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Network Working Group E. Fogelstroem
Request for Comments: 4857 A. Jonsson
Category: Experimental Ericsson
C. Perkins
Nokia Siemens Networks
June 2007
Mobile IPv4 Regional Registration
Status of This Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Using Mobile IP, a mobile node registers with its home agent each
time it changes care-of address. This document describes a new kind
of "regional registrations", i.e., registrations local to the visited
domain. The regional registrations are performed via a new network
entity called a Gateway Foreign Agent (GFA) and introduce a layer of
hierarchy in the visited domain. Regional registrations reduce the
number of signaling messages to the home network, and reduce the
signaling delay when a mobile node moves from one foreign agent to
another within the same visited domain. This document is an optional
extension to the Mobile IPv4 protocol.
Table of Contents
1. Introduction ....................................................3
2. Overview of Regional Registrations ..............................4
3. Terminology .....................................................5
4. Description of the Protocol .....................................7
4.1. General Assumptions ........................................7
4.1.1. Visited Domain ......................................8
4.1.2. Authentication ......................................8
4.2. Protocol Overview ..........................................9
4.3. Advertising Foreign Agent and GFA .........................10
4.4. Backwards Compatibility with RFC 3344 .....................10
5. Home Registration ..............................................11
5.1. Mobile Node Considerations ................................11
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RFC 4857 Mobile IPv4 Regional Registration June 2007
5.2. Foreign Agent Considerations ..............................12
5.3. GFA Considerations ........................................13
5.4. Home Agent Considerations .................................14
6. Regional Registration ..........................................14
6.1. Mobile Node Considerations ................................15
6.2. Foreign Agent Considerations ..............................16
6.3. GFA Considerations ........................................16
7. Dynamic GFA Assignment .........................................17
7.1. Mobile Node Considerations for Dynamic GFA Assignment .....17
7.2. Foreign Agent Considerations for Dynamic GFA Assignment ...17
7.3. GFA Considerations for Dynamic GFA Assignment .............18
7.4. Home Agent Considerations for Dynamic GFA Assignment ......18
7.5. Regional Registration .....................................19
8. Router Discovery Extensions ....................................19
8.1. Regional Registration Flag ................................19
8.2. Foreign Agent NAI Extension ...............................19
9. Regional Extensions to Mobile IPv4 Registration Messages .......20
9.1. GFA IP Address Extension ..................................20
9.2. Hierarchical Foreign Agent Extension ......................21
9.3. Replay Protection Style ...................................22
9.4. Regional Registration Lifetime Extension ..................23
9.5. New Code Values for Registration Reply ....................24
10. Regional Registration Message Formats .........................25
10.1. Regional Registration Request ............................26
10.2. Regional Registration Reply ..............................27
10.3. New Regional Registration Reply Code Values ..............28
11. Authentication Extensions .....................................29
12. Security Considerations .......................................29
13. IANA Considerations ...........................................30
14. Acknowledgements ..............................................31
15. References ....................................................32
15.1. Normative References .....................................32
15.2. Informative References ...................................32
Appendix A. Authentication, Authorization, and Accounting (AAA)
Interactions ..........................................33
Appendix B. Anchoring at a GFA ....................................33
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RFC 4857 Mobile IPv4 Regional Registration June 2007
1. Introduction
This document is an optional extension to the Mobile IPv4 protocol,
and proposes a means for mobile nodes to register locally within a
visited domain. By registering locally, the number of signaling
messages to the home network are kept to a minimum, and the signaling
delay is reduced.
In Mobile IP, as specified in [RFC3344], a mobile node registers with
its home agent each time it changes care-of address. If the distance
between the visited network and the home network of the mobile node
is large, the signaling delay for these registrations may be long.
We propose a solution for performing registrations locally in the
visited domain: regional registrations. Regional registrations
minimize the number of signaling messages to the home network, and
reduce the signaling delay when a mobile node moves from one foreign
agent to another within the same visited domain. This will both
decrease the load on the home network, and speed up the process of
handover within the visited domain.
Regional registrations introduce a new network node: the Gateway
Foreign Agent (GFA). The address of the GFA is advertised by the
foreign agents in a visited domain. When a mobile node first arrives
at this visited domain, it performs a home registration -- that is, a
registration with its home agent. At this registration, the mobile
node registers the address of the GFA as its care-of address with its
home agent. When moving between different foreign agents within the
same visited domain, the mobile node only needs to make a regional
registration to the GFA.
In their simplest form, regional registrations are performed
transparently to the home agent. Additionally, regional
registrations may also allow dynamic assignment of GFA. The solution
for dynamic GFA assignment requires support in the mobile node, the
foreign agent, the GFA, and the home agent.
The proposed regional registration protocol supports one level of
foreign agent hierarchy beneath the GFA, but the protocol may be
utilized to support several levels of hierarchy. Multiple levels of
hierarchy are not discussed in this document.
Although this document focuses on regional registrations in visited
domains, regional registrations are also possible in the home domain.
Foreign agents that support regional registrations are also required
to support registrations according to Mobile IPv4 [RFC3344].
The following section gives an overview of regional registrations.
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2. Overview of Regional Registrations
In standard Mobile IP, there are three entities of interest. The
Mobile Node (MN), the Foreign Agent (FA), and the Home Agent (HA).
The MN communicates with the HA, either through an FA or directly (if
it has a co-located care-of address). With Regional Registrations, a
new entity is defined: the Gateway Foreign Agent (GFA). The GFA sits
between the MN/FA and HA, and to the HA, it appears as if the MN's
temporary care-of address is that of the GFA. When a MN moves within
a site, it only need interact with the GFA, so that the GFA knows at
what temporary address the MN is currently reachable.
Two types of registration messages are used. Regular [RFC3344]
Registration Requests/Replies are still used for when the MN
exchanges Registration Requests/Replies with the HA, but these
messages get forwarded through a GFA, and include new extensions.
In addition, a new pair of registration messages, Regional
Registration Requests/Replies, are used between MNs/FAs/GFAs for
intra-site signaling. A MN uses these messages to communicate its
new addresses to the GFA as it moves around within a site.
There are two models of how the MN uses Regional Registrations. The
FA can advertise a GFA to the MN. Alternatively, the FA can indicate
that dynamic assignment of GFA is to be used. With dynamic GFA
assignment, the MN does not choose the GFA, rather the FA (or GFA)
does so after receiving a Registration Request from the MN. However,
in this mode the HA must understand (and support) Regional
Registrations in order for them to be used. This last form is not
transparent because the MN doesn't know in advance what GFA will be
used, and cannot include it in a signed message to the HA.
