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IETF RFC 5648
Multiple Care-of Addresses Registration
Last modified on Saturday, October 3rd, 2009
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Network Working Group R. Wakikawa, Ed.
Request for Comments: 5648 Toyota ITC
Category: Standards Track V. Devarapalli
Wichorus
G. Tsirtsis
Qualcomm
T. Ernst
INRIA
K. Nagami
INTEC NetCore
October 2009
Multiple Care-of Addresses Registration
 Abstract
According to the current Mobile IPv6 specification, a mobile node may
have several care-of addresses but only one, called 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
multiple accesses simultaneously, in which case the mobile node would
be configured with multiple active IPv6 care-of addresses. This
document proposes extensions to the Mobile IPv6 protocol to register
and use multiple care-of addresses. The extensions proposed in this
document can be used by mobile routers using the NEMO (Network
Mobility) Basic Support protocol as well.
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright and License Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Wakikawa, et al. Standards Track PAGE 1 
RFC 5648 MCoA October 2009
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Protocol Overview ...............................................4
4. Mobile IPv6 Extensions .........................................10
4.1. Binding Cache Structure and Binding Update List ...........10
4.2. Binding Update Message ....................................10
4.3. Binding Identifier Mobility Option ........................11
4.4. New Status Values for Binding Acknowledgement .............13
5. Mobile Node Operation ..........................................14
5.1. Management of Care-of Address(es) and Binding
Identifier(s) .............................................14
5.2. Binding Registration ......................................15
5.3. Bulk Registration .........................................16
5.4. Binding De-Registration ...................................16
5.5. Returning Home with Complete Binding
De-Registration: Using a Single Interface .................17
5.5.1. Using Only the Interface Attached to the
Home Link ..........................................17
5.5.2. Using Only the Interface Attached to the
Visited Link .......................................17
5.6. Returning Home: Simultaneous Home and Visited Link
Operation .................................................18
5.6.1. Problems of Simultaneous Home and Foreign
Attachments ........................................18
5.6.2. Overview and Approach ..............................18
5.6.3. Home Binding Support ...............................19
5.6.4. Sending Packets from the Home Link .................20
5.6.5. Leaving from the Home Link .........................20
5.7. Receiving Binding Acknowledgement .........................21
5.8. Receiving Binding Refresh Request .........................22
5.9. Bootstrapping .............................................22
6. Home Agent and Correspondent Node Operation ....................22
6.1. Searching Binding Cache with Binding Identifier ...........22
6.2. Processing Binding Update .................................23
6.3. Sending a Binding Acknowledgement for Home Link
Registration ..............................................25
6.4. Sending Binding Refresh Request ...........................27
6.5. Receiving Packets from Mobile Node ........................27
7. Network Mobility Applicability .................................27
8. DSMIPv6 Applicability ..........................................27
8.1. IPv4 Care-of Address Registration .........................28
8.2. IPv4 Home Address Management ..............................29
Wakikawa, et al. Standards Track PAGE 2
RFC 5648 MCoA October 2009
9. IPsec and IKEv2 Interaction ....................................30
9.1. Use of Care-of Address in the IKEv2 Exchange ..............31
9.2. Transport Mode IPsec-Protected Messages ...................31
9.3. Tunnel Mode IPsec-Protected Messages ......................31
9.3.1. Tunneled Home Test Init and Home Test Messages .....31
9.3.2. Tunneled Payload Traffic ...........................32
10. Security Considerations .......................................33
11. IANA Considerations ...........................................34
12. Acknowledgements ..............................................35
13. References ....................................................35
13.1. Normative References .....................................35
13.2. Informative References ...................................35
1. Introduction
A mobile node may use various types of network interfaces to obtain
durable and wide area network connectivity. This has increasingly
become true with mobile nodes having multiple interfaces, such as
802.2, 802.11, 802.16, cellular radios, etc. The motivations for and
benefits of using multiple points of attachment are discussed in
[MOTIVATION]. When a mobile node with multiple interfaces uses
Mobile IPv6 [RFC 3775] for mobility management, it cannot use its
multiple interfaces to send and receive packets while taking
advantage of session continuity provided by Mobile IPv6. This is
because Mobile IPv6 allows the mobile node to bind only one care-of
address at a time with its home address. See [MIP6ANALYSIS] for a
further analysis of using multiple interfaces and addresses with
Mobile IPv6.
This document proposes extensions to Mobile IPv6 to allow a mobile
node to register multiple care-of addresses for a home address and
create multiple binding cache entries. A new Binding Identification
(BID) number is created for each binding the mobile node wants to
create and is sent in the Binding Update. The home agent that
receives this Binding Update creates a separate binding for each BID.
The BID information is stored in the corresponding binding cache
entry. The BID information can now be used to identify individual
bindings. The same extensions can also be used in Binding Updates
sent to the correspondent nodes.
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].
Wakikawa, et al. Standards Track PAGE 3
RFC 5648 MCoA October 2009
Terms used in this document are defined in [RFC 3775], [RFC 3753], and
[RFC 4885]. In addition to or as a replacement of these, the
following terms are defined or redefined:
Binding Identification Number (BID)
The BID is an identification number used to distinguish multiple
bindings registered by the mobile node. Assignment of distinct
BIDs allows a mobile node to register multiple binding cache
entries for a given home address. BIDs assigned to the same home
address must not be duplicated at the same time. The value zero
is reserved for future extensions. Each BID is generated and
managed by a mobile node. The BID is stored in the Binding Update
List and is sent by the mobile node in the 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.
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 Identifier Mobility Option
The Binding Identifier mobility option is used to carry the BID
information.
Bulk Registration
A mobile node can register multiple bindings at once by sending a
single Binding Update. A mobile node can also replace some or all
of the bindings available at the home agent with the new bindings
by using the bulk registration. Bulk registration is supported
only for home registration (i.e., with the home agent) as
explained in Section 5.3. A mobile node must not perform the bulk
registration mechanism described in this specification with a
correspondent node.
3. Protocol Overview
A new extension called the Binding Identification number (BID) is
introduced to distinguish between multiple bindings pertaining to the
same home address. If a mobile node configures several IPv6 global
addresses on one or more of its interfaces, it can register these
addresses with its home agent as care-of addresses. If the mobile
node wants to register multiple bindings, it MUST generate a BID for
each care-of address and store the BID in the Binding Update List. A
mobile node can manipulate each binding independently by using the
BIDs. The mobile node then registers its care-of addresses by
sending a Binding Update with a Binding Identifier mobility option.
Wakikawa, et al. Standards Track PAGE 4
RFC 5648 MCoA October 2009
The BID is included in the Binding Identifier mobility option. After
receiving the Binding Update with a Binding Identifier mobility
option, the home agent MUST copy the BID from the Binding Identifier
mobility option to the corresponding field in the binding cache
entry. If there is an existing binding cache entry for the mobile
node, and if the BID in the Binding Update does not match the one
with the existing entry, the home agent MUST create a new binding
cache entry for the new care-of address and BID. The mobile node can
either register multiple care-of addresses at once in a single
Binding Update or independently in individual Binding Updates.
If the mobile host wishes to register its binding with a
correspondent node, it must perform return routability operations as
described in [RFC 3775]. This includes managing a Care-of Keygen
token per care-of address and exchanging Care-of Test Init and Care-
of Test messages with the correspondent node for each care-of
address. The mobile node MAY use the same BID that it used with the
home agent for a particular care-of address. For protocol
simplicity, bulk registration to correspondent nodes is not supported
in this document. This is because the return routability mechanism
introduced in [RFC 3775] cannot be easily extended to verify multiple
care-of addresses stored in a single Binding Update.
Figure 1 illustrates the configuration where the mobile node obtains
multiple care-of addresses at foreign links. The mobile node can
utilize all the care-of addresses. In Figure 1, the home address of
the mobile node (MN) is 2001:db8::EUI. The mobile node has 3
different interfaces and possibly acquires care-of addresses 1-3
(CoA1, CoA2, CoA3). The mobile node assigns BID1, BID2, and BID3 to
each care-of address.
