Network Working Group A. Patel Internet-Draft K. Leung Expires:
August 11, 2005February 23, 2006 Cisco Systems M. Khalil H. Akhtar Nortel Networks K. Chowdhury Starent Networks February 10,August 22, 2005 Authentication Protocol for Mobile IPv6 draft-ietf-mip6-auth-protocol-04.txtdraft-ietf-mip6-auth-protocol-05.txt Status of this Memo By submitting this Internet-Draft, I certifyeach author represents that any applicable patent or other IPR claims of which I amhe or she is aware have been or will be disclosed, and any of which I becomehe or she becomes aware will be disclosed, in accordance with RFC 3668.Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 11, 2005.February 23, 2006. Copyright Notice Copyright (C) The Internet Society (2005). 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 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 3.13.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 5 4. Operational flow . . . . . . . . . . . . . . . . . . . . . . . 6 5. Mobility message authentication option . . . . . . . . . . . . 7 5.15.1. MN-HA authentication mobility option . . . . . . . . . . . 8 126.96.36.199.1. Processing Considerations . . . . . . . . . . . . . . 9 5.25.2. MN-AAA authentication mobility option . . . . . . . . . . 9 5.2.110 5.2.1. Processing Considerations . . . . . . . . . . . . . . 10 5.35.3. Authentication Failure Detection at the Mobile Node . . . 1011 6. Mobility message replay protection option . . . . . . . . . . 1112 7. Security Considerations . . . . . . . . . . . . . . . . . . . 1415 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 1516 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 10. Normative References . . . . . . . . . . . . . . . . . . . . . 17 Appendix A. Rationale for mobility message replay protection option . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17 A. Rationale for mobility message replay protection option .. . 19 Intellectual Property and Copyright Statements . . . . . . . . 20. . 21 1. Introduction The base Mobile IPv6 specification [RFC3775] specifies the signaling messages, Binding Update (BU) and Binding Acknowledgement (BA), between the Mobile Node and Home agent to be secured by the IPsec Security Associations (IPsec SAs) that are 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 an Authentication, Authorization and Accounting (AAA) infrastructure for authenticatingThe draft draft-patil-mip6-whyauthdataoption-01.txt describes the subscriber 2. require dynamic assignmentarchitecture of Home Agentcdma2000 networks and home addresses 3. have constraints onthe numbermotivation of messages involved in setting up IPsec SAs 4. include Mobile Nodes that do not support IKEv1 This indicatesusing the need for a solution that does not necessarily require an IPsec SAauthentication option for securing the signaling messages that deal with the Registration process of aMobile Node with a home agent.IP in that architecture. 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 a host 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 does not imply that the availability of such a solution deprecates the use of IPsec for securing Mobile IPv6 signaling between Mobile Nodes and Home Agents. Home agents still have to implement and support registrations from Mobile Nodes that are secured via IPsec as well as with the authentication option. The authentication mechanism proposed here is similar to the authentication mechanism used in Mobile IPv4 [RFC3344]. 2. Overview This document presents a lightweight mechanism to authenticate the Mobile Node at the Home Agent or at the Authentication, Authorization and Accounting (AAA) server in Home network (AAAH) based on a shared key based mobility security association between the Mobile Node and the respective authenticating entity. This shared key based mobility security association (shared-key based SA) may be statically provisioned or dynamically created. The term "security"mobility security association" referred to in this document is understood to be a "shared-key based Mobile IPv6 authentication" security association. The Mobile Node MUST use only one means of authentication, based on either the shared key based authentication or IPsec security association with a selected Home Agent at any given time. However a MN that implements both schemes of authentication may choose any appropriate scheme with the chosen HA. The determination of what authentication scheme to use is beyond the scope of this document. Home agents still have to implement and support registrations from Mobile Nodes that are secured via IPsec as well as with the authentication option.This document introduces new mobility options to aid in authentication of the Mobile Node to the Home Agent or AAAH server. The confidentiality protection of Return Routability messages and authentication/integrity protection of Mobile Prefix Discovery (MPD) is outside the scope of this document. The Home Agent SHOULD prevent these operations for a Mobile Node when such protection cannot be provided by the network. 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. 