LLA option (see below) in
this case is 1 reflecting the LLA of the access point for which the
rest of the options are related.
A Proxy Router Advertisement with Code 2 means that no new router
information is present. Each New Access Point LLA option contains an
Option-Code value (described below) that indicates a specific
outcome.
When the Option-Code field in the New Access Point LLA option is
5, handover to that access point does not require a change of CoA.
This would be the case, for instance, when a number of access
points are connected to the same router interface, or when network
based mobility management mechanisms ensure that the specific
mobile node always observes the same prefix regardless of whether
there is a separate router attached to the target access point.
No other options are required in this case.
When the Option-Code field in the New Access Point LLA option is
6, the PAR is not aware of the Prefix Information requested. The
MN SHOULD attempt to send an FBU as soon as it regains
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connectivity with the NAR. No other options are required in this
case.
When the Option-Code field in the New Access Point LLA option is
7, it means that the NAR does not support fast handover. The MN
MUST stop fast handover protocol operations. No other options are
required in this case.
A Proxy Router Advertisement with Code 3 means that new router
information is only present for a subset of access points requested.
The Option-Code field values (defined above including a value of 1)
distinguish different outcomes for individual access points.
A Proxy Router Advertisement with Code 4 means that the subnet
information regarding neighboring access points is sent unsolicited,
but the message is not a handover trigger, unlike when the message is
sent with Code 1. Multiple tuples may be present.
A Proxy Router Advertisement with Code 5 means that the MN may use
the new router information present for detecting movement to a new
subnet, but the MN must perform DHCP [rfc3315] upon attaching to the
NAR's link. The PAR and NAR will forward packets to the PCoA of the
MN. The MN must still formulate an NCoA for transmitting FBU (using
the information sent in this message), but that NCoA will not be used
for forwarding packets.
When a wildcard AP identifier is supplied in the RtSolPr message, the
PrRtAdv message should include any 'n' [Access Point Identifier,
Link-layer address option, Prefix Information Option] tuples
corresponding to the PAR's neighborhood.
6.2. Inter-Access Router Messages
6.2.1. Handover Initiate (HI)
The Handover Initiate (HI) is an ICMPv6 message sent by an Access
Router (typically PAR) to another Access Router (typically NAR) to
initiate the process of an MN's handover.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype |S|U| Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 6: Handover Initiate (HI) Message
IP Fields:
Source Address: The IP address of the PAR
Destination Address: The IP address of the NAR
ICMP Fields:
Type: To be assigned by IANA
Code: 0 or 1. See below
Checksum: The ICMPv6 checksum.
Subtype: 4
'S' flag: Assigned address configuration flag. When set, this
message requests a new CoA to be returned by the destination.
May be set when Code = 0. MUST be 0 when Code = 1.
'U' flag: Buffer flag. When set, the destination SHOULD buffer
any packets toward the node indicated in the options of this
message. Used when Code = 0, SHOULD be set to 0 when Code = 1.
Reserved: MUST be set to zero by the sender and ignored by the
receiver.
Identifier: MUST be set by the sender so replies can be matched
to this message.
Valid Options:
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Link-layer address of MN: The link-layer address of the MN that is
undergoing handover to the destination (i.e., NAR). This option
MUST be included so that the destination can recognize the MN.
Previous Care of Address: The IP address used by the MN while
attached to the originating router. This option SHOULD be
included so that a host route can be established if necessary.
New Care of Address: The IP address the MN wishes to use when
connected to the destination. When the `S' bit is set, the NAR
MAY assign this address.
The PAR uses a Code value of 0 when it processes an FBU with PCoA as
source IP address. The PAR uses a Code value of 1 when it processes
an FBU whose source IP address is not PCoA.
If a Handover Acknowledge (HAck) message is not received as a
response in a short time period (no less than twice the typical round
trip time (RTT) between source and destination, or 100 milliseconds
if RTT is not known), the Handover Initiate SHOULD be resent.
Subsequent retransmissions can be up to HI_RETRIES, but MUST use
exponential backoff in which the timeout period (i.e., 2xRTT or 100
milliseconds) is doubled during each instance of retransmission.
6.2.2. Handover Acknowledge (HAck)
The Handover Acknowledgment message is a new ICMPv6 message that MUST
be sent (typically by NAR to PAR) as a reply to the Handover Initiate
message.