Wakikawa, et al. Standards Track PAGE 5
RFC 5648 MCoA October 2009
+----+
| CN |
+--+-+
|
+---+------+ +----+
+------+ Internet |----------+ HA |
| +----+---+-+ +--+-+
CoA2| | | | Home Link
+--+--+ | | ------+------
| MN +--------+ |
+--+--+ CoA1 |
CoA3| |
+---------------+
Binding Cache Database:
home agent's binding (Proxy neighbor advertisement is active)
binding [2001:db8::EUI BID1 care-of address1]
binding [2001:db8::EUI BID2 care-of address2]
binding [2001:db8::EUI BID3 care-of address3]
correspondent node's binding
binding [2001:db8::EUI BID1 care-of address1]
binding [2001:db8::EUI BID2 care-of address2]
binding [2001:db8::EUI BID3 care-of address3]
Figure 1: Multiple Care-of Addresses Registration
If the mobile node decides to act as a regular mobile node compliant
with [RFC 3775], it sends a Binding Update without any Binding
Identifier mobility options. The receiver of the Binding Update
deletes all the bindings registered with a BID and registers only a
single binding for the mobile node. Note that the mobile node can
continue using the BID even if it has only a single binding that is
active.
Binding cache lookup is done based on the home address and BID
information if a BID is available. This is different from RFC 3775,
where only the home address is used for binding cache lookup.
Binding cache lookup is operated for either protocol signaling or
data packets. For protocol signaling such as a Binding Update, BID
should be always carried by a BID sub-option in a protocol signaling.
Therefore, a correspondent binding cache that matches the specified
BID MUST be found from the binding cache database. On the other
hand, for the data packets, no BID information is carried in a
packet. The binding cache lookup may involve policy or flow filters
to retrieve a correspondent BID per packet in cases where some policy
or flow filters are used to direct a certain packet or flow to a
particular care-of address. However, the binding cache lookup using
policy or flow filters is out of scope for this document. If no such
Wakikawa, et al. Standards Track PAGE 6
RFC 5648 MCoA October 2009
mechanism is available and no BID is found for a packet, a node
SHOULD use the binding that was last verified by receiving data
packets or signaling from the mobile node. In case the binding cache
lookup for data packets, using the combination of home address and
BID, does not return a valid binding cache entry, the home agent
SHOULD perform the lookup based on only the home address as described
in [RFC 3775].
In any case, to avoid problems with upper-layer protocols and TCP in
particular, a single packet flow as identified by the 5-tuple SHOULD
only be sent to a single care-of address at a time.
The mobile node may return to the home link through one of its
interfaces. There are two options possible for the mobile node when
it returns home. Sections 5.5.1 and 5.6 describe the returning-home
procedures in more detail.
1. The mobile node uses only the interface with which it attaches to
the home link and takes back full ownership of its HoA (home
address) on the home link. This is illustrated in Figure 2. It
de-registers all bindings with the home agent related to all
care-of addresses. The interfaces still attached to the visited
link(s) are no longer going to be receiving any encapsulated
traffic from the home agent. On the other hand, the mobile node
can continue communicating with the correspondent nodes from the
other interfaces attached to foreign links by using route
optimization. Even if the mobile node is attached to the home
link, it can still send Binding Updates for other active care-of
addresses (CoA1 and CoA2) to correspondent nodes. Since the
correspondent node has bindings, packets are routed from and to
each care-of address directly.
Wakikawa, et al. Standards Track PAGE 7
RFC 5648 MCoA October 2009
+----+
| CN |
+--+-+
|
+---+------+ +----+
+------+ Internet |----------+ HA |
| +----+-----+ +--+-+
CoA2| | | Home Link
+--+--+ | --+---+------
| MN +--------+ |
+--+--+ CoA1 |
| |
+---------------------------+
Binding Cache Database:
home agent's binding
none
correspondent node's binding
binding [2001:db8::EUI BID1 care-of address1]
binding [2001:db8::EUI BID2 care-of address2]
Figure 2: Using Only an Interface Attached to the Home Link
2. The mobile node may simultaneously use both the interface
attached to the home link and the interfaces still attached to
the visited link(s) as shown in Figure 3. There are two possible
topologies, depending on whether or not the home agent is the
only router on the home link. The operation of Neighbor
Discovery [RFC 4861] is different in the two topologies. More
details can be found in Section 5.6. The home agent and the
correspondent node have the binding entries listed in Figure 3 in
their binding cache database in both topologies. The home agent
also knows that the mobile node is attached to the home link.
All the traffic from the Internet is intercepted by the home
agent first and routed to either the interface attached to the
home link or to one of the foreign links. How the home agent
decides to route a particular flow to the interface attached to
the home link or foreign link is out of scope for this document.
Wakikawa, et al. Standards Track PAGE 8
RFC 5648 MCoA October 2009
Topology-a)
+----+
| CN |
+--+-+
|
+---+------+ +----+
+------+ Internet |----------+ HA |
| +----+-----+ +--+-+
CoA2| | | Home Link
+--+--+ | --+---+------
| MN +--------+ |
+--+--+ CoA1 |
| |
+---------------------------+
Topology-b)
+----+
| CN |
+--+-+
|
+---+------+ Router +----+
+------+ Internet |-------R | HA |
| +----+-----+ | +--+-+
CoA2| | | | Home Link
+--+--+ | --+-+-------+------
| MN +--------+ |
+--+--+ CoA1 |
| |
+---------------------------+
Binding Cache Database:
home agent's binding
binding [2001:db8::EUI BID1 care-of address1]
binding [2001:db8::EUI BID2 care-of address2]
correspondent node's binding
binding [2001:db8::EUI BID1 care-of address1]
binding [2001:db8::EUI BID2 care-of address2]
Figure 3: Simultaneous Home and Visited Link Operation
This specification keeps backwards compatibility with [RFC 3775]. If
a receiver (either home agent or correspondent node) does not support
this specification, it does not understand the Binding Identifier
mobility option. The receiver skips the unknown mobility option
(i.e., the Binding Identifier mobility option) and processes the
Binding Update as defined in [RFC 3775]. In order to keep backwards
compatibility with [RFC 3775], when a mobile node sends a Binding
Wakikawa, et al. Standards Track PAGE 9
RFC 5648 MCoA October 2009
Update message with extensions described in this document, the
receiver needs to reflect the Binding Identifier mobility option in
the Binding Acknowledgement. If the mobile node finds no Binding
Identifier mobility options in the received Binding Acknowledgement,
it assumes the other end node does not support this specification.
In such case, the mobile node needs to fall back to the legacy
[RFC 3775]-compliant mobile node. If it is the home registration, the
mobile node MAY try to discover another home agent that supports the
Binding Identifier mobility option for the home registration.
4. Mobile IPv6 Extensions
This section summarizes the extensions to Mobile IPv6 that are
necessary to manage multiple bindings.
4.1. Binding Cache Structure and Binding Update List
The BID is required to be stored in the binding cache and Binding
Update List structure.
The sequence number value MUST be shared among all the Binding Update
List entries related to Binding Updates sent to a particular home
agent or correspondent node. Whenever a mobile node sends either an
individual or a bulk Binding Update, the sequence number is
incremented. When a home agent receives an individual Binding
Update, it should update the sequence number for all the bindings for
a particular mobile node, with the sequence number in the received
Binding Update.
4.2. Binding Update Message
This specification extends the Binding Update message with a new
flag. The flag is shown and described below.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K|M|R|P|F|T|O| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Binding Update Message
Wakikawa, et al. Standards Track PAGE 10
RFC 5648 MCoA October 2009
Overwrite (O) flag
When this flag is set, all the binding cache entries for a mobile
node are replaced by new entries registering with this Binding
Update message. This flag is only used when the BID mobility
option is carried with the Binding Update.
Reserved
6-bit Reserved field.
