rfc3012.txt   draft-ietf-mip4-rfc3012bis-04.txt 
Network Working Group C. Perkins Network Working Group Charles E. Perkins
Request for Comments: 3012 Nokia Research Center Internet-Draft Nokia Research Center
Category: Standards Track P. Calhoun Expires: December 19, 2005 Pat R. Calhoun
Sun Microsystems Laboratories Black Storm Networks
November 2000 Jayshree. Bharatia
Nortel Networks
June 17, 2005
Mobile IPv4 Challenge/Response Extensions Mobile IPv4 Challenge/Response Extensions (revised)
draft-ietf-mip4-rfc3012bis-04.txt
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Copyright (C) The Internet Society (2000). All Rights Reserved. Copyright (C) The Internet Society (2005).
Abstract Abstract
Mobile IP, as originally specified, defines an authentication Mobile IP, as originally specified, defines an authentication
extension (the Mobile-Foreign Authentication extension) by which a extension (the Mobile-Foreign Authentication extension) by which a
mobile node can authenticate itself to a foreign agent. mobile node can authenticate itself to a foreign agent.
Unfortunately, this extension does not provide ironclad replay Unfortunately, that extension does not provide the foreign agent any
protection for the foreign agent, and does not allow for the use of direct guarantee that the protocol is protected from replays, and
existing techniques (such as CHAP) for authenticating portable does not allow for the use of existing techniques (such as CHAP) for
computer devices. In this specification, we define extensions for authenticating portable computer devices.
the Mobile IP Agent Advertisements and the Registration Request that
allow a foreign agent to use a challenge/response mechanism to In this specification, we define extensions for the Mobile IP Agent
authenticate the mobile node. Advertisements and the Registration Request that allow a foreign
agent to use a challenge/response mechanism to authenticate the
mobile node.
Furthermore, this document updates RFC3344 by including new
authentication extension called the Mobile-AAA Authentication
extension. This new extension is provided so that a mobile node can
supply credentials for authorization using commonly available AAA
infrastructure elements. This Authorization-enabling extension MAY
co-exist in the same Registration Request with Authentication
extensions defined for Mobile IP Registration by RFC3344. This
document obsoletes RFC3012.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Mobile IP Agent Advertisement Challenge Extension . . . . . 3 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Mobile IP Agent Advertisement Challenge Extension . . . . . . 6
3.1. Mobile Node Processing for Registration Requests . . . 3 2.1 Handling of Solicited Agent Advertisements . . . . . . . . 6
3.2. Foreign Agent Processing for Registration Requests . . 5 3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Foreign Agent Processing for Registration Replies . . 7 3.1 Mobile Node Processing for Registration Requests . . . . . 8
3.4. Home Agent Processing for the Challenge Extensions . . 7 3.2 Foreign Agent Processing for Registration Requests . . . . 9
4. MN-FA Challenge Extension . . . . . . . . . . . . . . . . . 7 3.3 Foreign Agent Processing for Registration Replies . . . . 11
5. Generalized Mobile IP Authentication Extension . . . . . . . 8 3.4 Home Agent Processing for the Challenge Extensions . . . . 12
6. MN-AAA Authentication subtype. . . . . . . . . . . . . . . . 9 3.5 Mobile Node Processing for Registration Replies . . . . . 12
7. Reserved SPIs for Mobile IP. . . . . . . . . . . . . . . . . 9 4. Mobile-Foreign Challenge Extension . . . . . . . . . . . . . . 15
8. SPI For RADIUS AAA Servers . . . . . . . . . . . . . . . . . 10 5. Generalized Mobile IP Authentication Extension . . . . . . . . 16
9. Configurable Parameters. . . . . . . . . . . . . . . . . . . 10 6. Mobile-AAA Authentication subtype . . . . . . . . . . . . . . 18
10. Error Values . . . . . . . . . . . . . . . . .. . . . . . . 10 7. Reserved SPIs for Mobile IP . . . . . . . . . . . . . . . . . 19
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 11 8. SPIs for RADIUS AAA Servers . . . . . . . . . . . . . . . . . 20
12. Security Considerations . . . . . . . . . . . . . . . . . . 12 9. Configurable Parameters . . . . . . . . . . . . . . . . . . . 21
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 10. Error Values . . . . . . . . . . . . . . . . . . . . . . . . 22
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 23
A. Verification Infrastructure . . . . . . . . . . . . . . . . 14 12. Security Considerations . . . . . . . . . . . . . . . . . . 24
Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 25
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 17 14. Normative References . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 26
A. Change History . . . . . . . . . . . . . . . . . . . . . . . . 27
B. Verification Infrastructure . . . . . . . . . . . . . . . . . 30
C. Message Flow for FA Challenge Messaging with Mobile-AAA
Extension . . . . . . . . . . . . . . . . . . . . . . . . . . 32
D. Message Flow for FA Challenge Messaging with MN-FA
Authentication . . . . . . . . . . . . . . . . . . . . . . . . 34
E. Foreign Agent Algorithm for Tracking Used Challenges . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . 37
1. Introduction 1. Introduction
Mobile IP, as originally specified, defines an authentication Mobile IP defines the Mobile-Foreign Authentication extension to
extension (the Mobile-Foreign Authentication extension) by which a allow a mobile node to authenticate itself to a foreign agent. Such
mobile node can authenticate itself to a foreign agent. authentication mechanisms are mostly external to the principal
operation of Mobile IP, since the foreign agent can easily route
packets to and from a mobile node whether or not the mobile node is
reporting a legitimately owned home address to the foreign agent.
Unfortunately, that extension does not provide the foreign agent any
direct guarantee that the protocol is protected from replays, and
does not allow for the use of CHAP [RFC1994] for authenticating
portable computer devices. In this specification, we define
extensions for the Mobile IP Agent Advertisements and the
Registration Request that allow a foreign agent to use challenge/
response mechanism to authenticate the mobile node. Furthermore, an
additional authentication extension, the Mobile-AAA authentication
extension, is provided so that a mobile node can supply credentials
for authorization using commonly available AAA infrastructure
elements. The foreign agent may be able to interact with an AAA
infrastructure (using protocols outside the scope of this document)
to obtain a secure indication that the mobile node is authorized to
use the local network resources.
Unfortunately, this extension does not provide ironclad replay 1.1 Terminology
protection, from the point of view of the foreign agent, and does not
allow for the use of existing techniques (such as CHAP [12]) for
authenticating portable computer devices. In this specification, we
define extensions for the Mobile IP Agent Advertisements and the
Registration Request that allow a foreign agent to a use
challenge/response mechanism to authenticate the mobile node.
All SPI values defined in this document refer to values for the The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
Security Parameter Index, as defined in RFC 2002 [8]. The key words "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", document are to be interpreted as described in RFC 2119 [RFC2119].
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
are to be interpreted as described in [1]. This document uses the term Security Parameters Index (SPI) as
defined in the base Mobile IP protocol specification [RFC3344]. All
SPI values defined in this document refer to values for the SPI as
defined in that specification.
The following additional terminology is used in addition to that
defined in [RFC3344]:
previously used challenge:
The challenge is a previously used challenge if the mobile node
sent the same challenge to the foreign agent in a previous
Registration Request, and that previous Registration Request
passed all validity checks performed by the foreign agent. The
foreign agent may not be able to keep records for all
previously used challenges, but see Section 3.2 for minimal
requirements.
security association:
A "mobility security association", as defined in [RFC3344].
unknown challenge:
Any challenge from a particular mobile node that the foreign
agent has no record of having put either into one of its recent
Agent Advertisements or into a registration reply message to
that mobile node.
unused challenge:
A challenge that has not been already accepted by the foreign
agent from the mobile node in the Registration Request -- i.e.,
a challenge that is neither unknown nor previously used.
2. Mobile IP Agent Advertisement Challenge Extension 2. Mobile IP Agent Advertisement Challenge Extension
This section defines a new extension to the Router Discovery Protocol This section defines a new extension to the Router Discovery Protocol
[3] for use by foreign agents that need to issue a challenge for [RFC1256] for use by foreign agents that need to issue a challenge
authenticating mobile nodes. for authenticating mobile nodes.