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype | Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 7: Handover Acknowledge (HAck) Message
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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.
ICMP Fields:
Type: To be assigned by IANA
Code:
0: Handover Accepted, NCoA valid
1: Handover Accepted, NCoA not valid or in use
2: Handover Accepted, NCoA assigned (used in Assigned
addressing)
3: Handover Accepted, use PCoA
4: Message sent unsolicited, usually to trigger a HI message
128: Handover Not Accepted, reason unspecified
129: Administratively prohibited
130: Insufficient resources
Checksum: The ICMPv6 checksum.
Subtype: 5
Reserved: MUST be set to zero by the sender and ignored by the
receiver.
Identifier: Copied from the corresponding field in the Handover
Initiate message to which this message is a response.
Valid Options:
New Care of Address: If the S flag in the Handover Initiate message
is set, this option MUST be used to provide NCoA the MN should use
when connected to this router. This option MAY be included, even
when the 'S' bit is not set, e.g., Code 2 above.
Upon receiving a HI message, the NAR MUST respond with a Handover
Acknowledge message. If the `S' flag is set in the HI message, the
NAR SHOULD include the New Care of Address option and a Code 3.
The NAR MAY provide support for PCoA (instead of accepting or
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assigning NCoA), establish a host route entry for PCoA, and set up a
tunnel to the PAR to forward MN's packets sent with PCoA as source IP
address. This host route entry SHOULD be used to forward packets
once the NAR detects that the particular MN is attached to its link.
The NAR indicates forwarding support for PCoA using Code value 3 in
the HAck message. Subsequently, PAR establishes a tunnel to NAR in
order to forward packets arriving for PCoA.
When responding to a HI message containing a Code value 1, the Code
values 1, 2, and 4 in the HAck message are not relevant.
Finally, the new access router can always refuse handover, in which
case it should indicate the reason in one of the available Code
values.
6.3. New Mobility Header Messages
Mobile IPv6 uses a new IPv6 header type called Mobility Header
[rfc3775]. The Fast Binding Update, Fast Binding Acknowledgment and
the (deprecated) Fast Neighbor Advertisement messages use the
Mobility Header.
6.3.1. Fast Binding Update (FBU)
The Fast Binding Update message is identical to the Mobile IPv6
Binding Update (BU) message. However, the processing rules are
slightly different.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Fast Binding Update (FBU) Message
IP Fields:
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Source address: The PCoA or NCoA
Destination Address: The IP address of the Previous Access
Router
`A' flag: MUST be set to one to request that PAR send a Fast
Binding Acknowledgment message.
`H' flag: MUST be set to one. See [rfc3775].
`L' flag: See [rfc3775].
`K' flag: See [rfc3775].
Reserved: This field is unused. MUST be set zero.
Sequence Number: See See [rfc3775].
Lifetime: The requested time in seconds for which the sender
wishes to have a binding.
Mobility Options: MUST contain an alternate CoA option set to the
NCoA when an FBU is sent from PAR's link. MUST contain the
Binding Authorization Data for FMIP (BADF) option. See
Section 6.5.4. MAY contain the Mobility Header LLA option (see
Section 6.5.3).
The MN sends an FBU message any time after receiving a PrRtAdv
message. If the MN moves prior to receiving a PrRtAdv message, it
SHOULD send an FBU to the PAR after configuring NCoA on the NAR
according to Neighbor Discovery and IPv6 Address Configuration
protocols. When the MN moves without having received a PrRtAdv
message, it cannot transmit a UNA message upon attaching to the NAR's
link.
The source IP address is PCoA when the FBU is sent from PAR's link,
and the source IP address is NCoA when the FBU sent from NAR's link.
When source IP address is PCoA, the MN MUST include the alternate CoA
option set to NCoA. The PAR MUST process the FBU even though the
address in the alternate CoA option is different from that in the
source IP address, and ensure that the address in the alternate CoA
option is used in the New CoA option in the HI message to NAR.
The FBU MUST also include the Home Address Option set to PCoA. An
FBU message MUST be protected so that PAR is able to determine that
the FBU message is sent by an MN that legitimately owns the PCoA.
