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IETF RFC 3957
Authentication, Authorization, and Accounting (AAA) Registration Keys for Mobile IPv4
Last modified on Friday, March 4th, 2005
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Network Working Group C. Perkins
Request for Comments: 3957 Nokia Research Center
Category: Standards Track P. Calhoun
Airespace
March 2005
Authentication, Authorization, and Accounting (AAA)
Registration Keys for Mobile IPv4
 Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright © The Internet Society (2005).
Abstract
Authentication, Authorization, and Accounting (AAA) servers, such as
RADIUS and DIAMETER, are in use within the Internet today to provide
authentication and authorization services for dial-up computers.
Mobile IP for IPv4 requires strong authentication between the mobile
node and its home agent. When the mobile node shares an AAA Security
Association with its home AAA server, however, it is possible to use
that AAA Security Association to create derived Mobility Security
Associations between the mobile node and its home agent, and again
between the mobile node and the foreign agent currently offering
connectivity to the mobile node. This document specifies extensions
to Mobile IP registration messages that can be used to create
Mobility Security Associations between the mobile node and its home
agent, and/or between the mobile node and a foreign agent.
Perkins & Calhoun Standards Track PAGE 1 
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology. . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of Operations with Key Generation Nonce Extensions. . 5
4. Mobility Security Associations . . . . . . . . . . . . . . . . 7
5. Key Generation Nonce Creation and Key Derivation . . . . . . . 8
6. Key Generation Extensions. . . . . . . . . . . . . . . . . . . 9
6.1. Generalized MN-FA Key Generation Nonce Request Extension 10
6.2. Generalized MN-FA Key Generation Nonce Reply Extension . 11
6.3. Generalized MN-HA Key Generation Nonce Request Extension 13
6.4. Generalized MN-HA Key Generation Nonce Reply Extension . 14
7. Error Values . . . . . . . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 16
9. Security Considerations. . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
A. AAA Infrastructure. . . . . . . . . . . . . . . . . . . . . 20
B. Message Flow for Requesting and Receiving Registration Keys 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
AAA servers, such as RADIUS [11] and DIAMETER [12], are in use within
the Internet today to provide authentication and authorization
services for dial-up computers. Such services are likely to be
valuable for mobile nodes using Mobile IP for IPv4 [1], when the
nodes are attempting to connect to foreign domains with AAA servers.
In this document Mobile IP for IPv4 is called "Mobile IPv4" or just
"Mobile IP" for short, since no confusion with other versions is
expected. Requirements for interactions between AAA and Mobile IP
are outlined in RFC 2977 [13]; that document describes an
infrastructure which enables AAA servers to authenticate and
authorize network access requests from mobile nodes. See also
appendix A. The Mobile IP Registration Request is considered to be a
request for network access. It is then possible to augment the
functionality of the Mobile IP mobility agents so that they can
translate between Mobile IP registration messages and the messages
used within the AAA infrastructure, as described in RFC 2977.
Mobility agents and AAA servers that conform to the requirements of
RFC 2977 can be considered as appropriate network entities to support
the message types specified in this document. Please consult RFC
2977 [13] for further details.
Perkins & Calhoun Standards Track PAGE 2
RFC 3957 AAA Keys for Mobile IPv4 March 2005
This specification makes use of a single AAA Security Association to
create derivative Mobility Security Associations. A Mobility
Security Association in this specification is a simplex connection
that serves to authenticate MIPv4 control traffic between a MN and HA
and/or a MN and FA. A Mobility Security Association is identified by
the two end points, such as a MN IP address and a HA IP address, and
a SPI. Two nodes may have one or more Mobility Security Associations
established between each other; however, typically there is no reason
to have more than one Mobility Security Association between two
nodes.
This document specifies extensions to Mobile IP registration messages
that can be used to create Mobility Security Associations between the
MN and FA and/or MN and HA based on the AAA Security Association
between the MN and AAA server. These new Mobility Security
Associations may then be used to calculate the Authentication Data
needed by authentication extensions used in Mobile IP control
messages.
It is assumed that the security association between the mobile node
and its AAA server has been appropriately configured so that the AAA
server can provide key material to be used as the basis for the
necessary Mobility Security Association(s) between the mobile node
and its prospective mobility agents.
AAA servers typically use the Network Access Identifier (NAI) [2] to
uniquely identify the mobile node; the mobile node's home address is
not always necessary to provide that function. Thus, it is possible
for a mobile node to authenticate itself, and be authorized for
connection to the foreign domain, without having any home address.
However, for Mobile IP to work, the mobile node is required to have a
home address and a Mobility Security Association [1] with its home
agent. When the Mobile IP Registration Reply packet is authenticated
by the MN-AAA Authentication Extension [3], the mobile node can
verify that the key material contained in the extensions were
produced by the AAA server, and thus may be reliably used to create
Mobility Security Associations with the home agent and/or the foreign
agent.
It is also assumed that the AAA entities involved (i.e., the AAAH,
AAAL, and the AAA interface features of the foreign agents and home
agents) all have means outside of the scope of this document for
exchanging keys. The extensions within this document are intended to
work with any AAA protocol suite that allows for such key exchange,
as long as it satisfies the requirements specified in RFC 2977 [13].
One such AAA protocol is defined within the Diameter framework [14].
