Monami6 Working Group R. Wakikawa
Internet-Draft Keio University
Expires: April 4, 2007 T. Ernst
Keio University / WIDE
K. Nagami
INTEC NetCore
Oct 2006
Multiple Care-of Addresses Registration
draft-ietf-monami6-multiplecoa-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
According to the current Mobile IPv6 specification, a mobile node may
have several Care-of Addresses, but only one, termed the primary
Care-of Address, can be registered with its Home Agent and the
Correspondent Nodes. However, for matters of cost, bandwidth, delay,
etc, it is useful for the mobile node to get Internet access through
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multiple access media simultaneously, in which case multiple active
IPv6 Care-of Addresses would be assigned to the mobile node. We thus
propose Mobile IPv6 extensions designed to register multiple Care-of
Addresses bound to a single Home Address instead of the sole primary
Care-of Address. For doing so, a new identification number must be
carried in each binding for the receiver to distinguish between the
bindings corresponding to the same Home Address. Those extensions
are targeted to NEMO (Network Mobility) Basic Support as well as to
Mobile IPv6.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Multiple Care-of Addresses Registration . . . . . . . . . 8
3.2. Multiple Bindings Management . . . . . . . . . . . . . . . 8
3.3. Returning Home . . . . . . . . . . . . . . . . . . . . . . 9
4. Mobile IPv6 Extensions . . . . . . . . . . . . . . . . . . . . 11
4.1. Binding Cache Structure and Management . . . . . . . . . . 11
4.2. Binding Update List Structure and Management . . . . . . . 11
4.3. Message Format Changes . . . . . . . . . . . . . . . . . . 11
4.3.1. Binding Unique Identifier sub-option . . . . . . . . . 11
4.3.2. Binding Update . . . . . . . . . . . . . . . . . . . . 13
4.3.3. Binding Acknowledgment . . . . . . . . . . . . . . . . 13
5. Mobile Node Operation . . . . . . . . . . . . . . . . . . . . 15
5.1. Management of Care-of Addresses and Binding Unique
Identifier . . . . . . . . . . . . . . . . . . . . . . . . 15
5.2. Binding Registration . . . . . . . . . . . . . . . . . . . 15
5.3. Binding Bulk Registration . . . . . . . . . . . . . . . . 16
5.4. Binding De-Registration . . . . . . . . . . . . . . . . . 16
5.5. Returning Home . . . . . . . . . . . . . . . . . . . . . . 17
5.6. Using Alternate Care-of Address . . . . . . . . . . . . . 17
5.7. Receiving Binding Acknowledgment . . . . . . . . . . . . . 18
5.8. Receiving Binding Refresh Request . . . . . . . . . . . . 18
5.9. Receiving Binding Error . . . . . . . . . . . . . . . . . 19
6. Home Agent and Correspondent Node Operation . . . . . . . . . 20
6.1. Searching Binding Cache with Binding Unique Identifier . . 20
6.2. Receiving Binding Update . . . . . . . . . . . . . . . . . 20
6.3. Sending Binding Acknowledgment . . . . . . . . . . . . . . 22
6.4. Sending Binding Refresh Request . . . . . . . . . . . . . 23
6.5. Sending Binding Error . . . . . . . . . . . . . . . . . . 23
7. Network Mobility Applicability . . . . . . . . . . . . . . . . 24
8. IPsec and IKE interaction . . . . . . . . . . . . . . . . . . 25
9. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 26
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
11.1. Normative References . . . . . . . . . . . . . . . . . . . 27
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11.2. Informative References . . . . . . . . . . . . . . . . . . 27
Appendix A. Example Configurations . . . . . . . . . . . . . . . 28
Appendix B. Changes From Previous Versions . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 36
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1. Introduction
Permanent Internet connectivity is required by some applications
while a mobile node moves across several access networks (i.e. ISPs,
hotspots, etc). Unfortunately, there is no network interfaces
assuring global scale connectivity. Therefore, a mobile node should
use various type of network interfaces to obtain durable and wide
area network connectivity [8]. For example, it is desirable to
maintain the Internet connectivity while an automobile running on a
freeway receives voice or video streaming data from different access
networks. Such scenarios and motivations for multiple points of
attachment, and benefits for doing it are discussed at large in [9].
Once multiple interfaces are available to a mobile node, a backup
interface can be used to recover from the loss of Internet
connectivity on the other interface, therefrom maintaining Internet
connectivity of wide spread and reach. In addition, each
communication flow could be sent to a distinct network interface,
providing efficient network bandwidth consumption. It becomes
possible for users to select the most appropriate network interface
depending on a visiting network environment, since wireless networks
are mutable and less reliable than wired networks and since each
network interface has different cost, performance, bandwidth, access
range, and reliability. Users should also be able to select the most
appropriate interface per communication type. For example, TCP
traffic should be transmitted over the wireless interface, whereas
UDP traffic should be transmitted over the wired interface to avoid
disturbing TCP connections.
IPv6 [1] conceptually allows a node to have several addresses on a
given interface. Consequently, Mobile IPv6 [2] has mechanisms to
manage multiple ``Home Addresses'' based on Home Agent's managed
prefixes such as mobile prefix solicitation and mobile prefix
advertisement. But assigning a single Home Address to a given
network interface is more advantageous than assigning multiple Home
Addresses because applications do not need to be aware of the
multiplicity of Home Addresses. Of course, applications should be
aware of the active Home Address to be used for communicating. At
the TCP layer, TCP holds the Home Address as a source address of the
communication for connection management. Applications must be
restarted to reset the connection information when the mobile node
changes its active network interface (i.e. change the Home Address).