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6.3.2. Fast Binding Acknowledgment (FBack)
The Fast Binding Acknowledgment message is sent by the PAR to
acknowledge receipt of a Fast Binding Update message in which the `A'
bit is set. If PAR sends a HI message to the NAR after processing an
FBU, the FBack message SHOULD NOT be sent to the MN before the PAR
receives a HAck message from the NAR. The PAR MAY send the FBack
immediately in the reactive mode however. The Fast Binding
Acknowledgment MAY also be sent to the MN on the old link.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status |K| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Fast Binding Acknowledgment (FBack) Message
IP Fields:
Source address: The IP address of the Previous Access Router
Destination Address: The NCoA, and optionally PCoA
Status: 8-bit unsigned integer indicating the disposition of the
Fast Binding Update. Values of the Status field that are less
than 128 indicate that the Binding Update was accepted by the
receiving node. The following such Status values are currently
defined:
0 Fast Binding Update accepted
1 Fast Binding Update accepted but NCoA is invalid. Use NCoA
supplied in "alternate" CoA
Values of the Status field greater than or equal to 128 indicate
that the Binding Update was rejected by the receiving node. The
following such Status values are currently defined:
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128: Reason unspecified
129: Administratively prohibited
130: Insufficient resources
131: Incorrect interface identifier length
`K' flag: See See [rfc3775].
Reserved: An unused field. MUST be set to zero.
Sequence Number: Copied from FBU message for use by the MN in
matching this acknowledgment with an outstanding FBU.
Lifetime: The granted lifetime in seconds for which the sender of
this message will retain a binding for traffic redirection.
Mobility Options: MUST contain "alternate" CoA if Status is 1.
MUST contain the Binding Authorization Data for FMIP (BADF)
option. See 6.4.5.
6.4. Unsolicited Neighbor Advertisement (UNA)
This is the same message as in [rfc4861] with the requirement that
the 'O' bit is always set to zero. Since this is an unsolicited
message, the 'S' bit is zero, and since this is sent by an MN, the
'R' bit is also zero.
If NAR is proxying the NCoA (as a result of HI and HAck exchange),
then UNA processing has additional steps (see below). If NAR is not
proxying the NCoA (for instance, HI and HAck exchange has not taken
place), then UNA processing follows the same procedure as specified
in [rfc4861]. Implementations MAY retransmit UNA subject to the
specification in [rfc4861] (Section 7.2.6) while noting that the
default RetransTimer value is large for handover purposes.
The Source Address in UNA MUST be the NCoA. The Destination Address
is typically the all-nodes multicast address; however, some
deployments may not prefer transmission to a multicast address. In
such cases, the Destination Address SHOULD be the NAR's IP address.
The Target Address MUST include the NCoA, and Target link-layer
address MUST include the MN's LLA.
The MN sends a UNA message to the NAR, as soon as it regains
connectivity on the new link. Arriving or buffered packets can be
immediately forwarded. If NAR is proxying NCoA, it creates a
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neighbor cache entry in STALE state but forwards packets as it
determines bidirectional reachability according to the standard
Neighbor Discovery procedure. If there is an entry in INCOMPLETE
state without a link-layer address, it sets it to STALE, again
according to the procedure in [rfc4861].
The NAR MAY wish to provide a different IP address to the MN than the
one in UNA message. In such a case, NAR MUST delete the proxy entry
for NCoA and send a Router Advertisement with NAACK option containing
the new IP address.
The combination of NCoA (present in source IP address) and the Link-
Layer Address (present as a Target LLA) SHOULD be used to distinguish
the MN from other nodes.
6.5. New Options
All the options, with the exception of Binding Data Authorization for
FMIPv6 (BADF) discussed in Section 6.5.4, use Type, Length and
Option-Code format shown in Figure 10.
The Type values are defined from the Neighbor Discovery options
space. The Length field is in units of 8 octets, except for the
Mobility Header Link-Layer Address option, whose Length field is in
units of octets in accordance with Section 6.2 in [rfc3775]. And,
Option-Code provides additional information for each of the options
(see individual options below).
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 | Option-Code | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Option Format
6.5.1. IP Address/Prefix Option
This option is sent in the Proxy Router Advertisement, the Handover
Initiate, and Handover Acknowledge messages.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Option-Code | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: IPv6 Address/Prefix Option
Type: 17
Length: The size of this option in 8 octets including the Type,
Option-Code and Length fields.
