Network Working Group A. Patel
Internet-Draft K. Leung
Expires: May 2, 2005 Cisco Systems
M. Khalil
H. Akhtar
K. Chowdhury
Nortel Networks
November 2004
Authentication Protocol for Mobile IPv6
draft-ietf-mip6-auth-protocol-01.txt
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This Internet-Draft will expire on May 2, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
IPsec is specified as the sole means of securing all signaling
messages between the Mobile Node and Home agent for Mobile IPv6. A
flexible model for security between the mobile node and home agent is
required from the perspective of deployment of the Mobile IPv6
protocol. One instance of such deployment need comes from networks
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that are built on 3GPP2 standards. This document proposes an
alternate method for securing the signaling messages that are
responsible for performing Registration of a mobile node at a home
agent.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Operational flow . . . . . . . . . . . . . . . . . . . . . . . 6
5. Mobility message authentication option . . . . . . . . . . . . 7
5.1 MN-HA authentication mobility option . . . . . . . . . . . 8
5.1.1 Processing Considerations . . . . . . . . . . . . . . 9
5.2 MN-AAA authentication mobility option . . . . . . . . . . 9
5.2.1 Processing Considerations . . . . . . . . . . . . . . 10
5.3 Authentication Failure Detection at the MN . . . . . . . . 10
6. Mobility message identification option . . . . . . . . . . . . 11
6.1 Timestamp option . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
10. Normative References . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 16
A. Authentication using CHAP . . . . . . . . . . . . . . . . . . 18
A.1 Processing considerations . . . . . . . . . . . . . . . . 18
A.2 Mapping BU to Radius Attributes . . . . . . . . . . . . . 18
A.3 Processing of Radius response . . . . . . . . . . . . . . 18
B. Rationale for message identification option . . . . . . . . . 20
Intellectual Property and Copyright Statements . . . . . . . . 21
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1. Introduction
The base Mobile IPv6 specification [RFC3775] specifies the signaling
messages, Binding Update (BU) and Binding Acknowledegment (BA),
between the Mobile node and Home agent to be secured by the IPsec SA
that is established between these two entities. This security model
for Mobile IPv6 does not fit in very well for deployment scenarios
which:
1. rely on the use of a AAA infrastructure for authenticating the
subscriber
2. require dynamic assignment of home agent and home addresses
3. have constraints on the number of messages involved in setting up
a security association using protocols like IKEv1
4. include mobile nodes that do not support IKEv1
The conclusion drawn thereby is the need for a solution that does not
necessarily require an IPsec SA for securing the signaling messages
that deal with the Registration process of a mobile node with a home
agent.
This document proposes a solution for securing the Binding update and
Binding acknowledgment messages between the Mobile node and Home
agent using an authentication option which is included in these
messages. Such a mechanism enables IPv6 mobility in hosts without
having to establish an IPsec SA with its home agent. A mobile node
can implement Mobile IPv6 without having to integrate it with the
IPsec module, in which case the Binding update and Binding
Acknowldegement messages (between MN-HA) are secured with the
authentication option. It should be noted that it does not imply
that the availability of such a solution deprecates the use of IPsec
for securing Mobile IPv6 signaling between MNs and HAs. Home agents
however have to implement and support registrations from mobile nodes
that are secured via IPsec as well as with the authentication option.
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2. Overview
This document presents a lightweight mechanism to authenticate the MN
at the HA or at the Home AAA based on a shared security association
between the MN and the respective authenticating entity.
This document introduces new mobility options to aid in
authentication of the MN to the HA or AAA server. The
confidentiality protection of Return Routability messages and
authentication/integrity protection of Mobile Prefix Discovery (MPD)
is outside the scope of this document.
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3. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119.
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4. Operational flow
MN HA/HAAA
| BU to HA |
(a) |----------------------------------------------------->|
| (HoA option, MN-ID option [optional], |
| Message ID option [optional], authentication option)|
| |
| |
| HA/HAAA authenticates MN
| |
| |
| BA to MN |
(b) |<-----------------------------------------------------|
| (RH-2 option, MN-ID option [optional], |
| Message ID option [optional], auth option) |
| |
MN MAY use NAI option as defined in [MN_Ident] to identify itself
while authenticating with the HA or AAA infrastructure.