3.13.1. General Terms First (size, input) Some formulas in this specification use a functional form "First (size, input)" to indicate truncation of the "input" data so that only the first "size" bits remain to be used. 4. Operational flow The figure below describes the sequence of messages sent and received between the MN and HA in the registration process. Binding Update (BU) and Binding Acknowledgement (BA) messages are used in the registration process. MN HA/AAAH | BU to HA | (a) |----------------------------------------------------->| | (including MN-ID option [optional],option, | | Message ID option [optional], authentication option)| | | | | | HA/AAAH authenticates MN | | | | | BA to MN | (b) |<-----------------------------------------------------| | (including MN-ID option [optional],option, | | Message ID option [optional], authentication option)| | | Figure 1: Home Registration with Authentication Protocol Mobile Node MAYMUST use the Mobile Node Identifier OptionOption, specifically the MN-NAI mobility option as defined in [MN_Ident] or Home Addressto identify itself while authenticating with the Home Agent. The mobile node uses the Mobile Node Identifier option as defined in [MN_Ident] to identify itself as may be required for use with some existing AAA infrastructure designs. Mobile Node MAY use Message Identifier option as defined in Section 6 for additional replay protection. The authentication option described in Section 5 may be used by the mobile node to transfer authentication data when the mobile node and the home agent are utilizing an SPI to index between multiple mobility security associations. For the case when there is only one such mobility security association, and no SPI is needed, the Mobile Node and Home Agent can use the Binding Authorization Data option as defined in the base Mobile IPv6 specification [RFC3775] for this same purpose. Since that option does not have any SPI, the Mobile Node and the Home Agent implicitly agree that the mobility security association to be used is the only mobility security association that is defined for their mutual authentication needs. 5. Mobility message authentication option This section defines a message authentication mobility option that may be used to secure Binding Update and Binding Acknowledgement messages. This option can be used along with IPsec or preferably as an alternate mechanism to authenticate Binding Update and Binding Acknowledgement messages in the 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. Other subtypes may be defined for use 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 shared-key based mobility 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authentication Data .... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 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 Authentication Data fields. Subtype: A number assigned to identify the entity and/or mechanism to be used to authenticate the message. SPI: Security Parameter Index Authentication Data: 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. 5.15.1. MN-HA authentication mobility option The format of the MN-HA authentication mobility option is as defined in Figure 2. 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-key based security association between the Mobile Node and the Home Agent. The shared-key based mobility security association between Mobile Node and Home Agent used within this specification consists of a SPI, a key, an authentication algorithm and the replay protection mechanism in use. The SPI is a number in range [0-4294967296], where the range [0-255] is reserved. The key consists of an arbitrary value and is 16 octets in length. The authentication algorithm is HMAC_SHA1. The replay protection mechanism may use the Sequence number as specified in [RFC3775] or the option as defined in Section 6. If the Timestamp option is used for replay protection as defined in Section 6, the mobility security association includes a "close enough" field to account for clock drift. A default value of 7 seconds MAY be used. This value SHOULD be greater than 3 seconds. 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 Section 5.2 authentication option if both options are present in the message.The authentication data is calculated on the message starting from the mobility header upto and including the SPI value of this option. Authentication Data = 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 upto and including the SPI field of this option. The Checksum field in Mobility Header MUST be set to 0 to calculate the Mobility Data. The first 96 bits from the MAC result are used as the Authentication Data field. 188.8.131.52.1. Processing Considerations The assumption is that Mobile Node has a shared-key based security association with the Home Agent. The Mobile Node MUST include this option in a BU if it has a shared-key based mobility security association with the Home Agent. The Home Agent MUST include this option in the BA if it received this option in the corresponding BU and Home Agent has a shared-key based mobility security association with the Mobile Node. The Mobile Node or Home Agent receiving this option MUST verify the authentication data in the option. If authentication fails, the Home Agent MUST send BA with Status Code MIPV6-AUTH-FAIL. If the Home Agent does not have shared-key based SA, Home Agent MUST discard the BU. The Home Agent MAY log such events. 5.25.2. MN-AAA authentication mobility option The format of the MN-AAA authentication mobility option is as defined in Figure 2. 