Option-Code:
1: Old Care-of Address
2: New Care-of Address
3: NAR's IP address
4: NAR's Prefix, sent in PrRtAdv. The Prefix Length field
contains the number of valid leading bits in the prefix. The
bits in the prefix after the prefix length are reserved and
MUST be initialized to zero by the sender and ignored by the
receiver.
Prefix Length: 8-bit unsigned integer that indicates the length of
the IPv6 Address Prefix. The value ranges from 0 to 128.
Reserved: MUST be set to zero by the sender and MUST be ignored by
the receiver.
IPv6 address: The IP address defined by the Option-Code field.
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6.5.2. Link-layer Address (LLA) Option
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 | Option-Code | LLA...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Link-Layer Address Option
Type: 19
Length: The size of this option in 8 octets including the Type,
Option-Code and Length fields.
Option-Code:
0: wildcard requesting resolution for all nearby access points
1: Link-layer Address of the New Access Point
2: Link-layer Address of the MN
3: Link-layer Address of the NAR (i.e., Proxied Originator)
4: Link-layer Address of the source of RtSolPr or PrRtAdv
message
5: The access point identified by the LLA belongs to the
current interface of the router
6: No prefix information available for the access point
identified by the LLA
7: No fast handovers support available for the access point
identified by the LLA
LLA: The variable length link-layer address.
The LLA Option does not have a length field for the LLA itself. The
implementations must consult the specific link layer over which the
protocol is run in order to determine the content and length of the
LLA.
Depending on the size of individual LLA option, appropriate padding
MUST be used to ensure that the entire option size is a multiple of 8
octets.
The New Access Point Link Layer address contains the link-layer
address of the access point for which handover is about to be
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attempted. This is used in the Router Solicitation for Proxy
Advertisement message.
The MN Link-Layer address option contains the link-layer address of
an MN. It is used in the Handover Initiate message.
The NAR (i.e., Proxied Originator) Link-Layer address option contains
the Link Layer address of the Access Router for which the Proxy
Router Solicitation message refers to.
6.5.3. Mobility Header Link-layer Address (MH-LLA) Option
This option is identical to the LLA option, but is carried in the
Mobility Header messages, e.g., FBU. In the future, other Mobility
Header messages may also make use of this option. The format of the
option is shown in Figure 13. There are no alignment requirements
for this option.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option-Code | LLA ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Mobility Header Link-Layer Address Option
Type: 7
Length: The size of this option in octets not including the Type
and Length fields.
Option-Code: 2 Link-layer Address of the MN
LLA: The variable length link-layer address.
6.5.4. Binding Authorization Data for FMIPv6 (BADF)
This option MUST be present in FBU and FBack messages. The security
association between the MN and the PAR is established by companion
protocols [rfc-ho-send]. This option specifies how to compute and
verify a MAC using the established security association.
The format of this option is shown in Figure 14.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Authenticator |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Binding Authorization Data for FMIPv6 (BADF) Option
Type: To be assigned by IANA
Option Length: The length of the Authenticator in bytes
SPI: Security Parameter Index. SPI = 0 is reserved for the
Authenticator computed using SEND-based handover keys.
Authenticator: Same as in RFC 3775, with "correspondent" replaced
by PAR's IP address, and Kbm replaced by the shared key between
the MN and the PAR.
The default MAC calculation is done using HMAC_SHA1 with the first 96
bits used for the MAC. Since there is an Option Length field,
implementations can use other algorithms such as HMAC_SHA256 for
instance.
This option MUST be the last Mobility Option present.
6.5.5. Neighbor Advertisement Acknowledgment (NAACK)
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 | Option-Code | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 15: Neighbor Advertisement Acknowledgment Option
Type: 20
Length: 8-bit unsigned integer. Length of the option, in 8
octets. The length is 1 when a new CoA is not supplied. The
length is 3 when a new CoA is present (immediately following the
Reserved field)
Option-Code: 0
Status: 8-bit unsigned integer indicating the disposition of the
Unsolicited Neighbor Advertisement message. The following Status
values are currently defined:
1: NCoA is invalid, perform address configuration
2: NCoA is invalid, use the supplied NCoA. The supplied NCoA
(in the form of an IP Address Option) MUST be present following
the Reserved field.
3: NCoA is invalid, use NAR's IP address as NCoA in FBU
4: PCoA supplied, do not send FBU
128: Link Layer Address unrecognized
Reserved: MUST be set to zero by the sender and MUST be ignored by
the receiver.
