Transmission of IPv6 Packets over IEEE 802.11 Networks operating
in mode Outside the Context of a Basic Service Set
(IPv6-over-80211-OCB)
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Internet
Network Working Group
IPv6 over 802.11p, OCB, IPv6 over 802.11-OCB
In order to transmit IPv6 packets on IEEE 802.11 networks run
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.
In addition, the document lists what is different in
802.11-OCB (802.11p) links compared to more 'traditional'
802.11a/b/g/n links, where IPv6 protocols operate without
issues. Most notably, the operation outside the context of a
BSS (OCB) has impact on IPv6 handover behaviour and on IPv6
security.
This document describes the transmission of IPv6 packets on
IEEE Std 802.11-OCB networks (earlier known as 802.11p) . 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 required to the standards:
IPv6 works fine directly over 802.11-OCB too (with an LLC
layer).
The term "802.11p" is an earlier definition. As of year 2012,
the behaviour of "802.11p" networks has been rolled in the
document IEEE Std 802.11-2012. In that document the term
802.11p disappears. Instead, each 802.11p feature is
conditioned by a flag in the Management Information Base.
That flag is named "OCBActivated". Whenever OCBActivated is
set to true the feature it relates to, or represents, an
earlier 802.11p feature. 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.
The IPv6 network layer operates on 802.11-OCB in the same
manner as it operates on 802.11 WiFi, with a few particular
exceptions. The IPv6 network layer operates on WiFi by
involving an Ethernet Adaptation Layer; this Ethernet
Adaptation Layer maps 802.11 headers to Ethernet II headers.
The operation of IP on Ethernet is described in , and . The situation of IPv6
networking layer on Ethernet Adaptation Layer is illustrated
below:
(in the above figure, a WiFi profile is represented; this is
used also for OCB profile.)
A more theoretical and detailed view of layer stacking, and
interfaces between the IP layer and 802.11-OCB layers, is
illustrated below. 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 Accesss Point).
In addition to the description of interface between IP and MAC
using "Ethernet Adaptation Layer" and "Ethernet Protocol
Discrimination (EPD)" it is worth mentioning that SNAP is used to carry the IPv6 Ethertype.
However, there may be some deployment considerations helping
optimize the performances of running IPv6 over 802.11-OCB
(e.g. in the case of handovers between 802.11-OCB-enabled
access routers, or the consideration of using the IP security
architecture ).
There are currently no specifications for handover between OCB
links since these are currently specified as LLC-1 links (i.e.
connectionless). Any handovers must be performed above the
Data Link Layer. To realize handovers between OCB links there
is a need of specific indicators to assist in the handover
process. The indicators may be IP Router Advertisements, or
802.11-OCB's Time Advertisements, or higher layer messages
such as the 'Basic Safety Message' (in the US), or the
'Cooperative Awareness Message' (in the EU), or the 'WAVE
Routing Advertisement'. However, this document does not
describe handover behaviour.
The OCB operation is stripping off 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 does provide security services for
certain applications to use. A security mechanism provided at
networking layer, such as IPsec , may
provide data security protection to a wider range of
applications. See the section Security Considerations of this
document,
We briefly introduce the vehicular communication scenarios
where IEEE 802.11-OCB links are used. This is followed by a
description of differences in specification terms, between
802.11-OCB and 802.11a/b/g/n - we answer the question of what
are the aspects introduced by OCB mode to 802.11; the same
aspects, but expressed in terms of requirements to
implementation, are listed in .)
The document then concentrates on the parameters of layering
IP over 802.11-OCB as over Ethernet: value of MTU, the Frame
Format which includes a description of an Ethernet Adaptation
Layer, the forming of Link-Local Addresses the rules for
forming Interface Identifiers for Stateless Autoconfiguration,
the mechanisms for Address Mapping. These are precisely the
same as IPv6 over Ethernet . A
reference is made to ad-hoc networking characteristics of the
subnet structure in OCB mode.