0 1 2 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 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 | Challenge ... | Type | Length | Challenge ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The Challenge Extension Figure 1: The Challenge Extension
Type 24 Type:
Length The length of the Challenge value in bytes; SHOULD be 24
at least 4
Challenge A random value that SHOULD be at least 32 bits. Length:
The Challenge extension, illustrated in figure 1, is inserted in the The length of the Challenge value in bytes; SHOULD be at least
Agent Advertisements by the Foreign Agent, in order to communicate 4
the latest challenge value that can be used by the mobile node to
compute an authentication for its registration request message. The Challenge:
challenge is selected by the foreign agent to provide local assurance
that the mobile node is not replaying any earlier registration A random value that SHOULD be at least 32 bits
request. Eastlake, et al. [4] provides more information on
generating pseudo-random numbers suitable for use as values for the The Challenge extension, illustrated in Figure 1, is inserted in the
challenge. Agent Advertisements by the foreign agent, in order to communicate a
previously unused challenge value that can be used by the mobile node
to compute an authentication for its next registration request
message. The challenge is selected by the foreign agent to provide
local assurance that the mobile node is not replaying any earlier
registration request. Eastlake, et al. [RFC1750] provides more
information on generating pseudo-random numbers suitable for use as
values for the challenge.
Note that the storage of different Challenges received in Agent
Advertisements from multiple foreign agents is implementation
specific and hence, out of scope for this specification.
2.1 Handling of Solicited Agent Advertisements
When a foreign agent generates an Agent Advertisement in response to
a Router Solicitation [RFC1256], some additional considerations come
into play. According to the Mobile IP base specification [RFC3344],
the resulting Agent Advertisement may be either multicast or unicast.
If the solicited Agent Advertisement is multicast, it MUST NOT
generate a new Challenge value and update its window of remembered
advertised Challenges. It must instead re-use the most recent of the
CHALLENGE_WINDOW Advertisement Challenge values.
If the agent advertisement is unicast back to the soliciting mobile
node, it MUST be handled as follows: If the challenge most recently
unicast to the soliciting mobile node has not been previously used
(as defined in Section 1.1), it SHOULD be repeated in the newly
issued unicast agent advertisement, otherwise a new challenge MUST be
generated and remembered as the most recent challenge issued to the
mobile node. For further discussion of this, see Section 12.
3. Operation 3. Operation
This section describes modifications to the Mobile IP registration This section describes modifications to the Mobile IP registration
process which may occur after the Foreign Agent issues a Mobile IP process [RFC3344] which may occur after the foreign agent issues a
Agent Advertisement containing the Challenge on its local link. Mobile IP Agent Advertisement containing the Challenge on its local
link. See Appendix C for a diagram showing the canonical message
flow for messages related to the processing of the foreign agent
challenge values.
3.1. Mobile Node Processing for Registration Requests 3.1 Mobile Node Processing for Registration Requests
Retransmission behavior for Registration Requests is identical to
that specified in Mobile IP specification [RFC3344]. A retransmitted
Registration Request MAY use the same Challenge value as given in the
original Registration Request.
Whenever the Agent Advertisement contains the Challenge extension, if Whenever the Agent Advertisement contains the Challenge extension, if
the mobile node does not have a security association with the Foreign the mobile node does not have a security association with the foreign
Agent, then it MUST include the Challenge value in a MN-FA Challenge agent, then it MUST include the Challenge value in a Mobile-Foreign
extension to the Registration Request message. If, on the other Challenge extension to the Registration Request message. If, on the
hand, the mobile node does have a security association with the other hand, the mobile node does have a security association with the
foreign agent, it SHOULD include the Challenge value in its foreign agent, it SHOULD include the Challenge value in its
Registration Request message. Registration Request message.
If the Mobile Node has a security association with the Foreign Agent, If the mobile node has a security association with the Foreign Agent,
it MUST include a Mobile-Foreign Authentication extension in its it MUST include a Mobile-Foreign Authentication extension in its
Registration Request message, according to the base Mobile IP Registration Request message, according to the base Mobile IP
specification [8]. When the Registration Request contains the MN-FA specification [RFC3344]. When the Registration Request contains the
Challenge extension specified in section 4, the Mobile-Foreign Mobile-Foreign Challenge extension specified in Section 4, the
Authentication MUST follow the Challenge extension in the Mobile-Foreign Authentication MUST follow the Challenge extension in
Registration Request. the Registration Request. The mobile node MAY also include the
Mobile-AAA Authentication extension. If both the Mobile-Foreign
If the Mobile Node does not have a security association with the Authentication and the Mobile-AAA Authentication extensions are
Foreign Agent, the Mobile Node MUST include the MN-AAA Authentication present, the Mobile-Foreign Challenge extension MUST precede the
extension as defined in section 6. In addition, the Mobile Node Mobile-AAA Authentication extension and the Mobile-AAA Authentication
SHOULD include the NAI extension [2], to enable the foreign agent to extension MUST precede the Mobile-Foreign Authentication extension.
make use of any available verification infrastructure. The SPI field
of the MN-AAA Authentication extension specifies the particular
secret and algorithm (shared between the Mobile Node and the
verification infrastructure) that must be used to perform the
authentication. If the SPI value is chosen as CHAP_SPI (see section
9), then the mobile node specifies CHAP-style authentication [12]
using MD5 [11].
In either case, the MN-FA Challenge extension and one of the above
specified authentication extensions MUST follow the Mobile-Home
Authentication extension, if present.
A successful Registration Reply from the Foreign Agent MAY include a
new Challenge value (see section 3.3). The Mobile Node MAY use
either the value found in the latest Advertisement, or the one found
in the last Registration Reply from the Foreign Agent. This approach
enables the Mobile Node to make use of the challenge without having
to wait for advertisements.
A Mobile Node might receive an UNKNOWN_CHALLENGE error (see section If the mobile node does not have a security association with the
9) if it moves to a new Foreign Agent that cannot validate the foreign agent, the mobile node MUST include the Mobile-AAA
challenge provided in the Registration Request. In such instances, Authentication extension as defined in Section 6 when it includes the
the Mobile Node MUST use a new Challenge value in any new Mobile-Foreign Challenge extension. In addition, the mobile node
registration, obtained either from an Agent Advertisement, or from a SHOULD include the NAI extension [RFC2794], to enable the foreign
Challenge extension to the Registration Reply containing the error. agent to make use of available verification infrastructure which
requires this. The SPI field of the Mobile-AAA Authentication
extension specifies the particular secret and algorithm (shared
between the mobile node and the verification infrastructure) that
must be used to perform the authentication. If the SPI value is
chosen as CHAP_SPI (see Section 9), then the mobile node specifies
CHAP-style authentication [RFC1994] using MD5 [RFC1321].
A Mobile Node that does not include a Challenge when the Mobile- In either case, the Mobile-Foreign Challenge extension followed by
Foreign Authentication extension is present may receive a one of the above specified authentication extensions MUST follow the
MISSING_CHALLENGE (see section 10) error. In this case, the foreign Mobile-Home Authentication extension, if present.
agent will not process the request from the mobile node unless the
request contains a valid Challenge.
A Mobile Node that receives a BAD_AUTHENTICATION error code (see A mobile node MAY include the Mobile-AAA Authentication extension in
section 10) SHOULD include the MN-AAA Authentication Extension in the the Registration Request when the mobile node registers directly with
next Registration Request. This will make it possible for the its home agent (using a co-located care-of address). In this case,
Foreign Agent to use its AAA infrastructure in order to authenticate if the mobile node uses an SPI value of CHAP_SPI (Section 8) in the
the Mobile Node. MN-AAA Authentication extension, the mobile node MUST include the
Mobile-Foreign Challenge extension prior to the Mobile-AAA
Authentication extension. The mechanism used by the mobile node to
obtain the Challenge value in this case is outside the scope of this
document.