However, according to section 11.5.3 of the Mobile IPv6
specification, a mobile node is not allowed to register multiple
Care-of Addresses bound to a single Home Address. If a mobile node
sends Binding Updates for each Care-of Address, Correspondent Nodes
would always overwrite the Care-of Address recorded in the binding
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cache with the one contained in the latest received binding update.
It is thus impossible for a mobile node to register multiple Care-of
Addresses in the Correspondent Node's binding cache. Moreover, since
NEMO Basic Support [3] is based on Mobile IPv6, the same issues
applies to a mobile node acting as mobile router.
Multihoming issues pertaining to mobile nodes operating Mobile IPv6
and mobile routers operating NEMO Basic Support are respectively
discussed [4] and [10] in Monami6 and NEMO Working Group.
In this document, we thus propose a new identification number called
Binding Unique Identification (BID) number for each binding cache
entry to accommodate multiple bindings registration. We also propose
extension of binding cache management to store the BID and a new sub-
option for binding update to carry the BID. The BID is assigned to
either the interfaces or Care-of Addresses bound to a single home
address of a mobile node. The mobile node notifies the BID to both
its Home Agent and Correspondent Nodes by means of a Binding Update.
Correspondent nodes and the Home Agent record the BID into their
binding cache. The Home Address thus identifies a mobile node itself
whereas the BID identifies each binding registered by a mobile node.
By using the BID, multiple bindings can then be distinguished.
A user of a mobile node may be able to bind some policies to a BID.
The policy is used to divide flows to multiple network interfaces by
flow type, port number, or destination address, etc. How to
distribute or configure policies is not within the scope of this
document. There are solutions available in Monami6 WG, for example
[11].
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2. Terminology
Terms used in this draft are defined in [2], [5] and [6]. In
addition or in replacement of these, the following terms are defined
or redefined:
Binding Unique Identification number (BID)
The BID is an identification number used to distinguish multiple
bindings registered by the mobile node. Assignment of distinct
BID allows a mobile node to register multiple binding cache
entries for a given Home Address. The BID is generated to
register multiple bindings in the binding cache for a given
address in a way it cannot be duplicated with another BID. The
zero value and a negative value MUST NOT be used. After being
generated by the mobile node, the BID is stored in the Binding
Update List and is sent by the mobile node by means of a sub-
option of a Binding Update. A mobile node MAY change the value of
a BID at any time according to its administrative policy, for
instance to protect its privacy.
The BID is conceptually assigned to a binding. An implementation
must carefully assign the BID so as to keep using the same BID for
the same binding even when the status of the binding is changed.
More details can be found in Section 5.1.
Binding Unique Identifier sub-option
The Binding Unique Identifier sub-option is used to carry the BID.
Bulk Registration
A mobile node can register multiple bindings by sending a binding
update. Several care-of addresses can be stored in a Binding
Update. The bulk registration is supported only for home
registration. Note that a mobile node should not try to perform
bulk registration with Correspondent Nodes.
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3. Protocol Overview
We propose a new identification number (BID) to distinguish multiple
bindings pertaining to the same Home Address. The procedures for the
mobile node to register multiple bindings are described in the
paragraphs below.
3.1. Multiple Care-of Addresses Registration
Once a mobile node gets several IPv6 global addresses on interfaces,
it can register these addresses with its Home Agent (home
registration). If the mobile node wants to register multiple
bindings to its Home Agent, it MUST generate a BID for each Care-of
Address and record it into the binding update list. The mobile node
then registers its Care-of Addresses by sending a Binding Update with
a Binding Unique Identifier sub-option. The BID MUST be put in the
Binding Unique Identifier sub-option. After receiving the Binding
Update, the Home Agent verifies the request and records the binding
in its binding cache. If the newly defined sub-option is present in
the Binding Update, the Home Agent MUST copy the BID from the Binding
Update to the corresponding field in the binding entry. Even if
there is already an entry for the mobile node, the Home Agent MUST
register a new binding entry for the BID stored in the Binding Unique
Identifier sub-option. The mobile node registers multiple Care-of
Addresses either independently (in individual BUs) or multiple at
once (in a single BU).
If the mobile node wishes to register its binding with a
Correspondent Node, it MUST start return routability operations
before sending a Binding Update. The mobile node MUST sends CoTI for
each Care-of Addresses and MUST receive CoT for each Care-of
Addresses. The mobile node also uses a BID generated for the home
registration to register them as individual bindings. The
registration step is the same as for the home registration except for
calculating authenticator by using Binding Unique Identifier sub-
option as well as the other sub-options specified in RFC 3775. Since
return routability cannot be verified with multiple care-of addresses
in a binding update, bulk registration is not supported with
Correspondent Nodes in this document.
3.2. Multiple Bindings Management
The BID is used as a search key for a corresponding entry in the
binding cache in addition to the Home Address. When the Home Agent
checks the binding cache database for the mobile node, it searches a
corresponding binding entry with the Home Address and BID of the
desired binding.
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The desired binding can be selected with policy and filter
information. If a mobile node registers a binding with priority
value, the priority can be a key to select a binding. The capability
of searching the desired binding enables load-sharing and QoS with
flow separation. However, this selection and flow separation are
outside the scope of this document.
If there is no desired binding, it searches the binding cache
database with the Home Address as specified in Mobile IPv6. The
first matched binding entry may be found, although this is
implementation dependent.
If a node has multiple bindings and its packets meant for the mobile
node are not delivered correctly, the node can change the binding
entry for the mobile node so as to recover the connection
immediately. The node can detect a binding invalidation by packets
loss or ICMP error messages such as ICMP_UNREACHABLE. This provides
redundancy for Mobile IPv6.
When one of the care-of addresses is changed, the mobile node sends a
Binding Update with the new Care-of Address and the corresponding
BID. The receiver of the Binding Update updates the binding which
BID fits the BID contained in the received Binding Unique Identifier
sub-option. The mobile node can manage each binding independently
owing to BID.