Perkins & Calhoun Standards Track PAGE 3
RFC 3957 AAA Keys for Mobile IPv4 March 2005
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [4].
AAA Authentication, Authorization, and Accounting (see
[10]).
AAA entity A network node processing AAA messages according to the
requirements for AAA protocols (see [10]).
AAA Security Association
A security association between a AAA entity and another
node needing the services of that AAA entity. In this
document all AAA Security Associations are between a
mobile node and its home AAA server (AAAH). A mobile
node's AAA Security Association with its home AAA
server (AAAH) may be based either on the mobile node's
IP address or on its NAI [2]. The key is referred to
as "AAA-key" in this specification.
Key A number, kept secret. Only nodes in possession of the
key have any hope of using the security transform to
obtain correct results.
Key Generation Nonce
Nonce data used for the purpose of creating a key.
Mobility Security Association
A Mobility Security Association is a simplex connection
that applies security services to RFC 3344 MIPv4
control traffic between a MN and HA (or MN and FA)
using RFC 3344 Authentication Extensions. A Mobility
Security Association is uniquely identified by the peer
source and destination IP addresses and an SPI. Two
nodes may have one or more Mobility Security
Associations; however, typically there is no reason to
have more than one Mobility Security Association
between two nodes, except as a transient condition
during re-keying events.
Registration Key
A key used in the MN-FA or MN-HA Mobility Security
Association. A registration key is typically only used
once or a very few times, and only for the purposes of
verifying a small volume of Authentication data.
Perkins & Calhoun Standards Track PAGE 4
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Security Algorithm
A set of rules for using input data and a secret key
for producing data for use in security protocols.
SPI Security Parameters Index. The SPI is an arbitrary
32-bit value that assists in the identification of an
AAA, IP, or Mobility Security Association.
Other terminology is used as defined in the base Mobile IP
specification [1]. Furthermore, in order to simplify the discussion,
we have used the word "Extension" instead of "Subtype of the
Generalized Extension" in many cases. So, for instance, instead of
using the phrase "The MN-FA Key Generation Nonce From AAA Subtype of
the Generalized MN-FA Key Generation Nonce Reply Extension", we would
instead use the phrase "The MN-FA Key Generation Nonce From AAA
Extension".
3. Overview of Operations with Key Generation Nonce Extensions
When a mobile node depends on an AAA infrastructure to obtain
authorization for network connectivity and Mobile IP registration, it
may lack any pre-existing Mobility Security Associations with either
its home agent, or the foreign agent controlling the access to the
foreign network. The extensions defined in this document allow a AAA
entity to supply key material to mobile nodes to be used as the basis
of its Mobility Security Association with mobile agents. The AAA
entity that will act on these extensions is part of the AAA
infrastructure, and is typically identified within the foreign domain
by methods outside the scope of this specification (see appendix A).
The key material may be requested by the mobile node in new
extensions (defined below) to Mobile IP Registration Request
messages, and supplied to the mobile node in extensions to the Mobile
IP Registration Reply messages. Alternatively, the AAA server MAY
provide unsolicited key material via mobility agents to mobile nodes;
the mobile node MUST then calculate new keys and update or create its
relevant Mobility Security Association. The method by which key
material is supplied to the mobility agents themselves is out of
scope for this document, and would depend on the particular details
of the security architecture for the AAA servers in the foreign and
home domains (see RFC 2977 and appendix A). For the purposes of this
document, we assume that there is a suitable AAA infrastructure
available to the home and foreign agents, and that the mobile node
does have an AAA Security Association with at least one AAA server in
its home domain.
Perkins & Calhoun Standards Track PAGE 5
RFC 3957 AAA Keys for Mobile IPv4 March 2005
When a mobile node travels away from home, it may not have a Mobility
Security Association with its home agent, perhaps because it does not
yet have a home address [5]. The protocol and messages in this
document are intended to facilitate the following operations which
may occur between the mobile node, foreign agent, home agent, and AAA
servers in the visited (local) domain (Authentication, Authorization
and Accounting Local or AAAL) and in the home domain (Authentication,
Authorization, and Accounting Home or AAAH). In the following
sequence of messages, the only message flows specified in this
document are the Registration Request between the mobile node and the
foreign agent, and Registration Reply between the foreign agent and
the mobile node. The other messages described here result from the
presumed action of the AAA entities as described in RFC 2977. See
also appendix B.
1. If the mobile node does not have a Mobility Security Association
with the foreign agent, it SHOULD include an MN-FA Key Generation
Nonce Request extension (see Section 6.1) as part of its
Registration Request that it sends to the Foreign Agent.
2. If the mobile node does not have a Mobility Security Association
with the home agent, it MUST add an MN-HA Key Generation Nonce
Request extension (see Section 6.3) as part of its Registration
Request that it sends to the Foreign Agent.
3. If one or more AAA Key Generation Nonce Request extensions were
added, the mobile node MUST add the MN-AAA Authentication
extension to its Registration Request.
4. By action of the foreign agent, which is presumed to be also a
AAA entity, the mobile node's key requests and authentication
data are transferred to the local AAA server (AAAL), typically
after reformatting to fit into the appropriate AAA messages,
which are out of scope for this document.
5. After the information within the MN-AAA Authentication extension
is verified by the AAA server in the home domain (AAAH), it then
also generates the key material that has been requested by the
mobile node, for the necessary Mobility Security Associations.
