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IETF RFC 8064
Last modified on Wednesday, February 22nd, 2017
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Internet Engineering Task Force (IETF) F. Gont
Request for Comments: 8064 SI6 Networks / UTN-FRH
Updates: 2464, 2467, 2470, 2491, 2492, A. Cooper
2497, 2590, 3146, 3572, 4291, Cisco
4338, 4391, 5072, 5121 D. Thaler
Category: Standards Track Microsoft
ISSN: 2070-1721 W. Liu
Huawei Technologies
February 2017
Recommendation on Stable IPv6 Interface Identifiers
 Abstract
This document changes the recommended default Interface Identifier
(IID) generation scheme for cases where Stateless Address
Autoconfiguration (SLAAC) is used to generate a stable IPv6 address.
It recommends using the mechanism specified in RFC 7217 in such
cases, and recommends against embedding stable link-layer addresses
in IPv6 IIDs. It formally updates RFC 2464, RFC 2467, RFC 2470, RFC
2491, RFC 2492, RFC 2497, RFC 2590, RFC 3146, RFC 3572, RFC 4291, RFC
4338, RFC 4391, RFC 5072, and RFC 5121. This document does not
change any existing recommendations concerning the use of temporary
addresses as specified in RFC 4941.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 8064.
Gont, et al. Standards Track PAGE 1 
RFC 8064 Default Interface Identifiers February 2017
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Generation of IPv6 Interface Identifiers with SLAAC . . . . . 5
4. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
Gont, et al. Standards Track PAGE 2
RFC 8064 Default Interface Identifiers February 2017
1. Introduction
[RFC 4862] specifies Stateless Address Autoconfiguration (SLAAC) for
IPv6 [RFC 2460], which typically results in hosts configuring one or
more "stable" addresses composed of a network prefix advertised by a
local router, and an Interface Identifier (IID) [RFC 4291] that
typically embeds a stable link-layer address (e.g., an IEEE LAN MAC
address).
In some network technologies and adaptation layers, the use of an IID
based on a link-layer address may offer some advantages. For
example, [RFC 6282] allows for the compression of IPv6 datagrams over
IEEE 802.15.4-based networks [RFC 4944] when the IID is based on the
underlying link-layer address.
The security and privacy implications of embedding a stable link-
layer address in an IPv6 IID have been known for some time now and
are discussed in great detail in [RFC 7721]. They include:
o Network-activity correlation
o Location tracking
o Address scanning
o Device-specific vulnerability exploitation
More generally, the reuse of identifiers that have their own
semantics or properties across different contexts or scopes can be
detrimental for security and privacy [NUM-IDS]. In the case of
traditional stable IPv6 IIDs, some of the security and privacy
implications are dependent on the properties of the underlying link-
layer addresses (e.g., whether the link-layer address is ephemeral or
randomly generated), while other implications (e.g., reduction of the
entropy of the IID) depend on the algorithm for generating the IID
itself. In standardized recommendations for stable IPv6 IID
generation meant to achieve particular security and privacy
properties, it is necessary to recommend against embedding stable
link-layer addresses in IPv6 IIDs.
Furthermore, some popular IPv6 implementations have already deviated
from the traditional stable IID generation scheme to mitigate the
aforementioned security and privacy implications [Microsoft].
As a result of the aforementioned issues, this document changes the
recommended default IID generation scheme for generating stable IPv6
addresses with SLAAC to that specified in [RFC 7217] and recommends
against embedding stable link-layer addresses in IPv6 Interface
Gont, et al. Standards Track PAGE 3
RFC 8064 Default Interface Identifiers February 2017
Identifiers, such that the aforementioned issues are mitigated. That
is, this document simply replaces the default algorithm that is
recommended to be employed when generating stable IPv6 IIDs.
NOTE:
[RFC 4291] defines the "Modified EUI-64 format" for IIDs.
Appendix A of [RFC 4291] then describes how to transform an IEEE
EUI-64 identifier, or an IEEE 802 48-bit MAC address from which an
EUI-64 identifier is derived, into an IID in the Modified EUI-64
format.
In a variety of scenarios, addresses that remain stable for the
lifetime of a host's connection to a single subnet are viewed as
desirable. For example, stable addresses may be viewed as beneficial
for network management, event logging, enforcement of access control,
provision of quality of service, or for server or router interfaces.
Similarly, stable addresses (as opposed to temporary addresses
[RFC 4941]) allow for long-lived TCP connections and are also usually
desirable when performing server-like functions (i.e., receiving
incoming connections).
The recommendations in this document apply only in cases where
implementations otherwise would have configured a stable IPv6 IID
containing a link-layer address. For example, this document does not
change any existing recommendations concerning the use of temporary
addresses as specified in [RFC 4941] and the recommendations do not
apply to cases where SLAAC is employed to generate non-stable IPv6
addresses (e.g., by embedding a link-layer address that is
periodically randomized); in addition, this document does not
introduce any new requirements regarding when stable addresses are to
be configured. Thus, the recommendations in this document simply
improve the security and privacy properties of stable addresses.
