IPWAVE Working Group N. Benamar
Internet-Draft Moulay Ismail University
Intended status: Standards Track J. Haerri
Expires: October 25, 2019 Eurecom
J. Lee
Sangmyung University
T. Ernst
April 23, 2019

Transmission of IPv6 Packets over IEEE 802.11 Networks operating in mode Outside the Context of a Basic Service Set (IPv6-over-80211-OCB)


In order to transmit IPv6 packets on IEEE 802.11 networks running outside the context of a basic service set (OCB, earlier "802.11p") there is a need to define a few parameters such as the supported Maximum Transmission Unit size on the 802.11-OCB link, the header format preceding the IPv6 header, the Type value within it, and others. This document describes these parameters for IPv6 and IEEE 802.11-OCB networks; it portrays the layering of IPv6 on 802.11-OCB similarly to other known 802.11 and Ethernet layers - by using an Ethernet Adaptation Layer.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on October 25, 2019.

Copyright Notice

Copyright (c) 2019 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 (https://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

This document describes the transmission of IPv6 packets on IEEE Std 802.11-OCB networks [IEEE-802.11-2016] (a.k.a "802.11p" see Appendix B, Appendix C and Appendix D). This involves the layering of IPv6 networking on top of the IEEE 802.11 MAC layer, with an LLC layer. Compared to running IPv6 over the Ethernet MAC layer, there is no modification expected to IEEE Std 802.11 MAC and Logical Link sublayers: IPv6 works fine directly over 802.11-OCB too, with an LLC layer.

The IPv6 network layer operates on 802.11-OCB in the same manner as operating on Ethernet, but there are two kinds of exceptions:

In the published literature, many documents describe aspects and problems related to running IPv6 over 802.11-OCB: [I-D.ietf-ipwave-vehicular-networking].

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

IP-OBU (Internet Protocol On-Board Unit): an IP-OBU is a computer situated in a vehicle such as an automobile, bicycle, or similar. It has at least one IP interface that runs in mode OCB of 802.11, and that has an "OBU" transceiver. See the definition of the term "OBU" in section Appendix I.

IP-RSU (IP Road-Side Unit): an IP-RSU is situated along the road. It has at least two distinct IP-enabled interfaces; the wireless PHY/MAC layer of at least one of its IP-enabled interfaces is configured to operate in 802.11-OCB mode. An IP-RSU communicates with the IP-OBU in the vehicle over 802.11 wireless link operating in OCB mode. An IP-RSU is similar to an Access Network Router (ANR) defined in [RFC3753], and a Wireless Termination Point (WTP) defined in [RFC5415].

OCB (outside the context of a basic service set - BSS): A mode of operation in which a STA is not a member of a BSS and does not utilize IEEE Std 802.11 authentication, association, or data confidentiality.

802.11-OCB: mode specified in IEEE Std 802.11-2016 when the MIB attribute dot11OCBActivited is true. Note: compliance with standards and regulations set in different countries when using the 5.9GHz frequency band is required.

3. Communication Scenarios where IEEE 802.11-OCB Links are Used

The IEEE 802.11-OCB Networks are used for vehicular communications, as 'Wireless Access in Vehicular Environments'. The IP communication scenarios for these environments have been described in several documents; in particular, we refer the reader to [I-D.ietf-ipwave-vehicular-networking], that lists some scenarios and requirements for IP in Intelligent Transportation Systems.

The link model is the following: STA --- 802.11-OCB --- STA. In vehicular networks, STAs can be IP-RSUs and/or IP-OBUs. While 802.11-OCB is clearly specified, and the use of IPv6 over such link is not radically new, the operating environment (vehicular networks) brings in new perspectives.

4. IPv6 over 802.11-OCB

4.1. Maximum Transmission Unit (MTU)

The default MTU for IP packets on 802.11-OCB MUST be 1500 octets. It is the same value as IPv6 packets on Ethernet links, as specified in [RFC2464]. This value of the MTU respects the recommendation that every link on the Internet must have a minimum MTU of 1280 octets (stated in [RFC8200], and the recommendations therein, especially with respect to fragmentation).

4.2. Frame Format

IP packets MUST be transmitted over 802.11-OCB media as QoS Data frames whose format is specified in IEEE 802.11(TM) -2016 [IEEE-802.11-2016].

The IPv6 packet transmitted on 802.11-OCB MUST be immediately preceded by a Logical Link Control (LLC) header and an 802.11 header. In the LLC header, and in accordance with the EtherType Protocol Discrimination (EPD, see Appendix E), the value of the Type field MUST be set to 0x86DD (IPv6). In the 802.11 header, the value of the Subtype sub-field in the Frame Control field MUST be set to 8 (i.e. 'QoS Data'); the value of the Traffic Identifier (TID) sub-field of the QoS Control field of the 802.11 header MUST be set to binary 001 (i.e. User Priority 'Background', QoS Access Category 'AC_BK').

To simplify the Application Programming Interface (API) between the operating system and the 802.11-OCB media, device drivers MAY implement an Ethernet Adaptation Layer that translates Ethernet II frames to the 802.11 format and vice versa. An Ethernet Adaptation Layer is described in Section 4.2.1.

4.2.1. Ethernet Adaptation Layer

An 'adaptation' layer is inserted between a MAC layer and the Networking layer. This is used to transform some parameters between their form expected by the IP stack and the form provided by the MAC layer.

An Ethernet Adaptation Layer makes an 802.11 MAC look to IP Networking layer as a more traditional Ethernet layer. At reception, this layer takes as input the IEEE 802.11 header and the Logical-Link Layer Control Header and produces an Ethernet II Header. At sending, the reverse operation is performed.

The operation of the Ethernet Adaptation Layer is depicted by the double arrow in Figure 1.

|  802.11 header   | LLC Header | IPv6 Header | Payload |.11 Trailer|
 \                             /                         \         /
   ---------------------------                             --------
           802.11-to-Ethernet Adaptation Layer
| Ethernet II Header  | IPv6 Header | Payload |

Figure 1: Operation of the Ethernet Adaptation Layer

The Receiver and Transmitter Address fields in the 802.11 header MUST contain the same values as the Destination and the Source Address fields in the Ethernet II Header, respectively. The value of the Type field in the LLC Header MUST be the same as the value of the Type field in the Ethernet II Header. That value MUST be set to 0x86DD (IPv6).