If the mobile node decides to register only single binding, it just
sends a Binding Update without a Binding Unique Identifier sub-option
(i.e. normal Binding Update). The receiver of the Binding Update
registers only a single binding for the mobile node. If the receiver
has multiple bindings, one binding is registered without BID and the
rest of bindings are deleted.
3.3. Returning Home
When the mobile node returns home, there are two situations, since
the Home Agent defends the mobile node's Home Address by using the
proxy neighbor advertisement. It is impossible to utilize all the
interfaces when one interface is attached to the home link and the
others are attached to foreign links. If the proxy Neighbor
Advertisement for the Home Address is stopped, packets are always
routed to the interface attached to the home link. If proxy is not
stopped, packets are never routed to the interface attached to the
home link. The decision whether a mobile node returns home or not is
up to implementers.
The first situation is when a mobile node wants to return home with
interface attached to the home link. In this case, the mobile node
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MUST de-register all the bindings by sending a Binding Update with
lifetime set to zero. The mobile node MAY NOT put any Binding Unique
Identifier sub-option in this packet. Then, the receiver deletes all
the bindings from its binding cache database.
The second situation is when a mobile node does not want to return
home, though one of its interfaces is attached to its home link. The
mobile node disables the interface attached to the home link and
keeps using the rest of interfaces attached to foreign links. In
this case, the mobile node sends a de-registration Binding Update for
the interface attached to the home link with the Binding Unique
Identifier sub-option. The receiver of the de-registration Binding
Update deletes only the correspondent binding entry from the binding
cache database. The Home Agent does not stop proxying neighbor
advertisement as long as there are still bindings for the other
interfaces.
In the above two cases, a mobile node cannot use interfaces attached
to both home and foreign links simultaneously. If this is what a
mobile node wants, a home agent can set up another link other than
home link and uses the link for the mobile node to return virtually
to home network. The detail can be found in Figure 7
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4. Mobile IPv6 Extensions
In this section are described the changes to Mobile IPv6 necessary to
manage multiple bindings bound to a same Home Address.
4.1. Binding Cache Structure and Management
The following additional items are required in the binding cache
structure, i.e.:
BID of the Binding Cache Entry
The BID is notified by the mobile node by means of a Binding
Unique Identifier sub-option. The value MUST be zero if the
Binding Unique identifier does not appear in a Binding Update.
Priority of the Binding Cache Entry
The priority is notified by the mobile node by means of a Binding
Unique Identifier sub-option.
4.2. Binding Update List Structure and Management
The following additional items are required for the binding update
structure, i.e.:
BID
The BID MUST be generated whenever the mobile node registers
multiple bindings for its Home Address.
Priority
MUST be set if the priority field of a Binding Unique Identifier
is valid.
4.3. Message Format Changes
4.3.1. Binding Unique Identifier sub-option
If needed, the Binding Unique Identifier sub-option is included in
the Binding Update, Binding Acknowledgment, Binding Refresh Request,
or Binding Error messages.
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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 = TBD | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding Unique ID (BID) |Priority/Status|C|R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
+ +
+ Care-of Address (CoA) +
+ +
+---------------------------------------------------------------+
Figure 1: BID Sub-Option
Type
Type value for Binding Unique Identifier will be assigned later.
Length
Length value is 4 when the C flag is unset. Length value is 20
when the C flag is set.
Binding Unique ID (BID)
The BID which is assigned to the binding carried in the Binding
Update with this sub-option. BID is 16-bit unsigned integer. A
value of zero is reserved.
Priority/Status
When the Binding Unique Identifier sub-option is included in a
Binding Update, this field indicates the priority field assigned
to each binding. The receiver can utilize this priority to
determine which binding is used to deliver packets. The priority
is 8-bit unsigned integer. The higher value has higher priority.
Values of zero and 255 are reserved for specific meaning.
A value of zero indicates No Priority. A value of 255 indicates
that the binding corresponding to this BID is a default of this
mobile node. This default binding is used by the flow binding
scheme [11]. If the receiver cannot recognize 255, it MUST ignore
this field.
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When the Binding Unique Identifier sub-option is included in a
Binding Acknowledgment, this field indicates the status
correspondent to each binding in a bulk registration mode. The
mobile node can know the registration status of each binding. The
status is 8-bit unsigned integer. The possible status codes are
listed below. If the status field is below 128, it indicates that
the binding registration was successful.
ACCEPTING BID SUBOPTION (0)
The registration of the correspond binding is successfully
operated.
INCOMPLIANT BID SUBOPTION (128)
Registration failed because Binding Unique Identifier sub-
option is not compliant.
Care-of Address (C) flag
When this flag is set, a mobile node can store a Care-of Address
correspondent to BID in the Binding Unique Identifier sub-option.
This flag must be used whenever a mobile node sends multiple
bindings in a single Binding Update, i.e. bulk registration.
Removable (R) flag
When this flag is set, a mobile node request a Home Agent to
remove the binding correspondent to BID, even if the binding
update is not for de-registration. This flag is valid only when
bulk registration is used (C flag is set).
Reserved
6 bits Reserved field. Reserved field must be set with all 0.
4.3.2. Binding Update
No modification to Binding Update. A mobile node stores a Binding
Unique Identifier option in the Mobility Options field of a Binding
Update.
4.3.3. Binding Acknowledgment
The message format of Binding Acknowledgment is not changed, but
operations listed below are added in this draft.
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A receiver who gets a Binding Update with a Binding Unique Identifier
option MUST reply with a Binding Acknowledgment if the A flag is also
set. The receiver MUST also send a Binding Acknowledgment with
corresponding error codes if it finds an error while processing the
Binding Update and its sub-option described in section Section 4.3.