MN MAY use Message Identifier option as defined in Section 6 for
replay protection.
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5. Mobility message authentication option
This section defines the message authentication mobility option that
may be used to secure Binding Update and Binding Acknowledgement
messages. This extension can be used along with IPsec or preferably
as an alternate mechanism to authenticate Binding Update and Binding
Acknowledgement messages in absence of IPsec.
This document also defines subtype numbers, which identify the mode
of authentication and the peer entity to authenticate the message.
Two subtype numbers are specified in this document. It is expected
that other subtypes will be defined by other documents in the future.
Only one instance of an authentication option of a particular subtype
can be present in the message. One message may contain multiple
instances of authentication options with different subtype values.
When a Binding Update or Binding Acknowledgement is received without
an authentication option and the entity receiving it is configured to
use authentication option or has the security association for
authentication option, the entity should silently discard the
received message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Subtype |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authenticator . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type:
AUTH-OPTION-TYPE to be defined by IANA. An 8-bit identifier of
the type mobility option.
Option Length:
8-bit unsigned integer, representing the length in octets of
the Sub-type, Security Parameter Index (SPI) and Authenticator
fields.
Subtype:
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A number assigned to identify the entity and/or mechanism to be
used to authenticate the message.
SPI:
Used to identify the particular security association to use to
authenticate the message.
Authenticator:
This field has the information to authenticate the relevant
mobility entity. This protects the message beginning at the
Mobility Header upto and including the SPI field.
Alignment requirements :
The alignment requirement for this option is 4n + 1 octets.
5.1 MN-HA authentication mobility option
The format of the MN-HA authentication mobility option is as defined
in Section 5. This option uses the subtype value of 1. The MN-HA
authentication mobility option is used to authenticate the Binding
Update and Binding Acknowledgement messages based on the shared
security association between the MN and the HA.
This must be the last option in a message with mobility header if it
is the only authentication option in the message. It must occur
before the MN-AAA authentication option if both options are present
in the message.
The authenticator is calculated on the message starting from the
mobility header till (including) the SPI value of this option.
Authenticator = First (96,HMAC_SHA1(MN-HA Shared key, Mobility Data))
Mobility Data = care-of address | home address | Mobility Header(MH)
Data
MH Data is the content of the Mobility Header till (including) the
SPI field of this extension.
The first 96 bits from the MAC result are used as the Authenticator
field.
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5.1.1 Processing Considerations
MN MUST include this option in a BU if it shares a security
association with the HA. HA MUST include this option in the BA if
IPsec is not used and it has a security association with the MN.
MN or HA receiving this option MUST verify the authenticator in the
option. If authentication fails, HA MUST discard the BU and send BA
with Status Code MIPV6-AUTH-FAIL, if the HA has a SA with the MN.
5.2 MN-AAA authentication mobility option
The format of the MN-AAA authentication mobility option is as defined
in Section 5. This option uses the subtype value of 2. The MN-AAA
authentication mobility option is used to authenticate the Binding
Update message based on the shared security association between MN
and Home Authentication, Authorization and Accounting (AAA) server.
It is not used in Binding Acknowledgement message.
This must be the last option in a message with mobility header. If
both Mobile-Home and Mobile-AAA authentication mobility options 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 MN MAY use NAI option [MN_Ident] to enable the Home Agent to make
use of available AAA infrastructure which requires NAI.
The authenticator is calculated on the message starting from the
mobility header till (including) the SPI value of this option.
The authenticator shall be calculated as follows:
Authenticator = hash_fn(MN-AAA Shared key, MAC_Mobility Data)
hash_fn() is decided by the value of SPI field in the authentication
option. The SPI field in the MN-AAA authentication option also
defines how the mobility options in BU are mapped to AAA attributes
for authentication.
SPI = CHAP_SPI:
hash_fn() is MD5. When CHAP_SPI is used, the BU is authenticated via
AAA using Challenge Handshake Authentication Protocol (CHAP)
authentication. Specifics of how CHAP authentication is done using
RADIUS ([RFC2865]) is described in Appendix A.
