Network Working Group F. Dupont, Ed.
Internet-Draft CELAR
Expires: August 4, 2007 K. Weniger
Panasonic
January 31, 2007
IKEv2-based Home Agent Assignment in Mobile IPv6/NEMO Bootstrapping
draft-dupont-ikev2-haassign-02.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document specifies how to use IKEv2 for Home Agent assignment in
Mobile IPv6 or NEMO bootstrapping. It uses IPv6 anycast addresses
and should not introduce new security issues.
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1. Introduction
Home Agent (HA) assignment is an improvement over HA discovery: in
place of giving a list of possible HA addresses, this procedure gives
the HA to use in a way controlled by the Mobile Service Provider, for
(initial) load balancing, fail-over or DoS avoidance.
IKEv2 [RFC4306] is the tool of choice in bootstrapping scenarios
because not only it established the needed Security Associations but
it can allocate home Addresses, authenticate the Mobile Node (MN)
using EAP [RFC2284], etc [IKEv2-MIPv6]. The only function it did not
support is the HA assignment.
This document addresses both Mobile IPv6 [RFC3775] and NEMO [RFC3963]
cases, the second likely with another IPv6 subnet anycast address.
The goal of the document is to provide HA assignment support using an
IKEv2 initial message sent to an IPv6 anycast destination address
without introduction of new security issues.
This document could use the standard keywords [BCP14] to indicate
requirement levels.
2. The proposal
In the IKEv2 exchanges, the MN takes the initiator role and the HA
the responder role. The MN takes parameters from its configuration,
followed or not by a discovery phase. The HA address is a
recognizable IPv6 anycast address. So:
1. the MN sends an IKE_SA_INIT request to the HA anycast address
2. the anycast receiver forwards the request to the "best" HA
3. the HA answers using its own address as the source address and
includes an "under attack" cookie in its replies
4. the MN notes the HA own address and use it in subsequent
messages, the MN retries the IKE_SA_INIT request with the cookie
to the HA own address
The standard IKEv2 procedure follows as usual. The following figure
illustrates the initial exchanges:
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Initiator Responder ("best" HA)
----------- ---------------------
(IP_I:500 -> ANYCAST:500)
HDR(A,0), SAi1, KEi, Ni -->
(IP_R:500 -> IP_I:500)
<-- HDR(A,0), N(COOKIE)
(IP_I:500 -> IP_R:500)
HDR(A,0), N(COOKIE), SAi1, KEi, Ni -->
(IP_R:500 -> IP_I:500)
<-- HDR(A,B), SAr1, KEr, Nr, [CERTREQ]
(IP_I:500 -> IP_R:500)
HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] [IDr,]
AUTH, SAi2, TSi, TSr} -->
(IP_R:500 -> IP_I:500)
<-- HDR(A,B), SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr}
Figure 1: Initial exchanges
The proposal can be used in any environment, including Mobile IPv6
and NEMO, as soon as a recognizable IPv6 anycast address is assigned
to the provided service (cf. IANA (Section 3)).
The term "recognizable IPv6 anycast address" means an IPv6 anycast
address [RFC3513] which is recognizable as an IPv6 anycast address by
the initiator. This includes, but not exclusively, addresses in the
subnet anycast address format defined by [RFC2526].
3. IANA Considerations
Mobile IPv6 defines an IPv6 subnet anycast address [RFC2526] (value
decimal=126 / hexa=7E). In the case Mobile IPv6 and NEMO services
are not provided by the same HAs, a second IPv6 subnet anycast
address has to be assigned by IANA for NEMO HAs.
4. Security Considerations
As the anycast address can be well known, the cookie-based defense
against DoS ([RFC4306] section 2.6) is used by default. Another
advantage is the whole IKE_SA_INIT and IKE_AUTH exchanges are
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performed using the "right" addresses so the impact of the proposal
on IKEv2 implementations can be kept minimal.
As in the standard IKEv2 ([RFC4306] section 2.4 4th paragraph) the
initiator has to reject cryptographically invalid fake IKE_SA_INIT
replies so there is no new attack against the initiator side.
5. Acknowledgments
The initial idea was in a Kilian Weniger's message about HA
assignment. Jean-Michel Combes, speaking for a Mobile Service
Provider, insisted to improve the current HA discovery to HA
assignment. Kero Kivinen checked whether the proposal introduces new
security issue and whether it is reasonably easy to implement, and
proposed the figure for initial exchanges.
6. References
6.1. Normative References
[BCP14] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, March 1999.
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support Protocol",
RFC 3963, January 2005.
[RFC4306] Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
Protocol", RFC 4306, December 2005.
6.2. Informative References
[IKEv2-MIPv6]
Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
IKEv2 and the revised IPsec Architecture",
draft-ietf-mip6-ikev2-ipsec-08.txt (work in progress),
December 2006.
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[RFC2284] Blunk, L. and J. Vollbrecht, "PPP Extensible
Authentication Protocol (EAP)", RFC 2284, March 1998.
Appendix A. Possible Enhancements
The cookie phase is not strictly necessary so it is only RECOMMENDED.
Note that one of the main reasons to provide assignment in place of
discovery, i.e., perform the server selection by the network in place
of the client, is to protect servers against denial of service
attacks, so the cost of always using a cookie is in fact low.
The mechanism can be used for other contexts than Mobile IPv6 and
NEMO, for instance as a general Security Gateway assignment
mechanism. Instead of pre-configuring a well-known anycast addresses
on the client, the anycast address can also be discovered prior to
sending the IKE_SA_INIT, e.g., with DNS. This allows for more
flexibility, i.e., the operator can change the anycast address
anytime and it can allocate different anycast addresses to different
services. And this simplifies the IANA considerations.
The protocols used between the Home Agents, both to forward the
initial request and to select the real server, are not described in
this document. They are currently left to the implementor's choice
and can become the object of another document if needed.
Authors' Addresses
Francis Dupont (editor)
CELAR
Email: Francis.Dupont@fdupont.fr
Kilian Weniger
Panasonic R&D Center Germany
Monzastr. 4c
Langen 63225
Germany
Phone: +49 6103 766 137
Email: kilian.weniger@eu.panasonic.com
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