If a Binding Update has a Binding Unique Identifier sub-option is
present, the receiver node MUST reply with a Binding Acknowledgment
containing the same Binding Unique Identifier sub-option(s). There
are two status fields of multiple care-of address registration: one
in Binding Acknowledgment and another in Binding Unique Identifier
sub-option. The first field indicates the general registration
status and the latter field gives detail registration information for
each binding. The latter field is often used to indicate status
information for multiple bindings stored in a single binding update
(i.e. bulk registration). New status values for the status field in
Binding Acknowledgment are defined for handling the multiple Care-of
Addresses registration:
MCOA CONFLICT(144)
It implies conflicting a regular binding and a binding that has
BID in binding cache. The regular binding indicates the binding
that does not have BID field. The status value is TBD.
BULK REGISTRATION FAIL (145)
It implies that the bulk binding registration is failed. The
correspondent status which is defined in RFC3775 is stored in each
Binding Unique Identifier sub-option. The status value is TBD.
BULK REGISTRATION NOT SUPPORT (146)
It implies that the bulk binding registration is not supported.
The mobile node can process the Binding Acknowledgment for the
particular Care-of Address identified by the BID set in the Binding
Unique Identifier sub-option.
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5. Mobile Node Operation
5.1. Management of Care-of Addresses and Binding Unique Identifier
There are two cases when a mobile node has several Care-of Addresses:
1. A mobile node uses several physical network interfaces and
acquires a Care-of Address on each of its interfaces.
2. A mobile node uses a single physical network interface, but
multiple prefixes are announced on the link the interface is
attached to. Several global addresses are configured on this
interface for each of the announced prefixes.
The difference between the above two cases is only a number of
physical network interfaces and therefore does not matter in this
document. The Identification number is used to identify a binding.
To implement this, a mobile node MAY assign an identification number
for each Care-of Addresses. How to assign an identification number
is up to implementers.
A mobile node assigns a BID to each Care-of Address when it wants to
simultaneously register with its Home Address. The value should be
generated from a value comprised between 1 to 65535. Zero and
negative value MUST NOT be taken as a BID. If a mobile node has only
one Care-of Address, the assignment of a BID is not needed until it
has multiple Care-of Addresses to register with.
5.2. Binding Registration
When a mobile node sends a Binding Update, it MUST decide whether it
registers multiple Care-of Addresses or not. However, this decision
is out-of scope in this document. If a mobile node decides not to
register multiple Care-of Addresses, it completely follows standard
RFC 3775 specification.
If the mobile node needs to register multiple Care-of Addresses, it
MUST use BIDs to identify a Care-of Address. The mobile node puts a
Binding Unique Identifier sub-option into the Option field of the
Binding Update. The BID is copied from a Binding Update List to the
Binding Unique Identifier sub-option. No flag in the Binding Unique
Identifier sub-option should be set for independent binding
registration.
If the mobile node registers bindings to a Correspondent Node, it
MUST sends multiple CoTIs for multiple Care-of Addresses. After
getting CoTs, it sends Binding Updates with a Binding Unique
Identifier sub-option for all Care-of Addresses. In any case, the
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mobile node MUST set the A flag in Binding Updates and MUST wait for
a Binding Acknowledgment to confirm the registration was successful
as described in section Section 5.7.
5.3. Binding Bulk Registration
This bulk registration is an optimization for registering multiple
Care-of Addresses only to a Home Agent by using a single Binding
Update, although the current Mobile IPv6 specification does not allow
to send multiple bindings by means of a single Binding Update. In
this case, a mobile node sets the C flag into a Binding Unique
Identifier sub-option and stores the particular Care-of Address in
the Binding Unique Identifier sub-option. The mobile node can store
multiple sets of a Unique Binding Identifier sub-option in a Binding
Update. All the other binding information such as Lifetime, Sequence
Number, binding Flags are shared among the bulk Care-of Addresses.
Whether a mobile node registers multiple Care-of Addresses separately
or not is up to implementations.
If one of Care-of Address should be removed while the other Care-of
Address must be updated, a mobile node can set the R flag in a
Binding Unique Identifier sub-option correspondent to the removed
Care-of Address. When the R flag is set, the binding will be removed
from the binding cache of the Home Agent. Other bindings for which R
flag is unset will be registered or updated accordingly.
5.4. Binding De-Registration
When a mobile node decides to delete all bindings for its home
address, it sends a regular de-registration Binding Update (i.e.
exclusion of a Binding Unique Identifier sub-option). See
Section 6.2 for details.
If a mobile node wants to delete a particular binding from its Home
Agent and Correspondent Nodes (e.g. from foreign link), it MUST send
a Binding Update with lifetime is set to zero. If only single
Care-of Address is removed by a Binding Update, the mobile node
simply sets zero lifetime in a Binding Update and contains the single
correspondent Unique Binding Identifier Sub-option (C flag must be
unset). The receiver will remove only the Care-of Address which is
retrieved from the Source Address field of the IPv6 header. On the
other hand, if the mobile node wants to remove multiple Care-of
Addresses at once, it stores multiple Unique Binding Identifier sub-
options which C flag is set in a Binding Update. The Care-of
Addresses stored in the Binding Unique Identifier sub-options will
all be removed.
If a mobile node wants to remove a binding while it registers the
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other valid bindings, it can use R flag in a Binding Unique
Identifier sub-option. The detailed operation can be found in
Section 5.3.
5.5. Returning Home
When a mobile node returns home, it MUST de-register all bindings
with the Home Agent.
Although the mobile node MUST delete the bindings with Correspondent
Nodes as well, the node can still keep the binding of the other
interface active attached to foreign links at the Correspondent
Nodes. In such case, the mobile node still receives packets at the
other interface attached to a foreign link thanks to route
optimization. The mobile node also receives packets at the interface
attached to the home link when Correspondent Nodes does not use route
optimization.
