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Independent Submission                                      B. CarpenterRequest for Comments: 8136                             Univ. of AucklandCategory: Informational                                        R. HindenISSN: 2070-1721                                     Check Point Software                                                            1 April 2017Additional Transition Functionality for IPv6Abstract   This document proposes an additional mechanism intended to both   facilitate transition from IPv4 to IPv6 and improve the latter's   security and privacy.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This is a contribution to the RFC Series, independently of any other   RFC stream.  The RFC Editor has chosen to publish this document at   its discretion and makes no statement about its value for   implementation or deployment.  Documents approved for publication by   the RFC Editor are not a candidate for any level of Internet   Standard; seeSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc8136.Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Carpenter & Hinden            Informational                     [Page 1]

RFC 8136        Additional IPv6 Transition Functionality    1 April 2017Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .21.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .22.  Required Function of All IPv4 Nodes . . . . . . . . . . . . .23.  Security Flag for IPv6 Packets  . . . . . . . . . . . . . . .34.  Advanced Solution . . . . . . . . . . . . . . . . . . . . . .44.1.  Privacy Extension . . . . . . . . . . . . . . . . . . . .45.  Security Considerations . . . . . . . . . . . . . . . . . . .56.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .57.  References  . . . . . . . . . . . . . . . . . . . . . . . . .57.1.  Normative References  . . . . . . . . . . . . . . . . . .57.2.  Informative References  . . . . . . . . . . . . . . . . .6   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .71.  Introduction   In a recent statement [IABv6], the Internet Architecture Board deemed   that the Internet Engineering Task Force is expected to "stop   requiring IPv4 compatibility in new or extended protocols" and that   future work will "optimize for and depend on IPv6".  In the interest   of promoting these goals, this memo makes an important change to IPv4   node requirements [RFC1122] and adds a missing security feature to   IPv6 [RFC2460].1.1.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are not to be interpreted as described in   [RFC2119].2.  Required Function of All IPv4 Nodes   To ensure that all routers, firewalls, load balancers, and other   forms of middleboxes can readily identify IPv4 packets and deal with   them appropriately (selective dropping, switching to the slow path   through a router, sending them to the longest path first, etc.), all   IPv4 nodes MUST set the security flag defined by [RFC3514] to 1.   This should be sufficient to ensure that implementers of dual stack   applications prefer IPv6 when given the choice, and that the Happy   Eyeballs algorithm [RFC6555] will usually favour the IPv6 path.Carpenter & Hinden            Informational                     [Page 2]

RFC 8136        Additional IPv6 Transition Functionality    1 April 20173.  Security Flag for IPv6 Packets   The above requirement will somewhat nullify the practical effect of   the IPv4 security flag for benign traffic, but this disadvantage can   readily be overcome by adding an equivalent flag for IPv6; in fact,   this is highly desirable to maintain feature equivalence between IPv4   and IPv6.  Fortunately, this can easily be achieved since IPv6   supplies so many bits.  The solution defined here is that the   Security Flag bit for an IPv6 packet is simply the parity of the   source address of the packet.  In other words, if the source address   contains an odd number of 1s, the flag is True; otherwise, it's   False.  All other considerations for the flag are exactly as   described in [RFC3514].   For an interface whose IPv6 address is set by Stateless Address   Autoconfiguration [RFC4862], it is the host itself that determines   the state of its security flag, by choosing an appropriate Interface   Identifier value.  Fortunately this is now possible and compatible   with [RFC7136], [RFC7217], [RFC7421], and [RFC7721].   For an interface whose IPv6 address is set by DHCPv6 [RFC3315] or   manually, the network administrator is free to choose an Interface   Identifier that provides the desired security flag that is also   compatible with [RFC7721].   An exception case is a link with a 127-bit prefix [RFC6164].  Since   there is only one bit available as an Interface Identifier, one end   or the other will inevitably have its security flag set, and the   other won't.  In this case, the node at one end will simply interpret   the other end's security flag to mean the opposite of what it says,   and vice versa.   SinceRFC 6164 is designed for links between routers, in the case   where different ISPs are at each end of the link, it is normal   operational practice for one ISP to consider the other ISP to be   evil.Carpenter & Hinden            Informational                     [Page 3]