The ".11 Trailer" contains solely a 4-byte Frame Check Sequence.

The placement of IPv6 networking layer on Ethernet Adaptation Layer is illustrated in Figure 2.

 |                 IPv6                  |
 |       Ethernet Adaptation Layer       |
 |             802.11 MAC                |
 |             802.11 PHY                |

Figure 2: Ethernet Adaptation Layer stacked with other layers

(in the above figure, a 802.11 profile is represented; this is used also for 802.11-OCB profile.)

4.3. Link-Local Addresses

There are several types of IPv6 addresses [RFC4291], [RFC4193], that MAY be assigned to an 802.11-OCB interface. Among these types of addresses only the IPv6 link-local addresses MAY be formed using an EUI-64 identifier, in particular during transition time.

If the IPv6 link-local address is formed using an EUI-64 identifier, then the mechanism of forming that address is the same mechanism as used to form an IPv6 link-local address on Ethernet links. This mechanism is described in section 5 of [RFC2464].

4.4. Stateless Autoconfiguration

There are several types of IPv6 addresses [RFC4291], [RFC4193], that MAY be assigned to an 802.11-OCB interface. This section describes the formation of Interface Identifiers for IPv6 addresses of type 'Global' or 'Unique Local'. For Interface Identifiers for IPv6 address of type 'Link-Local' see Section 4.3.

The Interface Identifier for an 802.11-OCB interface is formed using the same rules as the Interface Identifier for an Ethernet interface; the RECOMMENDED method for forming stable Interface Identifiers (IIDs) is described in [RFC8064]. The method of forming IIDs described in section 4 of [RFC2464] MAY be used during transition time, in particular for IPv6 link-local addresses.

The bits in the Interface Identifier have no generic meaning and the identifier should be treated as an opaque value. The bits 'Universal' and 'Group' in the identifier of an 802.11-OCB interface are significant, as this is an IEEE link-layer address. The details of this significance are described in [RFC7136].

Semantically opaque Interface Identifiers, instead of meaningful Interface Identifiers derived from a valid and meaningful MAC address ([RFC2464], section 4), help avoid certain privacy risks (see the risks mentioned in Section 5.1.1). If semantically opaque Interface Identifiers are needed, they MAY be generated using the method for generating semantically opaque Interface Identifiers with IPv6 Stateless Address Autoconfiguration given in [RFC7217]. Typically, an opaque Interface Identifier is formed starting from identifiers different than the MAC addresses, and from cryptographically strong material. Thus, privacy sensitive information is absent from Interface IDs, because it is impossible to calculate back the initial value from which the Interface ID was first generated (intuitively, it is as hard as mentally finding the square root of a number, and as impossible as trying to use computers to identify quickly whether a large number is prime).

Some applications that use IPv6 packets on 802.11-OCB links (among other link types) may benefit from IPv6 addresses whose Interface Identifiers don't change too often. It is RECOMMENDED to use the mechanisms described in RFC 7217 to permit the use of Stable Interface Identifiers that do not change within one subnet prefix. A possible source for the Net-Iface Parameter is a virtual interface name, or logical interface name, that is decided by a local administrator.

4.5. Address Mapping

Unicast and multicast address mapping MUST follow the procedures specified for Ethernet interfaces in sections 6 and 7 of [RFC2464].

4.5.1. Address Mapping -- Unicast

The procedure for mapping IPv6 unicast addresses into Ethernet link-layer addresses is described in [RFC4861].

4.5.2. Address Mapping -- Multicast

The multicast address mapping is performed according to the method specified in section 7 of [RFC2464]. The meaning of the value "3333" mentioned in that section 7 of [RFC2464] is defined in section 2.3.1 of [RFC7042].

Transmitting IPv6 packets to multicast destinations over 802.11 links proved to have some performance issues [I-D.ietf-mboned-ieee802-mcast-problems]. These issues may be exacerbated in OCB mode. Solutions for these problems SHOULD consider the OCB mode of operation.

4.6. Subnet Structure

A subnet is formed by the external 802.11-OCB interfaces of vehicles that are in close range (not by their in-vehicle interfaces). A Prefix List conceptual data structure ([RFC4861] section 5.1) is maintained for each 802.11-OCB interface.

The subnet structure on which the Neighbor Discovery protocol (ND) on OCB works ok is a single-link subnet; the status of ND operation on a subnet that covers multiple OCB links that repeat the signal at PHY layer, or the messages at MAC layer, is unknown.

The structure of this subnet is ephemeral, in that it is strongly influenced by the mobility of vehicles: the hidden terminal effects appear; the 802.11 networks in OCB mode may be considered as 'ad-hoc' networks with an addressing model as described in [RFC5889]. On another hand, the structure of the internal subnets in each car is relatively stable.

As recommended in [RFC5889], when the timing requirements are very strict (e.g. fast drive through IP-RSU coverage), no on-link subnet prefix should be configured on an 802.11-OCB interface. In such cases, the exclusive use of IPv6 link-local addresses is RECOMMENDED.

Additionally, even if the timing requirements are not very strict (e.g. the moving subnet formed by two following vehicles is stable, a fixed IP-RSU is absent), the subnet is disconnected from the Internet (a default route is absent), and the addressing peers are equally qualified (impossible to determine that some vehicle owns and distributes addresses to others) the use of link-local addresses is RECOMMENDED.

The baseline Neighbor Discovery protocol (ND) [RFC4861] MUST be used over 802.11-OCB links. Transmitting ND packets may prove to have some performance issues. These issues may be exacerbated in OCB mode. Solutions for these problems SHOULD consider the OCB mode of operation. The best of current knowledge indicates the kinds of issues that may arise with ND in OCB mode; they are described in Appendix J.

Protocols like Mobile IPv6 [RFC6275] and DNAv6 [RFC6059], which depend on timely movement detection, might need additional tuning work to handle the lack of link-layer notifications during handover. This is for further study.

5. Security Considerations

Any security mechanism at the IP layer or above that may be carried out for the general case of IPv6 may also be carried out for IPv6 operating over 802.11-OCB.