The NAR responds to UNA with the NAACK option to notify the MN to use
a different NCoA than the one that the MN has used. If the NAR
proposes a different NCoA, the Router Advertisement MUST use the
source IP address in the UNA message as the destination address, and
use the L2 address present in UNA. The MN MUST use the NCoA if it is
supplied with the NAACK option. If the NAACK indicates that the Link
Layer Address is unrecognized, for instance if the MN uses an LLA
valid on PAR's link but the same LLA is not valid on NAR's link due
to a different access technology, the MN MUST NOT use the NCoA or the
PCoA and SHOULD start immediately the process of acquiring different
NCoA at the NAR.
In the future, new option types may be defined.
7. Related Protocol and Device Considerations
The protocol specified here, as a design principle, introduces no or
minimal changes to related protocols. For example, no changes to the
base Mobile IPv6 protocol are needed in order to implement this
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protocol. Similarly, no changes to the IPv6 stateless address
autoconfiguration protocol [rfc4862] and DHCP [rfc3315] are
introduced. The protocol specifies an optional extension to Neighbor
Discovery [rfc4861] in which an access router may send a router
advertisement as a response to the UNA message (see Section
Section 6.4). Other than this extension, the specification does not
modify Neighbor Discovery behavior (including the procedures
performed when attached to the PAR and when attaching to the NAR).
The protocol does not require changes to any intermediate layer 2
device between an MN and its access router which support this
specification. This includes the wireless access points, switches,
snooping devices and so on.
8. Evolution from and Compatibility with RFC 4068
This document has evolved from [rfc4068]. Specifically, a new
handover key establishment protocol (see [rfc-ho-send]) has been
defined to enable a security association between a mobile node and
its access router. This allows secure update of routing of packets
during a handover. In the future, new specifications may be defined
to establish such security associations depending on the particular
deployment scenario.
The protocol has improved from the experiences in implementing
[rfc4068], and from experimental usage. The input has improved the
specification of parameter fields (such as lifetime, codepoints etc.)
as well as inclusion of new parameter fields in the existing
messages. As of this writing, there are two publicly available
implementations [fmipv6], [tarzan] and multiple proprietary
implementations. Some experience suggests that the protocol meets
the delay and packet loss requirements when used appropriately with
particular radio access protocols. For instance, see [l2abs], and
[mip6-book]. Nevertheless, it is important to recognize that
handover performance is a function of both IP layer operations, which
this protocol specifies, and the particular radio access technology
itself, which this protocol relies upon but does not modify.
An existing implementation of [rfc4068] needs to be updated in order
to support this specification. The primary addition is the
establishment of a security association between an MN and its access
router (i.e., MN and PAR). One way to establish such a security
association is specified in [rfc-ho-send]. An implementation that
complies with the specification in this document is likely to also
work with [rfc4068], except for the Binding Authorization Data for
FMIPv6 option (see Section 6.5.4) which can only be processed when
security association is in place between a mobile node and its access
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router. This specification deprecates the Fast Neighbor
Advertisement (FNA) message. However, it is acceptable for a NAR to
process this message from a mobile node as specified in [rfc4068].
9. Configurable Parameters
Mobile nodes rely on configuration parameters shown in the table
below. Each mobile node MUST have a configuration mechanism to
adjust the parameters. Such a configuration mechanism may be either
local (such as a command line interface) or based on central
management of a number of mobile nodes.
+-------------------+---------------+---------------+
| Parameter Name | Default Value | Definition |
+-------------------+---------------+---------------+
| RTSOLPR_RETRIES | 3 | Section 6.1.1 |
| MAX_RTSOLPR_RATE | 3 | Section 6.1.1 |
| FBU_RETRIES | 3 | Section 6.3.1 |
| PROXY_ND_LIFETIME | 1.5 seconds | Section 6.2.2 |
| HI_RETRIES | 3 | Section 6.2.1 |
+-------------------+---------------+---------------+
10. Security Considerations
The following security vulnerabilities are identified, and suggested
solutions are mentioned.
Insecure FBU: in this case, packets meant for one address could be
stolen, or redirected to some unsuspecting node. This concern is
the same as that in an MN and Home Agent relationship.