3.2. Foreign Agent Processing for Registration Requests 3.2 Foreign Agent Processing for Registration Requests
Upon receipt of the Registration Request, if the Foreign Agent has Upon receipt of the Registration Request, if the foreign agent has
issued a Challenge as part of its Agent Advertisements, and it does issued a Challenge as part of its Agent Advertisements, and it does
not have a security association with the mobile node, then the not have a security association with the mobile node, then the
Foreign Agent MUST check that the MN-FA Challenge extension exists, foreign agent SHOULD check that the Mobile-Foreign Challenge
and that it contains a challenge value previously unused by the extension exists, and that it contains a challenge value previously
Mobile Node. This ensures that the mobile node is not attempting to unused by the mobile node. This ensures that the mobile node is not
replay a previous advertisement and authentication. If the challenge attempting to replay a previous advertisement and authentication. In
extension is needed and does not exist, the Foreign Agent MUST send a this case, if the Registration Request does not include a challenge
Registration Reply to the mobile node with the error code extension, the foreign agent MUST send a Registration Reply with the
MISSING_CHALLENGE. Code field set to set to MISSING_CHALLENGE. In this document,
whenever the foreign agent is required to reject a Registration
A foreign agent that sends Agent Advertisements containing a Request, it MUST put the given code in the usual Code field of the
Challenge value MAY send a Registration Reply message with a Registration Reply, unless the Registration Reply has already been
MISSING_CHALLENGE error if the mobile node sends a Registration received from the home agent. In this case the foreign agent MUST
Request with a Mobile-Foreign Authentication extension without preserve the value of the Code field set by the home agent and MUST
including a Challenge. In other words, such a foreign agent MAY put its own rejection code only in the Status field of the FA Error
refuse to process a Registration Request request from the mobile node extension (defined in [FAERR]).
unless the request contains a valid Challenge.
If a mobile node retransmits a Registration Request with the same If a mobile node retransmits a Registration Request with the same
Identification field and the same Challenge extension, and the Challenge extension, and the foreign agent still has a pending
Foreign Agent still has a pending Registration Request record in Registration Request record in effect for the mobile node, then the
effect for the mobile node, then the Foreign Agent forwards the foreign agent forwards the Registration Request to the Home Agent
Registration Request to the Home Agent again. In all other again. The foreign agent SHOULD check that the mobile node is
circumstances, if the Foreign Agent receives a Registration Request actually performing a retransmission, by verifying that the relevant
with a Challenge extension containing a Challenge value previously fields of the retransmitted request (including, if present, the
used by that mobile node, the Foreign Agent SHOULD send a mobile node NAI Extension [RFC2794]) are the same as represented in
Registration Reply to the mobile node containing the Code value the visitor list entry for the pending Registration Request (section
STALE_CHALLENGE. 3.7.1 of [RFC3344]). This verification MUST NOT include the
"remaining Lifetime of the pending registration", or the
Identification field since those values are likely to change even for
requests that are merely retransmissions and not new Registration
Requests. In all other circumstances, if the foreign agent receives
a Registration Request with a Challenge extension containing a
Challenge value previously used by that mobile node, the foreign
agent SHOULD send a Registration Reply to the mobile node containing
the Code value STALE_CHALLENGE.
The Foreign Agent MUST NOT accept any Challenge in the Registration The foreign agent MUST NOT accept any Challenge in the Registration
Request unless it was offered in last successful Registration Reply Request unless it was offered in the last Registration Reply or
issued to the Mobile Node, or else advertised as one of the last unicast Agent Advertisement sent to the mobile node, or else
CHALLENGE_WINDOW (see section 9) Challenge values inserted into the advertised as one of the last CHALLENGE_WINDOW (see Section 9)
immediately preceding Agent advertisements. If the Challenge is not Challenge values inserted into the immediately preceding Agent
one of the recently advertised values, the foreign Agent SHOULD send advertisements. If the Challenge is not one of the recently
a Registration Reply with Code UNKNOWN_CHALLENGE (see section 10). advertised values, the foreign Agent SHOULD send a Registration Reply
with Code value UNKNOWN_CHALLENGE (see Section 10). The foreign
agent MUST maintain the last challenge used by each mobile node that
has registered using any one of the last CHALLENGE_WINDOW challenge
values. This last challenge value can be stored as part of the
mobile node's registration records. Also, see Appendix E for a
possible algorithm that can be used to satisfy this requirement.
Furthermore, the Foreign Agent MUST check that there is either a Furthermore, the foreign agent MUST check that there is either a
Mobile-Foreign, or a MN-AAA Authentication extension after the Mobile-Foreign, or a Mobile-AAA Authentication extension after the
Challenge extension. Any registration message containing the Challenge extension. Any registration message containing the
Challenge extension without either of these authentication extensions Challenge extension without either of these authentication extensions
MUST be silently discarded. If the registration message contains a MUST be silently discarded. If the registration message contains a
Mobile-Foreign Authentication extension with an incorrect Mobile-Foreign Authentication extension with an incorrect
authenticator that fails verification, the Foreign Agent MAY send a authenticator that fails verification, the foreign agent MAY send a
Registration Reply to the mobile node with Code value Registration Reply to the mobile node with Code value
BAD_AUTHENTICATION (see Section 10). BAD_AUTHENTICATION (see Section 10).
If the MN-AAA Authentication extension (see Section 6) is present in If the Mobile-AAA Authentication extension (see Section 6) is present
the message, or if an NAI extension is included indicating that the in the message, or if an NAI extension is included indicating that
mobile node belongs to a different administrative domain, the foreign the mobile node belongs to a different administrative domain, the
agent may take actions outside the scope of this protocol foreign agent may take actions outside the scope of this protocol
specification to carry out the authentication of the mobile node. specification to carry out the authentication of the mobile node. If
The Foreign Agent MUST NOT remove the MN-AAA Authentication Extension the registration message contains a Mobile-AAA Authentication
from the Registration Request prior to the completion of the extension with an incorrect authenticator that fails verification,
authentication performed by the AAA infrastructure. The appendix the foreign agent MAY send a Registration Reply to the mobile node
provides an example of an action that could be taken by a foreign with Code value FA_BAD_AAA_AUTH. If the Mobile-AAA Authentication
agent. Extension is present in the Registration Request, the foreign agent
MUST NOT remove the Mobile-AAA Authentication Extension and the
Mobile-Foreign Challenge Extension from the Registration Request.
Appendix C provides an example of an action that could be taken by a
foreign agent.
In the event that the Challenge extension is authenticated through In the event that the Challenge extension is authenticated through
the Mobile-Foreign Authentication Extension, the Foreign Agent MAY the Mobile-Foreign Authentication extension and the Mobile-AAA
remove the Challenge Extension from the Registration Request without Authentication extension is not present, the foreign agent MAY remove
disturbing the authentication value computed by the Mobile Node for the Challenge Extension from the Registration Request without
use by the AAA or the Home Agent. If the Challenge extension is not disturbing the authentication value computed by the mobile node for
removed, it MUST precede the Foreign-Home Authentication extension. use by the AAA or the home agent. If the Mobile-AAA Authentication
extension is present and a security association exists between the
foreign agent and the home agent, the Mobile-Foreign Challenge
extension and the Mobile-AAA Authentication extension MUST precede
the Foreign-Home Authentication extension.
If the Foreign Agent does not remove the Challenge extension, then If the foreign agent does not remove the Challenge extension, then
the Foreign Agent SHOULD store the Challenge value as part of the the foreign agent SHOULD store the Challenge value as part of the
pending registration request list [8]. Also in this case, the pending registration request list [RFC3344]. Also, if the
Foreign Agent MUST reject any Registration Reply message coming from Registration Reply coming from the home agent does not include the
the Home Agent that does not also include the Challenge Extension Challenge Extension, the foreign agent SHOULD NOT reject the
with the same Challenge Value that was included in the Registration Registration Request message. If the Challenge Extension is present
Request. The Foreign Agent MUST send the rejected Registration in the Registration Reply, it MUST be the same Challenge value that
message to the mobile node, and change the status in the Registration was included in the Registration Request. If the Challenge value
Reply to the value MISSING_CHALLENGE (see section 10). differs in the Registration Reply received from the home agent, the
foreign agent MUST insert an FA Error extension with Status value
HA_WRONG_CHALLENGE in the Registration Reply sent to the mobile node
(see Section 10).
If the Foreign Agent does remove the Challenge extension and If the foreign agent does remove the Challenge extension and
applicable authentication from the Registration Request message, then applicable authentication from the Registration Request message, then
it SHOULD insert the Identification field from the Registration it SHOULD insert the Identification field from the Registration
Request message along with its record-keeping information about the Request message along with its record-keeping information about the
particular Mobile Node in order to protect against replays. particular mobile node in order to protect against replays.