The OCB operation is stripped off of all existing 802.11 link-layer security mechanisms. There is no encryption applied below the network layer running on 802.11-OCB. At application layer, the IEEE 1609.2 document [IEEE-1609.2] does provide security services for certain applications to use; application-layer mechanisms are out-of-scope of this document. On another hand, a security mechanism provided at networking layer, such as IPsec [RFC4301], may provide data security protection to a wider range of applications.

802.11-OCB does not provide any cryptographic protection, because it operates outside the context of a BSS (no Association Request/Response, no Challenge messages). Any attacker can therefore just sit in the near range of vehicles, sniff the network (just set the interface card's frequency to the proper range) and perform attacks without needing to physically break any wall. Such a link is less protected than commonly used links (wired link or protected 802.11).

The potential attack vectors are: MAC address spoofing, IP address and session hijacking, and privacy violation Section 5.1.

Within the IPsec Security Architecture [RFC4301], the IPsec AH and ESP headers [RFC4302] and [RFC4303] respectively, its multicast extensions [RFC5374], HTTPS [RFC2818] and SeND [RFC3971] protocols can be used to protect communications. Further, the assistance of proper Public Key Infrastructure (PKI) protocols [RFC4210] is necessary to establish credentials. More IETF protocols are available in the toolbox of the IP security protocol designer. Certain ETSI protocols related to security protocols in Intelligent Transportation Systems are described in [ETSI-sec-archi].

5.1. Privacy Considerations

As with all Ethernet and 802.11 interface identifiers ([RFC7721]), the identifier of an 802.11-OCB interface may involve privacy, MAC address spoofing and IP address hijacking risks. A vehicle embarking an IP-OBU whose egress interface is 802.11-OCB may expose itself to eavesdropping and subsequent correlation of data; this may reveal data considered private by the vehicle owner; there is a risk of being tracked. In outdoors public environments, where vehicles typically circulate, the privacy risks are more important than in indoors settings. It is highly likely that attacker sniffers are deployed along routes which listen for IEEE frames, including IP packets, of vehicles passing by. For this reason, in the 802.11-OCB deployments, there is a strong necessity to use protection tools such as dynamically changing MAC addresses Section 5.2, semantically opaque Interface Identifiers and stable Interface Identifiers Section 4.4. This may help mitigate privacy risks to a certain level.

5.1.1. Privacy Risks of Meaningful info in Interface IDs

The privacy risks of using MAC addresses displayed in Interface Identifiers are important. The IPv6 packets can be captured easily in the Internet and on-link in public roads. For this reason, an attacker may realize many attacks on privacy. One such attack on 802.11-OCB is to capture, store and correlate Company ID information present in MAC addresses of many cars (e.g. listen for Router Advertisements, or other IPv6 application data packets, and record the value of the source address in these packets). Further correlation of this information with other data captured by other means, or other visual information (car color, others) MAY constitute privacy risks.

5.2. MAC Address and Interface ID Generation

In 802.11-OCB networks, the MAC addresses MAY change during well defined renumbering events. In the moment the MAC address is changed on an 802.11-OCB interface all the Interface Identifiers of IPv6 addresses assigned to that interface MUST change.

The policy dictating when the MAC address is changed on the 802.11-OCB interface is to-be-determined. For more information on the motivation of this policy please refer to the privacy discussion in Appendix C.

A 'randomized' MAC address has the following characteristics:

To meet the randomization requirements for the 46 remaining bits, a hash function may be used. For example, the SHA256 hash function may be used with input a 256 bit local secret, the 'nominal' MAC Address of the interface, and a representation of the date and time of the renumbering event.

A randomized Interface ID has the same characteristics of a randomized MAC address, except the length in bits. An Interface ID SHOULD be of length specified in other documents.

5.3. Pseudonym Handling

The demand for privacy protection of vehicles' and drivers' identities, which could be granted by using a pseudonym or alias identity at the same time, may hamper the required confidentiality of messages and trust between participants - especially in safety critical vehicular communication.

6. IANA Considerations

No request to IANA.

7. Contributors

Christian Huitema, Tony Li.

Romain Kuntz contributed extensively about IPv6 handovers between links running outside the context of a BSS (802.11-OCB links).

Tim Leinmueller contributed the idea of the use of IPv6 over 802.11-OCB for distribution of certificates.

Marios Makassikis, Jose Santa Lozano, Albin Severinson and Alexey Voronov provided significant feedback on the experience of using IP messages over 802.11-OCB in initial trials.

Michelle Wetterwald contributed extensively the MTU discussion, offered the ETSI ITS perspective, and reviewed other parts of the document.

8. Acknowledgements

The authors would like to thank Alexandre Petrescu for initiating this work and for being the lead author until the version 43 of this draft.

The authors would like to thank Witold Klaudel, Ryuji Wakikawa, Emmanuel Baccelli, John Kenney, John Moring, Francois Simon, Dan Romascanu, Konstantin Khait, Ralph Droms, Richard 'Dick' Roy, Ray Hunter, Tom Kurihara, Michal Sojka, Jan de Jongh, Suresh Krishnan, Dino Farinacci, Vincent Park, Jaehoon Paul Jeong, Gloria Gwynne, Hans-Joachim Fischer, Russ Housley, Rex Buddenberg, Erik Nordmark, Bob Moskowitz, Andrew Dryden, Georg Mayer, Dorothy Stanley, Sandra Cespedes, Mariano Falcitelli, Sri Gundavelli, Abdussalam Baryun, Margaret Cullen, Erik Kline, Carlos Jesus Bernardos Cano, Ronald in 't Velt, Katrin Sjoberg, Roland Bless, Tijink Jasja, Kevin Smith, Brian Carpenter, Julian Reschke, Mikael Abrahamsson, Dirk von Hugo, Lorenzo Colitti, Pascal Thubert, Ole Troan, Jinmei Tatuya, Joel Halpern, Eric Gray and William Whyte. Their valuable comments clarified particular issues and generally helped to improve the document.

Pierre Pfister, Rostislav Lisovy, and others, wrote 802.11-OCB drivers for linux and described how.

