MIP4 Working Group E. Gustafsson
Internet-Draft A. Jonsson
Expires: May 23, 2005 Ericsson
C. Perkins
Nokia Research Center
November 22, 2004
Mobile IPv4 Regional Registration
draft-ietf-mip4-reg-tunnel-00
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
Using Mobile IP, 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. This document
describes a new kind of 'regional' registrations, i.e. registrations
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local to the visited domain. The regional signaling is performed via
a new network entity called a Gateway Foreign Agent and introduces 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Description of the Protocol . . . . . . . . . . . . . . . . . 6
3.1 General Assumptions . . . . . . . . . . . . . . . . . . . 6
3.1.1 Visited Domain . . . . . . . . . . . . . . . . . . . . 7
3.1.2 Authentication . . . . . . . . . . . . . . . . . . . . 7
3.2 Protocol Overview . . . . . . . . . . . . . . . . . . . . 8
3.3 Advertising Foreign Agent and GFA . . . . . . . . . . . . 9
3.4 Backwards compatibility with RFC3344 . . . . . . . . . . . 10
4. Home Registration . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Mobile Node Considerations . . . . . . . . . . . . . . . . 10
4.2 Foreign Agent Considerations . . . . . . . . . . . . . . . 12
4.3 GFA Considerations . . . . . . . . . . . . . . . . . . . . 13
4.4 Home Agent Considerations . . . . . . . . . . . . . . . . 14
5. Regional Registration . . . . . . . . . . . . . . . . . . . . 15
5.1 Mobile Node Considerations . . . . . . . . . . . . . . . . 16
5.2 Foreign Agent Considerations . . . . . . . . . . . . . . . 17
5.3 GFA Considerations . . . . . . . . . . . . . . . . . . . . 17
6. Generalized NAI Extension . . . . . . . . . . . . . . . . . . 18
7. Router Discovery Extensions . . . . . . . . . . . . . . . . . 19
7.1 Regional Registration Flag . . . . . . . . . . . . . . . . 19
7.2 Foreign Agent NAI Extension . . . . . . . . . . . . . . . 19
8. Regional Extensions to Mobile IPv4 Registration Messages . . . 20
8.1 GFA IP Address Extension . . . . . . . . . . . . . . . . . 20
8.2 Hierarchical Foreign Agent Extension . . . . . . . . . . . 21
8.3 Replay Protection Style . . . . . . . . . . . . . . . . . 22
8.4 New Code Values for Registration Reply . . . . . . . . . . 23
9. Regional Registration Message Formats . . . . . . . . . . . . 24
9.1 Regional Registration Request . . . . . . . . . . . . . . 24
9.2 Regional Registration Reply . . . . . . . . . . . . . . . 25
9.3 New Regional Registration Reply Code Values . . . . . . . 26
10. Authentication Extensions . . . . . . . . . . . . . . . . . 27
11. Security Considerations . . . . . . . . . . . . . . . . . . 28
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 28
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
14.1 Normative References . . . . . . . . . . . . . . . . . . . . 29
14.2 Informative References . . . . . . . . . . . . . . . . . . . 29
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30
A. Hierarchical Foreign Agents . . . . . . . . . . . . . . . . . 30
1. Registration with Home Agent . . . . . . . . . . . . . . . . . 31
2. Handling Binding Updates . . . . . . . . . . . . . . . . . . . 34
3. Regional Registration . . . . . . . . . . . . . . . . . . . . 35
4. Regional Registrations and Smooth Handover . . . . . . . . . . 36
5. Co-located care of address . . . . . . . . . . . . . . . . . . 37
6. Data Traffic . . . . . . . . . . . . . . . . . . . . . . . . . 37
B. Authentication, Authorization and Accounting (AAA)
Interactions . . . . . . . . . . . . . . . . . . . . . . . . . 38
C. Anchoring at a GFA/RFA/FA . . . . . . . . . . . . . . . . . . 38
Intellectual Property and Copyright Statements . . . . . . . . 40
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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. The regional registration
design introduces new Mobile IPv4 messages - Regional Registrations,
new Mobile IPv4 extensions to convey information between the mobile
node, foreign agent and home agent, and a new network entity: the
Gateway Foreign Agent (GFA). 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 will both decrease the
load on the home network, and speed up the process of handover within
the visited domain.
When a mobile node first arrives at a visited domain, it performs a
_home_registration - that is, a registration with its home agent. At
this registration, we assume that the home network generates a
registration key (e.g. using [I-D.ietf-mip4-aaa-key]) for the mobile
node. This registration key is distributed to the mobile node and to
the visited domain, and can be used for authentication of regional
registrations.
During a home registration, the home agent registers the care-of
address of the mobile node. When the visited domain supports
regional tunnel management, the care-of address that is registered at
the home agent is the publicly routable address of a Gateway Foreign
Agent (GFA). This care-of address will not change when the mobile
node changes foreign agent under the same GFA. When changing GFA, a
mobile node MUST perform a home registration; when changing foreign
agent under the same GFA, the mobile node MAY instead perform a
regional registration within the visited domain. 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, as discussed in Appendix A.
Foreign agents that support regional registrations are also required
to support registrations according to Mobile IPv4 [RFC3344]. If
there is a foreign agent address announced in the Agent
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Advertisement, the mobile node may register that foreign agent
care-of address with its home agent [RFC3344]. Similarly, if the
mobile node chooses not to employ regional registrations, it may
register a co-located care-of address directly with its home agent,
according to [RFC3344].
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [RFC2119] and indicate requirement
levels for compliant implementations.
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.
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Local Care-of Address
A Care-of Address which is either assigned to a mobile node, or to
a foreign agent offering local connectivity to a mobile node. A
registration message from the mobile node is subsequently sent to
a GFA (or another RFA, see Appendix A) 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].
Regional Foreign Agent (RFA)
A Foreign Agent which may be the target of a request for regional
registration.
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].
3. Description of the Protocol
This section provides an overview of the regional registration
protocol.
3.1 General Assumptions
Our general model of operation is illustrated in Figure 1, showing a
visited domain with foreign agent and GFA, and a home network with a
home agent:
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+---------------------------+ +----------------+
| Visited Domain | | Home |
| | +---------+ | Network |
| | | | | |
| +------+ +-------+ | | Public | | +------+ |
| | FA |------| GFA |-------------------------| HA | |
| +--+---+ +-------+ | | Network | | +------+ |
| | | | | | |
+-----|---------------------+ +---------+ +----------------+
|
+--+---+
| MN |
+------+
Figure 1
For mobile nodes that cannot process a NAI, or with mobility agents
that are not configured to advertise their NAI, regional registration
is still useful, but the lack of certain features may result in less
than optimal results.