4.3. Binding Identifier Mobility Option
The Binding Identifier mobility option is included in the Binding
Update, Binding Acknowledgement, Binding Refresh Request, and Care-of
Test Init and Care-of Test messages. The Binding Identifier mobility
option has an alignment requirement of 2n if the Care-of Address
field is not present. Otherwise, it has the alignment requirement of
8n + 2.
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 = 35 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding ID (BID) | Status |H| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------------------------+
+ +
: IPv4 or IPv6 care-of address (CoA) :
+ +
+---------------------------------------------------------------+
Figure 5: BID Mobility Option
Type
Type value for Binding Identifier is 35.
Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Type and Length fields. It MUST be set to either 4,
8, or 20 depending on the Care-of Address field. When the care-of
address is not carried by this option, the length value MUST be
set to 4. If the IPv4 care-of address is stored in the Care-of
Address field, the length MUST be 8. Otherwise, the length value
MUST be set to 20 for IPv6 care-of addresses.
Wakikawa, et al. Standards Track PAGE 11
RFC 5648 MCoA October 2009
Binding ID (BID)
The BID that is assigned to the binding indicated by the care-of
address in the Binding Update or the Binding Identifier mobility
option. The BID is a 16-bit unsigned integer. The value of zero
is reserved and SHOULD NOT be used.
Status
The Status field is an 8-bit unsigned integer. When the Binding
Identifier mobility option is included in a Binding
Acknowledgement, this field overwrites the Status field in the
Binding Acknowledgement only for this BID. If this field is set
to zero, the receiver ignores this field and uses the registration
status stored in the Binding Acknowledgement message. The
receiver MUST ignore this field if the Binding Identifier mobility
option is not carried within either the Binding Acknowledgement or
the Care-of Test messages. The possible status codes are the same
as the status codes of the Binding Acknowledgement. This Status
field is also used to carry error information related to the
care-of address test in the Care-of Test message.
Simultaneous Home and Foreign Binding (H) flag
This flag indicates that the mobile node registers multiple
bindings to the home agent while it is attached to the home link.
This flag is valid only for a Binding Update sent to the home
agent.
Reserved
7-bit Reserved field. The value MUST be initialized to zero by
the sender, and SHOULD be ignored by the receiver.
Care-of Address
If a Binding Identifier mobility option is included in a Binding
Update for the home registration, either IPv4 or IPv6 care-of
addresses for the corresponding BID can be stored in this field.
For the binding registration to correspondent nodes (i.e., route
optimization), only IPv6 care-of addresses can be stored in this
field. If no address is specified in this field, the length of
this field MUST be zero (i.e., not appear in the option). If the
option is included in any messages other than a Binding Update,
the length of this field MUST also be zero.
Wakikawa, et al. Standards Track PAGE 12
RFC 5648 MCoA October 2009
4.4. New Status Values for Binding Acknowledgement
New status values for the Status field in a Binding Acknowledgement
are defined for handling the multiple care-of addresses registration:
MCOA NOTCOMPLETE (4)
In bulk registration, not all the Binding Identifier mobility
options were successfully registered. Some of them were rejected.
The error status value of the failed mobility option is
individually stored in the Status field of the Binding Identifier
mobility option.
MCOA RETURNHOME WO/NDP (5)
When a mobile node returns home, it MUST NOT use the Neighbor
Discovery Protocol (NDP) for the home address on the home link.
This is explained in more detail in Section 5.6.
MCOA MALFORMED (164)
Registration failed because the Binding Identifier mobility option
was not formatted correctly. This value is used in the following
cases:
* when the wrong length value is specified (neither 4, 8, nor 20)
in the Length field of the Binding Identifier mobility option.
* when a unicast routable address is not specified in the Care-of
Address field of the Binding Identifier mobility option.
* when a care-of address does not appear in the Care-of Address
field of the Binding Identifier mobility option stored in an
IPsec Encapsulating Security Payload (ESP)-protected Binding
Update.
MCOA NON-MCOA BINDING EXISTS (165)
Indicates that a bootstrapping multiple care-of addresses
registration was performed without the 'O' flag set.
MCOA UNKOWN COA (167)
Indicates that a Binding Identifier mobility option did not
include a Care-of Address field and that the receiver has no
record for the Binding ID indicated in the same option.
Wakikawa, et al. Standards Track PAGE 13
RFC 5648 MCoA October 2009
MCOA PROHIBITED (166)
Implies that the multiple care-of addresses registration is
administratively prohibited.
MCOA BULK REGISTRATION PROHIBITED (168)
Bulk binding registration is either not permitted or not
supported. Note that the bulk registration is an optional
procedure and might not be available on a home agent.
MCOA SIMULTANEOUS HOME AND FOREIGN PROHIBITED (169)
Simultaneous home and foreign attachment is neither supported nor
permitted.
5. Mobile Node Operation
5.1. Management of Care-of Address(es) and Binding Identifier(s)
There are two cases when a mobile node might acquire several care-of
addresses. A mixture of the two cases is also possible. Note that a
mobile node can use BID regardless of the number of interfaces and
care-of addresses. Whether or not a mobile node uses BID is
determined by a local configuration.
1. A mobile node is using 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
receives advertisements for multiple prefixes on the link to
which the interface is attached. This will result in the mobile
node configuring several global addresses on the interface from
each of the announced prefixes.
The difference between the above two cases is only in the number of
physical network interfaces and is therefore irrelevant in this
document. What is of significance is the fact that the mobile node
has several addresses it can use as care-of addresses.
A mobile node assigns a BID to each care-of address when it wants to
register them simultaneously with its home address. The BID MUST be
unique for a given home address. The value is an integer between 1
and 65535. A zero value SHOULD NOT be used 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 with which to
register, at which time all of the care-of addresses MUST be mapped
to BIDs.
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RFC 5648 MCoA October 2009
When a mobile node registers a given BID for the first time, it MUST
include the Care-of Address field in the Binding Identifier mobility
option. For any subsequent registrations that either re-register or
de-register the same BID, the MN need not include the Care-of Address
field in the Binding Identifier mobility option.
5.2. Binding Registration
For the multiple care-of addresses registration, the mobile node MUST
include a Binding Identifier mobility option(s) in the Binding Update
as shown in Figure 6.
When IPsec ESP is used for protecting the Binding Update, a care-of
address MUST be carried in an alternate Care-of Address mobility
option as described in [RFC 4877]. However, in this specification,
the care-of address MUST be carried in the Care-of Address field of
the Binding Identifier mobility option. In order to save bits of the
Binding Update, the alternate Care-of Address option MUST NOT be
included.
For binding registration to a correspondent node, the mobile node
MUST have both active Home and Care-of Keygen tokens for Kbm (binding
management key; see Section 5.2.5 of [RFC 3775]) before sending the
Binding Update. The care-of Keygen tokens MUST be maintained for
each care-of address that the mobile node wants to register to the
correspondent node. The Binding Update to the correspondent node is
protected by the Binding Authorization Data mobility option that is
placed after the Binding Identifier mobility option.
IPv6 header (src=Care-of Address, dst=Home Agent Address)
IPv6 Home Address Option
ESP Header*
Mobility header
Binding Update
Mobility Options
Binding Identifier mobility option
Binding Authorization mobility option+
(*) if necessary, for home registration
(+) if necessary, for route optimization
Figure 6: Binding Update for Binding Registration
If the mobile node wants to replace existing registered bindings on
the home agent with the single binding in the sent Binding Update, it
sets the 'O' flag. If the 'O' flag is not set, then the binding will
be added to existing bindings in the home agent. The single binding
will be registered with the assigned BID. Section 6.2 describes this
registration procedure in detail.
Wakikawa, et al. Standards Track PAGE 15
RFC 5648 MCoA October 2009
5.3. Bulk Registration
Bulk registration is an optimization for binding multiple care-of
addresses to a home address using a single Binding Update. This is
very useful if the mobile node, for instance, does not want to send a
lot of signaling messages through an interface where the bandwidth is
scarce. This document specifies bulk registration only for the
mobile node's home registration. A mobile node performing bulk
registration with a correspondent node is out of scope.