For the multicast discussion, the authors would like to thank Owen DeLong, Joe Touch, Jen Linkova, Erik Kline, Brian Haberman and participants to discussions in network working groups.

The authors would like to thank participants to the Birds-of-a-Feather "Intelligent Transportation Systems" meetings held at IETF in 2016.

Human Rights Protocol Considerations review by Amelia Andersdotter.

9. References

9.1. Normative References

[RFC1042] Postel, J. and J. Reynolds, "Standard for the transmission of IP datagrams over IEEE 802 networks", STD 43, RFC 1042, DOI 10.17487/RFC1042, February 1988.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/RFC2818, May 2000.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology", RFC 3753, DOI 10.17487/RFC3753, June 2004.
[RFC3971] Arkko, J., Kempf, J., Zill, B. and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, DOI 10.17487/RFC3971, March 2005.
[RFC4086] Eastlake 3rd, D., Schiller, J. and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, June 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005.
[RFC4210] Adams, C., Farrell, S., Kause, T. and T. Mononen, "Internet X.509 Public Key Infrastructure Certificate Management Protocol (CMP)", RFC 4210, DOI 10.17487/RFC4210, September 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 10.17487/RFC4302, December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, DOI 10.17487/RFC4303, December 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W. and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007.
[RFC5374] Weis, B., Gross, G. and D. Ignjatic, "Multicast Extensions to the Security Architecture for the Internet Protocol", RFC 5374, DOI 10.17487/RFC5374, November 2008.
[RFC5415] Calhoun, P., Montemurro, M. and D. Stanley, "Control And Provisioning of Wireless Access Points (CAPWAP) Protocol Specification", RFC 5415, DOI 10.17487/RFC5415, March 2009.
[RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889, September 2010.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for Detecting Network Attachment in IPv6", RFC 6059, DOI 10.17487/RFC6059, November 2010.
[RFC6275] Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2011.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and IETF Protocol and Documentation Usage for IEEE 802 Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042, October 2013.
[RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6 Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136, February 2014.
[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.
[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.
[RFC8064] Gont, F., Cooper, A., Thaler, D. and W. Liu, "Recommendation on Stable IPv6 Interface Identifiers", RFC 8064, DOI 10.17487/RFC8064, February 2017.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017.

9.2. Informative References

[ETSI-sec-archi] "ETSI TS 102 940 V1.2.1 (2016-11), ETSI Technical Specification, Intelligent Transport Systems (ITS); Security; ITS communications security architecture and security management, November 2016. Downloaded on September 9th, 2017, freely available from ETSI website at URL http://www.etsi.org/deliver/etsi_ts/102900_102999/102940/01.02.01_60/ts_102940v010201p.pdf"
[I-D.ietf-ipwave-vehicular-networking] Jeong, J., "IP Wireless Access in Vehicular Environments (IPWAVE): Problem Statement and Use Cases", Internet-Draft draft-ietf-ipwave-vehicular-networking-08, March 2019.
[I-D.ietf-mboned-ieee802-mcast-problems] Perkins, C., McBride, M., Stanley, D., Kumari, W. and J. Zuniga, "Multicast Considerations over IEEE 802 Wireless Media", Internet-Draft draft-ietf-mboned-ieee802-mcast-problems-05, April 2019.
[IEEE-1609.2] "IEEE SA - 1609.2-2016 - IEEE Standard for Wireless Access in Vehicular Environments (WAVE) -- Security Services for Applications and Management Messages. Example URL http://ieeexplore.ieee.org/document/7426684/ accessed on August 17th, 2017."
[IEEE-1609.3] "IEEE SA - 1609.3-2016 - IEEE Standard for Wireless Access in Vehicular Environments (WAVE) -- Networking Services. Example URL http://ieeexplore.ieee.org/document/7458115/ accessed on August 17th, 2017."
[IEEE-1609.4] "IEEE SA - 1609.4-2016 - IEEE Standard for Wireless Access in Vehicular Environments (WAVE) -- Multi-Channel Operation. Example URL http://ieeexplore.ieee.org/document/7435228/ accessed on August 17th, 2017."
[IEEE-802.11-2016] "IEEE Standard 802.11-2016 - IEEE Standard for Information Technology - Telecommunications and information exchange between systems Local and metropolitan area networks - Specific requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Status - Active Standard. Description retrieved freely; the document itself is also freely available, but with some difficulty (requires registration); description and document retrieved on April 8th, 2019, starting from URL https://standards.ieee.org/findstds/standard/802.11-2016.html"
[IEEE-802.11p-2010] "IEEE Std 802.11p (TM)-2010, IEEE Standard for Information Technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, Amendment 6: Wireless Access in Vehicular Environments; document freely available at URL http://standards.ieee.org/getieee802/download/802.11p-2010.pdf retrieved on September 20th, 2013."

Appendix A. ChangeLog

The changes are listed in reverse chronological order, most recent changes appearing at the top of the list.

-43: removed the SHOULD 48bit of a MAC address, just stay silent about it; corrected 'global' address to 'Globally Reachable address'; added a paragraph scoping IPv6-over-OCB ND to work ok on single-link subnets.

-42: removed 118 len IID; points to 'other documents' for the length of Interface ID; removed 'directly using' phrase for LLs in a subnet.

-41: updated a reference from draft-ietf-ipwave-vehicular-networking-survey to draft-ietf-ipwave-vehicular-networking; clarified the link-local text by eliminating link-local addresses and prefixes altogether and referring to RFC4861 which requires the prefixes; added a statement about the subnet being a not multi-link subnet.

-40: added a phrase in appendix to further described a condition where ND on OCB may not work; that phrase contains a placeholder; the placeholder is 'TBD' (To Be Defined).

-39: removed a reference to an expired draft trying to update the IPv6-over-Ethernet spec 'RFC2464bis'; added text in the subnet structure section saying nodes MUST be able to communicate directly using their link-local addresses.

-38: removed the word "fe80::/10".

-37: added a section about issues on ND wireless; added the qualifier 'baseline' to using ND on 802.11-OCB; improved the description of the reference to 802.11-2016 document, with a qualifier about the difficulty of accessing it, even though it is free.