3.1.1 Visited Domain
We assume two hierarchy levels of foreign agents in the visited
domain. At the top level of the hierarchy, there is at least one
GFA, which is a foreign agent with additional features. A GFA must
have a publicly routable address. Beneath a GFA, there are one or
more regional foreign agents (RFAs). We assume that there exist
established security associations between a GFA and the RFAs beneath
it. Multiple hierarchy levels of foreign agents are discussed in
Appendix A. When designing a domain supporting regional
registrations, the RFAs and GFA must be compatible. That is, they
should support the same encapsulation types, compression mechanisms
etc.
When a mobile node changes care-of address under the same GFA, it MAY
perform a regional registration. If the mobile node changes GFA,
within a visited domain or between visited domains, it MUST perform a
home registration.
3.1.2 Authentication
With the regional registration protocol, a GFA address is registered
at the home agent as the care-of address of the mobile node. If a
Mobile-Foreign Authentication extension is present in a Registration
Request message directed to the home agent, the GFA will perform the
authentication. Similarly, if a Foreign-Home Authentication
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extension is present in a Registration Request message, the
authentication is performed between the GFA and the home agent. To
summarise, the GFA takes the role of a foreign agent as regards to
security associations in the home registrations.
Regional Registration messages also have to be protected with
authentication extensions in the same way as registrations with the
home agent. This means that the mobile node 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 mobile
node at its home network, the GFA is the agent within the visited
domain which has to have the appropriate security associations with
the home agent and the mobile node. The GFA's security association
with the mobile node is then used to enable proper authentication for
regional registrations (see Section 5). How the keys are distributed
is outside the scope of this draft. One example is that the keys are
distributed as part of the registration at the home network, for
example according to [I-D.ietf-aaa-diameter-mobileip],
[I-D.ietf-mip4-aaa-key]. Another example is pre-configured keys.
3.2 Protocol Overview
When a mobile node first arrives at a visited domain, it performs a
registration with its home network. At this registration, the home
agent registers the care-of address of the mobile node. In case the
visited domain supports regional registrations, the care-of address
that is registered at the home agent is the address of a GFA. The
GFA keeps a visitor list of all the mobile nodes currently registered
with it.
Since the care-of address registered at the home agent is the GFA
address, it will not change when the mobile node changes foreign
agent under the same GFA. Thus, the home agent does not need to be
informed of any further mobile node movements within the visited
domain.
Figure 2 illustrates the signaling message flow for registration with
the home network. After the registration at the home agent, the home
agent records the GFA address as the care-of address of the mobile
node. If the GFA address was dynamically assigned to the mobile
node, the Registration Reply has an extension indicating the IP
address of the GFA to the mobile node.
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Registration at the GFA and the home agent:
MN FA1 GFA HA
| | | |
| Registration Request | | |
|---------------------->| Reg. Request w/ext. | |
| |---------------------->| Reg. Request |
| | |--------------->|
| | | Reg. Reply |
| | Reg. Reply w/ext. |<---------------|
| Registration Reply |<----------------------| |
|<----------------------| | |
| | | |
Figure 2
Figure 3 illustrates the signaling message flow for regional
registration. Even though the mobile node's local care-of address
changes, the home agent continues to record the GFA address as the
care-of address of the mobile node. We introduce two new message
types for regional registrations: Regional Registration Request and
Regional Registration Reply.
Regional registration at the GFA:
MN FA2 GFA HA
| | | |
| Regional Reg. Req. | | |
|---------------------->| Regional Reg. Req. w/ext. | |
| |----------------------------->| |
| | Regional Reg. Reply w/ext. | |
| Regional Reg. Reply |<-----------------------------| |
|<----------------------| | |
| | | |
Figure 3
3.3 Advertising Foreign Agent and GFA
A foreign agent typically announces its presence via an Agent
Advertisement message [RFC3344]. If the domain to which a foreign
agent belongs supports regional registrations, the following changes
are applied to the Agent Advertisement message.
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The 'I' flag (see Section 7) MUST be set to indicate that the domain
supports regional tunnel management. If the 'I' flag is set, there
MUST be at least one care-of address in the Agent Advertisement
message, but that address MAY be set to the "all ones" address. If
the 'I' flag is set, and there is only one care-of address (which is
not all ones), it is the address of the FA. If the 'I' flag is set,
and there are multiple care-of addresses, the first care-of address
is the local FA, and the last care-of address is the GFA. The FA-NAI
(see Section 7.2) SHOULD also be present to enable the mobile node to
decide whether or not it is in its home domain. The decision is
based on whether the realm part of the advertised FA-NAI matches the
mobile node's realm.
3.4 Backwards compatibility with RFC3344
A domain that supports Regional Registrations SHOULD also be
backwards compatible. If the Foreign Agent does not advertise an
"all ones" care-of address, it MUST support registrations according
to Mobile IPv4 as defined in [RFC3344]. This allows mobile nodes
that don't support Regional Registrations to register via this
Foreign Agent using standard Mobile IPv4. If the Foreign Agent
advertises both its own care-of address and a GFA care-of address, a
mobile node that supports Regional Registrations but has a Home Agent
that doesn't, will still be able to make use of Regional
Registrations through that GFA care-of address. A Foreign Agent that
advertises an "all ones" care-of address will not be backwards
compatible with [RFC3344]. In that case, and in other cases when the
mobile node requests that a GFA address is dynamically assigned to it
by setting the care-of address in a Registration Request to zero, the
mobile node and its Home Agent MUST support the GFA IP address
extension.
4. Home Registration
This section gives a detailed description of home registration, i.e.,
registration with the home agent (on the home network). Home
registration is performed when a mobile node first arrives at a
visited domain, when it requests a new home agent, or when it changes
GFA. Home registration is also performed to renew bindings which
would otherwise expire.
4.1 Mobile Node Considerations
Upon receipt of an Agent Advertisement message with the 'I' flag set
and a FA-NAI extension, the mobile node compares the domain part of
the foreign agent NAI with the domain part of its own NAI, to
determine whether it is in its home domain or in a visited domain.
If the NAIs do not match, the mobile node MUST assume it is in a
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foreign domain. Otherwise, if the mobile node determines that it is
in its home domain, it acts as defined in [RFC3344].
If the mobile node determines that it is in a visited domain, it
SHOULD either use the advertised GFA address in the care-of address
field in the Registration Request message, or set this field to zero
to request to be assigned a GFA. If the mobile node sets the care-of
address to zero, the mobile node and its home agent MUST support the
GFA IP address extension (see Section 8.1). In that case, the mobile
node MUST check to make sure that it receives a GFA IP address
extension in the Registration Reply. If the Foreign Agent only
advertises an "all ones" care-of address, it only supports
dynamically assigned GFA care-of address, and the mobile node MUST
set the care-of address in the Registration Request to zero.