6. The respective keys for the Mobility Security Associations are
distributed to the Home Agent and Foreign Agent via the AAA
protocol.
7. The mobile node receives the Registration Reply message from the
Foreign Agent.
Perkins & Calhoun Standards Track PAGE 6
RFC 3957 AAA Keys for Mobile IPv4 March 2005
8. If a MN-HA Key Generation Nonce Request From AAA extension is
present in the Registration Request message, then the mobile node
MUST create or update its Mobility Security Association with the
Home Agent indicated in the corresponding Registration Reply,
using the key computed from the key material in the MN-HA Key
Generation Nonce From AAA extension. In this case, if no MN-HA
Key Generation Nonce Reply extension is present, the mobile node
MUST discard the Registration Reply.
9. Using its (perhaps newly created) Mobility Security Association
with the home agent, the mobile node authenticates the
Registration Reply message by checking the Authentication Data in
the Mobile-Home Authentication extension. If the check fails,
the MN MUST discard the Registration Reply and the new Mobility
Security Association, reverting to the old Mobility Security
Association with the home agent, if any.
10. If the Registration Reply passes authentication and contains a
MN-FA Key Generation Nonce From AAA extension (see section 6.2),
the mobile node generates the registration key using the Key
Generation Nonce provided, according to its AAA Security
Association with the AAA. The resulting registration key is used
to establish the mobile node's Mobility Security Association with
its foreign agent, and is used to compute the authentication data
used in the Mobile-Foreign authentication extension.
If verification of the Mobile-Foreign authentication extension
fails, and if the MN-FA Key Generation Nonce Reply extension was
not protected by another, valid authentication extension, the MN
MUST discard the new Mobility Security Association, reverting to
the old Mobility Security Association with the foreign agent, if
any.
Any registration reply containing the MN-HA Key Generation Nonce From
AAA extension MUST also contain a subsequent Mobile Home
Authentication extension, created using the generated MN-HA key.
Similarly, a reply containing the MN-FA Key Generation Nonce From AAA
extension MUST also contain a subsequent Mobile Foreign
Authentication extension, created using the registration key.
4. Mobility Security Associations
Mobility Security Associations between Mobile IP entities (mobile
nodes, home agents, foreign agents) contain both the necessary
cryptographic key information and a way to identify the cryptographic
transform that uses the key to produce the authentication information
that is present in the Mobile-Home Authentication extension or the
Mobile-Foreign Authentication extension. In order for the mobile
Perkins & Calhoun Standards Track PAGE 7
RFC 3957 AAA Keys for Mobile IPv4 March 2005
node to make use of key material created by the AAA server, the
mobile node also has to be able to identify and select the
appropriate cryptographic transform that uses the key to produce the
authentication.
The transform identifiers are the same as those used in IPsec. They
are tabulated in the list of Authentication Algorithms allowable as
values for the "Attribute Type" (5) (i.e., "Authentication
Algorithm"), one of the classifications in the tabulated Attribute
Types for "IPsec Security Association Attributes". See
http://www.iana.org/assignments/isakmp-registry for the full listing
of all Attribute Types and other Attributes for IPsec Security
Associations.
Mobility Security Associations shared between mobile nodes and home
agents also require a replay protection method. The following table
contains the supported replay detection methods.
Replay Method Name Reference
-------------- ------------ --------------
0,1 Reserved
2 Timestamps RFC 3344 [1]
3 Nonces RFC 3344 [1]
4-65535 Unallocated
5. Key Generation Nonce Creation and Key Derivation
This section contains the procedures followed in the creation of the
Key Generation Nonce by AAA servers, and the key derivation
procedures used by mobile nodes. Note that the AAA servers will also
deliver the keys to the mobility agents (home agent, foreign agent)
via the AAA protocol. AAA servers that follow these procedures will
produce results that can be understood by mobile nodes. The mobility
agents will faithfully transcribe the results into the appropriate
Mobile IP extensions.
The following example uses HMAC-SHA1 [6]. All mobile nodes and
mobility agents implementing Mobile IP [1] and implementing the
extensions specified in this document MUST implement HMAC-SHA1 [1].
Other message authentication codes or keyed hash functions MAY also
be used. The particular algorithm used is configured as part of the
AAA Security Association between the MN and the AAAH server, which is
in turn indexed by the AAA SPI.
Perkins & Calhoun Standards Track PAGE 8
RFC 3957 AAA Keys for Mobile IPv4 March 2005
The following steps are performed on the AAAH server:
1. The AAA server identifies the mobile node. If the NAI field is
present in the Registration Request, then the NAI is used as the
mobile node identifier. Otherwise, the Home Address field of the
Registration Request is used.
2. The AAA server generates a random [7] value of at least 128 bits
to be used as the Key Generation Nonce.
3. The AAA server inserts the random value into the Key Generation
Nonce Reply extension in the "Key Generation Nonce" field.
The following steps are performed by the mobile node (here ||
represents concatenation):
1. The mobile node calculates
key = HMAC-SHA1 (AAA-key, {Key Generation Nonce || mobile node
identifier})
Here the Key Generation Nonce is from the extension in the
Registration Reply, and the mobile node identifier is the MN's
NAI, if present in the Registration Request, or the Home Address
from the Registration Request otherwise.
2. The mobile node creates the Mobility Security Association(s),
using the resulting key and the other relevant information in the
Key Generation Nonce Extension.