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MAC_Mobility Data = MD5(care-of address | home address | MH Data)
MH Data is the content of the Mobility Header till (including) the
SPI field of this extension.
5.2.1 Processing Considerations
The MN-AAA authentication mobility option MUST be verified by the AAA
infrastructure that has the shared secret with the MN. The HA relays
the authenticating information to the home AAA. The HA relies on the
home AAA to admit or reject the Binding Update from the MN.
5.2.1.1 Home Agent Considerations
Upon receiving a BU from the MN, the HA SHALL extract the MN-AAA
authenticator and the SPI from the MN-AAA authentication mobility
option and extract the NAI from the NAI option [MN_Ident].
The HA SHALL include the extracted MN-AAA authenticator, SPI and the
NAI in AAA specific Attribute-Value Pairs (AVPs) while initiating the
authentication procedure via AAA infrastructure. Specifics of how
authentication is done using RADIUS ([RFC2865]) when CHAP_SPI is
used, are described in Appendix A.
5.3 Authentication Failure Detection at the MN
In case of authentication failure, the HA MUST send a Binding
Acknowledgement with error code MIPV6-AUTH-FAIL to the MN, if an SA
to be used between MN and HA for authentication exists. This MAY
need administrative intervention to resolve the cause of the
authentication failure.
Upon receiving a Binding Acknowledgement with error code
MIPV6-AUTH-FAIL, the MN SHOULD stop sending new Binding Updates to
the responding HA.
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6. Mobility message identification option
The Mobility message identification option MAY be used in a Binding
Update/Binding Acknowledgement messages when authenticated using the
mobility authentication option as described in Section 5.
The Identification option is used to let the home agent verify that a
Binding Update has been freshly generated by the mobile node, not
replayed by an attacker from some previous Binding Update. The
identification option when included is used by the MN for matching BA
with BU.
The subtype field in the identification option specifies the style of
replay protection used. This document specifies timestamps as one
style of replay protection, as described in Section 6.1. The
Identification in a new Binding Update MUST not be the same as in an
immediately preceding Binding Update.
The style of replay protection in effect between a mobile node and
the HA is part of the mobility security association. A mobile node
and the HA MUST agree on which method of replay protection will be
used. If the policy at HA mandates replay protection using this
option (as opposed to the sequence number in Mobility Header in
Binding Update) and the Binding Update from MN does not include this
option, HA discards the BU and sets the Status Code in BA to
MIPV6-MESG-ID-REQD.
When mobility message identification option is used along with
authentication option, the MN SHOULD set the Sequence Number in the
mobility header in Binding Update to 0 and SHOULD ignore the Sequence
Number in Mobility Header in BA. Appendix B provides details
regarding why message identification option MAY be used when using
the authentication option.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Subtype |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type:
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MESG-ID-OPTION-TYPE to be defined by IANA. An 8-bit identifier
of the type mobility option.
Option Length:
8-bit unsigned integer, representing the length in octets of
the Subtype and Identification field.
Subtype:
8-bit unsigned integer indicating the style of replay
protection in use.
Identification:
The Identification field carries Subtype specific data for
replay protection.
Alignment requirements :
This option does not have any specific alignment requirements.
6.1 Timestamp option
The format of the timestamp mobility option is as defined in Section
6. This option uses the subtype value of 1. The Identification
field carries timestamp for replay protection.
The basic principle of timestamp replay protection is that the node
generating a message inserts the current time of day, and the node
receiving the message checks that this timestamp is sufficiently
close to its own time of day. Unless specified differently in the
security association between the nodes, a default value of 7 seconds
MAY be used to limit the time difference. This value SHOULD be
greater than 3 seconds. Obviously the two nodes must have adequately
synchronized time-of-day clocks.
The mobile node MUST set the Identification field to a 64-bit value
formatted as specified by the Network Time Protocol [RFC1305]. The
low-order 32 bits of the NTP format represent fractional seconds, and
those bits which are not available from a time source SHOULD be
generated from a good source of randomness. Note, however, that when
using timestamps, the 64-bit Identification used in a Binding Update
from the mobile node MUST be greater than that used in any previous
Binding Update.