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 mobility security association between Mobile Node and AAA server in Home network (AAAH). It is not used in Binding Acknowledgement messages. The corresponding Binding Acknowledgement messages must be authenticated using the MN-HA authentication option Section 5.1. 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 option MUST appear prior to the Mobile-AAA Authentication option.The corresponding response MUST include the Mobile-Home Authentication option, and MUST NOT include the Mobile-AAA Authentication option. The Mobile Node MAY use Mobile Node Identifier option [MN_Ident] to enable the Home Agent to make use of available AAA infrastructure. The authentication data is calculated on the message starting from the mobility header upto and including the SPI value of this option. The authentication data shall be calculated as follows: Authentication data = hash_fn(MN-AAA Shared key, MAC_Mobility Data) hash_fn() is decided by the value of SPI field in the authentication option. SPI = HMAC_SHA1_SPI: If SPI has the well-known value HMAC_SHA1_SPI, then hash_fn() is HMAC_SHA1. When HMAC_SHA1_SPI is used, the BU is authenticated by AAA using HMAC_SHA1 authentication. In that case, MAC_Mobility Data is calculated as follows: MAC_Mobility Data = SHA1(care-of address | home address | MH Data) MH Data is the content of the Mobility Header upto and including the SPI field of this option. 184.108.40.206.1. Processing Considerations Interaction between the HA and the AAA server is beyond the scope of this document. When the Home Agent receives a Binding Update with the Mobile-AAA authentication option, the Binding Update is authenticated by an entity external to the Home Agent, typically a AAA server. 5.35.3. Authentication Failure Detection at the Mobile Node In case of authentication failure, the Home Agent MUST send a Binding Acknowledgement with status code MIPV6-AUTH-FAIL to the Mobile Node, if an SA to be used between Mobile Node and Home Agent for authentication exists. Upon receiving a Binding Acknowledgement with status code MIPV6-AUTH-FAIL,MIPV6-AUTH- FAIL, the Mobile Node SHOULD stop sending new Binding Updates to the Home Agent. 6. Mobility message replay protection option The Mobility message replay protection option MAY be used in Binding Update/Binding Acknowledgement messages when authenticated using the mobility message authentication option as described in Section 5. The mobility message replay protection option is used to let the Home Agent verify that a Binding Update has been freshly generated by the Mobile Node and not replayed by an attacker from some previous Binding Update. This is especially useful for cases where the Home Agent does not maintain stateful information about the Mobile Node after the binding entry has been removed. The Home Agent does the replay protection check after the Binding Update has been authenticated. The mobility message replay protection option when included is used by the Mobile Node for matching BA with BU. If the policy at Home Agent mandates replay protection using this option (as opposed to the sequence number in Mobility Header in Binding Update) and the Binding Update from Mobile Node does not include this option, Home Agent discards the BU and sets the Status Code in BA to MIPV6-MESG-ID-REQD. When the Home Agent receives the mobility message replay protection option in Binding Update, it SHOULD include the mobility message replay protection option in Binding Acknowledgement. Appendix A provides details regarding why the mobility message replay protection 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3 Option Type: 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 Timestamp field. Timestamp: This field carries the 64 bit timestamp. Alignment requirements : The alignment requirement for this option is 8n + 2. 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 shared-key based mobility 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. The two nodes must have adequately synchronized time-of-day clocks. The Mobile Node MUST set the Timestamp 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 Timestamp used in a Binding Update from the Mobile Node MUST be greater than that used in any previous successful Binding Update. After successful authentication of Binding Update (either locally at the Home Agent or when a success indication is received from the AAA server), the Home Agent MUST check the Timestamp field for validity. In order to be valid, the timestamp contained in the Timestamp 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 Timestamp field into the Timestamp 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, Home Agent MUST send a Binding Acknowledgement with status code MIPV6-ID-MISMATCH. The Home Agent does not create a binding cache entry if the timestamp check fails. If the Mobile Node receives a Binding Acknowledgement with the code MIPV6-ID-MISMATCH, the Mobile Node MUST authenticate the BA by processing the MN-HA authentication mobility option. If authentication succeeds, the Mobile Node 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 status code, the Mobile Node MUST compare the Timestamp value in the BA to the Timestamp value it sent in the corresponding BU. If the values match, the Mobile Node proceeds to process the MN-HA authentication data in the BA. If the values do not match, the Mobile Node silently discards the BA. 7. Security Considerations This document proposes new authentication options to authenticate the control message between Mobile Node, Home Agent 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 Mobile Node and Home Agent for subsequent authentication of BU/BA between Mobile Node and Home Agent via the MN-HA authentication option.This specification also introduces an optional replay protection mechanism in 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 mobility message replay protection. 