A mobile node 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 a Foreign Agent, or by some
means not described in this draft. The mobile node 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 a foreign
agent). In this case, the mobile node MUST add a Hierarchical
Foreign Agent extension (see Section 8.2), including its co-located
care-of address, to the Registration Request before sending it. The
Hierarchical Foreign Agent extension MUST be protected by an
authentication extension. If the mobile node has established a
mobility security association with the GFA, the Hierarchical Foreign
Agent extension SHOULD be placed after the MN-HA authentication
extension and before the MN-FA authentication extension. Otherwise
the Hierarchical Foreign Agent extension MUST be placed before the
MN-HA authentication extension.
If the mobile node 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 foreign agent instead of to the GFA.
If the home registration is about to expire, the mobile node performs
a new home registration using the same GFA care-of address to refresh
the binding [RFC3344]. If the mobile node has just moved to a new
Foreign Agent and not yet sent a Regional Registration Request when
the home registration is due to expire, the mobile node sends only a
home Registration Request, as this will update both the GFA and the
HA. This Registration Request MUST be constructed as if it was the
first registration in this domain. For example, if the new Foreign
Agent only advertises an "all ones" care-of address, the mobile node
MUST set the care-of address in the Registration Request to zero, to
avoid problems if this new Foregin Agent doesn't support the same GFA
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as the mobile node had before.
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 5.1).
4.2 Foreign Agent Considerations
When the foreign agent receives a Registration Request message from a
mobile node, it extracts the care-of address field in the
Registration Request message, to find the GFA to which the message
shall be relayed. All Foreign Agents that advertise the 'I' flag
MUST also be able to handle Registration Requests with a zero care-of
address. If the care-of address field is set to zero, the foreign
agent assigns a GFA to the mobile node. A Foreign Agent can either
have a default GFA that it assigns to all mobile nodes or it can
assign a GFA by some means not described in this specification.
If the Foreign Agent receives a Registration request where the
care-of address is set to "all ones" (which could happen if a mobile
node 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 mobile node is
requesting Reverse Tunneling [RFC3024]. In this case, the foreign
agent has to tunnel packets from the mobile node to the GFA for
further handling.
If the care-of address in the Registration Request is the address of
the foreign agent, the foreign agent relays the message directly to
the home agent, as described in [RFC3344]. For each pending or
current home registration, the foreign agent maintains a visitor list
entry as described in [RFC3344]. If reverse tunneling is being used,
the visitor list MUST, in addition to the fields required in
[RFC3344], contain the address of the GFA.
Otherwise, if the care-of address in the Registration Request is the
address of a GFA (or zero), the foreign agent adds a Hierarchical
Foreign Agent extension, including its own address, to the
Registration Request message, and relays it to the GFA. The
Hierarchical Foreign Agent extension MUST be appended at the end of
all previous extensions that were included in the Registration
Request message when the foreign agent received it, and it SHOULD be
protected by an FA-FA Authentication extension (see Section 10).
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4.3 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
mobile node. In addition to the fields required in [RFC3344], the
list entry MUST contain:
o the current care-of address of the mobile node (i.e., the foreign
agent or co-located address) in the Hierarchical Foreign Agent
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 mobile node 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
8.3) to the Registration Reply, with the GFAs time of day in the
Identification field to synchronize the mobile node with the GFA for
the Regional Registrations. If nonce based reply 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 mobile node in the following
Regional Registration.
If the Registration Request message contains a Replay Protection
extension (see Section 8.3) 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 8.4).
If the care-of address field of the Registration Request is set to
zero, the GFA assigns a GFA care-of address for this Mobile Node, and
adds a GFA IP Address extension with this address of to the
Registration Request message. The GFA MUST NOT insert the GFA
address directly in the care-of address field in the Registration
Request message, since that would cause the Mobile-Home
authentication to fail.
The GFA IP Address extension has to be protected so that it can't 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
HA-FA authentication extension. Otherwise the Registration Request
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MUST be sent to the HA in a secure way, for example via a secure AAA
protocol (see e.g. [I-D.ietf-aaa-diameter-mobileip],
[I-D.ietf-mip4-aaa-key]).
If the Hierarchical Foreign Agent extension comes after the MN-FA
authentication extension, the GFA MUST remove it from the
Registration Request message. The GFA then sends the request to the
home agent. Upon receipt of the Registration Reply message, the GFA
consults its pending registration record to find the care-of address
within its domain that is currently used by the mobile node, and
sends the Registration Reply to that care-of address.
If the Replay extension (see Section 8.3) is present in a home
registration, and follows the MN-HA authentication extension, the GFA
SHOULD remove the Replay extension after performing any necessary
processing, before sending the home registration to the home agent.
If the GFA receives a Registration Request from a mobile node 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 extension is the same as the current care-of address in the
visitor list for the mobile node, the entries in the visitor list
concerning regional registrations are not changed, except to update
the lifetime. If the address in the Hierarchical Foreign Agent
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 foreign agent and re-encapsulate
them for further delivery back to the home agent. These actions are
required because the home agent has to receive such packets from the
expected care-of address (i.e. that of the GFA) instead of the local
care-of address (that of the FA).
4.4 Home Agent Considerations
A Registration Request that does not contain a GFA IP Address
extension is processed by the home agent as described in [RFC3344].
If a home agent receives a Registration Request with this extension,
and the home agent does not allow the use of this extension, the home
agent must return a Registration Reply with the Code value set to
ZERO_COA_NOT_SUPP (see Section 8.4). (If a Home Agent that does not
support Regional Registrations receives a Registration Request with a
GFA IP Address extension, the request will be process as described in
[RFC3344].) If a home agent receives a Registration Request message
with the care-of address set to zero, and a GFA IP Address extension,
it MUST register the IP address of the GFA as the care-of address of
the mobile node in its mobility binding list. If the Registration
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Request is accepted, the home agent MUST include the GFA IP Address
extension in the Registration Reply, before the Mobile-Home
Authentication extension. If a home agent receives a Registration
Request message with the care-of address set to zero, 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 8.4). Otherwise, the home agent then generates a
Registration Reply message, including the GFA IP Address extension,
and sends it back to the GFA.
5. Regional Registration
This section describes in detail regional registration. Once the
home agent has registered the GFA address as the care-of address of
the mobile node, the mobile node may perform regional registrations.
When performing regional registrations, the mobile node may either
register a foreign agent care-of address or a co-located address with
the GFA (or, another RFA - see Appendix A). In the following, we
assume that a home registration has already occurred, as described in
Section 4, and that the GFA has a mobility security association with
the mobile node (the MN-FA security association in the home
registrations).