Note that when the mobile node does not want to return home even if
one of interfaces is attached to the home link, the mobile node MUST
disable the interface. Otherwise, address duplication will be
observed because the Home Agent still defend the Home Address by the
proxy neighbor advertisement and the mobile node also enables the
same Home Address on the home link. After disabling the interface
attached to the home link, the mobile node MUST delete the binding
for the interface by sending a de-registration binding update. The
de-registration binding update must be sent from one of active
interfaces attached to foreign links. As a result, the mobile node
no longer receives packets at the interface attached to the home
link. All packets are routed to other interfaces attached to a
foreign link.
5.6. Using Alternate Care-of Address
A mobile node can use an alternate Care-of Address in the following
situations.
o One Care-of Address becomes invalid (e.g because the link where it
is attached to is no longer available) and MUST be deleted. In
such case, the mobile node can not send a Binding Update from the
Care-of Address because the interface's link is lost. The mobile
node needs to de-register the remote binding of the Care-of
Address through one of its active Care-of Addresses.
o A mobile node has multiple interfaces, but it wants to send
Binding Updates for all Care-of Addresses from a specific
interface which has wider bandwidth depending on interface's
characteristics. A mobile node does not want to send a lot of
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control messages through an interface which bandwidth is scarce.
In these cases, the mobile node sends a Binding Update with both
Alternate Care-of Address sub-option and Binding Unique Identifier
sub-option.
5.7. Receiving Binding Acknowledgment
The verification of a Binding Acknowledgment is the same as in Mobile
IPv6 (section 11.7.3 of RFC 3775). The operation for sending a
Binding Acknowledgment is described in Section 6.3.
If a mobile node sends a Binding Update with a Binding Unique
Identifier sub-option, a Binding Acknowledgment MUST have a Binding
Unique Identifier sub-option in the Mobility options field. If there
is no such sub-option, the originator node of this Binding
Acknowledgment might not recognize the Binding Unique Identifier sub-
option. The mobile node SHOULD stop registering multiple Care-of
Addresses by using a Binding Unique Identifier sub-option. If the
originator is the Home Agent, the mobile node MAY try to discover a
new Home Agent supporting the multiple Care-of Address registration
or give up with the multiple Care-of Address registration.
If a Binding Unique Identifier sub-option is present, the mobile node
checks the Status field of the Binding Acknowledgment. If the status
code indicates successful registration (below 128), the originator
successfully registered the binding information and BID for the
mobile node.
If the status code is not zero and Binding Unique Identifier sub-
option is in the Binding Acknowledgment, the mobile node proceeds
with relevant operations according to the status code.
If the status code is 144, the mobile node has already registered a
regular binding before sending a Binding Update with a Binding Unique
Identifier sub-option. In such case, the mobile node SHOULD stop
sending Binding Updates without BID or SHOULD stop sending Binding
Updates with BID.
If the status code is 145, the mobile node should check the status
field of Binding Unique Identifier sub-option for the detail
information. After correcting errors, the mobile node can re-
register only the failed binding in separate registration or bulk
registration mode.
5.8. Receiving Binding Refresh Request
The verification of a Binding Refresh Request is the same as in
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Mobile IPv6 (section 11.7.4 of RFC 3775). The operation of sending a
Binding Refresh Request is described in section Section 6.4.
If a mobile node receives a Binding Refresh Request with a Binding
Unique Identifier sub-option, this Binding Refresh Request requests a
binding indicated by the BID. The mobile node SHOULD update only the
respective binding. The mobile node MUST put a Binding Unique
Identifier sub-option into a Binding Update.
If no Binding Unique Identifier sub-option is present in a Binding
Refresh Request, the mobile node sends a Binding Update according to
its Binding Update List for the requesting node. On the other hand,
if the mobile node does not have any Binding Update List entry for
the requesting node, the mobile node needs to register either a
single binding or multiple bindings depending on its binding
management policy.
5.9. Receiving Binding Error
When a mobile node receives a Binding Error with a Binding Unique
Identifier sub-option, the message is for a binding indicated by the
BID in the Binding Unique Identifier sub-option. Further operations
except for the text below are identical as in RFC 3775. The
operation for sending BE is described in the section Section 6.5.
When a mobile node receives a Binding Error with Status field set to
2 (Unrecognized MH Type value), it MAY stop trying to register
multiple Care-of Addresses and registers only primary Care-of Address
as performed in Mobile IPv6.
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6. Home Agent and Correspondent Node Operation
6.1. Searching Binding Cache with Binding Unique Identifier
If either a Correspondent Node or a Home Agent has multiple bindings
for a mobile node in their binding cache database, it can use any of
the bindings to communicate with the mobile node. How to select the
most suitable binding from the binding cache database is out of scope
in this document.
Whenever a Correspondent Node searches a binding cache for a home
address, it SHOULD uses both the Home Address and the BID as the
search key if it knows the corresponding BID. If the priority is
available for a binding cache entry, the priority can be used as
additional key to search a binding. In the example below, if a
Correspondent Node searches the binding with the Home Address and
BID2, it gets binding2 for this mobile node.
binding1 [a:b:c:d::EUI, Care-of Address1, BID1]
binding2 [a:b:c:d::EUI, Care-of Address2, BID2]
binding3 [a:b:c:d::EUI, Care-of Address3, BID3]
Figure 2: Searching the Binding Cache
A Correspondent Node basically learns the BID when it receives a
Binding Unique Identifier sub-option. At the time, the Correspondent
Node MUST look up its binding cache database with the Home Address
and the BID retrieved from Binding Update. If the Correspondent Node
does not know the BID, it searches for a binding with only a Home
Address as performed in Mobile IPv6. In such case, the first matched
binding is found. But which binding entry is returned for the normal
search depends on implementations. If the Correspondent Node does
not desire to use multiple bindings for a mobile node, it can simply
ignore the BID.