2. Terminology
Stable address:
An address that does not vary over time within the same network
(as defined in [RFC 7721]).
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 [RFC 2119].
Gont, et al. Standards Track PAGE 4
RFC 8064 Default Interface Identifiers February 2017
3. Generation of IPv6 Interface Identifiers with SLAAC
Nodes SHOULD implement and employ [RFC 7217] as the default scheme for
generating stable IPv6 addresses with SLAAC. A link layer MAY also
define a mechanism for stable IPv6 address generation that is more
efficient and does not address the security and privacy
considerations discussed in Section 1. The choice of whether or not
to enable the security- and privacy-preserving mechanism SHOULD be
configurable in such a case.
By default, nodes SHOULD NOT employ IPv6 address generation schemes
that embed a stable link-layer address in the IID. In particular,
this document RECOMMENDS that nodes do not generate stable IIDs with
the schemes specified in [RFC 2464], [RFC 2467], [RFC 2470], [RFC 2491],
[RFC 2492], [RFC 2497], [RFC 2590], [RFC 3146], [RFC 3572], [RFC 4338],
[RFC 4391], [RFC 5072], and [RFC 5121].
4. Future Work
At the time of this writing, the mechanisms specified in the
following documents might require updates to be fully compatible with
the recommendations in this document:
o "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based
Networks" [RFC 6282]
o "Transmission of IPv6 Packets over IEEE 802.15.4 Networks"
[RFC 4944]
o "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless
Personal Area Networks (6LoWPANs)" [RFC 6775]
o "Transmission of IPv6 Packets over ITU-T G.9959 Networks"
[RFC 7428]
Future revisions or updates of these documents should consider the
issues of privacy and security mentioned in Section 1 and explain any
design and engineering considerations that lead to the use of stable
IIDs based on a node's link-layer address.
5. Security Considerations
This document recommends against the (default) use of predictable
Interface Identifiers in IPv6 addresses. It recommends [RFC 7217] as
the default scheme for generating IPv6 stable addresses with SLAAC,
such that the security and privacy issues of IIDs that embed stable
link-layer addresses are mitigated.
Gont, et al. Standards Track PAGE 5
RFC 8064 Default Interface Identifiers February 2017
6. References
6.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<http://www.rfc-editor.org/info/RFC 2119>.
[RFC 2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC 2460,
December 1998, <http://www.rfc-editor.org/info/RFC 2460>.
[RFC 2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC 2464, December 1998,
<http://www.rfc-editor.org/info/RFC 2464>.
[RFC 2467] Crawford, M., "Transmission of IPv6 Packets over FDDI
Networks", RFC 2467, DOI 10.17487/RFC 2467, December 1998,
<http://www.rfc-editor.org/info/RFC 2467>.
[RFC 2470] Crawford, M., Narten, T., and S. Thomas, "Transmission of
IPv6 Packets over Token Ring Networks", RFC 2470,
DOI 10.17487/RFC 2470, December 1998,
<http://www.rfc-editor.org/info/RFC 2470>.
[RFC 2491] Armitage, G., Schulter, P., Jork, M., and G. Harter,
"IPv6 over Non-Broadcast Multiple Access (NBMA)
networks", RFC 2491, DOI 10.17487/RFC 2491, January 1999,
<http://www.rfc-editor.org/info/RFC 2491>.
[RFC 2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM
Networks", RFC 2492, DOI 10.17487/RFC 2492, January 1999,
<http://www.rfc-editor.org/info/RFC 2492>.
[RFC 2497] Souvatzis, I., "Transmission of IPv6 Packets over ARCnet
Networks", RFC 2497, DOI 10.17487/RFC 2497, January 1999,
<http://www.rfc-editor.org/info/RFC 2497>.
[RFC 2590] Conta, A., Malis, A., and M. Mueller, "Transmission of
IPv6 Packets over Frame Relay Networks Specification",
RFC 2590, DOI 10.17487/RFC 2590, May 1999,
<http://www.rfc-editor.org/info/RFC 2590>.
[RFC 3146] Fujisawa, K. and A. Onoe, "Transmission of IPv6 Packets
over IEEE 1394 Networks", RFC 3146, DOI 10.17487/RFC 3146,
October 2001, <http://www.rfc-editor.org/info/RFC 3146>.
Gont, et al. Standards Track PAGE 6
RFC 8064 Default Interface Identifiers February 2017
[RFC 4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC 4291, February
2006, <http://www.rfc-editor.org/info/RFC 4291>.
[RFC 4338] DeSanti, C., Carlson, C., and R. Nixon, "Transmission of
IPv6, IPv4, and Address Resolution Protocol (ARP) Packets
over Fibre Channel", RFC 4338, DOI 10.17487/RFC 4338,
January 2006, <http://www.rfc-editor.org/info/RFC 4338>.