Suppose the mobile node moves from one foreign agent to another
foreign agent within the same visited domain. It will then receive
an Agent Advertisement from the new foreign agent. Suppose further
that the Agent Advertisement indicates that the visited domain
supports regional registrations, and that either the advertised GFA
address is the same as the one the mobile node has registered as its
care-of address during its last home registration, or the realm part
of the newly advertised FA-NAI matches the FA-NAI advertised by the
mobile node's previous foreign agent. Then, the mobile node can
perform a regional registration with this foreign agent and GFA. The
mobile node issues a Regional Registration Request message to the GFA
via the new foreign agent. The request is authenticated using the
existing mobility security association between the GFA and the mobile
node (either using the SA established during the home registration,
or using pre-configured keys) and the message is authenticated by the
MN-GFA Authentication Extension (see Section 10). The care-of
address should be set to the address of the local foreign agent, or
else zero if the local foreign agent is not advertising its own
care-of address.
If the Regional Registration Request does not contain its care-of
address, the foreign agent adds a Hierarchical Foreign Agent
extension to the message and relays it to the GFA. Based on the
information in the Hierarchical Foreign Agent extension, the GFA
updates the mobile node's current point of attachment in its visitor
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list. The GFA then issues a Regional Registration Reply to the
mobile node via the foreign agent.
If the advertised GFA is not the same as the one the mobile node has
registered as its care-of address, and if the mobile node is still
within the same domain as it was when it registered that care-of
address, the mobile node MAY try to perform a regional registration
with its registered GFA. If the foreign agent cannot support
regional registration to a GFA, other than advertised, the foreign
agent denies the regional registration with code UNKNOWN_GFA (see
Section 9.3). In this case the MN has to do a new home registration
via the new GFA.
It is essential for the mobile node to distinguish regional
registrations from home registrations, since in the former case the
nonces are not synchronized with its home agent. Furthermore, a home
registration MUST be directed to the home network before the lifetime
of the GFA's regional care-of address expires. Since the mobile node
can use a zero Care-of Address either to request a GFA (in a home
registration) or to signify the use of an unspecified (perhaps
privately addressed) RFA (in a regional registration), it is
necessary to distinguish regional registrations from home
registration. Thus, we introduce new message types for the Regional
Registration messages.
5.1 Mobile Node Considerations
For each pending or current home registration, the mobile node
maintains the information described in [RFC3344]. The information is
also updated for the regional registrations performed by the mobile
node. In addition to the information described in [RFC3344], the
mobile node MUST maintain the following information, if present:
o the GFA address
o the style of replay protection in use for the regional
registration
o the Identification value for the regional registration.
The replay protection for registrations and regional registrations is
performed as described in [RFC3344]. Since the mobile node performs
regional registrations at the GFA in parallel with registrations at
its home network, the mobile node MUST be able to keep one replay
protection mechanism and sequence for the GFA, and a separate
mechanism and sequence for the home agent.
For regional registrations, replay protection may also be provided at
the foreign agent by the challenge-response mechanism, as described
in [RFC3012]. In this case, the mobile node inserts the 64 bit
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response value (timestamp or nonce, according to Mobile IPv4
[RFC3344]) in the Identification field in the Regional Registration
Request. Thus, the GFA SHOULD expect such an Identification field.
When a mobile node, which has already registered a GFA care-of
address with its home agent, changes foreign agent within the same
domain and receives an Agent Advertisement which advertises another
GFA address, it MAY still generate a Regional Registration Request
message destined to its old GFA.
5.2 Foreign Agent Considerations
When the foreign agent receives a Regional Registration Request
message from a mobile node, addressed to a GFA, it processes the
message generally according to the rules of processing a Registration
Request message addressed to a home agent (see Section 4.2). The
only difference is that the GFA IP address field replaces the home
agent address field. If that address belongs to a known GFA, the
foreign agent forwards the request to the indicated GFA. Otherwise,
the foreign agent MUST generate a Regional Registration Reply with
error code UNKNOWN_GFA.
For each pending or current registration, the foreign agent 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 foreign agent can tunnel datagrams, sent by the mobile node,
to the GFA. The GFA then decapsulates the datagrams, re-encapsulates
them and sends them to the home agent.
5.3 GFA Considerations
If the GFA accepts a request for regional registration, it MUST set
the lifetime to be no greater than the remaining lifetime of the
mobile node's registration with its home agent, 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
mobile node's registration with its home agent 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 a foreign agent 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, then 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 home agent as the
destination IP address.
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6. Generalized NAI Extension
The revised specification for "IP Mobility Support for IPv4"
[RFC3344] defines a new extension header format, that is intended to
extend the Mobile IP extension address space. The use of a Network
Access Identifier (NAI) [RFC2486] for mobile nodes is specified for
Mobile IPv4 in [RFC2794]. The Generalized NAI (GNAI) extension,
defined in this section, uses the new extension header format to
extend this idea, enabling NAIs to be used for identifying IPv4
mobility agents (i.e. the Foreign Agent or the Home agent) or other
possible network elements that may be involved with the processing of
Registration Requests. For Regional Registration, only a single
sub-type is defined; it is used to carry a Foreign Agent's NAI (see
Section 7.2).
The GNAI extension, illustrated below, may be carried by Registration
Request and Reply messages.
The Generalized NAI (GNAI) Extension:
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 | Sub-Type | NAI ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
(Type to be assigned by IANA) (skippable)
Length
8-bit unsigned integer. Length of the extension, in octets,
excluding the extension Type and the extension Length fields, but
including the Sub-Type field and the variable length NAI field.
Sub-Type
8-bit unsigned integer identifying the specific sub-type of the
GNAI extension, and thus be implication the type of the entity
which is to be identified by using the NAI.
NAI
A string containing the Network Access Identifier NAI in the
format prescribed in [RFC2486].
When a mobile node or home agent adds a GNAI extension to a
registration message, the extension MUST appear prior to any
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authentication extensions.
When the Foreign Agent adds an GNAI extension to a registration
message, the extension MUST appear prior to any authentication
extensions added by the FA.
7. 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].
7.1 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
foreign agent generating the Agent Advertisement belongs, supports
regional registrations. The flag is inserted after the flags defined
in [RFC3344], [RFC3024] and [route-optim].
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|V|T|S|I| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| zero or more Care-of Addresses |
| ... |
The flag is defined as follows:
I Regional registration. This domain supports Regional
Registration as specified in this document.
7.2 Foreign Agent NAI Extension
The FA-NAI extension is defined as a subtype 4 of the Generalized NAI
Extension (GNAIE) (see Section 6).