When a MN moves to a new domain (determined by comparing its Network
Access Identifier (NAI) [RFC4282] with the FA-NAI included in
received Agent Advertisements), it can opt to use Regional
Registrations. A site indicates support for Regional Registrations
by setting the I-bit of the Mobile IP Agent Advertisement extension.
In addition, such advertisements include a list of one or more care-
of addresses. If there is only one care-of address, this is the
address of the FA itself. In addition, the advertisement may include
the address of the GFA. A GFA care-of address of all-ones indicates
that dynamic assignment of GFA is supported.
A MN requests initial Regional Registration by sending a normal
Registration Request to the FA, but setting the care-of address to
that of the GFA (i.e., if it has selected it wishes to use this GFA)
or all-zeros (which signals a dynamic GFA assignment request). The
FA adds a Hierarchical FA (HFA) extension and relays the request to
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the appropriate GFA. The HFA extension contains a single field: the
IP address of the FA.
Note: the algorithm for MNs with co-located care-of addresses is
similar, except that there is no FA, so the MN behaves as the FA in
terms of the messages it sends.
A GFA receives Registration Requests relayed from an FA. If the
care-of address in the received Registration Request is zero, the GFA
assigns one. A GFA IP Address extension is then added to the
Registration Request, and the message is forwarded to the HA. The
GFA IP Address extension contains a single field: the IP address of
the GFA. (A separate field is needed for this because the
Registration Request message between the MN/HA is signed and cannot
be modified.)
HAs process received Registration Requests in the same way as before,
except in the case of dynamic GFA assignment. In this case, the HA
uses the GFA address from the GFA IP Address extension as the MN's
current care-of address. In addition, the Registration Reply message
must include the GFA IP Address extension.
The regular Registration Requests/Replies are protected as described
in [RFC3344], by use of the mobility security association between the
MN and the HA. For regional registrations, it is assumed that a
mobility security association is established between the MN and GFA
during registration with the HA. Regional Registration Requests/
Replies are protected by use of this security association between the
MN and the GFA, e.g., by use of a MN-GFA Authentication extension.
HFA extensions, added by an FA to a Registration Request or Regional
Registration Request, are protected by an FA-FA Authentication
extension. Security associations between FAs and GFAs within a
domain are assumed to exist prior to regional registrations.
Dynamic GFA assignment requires means for securely sending
Registration Requests from the GFA to the HA, in order to protect the
GFA IP Address extension.
3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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This document uses the following terms:
Critical type
A type value for an extension in the range 0-127, which indicates
that the extension MUST either be known to the recipient, or that
the message containing the extension MUST be rejected. In other
words, an extension with a critical type value is non-skippable.
Domain
A collection of networks sharing a common network administration.
Foreign Agent (FA)
As defined in [RFC3344].
Gateway Foreign Agent (GFA)
A Foreign Agent which has a publicly routable IP address. A GFA
may, for instance, be placed in or near a firewall.
Home Agent (HA)
As defined in [RFC3344].
Home domain
The domain where the home network and home agent are located.
Home network
As defined in [RFC3344].
Home Registration
A registration, processed by the home agent and the GFA, using the
specification in [RFC3344] possibly with additional extensions
defined in this document.
Local Care-of Address
A care-of address that is assigned to either a mobile node or a
foreign agent offering local connectivity to a mobile node. A
registration message from the mobile node is subsequently sent to
a GFA via the local care-of address.
Mobile Node (MN)
As defined in [RFC3344].
Mobility Agent (MA)
As defined in [RFC3344].
Network Access Identifier(NAI)
Some features of this protocol specification rely on use of the
Network Access Identifier (NAI) [RFC2794].
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RFC 4857 Mobile IPv4 Regional Registration June 2007
Regional Registration
A mobile node performs registration locally at the visited domain,
by sending a Regional Registration Request to a GFA, and receiving
a Regional Registration Reply in return.
Registration Key
A key used by mobile nodes and mobility agents to secure certain
signals and control messages specified by Mobile IP.
Visited domain
The domain where the visited network, the current foreign agent,
and the GFA are located.
Visited network
As defined in [RFC3344].
4. Description of the Protocol
This section provides an overview of the regional registration
protocol.
4.1. General Assumptions
Our general model of operation is illustrated in Figure 1, showing a
visited domain with FA and GFA, and a home network with a HA:
+---------------------------+ +----------------+
| Visited Domain | | Home |
| | +---------+ | Network |
| | | | | |
| +------+ +-------+ | | Public | | +------+ |
| | FA |------| GFA |-------------------------| HA | |
| +--+---+ +-------+ | | Network | | +------+ |
| | | | | | |
+-----|---------------------+ +---------+ +----------------+
|
+--+---+
| MN |
+------+
Figure 1: Model of Operation
For MNs that cannot process a NAI, or with mobility agents that are
not configured to advertise their NAI, regional registration is still
useful, but processing the NAI makes it easier for the mobile node to
reliably detect domain changes.
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4.1.1. Visited Domain
We assume two hierarchy levels of FAs in the visited domain. At the
top level of the hierarchy, there is at least one GFA, which is an FA
with additional features. A GFA must have a publicly routable
address. Beneath a GFA, there are one or more FAs. We assume that
there exist established security associations between a GFA and the
FAs beneath it. When designing a domain supporting regional
registrations, the FAs and GFAs in this domain must be compatible.
That is, they should support the same encapsulation types,
compression mechanisms, etc.
When a MN changes care-of address under the same GFA, it MAY perform
a regional registration. If the MN changes GFA, within a visited
domain or between visited domains, it MUST perform a home
registration.
4.1.2. Authentication
With regional registrations, a GFA address is registered at the HA as
the care-of address of the MN. If a Mobile-Foreign (MN-FA)
Authentication extension is present in a Registration Request message
directed to the HA, the GFA will perform the authentication.
Similarly, if a Foreign-Home (FA-HA) Authentication extension is
present in a Registration Request message, the authentication is
performed between the GFA and the HA. To summarize, the GFA takes
the role of an FA with regard to security associations in the home
registrations.