As an example, these characteristics of layering IPv6 straight
over LLC over 802.11-OCB MAC are illustrated by dissecting an
IPv6 packet captured over a 802.11-OCB link; this is described
in the section .
In the published literature, many documents describe aspects
related to running IPv6 over 802.11-OCB: .
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.
OBU (On-Board Unit): contrary to an RSU, an OBU is almost
always situated in a vehicle; it is a computer with at least
two IP interfaces; also, at least one IP interface runs in OCB
mode of 802.11. It may be an IP router.
RSU (Road Side Unit): It is a Wireless Termination Point
(WTP), as defined in , or an Access
Point (AP), or an Access Network Router (ANR) defined in , with one key particularity: the wireless
PHY/MAC layer is configured to operate in 802.11-OCB mode.
The RSU communicates with the On board Unit (OBU) in the
vehicle over 802.11 wireless link operating in OCB mode. An
RSU MAY be connected to the Internet, and MAY be an IP router.
When it is connected to the Internet, the term V2I (Vehicle to
Internet) is relevant.
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, or 802.11-OCB: text in document IEEE 802.11-2012
that is flagged by "dot11OCBActivated". The text flagged
"dot11OCBActivated" includes IEEE 802.11e for quality of
service, 802.11j-2004 for half-clocked operations and (what
was known earlier as) 802.11p for operation in the 5.9 GHz
band and in mode OCB.
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, among
which we refer the reader to one recently updated , about 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 RSUs and/or 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.
The 802.11-OCB links form and terminate; nodes connected to
these links peer, and discover each other; the nodes are
mobile. However, the precise description of how links
discover each other, peer and manage mobility is not given in
this document.
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. At link layer, it
is necessary to set a same channel number (or frequency) on
two stations that need to communicate with each other.
Stations STA1 and STA2 can exchange IP packets if they are set
on the same channel. At IP layer, they then discover each
other by using the IPv6 Neighbor Discovery protocol.
Briefly, the IEEE 802.11-OCB mode has the following
properties:
The use by each node of a 'wildcard' BSSID (i.e., each bit
of the BSSID is set to 1)
No IEEE 802.11 Beacon frames are transmitted No authentication is required in order to be able to communicate No association is needed in order to be able to communicate No encryption is provided in order to be able to communicate Flag dot11OCBActivated is set to true
All the nodes in the radio communication range (OBU and RSU)
receive all the messages transmitted (OBU and RSU) within the
radio communications range. The eventual conflict(s) are
resolved by the MAC CDMA function.
The following message exchange diagram 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 .
The link 802.11-OCB was specified in IEEE Std 802.11p (TM) -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 included
in IEEE 802.11(TM)-2012 ,
titled "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"; the modifications
are diffused throughout various sections (e.g. the Time
Advertisement message described in the earlier 802.11 (TM) p
amendment is now described in section 'Frame formats', and the
operation outside the context of a BSS described in section
'MLME').
In document 802.11-2012, specifically anything referring
"OCBActivated", or "outside the context of a basic service
set" is actually referring to OCB aspects introduced to
802.11. Note that in earlier 802.11p documents the term
"OCBEnabled" was used instead of the current "OCBActivated".
In order to delineate the aspects introduced by 802.11-OCB to
802.11, we refer to the earlier . 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 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.
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 WiFi and Ethernet layers do (802.11a/b/g/n and
802.3). A packet sent by an OBU may be received by one or
multiple 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 possible in 802.11-OCB
is 12Mbit/s; this bandwidth allows the operation of a wide
range of protocols relying on IPv6.
Operation Outside the Context of a BSS (OCB): the (earlier
802.11p) 802.11-OCB links are operated without a Basic
Service Set (BSS). This means that the frames IEEE 802.11
Beacon, Association Request/Response, Authentication
Request/Response, and similar, are not used. The used
identifier of BSS (BSSID) has a hexadecimal value always
0xffffffffffff (48 '1' bits, represented as MAC address
ff:ff:ff:ff:ff:ff, or otherwise the 'wildcard' BSSID), as
opposed to an arbitrary BSSID value set by administrator
(e.g. 'My-Home-AccessPoint'). The OCB operation - namely
the lack of beacon-based scanning and lack of
authentication - should be taken into account when the
Mobile IPv6 protocol and the
protocols for IP layer security
are used. The way these protocols adapt to OCB is not
described in this document.