The foreign agent SHOULD include its NAI in the Agent Advertisement
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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 foreign agent NAI with the domain
part of its own NAI, the mobile node can determine whether it is in
its home domain or in a visited domain, and whether it has changed
domain since it last registered.
8. Regional Extensions to Mobile IPv4 Registration Messages
In this section we specify new Mobile IP registration extensions for
the purpose of managing regional registrations.
8.1 GFA IP Address Extension
If the mobile node requests a dynamically assigned GFA, the GFA adds
a GFA IP Address extension to the Registration Request before
relaying it to the HA. The mobile node indicates that it wants a GFA
to be assigned by sending a Registration Request message with the
care-of address field set to zero. The GFA IP Address extension MUST
appear in the Registration Request message before the Foreign-Home
Authentication extension, if present.
If a home agent receives a Registration Request message with the
care-of address set to zero, and a GFA IP Address extension, it MUST
register the IP address of the GFA as the care-of address of the
mobile node. When generating a Registration Reply message, the home
agent 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
Mobile-Home 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 | GFA IP Address ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
GFA IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type
TBD (GFA IP Address)
Length
4
GFA IP Address
The GFA IP Address field contains the Gateway Foreign Agent's
publicly routable address.
8.2 Hierarchical Foreign Agent Extension
The Hierarchical Foreign Agent extension may be present in a
Registration Request or Regional Registration Request message. When
this extension is added to a Registration Request by a foreign agent,
the receiving mobility agent sets up a pending registration record
for the mobile node, using the IP address in the Hierarchical Foreign
Agent extension as the care-of address for the mobile node.
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 foreign agent. The Hierarchical Foreign
Agent extension SHOULD be protected by an FA-FA Authentication
extension. When the receiving foreign agent receives the
registration message, it MUST remove the Hierarchical Foreign Agent
extension added by the sending foreign agent.
The Hierarchical Foreign Agent 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 | FA IP Address ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
FA IP Address .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
TBD (Hierarchical Foreign Agent)
Length
4
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FA IP Address
The IP Address of the foreign agent relaying the Registration
Request.
8.3 Replay Protection Style
When a mobile node uses Mobile IP to register a care-of address with
its home agent, 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 mobile
node and the home agent receiving the request. No such pre-existing
security association between the mobile node and the GFA is likely to
be available. By default, the mobile node SHOULD treat replay
protection for Regional Registration messages exactly as specified in
Mobile IPv4 [RFC3344] for timestamp-based replay protection.
If the mobile node requires nonce-based replay protection, also as
specified in Mobile IPv4, it MAY append a Replay Protection extension
to a home registration message. Since home registrations are
forwarded to the home agent by way of the GFA, the GFA will be able
to establish the selected replay protection (see Section 4.3).
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 4.3).
The format of the Replay Protection 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
TBD (Replay Protection Style)
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Length
2
Replay Protection Style
An integer specifying the style of replay protection desired by
the mobile node.
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 mobile node has an established
mobility security association with the GFA, the Replay Protection
Style extension SHOULD be placed after the MN-HA authentication
extension and before the MN-FA authentication extension. Otherwise
the Replay Protection Style extension MUST be placed before the MN-HA
authentication extension.
Replay protection MAY also be provided through a challenge-response
mechanism, at the foreign agent issuing the Agent Advertisement, as
described in [RFC3012].
8.4 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 FA:
+--------------------+-------+---------------------+
| Error Name | Value | Section of Document |
+--------------------+-------+---------------------+
| SMOOTH_HO_REQUIRED | TBD | Section 4 |
+--------------------+-------+---------------------+
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Registration denied by the GFA:
+---------------------+-------+---------------------+
| Error Name | Value | Section of Document |
+---------------------+-------+---------------------+
| REPLAY_PROT_UNAVAIL | TBD | Section 8.3 |
| GFA_ID_MISMATCH | TBD | Section 4.3 |
+---------------------+-------+---------------------+
Registration denied by the HA:
+---------------------+-------+---------------------+
| Error Name | Value | Section of Document |
+---------------------+-------+---------------------+
| ZERO_CAREOF_ADDRESS | TBD | Section 4.4 |
| ZERO_COA_NOT_SUPP | TBD | Section 4.4 |
+---------------------+-------+---------------------+
9. 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 mobile node instead of the existing Registration
Request and Registration Reply, in order to make registration work
faster, and also to reduce network load for Mobile IP registration,
as described in Section 5.
Regional registration messages are protected by requiring
authentication extensions, in the same way as the existing Mobile IP
registration messages are protected. The following rules apply to
authentication extensions:
o The Mobile-GFA Authentication extension [RFC3344] MUST be included
in all regional registration messages.
o The Mobile-Foreign Authentication extension [RFC3344] MAY be
included in regional registration messages.
o The Foreign-Home Authentication extension [RFC3344] MUST NOT be
included in any regional registration message.
9.1 Regional Registration Request
The Regional Registration Request is used by a mobile node to
register with its current GFA.
Regional Registration Request:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |S|B|D|M|G|r|T|x| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GFA IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Care-of Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
The Regional Registration Request message is defined as the
Registration Request message in [RFC3344], but with the following
changes:
Type
TBD (Regional Registration Request)
GFA IP Address
The IP address of the Gateway Foreign Agent. (Replaces Home Agent
field in Registration Request message in [RFC3344].)
Care-of Address
Care-of address of local foreign agent; MAY be set to all ones.
Extensions
For the Regional Registration Request, the Hierarchical Foreign
Agent Extension is also an allowable extension in addition to
those which are allowable for the Registration Request message.
9.2 Regional Registration Reply
The Regional Registration Reply message delivers the indication of
regional registration acceptance or denial to a mobile node.
In the Regional Registration Reply message, the UDP header is
followed by the Mobile IP fields shown below:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Regional FA IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
This message is defined as the Registration Reply message in
[RFC3344], but with the following changes:
Type
TBD (Regional Registration Reply)
Regional FA IP Address
The IP address of the Gateway Foreign Agent. (Replaces Home Agent
field specified in Mobile IPv4 [RFC3344]).
Extensions
The Regional FA IP Address is the address of the regional foreign
agent generating the Regional Registration Reply message. For the
two-level hierarchy specified here, it is the address of the GFA.
For more levels of hierarchy, it may be the address of an
intermediate RFA.
9.3 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].