-36: removed a phrase about the IID formation and MAC generation, but left in the section 5.2 that describes how it happens.

-35: addressing the the intarea review: clarified a small apparent contradiction between two parts of text that use the old MAC-based IIDs (clarified by using qualifiers from each other: transition time, and ll addresses); sequenced closer the LL and Stateless Autoconf sections, instead of spacing them; shortened the paragraph of Opaque IIDs; moved the privacy risks of in-clear IIDs in the security section; removed a short phrase duplicating the idea of privacy risks; added third time a reference to the 802.11-2016 document; used 'the hidden terminal' text; updated the Terminology section with new BCP-14 text 'MUST' to include RFC8174.

-33: substituted 'movement detection' for 'handover behaviour' in introductory text; removed redundant phrase referring to Security Considerations section; removed the phrase about forming mechanisms being left out, as IP is not much concerned about L2 forming; moved the Pseudonym section from main section to end of Security Considerations section (and clarified 'concurrently'); capitalized SHOULD consider OCB in WiFi multicast problems, and referred to more recent I-D on topic; removed several phrases in a paragraph about oui.txt and MAC presence in IPv6 address, as they are well known info, but clarified the example of privacy risk of Company ID in MAC addresses in public roads; clarified that ND MUST be used over 802.11-OCB.

-32: significantly shortened the relevant ND/OCB paragraph. It now just states ND is used over OCB, w/o detailing.

-31: filled in the section titled "Pseudonym Handling"; removed a 'MAY NOT' phrase about possibility of having other prefix than the LL on the link between cars; shortened and improved the paragraph about Mobile IPv6, now with DNAv6; improved the ND text about ND retransmissions with relationship to packet loss; changed the title of an appendix from 'EPD' to 'Protocol Layering'; improved the 'Aspects introduced by OCB' appendix with a few phrases about the channel use and references.

-30: a clarification on the reliability of ND over OCB and over 802.11.



-27: part 1 of addressing Human Rights review from IRTF. Removed appendices F.2 and F.3. Shortened definition of IP-RSU. Removed reference to 1609.4. A few other small changes, see diff.

-26: moved text from SLAAC section and from Design Considerations appendix about privacy into a new Privacy Condiderations subsection of the Security section; reformulated the SLAAC and IID sections to stress only LLs can use EUI-64; removed the "GeoIP" wireshark explanation; reformulated SLAAC and LL sections; added brief mention of need of use LLs; clarified text about MAC address changes; dropped pseudonym discussion; changed title of section describing examples of packet formats.

-25: added a reference to 'IEEE Management Information Base', instead of just 'Management Information Base'; added ref to further appendices in the introductory phrases; improved text for IID formation for SLAAC, inserting recommendation for RFC8064 before RFC2464.

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Appendix B. 802.11p

The term "802.11p" is an earlier definition. The behaviour of "802.11p" networks is rolled in the document IEEE Std 802.11-2016. In that document the term 802.11p disappears. Instead, each 802.11p feature is conditioned by the IEEE Management Information Base (MIB) attribute "OCBActivated" [IEEE-802.11-2016]. Whenever OCBActivated is set to true the IEEE Std 802.11-OCB state is activated. For example, an 802.11 STAtion operating outside the context of a basic service set has the OCBActivated flag set. Such a station, when it has the flag set, uses a BSS identifier equal to ff:ff:ff:ff:ff:ff.

Appendix C. Aspects introduced by the OCB mode to 802.11

In the IEEE 802.11-OCB mode, all nodes in the wireless range can directly communicate with each other without involving authentication or association procedures. In OCB mode, the manner in which channels are selected and used is simplified compared to when in BSS mode. Contrary to BSS mode, at link layer, it is necessary to set statically the same channel number (or frequency) on two stations that need to communicate with each other (in BSS mode this channel set operation is performed automatically during 'scanning'). The manner in which stations set their channel number in OCB mode is not specified in this document. Stations STA1 and STA2 can exchange IP packets only if they are set on the same channel. At IP layer, they then discover each other by using the IPv6 Neighbor Discovery protocol. The allocation of a particular channel for a particular use is defined statically in standards authored by ETSI (in Europe), FCC in America, and similar organisations in South Korea, Japan and other parts of the world.

Briefly, the IEEE 802.11-OCB mode has the following properties:

All the nodes in the radio communication range (IP-OBU and IP-RSU) receive all the messages transmitted (IP-OBU and IP-RSU) within the radio communications range. The eventual conflict(s) are resolved by the MAC CDMA function.

The message exchange diagram in Figure 3 illustrates a comparison between traditional 802.11 and 802.11 in OCB mode. The 'Data' messages can be IP packets such as HTTP or others. Other 802.11 management and control frames (non IP) may be transmitted, as specified in the 802.11 standard. For information, the names of these messages as currently specified by the 802.11 standard are listed in Appendix G.

   STA                    AP              STA1                   STA2
   |                      |               |                      |
   |<------ Beacon -------|               |<------ Data -------->|
   |                      |               |                      |
   |---- Probe Req. ----->|               |<------ Data -------->|
   |<--- Probe Res. ------|               |                      |
   |                      |               |<------ Data -------->|
   |---- Auth Req. ------>|               |                      |
   |<--- Auth Res. -------|               |<------ Data -------->|
   |                      |               |                      |
   |---- Asso Req. ------>|               |<------ Data -------->|
   |<--- Asso Res. -------|               |                      |
   |                      |               |<------ Data -------->|
   |<------ Data -------->|               |                      |
   |<------ Data -------->|               |<------ Data -------->|

      (i) 802.11 Infrastructure mode         (ii) 802.11-OCB mode

Figure 3: Difference between messages exchanged on 802.11 (left) and 802.11-OCB (right)

The interface 802.11-OCB was specified in IEEE Std 802.11p (TM) -2010 [IEEE-802.11p-2010] as an amendment to IEEE Std 802.11 (TM) -2007, titled "Amendment 6: Wireless Access in Vehicular Environments". Since then, this amendment has been integrated in IEEE 802.11(TM) -2012 and -2016 [IEEE-802.11-2016].