Regional registration messages also need to be protected with
authentication extensions in the same way as registrations with the
HA. This means that the MN and the GFA MUST have received the keys
needed to construct the authentication extensions before any regional
registration is performed. As described above, since the GFA address
is the registered care-of address of the MN at its home network, the
GFA is the agent within the visited domain that has to have the
appropriate security associations with the HA and the MN. The GFA's
security association with the MN is then used to enable proper
authentication for regional registrations (see Section 6). How the
keys are distributed is outside the scope of this draft. One example
is to distribute the keys as part of the home registration, for
example according to [RFC4004] and [RFC3957]. Another example is
pre-configured keys.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
4.2. Protocol Overview
When a MN first arrives at a visited domain, it performs a
registration with its home network. During this registration, the HA
registers the care-of address of the MN. In case the visited domain
supports regional registrations, the care-of address that is
registered at the HA is the address of a GFA. The GFA keeps a
visitor list of all the MNs currently registered with it.
Since the care-of address registered at the HA is the GFA address, it
will not change when the MN changes FA under the same GFA. Thus, the
HA does not need to be informed of further MN movements within the
visited domain.
Figure 2 illustrates the signaling message flow for home
registration. During the home registration, the HA records the GFA
address as the care-of address of the MN.
MN FA1 GFA HA
| | | |
| Registration Request | | |
|---------------------->| Reg. Request | |
| |---------------------->| Reg. Request |
| | |--------------->|
| | | Reg. Reply |
| | Reg. Reply |<---------------|
| Registration Reply |<----------------------| |
|<----------------------| | |
| | | |
Figure 2: Home Registration
Figure 3 illustrates the signaling message flow for regional
registration. Even though the MN's local care-of address changes,
the HA continues to use the GFA address as the care-of address of the
MN. We introduce two new message types for regional registrations:
Regional Registration Request and Regional Registration Reply.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
MN FA2 GFA HA
| | | |
| Regional Reg. Req. | | |
|---------------------->| Regional Registration Req. | |
| |----------------------------->| |
| | Regional Registration Reply | |
| Regional Reg. Reply |<-----------------------------| |
|<----------------------| | |
| | | |
Figure 3: Regional Registration
4.3. Advertising Foreign Agent and GFA
A FA typically announces its presence via an Agent Advertisement
message [RFC3344]. If the domain to which an FA belongs supports
regional registrations, the following changes apply to the Agent
Advertisement.
The 'I' flag (see Section 8.1) MUST be set to indicate that the
domain supports regional registrations. If the 'I' flag is set,
there MUST be at least one care-of address in the Agent
Advertisement. If the 'I' flag is set and there is only one care-of
address, it is the address of the FA. If the 'I' flag is set, and
there is more than one care-of address, the first care-of address is
the local FA, and the last care-of address is the GFA. (Any care-of
addresses advertised in addition to these two are out of scope for
this document).
The FA-NAI (see Section 8.2) SHOULD also be present in the Agent
Advertisement to enable the MN to decide whether or not it has moved
to a new domain since its last registration. The decision is based
on whether the realm part of the advertised FA-NAI matches the realm
of the FA-NAI advertised by the MN's previous FA.
4.4. Backwards Compatibility with RFC 3344
A domain that supports regional registrations should also be
backwards compatible.
An FA MUST support registrations according to Mobile IPv4 as defined
in [RFC3344]. This allows MNs that don't support regional
registrations to register via this FA using standard Mobile IPv4. If
the FA advertises both its own care-of address and a GFA care-of
address, a MN that supports regional registrations but has a HA that
doesn't, will still be able to make use of regional registrations
through that GFA care-of address.
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The advertised GFA care-of address MAY be set to all-ones, to
indicate dynamic GFA assignment. If the MN supports regional
registrations, and an all-ones GFA care-of address is advertised, the
MN SHOULD use dynamic GFA assignment (see Section 7.1).
5. Home Registration
This section gives a detailed description of home registration, i.e.,
registration with the HA (on the home network). Home registration is
performed when a MN first arrives at a visited domain, when it
requests a new HA, or when it changes GFA. Home registration is also
performed to renew bindings which would otherwise expire.
5.1. Mobile Node Considerations
Upon receipt of an Agent Advertisement message with the 'I' flag set
and an FA-NAI extension, the MN compares the domain part of the FA
NAI with the one received in the previous Agent Advertisement, to
determine whether it has moved to a new domain since its last
registration. If the NAIs do not match, the MN MUST assume it has
moved to a new domain.
If the MN determines that it has moved to a new domain, it SHOULD
insert the advertised GFA address in the care-of address field in the
Registration Request message. For dynamic GFA assignment, see
Section 7.1.
A MN with a co-located care-of address might also want to use
regional registrations. It then finds out the address of a GFA,
either from Agent Advertisements sent by an FA, or by some means not
described in this document. The MN MAY then generate a Registration
Request message, with the GFA address in the care-of address field,
and send it directly to the GFA (not via an FA). In this case, the
MN MUST add a Hierarchical Foreign Agent (HFA) extension (see Section
9.2), including its co-located care-of address, to the Registration
Request before sending it. The HFA extension MUST be protected by an
authentication extension. If the MN has established a mobility
security association with the GFA, the HFA extension MUST be placed
before the MN-FA Authentication extension, and it SHOULD be placed
after the Mobile-Home (MN-HA) Authentication extension. Otherwise,
if the MN has no established mobility security association with the
GFA, the HFA extension MUST be placed before the MN-HA authentication
extension.
If the MN receives an Agent Advertisement with the 'R' bit set, even
if it has a co-located care-of address, it still formulates the same
Registration Request message with extensions, but it sends the
message to the advertising FA instead of to the GFA.
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If the home registration is about to expire, the MN performs a new
home registration using the same GFA care-of address to refresh the
binding [RFC3344]. If the MN has just moved to a new FA and not yet
sent a Regional Registration Request when the home registration is
due to expire, the MN sends only a Registration Request, as this will
update both the GFA and the HA.
If the Registration Reply includes a Replay Protection Style
extension, the value in the Initial Identification field is the value
to be used for replay protection in the next Regional Registration
Request (see Section 6.1).
5.2. Foreign Agent Considerations
When the FA receives a Registration Request message from a MN, it
extracts the care-of address field to find the GFA to which the
message shall be relayed. All FAs that advertise the 'I' flag MUST
also be able to handle Registration Requests with an all-zeros care-
of address (used for dynamic GFA assignment).
If the FA receives a Registration Request where the care-of address
is set to all-ones (which could happen if a MN that doesn't support
Regional Registrations copied an all-ones care-of address from an
Agent Advertisement), it MUST reply with the Code field set to
"poorly formed request" [RFC3344].
If the Registration Request has the 'T' bit set, the MN is requesting
Reverse Tunneling [RFC3024]. In this case, the FA has to tunnel
packets from the MN to the GFA for further handling.