8. IANA Considerations IANA services are required for this specification. The values for new mobility options and status 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,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, Section 6 and Section 5.3 also need to be assigned. The suggested values are 144 for MIPV6-ID-MISMATCHMIPV6-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 currently defined values are as follows: The value 0 should not be assigned. The value 3 is suggested for HMAC_SHA1_SPI as defined in Section 5.2. The value 5 is reserved for use by 3GPP2. New values for this namespace can be allocated using Standards Action [RFC2434]. In addition, IANA needs to create a new namespace for the subtype field of the MN-HA and MN-AAA authentication mobility options under http://www.isi.edu/in-notes/iana/assignments/mobility-parameters The currently allocated values are as follows: 1 MN-HA authentication mobility option Section 5.1 2 MN-AAA authentication mobility option Section 5.2 New values for this namespace can be allocated using Standards Action [RFC2434]. 9. Acknowledgements The authors would like to thank Basavaraj Patil, Charlie Perkins Vijay Devarapalli and Jari Arkko for their thorough review and suggestions on the document. The authors would like to acknowledge the fact that a similar authentication method was considered in base protocol [RFC3775] at one time. 1010. Normative References [MN_Ident] Patel et. al., A., "Mobile Node Identifier Option for Mobile IPv6", draft-ietf-mip6-mn-ident-option-01.txtdraft-ietf-mip6-mn-ident-option-03.txt (work in progress), December 2004. [RFC1305] Mills, D., "Network Time Protocol (Version 3) Specification, Implementation", RFC 1305, March 1992. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC2865] Rigney, C., Willens, S., Rubens, A.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.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: email@example.com Kent Leung Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 US Phone: +1 408-526-5030 EMail: firstname.lastname@example.org Mohamed Khalil Nortel Networks 2221 Lakeside Blvd. Richardson, TX 75082 US Phone: +1 972-685-0574 EMail: email@example.com Haseeb Akhtar Nortel Networks 2221 Lakeside Blvd. Richardson, TX 75082 US Phone: +1 972-684-4732 EMail: firstname.lastname@example.org Kuntal Chowdhury Starent Networks 2540 Coolwater Dr. Plano, TX 75025 US Phone: +1 214 550 1416 EMail: email@example.comAppendix A. Rationale for mobility message replay protection 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 Home Agent should accept a BU with a Sequence Number greater than the Sequence Number from previous Binding Update. This implicitly assumes that the Home Agent 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 Home Agent 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 Mobile Node to register with a different Home Agent during each mobility session. Thus, it is unreasonable to expect each Home Agent in the network to maintain state about the Mobile Node. Also, if the Home Agent 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 Mobile Node. Thus, when authentication option is used, Sequence Number does not provide protection against replay attack. One solution to this problem (when Home Agent does not save state information for every Mobile Node) would be for the Home Agent to reject the first BU and assign a (randomly generated) starting sequence number for the session and force the Mobile Node 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 mobility message replay protection option to prevent replay attacks. Specifically, timestamps are used to prevent replay attacks as described in Section 6. 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 Mobile Node and CN, the liveness proof is provided by the use of nonces which the CN generates. Authors' Addresses Alpesh Patel Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 US Phone: +1 408-853-9580 Email: firstname.lastname@example.org Kent Leung Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 US Phone: +1 408-526-5030 Email: email@example.com Mohamed Khalil Nortel Networks 2221 Lakeside Blvd. Richardson, TX 75082 US Phone: +1 972-685-0574 Email: firstname.lastname@example.org Haseeb Akhtar Nortel Networks 2221 Lakeside Blvd. Richardson, TX 75082 US Phone: +1 972-684-4732 Email: email@example.com Kuntal Chowdhury Starent Networks 30 International Place Tewksbury, MA 01876 US Phone: +1 214 550 1416 Email: firstname.lastname@example.org Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 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. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society.