After successful authentication of Binding Update (either locally at
the HA or when a success indication is received from the AAA server),
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the home agent MUST check the Identification field for validity. In
order to be valid, the timestamp contained in the Identification
field MUST be close enough to the home agent's time of day clock and
the timestamp MUST be greater than all previously accepted timestamps
for the requesting mobile node.
If the timestamp is valid, the home agent copies the entire
Identification field into the Identification field in the BA it
returns to the mobile node. If the timestamp is not valid, the home
agent copies only the low-order 32 bits into the BA, and supplies the
high-order 32 bits from its own time of day. If the timestamp field
is not valid but the authentication of the BU succeeds, HA MUST send
a Binding Acknowledgement with error code MIPV6-ID-MISMATCH. HA does
not create a binding cache entry if the timestamp check fails.
If the MN receives a Binding Acknowledgement with the code
MIPV6-ID-MISMATCH, the MN MUST authenticate the BA by processing the
MN-HA authentication mobility option. If authentication succeeds,
the MN MUST adjust its timestamp and send subsequent Binding Update
using the updated value. Upon receiving a BA that does not contain
the MIPV6-ID-MISMATCH error code, the MN MUST compare the
Identification value in the BA to the Identification value it sent in
the corresponding BU. If the values match, the MN proceeds to
process the MN-HA authenticator in the BA. If the values do not
match, the MN silently discards the BA.
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7. Security Considerations
This document proposes new authentication options to authenticate the
control message between MN, HA and/or home AAA (as an alternative to
IPsec). The new options provide for authentication of Binding Update
and Binding Acknowledgement messages. The MN-AAA authentication
options provides for authentication with AAA infrastructure. It can
be used to generate a per session key between MN and HA for
subsequent authentication of BU/BA between MN and HA via the MN-HA
authentication option.
This memo also introduces an optional replay protection mechanism
Section 6, to prevent replay attacks. The sequence number field in
the Binding Update is not used if this mechanism is used. This memo
defines the timestamp option to be used for message identification.
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8. IANA Considerations
IANA services are required for this document. The values for new
mobility options and error codes must be assigned from the Mobile
IPv6 [RFC3775] numbering space.
The values for Mobility Option types AUTH-OPTION-TYPE and
MESG-ID-OPTION-TYPE, as defined in Section 5 and Section 6 need to be
assigned. The suggested values are 8 for the AUTH-OPTION-TYPE and 9
for the MESG-ID-OPTION-TYPE Mobility Option.
The values for Status Codes MIPV6-ID-MISMATCH, MIPv6-AUTH-FAIL and
MIPV6-MESG-ID-REQD as defined in Section 6.1, Section 6 and Section
5.3 also need to be assigned. The suggested values are 144 for
MIPV6-ID-MISMATCH 145 for MIPV6-MESG-ID-REQD and 146 for
MIPV6-AUTH-FAIL.
IANA should record values for these new Mobility Options and the new
Status Codes.
A new section for enumerating algorithms identified by specific SPIs
within the range 0-255 is to be added to
http://www.isi.edu/in-notes/iana/assignments/mobility-parameters
The value 0 should not be assigned.
The value 2 is suggested for CHAP_SPI as defined in section Section
5.2.
The value 3 is suggested for HMAC_SHA1.
The value 5 is reserved for use by 3GPP2.
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9. Acknowledgements
The authors would like to thank Basavaraj Patil, Charlie Perkins and
Vijay Devarapalli for their suggestions and comments on the draft.
The authors would like to acknowledge the fact that a similar
authentication method was considered in base protocol [RFC3775] at
one time.
10 Normative References
[3012bis] Perkins et. al., C., "Mobile IPv4 Challenge/Response
Extensions (revised)", draft-ietf-mip4-rfc3012bis-01 (work
in progress), April 2004.
[MN_Ident]
Patel et. al., A., "MN Identifier Option for Mobile IPv6",
draft-ietf-mip6-mn-ident-option-01.txt (work in progress),
December 2004.
[RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation", RFC 1305, March 1992.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[RFC3775] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
Authors' Addresses
Alpesh Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
US
Phone: +1 408-853-9580
EMail: alpesh@cisco.com
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Kent Leung
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
US
Phone: +1 408-526-5030
EMail: kleung@cisco.com
Mohamed Khalil
Nortel Networks
2221 Lakeside Blvd.
Richardson, TX 75082
US
Phone: +1 972-685-0574
EMail: mkhalil@nortelnetworks.com
Haseeb Akhtar
Nortel Networks
2221 Lakeside Blvd.
Richardson, TX 75082
US
Phone: +1 972-684-4732
EMail: haseebak@nortelnetworks.com
Kuntal Chowdhury
Nortel Networks
2221 Lakeside Blvd.
Richardson, TX 75082
US
Phone: +1 972 685 7788
EMail: chowdury@nortelnetworks.com
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Appendix A. Authentication using CHAP
A.1 Processing considerations
The HA acts as a Radius client in accordance with ([RFC2865]) when
MN-AAA mobility option is received in a BU. On receipt of the BU
from the MN, and if SPI in the MN-AAA mobility option is set to
CHAP-SPI, the HA shall create a Radius Access-Request message to
authenticate the BU.
If the SPI in the MN-AAA Authentication Extension is set to CHAP-SPI,
the HA shall use MD5 when computing the CHAP challenge.
A.2 Mapping BU to Radius Attributes
The home agent maps the mobility options to the Radius attributes as
follows:
User-Name(1):
obtained from NAI mobility option in BU.
Chap-Password(3):
CHAP Ident field:
High-order byte of the identification field in the
Identification mobility option
String field:
Authenticator field from the MN-AAA Authentication option
Chap-Challenge(60):
MD5(care-of address | home address | Mobility header till
(including) SPI field in MN-AAA mobility option), followed by the
Identification field in the identification mobility option.
NAS-IP-Address:
NAS-IPv6-Address:
Address of the HA. HA uses the v4/v6 address or both if
available.
A.3 Processing of Radius response
If the authentication succeeds, the Home Radius server sends a Radius
Access-Accept message to the HA. HA proceeds to process the BU
message and sends a BA with appropriate code.
If the authentication fails, the Home Radius server sends a Radius
Access-Reject message to the HA. If Access-Reject is received from
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AAA, HA drops the BU. HA does not send a BA to the MN in response to
this BU. An existing binding cache entry from a previous successful
Binding Update MUST not be modified due to this authentication
failure.
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Appendix B. Rationale for message identification option
Mobile IPv6 [RFC3775] defines a Sequence Number in the mobility
header to prevent replay attacks. There are two aspects that stand
out in regards to using the Sequence Number to prevent replay
attacks.
Firstly, the specification states that HA should accept a BU with a
Sequence Number greater than the Sequence Number from previous
Binding Update. This implicitly assumes that the HA has some
information regarding the Sequence Number from previous BU (even when
the binding cache entry is not present). Secondly, the specification
states that if the HA has no binding cache entry for the indicated
home address, it MUST accept any Sequence Number value in a received
Binding Update from this mobile node.
With the mechanism defined in this draft, it is possible for the MN
to register with a different home agent during each mobility session.
Thus, it is unreasonable to expect each HA in the network to maintain
state about the MN. Also, if the HA does not cache information
regarding sequence number, as per the second point above, a replayed
BU can cause a Home Agent to create a binding cache entry for the MN.
Thus, when authentication option is used, Sequence Number does not
provide protection against replay attack.
One solution to this problem would be for the HA to reject the first
BU and assign a starting sequence number for the session and force
the MN to send a fresh BU with the suggested sequence number. While
this would work in most cases, it would require an additional round
trip and this extra signalling and latency is not acceptable in
certain deployments (3GPP2). Also, this rejection and using sequence
number as a nonce in rejection is a new behavior that is not
specified in [RFC3775].
Thus, this specification uses the message identification option to
prevent replay attacks. Specifically, timestamps are used for
message identification to prevent replay attacks as described in
Section 6.1.
It is important to note that as per Mobile IPv6 [RFC3775] this
problem with sequence number exists. Since the base specification
mandates the use of IPsec (and naturally that goes with IKE in most
cases), the real replay protection is provided by IPsec/IKE. In case
of BU/BA between MN and CN, the liveness proof is provided by the use
of nonces which the CN generates.
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