If the care-of address in the Registration Request is the address of
the FA, the FA relays the message directly to the HA, as described in
[RFC3344]. For each pending or current home registration, the FA
maintains a visitor list entry as described in [RFC3344]. If reverse
tunneling is being used, the visitor list MUST contain the address of
the GFA, in addition to the fields required in [RFC3344].
Otherwise, if the care-of address in the Registration Request is the
address of a GFA (or all-zeros), the FA adds a Hierarchical Foreign
Agent (HFA) extension, including its own address, to the Registration
Request, and relays it to the GFA. The HFA extension MUST be
appended at the end of all previous extensions that were included in
the Registration Request when the FA received it, and it MUST be
protected by a Foreign-Foreign (FA-FA) Authentication extension (see
Section 11).
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RFC 4857 Mobile IPv4 Regional Registration June 2007
5.3. GFA Considerations
For each pending or current home registration, the GFA maintains a
visitor list entry as described in [RFC3344]. This visitor list
entry is also updated for the regional registrations performed by the
MN. In addition to the fields required in [RFC3344], the list entry
MUST contain:
o the current care-of address of the MN (i.e., the FA or co-located
address) received in the HFA extension
o the remaining Lifetime of the regional registration
o the style of replay protection in use for the regional
registration
o the Identification value for the regional registration.
The default replay protection style for regional registrations is
timestamp-based replay protection, as defined in Mobile IPv4
[RFC3344]. If the timestamp sent by the MN in the Registration
Request is not close enough to the GFA's time-of-day clock, the GFA
adds a Replay Protection Style extension (see Section 9.3) to the
Registration Reply, with the GFA's time of day in the Identification
field to synchronize the MN with the GFA for the regional
registrations.
If nonce-based replay protection is used, the GFA adds a Replay
Protection Style extension to the Registration Reply, where the high-
order 32 bits in the Identification fields is the nonce that should
be used by the MN in the following regional registration.
If the Registration Request contains a Replay Protection Style
extension (see Section 9.3) requesting a style of replay protection
not supported by the GFA, the GFA MUST reject the Registration
Request and send a Registration Reply with the value in the Code
field set to REPLAY_PROT_UNAVAIL (see Section 9.5).
If the Hierarchical Foreign Agent (HFA) extension comes after the
MN-FA Authentication extension, the GFA MUST remove it from the
Registration Request. The GFA then sends the Registration Request to
the HA. Upon receipt of the Registration Reply, the GFA consults its
pending registration record to find the care-of address within its
domain that is currently used by the MN, and sends the Registration
Reply to that care-of address.
If the Replay Protection Style extension (see Section 9.3) is present
in a Registration Request, and follows the MN-HA Authentication
extension, the GFA SHOULD remove the Replay Protection Style
extension after performing any necessary processing and before
sending the Registration Request to the HA.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
If the GFA receives a Registration Request from a MN that it already
has a mobility binding for, this is an update of a binding that is
about to expire. If the address in the Hierarchical Foreign Agent
(HFA) extension is the same as the current care-of address in the
visitor list for the MN, the entries in the visitor list concerning
regional registrations are not changed, except to update the
lifetime. If the address in the HFA extension is a new address, the
values for the regional registration are updated.
If the Registration Request has the 'T' bit set, the GFA has to
decapsulate the packets from the FA and re-encapsulate them for
further delivery back to the HA. These actions are required because
the HA has to receive such packets from the expected care-of address
(i.e., that of the GFA) instead of the local care-of address (i.e.,
that of the FA).
When receiving a Registration Reply from the HA, the GFA MAY add a
Regional Registration Lifetime extension to the message before
relaying it to the FA. The extension defines the lifetime that the
GFA allows the MN before it has to renew its regional registration.
The GFA MUST set the lifetime of the regional registration to be no
greater than the remaining lifetime of the MN's registration with its
HA. If used, the Regional Registration Lifetime extension MUST be
added after any other extensions, and MUST be protected by an MN-FA
Authentication extension.
5.4. Home Agent Considerations
The Registration Request is processed by the HA as described in
[RFC3344].
6. Regional Registration
This section describes regional registrations. Once the HA has
registered the GFA address as the care-of address of the MN, the MN
may perform regional registrations. When performing regional
registrations, the MN may either register an FA care-of address or a
co-located address with the GFA. In the following, we assume that a
home registration has already occurred, as described in Section 5,
and that the GFA has a mobility security association with the MN.
Suppose the MN moves from one FA to another FA within the same
visited domain. It will then receive an Agent Advertisement from the
new FA. Suppose further that the Agent Advertisement indicates that
the visited domain supports regional registrations, and either that
the advertised GFA address is the same as the one the MN has
registered as its care-of address during its last home registration,
or that the realm part of the newly advertised FA-NAI matches the FA-
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RFC 4857 Mobile IPv4 Regional Registration June 2007
NAI advertised by the MN's previous FA. Then, the MN can perform a
regional registration with this FA and GFA. The MN issues a Regional
Registration Request to the GFA via the new FA. The request is
authenticated using the existing mobility security association
between the GFA and the MN and the message is authenticated by the
MN-GFA Authentication extension (see Section 11). The care-of
address should be set to the address of the local FA.
If the Regional Registration Request contains a care-of address field
of all-zeros, the FA adds a Hierarchical Foreign Agent (HFA)
extension to the message and relays it to the GFA. Based on the
information in the HFA extension, the GFA updates the MN's current
point of attachment in its visitor list. The GFA then issues a
Regional Registration Reply to the MN via the FA.
If the advertised GFA is not the same as the one the MN has
registered as its care-of address, and if the MN is still within the
same domain as it was when it registered that care-of address, the MN
MAY try to perform a regional registration with its registered GFA.
If the FA cannot support regional registration to a GFA, other than
advertised, the FA denies the Regional Registration Request with code
UNKNOWN_GFA (see Section 10.3). In this case, the MN has to do a new
home registration via the new GFA.
New message types are introduced for the Regional Registration
Request and Reply. The motivation for introducing new message types,
rather than using the Registration Request and Reply defined in
[RFC3344] is: (1) the MN must be able to distinguish regional
registrations from home registrations, since in the former case the
timestamps/nonces are synchronized with its GFA and in the latter
with its HA; and (2) a home registration MUST be directed to the home
network before the lifetime of the GFA care-of address expires.
6.1. Mobile Node Considerations
For each pending or current home registration, the MN maintains the
information described in [RFC3344]. The information is also updated
for the regional registrations performed by the MN. In addition to
the information described in [RFC3344], the MN MUST maintain the
following information, if present:
o the GFA address
o the remaining Lifetime of the regional registration
o the style of replay protection in use for the regional
registration
o the Identification value for the regional registration.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
The replay protection for home registrations and regional
registrations is performed as described in [RFC3344]. Since the MN
performs regional registrations at the GFA in parallel with home
registrations at the HA, the MN MUST be able to keep one replay
protection mechanism and sequence for the GFA, and a separate
mechanism and sequence for the HA.