The secret key used within the HMAC-SHA1 computation is indicated by
the AAA Security Association indexed by the AAA SPI, which has been
previously configured as the basis for the AAA Security Association
between the mobile node and the AAA server creating the key material.
6. Key Generation Extensions
This section defines new Extensions to Mobile IP Registration
Requests and Replies [1].
Perkins & Calhoun Standards Track PAGE 9
RFC 3957 AAA Keys for Mobile IPv4 March 2005
6.1. Generalized MN-FA Key Generation Nonce Request Extension
Figure 1 illustrates the Generalized MN-FA Key Generation Nonce
Request Extension (MN-FA KeyGen Request for short).
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 | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile Node SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MN-FA Key Generation Nonce Request Subtype Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The Generalized Mobile IP MN-FA Key Generation
Nonce Request Extension
Type 40 (not skippable) (see [1] and section 8)
Subtype A number assigned to identify the way in which the
MN-FA Key Generation Nonce Request Subtype Data is
to be used when generating the registration key.
Length The 16-bit Length field indicates the length of the
extension. It is equal to the number of bytes in
the MN-FA Key Generation Nonce Request Subtype Data
plus 4 (for the Mobile Node SPI field).
Mobile Node SPI The Security Parameters Index that the mobile node
will assign for the Mobility Security Association
created for use with the registration key.
MN-FA Key Generation Nonce Request Subtype Data
Data needed to carry out the creation of the
registration key on behalf of the mobile node.
The MN-FA KeyGen Request defines a set of extensions, identified by
subtype, which may be used by a mobile node in a Mobile IP
Registration Request message to request that some other entity create
a Registration Key for use by the mobile node with the mobile node's
new foreign agent.
Perkins & Calhoun Standards Track PAGE 10
RFC 3957 AAA Keys for Mobile IPv4 March 2005
This document defines the subtype 1 for the MN-FA Key Generation
Nonce >From AAA Request (MN-FA AAA KeyGen Request for short). The
MN-FA AAA KeyGen Request has a zero-length Subtype Data field and
MUST appear in the Registration Request before the MN-AAA
Authentication extension.
6.2. Generalized MN-FA Key Generation Nonce Reply Extension
The Generalized MN-FA Key Generation Nonce Reply extension (MN-FA
KeyGen Reply for short) supplies keying material requested by the
MN-FA KeyGen Request extension. Figure 2 illustrates the format of
the Generalized MN-FA Key Generation Nonce Reply 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 | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MN-FA Key Generation Nonce Reply Subtype Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The Generalized Mobile IP MN-FA Key
Generation Nonce Reply Extension
Type 41 (not skippable) (see [1] and section 8)
Subtype A number assigned to identify the way in which the MN-FA
Key Generation Nonce Reply Subtype Data is to be used to
obtain the registration key.
Length The 16-bit Length field is equal to the number of bytes in
the MN-FA Key Generation Nonce Reply Subtype Data.
MN-FA Key Generation Nonce Reply Subtype Data
An encoded copy of the keying material, along with any
other information needed by the recipient to create the
designated Mobility Security Association.
For each subtype, the format of the MN-FA Key Generation Nonce Reply
Subtype Data has to be separately defined according to the particular
method required to set up the Mobility Security Association.
For the subtype defined in this document, the MN-FA Key Generation
Nonce supplied in the data for a subtype of this extension may come
as a result of a request which was sent using a subtype of the
Generalized MN-FA Key Generation Nonce Request Extension. In such
Perkins & Calhoun Standards Track PAGE 11
RFC 3957 AAA Keys for Mobile IPv4 March 2005
cases, the SPI to be used when employing the Mobility Security
Association defined by the registration key is the same as given in
the original request.
Once the mobile node creates the Mobility Security Association with
the foreign agent, by using the transform indexed by the AAA SPI, it
stores that Mobility Security Association indexed by the FA SPI in
its list of Mobile Security Associations.
If the foreign agent receives a Registration Reply that has no MN-FA
Key Generation Nonce Reply extension, and if it has no existing
Mobility Security Association with the mobile node, the foreign agent
MAY change the Code value of the Registration Reply to MISSING_MN_FA
(see section 7), effectively causing the registration to fail.
This document defines subtype 1 of the MN-FA KeyGen Reply for the
MN-FA Key Generation Nonce From AAA extension (MN-FA AAA KeyGen Reply
for short), shown in figure 3.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AAA SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FA SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm Identifier | Key Generation Nonce ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The MN-FA Key Generation Nonce From AAA
Subtype-Specific Data
lifetime This field indicates the duration of time (in seconds) for
which the keying material used to create the registration
key is valid.
AAA SPI A 32-bit opaque value, indicating the SPI that the mobile
node must use to determine the transform to use for
establishing the Mobility Security Association between the
mobile node and its prospective foreign agent.
FA SPI The SPI for the Mobility Security Association to the FA
that the mobile node creates using the Key Generation
Nonce.
Perkins & Calhoun Standards Track PAGE 12
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Algorithm Identifier
This field indicates the transform to be used (stored as
part of the Mobility Security Association with the foreign
agent, and selected from among the values in the
"Authentication Algorithm" table cited in section 4), for
future computations of the Mobile-Foreign Authentication
Extension.