6.2. Receiving Binding Update
If a Binding Update does not have a Binding Unique Identifier, the
processing of the regular Binding Update is the same as in RFC 3775.
But if the receiver already has multiple bindings for the Home
Address, it MUST overwrite all existing bindings for the mobile node
with the received binding. As a result, the receiver node MUST have
only a binding for the mobile node. If the Binding Update is for de-
registration, the receiver MUST delete all existing bindings for the
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mobile node.
On the other hand, if a Binding Update contains a Binding Unique
Identifier sub-option(s), a receiver node MUST perform additional
validations as follows:
o A receiver node MUST validate the Binding Update according to
section 9.5.1 of RFC 3775.
o If a Binding Unique Identifier sub-option(s) is present, the
receiver node MUST process the sub-option.
o If the C flag is unset in a Binding Unique Identifier sub-
option(s), the length field MUST be 4. Otherwise, the receiver
MUST return the error code 128 in the status field of the Binding
Unique Identifier sub-option and send a Binding Acknowledgment
with status code set to 145 with the Binding Unique Identifier
sub-option. When the length field is more than 4, the receiver
MAY process this sub-option by ignoring the rest of field beyond
the 4 octets (i.e. after Reserved field).
o If the Binding Unique Identifier sub-option is with the C flag set
and no care-of address is present in the sub-option, the receiver
node MUST set 128 in the Status field of the Binding Unique
Identifier sub-option and send a Binding Acknowledgment with
status code set to 145 with the Binding Unique Identifier sub-
option. If either a Correspondent Node or a Home Agent not
supporting bulk registration receives the Binding Unique
Identifier sub-option with C flag set, it MUST return the error
code 146 in a Binding Acknowledgment.
o If the Lifetime field is not zero, the receiver node registers a
binding that includes the BID as a mobile node's binding.
* If the C flag is set in the Binding Unique Identifier sub-
option, the Care-of Address must be taken from the Care-of
Address in the Binding Unique Identifier sub-option.
* If the C flag is not set in the Binding Unique Identifier sub-
option, the Care-of Address must be taken from the Source
Address field of the IPv6 header.
* If the C flag is not set and an alternate care-of address is
present, the care-of address is taken from the Alternate
Care-of Address sub-option.
* If the receiver does not have any binding for the mobile node,
it registers a binding which includes BID field.
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* If the receiver has a regular binding which does not have BID
for the mobile node, it de-registers the regular binding and
registers a new binding including BID according to the Binding
Update. In this case, the receiver MUST send Binding
Acknowledgment with status code set to 144.
* If the receiver node has already registered the binding which
BID is matched with requesting BID, then it MUST update the
binding with the Binding Update. Meanwhile, if the receiver
does not have a binding entry which BID is matched with the
requesting BID, it registers a new binding for the BID.
* If the receiver node found R flag in a Binding Unique
Identifier sub-option, the C flag must be set. Otherwise, it
replies with 128 in a Binding Unique Identifier sub-option and
set 145 in a Binding Acknowledgment. The receiver node must
remove the binding correspondent to the Binding Unique
Identifier sub-option for which R flag is set.
o If Lifetime field is zero, the receiver node deletes the
registering binding entry which BID is same as BID sent by the
Binding Unique Identifier sub-option. If the receiver node does
not have appropriate binding which BID is matched with the Binding
Update, it MUST reject this de-registration Binding Update. If
the receiver is a Home Agent, it SHOULD also return a Binding
Acknowledgment to the mobile node, in which the Status field is
set to 133 (not Home Agent for this mobile node).
6.3. Sending Binding Acknowledgment
If a Binding Update does not contain a Binding Unique Identifier sub-
option, the receiver, either a Correspondent Node or a Home Agent,
MUST reply with a Binding Acknowledgment according to section 9.5.4
of RFC 3775. Otherwise, whenever the Binding Unique Identifier sub-
option is present, the receiver MUST follow the additional procedure
below. The receiver MUST reply with a Binding Acknowledgment whether
the A flag is set or not in the Binding Update.
If the receiver successfully registers a binding for the BID stored
in a Binding Unique Identifier sub-option, it returns a Binding
Acknowledgment with Status field set to successful value (0 to 128)
and a Binding Unique Identifier sub-option copied from the received
Binding Update. If the receiver deletes an existing binding which
does not have a BID and registers a new binding for the BID, it MUST
return a Binding Acknowledgment with Status field set to 144. On the
other hand, if the node encounters an error during the processing of
a Binding Update, it must return a Binding Acknowledgment with an
appropriate error number as described in RFC 3775. The node SHOULD
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put a Binding Unique Identifier sub-option if the BID is available
for the Binding Acknowledgment.
6.4. Sending Binding Refresh Request
When either a Correspondent Node or Home Agent notices that a
registered binding will be expired soon, it MAY send a Binding
Refresh Request. If the registered binding has BID, the
Correspondent Node SHOULD contain a Binding Unique Identifier sub-
option in the Binding Refresh Request. Then, the Correspondent Node
can receive a Binding Update with a Binding Unique Identifier sub-
option and can update only the particular binding. If the registered
binding does not have BID, then the Correspondent Node sends a
Binding Refresh Request without the sub-option.
6.5. Sending Binding Error
When a Correspondent Node sends a Binding Error with Status field set
to 2 (Unrecognized MH Type value), it MAY put a Binding Unique
Identifier sub-option into Mobility Options field if BID is available
in a received binding message.