For regional registrations, replay protection may also be provided at
the FA by the challenge-response mechanism, as described in
[RFC4721].
6.2. Foreign Agent Considerations
When the FA receives a Regional Registration Request from a MN,
addressed to a GFA, it generally processes the message according to
the rules of processing a Registration Request addressed to a HA (see
Section 5.2). The only difference is that the GFA IP address field
replaces the HA address field. If that address belongs to a known
GFA, the FA forwards the request to the indicated GFA. Otherwise,
the FA MUST generate a Regional Registration Reply with error code
UNKNOWN_GFA.
For each pending or current registration, the FA maintains a visitor
list entry as described in [RFC3344]. If reverse tunneling is being
used, the visitor list MUST contain the address of the GFA, in
addition to the fields required in [RFC3344]. This is required so
that the FA can tunnel datagrams, sent by the MN, to the GFA. The
GFA then decapsulates the datagrams, re-encapsulates them, and sends
them to the HA.
6.3. GFA Considerations
If the GFA accepts a Regional Registration Request, it MUST set the
lifetime of the regional registration to be no greater than the
remaining lifetime of the MN's registration with its HA, and put this
lifetime into the corresponding Regional Registration Reply. The GFA
MUST NOT accept a request for a regional registration if the lifetime
of the MN's registration with its HA has expired. In that case, the
GFA sends a Regional Registration Reply with the value in the Code
field set to NO_HOME_REG.
If the GFA receives a tunneled packet from an FA in its domain, then
after decapsulation the GFA looks to see whether it has an entry in
its visitor list for the source IP address of the inner IP header
after decapsulation. If so, it checks the visitor list to see
whether reverse tunneling has been requested; if it was requested,
the GFA re-encapsulates the packet with its own address as the source
IP address, and the address of the HA as the destination IP address.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
7. Dynamic GFA Assignment
Regional registrations may also allow dynamic assignment of a GFA to
a MN. The visited network (i.e., the FA) indicates support for
dynamic GFA assignment by advertising an all-ones care-of address in
the Agent Advertisement. The MN then sets the care-of address in the
Registration Request to all-zeros to request a dynamically assigned
GFA. Upon receiving this Registration Request, the FA relays it to
the appropriate GFA, and the GFA assigns its address to the MN by
means of a GFA IP Address extension added to the Registration
Request.
In order for dynamic GFA assignment to work, the MN, GFA, and HA,
respectively, MUST support the GFA IP Address extension. Also, the
FA MUST be able to advertise an all-ones care-of address and handle a
Registration Request with an all-zeros care-of address.
Note also that protection of the GFA IP Address extension, added to
the Registration Request, requires either the use of an FA-HA
Authentication extension or other means to secure the Registration
Request when forwarded from the GFA to the HA.
7.1. Mobile Node Considerations for Dynamic GFA Assignment
If the 'I' flag in the Agent Advertisement sent out by the FA is set,
and the care-of address indicating the GFA is set to all-ones, this
indicates support for dynamic GFA assignment.
If the MN supports dynamic GFA assignment, and if the advertised GFA
address is all-ones, the MN SHOULD set the care-of address field in
the Registration Request to all-zeros to request to be assigned a
GFA.
When requesting dynamic GFA assignment, the MN MUST check to make
sure that it receives a GFA IP Address extension in the Registration
Reply.
7.2. Foreign Agent Considerations for Dynamic GFA Assignment
If an FA supports dynamic GFA assignment, and receives a Registration
Request with the care-of address field set to all-zeros, the FA
assigns a GFA to the MN. A FA can either have a default GFA that it
assigns to all MNs or it can assign a GFA by some means not described
in this specification.
If an FA that does not support dynamic GFA assignment receives a
Registration Request with the care-of address field set to all-zeros,
the FA will deny the request as described in [RFC3344], i.e., by
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RFC 4857 Mobile IPv4 Regional Registration June 2007
sending a Registration Reply with the Code field set to "invalid
care-of address".
7.3. GFA Considerations for Dynamic GFA Assignment
If a GFA supports dynamic GFA assignment, and receives a Registration
Request with the care-of address field set to all-zeros, the GFA
assigns its own IP address as care-of address for this MN, and adds a
GFA IP Address extension with this address to the Registration
Request. The GFA MUST NOT insert the GFA IP address directly in the
care-of address field in the Registration Request, since that would
cause the MN-HA authentication to fail.
The GFA IP Address extension has to be protected so that it cannot be
changed by a malicious node when the Registration Request is
forwarded to the HA. If the HA and the GFA have a mobility security
association, the GFA IP Address extension MUST be protected by the
FA-HA authentication extension. Otherwise, the Registration Request
MUST be sent to the HA in a secure way, for example via a secure AAA
protocol (e.g., [RFC4004], [RFC3957]).
If the GFA does not support dynamic GFA assignment, it will deny the
request by sending a Registration Reply with the Code field set to
ZERO_COA_NOT_SUPP (see Section 9.5).
7.4. Home Agent Considerations for Dynamic GFA Assignment
If a HA receives a Registration Request with a GFA IP Address
extension, and the HA does not allow the use of this extension, the
HA MUST return a Registration Reply with the Code value set to
DYN_GFA_NOT_SUPP (see Section 9.5).
If a HA receives a Registration Request message with the care-of
address set to all-zeros, but no GFA IP Address extension, it MUST
deny the request by sending a Registration Reply message with the
Code field set to ZERO_CAREOF_ADDRESS (see Section 9.5).
If a HA that does not support dynamic GFA assignment receives a
Registration Request with a GFA IP Address extension, the request
will be denied by the HA, as described in [RFC3344].
If a HA that supports dynamic GFA assignment receives a Registration
Request with the care-of address set to all-zeros and a GFA IP
Address extension, it MUST register the IP address of the GFA as the
care-of address of the MN in its mobility binding list. If the
Registration Request is accepted, the HA MUST include the GFA IP
Address extension in the Registration Reply, before the MN-HA
Authentication extension.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
7.5. Regional Registration
If the MN receives an Agent Advertisement with the care-of address
field indicating the GFA set to all-ones, and if the MN determines
that it is within the same visited domain as when it did its last
home registration, it MAY send a Regional Registration Request to its
current GFA. Otherwise, it MUST send a Registration Request to its
HA as described in Section 7.1.
