Internet Engineering Task Force Y. Liu
Internet Draft Huawei
Expires: August 2007 R. White
B. Weis
M. Barnes
Cisco
February 26, 2007
OSPFv3 Automated Group Keying Requirements
draft-liu-ospfv3-automated-keying-req-00.txt
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Copyright (C) The IETF Trust (2007).
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Abstract
RFC4552 describes how to provide authentication/confidentiality to
OSPFv3 using IPsec. It specifies that same IPsec SA parameters be
configured for both inbound and outbound SAs to provide the "one to
many" security for multicast OSPFv3 communications over broadcast
links (e.g., Ethernet). Manual keying is specified as the mandatory
and default group key management solution. However, issues of
scalability and security exist with manual keying. It is better to
replace manual keying with automated group key management. This
document discusses the requirements on OSPFv3 automated group key
management, assuming that the centralized group key management
architecture introduced in [RFC4046] is used.
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Table of Contents
1. Introduction..................................................3
2. Terminology...................................................4
3. Requirements..................................................4
3.1. REQ-1: Protecting neighboring routers' start process.....5
3.2. REQ-2: Protecting a single router's join process.........6
3.3. REQ-3: Protecting neighboring routers' restart process...6
3.4. REQ-4: Dealing with single point of key server failure...6
3.5. REQ-5: Secure distribution of group SA...................6
3.6. REQ-6: Dealing with route flap...........................6
3.7. REQ-7: Improving key server scalability..................7
4. Security Considerations.......................................7
5. IANA Considerations...........................................7
6. Acknowledgments...............................................7
7. References....................................................7
7.1. Normative References.....................................7
7.2. Informative References...................................8
Author's Addresses...............................................9
Intellectual Property Statement.................................10
Full Copyright Statement........................................10
Acknowledgment..................................................10
1. Introduction
OSPFv3 [RFC2740] relies on IPSec to provide integrity, authentication,
and/or confidentiality. RFC4552 describes how to provide
authentication/confidentiality to OSPFv3 using AH/ESP. In Section 7
of RFC4552, it is proved that best scalability and feasibility can be
achieved if the same parameters are used for both inbound and
outbound AH/ESP SAs to provide the "one to many" communication
security while running OSPFv3 over broadcast interfaces. It means
that group security model be used to protect OSPFv3 multicast
communications over broadcast network.
However, RFC4552 specifies Manual Keying [RFC4301] as the default
group key management method, which is neither scalable nor secure.
This document discusses replacing manual keying with automated keying.
It is based on the fact that several GKM protocols have been, or
being, standardized by MSEC working group [RFC3547] [RFC3830]
[RFC4535] [GKDP], which makes it feasible to provide automated group
key management for OSPFv3 using GKM protocols.
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Meanwhile, [I-D: draft-ietf-msec-ipsec-extensions] describes
multicast extensions to IPsec, which makes it feasible to provide
group security to OSPFv3 using standard multicast IPsec.
This document describes the requirements on OSPFv3 automated group
key management. It is assumed that the centralized group security
architecture [RFC3740] and group key management architecture [RFC4046]
would be used, where group SAs are centrally managed on separate key
server(s). Use of group key agreement techniques, for example,
Cliques [CLIQUES], is out of consideration.
2. Terminology
The key words "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.
Group Key Management (GKM) Protocol
A group key management protocol used by a GCKS to distribute
IPsec Security Association policy and keying material. A GKM
protocol is used when a group of IPsec devices require the same
SAs. For example, when an IPsec SA describes an IP multicast
destination, the sender and all receivers MUST have the group SA.
Group Member
An IPsec device that belongs to a group. A Group Member is
authorized to be a Group Speaker and/or a Group Receiver.
Group Security Association (Group SA)
A collection of IPsec Security Associations (SAs) and GKM SAs
necessary for a Group Member to receive key updates. A GSA
describes the working policy for a group. Refer to RFC 4046
[RFC4046] for additional information.
State Synchronization (SS)
A generalization of OSPFv3 communications that occur after two
routers discover each other. It includes neighbor discovering,
exchanging DDs and LSAs, etc.
3. Requirements
The scenario shown in Fig.1 is used as the sample OSPFv3 deployment
case to discuss the following requirements.
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N2 N3
+-----+ +-----+
| |
|2 |
+---+ +---+
|RT1| |RT2|
+---+ +---+
|1 |1
N1 | |
+------------------------------------+
| | |
|1 |1 |1
+---+ +---+ +---+
|RT3| |RT4| |RT5|
+---+ +---+ +---+
| | |
| | |
+-----+ +-----+ +-----+
N4 N5 N6
Figure 1 : The scenario used to derive the requirements
N1 is a broadcast network, where group SA is used to protect the
OSPFv3 multicast communications among RT1~RT5. A separate machine
serves as key server, which is not depicted in Fig. 1. Group members
attached to N1, including RT1~RT5, get the group SA from key server.
Every group member should know through which of its interfaces it
reaches the key server. For convenience, broadcast interfaces
attached to N1 are numbered as #1, which makes sense inside each
router.
Types of networks N2~N6 are not fixed. They MAY be either broadcast,
P2MP, or NBMA. It is likely that one, or more, of N2~N6 is a
broadcast network either, and shares same group SA and key server
with N1.