To use bulk registration, the mobile node includes a Binding
Identifier mobility option for each BID it wants to register in the
same Binding Update message. As with single registrations (see
Section 5.1), the Care-of Address field is included for each BID
registered for the first time. This is shown in Figure 7. The rest
of the fields and options in the Binding Update (such as Lifetime,
Sequence Number, and the flags in the Binding Update) are common
across all care-of addresses.
IPv6 header (src=Care-of Address, dst=Home Agent Address)
IPv6 Home Address Option
ESP Header
Mobility header
Binding Update
Mobility Options
Binding Identifier1 (including Care-of Address)
Binding Identifier2 (including Care-of Address)
Binding Identifier3 (no Care-of Address)
Binding IdentifierN (no Care-of Address)
:
Figure 7: Binding Update for Bulk Registration
As with regular registrations, if the mobile node wants to replace
existing registered bindings on the home agent with the multiple
bindings in the sent Binding Update, it sets the 'O' flag in the
Binding Update; otherwise, the bindings are added to the existing
bindings in the home agent.
5.4. Binding De-Registration
When a mobile node decides to delete all the bindings for its home
address, it sends a regular de-registration Binding Update with
lifetime set to zero as defined in [RFC 3775]. The Binding Identifier
mobility option is not required.
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If a mobile node wants to delete a particular binding(s) from its
home agent and correspondent nodes, the mobile node sends a Binding
Update with lifetime set to zero and includes a Binding Identifier
mobility option(s) with the BID(s) it wants to de-register. The
receiver will remove only the care-of address(es) that match(es) the
specified BID(s). Since de-registration attempts to remove a BID
that already exists, the Care-of Address field in each Binding
Identifier option can be omitted by the sender as defined in Section
5.1.
5.5. Returning Home with Complete Binding De-Registration: Using a
Single Interface
The mobile node may return to the home link by attaching to the home
link through one of its interfaces. When the mobile node wants to
return home, it should be configured with information on what
interface it needs to use.
5.5.1. Using Only the Interface Attached to the Home Link
The mobile node returns home and de-registers all the bindings it has
with the home agent, as shown in Figure 2 and as defined in
[RFC 3775]. After the de-registration step, all the packets routed by
the home agent are only forwarded to the interface attached to the
home link, even if there are other active interfaces attached to the
visited link(s). While the mobile node de-registers all the bindings
from the home agent, it may continue registering, to the
correspondent node, bindings for interfaces attached to visited links
as shown in Figure 2.
5.5.2. Using Only the Interface Attached to the Visited Link
The mobile node returns home physically but shuts down the interface
attached to the home link. As a result, a mobile node does not
return home even though it attaches to the home link by one of the
interfaces. Before shutting down the interface, any binding for the
care-of address previously associated with the interface should be
deleted as defined in Section 5.4.
In this scenario, despite the fact that the mobile node is connected
to its home link, all of its traffic is sent and received via the
home agent and its foreign links.
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5.6. Returning Home: Simultaneous Home and Visited Link Operation
5.6.1. Problems of Simultaneous Home and Foreign Attachments
The mobile node returns home and continues using all the interfaces
attached to both foreign and home links as shown in Figure 3.
In [RFC 3775], the home agent intercepts packets meant for the mobile
node using proxy Neighbor Discovery [RFC 4861] while the mobile node
is away from the home link. When the mobile node returns home, the
home agent deletes the binding cache and stops proxying for the home
address so that a mobile node can configure its home address on the
interface attached to the home link. In this specification, a mobile
node may return home and configure the home address on the interface
attached to the home link, but still use the interfaces attached to
the foreign links. In this case, a possible conflict arises when
both the home agent and the mobile node try to defend the home
address. If the home agent stops proxying for the home address, the
packets are always routed to the interface attached to the home link
and are never routed to the interfaces attached to the visited links.
Deployments making use of multiple care-of addresses are required to
avoid configuration conflict between the home agent and the mobile
node, while still allowing the simultaneous use of home and foreign
links. The following describes the mechanism for achieving this.
5.6.2. Overview and Approach
The home agent MUST intercept all the packets meant for the mobile
node, whether or not the mobile node is attached to the home link,
and decide whether to send the traffic directly to the home address
on the link or tunnel to the care-of address.
Two scenarios are illustrated in Figure 3, depending on whether or
not the home agent is the only router at the home link. The
difference is on who defends the home address by (Proxy) Neighbor
Discovery on the home link.
1. Mobile node defends the home address by the regular Neighbor
Discovery protocol (illustrated as topology-a in Figure 3). The
home agent is the only router on the home link. Therefore, the
home agent is capable of intercepting packets without relying on
the proxy Neighbor Discovery protocol, and the mobile node can
manage the neighbor cache entry of the home address on the home
link as a regular IPv6 node. However, there is one limitation of
this scenario. If a correspondent node is located at the home
link, the home agent may not intercept the packets destined to
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the mobile node. These packets are routed only via the home
link, but this is the most optimal path for the mobile node to
communicate with nodes on the home link.
2. If there are routers other than the home agent on the home link,
then it cannot be guaranteed that all packets meant for the
mobile node are routed to the home agent. In this case, the
mobile node MUST NOT operate the Neighbor Discovery protocol for
the home address on the home link. This allows the home agent to
keep using proxy Neighbor Discovery, and thus it keeps receiving
all the packets sent to the mobile node's home address. If the
home agent, according to its local policy, needs to deliver
packets to the mobile node over the home link, an issue arises
with respect to how the home agent discovers the mobile node's
link local address. This specification uses the Mobility Header
Link-Layer Address option defined in [RFC 5568] in order to carry
the mobile node's link-layer address in the Binding Update.
Likewise, the mobile node would also know the link-layer address
of the default router address to send packets from the home link
without Neighbor Discovery. The link-layer address is used to
transmit packets from and to the mobile node on the home link.
The packets are transmitted without the Neighbor Discovery
protocol by constructing the link-layer header manually. This
operation is similar to Mobile IPv6 [RFC 3775] when a mobile node
sends a de-registration Binding Update to the home agent's link-
layer address in the operation for returning home.
5.6.3. Home Binding Support
When the home binding is used, the mobile node MUST send a
registering Binding Update with a Binding Identifier mobility option
with the 'H' flag set. The lifetime MUST be set to a non-zero
lifetime of the home binding, and the Care-of Address field MUST be
set to the home address. The mobile node registers only one home
binding at a time, even if it attaches to the home link by multiple
interfaces.
The mobile node SHOULD include the Mobility Header Link-Layer Address
option [RFC 5568] to notify the mobile node's link-layer address to
the home agent, too. The option code of the Mobility Header Link-
Layer Address option MUST be set to '2' (link-layer address of the
mobile node). This link-layer address is required for the home agent
to send the Binding Acknowledgement and to forward the mobile node's
packet.
According to [RFC 3775], the mobile node MUST start responding to
Neighbor Solicitation for its home address right after it sends the
de-registration Binding Update to the home agent. However, in this
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specification, the mobile node MUST NOT respond to Neighbor
Solicitation before receiving a Binding Acknowledgement, since the
home agent may continue proxying for the home address. If the mobile
node receives [MCOA RETURNHOME WO/NDP (5)] status value in the
received Binding Acknowledgment, it MUST NOT respond to Neighbor
Solicitation even after the Binding Acknowledgement.
The management of the home binding is the same as the binding
management described in this specification. The home binding can be
included in a bulk binding registration (Section 5.3). The MN SHOULD
refresh the lifetime of the home binding by sending appropriate
Binding Updates as with any other binding.