In document 802.11-2016, anything qualified specifically as "OCBActivated", or "outside the context of a basic service" set to be true, then it is actually referring to OCB aspects introduced to 802.11.

In order to delineate the aspects introduced by 802.11-OCB to 802.11, we refer to the earlier [IEEE-802.11p-2010]. The amendment is concerned with vehicular communications, where the wireless link is similar to that of Wireless LAN (using a PHY layer specified by 802.11a/b/g/n), but which needs to cope with the high mobility factor inherent in scenarios of communications between moving vehicles, and between vehicles and fixed infrastructure deployed along roads. While 'p' is a letter identifying the Ammendment, just like 'a, b, g' and 'n' are, 'p' is concerned more with MAC modifications, and a little with PHY modifications; the others are mainly about PHY modifications. It is possible in practice to combine a 'p' MAC with an 'a' PHY by operating outside the context of a BSS with OFDM at 5.4GHz and 5.9GHz.

The 802.11-OCB links are specified to be compatible as much as possible with the behaviour of 802.11a/b/g/n and future generation IEEE WLAN links. From the IP perspective, an 802.11-OCB MAC layer offers practically the same interface to IP as the 802.11a/b/g/n and 802.3. A packet sent by an IP-OBU may be received by one or multiple IP-RSUs. The link-layer resolution is performed by using the IPv6 Neighbor Discovery protocol.

To support this similarity statement (IPv6 is layered on top of LLC on top of 802.11-OCB, in the same way that IPv6 is layered on top of LLC on top of 802.11a/b/g/n (for WLAN) or layered on top of LLC on top of 802.3 (for Ethernet)) it is useful to analyze the differences between 802.11-OCB and 802.11 specifications. During this analysis, we note that whereas 802.11-OCB lists relatively complex and numerous changes to the MAC layer (and very little to the PHY layer), there are only a few characteristics which may be important for an implementation transmitting IPv6 packets on 802.11-OCB links.

The most important 802.11-OCB point which influences the IPv6 functioning is the OCB characteristic; an additional, less direct influence, is the maximum bandwidth afforded by the PHY modulation/demodulation methods and channel access specified by 802.11-OCB. The maximum bandwidth theoretically possible in 802.11-OCB is 54 Mbit/s (when using, for example, the following parameters: 20 MHz channel; modulation 64-QAM; coding rate R is 3/4); in practice of IP-over-802.11-OCB a commonly observed figure is 12Mbit/s; this bandwidth allows the operation of a wide range of protocols relying on IPv6.

Appendix D. Changes Needed on a software driver 802.11a to become a 802.11-OCB driver

The 802.11p amendment modifies both the 802.11 stack's physical and MAC layers but all the induced modifications can be quite easily obtained by modifying an existing 802.11a ad-hoc stack.

Conditions for a 802.11a hardware to be 802.11-OCB compliant:

Changes needed on the network stack in OCB mode:

Appendix E. Protocol Layering

A more theoretical and detailed view of layer stacking, and interfaces between the IP layer and 802.11-OCB layers, is illustrated in Figure 4. The IP layer operates on top of the EtherType Protocol Discrimination (EPD); this Discrimination layer is described in IEEE Std 802.3-2012; the interface between IPv6 and EPD is the LLC_SAP (Link Layer Control Service Access Point).

 |                 IPv6                  |
 +-+-+-+-+-+-{            }+-+-+-+-+-+-+-+
             {   LLC_SAP  }                 802.11-OCB
 +-+-+-+-+-+-{            }+-+-+-+-+-+-+-+  Boundary
 |            EPD          |       |     |
 |                         | MLME  |     |
 +-+-+-{  MAC_SAP   }+-+-+-|  MLME_SAP   |
 |      MAC Sublayer       |       |     |  802.11-OCB
 |     and ch. coord.      |       | SME |  Services
 +-+-+-{   PHY_SAP  }+-+-+-+-+-+-+-|     |
 |                         | PLME  |     |
 |            PHY Layer    |   PLME_SAP  |

Figure 4: EtherType Protocol Discrimination

Appendix F. Design Considerations

The networks defined by 802.11-OCB are in many ways similar to other networks of the 802.11 family. In theory, the encapsulation of IPv6 over 802.11-OCB could be very similar to the operation of IPv6 over other networks of the 802.11 family. However, the high mobility, strong link asymmetry and very short connection makes the 802.11-OCB link significantly different from other 802.11 networks. Also, the automotive applications have specific requirements for reliability, security and privacy, which further add to the particularity of the 802.11-OCB link.

Appendix G. IEEE 802.11 Messages Transmitted in OCB mode

For information, at the time of writing, this is the list of IEEE 802.11 messages that may be transmitted in OCB mode, i.e. when dot11OCBActivated is true in a STA:

Appendix H. Examples of Packet Formats

This section describes an example of an IPv6 Packet captured over a IEEE 802.11-OCB link.

By way of example we show that there is no modification in the headers when transmitted over 802.11-OCB networks - they are transmitted like any other 802.11 and Ethernet packets.

We describe an experiment of capturing an IPv6 packet on an 802.11-OCB link. In topology depicted in Figure 5, the packet is an IPv6 Router Advertisement. This packet is emitted by a Router on its 802.11-OCB interface. The packet is captured on the Host, using a network protocol analyzer (e.g. Wireshark); the capture is performed in two different modes: direct mode and 'monitor' mode. The topology used during the capture is depicted below.

The packet is captured on the Host. The Host is an IP-OBU containing an 802.11 interface in format PCI express (an ITRI product). The kernel runs the ath5k software driver with modifications for OCB mode. The capture tool is Wireshark. The file format for save and analyze is 'pcap'. The packet is generated by the Router. The Router is an IP-RSU (ITRI product).

     +--------+                                +-------+
     |        |        802.11-OCB Link         |       |
  ---| Router |--------------------------------| Host  |
     |        |                                |       |
     +--------+                                +-------+

Figure 5: Topology for capturing IP packets on 802.11-OCB

During several capture operations running from a few moments to several hours, no message relevant to the BSSID contexts were captured (no Association Request/Response, Authentication Req/Resp, Beacon). This shows that the operation of 802.11-OCB is outside the context of a BSSID.