Timing Advertisement: is a new message defined in
802.11-OCB, which does not exist in 802.11a/b/g/n. This
message is used by stations to inform other stations about
the value of time. It is similar to the time as delivered
by a GNSS system (Galileo, GPS, ...) or by a cellular
system. This message is optional for implementation.
Frequency range: this is a characteristic of the PHY
layer, with almost no impact to the interface between MAC
and IP. However, it is worth considering that the
frequency range is regulated by a regional authority
(ARCEP, ETSI, FCC, etc.); as part of the regulation
process, specific applications are associated with
specific frequency ranges. In the case of 802.11-OCB, the
regulator associates a set of frequency ranges, or slots
within a band, to the use of applications of vehicular
communications, in a band known as "5.9GHz". The 5.9GHz
band is different from the 2.4GHz and 5GHz bands used by
Wireless LAN. However, as with Wireless LAN, the
operation of 802.11-OCB in "5.9GHz" bands is exempt from
owning a license in EU (in US the 5.9GHz is a licensed
band of spectrum; for the the fixed infrastructure an
explicit FCC autorization is required; for an onboard
device a 'licensed-by-rule' concept applies: rule
certification conformity is required); however technical
conditions are different than those of the bands "2.4GHz"
or "5GHz". On one hand, the allowed power levels, and
implicitly the maximum allowed distance between vehicles,
is of 33dBm for 802.11-OCB (in Europe), compared to 20 dBm
for Wireless LAN 802.11a/b/g/n; this leads to a maximum
distance of approximately 1km, compared to approximately
50m. On the other hand, specific conditions related to
congestion avoidance, jamming avoidance, and radar
detection are imposed on the use of DSRC (in US) and on
the use of frequencies for Intelligent Transportation
Systems (in EU), compared to Wireless LAN (802.11a/b/g/n).
Prohibition of IPv6 on some channels relevant for IEEE
802.11-OCB, as opposed to IPv6 not being prohibited on any
channel on which 802.11a/b/g/n runs:
Some channels are reserved for safety communications;
the IPv6 packets should not be sent on these channels.
At the time of writing, the prohibition is explicit at
higher layer protocols providing services to the
application; these higher layer protocols are
specified in IEEE 1609 documents, i.e. the "WAVE"
stack.
National or regional specifications and regulations
specify the use of different channels; these regulations
must be followed.
'Half-rate' encoding: as the frequency range, this
parameter is related to PHY, and thus has not much
impact on the interface between the IP layer and the
MAC layer.
In vehicular communications using 802.11-OCB links, there
are strong privacy requirements with respect to
addressing. While the 802.11-OCB standard does not
specify anything in particular with respect to MAC
addresses, in these settings there exists a strong need
for dynamic change of these addresses (as opposed to the
non-vehicular settings - real wall protection - where
fixed MAC addresses do not currently pose some privacy
risks). This is further described in section . A relevant function is described in
IEEE 1609.3-2016 , clause 5.5.1
and IEEE 1609.4-2016 , clause
6.7.
Other aspects particular to 802.11-OCB, which are also
particular to 802.11 (e.g. the 'hidden node' operation), may
have an influence on the use of transmission of IPv6 packets
on 802.11-OCB networks. The OCB subnet structure is described
in section .
The default MTU for IP packets on 802.11-OCB is 1500 octets.
It is the same value as IPv6 packets on Ethernet links, as
specified in . This value of the
MTU respects the recommendation that every link in the
Internet must have a minimum MTU of 1280 octets (stated in
, and the recommendations therein,
especially with respect to fragmentation). If IPv6 packets
of size larger than 1500 bytes are sent on an 802.11-OCB
interface card then the IP stack will fragment. In case
there are IP fragments, the field "Sequence number" of the
802.11 Data header containing the IP fragment field is
increased.