8. Router Discovery Extensions
This section specifies a new flag within the Mobile IP Agent
Advertisement, and an optional extension to the ICMP Router Discovery
Protocol [RFC1256].
8.1. Regional Registration Flag
The only change to the Mobility Agent Advertisement Extension defined
in [RFC3344] is a flag indicating that the domain, to which the FA
generating the Agent Advertisement belongs, supports regional
registrations. The flag is inserted after the flags defined in
[RFC3344], [RFC3024], and [RFC3519].
Regional Registration flag:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |R|B|H|F|M|G|r|T|U|I| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| zero or more Care-of Addresses |
| ... |
The flag is defined as follows:
Type 16 (Mobility Agent Advertisement)
I Regional Registration. This domain supports
regional registration as specified in this document.
8.2. Foreign Agent NAI Extension
The FA-NAI extension is defined as subtype 3 of the NAI Carrying
Extension [RFC3846].
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RFC 4857 Mobile IPv4 Regional Registration June 2007
The FA SHOULD include its NAI in the Agent Advertisement message. If
present, the Foreign Agent NAI (FA-NAI) extension MUST appear in the
Agent Advertisement message after any of the advertisement extensions
defined in [RFC3344].
By comparing the domain part of the FA-NAI with the domain part of
the FA-NAI it received in the previous Agent Advertisement, the MN
can determine whether it has moved to a new domain since it last
registered.
9. Regional Extensions to Mobile IPv4 Registration Messages
In this section, we specify new Mobile IP registration extensions for
the purpose of managing regional registrations.
9.1. GFA IP Address Extension
The GFA IP Address extension is defined for the purpose of supporting
dynamic GFA assignment. If the MN requests a dynamically assigned
GFA, the GFA adds a GFA IP Address extension to the Registration
Request before relaying it to the HA. The MN indicates that it wants
a GFA to be assigned by sending a Registration Request with the
care-of address field set to all-zeros. The GFA IP Address extension
MUST appear in the Registration Request before the FA-HA
Authentication extension, if present.
If a HA receives a Registration Request message with the care-of
address set to all-zeros, and a GFA IP Address extension, it MUST
register the IP address of the GFA as the care-of address of the MN.
When generating a Registration Reply message, the HA MUST include the
GFA IP Address extension from the Registration Request in the
Registration Reply message. The GFA IP Address extension MUST appear
in the Registration Reply message before the MN-HA Authentication
extension.
The GFA IP Address Extension is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GFA IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
46 (GFA IP Address) (non-skippable)
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RFC 4857 Mobile IPv4 Regional Registration June 2007
Length
6
GFA IP Address
The GFA IP Address field contains the Gateway Foreign Agent's
(GFA) publicly routable address.
9.2. Hierarchical Foreign Agent Extension
The Hierarchical Foreign Agent (HFA) extension may be present in a
Registration Request or Regional Registration Request. When an FA
adds this extension to a Registration Request, the receiving mobility
agent (GFA) sets up a pending registration record for the MN, using
the IP address in the HFA extension as the care-of address for the
MN. Furthermore, in this case, the extension MUST be appended at the
end of all previous extensions that had been included in the
registration message as received by the FA. The HFA extension MUST
be protected by an FA-FA Authentication extension. When the
receiving mobility agent (GFA) receives the registration message, it
MUST remove the HFA extension added by the sending FA.
If a MN with a co-located care-of address adds the HFA extension to a
Registration Request, the receiving mobility agent (GFA) sets up a
pending registration record for the MN, using the IP address in the
HFA extension as the care-of address for the MN. The extension MUST
be protected by an authentication extension. If the MN has
established a mobility security association with the GFA, the HFA
extension MUST be placed before the MN-FA Authentication extension,
and it SHOULD be placed after the Mobile-Home (MN-HA) Authentication
extension. Otherwise, if the MN has no established mobility security
association with the GFA, the HFA extension MUST be placed before the
MN-HA authentication extension. If the HFA extension is placed after
all other extensions, the receiving mobility agent (GFA) MUST remove
the HFA extension added by the MN. Otherwise, when the HA receives
the registration message, it ignores the HFA extension.
The Hierarchical Foreign Agent (HFA) Extension is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FA IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
140 (Hierarchical Foreign Agent) (skippable)
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RFC 4857 Mobile IPv4 Regional Registration June 2007
Length
6
FA IP Address
The IP Address of the FA relaying the Registration Request.
9.3. Replay Protection Style
When a MN uses Mobile IPv4 to register a care-of address with its HA,
the style of replay protection used for the registration messages is
assumed to be known by way of a mobility security association that is
required to exist between the MN and the HA receiving the request.
No such pre-existing security association between the MN and the GFA
is likely to be available. By default, the MN SHOULD treat replay
protection for Regional Registration messages exactly as specified in
Mobile IPv4 [RFC3344] for timestamp-based replay protection.
If the MN requires nonce-based replay protection, also as specified
in Mobile IPv4, it MAY append a Replay Protection Style extension to
a Registration Request. Since Registration Requests are forwarded to
the HA by way of the GFA, the GFA will be able to establish the
selected replay protection (see Section 5.3).
The GFA also uses this extension by adding a Replay Protection Style
extension to a Registration Reply to synchronize the replay
protection for Regional Registrations (see Section 5.3).
The format of the Replay Protection Style extension is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Replay Protection Style |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Initial Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
141 (Replay Protection Style) (skippable)
Length
2
Replay Protection Style
An integer specifying the style of replay protection desired by
the MN.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
Initial Identification
The timestamp or nonce to be used for initial synchronization for
the replay mechanism.
Admissible values for the Replay Protection Style are as follows:
+-------+-------------------------+
| Value | Replay Protection Style |
+-------+-------------------------+
| 0 | timestamp [RFC3344] |
| 1 | nonce [RFC3344] |
+-------+-------------------------+
The Replay Protection Style extension MUST be protected by an
authentication extension. If the MN has an established mobility
security association with the GFA, the Replay Protection Style
extension MUST be placed before the MN-FA Authentication extension in
the Registration Request, and SHOULD be placed after the MN-HA
Authentication extension. Otherwise, the Replay Protection Style
extension MUST be placed before the MN-HA Authentication extension in
the Registration Request.
If the GFA adds a Replay Protection Style extension to a Registration
Reply, it SHOULD be placed before the MN-FA Authentication extension.
The MN-FA Authentication extension should be based on security
associations between the MN and GFA established during home
registration.
Replay protection MAY also be provided through a challenge-response
mechanism, at the FA issuing the Agent Advertisement, as described in
[RFC4721].