[RFC 4391] Chu, J. and V. Kashyap, "Transmission of IP over
InfiniBand (IPoIB)", RFC 4391, DOI 10.17487/RFC 4391,
April 2006, <http://www.rfc-editor.org/info/RFC 4391>.
[RFC 4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC 4862, September 2007,
<http://www.rfc-editor.org/info/RFC 4862>.
[RFC 4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC 4941, September 2007,
<http://www.rfc-editor.org/info/RFC 4941>.
[RFC 4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC 4944, September
2007, <http://www.rfc-editor.org/info/RFC 4944>.
[RFC 5072] Varada, S., Ed., Haskins, D., and E. Allen, "IP Version 6
over PPP", RFC 5072, DOI 10.17487/RFC 5072, September
2007, <http://www.rfc-editor.org/info/RFC 5072>.
[RFC 5121] Patil, B., Xia, F., Sarikaya, B., Choi, JH., and S.
Madanapalli, "Transmission of IPv6 via the IPv6
Convergence Sublayer over IEEE 802.16 Networks",
RFC 5121, DOI 10.17487/RFC 5121, February 2008,
<http://www.rfc-editor.org/info/RFC 5121>.
[RFC 6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC 6282, September 2011,
<http://www.rfc-editor.org/info/RFC 6282>.
[RFC 6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC 6775, November 2012,
<http://www.rfc-editor.org/info/RFC 6775>.
Gont, et al. Standards Track PAGE 7
RFC 8064 Default Interface Identifiers February 2017
[RFC 7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC 7217, April 2014,
<http://www.rfc-editor.org/info/RFC 7217>.
[RFC 7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets
over ITU-T G.9959 Networks", RFC 7428,
DOI 10.17487/RFC 7428, February 2015,
<http://www.rfc-editor.org/info/RFC 7428>.
6.2. Informative References
[Microsoft] Davies, J., "Understanding IPv6, 3rd. ed",
page 83, Microsoft Press, 2012,
<http://it-ebooks.info/book/1022/>.
[NUM-IDS] Gont, F. and I. Arce, "Security and Privacy Implications
of Numeric Identifiers Employed in Network Protocols",
Work in Progress, February 2016.
[RFC 3572] Ogura, T., Maruyama, M., and T. Yoshida, "Internet
Protocol Version 6 over MAPOS (Multiple Access Protocol
Over SONET/SDH)", RFC 3572, DOI 10.17487/RFC 3572, July
2003, <http://www.rfc-editor.org/info/RFC 3572>.
[RFC 7721] Cooper, A., Gont, F., and D. Thaler, "Security and
Privacy Considerations for IPv6 Address Generation
Mechanisms", RFC 7721, DOI 10.17487/RFC 7721, March 2016,
<http://www.rfc-editor.org/info/RFC 7721>.
Acknowledgements
The authors would like to thank (in alphabetical order) Bob Hinden,
Ray Hunter, and Erik Nordmark, for providing a detailed review of
this document.
The authors would like to thank (in alphabetical order) Fred Baker,
Carsten Bormann, Scott Brim, Brian Carpenter, Samita Chakrabarti, Tim
Chown, Lorenzo Colitti, Jean-Michel Combes, Greg Daley, Esko Dijk,
Ralph Droms, David Farmer, Brian Haberman, Ulrich Herberg, Philip
Homburg, Jahangir Hossain, Jonathan Hui, Christian Huitema, Ray
Hunter, Erik Kline, Sheng Jiang, Roger Jorgensen, Dan Luedtke, Kerry
Lynn, George Mitchel, Gabriel Montenegro, Erik Nordmark, Simon
Perreault, Tom Petch, Alexandru Petrescu, Michael Richardson, Arturo
Servin, Mark Smith, Tom Taylor, Ole Troan, Tina Tsou, Glen Turner,
Randy Turner, James Woodyatt, and Juan Carlos Zuniga, for providing
valuable comments on earlier draft versions of this document.
Gont, et al. Standards Track PAGE 8
RFC 8064 Default Interface Identifiers February 2017
Authors' Addresses
Fernando Gont
SI6 Networks / UTN-FRH
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
Email: fgont@si6networks.com
URI: https://www.si6networks.com
Alissa Cooper
Cisco
707 Tasman Drive
Milpitas, CA 95035
United States of America
Phone: +1-408-902-3950
Email: alcoop@cisco.com
URI: https://www.cisco.com/
Dave Thaler
Microsoft
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: +1 425 703 8835
Email: dthaler@microsoft.com
Will (Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
China
Email: liushucheng@huawei.com
Gont, et al. Standards Track PAGE 9
RFC TOTAL SIZE: 19179 bytes
PUBLICATION DATE: Wednesday, February 22nd, 2017
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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