Non-IP packets such as WAVE Short Message Protocol (WSMP)
can be delivered on 802.11-OCB links. Specifications of
these packets are out of scope of this document, and do not
impose any limit on the MTU size, allowing an arbitrary
number of 'containers'. Non-IP packets such as ETSI
GeoNetworking packets have an MTU of 1492 bytes. The
operation of IPv6 over GeoNetworking is specified at .
IP packets are transmitted over 802.11-OCB as standard
Ethernet packets. As with all 802.11 frames, an Ethernet
adaptation layer is used with 802.11-OCB as well. This
Ethernet Adaptation Layer performing 802.11-to-Ethernet is
described in . The Ethernet Type code
(EtherType) for IPv6 is 0x86DD (hexadecimal 86DD, or
otherwise #86DD).
The Frame format for transmitting IPv6 on 802.11-OCB
networks is the same as transmitting IPv6 on Ethernet
networks, and is described in section 3 of . The frame format for transmitting IPv6
packets over Ethernet is illustrated below:
Ethernet II Fields:
the MAC destination address.
the MAC source address.
binary representation of the EtherType value 0x86DD.
the IPv6 packet containing IPv6 header and payload.
In general, 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.
For example, an 802.15.4 adaptation layer may perform
fragmentation and reassembly operations on a MAC whose
maximum Packet Data Unit size is smaller than the
minimum MTU recognized by the IPv6 Networking layer.
Other examples involve link-layer address
transformation, packet header insertion/removal, and so
on.
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 Data Header and the Logical-Link Layer Control
Header and produces an Ethernet II Header. At sending,
the reverse operation is performed.
The Receiver and Transmitter Address fields in the
802.11 Data Header 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 is the same as the value of the
Type field in the Ethernet II Header.
The ".11 Trailer" contains solely a 4-byte Frame Check
Sequence.
The Ethernet Adaptation Layer performs operations in
relation to IP fragmentation and MTU. One of these
operations is briefly described in section .
In OCB mode, IPv6 packets can be transmitted either as
"IEEE 802.11 Data" or alternatively as "IEEE 802.11 QoS
Data", as illustrated in the figure below. Some
commercial OCB products use 802.11 Data, and others 802.11
QoS data. In the future, both could be used.
The distinction between the two formats is given by the
value of the field "Type/Subtype". The value of the field
"Type/Subtype" in the 802.11 Data header is 0x0020. The
value of the field "Type/Subtype" in the 802.11 QoS header
is 0x0028.
The mapping between qos-related fields in the IPv6 header
(e.g. "Traffic Class", "Flow label") and fields in the
"802.11 QoS Data Header" (e.g. "QoS Control") are not
specified in this document. Guidance for a potential
mapping is provided in , although it is not
specific to OCB mode.
The link-local address of an 802.11-OCB interface is formed
in the same manner as on an Ethernet interface. This manner
is described in section 5 of .
For unicast as for multicast, there is no change from the
unicast and multicast address mapping format of Ethernet
interfaces, as defined by sections 6 and 7 of .
The procedure for mapping IPv6 unicast addresses into
Ethernet link-layer addresses is described in . The Source/Target Link-layer Address
option has the following form when the link-layer is
Ethernet.
Option fields:
1 for Source Link-layer address.
2 for Target Link-layer address.
1 (in units of 8 octets).
The 48 bit Ethernet IEEE 802 address, in canonical bit
order.
IPv6 protocols often make use of IPv6 multicast addresses in
the destination field of IPv6 headers. For example, an ICMPv6
link-scoped Neighbor Advertisement is sent to the IPv6 address
ff02::1 denoted "all-nodes" address. When transmitting these
packets on 802.11-OCB links it is necessary to map the IPv6
address to a MAC address.