3.3. Foreign Agent Processing for Registration Replies 3.3 Foreign Agent Processing for Registration Replies
The Foreign Agent MAY include a new Challenge extension in any The foreign agent SHOULD include a new Mobile-Foreign Challenge
Registration Reply, successful or not. If the foreign agent includes Extension in any Registration Reply, successful or not. If the
this extension in a successful Registration Reply, the extension foreign agent includes this extension in a successful Registration
SHOULD precede a MN-FA authentication extension. Reply, the extension SHOULD precede a Mobile-Foreign authentication
extension if present. Suppose the Registration Reply includes a
Challenge extension from the home agent, and the foreign agent wishes
to include another Challenge extension with the Registration Reply
for use by the mobile node. In that case, the foreign agent MUST
delete the Challenge extension from the home agent from the
Registration Reply, along with any Foreign-Home authentication
extension, before appending the new Challenge extension to the
Registration Reply.
Suppose the Registration Reply includes a Challenge extension from One example of a situation where the foreign agent MAY omit the
the Home Agent, and the foreign agent wishes to include another inclusion of a Mobile-Foreign Challenge Extension in the Registration
Challenge extension with the Registration Reply for use by the mobile Reply would be when a new challenge has been multicast recently.
node. In that case, the foreign agent MUST delete the Challenge
extension from the Home Agent from the Registration Reply, along with
any FA-HA authentication extension, before appending the new
Challenge extension to the Registration Reply.
3.4. Home Agent Processing for the Challenge Extensions If a foreign agent has conditions in which it omits the inclusion of
a Mobile-Foreign Challenge Extension in the Registration Reply, it
still MUST respond with an agent advertisement containing a
previously unused challenge in response to a subsequent agent
solicitation from the same mobile node. Otherwise (when the said
conditions are not met) the foreign agent MUST include a previously
unused challenge in any Registration Reply, successful or not.
If the Home Agent receives a Registration Request with the MN-FA A mobile node MUST be prepared to use a challenge from a unicast or
Challenge extension, and recognizes the extension, the Home Agent multicast Agent Advertisement in lieu of one returned in a
MUST include the Challenge extension in the Registration Reply. The Registration Reply, and MUST solicit for one if it has not already
Challenge Extension MUST be placed after the Mobile-Home received one in a Registration Reply.
If the foreign agent receives a Registration Reply with the Code
value HA_BAD_AAA_AUTH, it MUST be relayed to the mobile node.
3.4 Home Agent Processing for the Challenge Extensions
If the home agent receives a Registration Request with the Mobile-
Foreign Challenge extension, and recognizes the extension, the home
agent MUST include the Challenge extension in the Registration Reply.
The Challenge Extension MUST be placed after the Mobile-Home
authentication extension, and the extension SHOULD be authenticated authentication extension, and the extension SHOULD be authenticated
by a Foreign-Home Authentication extension. by a Foreign-Home Authentication extension.
The home agent MAY receive a Registration Request with the Mobile-AAA
Authentication extension. If the Mobile-AAA Authentication extension
is used by the home agent as an authorization-enabling extension and
the verification fails due to incorrect authenticator, the home agent
MAY reject the Registration Reply with the error code
HA_BAD_AAA_AUTH.
Since the extension type for the Challenge extension is within the Since the extension type for the Challenge extension is within the
range 128-255, the Home Agent MUST process such a Registration range 128-255, the home agent MUST process such a Registration
Request even if it does not recognize the Challenge extension [8]. Request even if it does not recognize the Challenge extension
In this case, the Home Agent will send a Registration Reply to the [RFC3344]. In this case, the home agent will send a Registration
Foreign Agent that does not include the Challenge extension. Reply to the foreign agent that does not include the Challenge
extension.
4. MN-FA Challenge Extension 3.5 Mobile Node Processing for Registration Replies
A mobile node might receive the following error codes in the
Registration Reply from the foreign agent as a response to the
Registration Request. The error codes are defined in Section 10.
UNKNOWN_CHALLENGE: This error code is received by the mobile node in
the case where the mobile node has moved to a new foreign agent that
cannot validate the challenge provided in the Registration Request.
In such instances, the mobile node MUST use a new Challenge value in
any new registration, obtained either from an Agent Advertisement, or
from a Challenge extension to the Registration Reply containing the
error.
MISSING_CHALLENGE: A mobile node that does not include a Challenge
when the Mobile-Foreign Authentication extension is present may
receive a MISSING_CHALLENGE error. In this case, the mobile node
SHOULD send a Challenge extension containing an unused challenge in
the next Registration Request.
BAD_AUTHENTICATION: This error is sent by the foreign agent if the
Registration Request contains a Mobile-Foreign Authentication
extension with an incorrect authenticator that fails verification. A
mobile node that receives a BAD_AUTHENTICATION Code value SHOULD
include the Mobile-AAA Authentication Extension in the next
Registration Request. This will make it possible for the Foreign
Agent to use its AAA infrastructure in order to authenticate the
mobile node. In this case, the mobile node MUST use a new Challenge
value in any new registration, obtained either from an Agent
Advertisement, or from a Challenge extension to the Registration
Reply containing the error.
FA_BAD_AAA_AUTH: This error is sent by the foreign agent if the
Registration Request contains a Mobile-AAA Authentication extension
with an incorrect authenticator that fails verification. A mobile
node that receives a FA_BAD_AAA_AUTH MUST use a new Challenge value
in any new registration, obtained either from an Agent Advertisement,
or from a Challenge extension to the Registration Reply containing
the error.
HA_BAD_AAA_AUTH: This error is sent by the home agent if the
Registration Request contains a Mobile-AAA Authentication extension
with an incorrect authenticator that fails verification. A mobile
node that receives a HA_BAD_AAA_AUTH MUST use a new Challenge value
in any new registration, obtained either from an Agent Advertisement,
or from a Challenge extension to the Registration Reply containing
the error.
STALE_CHALLENGE: If the foreign agent receives a Registration Request
with a Challenge extension containing a Challenge value previously
used by that mobile node, the mobile node MAY receive a Registration
Reply to the mobile node containing the Code value STALE_CHALLENGE.
In such instances, the mobile node MUST use a new Challenge value in
next Registration Request, obtained either from an Agent
Advertisement, or from a Challenge extension to the Registration
Reply containing the error.
HA_WRONG_CHALLENGE: This error is sent by the foreign agent if the
Registration Reply from the home agent contains a different Challenge
value from the one included in the Registration Request.
4. Mobile-Foreign Challenge Extension
This section specifies a new Mobile IP Registration extension that is This section specifies a new Mobile IP Registration extension that is
used to satisfy a Challenge in an Agent Advertisement. The Challenge used to satisfy a Challenge in an Agent Advertisement. The Challenge
extension to the Registration Request message is used to indicate the extension to the Registration Request message is used to indicate the
challenge that the mobile node is attempting to satisfy. challenge that the mobile node is attempting to satisfy.
0 1 2 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 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 | Challenge... | Type | Length | Challenge...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The MN-FA Challenge Extension Figure 2: The Mobile-Foreign Challenge Extension
Type 132 (skippable) (see [8]) Type:
Length Length of the Challenge value 132 (skippable) (see [RFC3344])
Challenge The Challenge field is copied from the Challenge field
found in the Agent Advertisement Challenge extension Length:
(see section 2).
Length of the Challenge value
Challenge:
The Challenge field is copied from the Challenge field found in
the Agent Advertisement Challenge extension (see section 2).
Suppose the mobile node has successfully registered using one of the
Challenge Values within the CHALLENGE_WINDOW values advertised by the
foreign agent. In that case, in any new Registration Request the
mobile node MUST NOT use any Challenge Value which was advertised by
the foreign agent before the Challenge Value in the mobile node's
last Registration Request.