5.6.4. Sending Packets from the Home Link
o When the mobile node receives the Binding Acknowledgement with the
status value 'Binding Update Accepted' and the BID option, it can
configure its home address to the interface attached to the home
link and start operating Neighbor Discovery for the home address
on the home link. Packets can be transmitted from and to the
mobile node as if the mobile node were a regular IPv6 node.
o If the mobile node receives the status [MCOA RETURNHOME WO/NDP] in
the Binding Acknowledgement, it MUST NOT operate Neighbor
Discovery for the home address. When the mobile node sends
packets from the interface attached to the home link, it MUST
learn the link-layer address of the next hop (i.e., default router
of the mobile node). A mobile node learns the default router's
link-layer address from a Source Link-Layer Address option in
Router Advertisements. The mobile node sends packets directly to
the default router's link-layer address. This is done by
constructing the packet to include a link-layer header with the
learned link-layer address of the default router. The home agent
also forwards the packet to the mobile node on the home link by
using the mobile node's link-layer address. The link-layer
address SHOULD be cached when the home agent receives the
de-registration Binding Update message. Note that the default
router MUST NOT cache the mobile node's link-layer address in the
neighbor cache when it forwards the packet from the mobile node to
the home agent.
5.6.5. Leaving from the Home Link
When the mobile node detaches from the home link, it SHOULD
immediately send a Binding Update for one of the active care-of
addresses with the 'H' flag unset. When the 'H' flag of the BID
option is unset in any Binding Update, the home agent stops
forwarding the mobile node's packets to the home link.
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5.7. Receiving Binding Acknowledgement
The verification of a Binding Acknowledgement is the same as Mobile
IPv6 (Section 11.7.3 of [RFC 3775]). The operation for sending a
Binding Acknowledgement is described in Section 6.2.
If a mobile node includes a Binding Identifier mobility option in a
Binding Update with the 'A' flag set, a Binding Acknowledgement
SHOULD carry a Binding Identifier mobility option. According to
[RFC 3775], the receiver of the Binding Update ignores unknown
mobility options and processes the Binding Update without the unknown
mobility option. Therefore, if no such mobility option is included
in the Binding Acknowledgement in response to a Binding Update for a
multiple care-of addresses registration, this indicates that the
originating node of the Binding Acknowledgement does not support
processing the Binding Identifier mobility option regardless of
status value. In such case, the receiver of the Binding Update may
create a regular binding. The mobile node then SHOULD no longer
attempt a multiple care-of addresses registration with that node. If
this occurs with home registration, the mobile node MAY attempt to
discover another home agent that supports the Binding Identifier
mobility option for the home registration.
If a Binding Identifier mobility option is present in the received
Binding Acknowledgement, the mobile node checks the Status field in
the option. If the status value in the Binding Identifier mobility
option is zero, the mobile node uses the value in the Status field of
the Binding Acknowledgement. Otherwise, it uses the value in the
Status field of the Binding Identifier mobility option.
If the status code is greater than or equal to 128, the mobile node
starts relevant operations according to the error code. Otherwise,
the mobile node assumes that the originator (home agent or
correspondent node) successfully registered the binding information
and BID for the mobile node.
o If the status value is [MCOA PROHIBITED], the mobile node MUST
stop registering multiple bindings with the node that sent the
Binding Acknowledgement.
o If the status value is [MCOA BULK REGISTRATION PROHIBITED], the
mobile node needs to stop using bulk registrations with the node
that sent the Binding Acknowledgement. It should assume that none
of the attempted registrations were successful.
o If [MCOA MALFORMED] is specified, it indicates that the Binding
Identifier mobility option is formatted wrong, presumably due to a
programming error or major packet corruption.
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o If [MCOA NON-MCOA BINDING EXISTS] is specified, it means that
there is a non-MCoA binding entry in the receiver. The mobile
node MUST set 'O' flag so that all the registered bindings are
replaced by an MCoA registration as described in Section 5.9.
o If [MCOA UNKNOWN COA] is specified, it means that the mobile node
sent a Binding Identifier mobility option without a Care-of
Address field, but the receiver could not find an entry for the
BID indicated. If the mobile node is trying to de-register a BID,
it need not do anything further. If the mobile node is trying to
refresh a binding, it SHOULD send a Binding Identifier mobility
option including the Care-of Address field.
5.8. Receiving Binding Refresh Request
The verification of a Binding Refresh Request is the same as in
Mobile IPv6 (Section 11.7.4 of [RFC 3775]). The operation of sending
a Binding Refresh Request is described in Section 6.4.
If a mobile node receives a Binding Refresh Request with a Binding
Identifier mobility option, it indicates that the node sending the
Binding Refresh Request message is requesting that the mobile node
send a new Binding Update for the BID. The mobile node SHOULD then
send a Binding Update at least for the respective binding, as
described in Sections 5.2 and 5.3.
5.9. Bootstrapping
When a mobile node bootstraps and registers multiple bindings for the
first time, it MUST set the 'O' flag in the Binding Update message.
If old bindings still exist at the home agent, the mobile node has no
knowledge of which bindings still exist at the home agent. This
scenario happens when a mobile node reboots and loses state regarding
the registrations. If the 'O' flag is set, all the bindings are
replaced by the new binding(s).
6. Home Agent and Correspondent Node Operation
6.1. Searching Binding Cache with Binding 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. This section
explains how to retrieve the desired binding for the binding
management. This document does not provide any mechanism to select
the suitable binding for forwarding data packets.
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A node that is either a correspondent node or a home agent SHOULD use
both the home address and the BID as the search key of the binding
cache if it knows the corresponding BID (for example, when processing
signaling messages). In the example below, if a node searches the
binding with the home address and BID2, it gets binding2 for this
mobile node.
binding1 [2001:db8::EUI, care-of address1, BID1]
binding2 [2001:db8::EUI, care-of address2, BID2]
binding3 [2001:db8::EUI, care-of address3, BID3]
Figure 8: Searching the Binding Cache
The node learns the BID when it receives a Binding Identifier
mobility option. At that time, the node MUST look up its binding
cache database with the home address and the BID retrieved from the
Binding Update. If the node does not know the BID, it searches for a
binding with only the home address. In such a case, the first
matched binding is found. If the node does not desire to use
multiple bindings for a mobile node, it can simply ignore the BID.
6.2. Processing Binding Update
If a Binding Update does not contain a Binding Identifier mobility
option, its processing is the same as in [RFC 3775]. If the receiver
already has multiple bindings for the home address, it MUST replace
all the existing bindings with the received binding. If the
[RFC 3775] Binding Update is for de-registration, the receiver MUST
delete all existing bindings from its binding cache.
If the Binding Update contains Binding Identifier mobility option(s),
it is first validated according to Section 9.5.1 of [RFC 3775]. Then
the receiver processes the Binding Identifier mobility option(s) as
described in the following steps.
o The length value is examined. The length value MUST be either 4,
8, or 20 depending on the Care-of Address field. If the length is
incorrect, the receiver MUST reject the Binding Update and return
the status value set to [MCOA MALFORMED].
o When the length value is either 8 or 20, the care-of address MUST
be present in the Binding Identifier mobility option. If the
unicast routable address [RFC 3775] is not present in the Care-of
Address field, the receiver MUST reject the Binding Identifier
mobility option and return the status value set to [MCOA
MALFORMED].
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o When multiple Binding Identifier mobility options are present in
the Binding Update, it is treated as bulk registration. If the
receiving node is a correspondent node, it MUST reject the Binding
Update and return the status value set to [MCOA BULK REGISTRATION
PROHIBITED] in the binding Acknowledgement.
o If the Lifetime field in the Binding Update is set to zero, the
receiving node deletes the binding entry that corresponds to the
BID in the Binding Identifier mobility option. If the receiving
node does not have an appropriate binding for the BID, it MUST
reject the Binding Update and send a Binding Acknowledgement with
status set to 133 [not home agent for this mobile node].
o If the 'O' flag is set in the de-registering Binding Update, it is
ignored. If the 'H' flag is set, the home agent stores a home
address in the Care-of Address field of the binding cache entry.
The home agent MUST follow the descriptions described in Section
5.6.
o If the Lifetime field is not set to zero, the receiving node
registers a binding with the specified BID as a mobile node's
binding. The care-of address is obtained from the Binding Update
packet as follows:
* If the length value of the Binding Identifier mobility option
is 20, the care-of address is the IPv6 address copied from the
Care-of Address field in the Binding Identifier mobility
option.