The same mapping requirement applies to the link-scoped
multicast addresses of other IPv6 protocols as well. In
DHCPv6, the "All_DHCP_Servers" IPv6 multicast address
ff02::1:2, and in OSPF the "All_SPF_Routers" IPv6 multicast
address ff02::5, need to be mapped on a multicast MAC address.
An IPv6 packet with a multicast destination address DST,
consisting of the sixteen octets DST[1] through DST[16], is
transmitted to the IEEE 802.11-OCB MAC multicast address whose
first two octets are the value 0x3333 and whose last four
octets are the last four octets of DST.
A Group ID named TBD, of length 112bits is requested to
IANA; this Group ID signifies "All 80211OCB Interfaces
Address". Only the least 32 significant bits of this "All
80211OCB Interfaces Address" will be mapped to and from a
MAC multicast address.
Transmitting IPv6 packets to multicast destinations over
802.11 links proved 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 Interface Identifier for an 802.11-OCB interface is
formed using the same rules as the Interface Identifier for
an Ethernet interface; this is described in section 4 of
. No changes are needed, but some
care must be taken when considering the use of the SLAAC
procedure.
The bits in the 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 .
As with all Ethernet and 802.11 interface identifiers (), the identifier of an 802.11-OCB
interface may involve privacy, MAC address spoofing and IP
address hijacking risks. A vehicle embarking an On-Board
Unit 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; see the privacy
considerations described in .
If stable Interface Identifiers are needed in order to form
IPv6 addresses on 802.11-OCB links, it is recommended to
follow the recommendation in .
A subnet is formed by the external 802.11-OCB interfaces of
vehicles that are in close range (not their on-board
interfaces). This ephemeral subnet structure is strongly
influenced by the mobility of vehicles: the 802.11 hidden
node effects appear. On another hand, the structure of the
internal subnets in each car is relatively stable.
For routing purposes, a prefix exchange mechanism could be
needed between neighboring vehicles.
The 802.11 networks in OCB mode may be considered as
'ad-hoc' networks. The addressing model for such networks
is described in .
An addressing model involves several types of addresses,
like Globally-unique Addresses (GUA), Link-Local Addresses
(LL) and Unique Local Addresses (ULA). The subnet structure
in 'ad-hoc' networks may have characteristics that lead to
difficulty of using GUAs derived from a received prefix, but
the LL addresses may be easier to use since the prefix is
constant.
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.
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.
Within the IPsec Security Architecture , the IPsec AH and ESP headers and respectively,
its multicast extensions , HTTPS and SeND protocols
can be used to protect communications. Further, the
assistance of proper Public Key Infrastructure (PKI) protocols
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 .
As with all Ethernet and 802.11 interface identifiers, there
may exist privacy risks in the use of 802.11-OCB interface
identifiers. Moreover, in outdoors vehicular settings, the
privacy risks are more important than in indoors settings.
New risks are induced by the possibility of attacker sniffers
deployed along routes which listen for 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. This may help mitigate
privacy risks to a certain level. On another hand, it may
have an impact in the way typical IPv6 address
auto-configuration is performed for vehicles (SLAAC would rely
on MAC addresses amd would hence dynamically change the
affected IP address), in the way the IPv6 Privacy addresses
were used, and other effects.
A Group ID named TBD, of length 112bits is requested to IANA;
this Group ID signifies "All 80211OCB Interfaces Address".
Romain Kuntz contributed extensively about IPv6 handovers
between links running outside the context of a BSS (802.11-OCB
links).
Tim Leinmüller contributed the idea of the use of IPv6 over
802.11-OCB for distribution of certificates.
Marios Makassikis, José 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.
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 Céspedes,
Mariano Falcitelli, Sri Gundavelli 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 authours would like to thank participants to the
Birds-of-a-Feather "Intelligent Transportation Systems"
meetings held at IETF in 2016.
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.
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 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 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.
802.11-2012 - 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. Downloaded on October 17th, 2013, from
IEEE Standards, document freely available at URL
http://standards.ieee.org/findstds/standard/802.11-2012.html
retrieved on October 17th, 2013.