Hence, the PAR MUST ensure that the FBU packet arrived from a node
that legitimately owns the PCoA. The access router and its hosts
may use any available mechanism to establish a security
association that MUST be used to secure FBU. The current version
of this protocol relies on a companion protocol [rfc-ho-send] to
establish such a security association. Using the shared handover
key from [rfc-ho-send], the Authenticator in BADF option (see
Section 6.5.4) MUST be computed, and the BADF option included in
FBU and FBack messages.
Secure FBU, malicious or inadvertent redirection: in this case,
the FBU is secured, but the target of binding happens to be an
unsuspecting node either due to inadvertent operation or due to
malicious intent. This vulnerability can lead to an MN with a
genuine security association with its access router redirecting
traffic to an incorrect address.
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However, the target of malicious traffic redirection is limited to
an interface on an access router with which the PAR has a security
association. The PAR MUST verify that the NCoA to which PCoA is
being bound actually belongs to NAR's prefix. In order to do
this, HI and HAck message exchanges are to be used. When NAR
accepts NCoA in HI (with Code = 0), it proxies NCoA so that any
arriving packets are not sent on the link until the MN attaches
and announces itself through UNA. Therefore, any inadvertent or
malicious redirection to a host is avoided. It is still possible
to jam NAR's buffer with redirected traffic. However, since NAR's
handover state corresponding to NCoA has a finite (and short)
lifetime corresponding to a small multiple of anticipated handover
latency, the extent of this vulnerability is arguably small.
Sending an FBU from NAR's link: A malicious node may send an FBU
from NAR's link providing an unsuspecting node's address as NCoA.
This is similar to base Mobile IP where the MN can provide some
other node's IP address as its CoA to its Home Agent; here the PAR
acts like a "temporary Home Agent" having a security association
with the Mobile Node, and providing forwarding support for the
handover traffic. As in base Mobile IP, this misdelivery is
traceable to the MN which has a security association with the
router. So, it is possible to isolate such an MN if it continues
to misbehave. Similarly, a MN which has a security association
with the PAR may provide the LLA of some other node on NAR's link,
which can cause misdelivery of packets (meant for NCoA) to an
unsuspecting node. It is possible to trace the MN in this case as
well.
Apart from the above, the RtSolPr (Section 6.1.1) and PrRtAdv
(Section 6.1.2) messages inherit the weaknesses of Neighbor Discovery
protocol [rfc4861]. Specifically, when its access router is
compromised, the MN's RtSolPr message may be answered by an attacker
that provides a rogue router as the resolution. Should the MN attach
to such a rogue router, its communication can be compromised.
Similarly, a network-initiated PrRtAdv message (see Section 3.3) from
an attacker could cause an MN to handover to a rogue router. Where
these weaknesses are a concern, a solution such as Secure Neighbor
Discovery (SEND) [rfc3971] SHOULD be considered.
The protocol provides support for buffering packets during an MN's
handover. This is done by securely exchanging the Handover Initiate
(HI) and Handover Acknowledgment (HAck) messages in response to the
FBU message from an MN. It is possible that an MN may fail, either
inadvertantly or purposely, to undergo handover to NAR which
typically provides buffering support. This can cause the NAR to
waste its memory containing the buffered packets, and in the worst
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case could create resource exhaustion concerns. Hence,
implementations must limit the size of the buffer as a local policy
configuration which may consider parameters such as the average
handover delay, expected size of packets and so on.
The Handover Initiate (HI) and Handover Acknowledgement (HAck)
messages exchanged between the PAR and NAR MUST be protected using
end-to-end security association(s) offering integrity and data origin
authentication.
The PAR and the NAR MUST implement IPsec [rfc4301] for protecting the
HI and HAck messages. IPsec ESP [rfc4303] in transport mode with
mandatory integrity protection SHOULD be used for protecting the
signaling messages. Confidentiality protection of these messages is
not required.
The security associations can be created by using either manual IPsec
configuration or a dynamic key negotiation protocol such as IKEv2
[rfc4306]. If IKEv2 is used, the PAR and the NAR can use any of the
authentication mechanisms, as specified in RFC 4306, for mutual
authentication. However, to ensure a baseline interoperability, the
implementations MUST support shared secrets for mutual
authentication. The following sections describe the Peer
Authorization Database (PAD) and Security Policy Database (SPD)
entries specified in [rfc4301] when IKEv2 is used for setting up the
required IPsec security associations.