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Registration denied by the FA:
+-----------------------+-------+---------------------+
| Error Name | Value | Section of Document |
+-----------------------+-------+---------------------+
| UNKNOWN_GFA | TBD | Section 5.2 |
| GFA_UNREACHABLE | TBD | |
| GFA_HOST_UNREACHABLE | TBD | |
| GFA_PORT_UNREACHABLE | TBD | |
| SMOOTH_HO_REQUIRED | TBD | Section 4 |
+-----------------------+-------+---------------------+
Registration denied by the GFA:
+--------------+-------+---------------------+
| Error Name | Value | Section of Document |
+--------------+-------+---------------------+
| NO_HOME_REG | TBD | Section 5.3 |
+--------------+-------+---------------------+
The four first Code values are returned to the mobile node in
response to ICMP errors that may be received by the foreign agent.
10. Authentication Extensions
In this section, two new subtypes for the Generalized Authentication
Extension [RFC3012] are specified. First, the FA-FA Authentication
extension is used by regional foreign agents to secure the
Hierarchical Foreign Agent (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 Mobile-Home (or some other
authorization-enabling [RFC3344] (e.g. MN-AAA [RFC2794], see
Appendix B) authentication extension.
The MN-GFA authentication extension is used whenever the mobile node
has a co-located address. Furthermore, the MN-GFA extension is 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 | TBD |
| MN-GFA authentication | TBD |
+------------------------+-------+
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The default algorithm for computation of the authenticator is the
same as for the MN-AAA Authentication subtype defined in [RFC3012].
11. Security Considerations
This document proposes a method for a mobile node to register locally
in a visited domain. The authentication extensions to be used are
those defined either in [RFC3344], [I-D.ietf-aaa-diameter-mobileip]
or [route-optim]. Key distribution is to be performed, for instance,
according to [I-D.ietf-aaa-diameter-mobileip] or
[I-D.ietf-mip4-aaa-key]. Or the keys can be pre-configured.
If the Hierarchical Foreign Agent (HFA) extension is appended to a
Registration Request message, that extension is to be followed by an
FA-FA Authentication Extension (see Section 10) to prevent any
modification to the data. Likewise, if the GFA IP Address extension
is added to such a message, it is to be followed by an authentication
extension.
12. IANA Considerations
This document defines:
o The Generalized NAI extension, specified in Section 6. The type
number for this new extension is to be assigned from the number
space for Mobile IPv4 skippable extensions (128-255).
o A Sub-Type for the GNAI extension is specified in Section 7.2,
which needs to have a value assigned from the space of GNAI
subtypes.
o Three new extensions to Mobile IP Registration messages: GFA IP
Address, Hierarchical Foreign Agent, and Replay Protection Style
(see Section 8.1, Section 8.2 and Section 8.3). The Type values
for the GFA IP Address extension must be within the range 0
through 127, while the other two must be within the range 128
through 255.
o New Code values for Registration Reply messages (see Section 8.4).
o Two new subtypes for the Generalized Authentication Extension
[RFC3012]; see Section 10.
o Two new message types for Mobile IP: Regional Registration Request
and Regional Registration Reply (see Section 9.1 and Section 9.2).
o Code values for Regional Registration Reply messages (see Section
9.3).
13. 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
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at the Nokia Research Center for his commentary on a rough version of
this document, and providing motivation for Section 4.
The text in Section 6 was taken directly from a previous Internet
Draft [I-D.ietf-mobileip-gnaie] written by Mohamed M. Khalil, Emad
Qaddoura, Haseeb Akhtar of Nortel Networks, along with Pat R.
Calhoun of Airespace Networks.
14. References
14.1 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.
[RFC2486] Aboba, B. and M. Beadles, "The Network Access Identifier",
RFC 2486, January 1999.
[RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access
Identifier Extension for IPv4", RFC 2794, March 2000.
[RFC3012] Perkins, C. and P. Calhoun, "Mobile IPv4
Challenge/Response Extensions", RFC 3012, November 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.
14.2 Informative References
[I-D.ietf-aaa-diameter-mobileip]
Calhoun, P., Johansson, T., Perkins, C. and T. Hiller,
"Diameter Mobile IPv4 Application",
draft-ietf-aaa-diameter-mobileip-20 (work in progress),
August 2004.
[I-D.ietf-mobileip-gnaie]
Khalil, M., Qaddoura, E., Akhtar, H. and P. Calhoun,
"Generalized NAI (GNAIE) Extension for Mobile IPv4",
draft-ietf-mobileip-gnaie-05 (work in progress), October
2001.
[I-D.ietf-mip4-aaa-key]
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Perkins, C. and P. Calhoun, "AAA Registration Keys for
Mobile IPv4", draft-ietf-mip4-aaa-key-06 (work in
progress), June 2004.
[route-optim]
Perkins, C. and D. Johnson, "Route Optimization in Mobile
IP", September 2001,
<http://www.watersprings.org/pub/id/draft-ietf-mobileip-op
tim-11.txt>.
Authors' Addresses
Eva Gustafsson
Ericsson
Torshamnsgatan 23
SE-164 80 Stockholm
Sweden
EMail: eva.gustafsson@ericsson.com
Annika Jonsson
Ericsson
Torshamnsgatan 23
SE-164 80 Stockholm
Sweden
EMail: annika.jonsson@ericsson.com
Charles E. Perkins
Nokia Research Center
313 Fairchild Drive
Mountain View, California 94043
USA
EMail: charles.perkins@nokia.com
Appendix A. Hierarchical Foreign Agents
The main body of this specification assumes two hierarchy levels of
foreign agents in the visited domain. At the top level, there is one
or several GFAs, and on the lower level, there is a number of foreign
agents. The structure can be extended to include multiple hierarchy
levels of foreign agents beneath the GFA level (Figure 5). Such
multiple hierarchy levels are discussed in this appendix.
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We assume that security associations have been established among a
GFA and all the foreign agents beneath it in the hierarchy. As
before, we assume that when a mobile node performs registration at
its home network, registration keys are generated and distributed to
the mobile node and to the GFA. The GFA may then in turn distribute
the registration keys to the foreign agents beneath it in the
hierarchy, using methods not specified in this document. We also
assume that all foreign agents and the mobile node support smooth
handover as specified in [route-optim], with some modifications as
explained below.
1 Registration with Home Agent
As described in this specification, a foreign agent announces itself
and a GFA in the Agent Advertisement in the first and last address in
the care-of address field in the Mobility Agent Advertisement
extension [RFC3344]. If there is a hierarchy of foreign agents
between the GFA and the announcing foreign agent, the foreign agent
MUST support smooth handover (specifically, the Previous Foreign
Agent Notification extension) as described in [route-optim]. The
foreign agent MAY also include the addresses of the foreign agents in
the hierarchy in order between its own address (first) and the GFA
address (last):
o Address of announcing foreign agent
o Address of the next higher-level Regional Foreign Agent (RFA)
o ...
o Address of GFA
If a foreign agent advertises the entire hierarchy between itself and
the GFA, the Registration Request messages MUST be delivered to each
RFA address in turn within that hierarchy.