RFC 8136        Additional IPv6 Transition Functionality    1 April 20174.  Advanced Solution   In the event that the previous solution proves too simple to deploy   in practice, a more advanced solution is also defined.  It uses a new   IPv6 hop-by-hop User Security Flag Option (UFO).   The UFO is a hop-by-hop option that can be included in any IPv6   packet.  Multiple UFOs MUST NOT be present in the packet.  The UFO   has no alignment requirement.  Its format is as follows:     0                   1                   2                   3     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1                                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                    |  Option Type  | Option Length |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    | UserSecFlag   |    +-+-+-+-+-+-+-+-+                  User Security Flag Option Layout     Option Type        8-bit identifier of the type of option.  The option identifier        for the User Security Flag Option (0x7g) has not been allocated        by the IANA.     Option Length        8-bit unsigned integer.  The length of the option (excluding the        Option Type and Option Length fields).  The value MUST be 1.     UserSecFlag        8-bit unsigned integer.  Bit 0 has the functionality defined in        [RFC3514].  The other bits are reserved and MUST be zero or one.4.1.  Privacy Extension   The mechanism can be extended to add a privacy flag.  With the   mechanism ofSection 3, the privacy flag could be encoded by using   quaternary parity (CRC-2) to obtain an extra bit.  However, this   would waste considerable amounts of address space and SHOULD NOT be   done.  With the UFO mechanism, bit 1 of UserSecFlag is defined as the   privacy flag.  If set, it means that the packet contains private   information and MUST NOT be inspected en route.  All firewalls,   monitoring devices, and government agencies MUST respect this rule.   This option is expected to be much more computationally efficientCarpenter & Hinden            Informational                     [Page 4]

RFC 8136        Additional IPv6 Transition Functionality    1 April 2017   than conventional privacy techniques like IPsec and Transport Layer   Security (TLS) as no encryption or key management is required to   achieve the desired privacy.5.  Security Considerations   The security considerations of [RFC3514] now apply to IPv6.  However,   with the security flag being set for all IPv4 packets, there is a   risk that all IPv4 traffic will now be treated as a very distributed   denial-of-service attack.   Given the recent experience with very large scale DDoS attacks from   Internet of Things (IoT) devices like IP Cameras, phishing attacks,   malware, etc., that occur on the IPv4 Internet, it is a safe   assumption that all IPv4 packets are evil.   Since the mechanism described inSection 3 is compatible with   [RFC7721], address privacy is not impacted.  Also, with that   mechanism, exactly half the IPv6 address space will indicate that the   security flag is set, so we can assert that the IPv6 Internet is only   half evil.6.  IANA Considerations   This document does not require any IANA actions.7.  References7.1.  Normative References   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -              Communication Layers", STD 3,RFC 1122,              DOI 10.17487/RFC1122, October 1989,              <http://www.rfc-editor.org/info/rfc1122>.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6              (IPv6) Specification",RFC 2460, DOI 10.17487/RFC2460,              December 1998, <http://www.rfc-editor.org/info/rfc2460>.Carpenter & Hinden            Informational                     [Page 5]

RFC 8136        Additional IPv6 Transition Functionality    1 April 2017   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,              C., and M. Carney, "Dynamic Host Configuration Protocol              for IPv6 (DHCPv6)",RFC 3315, DOI 10.17487/RFC3315, July              2003, <http://www.rfc-editor.org/info/rfc3315>.   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless              Address Autoconfiguration",RFC 4862,              DOI 10.17487/RFC4862, September 2007,              <http://www.rfc-editor.org/info/rfc4862>.   [RFC6164]  Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,              L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-              Router Links",RFC 6164, DOI 10.17487/RFC6164, April 2011,              <http://www.rfc-editor.org/info/rfc6164>.   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with              Dual-Stack Hosts",RFC 6555, DOI 10.17487/RFC6555, April              2012, <http://www.rfc-editor.org/info/rfc6555>.   [RFC7136]  Carpenter, B. and S. Jiang, "Significance of IPv6              Interface Identifiers",RFC 7136, DOI 10.17487/RFC7136,              February 2014, <http://www.rfc-editor.org/info/rfc7136>.   [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,              <http://www.rfc-editor.org/info/rfc7217>.7.2.  Informative References   [IABv6]    IAB, "IAB Statement on IPv6", November 2016,              <https://www.iab.org/2016/11/07/iab-statement-on-ipv6/>.   [RFC3514]  Bellovin, S., "The Security Flag in the IPv4 Header",RFC 3514, DOI 10.17487/RFC3514, April 2003,              <http://www.rfc-editor.org/info/rfc3514>.   [RFC7421]  Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S.,              Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit              Boundary in IPv6 Addressing",RFC 7421,              DOI 10.17487/RFC7421, January 2015,              <http://www.rfc-editor.org/info/rfc7421>.   [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,              <http://www.rfc-editor.org/info/rfc7721>.Carpenter & Hinden            Informational                     [Page 6]

RFC 8136        Additional IPv6 Transition Functionality    1 April 2017Authors' Addresses   Brian Carpenter   Department of Computer Science   University of Auckland   PB 92019   Auckland  1142   New Zealand   Email: brian.e.carpenter@gmail.com   Robert M.  Hinden   Check Point Software   959 Skyway Road   San Carlos  CA 94070   United States of America   Email: bob.hinden@gmail.comCarpenter & Hinden            Informational                     [Page 7]