3.1. REQ-1: Protecting neighboring routers' start process
When neighboring routers initially start, e.g., routers attached to
N1, they have no routes to the key server and so, can not get the
group SA. Measures MUST be provisioned to protect the initial
communications among OSPFv3 routers before their adjacencies are
established and routes are calculated out.
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3.2. REQ-2: Protecting a single router's join process
When a new router joins, it first performs SS process with its
neighbors, and then calculates its routes. The new comer cannot
access the key server, and thus cannot get the current group SA until
the SS process is finished. Measures MUST be provided to protect the
new comer's OSPFv3 communications with existing routers before it
gets group SA.
Another case is single router's restart and re-join. During that
process, key server MAY update the group SA and redistribute it to
remaining routers. Therefore, after a router restarts and resumes the
GSA from its storage (e.g., flash), it MAY find that its local GSA is
out of synchronization with its neighbors' GSA. Measures MUST be
defined to deal with such de-synchronization.
3.3. REQ-3: Protecting neighboring routers' restart process
Neighboring routers MAY simultaneously restart because of accidents
(e.g., power-off). They need to re-perform SS and re-calculate their
routes. Similar to REQ-1, routers can not get the group SA from the
key server before routes converge. Measures MUST be provided to
protect the redoing SS process.
3.4. REQ-4: Dealing with single point of key server failure
This requirement is obvious. And it is common to all Client/Server
applications. The key servers MAY be out of service because of
attacks, accidents, etc. Measures MUST be prepared to provide
continuous keying service in case of single point of key server
failure.
3.5. REQ-5: Secure distribution of group SA
Eavesdroppers can not access the group keys by intercepting the group
SA distribution packets. All existing GKM protocols can meet this
requirement.
3.6. REQ-6: Dealing with route flap
Routers might be shortly out of contact with the key server by
reasons of route flaps, . During that process, the key server MAY
update the group keys and distribute them to group members. Measures
MUST be prepared for the group members to deal with such problems.
For example, only by #1 interface does RT1 reach the key server. If a
route flap (e.g. Interface down/up) occurs on #1 interface, RT1 will
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be out of contact with the key server, thus cannot receive the
server-pushed rekeying messages any more. After the route resumes,
RT1 will redo SS with its neighbors. Measures MUST be provided for
RT1 to synchronize its group SA with others before re-handshaking in
case that the server updates the group SA during the route flap.
3.7. REQ-7: Improving key server scalability
Some GKM protocols (e.g., GDOI and GKDP) support key server initiated
rekeying. It is better to push rekeying messages using IP multicast
to achieve better scalability for the key server when it serves a
number of OSPFv3 routers.
On the other hand, it MAY be unpractical to set up one key server for
each broadcast network. Therefore, it is likely to share same key
server, even same GSA, among broadcast links. Both N1 and N2, for
example, are broadcast networks and share same key server. Since
inter-network IP multicast is seldom deployed, scalability issue MUST
be carefully considered when key server initiated-rekeying mechanisms
are used in above scenarios. Measures MUST be defined to improve the
key server scalability in case that IP multicast is unavailable.
4. Security Considerations
This document lists requirements for automated group keying of OSPFv3.
No new protocol is specified. Hence there is no security
consideration.
5. IANA Considerations
This document has no IANA considerations.
6. Acknowledgments
Thank Zengjie Kou, Jinliang Feng and Zhenhai Li for technical
discussions.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and Overell, P. (Editors), "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, Internet Mail
Consortium and Demon Internet Ltd., November 1997.
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[RFC2740] Coltun, R., Ferguson, D. and J. Moy, "OSPF for IPv6", RFC
2740, December 1999.
[RFC3547] Baugher, M., Weis, B., Hardjono, T. and H. Harney, "The
Group Domain of Interpretation", RFC3547, July 2003.
[RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security
Architecture", RFC3740, March 2004.
[RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M. and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC3830,
August 2004.
[RFC4046] Baugher, M., Canetti, R., Dondeti, L. and F. Lindholm,
"Multicast Security (MSEC) Group Key Management
Architecture", RFC4046, April 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC4301, December 2005.
[RFC4535] Harney, H., Meth, U., Colegrove, A. and G. Gross, "GSAKMP:
Group Secure Association Key Management Protocol", RFC4535,
June 2006.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality for
OSPFv3", RFC4552, June 2006.
7.2. Informative References
[GKDP] Dondeti, L., Xiang, J. and S. Rowles, "GKDP: Group Key
Distribution Protocol", work in progress, October 2006.
[I-D: draft-ietf-msec-ipsec-extensions] Weis, B., Gross, G. and D.
Ignjatic, "Multicast Extensions to the Security
Architecture for the Internet Protocol", work in progress,
October 2006.
[CLIQUES] Steiner, M., Tsudik, G. and M. Waidner, "CLIQUES: A New
Approach to Group key Agreement", IEEE ICDCS'98 , MAY 1998.
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Author's Addresses
Ya Liu
Huawei Technologies
Kuike Bld., No.9 Xinxi Rd., Shang-Di Information Industry Base
Hai-Dian District, Beijing, P.R. China
Phone: 8610-82836072
Email: liuya@huawei.com
Russ White
Cisco Systems
Email: riw@cisco.com
Brian Weis
Cisco Systems
Email: bew@cisco.com
Michael Barnes
Cisco Systems
Email: mjbarnes@cisco.com
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