Key Generation Nonce
A random [7] value of at least 128 bits.
The MN-FA AAA KeyGen Reply extension MUST appear in the Registration
Reply before the Mobile-Foreign Authentication extension.
The Key Generation Nonce is provided by the AAA server for use by the
mobile node in creating the registration key, which is used to secure
future Mobile IP registrations with the same foreign agent.
6.3. Generalized MN-HA Key Generation Nonce Request Extension
Figure 4 illustrates the Generalized MN-HA Key Generation Nonce
Request Extension (MN-HA KeyGen Request for short).
Type 42 (not skippable) (see [1] and section 8)
Subtype a number assigned to identify the way in which the
MN-HA Key Generation Nonce Request Subtype Data is
to be used when generating the registration key.
Length The 16-bit Length field indicates the length of the
extension. It is equal to the number of bytes in
the MN-HA Key Generation Nonce 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 | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile Node SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MN-HA Key Generation Nonce Request Subtype Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The Generalized Mobile IP MN-HA Key Generation
Nonce Request Extension
Subtype Data plus 4 (for the Mobile Node SPI field).
Perkins & Calhoun Standards Track PAGE 13
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Mobile Node SPI The Security Parameters Index that the mobile node
will assign for the Mobility Security Association
created for use with the registration key.
MN-HA Key Generation Nonce Request Subtype Data
Data needed to carry out the creation of the MN-HA
key on behalf of the mobile node.
The MN-HA KeyGen Request Extension defines a set of extensions,
identified by subtype, which may be used by a mobile node in a Mobile
IP Registration Request message to request that some other entity
create an MN-HA key for use by the mobile node with the mobile node's
new home agent.
This document defines the subtype 1 for the MN-HA Key Generation
Nonce from AAA Request (MN-HA AAA KeyGen Request for short). The
MN-HA AAA KeyGen Request has a zero-length Subtype Data field and
MUST appear in the Registration Request before the MN-AAA
Authentication extension.
6.4. Generalized MN-HA Key Generation Nonce Reply Extension
The Generalized MN-HA Key Generation Nonce Reply extension (MN-HA
KeyGen Reply for short) supplies keying material requested by the
MN-HA KeyGen Request extension. Figure 5 illustrates the format of
the Generalized MN-HA Key Generation Nonce Reply 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 | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MN-HA Key Generation Nonce Reply Subtype Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: The Generalized Mobile IP MN-HA Key
Generation Nonce Reply Extension
Type 43 (not skippable) (see [1] and section 8)
Subtype a number assigned to identify the way in which the MN-HA
Key Generation Nonce Reply Subtype Data is to be used to
obtain the MN-HA key.
Perkins & Calhoun Standards Track PAGE 14
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Length The 16-bit Length field indicates the length of the
extension. It is equal to the number of bytes in the MN-
HA Key Generation Nonce Reply Subtype Data plus 4 (for the
Lifetime field).
Lifetime This field indicates the duration of time (in seconds) for
which the MN-HA key is valid.
MN-HA Key Generation Nonce Reply Subtype Data
Data used to derive the MN-HA key, along with any other
information needed by the mobile node to create the
designated Mobility Security Association with the home
agent.
For each subtype, the format of the MN-HA Key Generation Nonce Reply
Subtype Data has to be separately defined according to the particular
method required to set up the Mobility Security Association.
This document defines subtype 1 of the MN-HA KeyGen Reply for the
MN-HA Key Generation Nonce From AAA extension (MN-HA AAA KeyGen Reply
for short), shown in figure 6.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AAA SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HA SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm Identifier | Replay Method |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Generation Nonce ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: The MN-HA Key Generation Nonce From AAA
Subtype-Specific Data
AAA SPI A 32-bit opaque value, indicating the SPI that the mobile
node must use to determine the transform to use for
establishing the Mobility Security Association between the
mobile node and its home agent.
HA SPI The SPI for the Mobility Security Association to the HA
that the mobile node creates using the Key Generation
Nonce.
Perkins & Calhoun Standards Track PAGE 15
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Algorithm Identifier
This field indicates the transform to be used for future
computations of the Mobile-Home Authentication Extension
(see section 4).
Replay Method
This field contains the replay method to be used for
future Registration messages (see section 4).
Key Generation Nonce
A random [7] value of at least 128 bits.
The MN-HA AAA KeyGen Reply subtype-specific data is shown in figure
6. The Mobile Node calculates the MN-HA key using the Key Generation
Nonce provided by the AAA server. The calculation proceeds by using
the key shared between the mobile node and the AAA server that has
previously been configured for securing all such communication
requirements with the AAA server which will be contacted within the
AAA infrastructure (see appendix A). The MN-HA key is intended for
use by the mobile node to secure future Mobile IP registrations with
its home agent. The MN-HA AAA KeyGen Reply extension MUST appear in
the Registration Reply before the MN-HA Authentication extension.
Once the mobile node creates the MN-HA Key, by using the transform
specified in the AAA SPI, it stores the HA Security Information
indexed by the HA SPI in its list of Mobile Security Associations.
The mobile node uses the Identification field data from the
Registration Reply as its initial synchronization data with the home
agent.
7. Error Values
Each entry in the following table contains the name of the Code [1]
value to be returned in a Registration Reply, the value for that
Code, and the section in which the error is first mentioned in this
specification.