When a Correspondent Node receives data packets with a home address
destination option, it verifies the IPv6 source address field. If
the source address is not registered in the Correspondent Node's
binding cache, the Correspondent Node MUST return a Binding Error to
the sender with the status set to zero (Unknown binding for Home
Address destination option). The Correspondent Node MUST NOT put a
Binding Unique Identifier sub-option, because there is no binding
cache entry for the source address.
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7. Network Mobility Applicability
Support of multihomed mobile routers is advocated in the NEMO working
group (see R12 "The solution MUST function for multihomed MR and
multihomed mobile networks" in [7]
Issues regarding mobile routers with multiple interfaces and other
multihoming configurations are documented in [10].
Since the binding management mechanisms are the same for a mobile
host operating Mobile IPv6 and for a mobile router operating NEMO
Basic Support (RFC 3963), our extensions can also be used to deal
with multiple Care-of Addresses registration sent from a multihomed
mobile router.
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8. IPsec and IKE interaction
TBA
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9. Conclusion
In this document, we propose a solution to achieve multihomed mobile
node on Mobile IPv6 and Network Mobility. A binding unique
identifier is introduced to register multiple care-of addresses to a
Home Agent and a Correspondent Node. Those care-of addresses are
bound to the same home address. A few modifications to Mobile IPv6
and NEMO are required to support multiple care-of address
registration.
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10. Acknowledgments
The authors would like to thank Masafumi Aramoto (Sharp Corporation),
Julien Charbon, Tero Kauppinen (Ericsson), Susumu Koshiba, Martti
Kuparinen (Ericsson), Romain Kuntz (Keio-U), Heikki Mahkonen
(Ericsson), Hiroki Matutani (Tokyo-U), Koshiro Mitsuya (Keio-U),
Nicolas Montavont, Koji Okada (Keio-U), Keisuke Uehara (Keio-U),
Masafumi Watari (KDDI R&D) in alphabetical order, the Jun Murai Lab.
at KEIO University, and WIDE project for their contributions.
11. References
11.1. Normative References
[1] Deering, S. and R. Hinden, "Internet Protocol Version 6 (IPv6)",
IETF RFC 2460, December 1998.
[2] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[3] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
"Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
January 2005.
[4] Montavont, N., Wakikawa, R., Ernst, T., Ng, C., and K.
Kuladinithi, "Analysis of Multihoming in Mobile IPv6",
draft-ietf-monami6-mipv6-analysis-00 (work in progress),
February 2006.
[5] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[6] Ernst, T. and H. Lach, "Network Mobility Support Terminology",
draft-ietf-nemo-terminology-05 (work in progress),
February 2006.
[7] Ernst, T., "Network Mobility Support Goals and Requirements",
draft-ietf-nemo-requirements-05 (work in progress),
October 2005.
11.2. Informative References
[8] Stemm, M. and R. Katz, "Vertical Handoffs in Wireless Overlay
Networks", Journal Mobile Networks and Applications, vol. 3,
number 4, pages 335-350, 1998.
[9] Ernst, T., "Motivations and Scenarios for Using Multiple
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Interfaces and Global Addresses",
draft-ietf-monami6-multihoming-motivation-scenario-00 (work in
progress), February 2006.
[10] Ng, C., "Analysis of Multihoming in Network Mobility Support",
draft-ietf-nemo-multihoming-issues-05 (work in progress),
February 2006.
[11] Soliman, H., "Flow Bindings in Mobile IPv6",
draft-soliman-monami6-flow-binding-02 (work in progress),
September 2006.
Appendix A. Example Configurations
In this section, we describe typical scenarios when a mobile node has
multiple network interfaces and acquires multiple Care-of Addresses
bound to a Home Address.
The Home Address of the mobile node (MN in figures) is a:b:c:d::EUI.
MN has 3 different interfaces and possibly acquires Care-of Addresses
1-3 (CoA1, CoA2, CoA3). The MN assigns BID1, BID2 and BID3 to each
Care-of Addresses.
Figure 3 depicts the scenario where all interfaces of the mobile node
are attached to foreign links. After binding registrations, the Home
Agent (HA) and the Correspondent Node (CN) have the binding entries
listed in their binding cache database. The mobile node can utilize
all the interfaces.
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+----+
| CN |
+--+-+
|
+---+------+ +----+
+------+ Internet |----------+ HA |
| +----+---+-+ +--+-+
CoA2| | | | Home Link
+--+--+ | | ------+------
| MN +========+ |
+--+--+ CoA1 |
CoA3| |
+---------------+
Binding Cache Database:
Home Agent's binding (Proxy neighbor advertisement is active)
binding [a:b:c:d::EUI Care-of Address1 BID1]
binding [a:b:c:d::EUI Care-of Address2 BID2]
binding [a:b:c:d::EUI Care-of Address3 BID3]
Correspondent Node's binding
binding [a:b:c:d::EUI Care-of Address1 BID1]
binding [a:b:c:d::EUI Care-of Address2 BID2]
binding [a:b:c:d::EUI Care-of Address3 BID3]
Figure 3: Multiple Interfaces Attached to a Foreign Link
Figure 4 depicts the scenario where MN returns home with one of its
interfaces. After the successful de-registration of the binding to
HA, HA and CN have the binding entries listed in their binding cache
database of Figure 4. MN can communicate with the HA through only
the interface attached to the home link. On the other hand, the
mobile node can communicate with CN from the other interfaces
attached to foreign links (i.e. route optimization). Even when MN is
attached to the home link, it can still send Binding Updates for
other active Care-of Addresses (CoA2 and CoA3). If CN has bindings,
packets are routed to each Care-of Addresses directly. Any packet
arrived at HA are routed to the primary interface.