5. Generalized Mobile IP Authentication Extension 5. Generalized Mobile IP Authentication Extension
Several new authentication extensions have been designed for various Several new authentication extensions have been designed for various
control messages proposed for extensions to Mobile IP (see, for control messages proposed for extensions to Mobile IP. A new
example, [9]). A new authentication extension is required for a authentication extension is required for a mobile node to present its
mobile node to present its credentials to any other entity other than credentials to any other entity other than the ones already defined;
the ones already defined; the only entities defined in the base the only entities defined in the base Mobile IP specification
Mobile IP specification [8] are the home agent and the foreign agent. [RFC3344] are the home agent and the foreign agent. It is the
It is the purpose of the generalized authentication extension defined purpose of the generalized authentication extension defined here to
here to collect together data for all such new authentication collect together data for all such new authentication applications
applications into a single extension type with subtypes. into a single extension type with subtypes.
0 1 2 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 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 | | Type | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI | | SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authenticator ... | Authenticator ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The Generalized Mobile IP Authentication Extension Figure 3: The Generalized Mobile IP Authentication Extension
Type 36 (not skippable) (see [8]) Type:
Subtype a number assigned to identify the kind of 36 (not skippable) (see [RFC3344])
endpoints or characteristics of the particular
authentication strategy
Length 4 plus the number of bytes in the Authenticator; Subtype:
MUST be at least 20.
SPI Security Parameters Index A number assigned to identify the kind of endpoints or other
characteristics of the particular authentication strategy
Authenticator The variable length Authenticator field Length:
4 plus the number of bytes in the Authenticator; MUST be at
least 20.
SPI:
Security Parameters Index
Authenticator:
The variable length Authenticator field
In this document, only one subtype is defined: In this document, only one subtype is defined:
1 MN-AAA Authentication subtype (see section 6) 1 Mobile-AAA Authentication subtype (see Section 6)
6. MN-AAA Authentication subtype 6. Mobile-AAA Authentication subtype
The Generalized Authentication extension with subtype 1 will be The Generalized Authentication extension with subtype 1 will be
referred to as a MN-AAA Authentication extension. If the mobile node referred to as a Mobile-AAA Authentication extension. The mobile
does not include a Mobile-Foreign Authentication [8] extension, then node MAY include a Mobile-AAA Authentication extension in any
it MUST include the MN-AAA Authentication extension whenever the Registration Request. This extension MAY co-exist in the same
Challenge extension is present. If the MN-AAA Authentication Registration Request with Authentication extensions defined for
extension is present, then the Registration Message sent by the Mobile IP Registration by [RFC3344]. If the mobile node does not
mobile node MUST contain the Mobile-HA Authentication extension [8] include a Mobile-Foreign Authentication [RFC3344] extension, then it
if it shares a security association with the Home Agent. If present, MUST include the Mobile-AAA Authentication extension whenever the
the Mobile-HA Authentication Extension MUST appear prior to the MN- Challenge extension is present. If both are present, the Mobile-AAA
AAA Authentication extension. The mobile node MAY include a MN-AAA Authentication extension MUST precede the Mobile-Foreign
Authentication extension in any Registration Request. The Authentication extension.
corresponding response MUST include the MN-HA Authentication
Extension, and MUST NOT include the MN-AAA Authentication Extension. If the Mobile-AAA Authentication extension is present, then the
Registration Message sent by the mobile node MUST contain the Mobile-
Home Authentication extension [RFC3344] if it shares a security
association with the home agent. If both are present, the Mobile-
Home Authentication Extension MUST appear prior to the Mobile-AAA
Authentication extension. The corresponding response MUST include
the Mobile-Home Authentication Extension, and MUST NOT include the
Mobile-AAA Authentication Extension.
The default algorithm for computation of the authenticator is HMAC- The default algorithm for computation of the authenticator is HMAC-
MD5 [5] computed on the following data, in the order shown: MD5 [RFC2104] computed on the following data, in the order shown:
Preceding Mobile IP data || Type, Subtype, Length, SPI Preceding Mobile IP data || Type, Subtype, Length, SPI
where the Type, Length, Subtype, and SPI are as shown in section 5. where the Type, Length, Subtype, and SPI are as shown in Section 5.
The resulting function call, as described in [5], would be: The resulting function call, as described in [RFC2104], would be:
hmac_md5(data, datalen, Key, KeyLength, authenticator); hmac_md5(data, datalen, Key, KeyLength, authenticator);
Each mobile node MUST support the ability to produce the Each mobile node MUST support the ability to produce the
authenticator by using HMAC-MD5 as shown. Just as with Mobile IP, authenticator by using HMAC-MD5 as shown. Just as with Mobile IP, it
this default algorithm MUST be able to be configured for selection at must be possible to configure the use of any arbitrary 32-bit SPI
any arbitrary 32-bit SPI outside of the SPIs in the reserved range outside of the SPIs in the reserved range 0-255 for selection of this
0-255. default algorithm.
7. Reserved SPIs for Mobile IP 7. Reserved SPIs for Mobile IP
Mobile IP defines several authentication extensions for use in Mobile IP defines several authentication extensions for use in
Registration Requests and Replies. Each authentication extension Registration Requests and Replies. Each authentication extension
carries a Security Parameters Index (SPI) which should be used to carries a Security Parameters Index (SPI) which should be used to
index a table of security associations. Values in the range 0 - 255 index a table of security associations. Values in the range 0 - 255
are reserved for special use. A list of reserved SPI numbers is to are reserved for special use. A list of reserved SPI numbers is to
be maintained by IANA at the following URL: be maintained by IANA at the following URL:
http://www.iana.org/numbers.html http://www.iana.org/numbers.html
8. SPI For RADIUS AAA Servers 8. SPIs for RADIUS AAA Servers
Some AAA servers only admit a single security association, and thus Some AAA servers only admit a single security association, and thus
do not use the SPI numbers for Mobile IP authentication extensions do not use the SPI numbers for Mobile IP authentication extensions
for use when determining the security association that would be for use when determining the security association that would be
necessary for verifying the authentication information included with necessary for verifying the authentication information included with
the Authentication extension. the Authentication extension.
SPI number CHAP_SPI (see section 9) is reserved (see section 7) for SPI number CHAP_SPI (see Section 9) is reserved for indicating the
indicating the following procedure for computing authentication data following procedure for computing authentication data (called the
(called the "authenticator"), which is used by many RADIUS servers "authenticator"), which is used by many RADIUS servers [RFC2138]
[10] today. today.
To compute the authenticator, apply MD5 [11] computed on the To compute the authenticator, apply MD5 [RFC1321] computed on the
following data, in the order shown: following data, in the order shown:
High-order byte from Challenge || Key || High-order byte from Challenge || Key ||
MD5(Preceding Mobile IP data || MD5(Preceding Mobile IP data ||
Type, Subtype (if present), Length, SPI) || Type, Subtype (if present), Length, SPI) ||
Least-order 237 bytes from Challenge Least-order 237 bytes from Challenge
where the Type, Length, SPI, and possibly Subtype, are the fields of where the Type, Length, SPI, and possibly Subtype, are the fields of
the authentication extension in use. For instance, all four of these the authentication extension in use. For instance, all four of these
fields would be in use when SPI == CHAP_SPI is used with the fields would be in use when SPI == CHAP_SPI is used with the
Generalized Authentication extension. Since the RADIUS protocol Generalized Authentication extension. Since the RADIUS protocol
cannot carry attributes greater than 253 in size, the preceding cannot carry attributes of length greater than 253, the preceding
Mobile IP data, type, subtype (if present), length and SPI are hashed Mobile IP data, type, subtype (if present), length and SPI are hashed
using MD5. Finally, the least significant 237 bytes of the challenge using MD5. Finally, the least significant 237 bytes of the challenge
are concatenated. are concatenated. If the challenge has fewer than 238 bytes, this
algorithm includes the high-order byte in the computation twice, but
ensures that the challenge is used exactly as is. Additional padding
is never used to increase the length of the challenge; the input data
is allowed to be shorter than 237 bytes long.
9. Configurable Parameters 9. Configurable Parameters
Every Mobile IP agent supporting the extensions defined in this Every Mobile IP agent supporting the extensions defined in this
document SHOULD be able to configure each parameter in the following document SHOULD be able to configure each parameter in the following
table. Each table entry contains the name of the parameter, the table. Each table entry contains the name of the parameter, the
default value, and the section of the document in which the parameter default value, and the section of the document in which the parameter
first appears. first appears.