Error Name Value Section
---------------------- ----- ---------
MISSING_MN_FA 107 6.2
8. IANA Considerations
This document defines 4 new extensions (see Section 6) taken from the
(non-skippable) numbering space defined for Mobile IP registration
extensions defined in RFC 3344 [1] as extended in RFC 2356 [8]. The
values for these extensions are:
Perkins & Calhoun Standards Track PAGE 16
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Name Value Section
--------------------- ------- ---------
MN-FA-KeyGen Request 40 6.1
MN-FA-KeyGen Reply 41 6.2
MN-HA-KeyGen Request 42 6.3
MN-HA-KeyGen Reply 43 6.4
IANA has created and will maintain a new registry for the KeyGen
Request/Reply subtypes. The initial contents of the registry is a
single entry for the subtypes defined in this document:
Name Value Section
----------------------------- ------- ---------
KeyGen Request/Reply from AAA 1 6
New subtypes for these two registries are assigned through Standards
Action as defined in [9].
IANA has assigned a code value for error MISSING_MN_FA, listed in
section 7. This value has been taken from the space of error values
conventionally associated with rejection by the foreign agent (i.e.,
64-127).
IANA has created and will maintain a namespace for the Replay Method
Identifier. This specification makes use of 2 and 3; all other
values other than zero (0) and (1) are available for assignment,
pending review and approval by a Designated Expert [9].
9. Security Considerations
The extensions in this document are intended to provide the
appropriate level of security for Mobile IP entities (mobile node,
foreign agent, and home agent) to calculate the Authentication Data
needed by authentication extensions used with Mobile IP registration
messages. The Mobility Security Associations resulting from use of
these extensions do not offer any higher level of security than what
is already implicit in use of the AAA Security Association between
the mobile node and the AAAH. In order to deny any adversary the
luxury of unbounded time to analyze and break the secrecy of the AAA
Security Association between the mobile node and the AAA server, that
AAA Security Association MUST be refreshed periodically.
The provisioning and refreshing of the AAA key in the MN and AAA
server is outside the scope of this document.
Since the Reply extensions defined in this specification only carry
Key Generation Nonces, which are used to derive keys, they do not
expose any data that could be used in an attack aimed at recovering
Perkins & Calhoun Standards Track PAGE 17
RFC 3957 AAA Keys for Mobile IPv4 March 2005
the key shared between the mobile node and the AAA. The authors do
not believe this specification introduces any new security
vulnerability.
10. Acknowledgements
Thanks to Fredrik Johansson, Tom Hiller, and the members of the IESG
for their useful comments. Thanks especially to Tom Hiller who has
contributed many textual improvements to later revisions of this
document.
11. References
11.1. Normative References
[1] Perkins, C., Ed., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[2] Aboba, B. and M. Beadles, "The Network Access Identifier", RFC
2486, January 1999.
[3] Perkins, C. and P. Calhoun, "Mobile IPv4 Challenge/Response
Extension", RFC 3012, November 2000.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] Calhoun, P. and C. Perkins, "Mobile IP Network Access Identifier
Extension for IPv4", RFC 2794, March 2000.
[6] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[7] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
[8] Montenegro, G. and V. Gupta, "Sun's SKIP Firewall Traversal for
Mobile IP", RFC 2356, June 1998.
[9] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
Perkins & Calhoun Standards Track PAGE 18
RFC 3957 AAA Keys for Mobile IPv4 March 2005
11.2. Informative References
[10] Mitton, D., St.Johns, M., Barkley, S., Nelson, D., Patil, B.,
Stevens, M., and B. Wolff, "Authentication, Authorization, and
Accounting: Protocol Evaluation", RFC 3127, June 2001.
[11] Rigney, C., Willens, S., Rubens, A., and A. Simpson, "Remote
Authentication Dial In User Service (RADIUS)", RFC 2865, June
2000.
[12] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
"Diameter Base Protocol", RFC 3588, September 2003.
[13] Glass, S., Hiller, T., Jacobs, S., and C. Perkins, "Mobile IP
Authentication, Authorization, and Accounting Requirements", RFC
2977, October 2000.
[14] Calhoun, P. and C. Perkins, "DIAMETER mobile IP extensions",
Work in Progress, February 2004.
Perkins & Calhoun Standards Track PAGE 19
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Appendix A. AAA Infrastructure
In this appendix, we attempt to capture the main features of a basic
model for operation of AAA servers that is assumed for understanding
of the use of the Mobile IP registration extensions described in this
document. This information has been adapted from the discussion in
RFC 2977 [13].
Within the Internet, a mobile node belonging to one administrative
domain (called the home domain) often needs to use resources provided
by another administrative domain (called the foreign domain). A
foreign agent that handles the mobile node's Registration Request is
likely to require that the mobile node provide some credentials that
can be authenticated before access to the resources is permitted.
These credentials may be provided as part of the Mobile-AAA
Authentication extension [3], relying on the existence of an AAA
infrastructure such as is described in this section, and also
described in RFC 2977 and RFC 3012 [3]. Such credentials are
typically managed by entities within the mobile node's home domain.
They may be also used for setting up secure communications with the
mobile node and the foreign agent, or between the mobile node and its
home agent if necessary.