* When the length value is 8, the address MUST be the IPv4 valid
address. How to obtain an IPv4 care-of address is described in
Section 8.
* When the length value is 4 and the Binding Identifier is
present in the binding cache, the receiving node MUST update
the associated binding entry. Otherwise, the receiving node
MUST reject that Binding Identifier mobility option and send a
Binding Acknowledgement with the status for that Binding
Identifier mobility option set to [MCOA UNKNOWN].
o Once the care-of address(es) have been retrieved from the Binding
Update, the receiving nodes create new binding(s).
* If the 'O' flag is set in the Binding Update, the receiving
node removes all the existing bindings and registers the
received binding(s).
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* If the 'O' flag is unset in the Binding Update and the receiver
has a regular binding that does not have a BID for the mobile
node, it must not process the Binding Update. The receiver
should send a Binding Acknowledgement with status set to [MCOA
NON-MCOA BINDING EXISTS].
* If the receiver already has a binding with the same BID but
different care-of address, it MUST update the binding and
respond with a Binding Acknowledgement with status set to 0
[Binding Update accepted].
* If the receiver does not have a binding entry for the BID, it
registers a new binding for the BID and responds with a Binding
Acknowledgement with status set to 0 [Binding Update accepted].
If all the above operations are successfully completed and the 'A'
flag is set in the Binding Update, a Binding Acknowledgement
containing the Binding Identifier mobility options MUST be sent to
the mobile node. Whenever a Binding Acknowledgement is sent, all the
Binding Identifier mobility options stored in the Binding Update MUST
be copied to the Binding Acknowledgement except the Status field.
The Care-of Address field in each Binding Identifier mobility option,
however, MAY be omitted, because the mobile node can match a
corresponding Binding Update List entry using the BID.
When a correspondent node sends a Binding Acknowledgement, the status
value MUST always be stored in the Status field of the Binding
Acknowledgement and the Status field of the Binding Identifier
mobility option MUST always be set to zero.
When the home agent sends a Binding Acknowledgement, the status value
can be stored in the Status field of either a Binding Acknowledgement
or a Binding Identifier mobility option. If the status value is
specific to one of the bindings in the bulk registration, the status
value MUST be stored in the Status field in the corresponding Binding
Identifier mobility option. In this case, the Status field of the
Binding Acknowledgement MUST be set to [MCOA NOTCOMPLETE], so that
the receiver can examine the Status field of each Binding Identifier
mobility option for further operations. Otherwise, the Status field
of the Binding Identifier mobility option MUST be set to zero and the
home agent Status field of the Binding Acknowledgement is used.
6.3. Sending a Binding Acknowledgement for Home Link Registration
The operations described in this section are related to returning
home with simultaneous use of home and foreign links.
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o When the home agent sends the Binding Acknowledgement after
successfully processing the home binding registration, it MUST set
the status value to either 0 [Binding Update Accepted] or [MCOA
RETURNHOME WO/NDP (5)] in the Status field of the Binding
Acknowledgment, depending on home agent configuration at the home
link. The new values are:
* Binding Update Accepted (0): The Neighbor Discovery protocol is
permitted for the home address at the home link. This is the
regular returning home operation of [RFC 3775].
* MCOA RETURNHOME WO/NDP (5): The Neighbor Discovery protocol is
prohibited for the home address at the home link.
The respective Binding Identifier mobility options need to be
included in the Binding Acknowledgement.
o If the Binding Update is rejected, the appropriate error value
MUST be set in the Status field. In this case, the home agent
operation is the same as in [RFC 3775].
o Only if the home agent is the only router in the home link MAY it
turn off Neighbor Discovery for the requested home address and
respond with the [Binding Update Accepted] status value to the
mobile node. Since the mobile node will not reply to Neighbor
Solicitation for the home address before receiving the Binding
Acknowledgement, the home agent SHOULD use the link-layer address
carried by the Mobility Header Link-Layer Address option [RFC 5568]
in the received Binding Update. After the completion of the home
binding registration, the mobile node starts regular Neighbor
Discovery operations for the home address on the home link. The
neighbor cache entry for the home address is created by the
regular exchange of Neighbor Solicitation and Neighbor
Advertisement.
o If the home agent is not the only router in the home link, the
home agent returns [MCOA RETURNHOME WO/NDP] value in the Status
field of the Binding Identifier mobility option. The home agent
learns the mobile node's link-layer address by receiving the
Mobility Header Link-Layer Address option carried by the Binding
Update. It stores the link-layer address as a neighbor cache
entry for the mobile node so that it can send the packets to the
mobile node's link-layer address.
o Note that the use of proxy Neighbor Discovery is an easier way to
intercept the mobile nodes' packets instead of IP routing in some
deployment scenarios. Therefore, even if a home agent is the only
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router, it is an implementation and operational choice whether the
home agent returns [Binding Update Accepted] or [MCOA RETURNHOME
WO/NDP].
o If the BID option is not included in the Binding Acknowledgement,
the home agent might not recognize the home registration. The
home agent might have processed the home registration Binding
Update as a regular de-registration, as described in [RFC 3775],
and deleted all the registered binding cache entries for the
mobile node. Thus, the mobile node SHOULD stop using the
interface attached to the foreign link and use only the interface
attached to the home link.
6.4. Sending Binding Refresh Request
When a node (home agent or correspondent node) sends a Binding
Refresh Request for a particular binding created with the BID, the
node SHOULD include the Binding Identifier mobility option in the
Binding Refresh Request. The node MAY include multiple Binding
Identifier mobility options if there are multiple bindings that need
to be refreshed.
6.5. Receiving Packets from Mobile Node
When a node receives packets with a Home Address destination option
from a mobile node, it MUST check that the care-of address that
appears in the Source Address field of the IPv6 header is equal to
one of the care-of addresses in the binding cache entry. If no
binding is found, the packets MUST be discarded. The node MUST also
send a Binding Error message as specified in [RFC 3775]. This
verification MUST NOT be done for a Binding Update.
7. Network Mobility Applicability
The binding management mechanisms are the same for a mobile host that
uses Mobile IPv6 and for a mobile router that is using the NEMO Basic
Support protocol [RFC 3963]. Therefore, the extensions described in
this document can also be used to support a mobile router with
multiple care-of addresses. [RFC 4980] contains an analysis of NEMO
multihoming.
8. DSMIPv6 Applicability
Dual Stack Mobile IPv6 (DSMIPv6) [RFC 5555] extends Mobile IPv6 to
register an IPv4 care-of address instead of the IPv6 care-of address
when the mobile node is attached to an IPv4-only access network. It
also allows the mobile node to acquire an IPv4 home address in
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addition to an IPv6 home address for use with IPv4-only correspondent
nodes. This section describes how the multiple care-of addresses
registration works with IPv4 care-of and home addresses.
8.1. IPv4 Care-of Address Registration
The mobile node can use the extensions described in the document to
register multiple care-of addresses, even if some of the care-of
addresses are IPv4 addresses.
Bulk registration MUST NOT be used for the initial binding
registration from an IPv4 care-of address. This is because the
Binding Update and Binding Acknowledgement exchange is used to detect
NAT on the path between the mobile node and the home agent. So the
mobile node needs to check for a NAT between each IPv4 care-of
address and the home agent.
The Binding Update MUST be sent to the IPv4 home agent address by
using UDP and IPv4 headers as shown in Figure 9. It is similar to
[RFC 5555] except that the IPv4 care-of address option MUST NOT be
used when the BID mobility option is used.
IPv4 header (src=V4ADDR, dst=HA_V4ADDR)
UDP Header
IPv6 header (src=V6HoA, dst=HAADDR)
ESP Header
Mobility header
-Binding Update
Mobility Options
- Binding Identifier (IPv4 CoA)
*V4ADDR, HA_V4ADDR, V6HOA, HAADDR are defined in [RFC 5555]
Figure 9: Initial Binding Update for IPv4 Care-of Address
If a NAT is not detected, the mobile node can update the IPv4 care-of
address by using bulk registration. The mobile node can register the
IPv4 care-of address along with other IPv4 and IPv6 care-of
addresses. Figure 10 shows the Binding Update format when the mobile
node sends a Binding Update from one of its IPv6 care-of addresses.