9.4. Regional Registration Lifetime Extension
The Regional Registration Lifetime extension allows the GFA to set a
lifetime for the regional registration with an MN during its home
registration. When receiving a Registration Reply from the HA, the
GFA MAY add this extension to the Registration Reply before relaying
it to the FA. The GFA MUST set the Regional Registration Lifetime to
be no greater than the remaining lifetime of the MN's home
registration.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
The Regional Registration Lifetime Extension is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Regional Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
142 (Regional Registration Lifetime) (skippable)
Length
6
Regional Registration Lifetime
If the Code field indicates that the registration was accepted,
the Regional Registration Lifetime field is set to the number of
seconds remaining before the regional registration is considered
expired. A value of zero indicates that the MN has been
deregistered with the GFA. A value of 0xffff indicates infinity.
If the Code field indicates that the home registration was denied,
the contents of the Regional Registration Lifetime field are
unspecified and MUST be ignored on reception.
If the GFA adds a Regional Registration Lifetime extension to a
Registration Reply, it MUST be placed before the MN-FA Authentication
extension. The MN-FA Authentication extension should be based on
security associations between the MN and GFA established during home
registration.
9.5. New Code Values for Registration Reply
The values to use within the Code field of the Registration Reply are
defined in [RFC3344]. In addition, the following values are defined:
Registration denied by the GFA:
+---------------------+-------+---------------------+
| Error Name | Value | Section of Document |
+---------------------+-------+---------------------+
| REPLAY_PROT_UNAVAIL | 110 | Section 5.3 |
| ZERO_COA_NOT_SUPP | 111 | Section 7.3 |
+---------------------+-------+---------------------+
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RFC 4857 Mobile IPv4 Regional Registration June 2007
Registration denied by the HA (for dynamic GFA assignment):
+---------------------+-------+---------------------+
| Error Name | Value | Section of Document |
+---------------------+-------+---------------------+
| ZERO_CAREOF_ADDRESS | 145 | Section 7.4 |
| DYN_GFA_NOT_SUPP | 146 | Section 7.4 |
+---------------------+-------+---------------------+
10. Regional Registration Message Formats
This section specifies two new registration message types: Regional
Registration Request and Regional Registration Reply. These messages
are used by the MN instead of the existing Mobile IPv4 Registration
Request and Registration Reply, as described in Section 6.
Regional registration messages are protected by required
authentication extensions, in the same way as the existing Mobile
IPv4 registration messages are protected. The following rules apply
to authentication extensions:
o The MN-GFA Authentication extension [RFC3344] MUST be included in
all regional registration messages.
o The MN-FA Authentication extension [RFC3344] MAY be included in
regional registration messages.
o The FA-HA Authentication extension [RFC3344] MUST NOT be included
in any regional registration message.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
10.1. Regional Registration Request
The Regional Registration Request is used by a MN to register with
its current GFA.
Regional Registration Request:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |S|B|D|M|G|r|T|x| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GFA IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Care-of Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
The Regional Registration Request is defined as the Registration
Request in [RFC3344], but with the following changes:
Type
18 (Regional Registration Request)
Lifetime
The number of seconds remaining before the Regional Registration
is considered expired. A value of zero indicates a request for
deregistration with the GFA. A value of 0xffff indicates
infinity.
GFA IP Address
The IP address of the Gateway Foreign Agent (GFA). (Replaces Home
Agent field in Registration Request message in [RFC3344].)
Care-of Address
Care-of address of local FA; MAY be set to all-ones.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
Identification
A 64-bit number, constructed by the MN, used for matching Regional
Registration Requests with Regional Registration Replies, and for
protecting against replay attacks of regional registration
messages.
Extensions
For the Regional Registration Request, the Hierarchical Foreign
Agent (HFA) Extension is an allowable extension (in addition to
those which are allowable for the Registration Request).
10.2. Regional Registration Reply
The Regional Registration Reply delivers the indication of regional
registration acceptance or denial to a MN.
In the Regional Registration Reply, the UDP header is followed by the
Mobile IP fields shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GFA IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
This message is defined as the Registration Reply message in
[RFC3344], but with the following changes:
Type
19 (Regional Registration Reply)
Code
A value indicating the result of the Regional Registration
Request. See [RFC3344] for a list of currently defined Code
values.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
Lifetime
If the Code field indicates that the regional registration was
accepted, the Lifetime field is set to the number of seconds
remaining before the regional registration is considered expired.
A value of zero indicates that the MN has been deregistered with
the GFA. A value of 0xffff indicates infinity. If the Code field
indicates that the regional registration was denied, the contents
of the Lifetime field are unspecified and MUST be ignored on
reception.
GFA IP Address
The IP address of the Gateway Foreign Agent (GFA) generating the
Regional Registration Reply. (Replaces Home Agent field specified
in Mobile IPv4 [RFC3344].)
Identification
A 64-bit number used for matching Regional Registration Requests
with Regional Registration Replies, and for protecting against
replay attacks of regional registration messages. The value is
based on the Identification field from the Regional Registration
Request message from the MN, and on the style of replay protection
used in the security context between the MN and its GFA (defined
by the mobility security association between them).
10.3. New Regional Registration Reply Code Values
For a Regional Registration Reply, the following additional Code
values are defined in addition to those specified in Mobile IPv4
[RFC3344].
Registration denied by the FA:
+----------------------+-------+---------------------+
| Error Name | Value | Section of Document |
+----------------------+-------+---------------------+
| UNKNOWN_GFA | 112 | Section 6.2 |
| GFA_UNREACHABLE | 113 | |
| GFA_HOST_UNREACHABLE | 114 | |
| GFA_PORT_UNREACHABLE | 115 | |
+----------------------+-------+---------------------+
Registration denied by the GFA:
+-------------+-------+---------------------+
| Error Name | Value | Section of Document |
+-------------+-------+---------------------+
| NO_HOME_REG | 193 | Section 6.3 |
+-------------+-------+---------------------+
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RFC 4857 Mobile IPv4 Regional Registration June 2007
The four first Code values are returned to the MN in response to ICMP
errors that may be received by the FA.
11. Authentication Extensions
In this section, two new subtypes for the Generalized Authentication
Extension [RFC4721] are specified. First, the FA-FA Authentication
extension is used by FAs to secure the HFA extension to the
Registration Request and Regional Registration Request messages. A
new authentication extension is necessary because the HFA extension
is typically added after the MN-HA Authentication extension or, e.g.,
the MN-AAA Authentication extension [RFC4721].