Parameter Name Default Value Section(s) of Document +------------------+---------------+---------------------+
-------------- ------------- ---------------------- | Parameter Name | Default Value | Section of Document |
CHALLENGE_WINDOW 2 3.2 +------------------+---------------+---------------------+
CHAP_SPI 2 8 | CHALLENGE_WINDOW | 2 | 3.2 |
| | | |
10. Error Values | CHAP_SPI | 2 | 8 |
+------------------+---------------+---------------------+
Each entry in the following table contains the name of Code [8] to be
returned in a Registration Reply, the value for the Code, and the
section in which the error is first mentioned in this specification.
Error Name Value Section of Document
---------------------- ----- -------------------
UNKNOWN_CHALLENGE 104 3.2
BAD_AUTHENTICATION 67 3.2 - also see [8]
MISSING_CHALLENGE 105 3.1,3.2
STALE_CHALLENGE 106 3.2
11. IANA Considerations Table 1: Configurable Parameters
The Generalized Mobile IP Authentication extension defined in Section Note that CHALLENGE_WINDOW SHOULD be at least 2. This makes it far
5 is a Mobile IP registration extension as defined in RFC 2002 [8] less likely that mobile nodes will register using a Challenge value
and extended in RFC 2356 [7]. IANA should assign a value of 36 for that is outside the set of values allowable by the foreign agent.
this extension.
A new number space is to be created for enumerating subtypes of the 10. Error Values
Generalized Authentication extension (see section 5). New subtypes
of the Generalized Authentication extension, other than the number
(1) for the MN-AAA authentication extension specified in section 6,
must be specified and approved by a designated expert.
The MN-FA Challenge Extension defined in Section 4 is a router Each entry in the following table contains the name of the Code
advertisement extension as defined in RFC 1256 [3] and extended in [RFC3344] to be returned in a Registration Reply, the value for the
RFC 2002 [8]. IANA should assign a value of 132 for this purpose. Code, and the section in which the error is first mentioned in this
specification.
The Code values defined in Section 10 are error codes as defined in +--------------------+-------+--------------------------+
RFC 2002 [8] and extended in RFC 2344 [6] and RFC 2356 [7]. They | Error Name | Value | Section of Document |
correspond to error values conventionally associated with rejection +--------------------+-------+--------------------------+
by the foreign agent (i.e., values from the range 64-127). The Code | UNKNOWN_CHALLENGE | 104 | 3.2 |
value 67 is a pre-existing value which is to be used in some cases | | | |
with the extension defined in this specification. IANA should record | BAD_AUTHENTICATION | 67 | 3.2 - also see [RFC3344] |
the values as defined in Section 10. | | | |
| MISSING_CHALLENGE | 105 | 3.1, 3.2 |
| | | |
| STALE_CHALLENGE | 106 | 3.2 |
| | | |
| FA_BAD_AAA_AUTH | TBD | 3.2 |
| | | |
| HA_BAD_AAA_AUTH | TBD | 3.4 |
| | | |
| HA_WRONG_CHALLENGE | TBD | 3.2 |
+--------------------+-------+--------------------------+
A new section for enumerating algorithms identified by specific SPIs Table 2: Error Values
within the range 0-255 is to be added to
http://www.isi.edu/in-notes/iana/assignments/mobileip-numbers. 11. IANA Considerations
The CHAP_SPI number (2) discussed in section 8 is to be assigned from All protocol values in this specification are to be the same as
this range of reserved SPI numbers. New assignments from this defined in RFC 3012 [RFC3012]. Additionaly, new error codes
reserved range must be specified and approved by the Mobile IP FA_BAD_AAA_AUTH, HA_BAD_AAA_AUTH, and HA_WRONG_CHALLENGE are defined
working group. SPI number 1 should not be assigned unless in the by this document. Among these, HA_WRONG_CHALLENGE may appear in the
future the Mobile IP working group decides that SKIP is not important Status code of the FA Error extension defined in [FAERR].
for enumeration in the list of reserved numbers. SPI number 0 should
not be assigned.
12. Security Considerations 12. Security Considerations
In the event that a malicious mobile node attempts to replay the In the event that a malicious mobile node attempts to replay the
authenticator for an old MN-FA Challenge, the Foreign Agent would authenticator for an old Mobile-Foreign Challenge, the foreign agent
detect it since the agent always checks whether it has recently would detect it since the agent always checks whether it has recently
advertised the Challenge (see section 3.2). Allowing mobile nodes advertised the Challenge (see Section 3.2). Allowing mobile nodes
with different IP addresses or NAIs to use the same Challenge value with different IP addresses or NAIs to use the same Challenge value
does not represent a security vulnerability, because the does not represent a security vulnerability, because the
authentication data provided by the mobile node will be computed over authentication data provided by the mobile node will be computed over
data that is different (at least by the bytes of the mobile nodes' IP data that is different (at least by the bytes of the mobile nodes' IP
addresses). addresses).
Whenever a Foreign Agent updates a field of the Registration Reply If the foreign agent chooses a Challenge value (see Section 2) with
(as suggested in section 3.2), it invalidates the authentication data fewer than 4 bytes, the foreign agent SHOULD include the value of the
supplied by the Home Agent in the MN-HA Authentication extension to Identification field in the records it maintains for the mobile node.
the Registration Reply. Thus, this opens up a security exposure The foreign agent can then determine whether the Registration
whereby a node might try to supply a bogus Registration Reply to a messages using the short Challenge value are in fact unique, and thus
mobile node that causes the mobile node to act as if its Registration assuredly not replayed from any earlier registration.
Reply were rejected. This might happen when, in fact, a Registration
Reply showing acceptance of the registration might soon be received
by the mobile node.
If the foreign agent chooses a Challenge value (see section 2) with
fewer than 4 bytes, the foreign agent SHOULD maintain records that
also the Identification field for the mobile node. The foreign agent
can then find assurance that the Registration messages using the
short Challenge value are in fact unique, and thus assuredly not
replayed from any earlier registration.
Section 8 (SPI For RADIUS AAA Servers) defines a method of computing Section 8 (SPI For RADIUS AAA Servers) defines a method of computing
the Generalized Mobile IP Authentication Extension's authenticator the Generalized Mobile IP Authentication Extension's authenticator
field using MD5 in a manner that is consistent with RADIUS [10]. The field using MD5 in a manner that is consistent with RADIUS [RFC2138].
use of MD5 in the method described in Section 8 is less secure than The use of MD5 in the method described in Section 8 is less secure
HMAC-MD5 [5], and should be avoided whenever possible. than HMAC-MD5 [RFC2104], and should be avoided whenever possible.
13. Acknowledgements Note that an active attacker may try to prevent successful
registrations by sending a large number of Agent Solicitations or
bogus Registration Requests, each of which could cause the foreign
agent to respond with a fresh challenge, invalidating the challenge
that the MN is currently trying to use. To prevent such attacks, the
foreign agent MUST NOT invalidate previously unused challenges when
responding to unauthenticated Registration Requests or Agent
Solicitations. In addition, the foreign agent MUST NOT allocate new
storage when responding to such messages, because this would also
create the possibility of denial of service.
The authors would like to thank Tom Hiller, Mark Munson, the TIA 13. Acknowledgments
TR45-6 WG, Gabriel Montenegro, Vipul Gupta, and Pete McCann for their
useful discussions. A recent draft by Mohamed Khalil, Raja
Narayanan, Emad Qaddoura, and Haseeb Akhtar has also suggested the
definition of a generalized authentication extension similar to the
specification contained in section 5.
References The authors would like to thank Tom Hiller, Mark Munson, the TIA
TR45-6 WG, Gabriel Montenegro, Vipul Gupta, Pete McCann, Robert
Marks, Ahmad Muhanna, and Luca Salgarelli for their useful
discussions. A recent draft by Mohamed Khalil, Raja Narayanan, Emad
Qaddoura, and Haseeb Akhtar has also suggested the definition of a
generalized authentication extension similar to the specification
contained in Section 5.
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 14. Normative References
Levels", BCP 14, RFC 2119, March 1997.
[2] Calhoun, P. and C. Perkins. "Mobile IP Network Access Identifier [FAERR] Perkins, C., "Foreign Agent Error Extension for Mobile
Extension for IPv4", RFC 2794, January 2000. IPv4", draft-perkins-mip4-faerr-00.txt (work in progress),
January 2004.