If the mobile node sends a Binding Update from an IPv4 care-of
address, it MUST follow the format described in Figure 9. Note that
the IPv4 care-of address must be registered by a non-bulk binding
registration whenever it is changed.
As shown in Figure 9, the IPv4 care-of address will appear in the
Binding Identifier mobility option. The IPv4 Care-of Address
mobility option defined in [RFC 5555] MUST always be omitted. The
receiver of the Binding Update message for an IPv4 care-of address
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MUST treat the IPv4 address stored in the Binding Identifier mobility
option as the one in the IPv4 Care-of Address mobility option of
[RFC 5555]. If the IPv4 address in the Binding Identifier mobility
option is different from one in the Source Address field in the IPv4
header of the Binding Update (i.e., V4ADDR in Figure 9), the source
address is used as an IPv4 care-of address. Otherwise, the IPv4
address in the Binding Identifier mobility option is used as an IPv4
care-of address.
IPv6 header (src=Care-of Address, dst=Home Agent Address)
IPv6 Home Address Option
ESP Header
Mobility header
-Binding Update
Mobility Options
- Binding Identifier (IPv6/v4 CoA)
- Binding Identifier (IPv6/v4 CoA)
- ...
Figure 10: Binding Bulk Registration for an IPv4 Care-of Address
When the home agent returns a Binding Acknowledgement for the IPv4
care-of address registration, it SHOULD NOT use the IPv4 Address
Acknowledgement mobility option and SHOULD use only the Binding
Identifier mobility option. The registration status for the IPv4
care-of address is stored in the Status field of the Binding
Identifier mobility option. However, if the home agent needs to
store the status value specially defined for the IPv4 Address
Acknowledgement mobility option, it MUST store the status value in
the IPv4 Address Acknowledgement mobility option and MUST NOT store
it in the Binding Identifier mobility option. In such case, the home
agent MUST include both the IPv4 Address Acknowledgement mobility
option and the Binding Identifier mobility option.
8.2. IPv4 Home Address Management
When the mobile node wants to configure an IPv4 home address in
addition to the IPv6 home address, it can request one using the IPv4
Home Address option in the Binding Update. If the home agent accepts
the Binding Update, the mobile node can now register multiple care-of
addresses for the IPv4 home address in addition to the IPv6 home
address. The mobile node MUST always use the IPv4 Home Address
mobility option for any purposes of the IPv4 home address management.
The same set of care-of addresses will be registered for both IPv6
and IPv4 home addresses. The mobile node cannot bind a different set
of care-of addresses to each home address.
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According to [RFC 5555], the home agent includes the IPv4 Address
Acknowledgement option in the Binding Acknowledgement only if the
mobile node had requested an IPv4 home address in the corresponding
Binding Update. The IPv4 Address Acknowledgement option MUST be
present before any Binding Identifier mobility option. The Status
field of the IPv4 Address Acknowledgement option contains only the
error code defined in Section 3.2.1 of [RFC 5555]. The home agent
MUST always include the IPv4 Address Acknowledgement mobility option
in the Binding Acknowledgement for the IPv4 home address
registration.
9. IPsec and IKEv2 Interaction
Mobile IPv6 [RFC 3775] and the NEMO protocol [RFC 3963] require the use
of IPsec to protect signaling messages, including Binding Updates,
Binding Acknowledgements, and return routability messages. IPsec may
also be used to protect all tunneled data traffic. The Mobile IPv6-
IKEv2 specification [RFC 4877] specifies how IKEv2 can be used to set
up the required IPsec security associations. The following
assumptions were made in [RFC 3775], [RFC 3963], and [RFC 4877] with
respect to the use of IKEv2 and IPsec.
o There is only one primary care-of address per mobile node.
o The primary care-of address is stored in the IPsec database for
tunnel encapsulation and decapsulation.
o When the home agent receives a packet from the mobile node, the
source address is verified against the care-of address in the
corresponding binding cache entry. If the packet is a reverse-
tunneled packet from the mobile node, the care-of address check is
done against the source address on the outer IPv6 header. The
reverse-tunneled packet could either be a tunneled Home Test Init
message or tunneled data traffic to the correspondent node.
o The mobile node runs IKEv2 (or IKEv1) with the home agent using
the care-of address. The IKE SA is based on the care-of address
of the mobile node.
The above assumptions may not be valid when multiple care-of
addresses are used by the mobile node. In the following sections,
the main issues with the use of multiple care-of addresses with IPsec
are addressed.
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RFC 5648 MCoA October 2009
9.1. Use of Care-of Address in the IKEv2 Exchange
For each home address for which the mobile node sets up security
associations with the home agent, the mobile node must pick one
care-of address and use that as the source address for all IKEv2
messages exchanged to create and maintain the IPsec security
associations associated with the home address. The resultant IKEv2
security association is created based on this care-of address.
If the mobile node needs to change the care-of address, it just sends
a Binding Update with the care-of address it wants to use, with the
corresponding Binding Identifier mobility option, and with the 'K'
bit set. This will force the home agent to update the IKEv2 security
association to use the new care-of address. If the 'K' bit is not
supported on the mobile node or the home agent, the mobile node MUST
re-establish the IKEv2 security association with the new care-of
address. This will also result in new IPsec security associations
being set up for the home address.
9.2. Transport Mode IPsec-Protected Messages
For Mobile IPv6 signaling message protected using IPsec in transport
mode, the use of a particular care-of address among multiple care-of
addresses does not matter for IPsec processing.
The home agent processes Mobile Prefix Discovery messages with the
same rules of data packets described in Section 6.5.
9.3. Tunnel Mode IPsec-Protected Messages
The use of IPsec in tunnel mode with multiple care-of addresses
introduces a few issues that require changes to how the mobile node
and the home agent send and receive tunneled traffic. The route
optimization mechanism described in [RFC 3775] mandates the use of
IPsec protection in tunnel mode for the Home Test Init and Home Test
messages. The mobile node and the home agent may also choose to
protect all reverse-tunneled payload traffic with IPsec in tunnel
mode. The following sections address multiple care-of address
support for these two types of messages.
9.3.1. Tunneled Home Test Init and Home Test Messages
The mobile node MAY use the same care-of address for all Home Test
Init messages sent reverse tunneled through the home agent. The
mobile node may use the same care-of address irrespective of which
correspondent node the Home Test Init message is being to. RFC 3775
requires the home agent to verify that the mobile node is using the
care-of address that is in the binding cache entry when it receives a
Wakikawa, et al. Standards Track PAGE 31
RFC 5648 MCoA October 2009
reverse-tunneled Home Test Init message. If a different address is
used as the source address, the message is silently dropped by the
home agent. This document requires the home agent implementation to
decapsulate and forward the Home Test Init message as long as the
source address is one of the care-of addresses in the binding cache
entry for the mobile node.
When the home agent tunnels a Home Test message to the mobile node,
the care-of address used in the outer IPv6 header is not relevant to
the Home Test message. So regular IPsec tunnel encapsulation with
the care-of address known to the IPsec implementation on the home
agent is sufficient.