The MN-GFA Authentication extension is used whenever the MN has a co-
located address. The MN-GFA Authentication extension is also used to
provide authentication for a Regional Registration Request.
The subtype values for these new subtypes are as follows:
+-----------------------+-------+
| Subtype Name | Value |
+-----------------------+-------+
| FA-FA authentication | 2 |
| MN-GFA authentication | 3 |
+-----------------------+-------+
The default algorithm for computation of the authenticator is the
same as for the MN-AAA Authentication subtype defined in [RFC4721].
12. Security Considerations
This document proposes a method for a MN to register locally in a
visited domain. The authentication extensions to be used are those
defined in [RFC3344] and [RFC4721]. Key distribution, assumed to
take place during home registration, is to be performed, for
instance, according to [RFC4004] or [RFC3957]. Alternatively, the
keys can be pre-configured.
If the Hierarchical Foreign Agent (HFA) extension is appended to a
Registration Request, this extension is to be followed by an FA-FA
Authentication extension (see Section 11) to prevent any modification
to the data. Security associations between FAs and GFAs within a
domain are assumed to exist prior to regional registrations.
If the GFA IP Address extension is added to a registration message,
it is to be followed by a authentication extension. In case of the
GFA IP Address extension being added to a Registration Request, it
should be protected by an FA-HA Authentication extension. If no
Fogelstroem, et al. Experimental [Page 29]
RFC 4857 Mobile IPv4 Regional Registration June 2007
security association exists between the GFA and the HA, the
Registration Request needs to be protected by other means not defined
in this document. When a GFA IP Address extension is added to a
Registration Reply, it is protected by the Mobile-Home Authentication
extension as defined in [RFC3344].
Replay protection for regional registrations is defined similarly to
[RFC3344], with the addition of a Replay Protection Style extension.
If this extension is added to a Registration Reply by a GFA, it needs
to be protected by a MN-FA Authentication extension.
A co-operating malicious MN-HA pair can trick the GFA into setting up
state for an incorrect MN home address. This would result in
redirection of data of the node that actually owns that IP address to
the malicious MN. Given that the forwarding happens based on the
home address at the GFA, such an attack is scoped to the prefix of
the HA, not that of the GFA. This type of attack, or its
consequences, is not considered in this document.
13. IANA Considerations
This document defines:
o A subtype for the NAI Carrying Extension [RFC3846] is specified in
Section 8.2, which needs to have a value assigned from the space
of NAI Carrying Extension subtypes.
o Four new extensions to Mobile IP Registration messages: GFA IP
Address, Hierarchical Foreign Agent, Replay Protection Style, and
Regional Registration Lifetime (see Sections 9.1, 9.2, 9.3, and
9.4). The Type values for the GFA IP Address extension must be
within the range 0 through 127, while the other three must be
within the range 128 through 255.
o New Code values for Registration Reply messages (see Section 9.5).
o Two new subtypes for the Generalized Authentication Extension
[RFC4721]; see Section 11.
o Two new message types for Mobile IP: Regional Registration Request
and Regional Registration Reply (see Sections 10.1 and 10.2).
o Code values for Regional Registration Reply messages (see Section
10.3).
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RFC 4857 Mobile IPv4 Regional Registration June 2007
14. Acknowledgements
This document is a logical successor to documents written with Pat
Calhoun and Gabriel Montenegro; thanks to them and their many efforts
to help explore this problem space. Many thanks also to Jari Malinen
for his commentary on a rough version of this document.
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RFC 4857 Mobile IPv4 Regional Registration June 2007
15. References
15.1. Normative References
[RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", RFC 4282, December 2005.
[RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access
Identifier Extension for IPv4", RFC 2794, March 2000.
[RFC3024] Montenegro, G., "Reverse Tunneling for Mobile IP,
revised", RFC 3024, January 2001.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[RFC3519] Levkowetz, H. and S. Vaarala, "Mobile IP Traversal of
Network Address Translation (NAT) Devices", RFC 3519, May
2003.
[RFC3846] Johansson, F. and T. Johansson, "Mobile IPv4 Extension for
Carrying Network Access Identifiers", RFC 3846, June 2004.
[RFC4721] Perkins, C., Calhoun, P., and J. Bharatia, "Mobile IPv4
Challenge/Response Extensions (Revised)", RFC 4721,
January 2007.
15.2. Informative References
[RFC3957] Perkins, C. and P. Calhoun, "Authentication,
Authorization, and Accounting (AAA) Registration Keys for
Mobile IPv4", RFC 3957, March 2005.
[RFC4004] Calhoun, P., Johansson, T., Perkins, C., Hiller, T., and
P. McCann, "Diameter Mobile IPv4 Application", RFC 4004,
August 2005.
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Appendix A. Authentication, Authorization, and Accounting (AAA)
Interactions
When the mobile node has to obtain authorization by way of
Authentication, Authorization, and Accounting (AAA) infrastructure
services, the control flow implicit in the main body of this
specification is likely to be modified. Typically, the mobile node
will supply credentials for authorization by AAA as part of its
registration messages. The GFA will parse the credentials supplied
by the mobile and forward the appropriate authorization request to a
local AAA server (see [RFC3012] and [RFC4004]).
Concretely, this means that:
o The GFA MAY include the Mobile IP Registration Request data inside
an authorization request, directed to a local AAA server.
o The GFA MAY receive the Mobile IP Registration Reply data from a
message granting authorization, received from the AAA
infrastructure.
Appendix B. Anchoring at a GFA
As described earlier in this draft, once a mobile node has registered
the address of a GFA as its care-of address with its home agent, it
MAY perform regional registrations when changing foreign agent under
the same GFA. When detecting that is has changed foreign agent, and
if the new foreign agent advertises the 'I' flag, the mobile node MAY
address a Regional Registration Request message to its registered
GFA, even if the address of that particular GFA is not advertised by
the new foreign agent. The foreign agent MAY then relay the request
to the GFA in question, or deny the request with error code
UNKNOWN_GFA.
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Authors' Addresses
Eva Fogelstroem
Ericsson
Torshamnsgatan 23
SE-164 80 Stockholm
Sweden
EMail: eva.fogelstrom@ericsson.com
Annika Jonsson
Ericsson
Tellusborgsvagen 83-87
S-126 37 Hagersten
Sweden
EMail: annika.jonsson@ericsson.com
Charles E. Perkins
Nokia Siemens Networks
313 Fairchild Drive
Mountain View, California 94043
USA
EMail: charles.perkins@nsn.com
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RFC 4857 Mobile IPv4 Regional Registration June 2007
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