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The figure below shows a domain with a GFA and multiple hierarchies
of FAs, enabled for regional registrations:
+--------+
| |
| GFA |
| |
+--------+
/ | \
... ... ...
|
+--------+
| |
| RFA3 |
| |
+--------+
/ \
+--------+ +--------+
| | | |
| FA2 | | FA1 |
| | | |
+--------+ +--------+
| |
| +--------+
... | |
| MN |
| |
+--------+
Figure 5
When newly arriving at a visited domain, the mobile node sends a
Registration Request, with the care-of address set to the GFA address
announced in the Agent Advertisement. The mobile node may also
request a GFA to be assigned, as described earlier in this
specification. The registration Request MUST include the Previous
Foreign Agent Notification Extension defined in [route-optim]. The
Binding Update that results is processed as described in Section 2.
When the foreign agent closest to the mobile node receives the
Registration Request, processing is as described in Section 4.2. It
adds a Hierarchical Foreign Agent extension to the Registration
Request, including its own address, and relays the Registration
Request to the next RFA in the hierarchy toward the GFA. It also
constructs a Binding Update and sends it to the previous foreign
agent, as defined in [route-optim].
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The next RFA receives the Registration Request. For each pending or
current registration, an RFA maintains a visitor list entry. In
addition to the list entry contents (described in [RFC3344]), the
list entry for regional registrations MUST contain:
o the address of the next lower-level RFA, or FA, in the hierarchy
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 RFA removes the Hierarchical Foreign Agent extension that the
last FA or RFA added, and adds a new Hierarchical Foreign Agent
extension with its own address. This procedure is repeated at each
RFA, or FA, in the hierarchy under the GFA.
When the GFA receives the Registration Request, it removes the
Hierarchical Foreign Agent extension and caches information about the
next lower-level RFA in the hierarchy. It then relays the
Registration Request to the home agent, possibly via AAA servers.
For each pending or current home registration, the GFA maintains a
visitor list entry as described in [RFC3344]. The list entry is also
updated for regional registrations reaching the GFA. In addition to
the list entry contents required in [RFC3344], the list entry MUST
contain:
o the address of the next lower-level RFA in the hierarchy
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.
If there is only one level of hierarchy beneath the GFA, the address
of the next lower-level RFA is the current care-of address of the
mobile node, as stated in Section 4.3.
The home agent, as described before, processes the Registration
Request, stores the GFA address as the current care-of address of the
mobile node, generates a Registration Reply, and sends it to the GFA.
The home agent also distributes a registration key to the mobile
node, perhaps with the assistance of the GFA, for instance by way of
other AAA functions [I-D.ietf-mip4-aaa-key]. When the GFA receives
the Registration Reply, it checks its pending Registration Request
record to see which next lower-level RFA to send the Registration
Reply message to. It SHOULD then add, for instance, a new FA-FA Key
Reply extension to the Registration Reply message, before relaying it
to the next foreign agent. The new FA-FA Agent Key Reply extension
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contains the registration key, encrypted with a secret shared between
the GFA and the next lower-level RFA in the hierarchy. Similar
procedures are to be used with [I-D.ietf-mip4-aaa-key].
The next lower-level RFA receives the Registration Reply and checks
its pending Registration Request record to see which lower-level
foreign agent should next receive the Registration Reply. It
extracts, decrypts and caches the registration key, and relays the
Registration Reply to the next foreign agent. This procedure is
repeated in every foreign agent in the hierarchy, until the message
reaches the foreign agent closest to the mobile node.
When the lowest-level foreign agent receives the Registration Reply,
it checks its cached information, as described in [RFC3344], and
relays the Registration Reply to the mobile node.
2 Handling Binding Updates
Meanwhile, when the previous foreign agent receives the Binding
Update, it will process it according to [route-optim], except that
instead of sending back a Binding Acknowledge message, it sends the
Binding Update to the next RFA in the hierarchy towards the GFA.
This is done to make sure that all RFAs in the path to the previous
FA are notified that the mobile node has moved. The previous foreign
agent must be sure that the next RFA received the Binding Update,
therefore the RFA MUST send a Binding Acknowledge message back to the
foreign agent that it got the Binding Update from. Note that this is
the same Binding Acknowledge message than the one defined in
[route-optim], but this one is addressed to the IP address of the
Foreign Agent that sent the Binding Update instead of to the mobile
node.
The RFA that received the Binding Update sends the Binding
Acknowledge message back to the lower-layer Foreign Agent, and relays
the Binding Update to the next RFA in the hierarchy towards the GFA.
The RFA will also update the binding cache for the mobile node so
that it will expire according to the lifetime in the Binding Update,
but the binding cache entry will still point to the same lower-level
foreign agent.
The crossover FA is the foreign agent lowest in the hierarchy which
is part of both the old and the new path to the mobile node. When
the Binding Update reaches the crossover FA, which might be an RFA or
the GFA, it will, in addition to sending a Binding Acknowledge back
to the sending RFA, also send a Binding Acknowledge to the mobile
node. This Binding Acknowledge message is the one defined in
[route-optim] and it is addressed to the mobile node and sent down
the hierarchy via the old path and the previous Foreign Agent, who
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tunnels it to the new Foreign Agent.
The crossover FA will receive both a Registration Request and a
Binding Update for the mobile node. When the crossover FA receives
the Registration Request, it continues to send traffic via the old
path until it receives a valid Registration Reply with a Code
indicating success. Then it starts sending traffic via the new
route.
In the unlikely event that the crossover FA receives the Binding
Update before it receives the Registration Request, it doesn't know
that it is the crossover FA yet, and therefore relays the Binding
Update to the next Foreign Agent. When the crossover FA later
receives the Registration Request, it will know that it is the
crossover FA, and will send a Binding Acknowledge message to the
mobile node (via the old route). It also forwards the Registration
Request up to the next FA. The foreign agents above the crossover FA
in the hierarchy that already got the Binding Update will see that
the Registration Request does not supply any new care-of address
information (the care-of address is the same as the address in the
Binding Update) and will therefor ignore the previous Binding Update
and update the mobility binding according to the Registration
Request.
3 Regional Registration
A Regional Registration Request is forwarded to the GFA by way of one
or more intermediate regional foreign agents. When the Regional
Registration Request message arrives at the first foreign agent, the
foreign agent checks its visitor list to see if this mobile node is
already registered with it. If it is not, the foreign agent checks
which next higher-level RFA to relay the Regional Registration
Request to. It adds a Hierarchical Foreign Agent extension to the
Regional Registration Request, including its address, and relays the
message to the next RFA in the hierarchy toward the GFA.