9.3.2. Tunneled Payload Traffic
When the mobile node sends and receives multiple traffic flows
protected by IPsec to different care-of addresses, the use of the
correct care-of address for each flow becomes important. Support for
this requires the following two considerations on the home agent.
o When the home agent receives a reverse-tunneled payload message
protected by IPsec in tunnel mode, the source address used in the
outer IPv6 header is irrelevant to IPsec, since the tunnel mode
security association is based on the addresses in the inner IPv6
header. Therefore, the same IPsec security association can be
used for payload traffic tunneled from any of the care-of
addresses. Note that the care-of address used in the reverse-
tunneled traffic can be different from the care-of address used as
the source address in the IKEv2 exchange. However, this does not
cause an issue due to the above-mentioned reason.
o For tunneled IPsec traffic from the home agent to the mobile node,
the IPsec implementation on the home agent will not be aware of
which care-of address to use when performing IPsec tunnel
encapsulation. The Mobile IP stack on the home agent, based on
the binding cache entries created by the mobile node, knows to
which care-of address the packet belonging to a particular flow
needs to be tunneled. The destination address for the outer IP
header must either be conveyed dynamically per packet to the IPsec
stack when it performs the encapsulation or the Mobile IPv6 stack
must get access to the packet after IPsec processing is done and
modify the destination address. The first option requires changes
to the IPsec implementation. In the second option, there is a
need for special processing in the forwarding function to replace
the destination address on the outer header with the correct
care-of address. The exact technique to achieve the above is
implementation specific.
Wakikawa, et al. Standards Track PAGE 32
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10. Security Considerations
The security considerations for securing the Binding Update and
Binding Acknowledgement messages with multiple care-of addresses are
very similar to the security considerations for securing the Binding
Update and Binding Acknowledgement. Please see [RFC 3775] for more
information. The Binding Update and Binding Acknowledgement messages
with multiple care-of addresses are securely exchanged as described
in [RFC 3775], [RFC 4877], and Section 9 of this document. Additional
security considerations are described below.
With simultaneous binding support, it is possible for a malicious
mobile node to successfully bind a number of victims' addresses as
valid care-of addresses for the mobile node with its home agent.
Once these addresses have been bound, the malicious mobile node can
perform a re-direction attack by instructing the home agent (e.g.,
setting filtering rules to direct a large file transfer) to tunnel
packets to the victims' addresses. Such risk is highlighted in
[MIP6ANALYSIS]. These attacks are possible because the care-of
addresses sent by the mobile node in the Binding Update messages are
not verified by the home agent, i.e., the home agent does not check
if the mobile node is at the care-of address at which it claims to
be. The security model for Mobile IPv6 assumes that there is a trust
relationship between the mobile node and its home agent. Any
malicious attack by the mobile node is traceable by the home agent.
This acts as a deterrent for the mobile node to launch such attacks.
Although such a risk exists in Mobile IPv6, the risk level is
increased when simultaneous multiple care-of address bindings are
performed. In Mobile IPv6, a mobile node can only have a single
care-of address binding per home address at a given time. However,
for simultaneous multiple care-of address bindings, a mobile node can
have more than one care-of address binding per home address at a
given time. This implies that a mobile node using simultaneous
binding support can effectively bind more than a single victim's
address. Another difference is the degree of risk involved. In the
single care-of address binding case, once the re-direction attack is
initiated, a malicious mobile node would be unable to use its home
address for communications (such as to receive control packets
pertaining to the file transfer). However, in the simultaneous
binding support case, a malicious mobile node could bind a valid
care-of address in addition to multiple victims addresses. This
valid care-of address could then be used by the malicious mobile node
to set up flow filtering rules at its home agent, thereby controlling
and/or launching new re-direction attacks.
Wakikawa, et al. Standards Track PAGE 33
RFC 5648 MCoA October 2009
Thus, in view of such risks, it is advisable for a home agent to
employ some form of care-of address verification mechanism before
using the care-of addresses as a valid routing path to a mobile node.
These mechanisms are out of scope for this document.
In the binding registration of Mobile IPv6, a care-of address is
always verified by its reachability by a home agent. This
reachability test may decrease the above risks. However, when bulk
registration is used, a home agent cannot verify reachability of
care-of addresses carried in a Binding Identifier mobility option.
Therefore, the home agent can choose to reject bulk registration by
using [MCOA BULK REGISTRATION PROHIBITED] in a Binding
Acknowledgement. Alternatively, when a mobile node first registers a
care-of address, it uses the individual Binding Updates for the first
appeared care-of address. During the initial binding registration, a
home agent can verify the address reachability for that given care-of
address. After that, the mobile node uses bulk registration to
refresh the care-of address.
11. IANA Considerations
The following Extension Types have been assigned by IANA:
o Binding Identifier mobility option type: (35) has been assigned
from the same space as the mobility option in [RFC 3775].
o New Successful Status of Binding Acknowledgement: These status
codes have been assigned from the same space as the Binding
Acknowledgement status codes in [RFC 3775].
* MCOA NOTCOMPLETE (4)
* MCOA RETURNHOME WO/NDP (5)
o New Unsuccessful Status of Binding Acknowledgement: These status
codes have also been assigned from the same space as the Binding
Acknowledgement status codes in [RFC 3775].
* MCOA MALFORMED (164)
* MCOA NON-MCOA BINDING EXISTS (165)
* MCOA PROHIBITED (166)
* MCOA UNKNOWN COA (167)
* MCOA BULK REGISTRATION PROHIBITED (168)
Wakikawa, et al. Standards Track PAGE 34
RFC 5648 MCoA October 2009
* MCOA SIMULTANEOUS HOME AND FOREIGN PROHIBITED (169)
12. Acknowledgements
Ryuji Wakikawa and Thierry Ernst are grateful to Keio University for
its initial support on this specification at the time when they were
working there. In addition, the authors would like to thank Masafumi
Aramoto, Keigo Aso, Julien Charbon, Tero Kauppinen, Martti Kuparinen,
Romain Kuntz, Benjamin Lim, Heikki Mahkonen, Nicolas Montavont, and
Chan-Wah Ng for their discussions and inputs. Thanks to Susumu
Koshiba, Hiroki Matutani, Koshiro Mitsuya, Koji Okada, Keisuke
Uehara, Masafumi Watari, and Jun Murai for earlier work on this
subject.
13. References
13.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC
4861, September 2007.
[RFC 3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility
Support in IPv6", RFC 3775, June 2004.
[RFC 4877] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation
with IKEv2 and the Revised IPsec Architecture", RFC
4877, April 2007.
[RFC 3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support
Protocol", RFC 3963, January 2005.
[RFC 5555] Soliman, H., Ed., "Mobile IPv6 Support for Dual Stack
Hosts and Routers", RFC 5555, June 2009.
[RFC 5568] Koodli, R., Ed., "Mobile IPv6 Fast Handovers", RFC
5568, July 2009.
13.2. Informative References
[MOTIVATION] Ernst, T., Montavont, N., Wakikawa, R., Ng, C., and K.
Kuladinithi, "Motivations and Scenarios for Using
Multiple Interfaces and Global Addresses", Work in
Progress, May 2008.
Wakikawa, et al. Standards Track PAGE 35
RFC 5648 MCoA October 2009
[RFC 4980] Ng, C., Ernst, T., Paik, E., and M. Bagnulo, "Analysis
of Multihoming in Network Mobility Support", RFC 4980,
October 2007.
[MIP6ANALYSIS] Montavont, N., Wakikawa, R., Ernst, T., Ng, C., and K.
Kuladinithi, "Analysis of Multihoming in Mobile IPv6",
Work in Progress, May 2008.
[RFC 3753] Manner, J., Ed., and M. Kojo, Ed., "Mobility Related
Terminology", RFC 3753, June 2004.
[RFC 4885] Ernst, T. and H-Y. Lach, "Network Mobility Support
Terminology", RFC 4885, July 2007.
Authors' Addresses
Ryuji Wakikawa (Editor)
TOYOTA InfoTechnology Center Co., Ltd.
EMail: ryuji.wakikawa@gmail.com (ryuji@jp.toyota-itc.com)
Vijay Devarapalli
Wichorus
EMail: vijay@wichorus.com
George Tsirtsis
Qualcomm
EMail: Tsirtsis@gmail.com
Thierry Ernst
INRIA
EMail: thierry.ernst@inria.fr
Kenichi Nagami
INTEC NetCore Inc.
EMail: nagami@inetcore.com
Wakikawa, et al. Standards Track PAGE 36
Multiple Care-of Addresses Registration
RFC TOTAL SIZE: 90112 bytes
PUBLICATION DATE: Saturday, October 3rd, 2009
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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