Local Domain Home Domain
+--------------+ +----------------------+
| +------+ | | +------+ |
| | | | | | | |
| | AAAL | | | | AAAH | |
| | +-------------------+ | |
| +---+--+ | | +------+ |
| | | | |
| | | +----------------------+
+------+ | +---+--+ |
| | | | | | MN = mobile node
| MN |- -|- -| FA | | FA = foreign agent
| | | | | | AAAL = local authority
+------+ | +------+ | AAAH = home authority
| |
+--------------+
Figure 7: AAA Servers in Home and Local Domains
The foreign agent often does not have direct access to the data
needed to verify the credentials. Instead, the foreign agent is
expected to consult an authority (typically in the same foreign
domain) in order to request proof that the mobile node has acceptable
credentials. Since the foreign agent and the local authority (AAAL)
are part of the same administrative domain, they are expected to have
Perkins & Calhoun Standards Track PAGE 20
RFC 3957 AAA Keys for Mobile IPv4 March 2005
established, or be able to establish for the necessary lifetime, a
secure channel for the purposes of exchanging sensitive (access)
information, and keeping it private from (at least) the visiting
mobile node.
The local authority (AAAL) itself may not have enough information
stored locally to carry out the verification for the credentials of
the mobile node. In contrast to the foreign agent, however, the AAAL
is expected to be configured with enough information to negotiate the
verification of mobile node credentials with its home domain. The
home and foreign domains should be configured with sufficient IP
Security Associations (i.e., IPsec) and access controls so that they
can negotiate the authorization, and also enable the mobile node to
acquire Mobility Security Associations with the mobility agents
within the foreign domain. For the purposes of the key exchanges
specified within this document, the authorization is expected to
depend only upon secure authentication of the mobile node's
credentials.
Once the authorization has been obtained by the local authority, and
the authority has notified the foreign agent about the successful
negotiation, the foreign agent can deliver the Registration Reply to
the mobile node along with the key material.
In figure 7, there might be many mobile nodes from many different
Home Domains. Each Home Domain provides a AAAH that can check
credentials originating from mobile nodes administered by that Home
Domain. There is a security model implicit in figure 7, and it is
crucial to identify the specific security associations assumed in the
security model. These IP Security Associations are illustrated in
figure 8, and are considered to be relatively long-lived security
associations.
First, it is natural to assume that the mobile node has an AAA
Security Association with the AAAH, since that is roughly what it
means for the mobile node to belong to the home domain.
Second, from the model illustrated in figure 7 it is clear that AAAL
and AAAH have to share an IP Security Association, because otherwise
they could not rely on the authentication results, authorizations,
nor even the accounting data which might be transacted between them.
Requiring such bilateral IP Security Associations is, however, in the
end not scalable; the AAA framework must provide for more scalable
mechanisms, but the methods by which such a broker model is to be
created are out of scope for this document. See RFC 2977 for more
details.
Perkins & Calhoun Standards Track PAGE 21
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Finally, from figure 7, it is clear that the foreign agent can
naturally share an IP Security Association with the AAAL. This is
necessary in order for the model to work because the foreign agent
has to have a way to find out that it is permissible to allocate the
local resources to the mobile node, and further to transmit any
successful Registration Reply to the mobile node.
Figure 8 illustrates the IP Security Associations we understand from
our proposed model. Note that there may be, by mutual agreement
between AAAL and AAAH, a third party inserted between AAAL and AAAH
to help them arbitrate secure transactions in a more scalable
fashion. The broker model which has been designed to enable such
third-party processing should not have any effect on the Mobile IP
extensions specified in this document, and so no description is
provided here; see RFC 2977 [13] for more details.
+------+ +------+
| | | |
| AAAL +--------------+ AAAH |
| | | |
+---+--+ +--+---+
| |
| |
+---+--+ +--+---+
MN = mobile node | | | |
FA = foreign agent | FA | | MN |
AAAL = local authority | | | |
AAAH = home authority +------+ +------+
Figure 8: IP Security Associations
Nodes in two separate administrative domains (for instance, AAAH and
AAAL) often must take additional steps to verify the identity of
their communication partners, or alternatively to guarantee the
privacy of the data making up the communication. While these
considerations lead to important security requirements, as mentioned
above in the context of security between servers, we consider the
exact choice of IP Security Associations between the AAA servers to
be beyond the scope of this document. The choices are unlikely to
depend upon Mobile IP, or any specific features of the general model
illustrated in figure 7. On the other hand, the Mobility Security
Associations needed between Mobile IP entities are of central
importance in the design of the key derivation extensions in this
document.
Perkins & Calhoun Standards Track PAGE 22
RFC 3957 AAA Keys for Mobile IPv4 March 2005
One further detail deserves mention. The Mobility Security
Association to be established between the mobile node and the foreign
agent has to be communicated to the foreign agent as well as to the
mobile node. The following requirements are placed on the mechanism
used by the AAA infrastructure to effect key distribution:
- The AAAH must establish strong, fresh session keys.
- The mechanism must maintain algorithm independence, allowing for
the distribution of authentication algorithm identification along
with the keys.
- The mechanism must include replay detection.
- The mechanism must authenticate all parties, including the AAA
servers and the FA and HA.
- The mechanism must provide for authorization of the client, FA,
and HA.
- The mechanism must not rely on plaintext passwords.
- The mechanism must maintain confidentiality of session keys.
- The mechanism must uniquely name session keys.
