Internet Engineering Task Force (IETF)
Request for Comments: 8064
Updates: 2464, 2467, 2470, 2491, 2492
Category: Standards Track
ISSN: 2070-1721
F. Gont
SI6 Networks / UTN-FRH
A. Cooper
2497, 2590, 3146, 3572, 4291, Cisco
4338, 4391, 5072, 5121 D. Thaler
W. Liu
Huawei Technologies
February 2017

Recommendation on Stable IPv6 Interface Identifiers


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

Copyright Notice

Copyright © 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 ( 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

1. Introduction

[RFC4862] specifies Stateless Address Autoconfiguration (SLAAC) for IPv6 [RFC2460], 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) [RFC4291] 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, [RFC6282] allows for the compression of IPv6 datagrams over IEEE 802.15.4-based networks [RFC4944] 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 [RFC7721]. They include:

  • Network-activity correlation
  • Location tracking
  • Address scanning
  • 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 [RFC7217] and recommends against embedding stable link-layer addresses in IPv6 Interface

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.


[RFC4291] defines the "Modified EUI-64 format" for IIDs. Appendix A of [RFC4291] 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 [RFC4941]) 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 [RFC4941] 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 [RFC7721]).

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 [RFC2119].

3. Generation of IPv6 Interface Identifiers with SLAAC

Nodes SHOULD implement and employ [RFC7217] 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 [RFC2464], [RFC2467], [RFC2470], [RFC2491],
   [RFC2492], [RFC2497], [RFC2590], [RFC3146], [RFC3572], [RFC4338],
   [RFC4391], [RFC5072], and [RFC5121].

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:

  • "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks" [RFC6282]
  • "Transmission of IPv6 Packets over IEEE 802.15.4 Networks" [RFC4944]
  • "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)" [RFC6775]
  • "Transmission of IPv6 Packets over ITU-T G.9959 Networks" [RFC7428]

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 [RFC7217] 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.

6. References

6.1. Normative References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119,
               DOI 10.17487/RFC2119, March 1997,
   [RFC2460]   Deering, S. and R. Hinden, "Internet Protocol, Version 6
               (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
               December 1998, <>.
   [RFC2464]   Crawford, M., "Transmission of IPv6 Packets over Ethernet
               Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
   [RFC2467]   Crawford, M., "Transmission of IPv6 Packets over FDDI
               Networks", RFC 2467, DOI 10.17487/RFC2467, December 1998,
   [RFC2470]   Crawford, M., Narten, T., and S. Thomas, "Transmission of
               IPv6 Packets over Token Ring Networks", RFC 2470,
               DOI 10.17487/RFC2470, December 1998,
   [RFC2491]   Armitage, G., Schulter, P., Jork, M., and G. Harter,
               "IPv6 over Non-Broadcast Multiple Access (NBMA)
               networks", RFC 2491, DOI 10.17487/RFC2491, January 1999,
   [RFC2492]   Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM
               Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999,
   [RFC2497]   Souvatzis, I., "Transmission of IPv6 Packets over ARCnet
               Networks", RFC 2497, DOI 10.17487/RFC2497, January 1999,
   [RFC2590]   Conta, A., Malis, A., and M. Mueller, "Transmission of
               IPv6 Packets over Frame Relay Networks Specification",
               RFC 2590, DOI 10.17487/RFC2590, May 1999,
   [RFC3146]   Fujisawa, K. and A. Onoe, "Transmission of IPv6 Packets
               over IEEE 1394 Networks", RFC 3146, DOI 10.17487/RFC3146,
               October 2001, <>.
   [RFC4291]   Hinden, R. and S. Deering, "IP Version 6 Addressing
               Architecture", RFC 4291, DOI 10.17487/RFC4291, February
               2006, <>.
   [RFC4338]   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/RFC4338,
               January 2006, <>.
   [RFC4391]   Chu, J. and V. Kashyap, "Transmission of IP over
               InfiniBand (IPoIB)", RFC 4391, DOI 10.17487/RFC4391,
               April 2006, <>.
   [RFC4862]   Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
               Address Autoconfiguration", RFC 4862,
               DOI 10.17487/RFC4862, September 2007,
   [RFC4941]   Narten, T., Draves, R., and S. Krishnan, "Privacy
               Extensions for Stateless Address Autoconfiguration in
               IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
   [RFC4944]   Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
               "Transmission of IPv6 Packets over IEEE 802.15.4
               Networks", RFC 4944, DOI 10.17487/RFC4944, September
               2007, <>.
   [RFC5072]   Varada, S., Ed., Haskins, D., and E. Allen, "IP Version 6
               over PPP", RFC 5072, DOI 10.17487/RFC5072, September
               2007, <>.
   [RFC5121]   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/RFC5121, February 2008,
   [RFC6282]   Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
               Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
               DOI 10.17487/RFC6282, September 2011,
   [RFC6775]   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/RFC6775, November 2012,
   [RFC7217]   Gont, F., "A Method for Generating Semantically Opaque
               Interface Identifiers with IPv6 Stateless Address
               Autoconfiguration (SLAAC)", RFC 7217,
               DOI 10.17487/RFC7217, April 2014,
   [RFC7428]   Brandt, A. and J. Buron, "Transmission of IPv6 Packets
               over ITU-T G.9959 Networks", RFC 7428,
               DOI 10.17487/RFC7428, February 2015,

6.2. Informative References

   [Microsoft] Davies, J., "Understanding IPv6, 3rd. ed",
               page 83, Microsoft Press, 2012,
   [NUM-IDS]   Gont, F. and I. Arce, "Security and Privacy Implications
               of Numeric Identifiers Employed in Network Protocols",
               Work in Progress, February 2016.
   [RFC3572]   Ogura, T., Maruyama, M., and T. Yoshida, "Internet
               Protocol Version 6 over MAPOS (Multiple Access Protocol
               Over SONET/SDH)", RFC 3572, DOI 10.17487/RFC3572, July
               2003, <>.
   [RFC7721]   Cooper, A., Gont, F., and D. Thaler, "Security and
               Privacy Considerations for IPv6 Address Generation
               Mechanisms", RFC 7721, DOI 10.17487/RFC7721, March 2016,


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.

Authors' Addresses

   Fernando Gont
   SI6 Networks / UTN-FRH
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706
   Phone: +54 11 4650 8472
   Alissa Cooper
   707 Tasman Drive
   Milpitas, CA  95035
   United States of America
   Phone: +1-408-902-3950
   Dave Thaler
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052
   Phone: +1 425 703 8835
   Will (Shucheng) Liu
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129