ETSI EN 302 636-6-1 v1.2.1 (2014-05), ETSI, European
Standard, Intelligent Transportation Systems (ITS);
Vehicular Communications; Geonetworking; Part 6: Internet
Integration; Sub-part 1: Transmission of IPv6 Packets over
Geonetworking Protocols. Downloaded on September 9th,
2017, freely available from ETSI website at URL
http://www.etsi.org/deliver/etsi_en/302600_302699/30263601/01.02.01_60/en_30263601v010201p.pdf
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. Dowloaded 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
The changes are listed in reverse chronological order, most
recent changes appearing at the top of the list.
From draft-ietf-ipwave-ipv6-over-80211ocb-04 to
draft-ietf-ipwave-ipv6-over-80211ocb-05
Lengthened the title and cleanded the abstract.
Added text suggesting LLs may be easy to use on OCB,
rather than GUAs based on received prefix.
Added the risks of spoofing and hijacking.
Removed the text speculation on adoption of the TSA
message.
Clarified that the ND protocol is used.
Clarified what it means "No association needed".
Added some text about how two STAs discover each other.
Added mention of external (OCB) and internal network
(stable), in the subnet structure section.
Added phrase explaining that both .11 Data and .11 QoS
Data headers are currently being used, and may be used in
the future.
Moved the packet capture example into an Appendix
Implementation Status.
Suggested moving the reliability requirements appendix out
into another document.
Added a IANA Consiserations section, with content,
requesting for a new multicast group "all OCB interfaces".
Added new OBU term, improved the RSU term definition,
removed the ETTC term, replaced more occurences of
802.11p, 802.11 OCB with 802.11-OCB.
References:
Added an informational reference to ETSI's
IPv6-over-GeoNetworking.
Added more references to IETF and ETSI security protocols.
Updated some references from I-D to RFC, and from old RFC
to new RFC numbers.
Added reference to multicast extensions to IPsec
architecture RFC.
Added a reference to 2464-bis.
Removed FCC informative references, because not used.
Updated the affiliation of one author.
Reformulation of some phrases for better readability, and
correction of typographical errors.
From draft-ietf-ipwave-ipv6-over-80211ocb-03 to
draft-ietf-ipwave-ipv6-over-80211ocb-04
Removed a few informative references pointing to Dx draft
IEEE 1609 documents.
Removed outdated informative references to ETSI documents.
Added citations to IEEE 1609.2, .3 and .4-2016.
Minor textual issues.
From draft-ietf-ipwave-ipv6-over-80211ocb-02 to
draft-ietf-ipwave-ipv6-over-80211ocb-03
Keep the previous text on multiple addresses, so remove
talk about MIP6, NEMOv6 and MCoA.
Clarified that a 'Beacon' is an IEEE 802.11 frame Beacon.
Clarified the figure showing Infrastructure mode and OCB
mode side by side.
Added a reference to the IP Security Architecture RFC.
Detailed the IPv6-per-channel prohibition paragraph which
reflects the discussion at the last IETF IPWAVE WG
meeting.
Added section "Address Mapping -- Unicast".
Added the ".11 Trailer" to pictures of 802.11 frames.
Added text about SNAP carrying the Ethertype.
New RSU definition allowing for it be both a Router and
not necessarily a Router some times.
Minor textual issues.
From draft-ietf-ipwave-ipv6-over-80211ocb-01 to
draft-ietf-ipwave-ipv6-over-80211ocb-02
Replaced almost all occurences of 802.11p with 802.11-OCB,
leaving only when explanation of evolution was necessary.
Shortened by removing parameter details from a paragraph
in the Introduction.
Moved a reference from Normative to Informative.
Added text in intro clarifying there is no handover spec
at IEEE, and that 1609.2 does provide security services.
Named the contents the fields of the EthernetII header
(including the Ethertype bitstring).
