Network Working Group F. Dupont Internet-Draft Point6 Expires: December 25, 2005 J-M. Combes France Telecom DR&D June 23, 2005 Care-of Address Test for MIPv6 using a State Cookie draft-dupont-mipv6-rrcookie-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with 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 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 December 25, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document defines a procedure which performs a "care-of address test" using a state cookie for routing optimization in Mobile IPv6 not protected by the routing routability procedure, i.e., protected by some alternative mechanisms like pre-shared secret or pre- established IPsec security associations. Dupont & Combes Expires December 25, 2005 [Page 1] Internet-Draft CoA Test Cookie June 2005 1. Introduction The Mobile IPv6 specifications [RFC3775] defines a default protection for routing optimization, the routing routability procedure, which includes an explicit "care-of address test". Alternative protection mechanisms like pre-shared secret [pcfgkbm] or pre-established IPsec security associations [CNIPsec] are more efficient and secure but require in some cases a care-of address test to avoid a "3rd party bombing" vulnerability. This document proposes a care-of address test procedure at the initiative of the correspondent node using a state cookie as in SCTP [RFC2960] or IKEv2 [IKEv2]. 2. Keywords 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 BCP 14, RFC 2119 [RFC2119]. 3. A signaling extension for a care-of address test using a state cookie 3.1 Applicability The care-of address test procedure defined by this document MAY be used in order to check whether the mobile node can really receive packets sent to the care-of address of a new binding update. It SHOULD NOT be used for entry deletion, i.e., when the care-of address is the home address. It MUST be used for real alternate care-of address, i.e., when the address carried by an alternate care-of address option is not the source address of the IP header nor the home address of the mobile node (following the recommendation of [bombing]). 3.2 Protocol The procedure is based on the state cookie idea of SCTP [RFC2960] which can be found again in IKEv2 proposal [IKEv2]. The binding update is in a first time (1) rejected by a binding acknowledgment with a new dedicated status and a cookie option sent to the tested care-of address. Upon the reception (2) of this binding acknowledgment, the mobile node retransmits (3) the binding update with the exact received cookie placed in a cookie option. When the correspondent node receives (4) the augmented binding update, it can check by recomputing the cookie and comparing it to the cookie option data that the binding update is from the same mobile node and for the Dupont & Combes Expires December 25, 2005 [Page 2] Internet-Draft CoA Test Cookie June 2005 same care-of address (so it can infer the mobile node is reachable at this care-of address, i.e., a "care-of address test" has been successfully performed). The cookie MUST reflect the mobile node identity or the binding cache entry or an equivalent, and MUST reflect the tested care-of address. It MUST NOT be easy to infer by the mobile node, including with the knowledge of previous cookies from the same node. The last point is what to do waiting the retransmitted and augmented binding update. Possibilities are: - apply the binding update with the new care-of address. It defeats the purpose of the care-of address test so it SHOULD NOT be done, and it MUST NOT be done for a real alternate care-of address. - keep the previous care-of address. As it is not possible to know whether the previous care-of address is still usable, i.e., whether the mobile node is still reachable at this previous care-of address, the default policy SHOULD NOT be to keep the previous care-of address. The correspondent node MAY keep the previous care-of address in special cases where this is known to be the best solution. - temporarily disable the binding cache entry, i.e., by using the home address for communication to the mobile node until another binding update is received. This SHOULD be the default policy. 3.3 Cookie Generation Example This method assumes a global secret key is available and uses in sequence: - a 16 bit timestamp of when the cookie is created - the tested care-of address - the truncated HMAC [RFC2104], keyed by a secret key, of the preceding two fields, the home address and the correspondent address. The secret key SHOULD be random or pseudo-random and SHOULD be changed reasonably frequently. The timestamp MAY be used to determine which key was used. The HMAC has to be truncated in order to keep the cookie option length less than the maximum, the higher 96 bits of the HMAC should be enough. 4. Acknowledgments This document was extracted from [CNIPsec] because what it provides is needed by any alternative to the return routability procedure which has no built-in care-of address test. Dupont & Combes Expires December 25, 2005 [Page 3] Internet-Draft CoA Test Cookie June 2005 5. Security Considerations Without a test of the care-of address or an other way to trust it, the care-of address presented by the mobile node can be a fake one and offers a 3rd party bombing attack. Binding updates and acknowledgments are validated using an alternative protection mechanisms so they can't be injected by third parties. The cookie sub-option is small enough to make this procedure a poor candidate for a third party bombing mechanism. 6. IANA Considerations This document requires: - a new status for binding acknowledgment. - a new option for mobility messages used in binding update and acknowledgment messages. 7. References 7.1 Normative References [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, March 1997. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. 7.2 Informative References [CNIPsec] Dupont, F. and J-M. Combes, "Using IPsec between Mobile and Correspondent IPv6 Nodes", draft-ietf-mip6-cn-ipsec-01.txt (work in progress), June 2005. [IKEv2] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) Protocol", draft-ietf-ipsec-ikev2-17.txt (work in progress), September 2004. [RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson, "Stream Control Transmission Protocol", RFC 2960, October 2000. [bombing] Dupont, F., "A note about 3rd party bombing in Mobile Dupont & Combes Expires December 25, 2005 [Page 4] Internet-Draft CoA Test Cookie June 2005 IPv6", draft-dupont-mipv6-3bombing-02.txt (work in progress), June 2005. [pcfgkbm] Perkins, C., "Preconfigured Binding Management Keys for Mobile IPv6", draft-ietf-mip6-precfgkbm-02.txt (work in progress), May 2005. Authors' Addresses Francis Dupont Point6 c/o GET/ENST Bretagne 2 rue de la Chataigneraie CS 17607 35576 Cesson-Sevigne Cedex France Fax: +33 2 99 12 70 30 Email: Francis.Dupont@enst-bretagne.fr Jean-Michel Combes France Telecom DR&D 38/40 rue du General Leclerc 92794 Issy-les-Moulineaux Cedex 9 France Fax: +33 1 45 29 65 19 Email: jeanmichel.combes@francetelecom.com Dupont & Combes Expires December 25, 2005 [Page 5] Internet-Draft CoA Test Cookie June 2005 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. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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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. Dupont & Combes Expires December 25, 2005 [Page 6]