The next RFA checks its visitor list to see if the mobile node is
already registered with it. If it is not, the RFA removes the
Hierarchical Foreign Agent extension and adds a new one, with its own
address, and relays the message to the next higher-level RFA in the
hierarchy toward the GFA.
This process is repeated in each RFA in the hierarchy, until an RFA
recognizes the mobile node as already registered. This RFA may be
the GFA, or any RFA beneath it in the hierarchy. If the mobile node
is already registered with this RFA, the RFA generates a Regional
Registration Reply and sends it to the next lower-level RFA in the
hierarchy. The lifetime field in the Regional Registration Reply is
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set to the remaining lifetime that was earlier agreed upon between
the mobile node and the GFA. If the lifetime of the GFA registration
has expired, the Regional Registration Request is relayed all the way
to the GFA.
The Previous Foreign Agent Notification Extension, Binding Updates
and Binding Acknowledge messages are used for Regional Registrations
in the same way as for Home Registrations. That means that if the
crossover FA receives the Binding Update before it receives the
Registration Request, it forwards the Registration Request to the
higher level FA, so that that FA updates its visitor list according
to the Registration Request, and ignores the Binding Update. That FA
also forwards the Registration Request to any FA or GFA that it has
sent the corresponding Binding Update to.
If the hierarchy between the advertising foreign agent and the GFA is
announced in the Agent Advertisement, the mobile node may generate a
Regional Registration Request not destined to the GFA, but to the
closest RFA with which it can register.
Replay protection can be provided at the announcing foreign agent,
through the challenge-response mechanism described in [RFC3012]. If
the GFA, and the RFAs in the hierarchy, trust the announcing foreign
agent to perform the replay protection, timestamps or nonces between
the mobile node and the GFA, or between the mobile node and each RFA,
are not needed. If the challenge-response mechanism is used for
replay protection, the mobile node inserts the 64 bit response value
in the Identification field in the Regional Registration Request
message. If a mobile node includes a Hierarchical Foreign Agent
extension in its Registration Request message, it MAY insert the
extension before the MN-HA or MN-FA authentication extension. In
this case, the Hierarchical Foreign Agent extension MUST NOT be
removed by the GFA or any other RFA prior to the generation of the
Registration Reply message.
If more than one Hierarchical Foreign Agent extension is inserted by
the mobile node into the registration message, the order of the
extensions MUST be maintained through the hierarchy. When sending a
Regional Registration Reply, the GFA MUST ensure that the order of
the Hierarchical Foreign Agent extensions is reversed from the order
found in the Regional Registration Request.
4 Regional Registrations and Smooth Handover
Multiple hierarchy levels of foreign agents requires the use of
smooth handover from [route-optim], as discussed in Appendix A. This
is not needed in a two level hierarchy. But a mobile node might not
know how many levels of hierarchy a network has, so if the foreign
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agents in one network support both Regional Registrations and Smooth
Handover a mobile node MAY try to use Regional Registrations without
Smooth Handover. If the network requires the use of Smooth Handover
(because it has more than two levels of hierarchy, or for other
reasons) the Foreign Agent MUST deny the request by sending back a
Registration Reply message with the Code field set to
SMOOTH_HO_REQUIRED.
The Foreign Agent NAI extension (see Section 7.2) is also used during
Smooth Handover. If Smooth Handovers are used, and the foreign agent
does not advertise its own address in the Agent Advertisement
message, the FA-NAI will be used to identify the Previous Foreign
agent instead. This will be done by adding an FA-NAI extension
(defined in Section 6) to the Registration Request (together with the
Previous Foreign Agent Notification extension) and in the Binding
Update and setting the care-of address to zero.
5 Co-located care of address
If a mobile node uses a co-located care-of address, it MAY use
Regional Registrations directly to the GFA (see Section 4.1 and
Section 5). It MAY also use the same method to make use of multiple
levels of Foreign Agents, if it can find out about the hierarchy,
either from Mobility Agent Advertisements, or in some other way
outside the scope of this specification.
6 Data Traffic
When a correspondent node sends traffic to the mobile node, the
traffic arrives at the home agent, and the home agent tunnels the
traffic to the GFA. The GFA or RFA at each level of the hierarchy
has a visitor list for the mobile node, showing the address of the
next lower-level RFA or FA in the hierarchy. Thus, a datagram
arriving at the top level of the hierarchy, that is, the GFA, will be
re-routed to the next lower-level RFA in the hierarchy. This
re-routing occurs at each level of the hierarchy, until the datagram
reaches the last point which is either the mobile node itself (in
case of a co-located care-of address) or a foreign agent that can
deliver the datagram to the mobile node with no further special
Mobile IP handling.
In case of decapsulation and re-encapsulation, it should be noted
that the actual decapsulation need not occur at each step of the
hierarchy. Instead, the foreign agent at that level can merely
change the source and destination IP addresses of the encapsulating
IP header.
Traffic from the mobile node is sent as described in [RFC3344] or
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[RFC3024].
According to the Route Optimization specification [route-optim],
Binding Updates send to the correspondent node from the Home Agent
will contain the address of the GFA, since this is the only care-of
address known to the Home Agent. Therefore, Binding Updates from the
mobile node sent to the correspondent node SHOULD also have the
care-of address belonging to the GFA. This also has the advantage of
reducing the number of Binding Update messages that have to be sent
to the correspondent node, at a modest increase in routing path
length. Furthermore, the local network domain may be configured to
admit such traffic into the local domain only if packets are tunneled
directly to the GFA.
Appendix B. 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], [I-D.ietf-aaa-diameter-mobileip]).
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 C. Anchoring at a GFA/RFA/FA
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'.
Similarly, a mobile node MAY address a Regional Registration Request
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message to any Regional Foreign Agent or foreign agent that it has
registered as the current care-of address with its home agent.
Assume that a mobile node has registered the address of an RFA or
foreign agent as its care-of address with its home agent. When
detecting that it changes foreign agent, and if the new foreign agent
advertises the 'I' flag, the mobile node MAY address a Regional
Registration Request to that RFA/FA. The new foreign agent MAY then
relay the request to the RFA/FA in question, or deny the request with
error code "unknown GFA". If the Regional Registration Request
reaches the RFA/FA, and if the RFA/FA also has the capability to act
as a GFA, it MAY accept the request and generate a Regional
Registration Reply to the mobile node. This scenario assumes that
keys have been distributed to the RFA/FA and to the mobile node prior
to the regional registration, so that the Regional Registration
Request message can be authenticated with the MN-GFA Authentication
extension.
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