Improved relationship between two paragraphs describing
the increase of the Sequence Number in 802.11 header upon
IP fragmentation.
Added brief clarification of "tracking".
From draft-ietf-ipwave-ipv6-over-80211ocb-00 to
draft-ietf-ipwave-ipv6-over-80211ocb-01
Introduced message exchange diagram illustrating
differences between 802.11 and 802.11 in OCB mode.
Introduced an appendix listing for information the set of
802.11 messages that may be transmitted in OCB mode.
Removed appendix sections "Privacy Requirements",
"Authentication Requirements" and "Security Certificate
Generation".
Removed appendix section "Non IP Communications".
Introductory phrase in the Security Considerations
section.
Improved the definition of "OCB".
Introduced theoretical stacked layers about IPv6 and IEEE
layers including EPD.
Removed the appendix describing the details of prohibiting
IPv6 on certain channels relevant to 802.11-OCB.
Added a brief reference in the privacy text about a
precise clause in IEEE 1609.3 and .4.
Clarified the definition of a Road Side Unit.
Removed the discussion about security of WSA (because is
non-IP).
Removed mentioning of the GeoNetworking discussion.
Moved references to scientific articles to a separate
'overview' draft, and referred to it.
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:
The chip must support the frequency bands on which the
regulator recommends the use of ITS communications, for
example using IEEE 802.11-OCB layer, in France: 5875MHz to
5925MHz.
The chip must support the half-rate mode (the internal
clock should be able to be divided by two).
The chip transmit spectrum mask must be compliant to the
"Transmit spectrum mask" from the IEEE 802.11p amendment
(but experimental environments tolerate otherwise).
The chip should be able to transmit up to 44.8 dBm when
used by the US government in the United States, and up to
33 dBm in Europe; other regional conditions apply.
Changes needed on the network stack in OCB mode:
Physical layer:
The chip must use the Orthogonal Frequency Multiple
Access (OFDM) encoding mode.
The chip must be set in half-mode rate mode (the
internal clock frequency is divided by two).
The chip must use dedicated channels and should allow
the use of higher emission powers. This may require
modifications to the regulatory domains rules, if used
by the kernel to enforce local specific
restrictions. Such modifications must respect the
location-specific laws.
MAC layer:
All management frames (beacons, join, leave, and
others) emission and reception must be disabled
except for frames of subtype Action and Timing
Advertisement (defined below).
No encryption key or method must be used.
Packet emission and reception must be performed as in
ad-hoc mode, using the wildcard BSSID
(ff:ff:ff:ff:ff:ff).
The functions related to joining a BSS (Association
Request/Response) and for authentication
(Authentication Request/Reply, Challenge) are not
called.
The beacon interval is always set to 0 (zero).
Timing Advertisement frames, defined in the
amendment, should be supported. The upper layer
should be able to trigger such frames emission and to
retrieve information contained in received Timing
Advertisements.
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.
In automotive networks it is required that each node is
represented uniquely. Accordingly, a vehicle must be
identified by at least one unique identifier. The current
specification at ETSI and at IEEE 1609 identifies a vehicle
by its MAC address, which is obtained from the 802.11-OCB
Network Interface Card (NIC).
In case multiple 802.11-OCB NICs are present in one car,
implicitely multiple vehicle IDs will be generated.
Additionally, some software generates a random MAC address
each time the computer boots; this constitutes an additional
difficulty.
A mechanim to uniquely identify a vehicle irrespectively to
the multiplicity of NICs, or frequent MAC address
generation, is necessary.
This section may need to be moved out into a separate
requirements document.
The dynamically changing topology, short connectivity,
mobile transmitter and receivers, different antenna heights,
and many-to-many communication types, make IEEE 802.11-OCB
links significantly different from other IEEE 802.11 links.
Any IPv6 mechanism operating on IEEE 802.11-OCB link MUST
support strong link asymmetry, spatio-temporal link quality,
fast address resolution and transmission.
IEEE 802.11-OCB strongly differs from other 802.11 systems
to operate outside of the context of a Basic Service Set.