10.1. Peer Authorization Database Entries when using IKEv2
This section describes PAD entries on the PAR and the NAR. The PAD
entries are only example configurations. Note that the PAD is a
logical concept and a particular PAR or NAR implementation can
implement the PAD in any implementation specific manner. The PAD
state may also be distributed across various databases in a specific
implementation.
PAR PAD:
- IF remote_identity = nar_identity_1
THEN authenticate (shared secret/certificate/EAP) and authorize
CHILD_SA for remote address nar_address_1
NAR PAD:
- IF remote_identity = par_identity_1
THEN authenticate (shared secret/certificate/EAP) and authorize
CHILD_SAs for remote address par_address_1
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The list of authentication mechanisms in the above examples is not
exhaustive. There could be other credentials used for authentication
stored in the PAD.
10.2. Security Policy Database Entries
This section describes the security policy entries on the PAR and the
NAR required to protect the HI and HAck messages. The SPD entries
are only example configurations. A particular PAR or NAR
implementation could configure different SPD entries as long as they
provide the required security.
In the examples shown below, the identity of the PAR is assumed to be
par_1, the address of the PAR is assumed to be par_address_1, and the
address of the NAR is assumed to be nar_address_1.
PAR SPD-S:
- IF local_address = par_address_1 & remote_address =
nar_address_1 & proto = ICMPv6 & local_icmpv6_type = HI &
remote_icmpv6_type = HAck
THEN use SA ESP transport mode Initiate using IDi = par_1 to
address nar_address_1
NAR SPD-S:
- IF local_address = nar_address_1 & remote_address =
par_address_1 & proto = ICMPv6 & local_icmpv6_type = HAck &
remote_icmpv6_type = HI
THEN use SA ESP transport mode
11. IANA Considerations
This document defines the following ICMPv6 messages, all of which can
share a single ICMPv6 Type from the registry in
http://www.iana.org/assignments/icmpv6-parameters.
+------+-------------+---------------+
| Type | Description | Reference |
+------+-------------+---------------+
| TBD | RtSolPr | Section 6.1.1 |
| TBD | PrRtAdv | Section 6.1.2 |
| TBD | HI | Section 6.2.1 |
| TBD | HAck | Section 6.2.2 |
+------+-------------+---------------+
The document defines a new Mobility Option which needs Type
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assignment from the Mobility Options Type registry at
http://www.iana.org/assignments/mobility-parameters:
1. Binding Authorization Data for FMIPv6 (BADF) option, described
in Section 6.5.4
The document has already received Type assignments for the following
(see [rfc4068]):
The document defines the following Neighbor Discovery [rfc4861]
options which have received Type assignment from IANA.
+---------+-----------------------------------------+---------------+
| Subtype | Description | Reference |
+---------+-----------------------------------------+---------------+
| 17 | IP Address/Prefix Option | Section 6.5.1 |
| 19 | Link-layer Address Option | Section 6.5.2 |
| 20 | Neighbor Advertisement Acknowledgment | Section 6.5.5 |
| | Option | |
+---------+-----------------------------------------+---------------+
The document defines the following Mobility Header messages which
have received Type allocation from the Mobility Header Types registry
at http://www.iana.org/assignments/mobility-parameters:
1. Fast Binding Update, described in Section 6.3.1
2. Fast Binding Acknowledgment, described in Section 6.3.2
The document defines the following Mobility Option which has received
Type assignment from the Mobility Options Type registry at
http://www.iana.org/assignments/mobility-parameters:
1. Mobility Header Link-Layer Address option, described in
Section 6.5.3
12. Acknowledgments
The editor would like to thank all those who have provided feedback
on this specification, but can only mention a few here: Vijay
Devarapalli, Youn-Hee Han, Emil Ivov, Syam Madanapalli, Suvidh
Mathur, Andre Martin, Javier Martin, Koshiro Mitsuya, Gabriel
Montenegro, Takeshi Ogawa, Sun Peng, YC Peng, Alex Petrescu, Domagoj
Premec, Subba Reddy, K. Raghav, Ranjit Wable and Jonathan Wood.