- The mechanism must be such that the compromise of a single FA and
HA cannot compromise any other part of the system, including
session keys and long-term keys
- The mechanism must bind key(s) to an appropriate context
- The mechanism must not expose the keys to entities other than the
AAAH and FA (or HA in the case of key distribution to the HA).
The way that the key is distributed to the foreign agent (or home
agent) is expected to be handled as part of the AAA protocol
processing between the AAAH and AAAL, and the further AAA protocol
processing between the AAAL and the foreign agent. Such processing
is outside the scope of this document, but must satisfy the above
requirements.
Perkins & Calhoun Standards Track PAGE 23
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Appendix B. Message Flow for Requesting and Receiving Registration Keys
In this section, we show message flows for requesting and receiving a
registration key from the AAA infrastructure, described in section A.
Challenge values, as specified in [3], might be added to the
Advertisement and Registration messages for additional replay
protection, but are not illustrated here.
Diagram 9 illustrates the message flow for the case when the mobile
node explicitly requests keying material to create registration keys.
MN FA AAA Infrastructure
| | |
|<--- Advertisement-----| |
| (if needed) | |
| | |
|-- RReq+AAA Key Req.-->| |
| |--- RReq + AAA Key Req.--->|
| | |
| |<--- RRep + AAA Key Rep.---|
|<-- RRep+AAA Key Rep.--| |
| | |
Figure 9: Message Flows for Requesting and
Receiving Key Generation Nonce
In diagram 9, the following message flow is illustrated:
1. The foreign agent disseminates an Agent Advertisement. This
advertisement MAY have been produced after receiving an Agent
Solicitation from the mobile node (not shown in the diagram).
2. The mobile node creates a Registration Request including the MN-HA
AAA KeyGen Request and/or MN-FA AAA KeyGen Request, as needed,
along with an authorization-enabling authentication extension as
required by Mobile IP [1].
3. The foreign agent relays the Registration Request and/or Key
Request(s) to its locally configured AAA Infrastructure (see
appendix A), according to local policy.
4. The foreign agent receives a AAA Response with the appropriate
indications for authorizing connectivity for the mobile node.
Along with this AAA Response, the foreign agent may also receive
key material by some secure method appropriate for communications
between it and its local AAA infrastructure. At this point if the
Perkins & Calhoun Standards Track PAGE 24
RFC 3957 AAA Keys for Mobile IPv4 March 2005
foreign agent has not relayed the Registration Request, it
forwards it directly to the Home Agent and waits for a
Registration Reply (not shown in the figure).
5. The foreign agent relays the Registration Reply to the mobile
node, along with the new AAA KeyGen Reply extensions to be used by
the mobile node to establish Mobility Security Associations with
the relevant mobility agents (foreign agent and/or home agent).
Diagram 10 illustrates the message flow for the case when the mobile
node receives unsolicited keying material from the AAA
Infrastructure.
MN FA AAA Infrastructure
| | |
|<--- Advertisement-----| |
| (if needed) | |
| | |
| ------ RReq --------->| |
| |------- RReq ------------->|
| | |
| |<--- RRep + AAA Key Rep.---|
|<-- RRep+AAA Key Rep.--| |
| | |
Figure 10: Message Flow for Receiving Unsolicited
Key Generation Nonce
In diagram 10, the following message flow is illustrated:
1. The foreign agent disseminates an Agent Advertisement. This
advertisement MAY have been produced after receiving an Agent
Solicitation from the mobile node (not shown in the diagram).
2. The mobile node creates a Registration Request including an
authorization-enabling authentication extension as required by
Mobile IP [1].
3. The foreign agent sends a AAA Request (possibly containing the
Registration Request) to its locally configured AAA Infrastructure
(see appendix A), according to local policy.
4. The foreign agent receives a AAA Response with the appropriate
indications for authorizing connectivity for the mobile node.
Along with this AAA Response, the foreign agent may also receive
key material by some secure method appropriate for communications
between it and its local AAA infrastructure. At this point, if
the foreign agent has not relayed the Registration Request, it
Perkins & Calhoun Standards Track PAGE 25
RFC 3957 AAA Keys for Mobile IPv4 March 2005
forwards it directly to the Home Agent and waits for a
Registration Reply (not shown in the figure).
5. The foreign agent relays the Registration Reply to the mobile
node, along with the new KeyGen Reply extensions to be used by the
mobile node to establish Mobility Security Associations with the
relevant mobility agents (foreign agent and/or home agent).
Authors' Addresses
Charles E. Perkins
Nokia Research Center
313 Fairchild Drive
Mountain View, California 94043
USA
Phone: +1 650 625-2986
Fax: +1 650 625-2502
EMail: charles.perkins@nokia.com
Pat R. Calhoun
Airespace, Inc.
110 Nortech Parkway
San Jose, CA 95134
USA
Phone: +1 408 635 2000
Fax: +1 408 635 2020
EMail: pcalhoun@airespace.com
Perkins & Calhoun Standards Track PAGE 26
RFC 3957 AAA Keys for Mobile IPv4 March 2005
Full Copyright Statement
Copyright © The Internet Society (2005).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
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Perkins & Calhoun Standards Track PAGE 27
Authentication, Authorization, and Accounting (AAA) Registration Keys for Mobile IPv4
RFC TOTAL SIZE: 63576 bytes
PUBLICATION DATE: Friday, March 4th, 2005
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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