This means in practice that IEEE 802.11-OCB does not rely on
a Base Station for all Basic Service Set management. In
particular, IEEE 802.11-OCB SHALL NOT use beacons. Any IPv6
mechanism requiring L2 services from IEEE 802.11 beacons
MUST support an alternative service.
Channel scanning being disabled, IPv6 over IEEE 802.11-OCB
MUST implement a mechanism for transmitter and receiver to
converge to a common channel.
Authentication not being possible, IPv6 over IEEE 802.11-OCB
MUST implement an distributed mechanism to authenticate
transmitters and receivers without the support of a DHCP
server.
Time synchronization not being available, IPv6 over IEEE
802.11-OCB MUST implement a higher layer mechanism for time
synchronization between transmitters and receivers without
the support of a NTP server.
The IEEE 802.11-OCB link being asymmetric, IPv6 over IEEE
802.11-OCB MUST disable management mechanisms requesting
acknowledgements or replies.
The IEEE 802.11-OCB link having a short duration time, IPv6
over IEEE 802.11-OCB SHOULD implement fast IPv6 mobility
management mechanisms.
There are considerations for 2 or more IEEE 802.11-OCB
interface cards per vehicle. For each vehicle taking part in
road traffic, one IEEE 802.11-OCB interface card could be
fully allocated for Non IP safety-critical communication.
Any other IEEE 802.11-OCB may be used for other type of
traffic.
The mode of operation of these other wireless interfaces is
not clearly defined yet. One possibility is to consider each
card as an independent network interface, with a specific
MAC Address and a set of IPv6 addresses. Another
possibility is to consider the set of these wireless
interfaces as a single network interface (not including the
IEEE 802.11-OCB interface used by Non IP safety critical
communications). This will require specific logic to ensure,
for example, that packets meant for a vehicle in front are
actually sent by the radio in the front, or that multiple
copies of the same packet received by multiple interfaces
are treated as a single packet. Treating each wireless
interface as a separate network interface pushes such issues
to the application layer.
Certain privacy requirements imply that if these multiple
interfaces are represented by many network interface, a
single renumbering event SHALL cause renumbering of all
these interfaces. If one MAC changed and another stayed
constant, external observers would be able to correlate old
and new values, and the privacy benefits of randomization
would be lost.
The privacy requirements of Non IP safety-critical
communications imply that if a change of pseudonyme occurs,
renumbering of all other interfaces SHALL also occur.
When designing the IPv6 over 802.11-OCB address mapping, we
will assume that the MAC Addresses will change during well
defined "renumbering events". The 48 bits randomized MAC
addresses will have the following characteristics:
Bit "Local/Global" set to "locally admninistered".
Bit "Unicast/Multicast" set to "Unicast".
46 remaining bits set to a random value, using a random
number generator that meets the requirements of .
The way to meet the randomization requirements is to retain
46 bits from the output of a strong hash function, such as
SHA256, taking as 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.
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:
The STA may send management frames of subtype Action and,
if the STA maintains a TSF Timer, subtype Timing
Advertisement;
The STA may send control frames, except those of subtype
PS-Poll, CF-End, and CF-End plus CFAck;
The STA may send data frames of subtype Data, Null, QoS
Data, and QoS Null.
This section describese 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 this experiment, 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.
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.
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.
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 .
The IPv6 header contains the link local address of the router
(source) configured via EUI-64 algorithm, and destination
address set to ff02::1. Recent versions of network protocol
analyzers (e.g. Wireshark) provide additional informations for
an IP address, if a geolocalization database is present. In
this example, the geolocalization database is absent, and the
"GeoIP" information is set to unknown for both source and
destination addresses (although the IPv6 source and
destination addresses are set to useful values). This "GeoIP"
can be a useful information to look up the city, country, AS
number, and other information for an IP address.
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.
The same IPv6 Router Advertisement packet described above
(monitor mode) is captured on the Host, in the Normal mode,
and depicted below.
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.