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Behcet Sarikaya and Frank Xia are acknowledged for the feedback on
operation over point-point links. The editor would like to
acknowledge a contribution from James Kempf to improve this
specification. Vijay Devarapalli provided text for the security
configuration between access routers in Section 10. Thanks to Jari
Arkko for the detailed AD Review which has improved this document.
The editor would also like to thank the [mipshop] working group chair
Gabriel Montenegro and the erstwhile [mobile ip] working group chairs
Basavaraj Patil and Phil Roberts for providing much support for this
work.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[rfc-ho-send]
Kempf, J. and R. Koodli, "Distributing a Symmetric FMIPv6
Handover Key using SEND (work in progress)",
September 2007.
[rfc2463] Conta, A. and S. Deering, "Internet Control Message
Protocol (ICMPv6) for the Internet Protocol Version 6
(IPv6) Specification", RFC 2463, December 1998,
<ftp://ftp.isi.edu/in-notes/rfc2463>.
[rfc3315] Droms (Editor), R., "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, July 2003,
<ftp://ftp.isi.edu/in-notes/rfc3315>.
[rfc3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004,
<ftp://ftp.isi.edu/in-notes/rfc3775>.
[rfc4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005,
<ftp://ftp.isi.edu/in-notes/rfc4301>.
[rfc4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005,
<ftp://ftp.isi.edu/in-notes/rfc4303>.
[rfc4306] Kaufman (Editor), C., "Internet Key Exchange (IKEv2)
Protocol", RFC 4306, December 2005,
<ftp://ftp.isi.edu/in-notes/rfc4306>.
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[rfc4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP Version 6 (IPv6)", RFC 4861,
September 2007, <ftp://ftp.isi.edu/in-notes/rfc4861>.
[rfc4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007,
<ftp://ftp.isi.edu/in-notes/rfc4862>.
13.2. Informative References
[fmipv6] "http://fmipv6.org", .
[l2abs] Teraoka, F., Gogo, K., Mitsuya, K., Shibui, R., and K.
Mitani, "Unified L2 Abstractions for L3-Driven Fast
Handover", , February 2008.
[mip6-book]
Koodli, R. and C. Perkins, "Mobile Internetworking with
IPv6, Chapter 22, John Wiley & Sons.", , July 2007.
[rfc3971] Arkko (Editor), J., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[rfc4065] Kempf, J., "Instructions for Seamoby and Experimental
Mobility Protocol IANA Allocations", RFC 4065, June 2004.
[rfc4068] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068,
July 2005.
[tarzan] "http://software.nautilus6.org/TARZAN/", .
Appendix A. Contributors
This document has its origins in the fast handover design team in the
erstwhile [mobile ip] working group. The members of this design team
in alphabetical order were; Gopal Dommety, Karim El-Malki, Mohammed
Khalil, Charles Perkins, Hesham Soliman, George Tsirtsis and Alper
Yegin.
Appendix B. Changes Since RFC 4068
Following are the major changes and clarifications:
o Specified security association between the MN and its Access
Router in the companion document [rfc-ho-send].
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o Specified Binding Authorization Data for Fast Handovers (BADF)
option to carry the security parameters used for verifying the
authenticity of FBU and FBack messages. The handover key used for
computing the Authenticator is specified in companion documents.
o Specified the security configuration for inter - access router
signaling (HI, HAck).
o Added a section on prefix management between access routers and
illustrated protocol operation over point-point links.
o Deprecated FNA, which is a Mobility Header message. In its
place, the Unsolicited Neighbor Advertisement (UNA) message from
RFC 4861 is used.
o Combined the IPv6 Address Option and IPv6 Prefix Option.
o Added description of DAD requirement on NAR when determining
NCoA uniqueness - Section 'Protocol Details'.
o Added a new code value for gratuitous HAck message to trigger a
HI message.
o Added Option-Code 5 in PrRtAdv message to indicate NETLMM usage
o Clarified protocol usage when DHCP is used for NCoA formulation
(Sections 6.1.2, 3.1, 5.2). Added a new Code value (5) in PrRtAdv
(Section 6.1.2).
o Clarified that IPv6 Neighbor Discovery operations are a must in
'Related Proto Considerations'.
o Clarified "PAR = temporary HA" for FBUs sent by a genuine MN to
an unsuspecting CoA.
Author's Address
Rajeev Koodli (Editor)
Starent Networks
USA
Email: rkoodli@starentnetworks.com
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