[3] Deering, S., "ICMP Router Discovery Messages", RFC 1256, [RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991. September 1991.
[4] Eastlake, D., Crocker, S. and J. Schiller, "Randomness [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[RFC1750] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994. Recommendations for Security", RFC 1750, December 1994.
[5] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing [RFC1994] Simpson, W., "PPP Challenge Handshake Authentication
for Message Authentication", RFC 2104, February 1997. Protocol (CHAP)", RFC 1994, August 1996.
[6] Montenegro, G., "Reverse Tunneling for Mobile IP", RFC 2344, May [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
1998. Hashing for Message Authentication", RFC 2104,
February 1997.
[7] Montenegro, G. and V. Gupta, "Sun's SKIP Firewall Traversal for [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Mobile IP", RFC 2356, June 1998. Requirement Levels", BCP 14, RFC 2119, March 1997.
[8] Perkins, C., "IP Mobility Support", RFC 2002, October 1996. [RFC2138] Rigney, C., Rigney, C., Rubens, A., Simpson, W., and S.
Willens, "Remote Authentication Dial In User Service
(RADIUS)", RFC 2138, April 1997.
[9] Perkins, C. and D. Johnson, "Route Optimization in Mobile IP", [RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access
Work in Progress. Identifier Extension for IPv4", RFC 2794, March 2000.
[10] Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote [RFC3012] Perkins, C. and P. Calhoun, "Mobile IPv4 Challenge/
Authentication Dial In User Service (RADIUS)", RFC 2138, April Response Extensions", RFC 3012, November 2000.
1997.
[11] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April [RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
1992. August 2002.
[12] Simpson, W., "PPP Challenge Handshake Authentication Protocol Authors' Addresses
(CHAP)", RFC 1994, August 1996.
A. Verification Infrastructure Charles E. Perkins
Nokia Research Center
Communications Systems Lab
313 Fairchild Drive
Mountain View, California 94043
Fax: +1 650 625-2502
Email: charles.perkins@nokia.com
Pat R. Calhoun
Black Storm Networks
110 Nortech Parkway
San Jose, CA 95134
Fax: +1 720-293-7501
Email: pcalhoun@diameter.org
Jayshree Bharatia
Nortel Networks
2221, Lakeside Blvd
Richardson, TX 75082
Fax: +1 972-684-3775
Email: jayshree@nortelnetworks.com
Appendix A. Change History
List of the changes for draft-ietf-mobileip-rfc3012bis-03:
o Foreign agent recommended to include a Challenge in every
Registration Reply, so that mobile node can re-register without
waiting for an Advertisement.
o Foreign agent MUST record applicable challenge values used by each
mobile node.
o Mobile node forbidden to use Challenge values which were
advertised previous to the last Challenge value which it had used
for a registration.
o Terminology for stale challenge vs. unused challenge clarified.
o Terminology for "valid" challenge deleted in favor of "unused
challenge".
o Programming suggestion added as an appendix.
List of the changes for draft-ietf-mobileip-rfc3012bis-04:
o The definition of "previously used challenge" is merged with
"stale challenge" definition in section 1.1.
o Reference 7 is updated from RFC 3320 to RFC 3344 and reference 9
is updated from RFC 2138 to RFC 2865 in "Reference" section.
o Reference to RFC 3344 is added in section 3.
o HMAC_CHAP_SPI option is added for Generalized Mobile IP
Authentication extension. Upon receipt of HMAC_CHAP_SPI, HMAC-MD5
is used instead of MD5 for computing the authenticator.
o Clarified processing of error messages at the mobile node (section
3.1).
o Modified text of section 2.1 and 3.2 for further clarity.
List of the changes for draft-ietf-mobileip-rfc3012bis-05:
o Added BAD_AAA_AUTHENTICATION_SET_BY_FA and
BAD_AAA_AUTHENTICATION_SET_BY_HA error codes to report
authentication errors caused while processing Mobile-AAA
Authentication extension.
o Processing of the Mobile-AAA Authentication extension is clarified
for the foreign agent and the home agent.
o Co-existence of the Mobile-AAA Authentication extension in the
same Registration Request is made explicit.
o The situation in which the foreign agent sets MISSING_CHALLENGE is
clarified further.
o The use of Mobile-AAA Authentication Extension is allowed by the
mobile node with co-located care-of-address.
List of the changes for draft-ietf-mip4-rfc3012bis-00:
o Minor editorial changes are made through out the document.
o Added definition of "previously used challenge" and removed
definition of "stale challenge" from section 1.1.
o Renamed BAD_AAA_AUTHENTICATION_SET_BY_FA to FA_BAD_AAA_AUTH and
BAD_AAA_AUTHENTICATION_SET_BY_HA to HA_BAD_AAA_AUTH.
o Defined an order of the Mobile-AAA Authentication extension
received with the authentication extension(s) defined in RFC 3344
[RFC3344].
o Added protection against bogus Registration Reply and Agent
Advertisement. Also, the processing of the Challenge is clarified
if it is received in the multicast/unicast Agent Advertisement.
List of the changes for draft-ietf-mip4-rfc3012bis-01:
o Minor editorial changes are made through out the document.
o Added reference of FA Error extension in the References section
and also updated relevant text in section 3.2 and section 11.
List of the changes for draft-ietf-mip4-rfc3012bis-02:
o Minor editorial changes are made in Appendix C and Appendix D.
o Updated Boilerplate.
List of the changes for draft-ietf-mip4-rfc3012bis-03:
o Removed HMAC_MD5_SPI support from section 3.1, 8 and 9.
o Corrected figure titles 1 and 3.
List of the changes for draft-ietf-mip4-rfc3012bis-04:
o Clarified use of FA Error extension in section 3.2. Also,
editorial changes are made in 1, 1.1, 3.1 and 3.2 sections.
o Introduced HA_WRONG_CHALLENGE error code.
Appendix B. Verification Infrastructure
The Challenge extensions in this protocol specification are expected The Challenge extensions in this protocol specification are expected
to be useful to help the Foreign Agent manage connectivity for to be useful to help the foreign agent manage connectivity for
visiting mobile nodes, even in situations where the foreign agent visiting mobile nodes, even in situations where the foreign agent
does not have any security association with the mobile node or the does not have any security association with the mobile node or the
mobile node's home agent. In order to carry out the necessary mobile node's home agent. In order to carry out the necessary
authentication, it is expected that the foreign agent will need the authentication, it is expected that the foreign agent will need the
assistance of external administrative systems, which have come to be assistance of external administrative systems, which have come to be
called AAA systems. For the purposes of this document, we call the called AAA systems. For the purposes of this document, we call the
external administrative support the "verification infrastructure". external administrative support the "verification infrastructure".
The verification infrastructure is described to motivate the design The verification infrastructure is described to motivate the design
of the protocol elements defined in this document, and is not of the protocol elements defined in this document, and is not
strictly needed for the protocol to work. The foreign agent is free strictly needed for the protocol to work. The foreign agent is free
to use any means at its disposal to verify the credentials of the to use any means at its disposal to verify the credentials of the
mobile node. This could, for instance, rely on a separate protocol mobile node. This could, for instance, rely on a separate protocol
between the foreign agent and the Mobile IP home agent, and still be between the foreign agent and the Mobile IP home agent, and still be
completely invisible to the mobile node. completely invisible to the mobile node.
In order to verify the credentials of the mobile node, we imagine In order to verify the credentials of the mobile node, we imagine
that the foreign agent has access to a verification infrastructure that the foreign agent has access to a verification infrastructure
that can return a secure notification to the foreign agent that the that can return a secure notification to the foreign agent that the
authentication has been performed, along with the results of that authentication has been performed, along with the results of that
authentication. This infrastructure may be visualized as shown in authentication. This infrastructure may be visualized as shown in
figure 4. Figure 4.