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+----+
| CN |
+--+-+
|
+---+------+ +----+
+------+ Internet |----------+ HA |
| +--------+-+ +--+-+
CoA2| | | Home Link
+--+--+ | --+---+------
| MN +========+ | |
+--+--+ | | |
CoA3| +---|-----------+
+---------------+
Binding Cache Database:
Home Agent's binding (Proxy neighbor advertisement is inactive)
none
Correspondent Node's binding
binding [a:b:c:d::EUI Care-of Address2 BID2]
binding [a:b:c:d::EUI Care-of Address3 BID3]
Figure 4: One of Interface Attached to Home Link and Returing Home
Figure 5 depicts the scenario where MN disables the interface
attached to the home link and communicates with the interfaces
attached to foreign links. The HA and the CN have the binding
entries listed in their binding cache database. MN disable the
interface attached to the home link, because the HA still defends the
home address of the MN by proxy neighbor advertisements. All packets
routed to the home link are intercepted by the HA and tunneled to the
other interfaces attached to the foreign link according to the
binding entries.
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+----+
| CN |
+--+-+
|
+---+------+ +----+
+------+ Internet |----------+ HA |
| +----+-----+ +--+-+
CoA2| | | Home Link
+--+--+ | --+---+------
| MN +========+ |
+--+--+ CoA1 |
| |
+---------------------------+
(Disable interface)
Binding Cache Database:
Home Agent's binding (Proxy neighbor advertisement is active)
binding [a:b:c:d::EUI Care-of Address1 BID1]
binding [a:b:c:d::EUI Care-of Address2 BID2]
Correspondent Node's binding
binding [a:b:c:d::EUI Care-of Address1 BID1]
binding [a:b:c:d::EUI Care-of Address2 BID2]
Figure 5: One of Interface Attached to Home Link and Not Returing
Home
Figure 6 depicts the scenario where multiple interfaces of MN are
attached to the home link. The HA and CN have the binding entries
listed in Figure 6 in their binding cache database. The MN can not
use the interface attached to a foreign link unless a CN has a
binding for the interface. All packets which arrive at the HA are
routed to one of the MN's interfaces attached to the home link.
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+----+
| CN |
+--+-+
|
+---+------+ +----+
+------+ Internet |----------+ HA |
| +----------+ +--+-+
CoA2| | Home Link
+--+--+ --+----+---+------
| MN +===================+ |
+--+--+ |
| |
+---------------------------+
Binding Cache Database:
Home Agent's binding (Proxy neighbor advertisement is inactive)
none
Correspondent Node's binding
binding [a:b:c:d::EUI Care-of Address2 BID2]
Figure 6: Several Interfaces Attached to Home Link and Returning Home
Figure 7 depicts the scenario where interfaces of MN are attached to
the foreign links. One of foreign link is managed by the home agent.
The HA and CN have the binding entries listed in Figure 7 in their
binding cache database. The home agent advertises a prefix which is
other than home prefix. The mobile node will generate a care-of
address from the prefix and registers it to the home agent. Even if
the mobile node attaches to a foreign link, the link is managed by
its home agent. It will tunnel the packets to the home agent, but
the home agent is one-hop neighbor. The cost of tunnel is
negligible. If the mobile node wants to utilize not only an
interface attached to home but also interfaces attached to foreign
link, it can use this foreign link of the home agent to return home.
This is different from the general returning home, but this enable
the capability of using interfaces attached to both home and foreign
link without any modifications to Mobile IPv6 and NEMO basic support.
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+----+
| CN |
+--+-+
|
+---+------+ +----+
+------+ Internet |----------+ HA |
| +----+-----+ ++-+-+
CoA2| | | | Home Link
+--+--+ | ----|-+------
| MN +========+ |
+--+--+ CoA1 ---+-+------
CoA3 | | Foreign Link
+---------------------------+
(Disable interface)
Binding Cache Database:
Home Agent's binding (Proxy neighbor advertisement is active)
binding [a:b:c:d::EUI Care-of Address1 BID1]
binding [a:b:c:d::EUI Care-of Address2 BID2]
binding [a:b:c:d::EUI Care-of Address3 BID3]
Correspondent Node's binding
binding [a:b:c:d::EUI Care-of Address1 BID1]
binding [a:b:c:d::EUI Care-of Address2 BID2]
binding [a:b:c:d::EUI Care-of Address3 BID3]
Figure 7: Emulating to Utilize Interfaces Attached to both Home and
Foreign Links
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Appendix B. Changes From Previous Versions
Changes from draft-ietf-monami6-multiplecoa-00.txt
o Adding a default value for the BID priority field. This default
value is used by the flow binding scheme [11].
o Updating the text of BID definition. The older text was unclear
whether a BID is assigned to a binding or a interface. It is now
clearly defined that BID is assigned to each binding.
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Authors' Addresses
Ryuji Wakikawa
Keio University
Department of Environmental Information, Keio University.
5322 Endo
Fujisawa, Kanagawa 252-8520
Japan
Phone: +81-466-49-1100
Fax: +81-466-49-1395
Email: ryuji@sfc.wide.ad.jp
URI: http://www.wakikawa.org/
Thierry Ernst
Keio University / WIDE
Jun Murai Lab., Keio University.
K-square Town Campus, 1488-8 Ogura, Saiwa-Ku
Kawasaki, Kanagawa 212-0054
Japan
Phone: +81-44-580-1600
Fax: +81-44-580-1437
Email: ernst@sfc.wide.ad.jp
URI: http://www.sfc.wide.ad.jp/~ernst/
Kenichi Nagami
INTEC NetCore Inc.
1-3-3, Shin-suna
Koto-ku, Tokyo 135-0075
Japan
Phone: +81-3-5565-5069
Fax: +81-3-5565-5094
Email: nagami@inetcore.com
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