Overall, the captured message is identical with a capture of an IPv6 packet emitted on a 802.11b interface. The contents are precisely similar.

H.1. Capture in Monitor Mode

The IPv6 RA packet captured in monitor mode is illustrated below. The radio tap header provides more flexibility for reporting the characteristics of frames. The Radiotap Header is prepended by this particular stack and operating system on the Host machine to the RA packet received from the network (the Radiotap Header is not present on the air). The implementation-dependent Radiotap Header is useful for piggybacking PHY information from the chip's registers as data in a packet understandable by userland applications using Socket interfaces (the PHY interface can be, for example: power levels, data rate, ratio of signal to noise).

The packet present on the air is formed by IEEE 802.11 Data Header, Logical Link Control Header, IPv6 Base Header and ICMPv6 Header.


Radiotap Header v0
|Header Revision|  Header Pad   |    Header length              |
|                         Present flags                         |
| Data Rate     |             Pad                               |

IEEE 802.11 Data Header
|  Type/Subtype and Frame Ctrl  |          Duration             | 
|                      Receiver Address...                       
... Receiver Address           |      Transmitter Address...    
 ... Transmitter Address                                        |
|                            BSS Id...                           
 ... BSS Id                     |  Frag Number and Seq Number   |

Logical-Link Control Header
|      DSAP   |I|     SSAP    |C| Control field | Org. code...   
 ... Organizational Code        |             Type              |

IPv6 Base Header
|Version| Traffic Class |           Flow Label                  |
|         Payload Length        |  Next Header  |   Hop Limit   |
|                                                               |
+                                                               +
|                                                               |
+                         Source Address                        +
|                                                               |
+                                                               +
|                                                               |
|                                                               |
+                                                               +
|                                                               |
+                      Destination Address                      +
|                                                               |
+                                                               +
|                                                               |

Router Advertisement
|     Type      |     Code      |          Checksum             |
| Cur Hop Limit |M|O|  Reserved |       Router Lifetime         |
|                         Reachable Time                        |
|                          Retrans Timer                        |
|   Options ...

The value of the Data Rate field in the Radiotap header is set to 6 Mb/s. This indicates the rate at which this RA was received.

The value of the Transmitter address in the IEEE 802.11 Data Header is set to a 48bit value. The value of the destination address is 33:33:00:00:00:1 (all-nodes multicast address). The value of the BSS Id field is ff:ff:ff:ff:ff:ff, which is recognized by the network protocol analyzer as being "broadcast". The Fragment number and sequence number fields are together set to 0x90C6.

The value of the Organization Code field in the Logical-Link Control Header is set to 0x0, recognized as "Encapsulated Ethernet". The value of the Type field is 0x86DD (hexadecimal 86DD, or otherwise #86DD), recognized as "IPv6".

A Router Advertisement is periodically sent by the router to multicast group address ff02::1. It is an icmp packet type 134. The IPv6 Neighbor Discovery's Router Advertisement message contains an 8-bit field reserved for single-bit flags, as described in [RFC4861].

The IPv6 header contains the link local address of the router (source) configured via EUI-64 algorithm, and destination address set to ff02::1.

The Ethernet Type field in the logical-link control header is set to 0x86dd which indicates that the frame transports an IPv6 packet. In the IEEE 802.11 data, the destination address is 33:33:00:00:00:01 which is the corresponding multicast MAC address. The BSS id is a broadcast address of ff:ff:ff:ff:ff:ff. Due to the short link duration between vehicles and the roadside infrastructure, there is no need in IEEE 802.11-OCB to wait for the completion of association and authentication procedures before exchanging data. IEEE 802.11-OCB enabled nodes use the wildcard BSSID (a value of all 1s) and may start communicating as soon as they arrive on the communication channel.

H.2. Capture in Normal Mode

The same IPv6 Router Advertisement packet described above (monitor mode) is captured on the Host, in the Normal mode, and depicted below.


Ethernet II Header
|                       Destination...                           
...Destination                 |           Source...            
...Source                                                      |
|          Type                 |

IPv6 Base Header
|Version| Traffic Class |           Flow Label                  |
|         Payload Length        |  Next Header  |   Hop Limit   |
|                                                               |
+                                                               +
|                                                               |
+                         Source Address                        +
|                                                               |
+                                                               +
|                                                               |
|                                                               |
+                                                               +
|                                                               |
+                      Destination Address                      +
|                                                               |
+                                                               +
|                                                               |

Router Advertisement
|     Type      |     Code      |          Checksum             |
| Cur Hop Limit |M|O|  Reserved |       Router Lifetime         |
|                         Reachable Time                        |
|                          Retrans Timer                        |
|   Options ...

One notices that the Radiotap Header, the IEEE 802.11 Data Header and the Logical-Link Control Headers are not present. On the other hand, a new header named Ethernet II Header is present.

The Destination and Source addresses in the Ethernet II header contain the same values as the fields Receiver Address and Transmitter Address present in the IEEE 802.11 Data Header in the "monitor" mode capture.

The value of the Type field in the Ethernet II header is 0x86DD (recognized as "IPv6"); this value is the same value as the value of the field Type in the Logical-Link Control Header in the "monitor" mode capture.

The knowledgeable experimenter will no doubt notice the similarity of this Ethernet II Header with a capture in normal mode on a pure Ethernet cable interface.

An Adaptation layer is inserted on top of a pure IEEE 802.11 MAC layer, in order to adapt packets, before delivering the payload data to the applications. It adapts 802.11 LLC/MAC headers to Ethernet II headers. In further detail, this adaptation consists in the elimination of the Radiotap, 802.11 and LLC headers, and in the insertion of the Ethernet II header. In this way, IPv6 runs straight over LLC over the 802.11-OCB MAC layer; this is further confirmed by the use of the unique Type 0x86DD.

Appendix I. Extra Terminology

The following terms are defined outside the IETF. They are used to define the main terms in the main terminology section Section 2.

DSRC (Dedicated Short Range Communication): a term defined outside the IETF. The US Federal Communications Commission (FCC) Dedicated Short Range Communication (DSRC) is defined in the Code of Federal Regulations (CFR) 47, Parts 90 and 95. This Code is referred in the definitions below. At the time of the writing of this Internet Draft, the last update of this Code was dated October 1st, 2010.