+----------------------------------------------------+ +----------------------------------------------------+
| | | |
| Verification and Key Management Infrastructure | | Verification and Key Management Infrastructure |
| | | |
+----------------------------------------------------+ +----------------------------------------------------+
^ | ^ | ^ | ^ |
| | | | | | | |
| v | v | v | v
+---------------+ +---------------+ +---------------+ +---------------+
| | | | | | | |
| Foreign Agent | | Home Agent | | foreign agent | | home agent |
| | | | | | | |
+---------------+ +---------------+ +---------------+ +---------------+
Figure 4: The Verification Infrastructure Figure 4: The Verification Infrastructure
After the foreign agent gets the Challenge authentication, it MAY After the foreign agent gets the Challenge authentication, it MAY
pass the authentication to the (here unspecified) infrastructure, and pass the authentication to the (here unspecified) infrastructure, and
await a Registration Reply. If the Reply has a positive status await a Registration Reply. If the Reply has a positive status
(indicating that the registration was accepted), the foreign agent (indicating that the registration was accepted), the foreign agent
accepts the registration. If the Reply contains the Code value accepts the registration. If the Reply contains the Code value
BAD_AUTHENTICATION (see Section 10), the foreign agent takes actions BAD_AUTHENTICATION (see Section 10), the foreign agent takes actions
indicated for rejected registrations. indicated for rejected registrations.
Implicit in this picture, is the important observation that the Implicit in this picture, is the important observation that the
Foreign Agent and the Home Agent have to be equipped to make use of foreign agent and the home agent have to be equipped to make use of
whatever protocol is made available to them by the challenge whatever protocol is made available to them by the challenge
verification and key management infrastructure shown in the figure. verification and key management infrastructure shown in the figure.
The protocol messages for handling the authentication within the The protocol messages for handling the authentication within the
verification infrastructure, and identity of the agent performing the verification infrastructure, and identity of the agent performing the
verification of the Foreign Agent challenge, are not specified in verification of the foreign agent challenge, are not specified in
this document, because those operations do not have to be performed this document, because those operations do not have to be performed
by any Mobile IP entity. by any Mobile IP entity.
Addresses Appendix C. Message Flow for FA Challenge Messaging with Mobile-AAA
Extension
The working group can be contacted via the current chairs: MN FA Verification home agent
|<-- Adv+Challenge--| Infrastructure |
| (if needed) | | |
| | | |
|-- RReq+Challenge->| | |
| + Auth.Ext. | | |
| | Auth. Request, incl. | |
| |--- RReq + Challenge --->| |
| | + Auth.Ext | RReq + |
| | |-- Challenge -->|
| | | |
| | | |
| | |<--- RRep ----- |
| | Authorization, incl. | |
| |<-- RRep + Auth.Ext.-----| |
| | | |
|<-- RRep+Auth.Ext--| | |
| + New Challenge | | |
Basavaraj Patil Figure 5: Message Flows for FA Challenge Messaging
Nokia Corporation
6000 Connection Drive
M/S M8-540
Irving, Texas 75039
USA
Phone: +1 972-894-6709 In Figure 5, the following informational message flow is illustrated:
Fax : +1 972-894-5349
EMail: Basavaraj.Patil@nokia.com
Phil Roberts 1. The foreign agent disseminates a Challenge Value in an Agent
Motorola Advertisement if needed. This advertisement MAY have been
1501 West Shure Drive produced after receiving an Agent Solicitation from the mobile
Arlington Heights, IL 60004 node (not shown in the diagram).
USA
Phone:+1 847-632-3148 2. The mobile node creates a Registration Request including the
EMail: QA3445@email.mot.com advertised Challenge Value in the Challenge Extension, along with
Questions about this memo can also be directed to the authors: an Mobile-AAA authentication extension.
Charles E. Perkins 3. The foreign agent relays the Registration Request either to the
Communications Systems Lab home agent specified by the mobile node, or else to its locally
Nokia Research Center configured Verification Infrastructure (see Appendix B),
313 Fairchild Drive according to local policy.
Mountain View, California 94043
USA
Phone: +1-650 625-2986 4. The foreign agent receives a Registration Reply with the
Fax: +1 650 625-2502 appropriate indications for authorizing connectivity for the
EMail: charliep@iprg.nokia.com mobile node.
Pat R. Calhoun 5. The foreign agent relays the Registration Reply to the mobile
Network & Security Center node, possibly along with a new Challenge Value to be used by the
Sun Microsystems Laboratories mobile node in its next Registration Request message.
15 Network Circle
Menlo Park, California 94025
USA
Phone: +1 650-786-7733 Appendix D. Message Flow for FA Challenge Messaging with MN-FA
Fax: +1 650-786-6445 Authentication
EMail: pcalhoun@eng.sun.com
Full Copyright Statement MN FA home agent
|<-- Adv+Challenge--| |
| (if needed) | |
| | |
|-- RReq+Challenge->| |
| + Auth.Ext. | |
| |--- RReq + Challenge --->|
| | + HA-FA Auth.Ext |
| | |
| |<-- RRep + Challenge ----|
| | + HA-FA Auth.Ext |
| | |
|<-- RRep+Auth.Ext--| |
| + New Challenge | |
Copyright (C) The Internet Society (2000). All Rights Reserved. Figure 6: Message Flows for FA Challenge Messaging with MN-FA
Authentication
This document and translations of it may be copied and furnished to In Figure 6, the following informational message flow is illustrated:
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be 1. The foreign agent disseminates a Challenge Value in an Agent
revoked by the Internet Society or its successors or assigns. Advertisement if needed. This advertisement MAY have been
produced after receiving an Agent Solicitation from the mobile
node (not shown in the diagram).
This document and the information contained herein is provided on an 2. The mobile node creates a Registration Request including the
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING advertised Challenge Value in the Challenge Extension, along with
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING an Mobile-Foreign Authentication extension.
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement 3. The foreign agent relays the Registration Request to the home
agent specified by the mobile node.
4. The foreign agent receives a Registration Reply with the
appropriate indications for authorizing connectivity for the
mobile node.
5. The foreign agent relays the Registration Reply to the mobile
node, possibly along with a new Challenge Value to be used by the
mobile node in its next Registration Request message. If the
Reply contains the Code value HA_BAD_AAA_AUTH (see Section 10),
the foreign agent takes actions indicated for rejected
registrations.
Appendix E. Foreign Agent Algorithm for Tracking Used Challenges
If the foreign agent maintains a large CHALLENGE_WINDOW, it becomes
more important for scalability purposes to efficiently compare
incoming challenges against the set of Challenge values which have
been advertised recently. This can be done by keeping the Challenge
values in order of advertisement, and by making use of the mandated
behavior that mobile nodes MUST NOT use Challenge values which were
advertised before the last advertised Challenge value that the mobile
node has attempted to use. The following stylized programmatic
algorithm accomplishes this objective. The maximum amount of total
storage required by this algorithm is equal to Size*(CHALLENGE_WINDOW
+ (2*N)), where N is the current number of mobile nodes for which the
foreign agent is storing challenge values. Note that, whenever the
stored challenge value is no longer in the CHALLENGE_WINDOW, it can
be deleted from the foreign agent's records, perhaps along with all
other registration information for the mobile node if it is no longer
registered.
In the program fragment, it is presumed that the foreign agent keeps
an array of advertised Challenges ("VALID_ADV_CHALLENGES"), a record
of the last advertised challenge used by a mobile node, and also a
record of the last challenge provided to a mobile node in a
Registration Reply or unicast Agent Advertisement.
To meet the security obligations outlined in Section 12, the foreign
agent SHOULD use one of the already stored, previously unused
challenges when responding to an unauthenticated Registration Request
or Agent Solicitation. If none of the already stored challenges are
previously unused, the foreign agent SHOULD generate a new challenge,
include it in the response, and store it in the per-Mobile data
structure.
current_chal := RegistrationRequest.challenge_extension_value
last_chal := mobile_node_record.last_used_adv_chal
if (current_chal == mobile_node_record.RegReply_challenge) {
update (mobile_node_record, current_chal)
return (OK)
}
else if (current_chal "among" VALID_ADV_CHALLENGES[]{
if (last_chal "among" VALID_ADV_CHALLENGES[]) {
if (current_chal is "before" last_chal) {
send_error(STALE_CHALLENGE)
return (FAILURE)
}
else {
update (mobile_node_record, current_chal)
return (OK)
}
}
else {
update (mobile_node_record, current_chal)
return (OK)
}
}
else {
send_error(UNKNOWN_CHALLENGE);
}
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Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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