DSRCS (Dedicated Short-Range Communications Services): a term defined outside the IETF. The use of radio techniques to transfer data over short distances between roadside and mobile units, between mobile units, and between portable and mobile units to perform operations related to the improvement of traffic flow, traffic safety, and other intelligent transportation service applications in a variety of environments. DSRCS systems may also transmit status and instructional messages related to the units involve. [Ref. 47 CFR 90.7 - Definitions]

OBU (On-Board Unit): a term defined outside the IETF. An On-Board Unit is a DSRCS transceiver that is normally mounted in or on a vehicle, or which in some instances may be a portable unit. An OBU can be operational while a vehicle or person is either mobile or stationary. The OBUs receive and contend for time to transmit on one or more radio frequency (RF) channels. Except where specifically excluded, OBU operation is permitted wherever vehicle operation or human passage is permitted. The OBUs mounted in vehicles are licensed by rule under part 95 of the respective chapter and communicate with Roadside Units (RSUs) and other OBUs. Portable OBUs are also licensed by rule under part 95 of the respective chapter. OBU operations in the Unlicensed National Information Infrastructure (UNII) Bands follow the rules in those bands. - [CFR 90.7 - Definitions].

RSU (Road-Side Unit): a term defined outside of IETF. A Roadside Unit is a DSRC transceiver that is mounted along a road or pedestrian passageway. An RSU may also be mounted on a vehicle or is hand carried, but it may only operate when the vehicle or hand- carried unit is stationary. Furthermore, an RSU operating under the respectgive part is restricted to the location where it is licensed to operate. However, portable or hand-held RSUs are permitted to operate where they do not interfere with a site-licensed operation. A RSU broadcasts data to OBUs or exchanges data with OBUs in its communications zone. An RSU also provides channel assignments and operating instructions to OBUs in its communications zone, when required. - [CFR 90.7 - Definitions].

Appendix J. Neighbor Discovery (ND) Potential Issues in Wireless Links

IPv6 Neighbor Discovery (IPv6 ND) [RFC4861][RFC4862] was designed for point-to-point and transit links such as Ethernet, with the expectation of a cheap and reliable support for multicast from the lower layer. Section 3.2 of RFC 4861 indicates that the operation on Shared Media and on non-broadcast multi-access (NBMA) networks require additional support, e.g., for Address Resolution (AR) and duplicate address detection (DAD), which depend on multicast. An infrastructureless radio network such as OCB shares properties with both Shared Media and NBMA networks, and then adds its own complexity, e.g., from movement and interference that allow only transient and non-transitive reachability between any set of peers.

The uniqueness of an address within a scoped domain is a key pillar of IPv6 and the base for unicast IP communication. RFC 4861 details the DAD method to avoid that an address is duplicated. For a link local address, the scope is the link, whereas for a Globally Reachable address the scope is much larger. The underlying assumption for DAD to operate correctly is that the node that owns an IPv6 address can reach any other node within the scope at the time it claims its address, which is done by sending a NS multicast message, and can hear any future claim for that address by another party within the scope for the duration of the address ownership.

In the case of OCB, there is a potentially a need to define a scope that is compatible with DAD, and that cannot be the set of nodes that a transmitter can reach at a particular time, because that set varies all the time and does not meet the DAD requirements for a link local address that could possibly be used anytime, anywhere. The generic expectation of a reliable multicast is not ensured, and the operation of DAD and AR (Address Resolution) as specificed by RFC 4861 cannot be guaranteed. Moreoever, multicast transmissions that rely on broadcast are not only unreliable but are also often detrimental to unicast traffic (see [draft-ietf-mboned-ieee802-mcast-problems]).

Early experience indicates that it should be possible to exchange IPv6 packets over OCB while relying on IPv6 ND alone for DAD and AR (Address Resolution) in good conditions. However, this does not apply if TBD TBD TBD. In the absence of a correct DAD operation, a node that relies only on IPv6 ND for AR and DAD over OCB should ensure that the addresses that it uses are unique by means others than DAD. It must be noted that deriving an IPv6 address from a globally unique MAC address has this property but may yield privacy issues.

RFC 8505 provides a more recent approach to IPv6 ND and in particular DAD. RFC 8505 is designed to fit wireless and otherwise constrained networks whereby multicast and/or continuous access to the medium may not be guaranteed. RFC 8505 Section 5.6 "Link-Local Addresses and Registration" indicates that the scope of uniqueness for a link local address is restricted to a pair of nodes that use it to communicate, and provides a method to assert the uniqueness and resolve the link-Layer address using a unicast exchange.

RFC 8505 also enables a router (acting as a 6LR) to own a prefix and act as a registrar (acting as a 6LBR) for addresses within the associated subnet. A peer host (acting as a 6LN) registers an address derived from that prefix and can use it for the lifetime of the registration. The prefix is advertised as not onlink, which means that the 6LN uses the 6LR to relay its packets within the subnet, and participation to the subnet is constrained to the time of reachability to the 6LR. Note that RSU that provides internet connectivity MAY announce a default router preference [RFC 4191], whereas a car that does not provide that connectivity MUST NOT do so. This operation presents similarities with that of an access point, but at Layer-3. This is why RFC 8505 well-suited for wireless in general.

Support of RFC 8505 is may be implemented on OCB. OCB nodes that support RFC 8505 would support the 6LN operation in order to act as a host, and may support the 6LR and 6LBR operations in order to act as a router and in particular own a prefix that can be used by RFC 8505-compliant hosts for address autoconfiguration and registration.

Authors' Addresses

Nabil Benamar Moulay Ismail University Morocco Phone: +212670832236 EMail: n.benamar@est.umi.ac.ma
Jerome Haerri Eurecom Sophia-Antipolis , 06904 France Phone: +33493008134 EMail: Jerome.Haerri@eurecom.fr
Jong-Hyouk Lee Sangmyung University 31, Sangmyeongdae-gil, Dongnam-gu Cheonan , 31066 Republic of Korea EMail: jonghyouk@smu.ac.kr
Thierry Ernst YoGoKo France EMail: thierry.ernst@yogoko.fr